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Radiochemical determination of nuclear data for theory and applications

  • S. M. Qaim
Article

Abstract

A vast knowledge of nuclear data is available and is grouped under three headings, namely, nuclear structure, nuclear decay and nuclear reaction data. Still newer aspects are under continuous investigation. Data measurements are done using a large number of techniques, including the radiochemical method, which has been extensively worked out at Jülich. This method entails preparation of high-quality sample for irradiation, isolation of the desired radioactive product from the strong matrix activity, and preparation of thin source suitable for accurate measurement of the radioactivity. It is especially useful for fundamental studies on light complex particle emission reactions and formation of low-lying isomeric states, both of which are rather difficult to describe by nuclear model calculations. The neutron induced reaction cross section data are of practical application in fusion reactor technology, particularly for calculations on tritium breeding, gas production in structural materials and activation of reactor components. The charged particle induced reaction cross section data, on the other hand, are of significance in medicine, especially for developing new production routes of novel positron emitters and therapeutic radionuclides at a cyclotron. Both neutron and charged particle data also find application in radiation therapy. A brief overview of advances made in all those areas is given, with major emphasis on nuclear reaction cross section data.

Keywords

Nuclear reactions Nuclear data Radiochemical methods Complex particle emission Isomeric cross section Fusion reactor technology Medical radionuclide production 

Introduction

The term “nuclear data” is very broad. It includes all data which describe either the properties of nuclei or their interactions. In general, all those data can be grouped under three headings, namely, nuclear structure, nuclear decay and nuclear reaction data. The amount of available information is extensive. The compilation, storage and dissemination of data is well organised and is generally managed via four major regional data centres located at Brookhaven (USA), Paris (France), Vienna (Austria) and Obninsk (Russia). The worldwide exchange of nuclear data for peaceful applications is effected via the IAEA. Those applications pertain to both energy-related research (fission, fusion, accelerator driven systems, etc.) and non-energy related studies (medical radionuclide production, radiation therapy, astrophysics, cosmochemistry, etc.). Despite the vast available information, some newer aspects of nuclear data research are still under investigation. Accurate experimental work in less investigated areas allows to test nuclear models; it also opens up new vistas in many applications.

A large number of physico-chemical techniques are used to determine the nuclear data, each of them having its own merits and limitations. This article deals with the radiochemical technique which, though limited in some ways, is applicable to studies of all three types of data mentioned above. It consists of irradiating a material with neutrons or charged particles, separating the activated (radioactive) product, and measuring its decay characteristics or absolute radioactivity by standard counting techniques. Thus in contrast to purely physical methods, which aim at on-line measurement of the emitted radiation spectra, the activation (or radiochemical, when combined with a chemical separation) technique deals with the residual radioactive nucleus, i.e. off-line detection and measurement of the activated reaction product. The technique has very high sensitivity, especially in the case of short-lived radioactive products. In case of stable or very long-lived radioactive products, mass spectrometry (MS) and accelerator mass spectrometry (AMS) are more useful. The radiochemically obtained data are generally application oriented; but some information can be deduced on the reaction mechanism as well. We consider briefly some of the relevant aspects below.

Nuclear structure and nuclear decay data

In general, nuclear decay data are well known [1, 2]. They encompass information on the decay of radioactive nuclei, such as half-lives, energies, intensities and angular correlations of the emitted radiation, as well as on the formation of secondary radiation like electrons, X-rays, etc. The nuclear structure data include information on the properties of the excited states of nuclei. Since many of the decaying nuclei have decay energies of up to about 3 MeV, or somewhat higher, the nuclear levels populated in the decay product are generally well characterised up to excitation energies of 2–3 MeV. More detailed information on the nuclear structure, i.e. all the discrete levels up to the continuum of the nucleus, and even beyond, is obtained via spectral studies on nuclear processes. A good example is the in-beam γ-ray spectroscopy following an (n,γ) reaction which can provide information on the level structure of the product nucleus up to about 8 MeV. Those studies are, however, beyond the scope of this article. The discussion here is limited to decay properties of radioactive nuclei and the levels of the daughter fed by the various transitions.

Radiochemical techniques have played a significant role in the study of nuclear decay and structure data. In particular, before the advent of the high-resolution solid state detectors, many new radionuclides were discovered by the author via radiochemical methods [3, 4, 5, 6]. After the discovery of the high-resolution solid state detectors, detailed decay schemes of a few radiochemically separated radionuclides were established and some systematics in level structure could be discussed [7]. Today, extensive information is available. There are, however, still some areas where more nuclear data work is necessary and where radiochemistry can play an important role. One such area is the study of radionuclides rather far from the stability line. Another area is the search and characterisation of super heavy elements. In both cases fast radiochemical separations are mandatory to isolate the desired product from the much stronger matrix activity, and to characterise it via measurement of the radioactivity.

The radioactive decay data find applications in many areas, e.g. calculation of total radioactivity, heat generation, transmutation products, etc. However, in recent years, with the enhancing application of radioactivity in medicine, especially for in vivo diagnostic and therapeutic studies, the demands on accurate decay data have considerably increased. A higher accuracy in the data means a higher accuracy in the internal radiation dose calculation. Two areas appear to need further attention—one involves the energies and intensities of low-energy electrons (e.g. conversion or Auger electrons) and the other branching ratios in the decay of non-standard positron emitters. Since decay schemes of many of the medically interesting radionuclides were generally determined using mixtures of radionuclides, often utilising rather poor resolution counters, it appears worthwhile to reinvestigate some of the special radionuclides in more detail using radiochemical techniques. Many of those medical radionuclides can now be produced with very high purities; the use of ultrapure sources should thus provide accurate information on the decay data as well.

An example of a recent decay data measurement is provided by 64Cu (T½ = 12.7 h). This radionuclide is becoming increasingly important in Positron Emission Tomography (PET) in connection with radioimmunotherapy. It was produced via the 64Ni(p,n)64Cu reaction [8] on highly enriched 64Ni as well as via the 66Zn(d,α)64Cu reaction [9] on highly enriched 66Zn. The chemical separation was based on ion-exchange chromatography [8, 9] and the final product was obtained as a very thin source with a radionuclidic purity of >99.9%. The measurements included β counting, γγ-coincidence counting, conventional high-resolution γ-ray spectrometry and, above all, high-resolution X-ray spectrometry using a Si(Li) detector. The latter was absolutely necessary to determine the low-energy (7.47 and 8.26 keV) K α and K β X-rays of the daughter Ni which describe the electron capture (EC) component in the decay of 64Cu. There was some discrepancy in the β+ branching and consequently in the intensity of EC decay; they are now fairly well established. Thus the availability of 64Cu of high radionuclidic purity made it possible to determine the decay scheme of that radionuclide with higher accuracy [10].

Similar to 64Cu, the positron emission intensities in the decay of the radionuclides 76Br, 120I and 124I have also been accurately determined [10, 11, 12]. The three radionuclides were obtained in pure forms via 76Se(p,n)76Br, 120Te(p,n)120I and 124Te(p,n)124I reactions, respectively, on highly enriched target isotopes, combined with thermochromatographic separations of the products. The obtained results are given in Table 1. It should be emphasized that accurate measurements were possible only through the availability of each of those radionuclides in a highly pure form.
Table 1

Recently determined Iβ+ values of some non-standard PET nuclides

Radionuclide

T½

Positron emission intensity (%)

Literature values

Precise value

64Cu

12.7 h

17.4–19

17.8 ± 0.4 [10]

76Br

16.2 h

56–62.5

58.2 ± 1.9 [10]

120I

1.35 h

39–81

56.1 ± 3.2 [11]

124I

4.18 d

21.6–26

22 ± 0.5 [10, 11, 12]

Nuclear reaction data

General

In contrast to nuclear structure and radioactive decay data, whose scope is generally limited up to excitation energies of about 10 MeV, the nuclear reaction data cover a very broad span of energies, extending from a few meV up to the region of several GeV. The lower side of the energy scale is typical of neutrons and encompasses cold, thermal and epithermal regions. The major applications of nuclear data in those regions are related to structural analysis of solids, quantitative determination of elements via activation analysis, and fission reactor technology. The neutron capture cross sections and fission yields are also useful for production of radionuclides, especially for medical applications. The energy region from about 10 keV to a few MeV can be reached both by neutrons and charged particles, and it is particularly interesting for astrophysics and fusion research, especially with respect to the interactions of light charged particles. Neutrons up to 20 MeV energy have been extensively utilised in the development work related to fast reactors and future fusion technology. With increasing energies, monoenergetic neutrons become rarer, so that work above 30 MeV is done mostly using charged particles or spectral neutrons.

The body of available nuclear reaction data is huge but well organised. Experimental data published in any part of the world are compiled within a few months in the EXFOR file, coordinated by the IAEA. The data evaluation is performed in many regions of the world and, after validation and quality assurance, the data are placed at the disposal of users in extensive evaluated nuclear data files (e.g. ENDF-B VII). In addition some special purpose files like Fission Products, Activation Data, Neutron Dosimetry, Fusion Data, Medical Applications, etc. are also prepared. The data files contain all reliable data, measured by all techniques (including the radiochemical method), and substantiated by nuclear model calculations.

Radiochemical technique

The radiochemical technique of cross section measurement is advantageously used in the following cases:
  • Preparation of thin samples for irradiation, especially with charged particles.

  • Study of low-yield reactions, i.e. when the cross section of the reaction under investigation is low and the matrix activity (i.e. the radioactivity of the undesired products) is high.

  • Study of soft-radiation emitters. This is the case when the product decays via β emission or EC without any accompanying γ-ray. The radionuclides decaying by EC are characterised by X-ray counting, which can be performed only when a thin source has been prepared.

  • Characterisation of low-lying isomeric states. The low energy transitions can be detected advantageously after chemical separation and using a high-resolution low-energy detector.

Extensive use was made of the radiochemical technique in the determination of fission yields and activation cross sections. With the increasing use of high-resolution solid state detectors in γ-ray spectrometry, the importance of radiochemical measurements has somewhat diminished. Nonetheless, there are still many interesting areas where this technique is almost ideally suited or where it has advantages over the other methods. An extensive programme of work utilising this technique has been underway at Jülich for more than 30 years. A brief description of the areas pursued is given below.

Nuclear model calculations

Low energy nuclear reactions are commonly treated in terms of the statistical model, generally using the Hauser–Feshbach formalism, which takes into account the angular momentum of the evaporated particle and the level structure of the product nucleus. An early code developed for calculations was named HELGA. Later the pre-compound effect was also introduced and the relevant codes GNASH (in USA) and STAPRE (in Europe) in several versions have been very successfully utilized over the last 30 years in evaluating excitation functions, especially of neutron induced reactions up to 20 MeV.

Above 20 MeV the pre-compound effect becomes increasingly important and, at energies above 50 MeV, it plays a dominant role. A very commonly used code in the intermediate energy region was ALICE, developed by Blann also about 30 years ago. Recently the Obninsk group introduced several modifications and termed it as the code ALICE-IPPE. The incorporated modifications include treatment of the level density in a sophisticated way and consideration of the pre-equilibrium cluster emission (d, t and 4He). The code has been successfully applied to the calculation of excitation functions of a large number of reactions.

In recent years two further calculational codes, namely EMPIRE-II and TALYS, have also been introduced. The former combines the general features of the statistical process, the pre-equilibrium excitation model and the various improvements mentioned above. The code TALYS incorporates all reaction mechanisms (including direct interactions) and appears to be very successful.

The radiochemical work at Jülich has mostly been substantiated by the model calculations using the code HELGA in early works and the codes STAPRE and ALICE-IPPE in later works. Only in a few recent studies EMPIRE and TALYS codes were also used.

Complex particle emission in interaction of neutrons with nuclei

In interactions between nuclei and neutrons mostly nucleons and electromagnetic radiation are emitted. The emission of light complex particles (d, t, 3He, α, 7Li, 7Be, etc.) may also occur with a low probability in the light mass region, but in the heavier nuclei, it is rather rare. Due to both experimental and calculational difficulties not many studies have been done (for a detailed review on this topic cf. Ref. [13]). First reliable results on trinucleon emission reactions in the medium and heavy mass elements were obtained via extensive use of radiochemical separations [14, 15, 16, 17, 18]. Tritium and 3He emission was studied mainly using residual product identification [14, 15, 16, 17, 18], tritium counting [19] and MS [20]. The α-particle emission data were obtained both via MS and measurement of the reaction products. In studies on deuteron emission, the radiochemical data [21] gave a sum of (n,d + pn) processes, so that the contribution of the deuteron could be deduced only by model calculation. For 7Be detection, γ-ray spectrometry in combination with radiochemical separations was applied.

Studies with 14 MeV neutrons

Systematic studies on the (n,t) reaction performed in the early 1970s at Jülich [14, 15] showed that the light elements have a high cross section. The cross section decreases with the increasing mass of the target nucleus and the results for medium and heavy mass nuclei are shown in Fig. 1. Some investigations done at Debrecen [22, 23] showed that the data for odd-mass target nuclei follow a somewhat different trend. Presumably the large differences in Q-values for the (n,t) reactions on odd- and even-mass target nuclei are responsible for this effect.
Fig. 1

Updated version of the systematics of (n,t) reaction cross sections at 14.6 ± 0.4 MeV for nuclei with Z > 22 (data from Refs. [14, 15, 22, 23])

The (n,3He) reaction was still more difficult to characterise since this process constitutes almost the weakest reaction channel at 14 MeV. Till 1970, only two reliable cross section values were available [24, 25]. Extensive measurements [16, 18] done by the author in the 1970s established the systematic trend in the cross section which is shown in Fig. 2. The trend is somewhat similar to that for (n,t) cross sections on even mass nuclei (cf. Fig. 1); in terms of absolute magnitude, however, the (n,3He) cross section is by an order of magnitude smaller than the (n,t) cross section. It is worth pointing out that several groups (e.g. in Algeria, China, Germany and Turkey) have recently attempted to establish new systematics of (n,3He) cross sections. The basis for all those studies, however, has been the 13 data points reported by the author 30 years ago (cf. Fig. 2).
Fig. 2

Systematics of (n,3He) reaction cross sections at 14.6 ± 0.4 MeV for medium and heavy mass nuclei (taken from Ref. [18])

Regarding deuteron emission, as mentioned above, the radiochemical technique gave only limited information since the measured data gave a sum of the cross sections of (n,d), (n,n′p) and (n,pn) processes. By comparison with some physical measurements, however, quite useful information could be obtained. A summary of extensive radiochemical studies [21] is given in Fig. 3. The data fall on two curves, one (A) for nuclei with the neutron separation energy (S n) higher than the proton separation energy (S p), and the other (B) for S n < S p. For comparison, the curve for proton emission (C) is also shown [26]. Interesting is the trend (D) for pure d emission which is based on the integration of emitted deuteron spectra [27, 28]. Obviously in the medium mass region the major contribution to the radiochemically determined cross section is furnished by deuteron emission. In more general terms, the deuteron emission probability amounts to about 10% of the proton emission probability.
Fig. 3

Gross trends in (n,p), (n,d) and (n,d + n′p + pn) reaction cross sections at 14–15 MeV. The curves A–C are based on radiochemical measurements and systematic analyses done at Jülich, and the curve D on deuteron spectral analysis [27, 28] (taken from Ref. [21])

In contrast to d, t and 3He-particle emission processes, the α-particle emission has been extensively investigated, both by radiochemical and spectral measurements. The reaction mechanism is known fairly well and the systematics of cross section data are comparable to those for proton emission. The radiochemical method proved to be particularly useful where the radioactive product is a soft radiation emitter [29, 30], e.g. in reactions 48Ti(n,α)45Ca and 58Ni(n,α)55Fe, or in the region of lanthanoids [31], where the γ-ray spectra are rather complex. The contribution of the (n,n′α) process to total α-emission could also be established [32]:it amounts to be about 10%.

Nuclear model calculations using the code HELGA, which was based on a statistical approach, incorporating the Hauser–Feshbach formalism (see above), showed [33] that whereas the nucleon emission, and to some extent α-particle emission, in the interactions of 14 MeV neutrons with medium and heavy mass nuclei, are described well by statistical processes, the emission of d and 3He occurs mostly via direct interactions. The emission of a triton, on the other hand, involves contributions of both statistical and direct processes.

Effect of increasing neutron energy

The dependence of complex particle emission on the energy of the incident neutron was investigated in two ways: (a) excitation function measurements using monoenergetic neutrons in the energy range of 3–20 MeV, (b) integral cross section measurements using fast spectral neutrons.

Regarding the first methodology, excitation functions of only two (n,d) [34, 35], two (n,3He) [36, 37] but 13 (n,t) reactions [38, 39, 40, 41, 42, 43] could be measured in various mass regions, mainly near their thresholds. The (n,t) cross section data for a few selected medium and heavy mass nuclei are reproduced in Fig. 4. As expected, the cross section increases with neutron energy but an interesting observation is that the cross section at a particular energy is practically constant while proceeding from 59Co to 209Bi. This may suggest the occurrence of surface reactions.
Fig. 4

Excitation functions of (n,t) reactions on 27Al, 59Co, 93Nb and 181Ta. The solid and open points give the experimental data. The solid line is an eye-guide, and the dashed curve denotes the results of Hauser–Feshbach calculations (taken from Refs. [23, 38, 43])

The results of statistical model calculations on the (n,t) reaction using the HELGA code (see above) are also shown in Fig. 4. Evidently, the statistical model reproduces the (n,t) excitation function of Al very well. With the increasing mass of the target nucleus, however, the statistical contribution appears to decrease drastically. In those cases possibly direct interactions play an important role. Similar calculations on the 93Nb(n,3He)91Y and 139La(n,3He)137Cs excitation functions [36, 37] showed that the emission of 3He is dominated by direct interactions. Regarding d emission, calculations on the 58Ni(n,d)57Co reaction [34] were done using HELGA and on the 92Mo(n,d)91Nb reaction [35] using a more sophisticated program STAPRE. In both cases the statistical process was found to be less significant than the direct interactions. In contrast, the experimental excitation functions of a large number of (n,α) reactions could be satisfactorily described [30] by a combination of statistical, precompound and direct processes, the contribution of the latter being relatively small.

As far as the second methodology was concerned, i.e. integral measurements using fast spectral neutrons, extensive studies were performed on about 35 target nuclei distributed over the whole periodic table of the elements. Two types of spectral neutrons with different average energies were utilized. They were produced by the breakup of deuterons on a thick Be target. In one study the energy of the deuterons used was 30 MeV and in the other 53 MeV. The neutron spectra generated in the two cases are well characterised from 2 MeV up to the maximum deuteron energy, with average neutron energies of about 13 and 22.5 MeV, respectively.

In all cross section measurements, extensive use was made of radiochemical separations, and the radioactivity was determined via β ray counting, high-resolution γ-ray spectrometry, scintillation counting or gas phase counting. On one hand the residual radioactive product of a nuclear reaction was assayed and, on the other, attempts were made to identify the emitted complex particle, accumulated in the thick target. This was extensively done for the (n,t) reaction [44, 45, 46] with 30 MeV d(Be) neutrons and the results of product identification and tritium counting were compared with those calculated using the statistical model code HELGA. The measured integral (n,t) cross sections confirmed the results of excitation function measurements. Furthermore, by performing a series of integral measurements on the accumulated tritium after irradiation of an element with spectral neutrons generated by bombarding a Be target with varying deuteron energies between 17.5 and 30 MeV, it was possible to calculate the excitation function of the (n,t) reaction on that element via an iterative unfolding technique [45, 46]. This work thus also established a new method for determining the excitation function of a reaction after irradiations with a set of standardised broad neutron spectra.

The 53 MeV d(Be) neutrons showing a hard spectrum were used to study t, 3He, 4He and 7Be emission [19, 20, 47, 48, 49]. In each case residual product identification was done as in the case of the 30 MeV d(Be) neutrons. Furthermore, the accumulated tritium was chemically separated and assayed by gas phase counting. 7Be was also chemically separated and subjected to γ-ray spectrometry. The ratio of 3He to 4He emitted particles was determined mass spectrometrically using a quadrupole mass spectrometer. The results showed that a triton is easily emitted from the light mass nuclei. In medium and heavy mass regions, on the other hand, a bound triton is emitted with a much lower probability than three nucleons; in the case of 3He emission, however, this could not be confirmed. The nuclear model calculations using the code HELGA gave integral results for (n,t), (n,3He) and (n,α) reactions again similar to those for the excitation functions described above. For the (n,7Be) reaction no model calculation could be done.

The trends in measured cross sections with 53 MeV d(Be) neutrons are shown in Fig. 5. The results for the (n,t) reaction on light mass nuclei fall on two curves, depending on whether the target is an even or an odd Z nucleus. Beyond titanium till bismuth, however, the cross section appears to be constant. The (n,α) reaction is an exception. Due to its extremely high binding energy, the probability of emission of an α-particle is almost comparable to that of a nucleon. The trends for t, 3He and 7Be emission, on the other hand, follow a definite pattern, i.e. the higher the charge of the emitted complex particle, the lower is its emission probability.
Fig. 5

Systematic trends in (n,t), (n,3He), (n,α) and (n,7Be) reaction cross sections induced by 53 MeV d(Be) breakup neutrons (taken from Refs. [13, 49])

Main conclusions of the study

Among the neutron induced complex particle emission reactions, most of the experimental and theoretical work to date has been performed on 4He emission. In general, the compound and precompound models together can adequately describe the 4He emission cross section. Relatively little radiochemical work has been done on d emission, but the few available results tend to show that this reaction is dominated by direct interactions. On the other hand, radiochemical methods have contributed appreciably to the study of trinucleon emission reactions. Whereas in the case of t emission both compound and direct processes play an important role, the 3He emission appears to be dominated by direct interactions. The emission of heavier particles like 7Be has been relatively little investigated. In particular, no excitation function has been measured and the available data refer to only integral measurements with a broad neutron spectrum. In general, with the exception of d and 4He emissions, it appears that the higher the charge of the emitted complex particle, the lower is its emission probability.

Isomeric cross sections

In comparison to the total cross section of a reaction channel, the partial cross section for the population of a particular nuclear level is more difficult to measure and to calculate. As mentioned above, the radiochemical technique is ideally suited for the measurement of isomeric cross sections since via a combination of clean chemical separation and high resolution X- or γ-ray spectrometry it is possible to characterise even low-lying levels. Over the last 20 years extensive investigations have been performed at FZ Jülich in cooperation with IRK Vienna University and IEP Debrecen University. The isomeric pairs investigated were: 52m,gMn, 58m,gCo, 60m,gCo, 69m,gZn, 71m,gZn, 75m,gGe, 73m,gSe, 94m,gTc, 141m,gNd, 120m,gI, 197m,gHg, etc., involving different combinations of target, projectile, ejectile, and level structure of the product nucleus [50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67]. It was found that the isomeric cross section ratio depends on the spins of the two concerned levels of the product nucleus and not on their separation energy. Furthermore, the yield of the high-spin isomer increases with the increasing projectile energy. The experimental results [64] for the formation of a typical isomeric pair 52m,gMn are given in Fig. 6. The important role of the spins of the involved states is confirmed. The cross section of the low-spin isomer in comparison to that of the high-spin ground state initially decreases with the increasing incident projectile energy, but becomes almost constant at high excitation energies. The magnitudes of the cross section ratio differ considerably. It is concluded that the reaction channel influences the isomeric cross section ratio appreciably, particularly when the channels differ widely, e.g. (p,n) and (3He,t) processes.
Fig. 6

Experimental isomeric cross section ratios for the formation of 52m,gMn in several nuclear reactions, plotted as a function of the incident particle energy (taken from Ref. [64])

As regards nuclear model calculations, mostly the code STAPRE was used which incorporates statistical and precompound effects, but not direct interactions. Good agreement could be obtained between the experimental data and theoretical calculations only after a very careful choice of the input parameters for the calculations. In particular it was found that a knowledge of the level structure of the product nucleus plays a very important role. Furthermore, the assumed spin distribution of the level density influenced the calculated isomeric cross section considerably. The results for a typical isomeric pair 58m,gCo in the 61Ni(p,α) reaction [55] are shown in Fig. 7. The metastable state has a spin value of (5+) and the ground state (2+). The characterisation of the low-energy transition (E = 25 keV) was facilitated by the radiochemical method. The experimental data are reproduced approximately by the STAPRE calculation, especially when the η value (ratio of θ eff to θ rigid, which refers to the spin distribution of the level density) is properly chosen. A recent study [65] indicated that the best value of η to describe the isomer ratio probably depends on the mass of the target nucleus. Further work is, however, needed to confirm this.
Fig. 7

Isomeric cross section ratio for the 61Ni(p,α)58m,gCo process as a function of proton energy. The nuclear model calculation was done using the code STAPRE for two values of η (ratio of θ eff to θ rig) to demonstrate the effect of spin distribution of level density (taken from Ref. [55])

Fusion reactor technology

Attempts to harness the energy released in the fusion of light nuclei have been underway for more than 40 years. Although, in principle, several fusion reactions could be used for power production, the fusion of deuterium and tritium, giving rise to a 14.06 MeV neutron and a 3.52 MeV α-particle, appears to be the most promising reaction due to several reasons: (a) it needs a relatively low ignition temperature, (b) the fusion cross section is high even at low energies, (c) the energy released is appreciably higher than in many other reactions. On the other hand, the neutron released has both some advantages and disadvantages. It is this neutron which will be the source of fusion energy but it is the same neutron which will cause most of the radioactivity in a fusion reactor.

An early analysis of the technological problems involved [68], nuclear data needs [69] and, above all, the role of radiochemical methods in the determination of nuclear data for fusion reactor technology [70], was performed at the Forschungszentrum Jülich. Regarding nuclear data, neutron reaction data from thermal energies up to about 20 MeV are of prime importance. The radiochemically determined data are of significance in estimation of nuclear transmutation products, especially hydrogen and helium gas production in first wall constituents, tritium breeding in blanket materials, and in making an inventory of total radioactivity, i.e. a summation of all activation products in various components of the reactor system. In 1970s and 1980s considerable attention was devoted to neutronics problems of a fusion system. But in 1990s those activities were considerably reduced. Some of the salient results are discussed below.

Transmutation products

Due to high energy and intensity of the neutrons generated during the thermonuclear fusion, a large number of nuclear reactions will be induced in the constituents of the first wall separating the plasma zone from the reactor blanket. In general, neutron emission processes (i.e. (n,xn) reactions) will dominate but charged particle emission reactions ((n,xp, (n,xα), etc.) will also occur [71].

The (n,xn) reaction cross sections are important with respect to neutron multiplication in the reactor blanket. The (n,xp) and (n,xα) processes, on the other hand, lead to the formation of a few new elements and, if the first wall remains in the reactor for a few years, the quantity of the new elements may become appreciable. Also the decay of the (n,xn) reaction products may lead to new elements. All those processes would eventually lead to a change in the physical and mechanical properties of the structural materials. Early estimates showed that if Nb were to be used as the first wall material, in 20 years time the amount of transmuted products (Tc, Mo, Zr, Y, etc.) may reach up to 20%.

The (n,xp) and (n,xα) reactions have two further serious effects. Firstly, they cause extra nuclear heat. Secondly, they lead to the accumulation of hydrogen and helium gases. Whereas the presence of hydrogen is not a very serious problem, since it rapidly diffuses out of the structural materials at elevated temperatures, the helium gas may facilitate void formation by nucleation, having thereby adverse effects on the quality of the materials.

In view of the great significance of (n,xp) and (n,xα) processes, and considering that radiochemical separations can be very useful in identification of some special radioactive products, an extensive research programme has been underway in our institute since early 1970s. Measurements of (n,p) and (n,α) reaction cross sections were performed on a large number of potential first wall constituents, e.g. Al, V, Ti, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, W, Pb, etc. [26, 29, 30, 31, 35, 51, 53, 54, 56, 58, 63, 66, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91]. The neutron energy region studied extended from about 3 to 20 MeV. Part of the work was done in collaboration with IRMM Geel, Belgium, and IEP, Debrecen University, Hungary. In several cases, the energy regions between 3 and 13 MeV and between 15 and 20 MeV were investigated for the first time, and experimental data showed good agreement with the results of modern nuclear model calculations. At 14 MeV, the radiochemically determined data were also found to be in agreement with the values obtained by an integration of the proton and α-particle spectra [27, 28]. For the (n,α) reaction, mass spectrometrically determined data [92] also agreed with the radiochemical and spectrum integrated data.

Through careful radiochemical measurements using highly enriched isotopes of a few elements as target materials, it was also shown for the first time that the contributions of the [(n,d) + (n,n′p)] and (n,n′α) processes at 14 MeV are not negligible. The cross section of the (n,n′α) reaction [32] was found to be about 10% of the respective (n,α) reaction cross section. Similarly the cross sections of the [(n,d) + (n,n′p)] reactions [21, 71, 74] on normal nuclei were found to be about 20% of the respective (n,p) reaction cross sections. In the special case of the lightest stable nucleus of an element, with the neutron separation energy higher than the proton separation energy, the [(n,d) + (n,n′p)] cross section [21] may be comparable to the respective (n,p) reaction cross section (see section “Studies with 14 MeV neutrons”).

In addition to the (n, charged particle) reactions, the (n,2n) reactions were also systematically studied [66, 75, 78, 81, 82, 83, 86, 87, 88, 93, 94]. The results obtained through the above mentioned investigations considerably strengthened the data base for the (n,2n), (n,xp) and (n,xα) reactions. The available data should thus now be very reliable for various calculations related to neutron multiplication, formation of transmutation products, accumulation of hydrogen and helium gases, and generation of nuclear heat in the first wall materials of a fusion reactor.

In addition to measurements of cross sections of neutron induced reactions on structural materials leading to the formation of transmutation products, the cross sections of interactions of neutrons with an expected long-lived transmuted species, namely 99Tc (T½ = 2.1 × 105 a), were also measured [95, 96, 97]. This was possible through a skilful radiochemical handling of the radioactive target material. The data should be useful in designing strategies for the transmutation of this long-lived radionuclide.

Tritium breeding

Out of the two presently discussed plasma fuel materials (deuterium and tritium), deuterium is available in nature. Tritium will, however, have to be bred in the blanket, i.e. the zone between the first wall and the outer parts of the reactor. This will be done via the (n,t) reaction. A literature survey shows that the (n,t) excitation function has been measured from threshold up to about 20 MeV only for 13 target nuclei. Among all those cases only the (n,t) reaction on 6Li and 7Li has high cross section and is thus suitable for breeding purposes. The fusion reactor blanket will therefore consist of 6,7Li-containing materials. The calculation of tritium breeding ratios in various types of lithium-containing materials thus requires, on the one hand, accurate (n,t) reaction cross sections on 6Li and 7Li and on the other, neutron economy, i.e. minimum loss of neutrons through interactions with materials other than 6,7Li. If the breeding ratio is too low, the whole process of fuel production and recovery may be jeopardized.

The excitation function of the 6Li(n,t)4He reaction is known very well. In the case of 7Li(n,n′t)4He reaction, however, considerable discrepancies existed. It is interesting to note that the cross section for this reaction could be determined through the following six routes.
  1. (a)

    Neutron scattering studies

     
  2. (b)

    Energy and angular distribution of the emitted tritons, followed by an integration of the spectrum

     
  3. (c)

    Energy and angular distribution of the associated α-particle, followed by an integration of the spectrum

     
  4. (d)

    Mass spectrometric determination of 4He

     
  5. (e)

    Mass spectrometric determination of tritium

     
  6. (f)

    Chemical separation and β counting of the accumulated tritium

     
Although in principle all the six routes could lead to satisfactory data, the occurrence of some competing reactions, like 7Li(n,2nd)4He, which do not contribute to the formation of tritium, may falsify the results. This was reflected in the evaluation ENDF/B-VI which was based on a consideration of all the existing data. Accurate tritium measurements [40] showed that the excitation function is about 20% lower than the ENDF/B-VI values. The results based on tritium counting are reproduced in Fig. 8. Evidently, for estimating tritium breeding ratios in the blanket, it is mandatory to consider only the tritium production reactions.
Fig. 8

7Li(n,n′t)4He reaction cross section (determined via tritium counting) as a function of incident neutron energy (taken from Ref. [40])

Activation products

Besides (n,xp), (n,xα), (n,2n) and (n,t) reactions mentioned above, (n,γ) and several other low-yield reactions also occur. They may all lead to activation products. Of major concern in this respect are the products with long half-lives. Considerable efforts have therefore been devoted to developing low activation materials. The IAEA identified 16 reactions of major concern, out of which the following processes were investigated at Jülich [88, 98, 99, 100, 101] in cooperation with other laboratories: 27Al(n,2n)26Al (T½ = 7.2 × 105 a), 63Cu(n,p)63Ni (T½ = 100 a), 94Mo(n,p)94Nb (T½ = 2.03 × 104 a), 109Ag(n,2n)108mAg (T½ = 418 a), 151Eu(n,2n)150mEu (T½ = 36.9 a) and 159Tb(n,2n)158Tb (T½ = 180 a). All the products could be determined via low-level γ-ray spectrometry except for 63Ni, which emits only a very soft β particle of end-point energy 67 keV. The excitation function of the 63Cu(n,p)63Ni reaction was therefore measured radiochemically [100] using low-level β counting. The results are shown in Fig. 9. For comparison the results of four evaluations, which were done before the measurements, are also given. All of them are based on the statistical model but used different input parameters. Evidently, the prediction of cross section via the model calculation was not very reliable. The need of careful experimental studies, especially for reactions of key importance, is thus imminent.
Fig. 9

Excitation function of the 63Cu(n,p)63Ni reaction (measured radiochemically). The results of four evaluations, all based on the statistical model but with different input parameters, are also shown (taken from Ref. [100])

Concluding remarks about nuclear data for fusion

Extensive efforts have led to the establishment of several data files and the status of data with regard to the formation of transmutation products, tritium breeding and activation of materials is now fairly good. Several sophisticated nuclear model calculational codes have also been developed. Nonetheless, there are still extensive needs of high-quality data and, with the upcoming demonstration experiment ITER, the nuclear data activities relevant to fusion are expected to be rejuvenated. The interdisciplinary approach of radiochemical methods will certainly contribute appreciably to this field.

Medical radionuclide production

General

In nuclear medicine programmes involving radionuclides, both radioactive decay data and nuclear reaction cross section data are needed. In general, the nuclear decay data are well known, except for some special cases, as discussed above in section “Nuclear structure and nuclear decay data”. They find application in determining the imaging modality and in internal radiation dose calculations. The nuclear reaction data, on the other hand, need constant improvement. They are needed in radionuclide production, mainly for optimisation of production routes, i.e. for maximising the yield of the desired radionuclide and minimising the level of radioactive impurities. Since radionuclides are produced in reactors as well as at cyclotrons, both neutron and charged particle induced reaction cross section data are required. The energy ranges involved are rather broad. In the case of neutrons mostly thermal energies and fission neutron spectrum are important, and in charged particles, energy ranges extending from a few MeV to several hundred MeV.

In reactor production of radionuclides, the most commonly used nuclear routes include (n,γ), (n, fission) and (n, charged particle) processes. The (n,γ) reaction has generally a high cross section at thermal neutron energies, so that the yield of the product is rather high. However, a serious drawback of the process is the low specific radioactivity which makes the radionuclide less suitable for medical applications. The fission process is a very suitable method to produce a large number of radionuclides in a “no-carrier-added” form. The chemical processing involved, however, is rather extensive. The (n,p) and (n,α) reaction cross sections are generally low; these processes are therefore used to produce only a few radionuclides in the light mass element region. In general, the cross section data base for the reactor production of radionuclides is well established.

In cyclotron production of radionuclides, the reaction cross section data play a very important role (for reviews cf. [102, 103, 104, 105]). Due to rapid degradation of the projectile energy in the target material, the energy range covered within the target is relatively broad, and since the reaction cross section varies rather rapidly with energy, it is not appropriate to adopt an average cross section over the whole energy range. One needs rather the full excitation function of the nuclear process to be able to calculate the yield with a reasonable accuracy. Production of radionuclides may be carried out using protons, deuterons, 3He- or α-particles. A knowledge of all the reaction cross sections is necessary. At small-sized cyclotrons, low-energy reactions like (p,n), (p,α), (d,n), (d,α), etc. are used. At higher energies, on the other hand, (p,xn) reactions are commonly employed. In some special cases, the (p,spall) process is applied.

Standard radionuclides

Some radiochemical measurements on cross sections for the production of a few radionuclides via neutron induced reactions were carried out [83, 106, 107, 108, 109, 110, 111], partly in collaboration with PINSTECH, Islamabad, Pakistan. The nuclear activities in our institute, however, have mainly concentrated on charged particle induced reactions. Here thin sample preparation plays a very special role. The determination of radioactivity, however, could be done in many cases via conventional γ-ray spectrometry (without chemical separation), though occasionally clean radiochemical separations were absolutely necessary to obtain accurate data (e.g. while investigating β ray, X-ray and low-energy γ-ray emitters).

Considerable efforts were devoted to optimisation and standardisation of data for production of commonly used diagnostic radionuclides [112, 113, 114, 115, 116, 117, 118, 119, 120, 121]. These included photon emitters like 123I (T½ = 13.2 h), 201Tl (T½ = 73.1 h) and 81Rb/81mKr (T½ = 4.6 h/13 s) generator, which find applications in Single Photon Emission Tomography (SPECT), and standard positron emitters 11C (T½ = 20.3 min), 13N (T½ = 10.0 min), 15O (T½ = 2.0 min) and 18F (T½ = 110 min), which are used in Positron Emission Tomography (PET). Furthermore, data for the formation of 82Sr (T½ = 25.3 d), which is the parent of the positron emitter 82Rb (T½ = 1.2 min), were also standardised [122].

Of particular interest were the measurements of cross sections of the 18O(p,n)18F reaction which is now commonly used for the production of the most widely used PET radionuclide 18F. Use of thin gaseous and solid samples containing highly enriched 18O, and utilization of several accelerators available at Jülich and Debrecen, made it possible to determine the cross section accurately [121] and thus to establish a reliable database. The results are shown in Fig. 10. The resonances at 5.1, 6.1 and 7.2 MeV are in agreement with those found in spectral measurements of emitted neutrons. It should be pointed out that nuclear model calculations cannot predict excitation functions of reactions on light nuclei with reliable accuracies; careful experimental activation measurements are thus absolutely necessary.
Fig. 10

Excitation function of the 18O(p,n)18F reaction. Results of both neutron and activation measurements are shown. The rather bold curve is an eye-guide to the activation data (taken from Ref. [121])

Novel radionuclides

In addition to nuclear data work on standard diagnostic radionuclides mentioned above, considerable efforts were devoted in our institute over the last 25 years, partly in collaboration with ATOMKI, Debrecen, Hungary, iThemba LABS, Cape Town, South Africa, and Cyclotron Laboratory of EAEA, Cairo, Egypt to development of novel radionuclides [114, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173]. A few radionuclides like 28Mg (T½ = 21.0 h) [123, 124], 43K (T½ = 22.2 h) [125], 48Cr (T½ = 21.6 h) [126], 57Co (T½ = 271.8 d) [127], 88Y (T½ = 106.6 d) [167, 168], 95Ru (T½ = 1.6 h), 97Ru (T½ = 2.9 d) [128], 117mSm (T½ = 13.6 d) [129], 147Gd (T½ = 38.1 h) [130], etc., were developed for a few special applications. The possibility of formation of 99mTc at a cyclotron was also investigated [131]. The emphasis was, however, on non-standard positron emitters and novel therapeutic radionuclides. A brief summary of those two areas of work is given below.

Non-standard positron emitters

The list of non-standard PET radionuclides whose production methods were developed includes 22Na (T½ = 2.6 a) [132], 30P (T½ = 2.5 min) [133], 38K (T½ = 7.5 min) [134, 135], 51Mn (T½ = 46.2 min) [136], 52Fe (T½ = 8.3 h) [137], 55Co (T½ = 17.6 h) [138, 139], 64Cu (T½ = 12.7 h) [8, 9], 72As (T½ = 26.0 h) [140], 73Se (T½ = 7.1 h) [141, 142], 75Br (T½ = 1.6 h), 76Br (T½ = 16.0 h) [143, 144, 145, 146, 147, 148, 149], 77Kr (T½ = 1.2 h) [150], 82mRb (T½ = 6.2 h) [151], 82Sr/82Rb (25.3 d/1.2 min) generator system [152, 153, 154], 83Sr (T½ = 32.4 h) [155], 86Y (T½ = 14.7 h) [156], 94mTc (T½ = 53 min) [157, 158, 159], 120gI (T½ = 1.3 h) [160, 161], 124I (T½ = 4.18 d) [114, 162, 163, 164]. Among them 64Cu, 86Y and 124I are finding worldwide attention.

Regarding 64Cu, the suggested nuclear route [8] 64Ni(p,n)64Cu, using highly enriched target material, is being commercialized. The labelling of monoclonal antibodies with 64Cu has led to several new therapeutic approaches.

Regarding 124I, extensive nuclear data studies [114, 162, 163, 164] made it possible to choose the reaction of choice. A summary of the results is given in Table 2. The method of choice is the 124Te(p,n)124I reaction. The excitation function of this reaction together with that of the competing 124Te(p,2n)123I reaction is shown in Fig. 11. Although over the suggested energy range the yield of 124I is not very high, the reaction leads to the purest form of 124I. The radionuclide is both a diagnostic and a therapeutic agent. Concerning diagnostic studies, the slow uptake kinetics of an iodo-radiopharmaceutical by an organ can be conveniently followed using this radionuclide and PET. Regarding therapeutic use, 124I was found to be very suitable for labelling organic molecules for tumour research.
Table 2

Production routes of 124Ia

Nuclear reaction

Energy range (MeV)

Thick target yield of 124I (MBq/μA h)

Impurity (%)

123I

125I

126I

124Te(d,2n)

14 → 10

17.5

1.7

124Te(p,n)

12 → 8

16

1.0

<0.1

125Te(p,2n)

21 → 15

81

7.4

0.9

126Te(p,3n)

38 → 28

222

148

1.0

1.0

natSb(α,xn)

22 → 13

1.02

890

13

16

121Sb(α,n)

22 → 13

2.1

895

<0.2

<0.2

natSb(3He,xn)

35 → 13

0.95

3,877

0.6

0.6

aAll values are based on measurements done at Jülich

Fig. 11

Excitation functions of 124Te(p,n)124I and 124Te(p,2n)123I reactions. The suitable energy range for the production of 123I is E p = 25.0 → 18.0 MeV and that for 124I it is E p = 12 → 8 MeV (taken from Ref. [114])

The radionuclide 86Y was produced via the 86Sr(p,n)86Y reaction [156]. This route is also being commercialized. The radionuclide finds application as a positron emitting analogue of the pure beta emitting therapeutic radionuclide 90Y. The uptake kinetics are measured via a PET study of 86Y and the therapeutic effect is induced by 90Y. This is a new approach and is finding considerable interest in internal open source radiotherapy.

Novel therapeutic radionuclides

Therapeutic radionuclides are generally produced in a nuclear reactor since they are mostly β emitters. In recent years the cyclotrons have been increasingly utilized, especially for production of radionuclides emitting low-energy β particles, Auger electrons, X-rays and α-particles. At Jülich novel production route were investigated for the therapeutic radionuclides 67Cu (T½ = 61.9 h) [165, 166], 103Pd (T½ = 16.96 d) [169, 170], 140Nd (T½ = 3.37 d) [171], 153Sm (T½ = 46.3 h) [172] and 193mPt (T½ = 4.33 d) [173]. The radionuclides 67Cu and 153Sm emit low-energy β particles whereas 103Pd, 140Nd and 193mPt emit Auger (or conversion) electrons and X-rays. We discuss a typical case below.

The radionuclide 193mPt is a pure X-ray and Auger electron emitter, each decay leading to about 33 secondary electrons. It has thus great potential in Auger electron therapy, provided it can be obtained as a high specific radioactivity product. It can be produced via the 192Pt(n,γ) reaction but, due to its very high spin, the yield is low and consequently the specific radioactivity is also very low. We studied the 192Os(α,3n)193mPt reaction [173] using highly enriched target material which was electrolytically deposited on a Ni foil. Each irradiated sample was radiochemically processed and the radioactivity of 193mPt was determined via high-resolution X-ray spectrometry. The results are shown in Fig. 12. The cross section of the reaction reaches an appreciable value at 27 MeV and it is expected to attain a saturation value of about 1 barn at an α-particle energy of about 35 MeV. The radionuclide could thus be produced in a high yield in no-carrier-added form. Further radiochemical work on these lines is needed.
Fig. 12

Cross section data (measured radiochemically) for the 192Os(α,n)195mPt and 192Os(α,3n)193mPt nuclear reactions. The curves give eye-guides (taken from Ref. [173])

Remarks about nuclear data work for medical radionuclide production

The work has led to optimisation and standardisation of common production routes of the SPECT radionuclides 123I and 201Tl, the most important PET radionuclide 18F and the commonly used therapeutic radionuclide 103Pd. Furthermore, it has contributed to the development of about 15 non-standard positron emitters and several potentially useful Auger electron emitting therapeutic radionuclides. In particular, the production routes of three longer-lived positron emitters, viz. 64Cu, 86Y and 124I, developed at Jülich, are finding worldwide attention and are now being commercialized. Those three novel positron emitters are opening new perspectives in radioimmunotherapy and radiation dosimetry.

Radiation therapy

The internal radiotherapy using suitable radionuclides, as discussed above, is a fast developing field. However, presently radiation therapy is carried out mostly using external radiation beams. Thus, standard radiation therapy implies almost exclusively teletherapy and involves the use of low-energy electrons, X-rays, γ-rays, high-energy electrons or high-energy photons. In all those cases only atomic interactions are important, and are well understood, the significance of nuclear data being negligible. Occasionally slow neutron capture therapy is also used. This may involve the introduction of a boron-containing chemical in some specific part of the body, followed by irradiation with slow neutrons. The captured neutron interacts with the boron according to the reaction 10B(n,α)7Li. The α- and 7Li-particles emitted in this reaction are absorbed in the tissue and generate a lot of heat, thereby inducing the therapeutic effect. The cross section of the nuclear reaction at thermal energies is well known. At higher neutron energies, however, the reaction 10B(n,t)2α may also occur; its cross section was unknown. We measured the excitation function of this reaction [39] in connection with our studies on (n,t) reactions described in section “Complex particle emission in interaction of neutrons with nuclei”. The data may be useful in optimisation of the therapy with neutrons containing some hard components.

An important and modern modality of therapy involves the use of hadrons, i.e. neutrons and charged particles, both produced at cyclotrons. Fast neutrons are generally generated via one of the two interactions: (a) deuteron break-up at a Be target and (b) protons on Be. Very commonly about 50 MeV deuterons and 66 MeV protons are utilized for neutron production. The therapeutic effect is induced by the secondary particles, especially charged particles, generated in the interactions of neutrons with the tissue constituents. In general, an accurate knowledge of the spectral distribution of the emitted particles is required, the radiochemically determined data being only of secondary importance. Nonetheless extensive data measurements with 53 MeV d(Be) neutrons [47, 48], described in section “Complex particle emission in interaction of neutrons with nuclei”, should provide some useful information on the formation of activation products during neutron therapy.

Beams of charged particles have a unique dose distribution, exhibiting a relatively flat entrance dose region (plateau) followed by a sharp dose peak, the Bragg peak, in which the particles lose rest of their energy [103]. Among various charged particles, protons are commonly used. Their therapeutic range of energies is between 60 and 250 MeV. The therapeutic effect is caused by secondary radiation. Thus, besides total, elastic and nonelastic scattering cross sections, the energy- and angle-dependent emission spectra of γ-rays, neutrons and secondary charged particles are needed. All those data are obtained either by physical measurements or nuclear model calculations. The radiochemical method, on the other hand, delivers useful information on the formation of activation products.

Measurement of activation products was done in the interactions of protons of energies up to 200 MeV with biologically relevant and beam collimator materials. It was found that the amount of 7Be accumulated is negligible [174]. Similarly the medium mass activation products are also not significant [175]. The activation of collimators, however, is appreciable [176, 177] and due precautions are necessary to protect the therapy personnel. The formation of short-lived positron emitters is, however, of considerable interest.

Comprehensive studies on the formation of the positron emitting radionuclides 11C, 13N, 15O and 18F exist in the literature (see section “Medical radionuclide production”), mainly due to their use in PET studies. The data are, however, generally limited up to 30 MeV. Since in proton therapy energies higher than 30 MeV are involved, it was considered worthwhile to strengthen the database by performing cross section measurements also in the higher energy range. It has been shown [178] that the activation products of major concern in proton therapy are 11C, 13N and 15O. The data for the formation of 15O are fairly well known, also in the high energy range. We therefore concentrated primarily on the proton induced reactions on nitrogen and oxygen, leading to the formation of 11C and 13N. Excitation functions were measured [120] using the activation technique up to 200 MeV.

It needs to be pointed out that the quantities of short-lived positron emitters formed during proton therapy are high enough to allow PET studies for dose localisation. Initially it was done after proton therapy but in recent years on-line monitoring is becoming more common. Despite this progress, an estimate of the total radioactivity was rather uncertain, mainly due to the weak database. Furthermore, the radiation dose caused by those positron emitters had not been calculated.

Using the strengthened database, the yields of the three radionuclides, viz. 11C, 13N and 15O, formed in the human tissue were calculated as a function of the incident proton energy [178]. Under standard therapy conditions of a brain tumour (150 MeV p, 2nA, 2 min), 280 MBq of the three positron emitters are formed. This quantity appears to be sufficient for on-line or subsequent PET studies to localise the dose. The calculated dose deposited by the positron emitters in the brain amounted to 5.5 mGy [178]. This dose turns out to be <1% of the total dose deposited in the proton therapy. It is thus negligible but has been quanified for the first time [178].

In summary, the standard radiation therapy involves mostly atomic interactions, the role of nuclear data being negligible. Also in proton therapy the secondary electrons cause the major therapeutic effect. Only in calculation of the activation products, nuclear reaction cross section data are needed. In fast neutron therapy, on the other hand, extensive sets of nuclear data are needed. The radiochemical technique leads to high quality data for the formation of activation products.

Conclusions

The radiochemical method of nuclear data determination is well established; it complements on-line physical measurements. The radiochemical technique is advantageously used in investigations on low-yield reaction products, soft-radiation emitters and low-lying isomeric states. Combined with nuclear model calculations, the measured data can lead to some mechanistic information on the nuclear reaction. The radiochemically measured data are of considerable practical importance, especially in nuclear technology, cyclotron production of medical radionuclides and radiation therapy. It should be emphasised that nuclear data research demands interdisciplinary approaches and cooperative efforts. It constitutes an interesting science and useful technology.

Notes

Acknowledgements

The article gives a brief review of the work carried out over a period of more than 35 years at the Institute of Nuclear Chemistry of the Research Centre Jülich, Germany. I am highly indebted to Professor Dr. G. Stöcklin and Prof. Dr. H. H. Coenen, the former and present directors of the Institute, for their continuous support of this field of study, and to my own research group for painstaking efforts in acquisition and analysis of data. A large number of Ph.D. students and guest scientists also contributed appreciably to our efforts. My special thanks are due to about 10 Hungarian scientists for a long-term and fruitful cooperation both in experimental studies and nuclear model calculations. The partial financial supports of some external funding agencies like DFG, DAAD, EU, IAEA, etc. are gratefully acknowledged.

References

  1. 1.
    Evaluated Nuclear Structure Data File (ENSDF) (2007) National Nuclear Data Center (NNDC), Brookhaven, USA, and International Atomic Energy Agency (IAEA), ViennaGoogle Scholar
  2. 2.
    Firestone RB (1996) Table of isotopes, CDROM-Edition, Version 1.0. Wiley-Interscience, New YorkGoogle Scholar
  3. 3.
    Butement FDS, Qaim SM (1964) J Inorg Nucl Chem 26:1481, 1491Google Scholar
  4. 4.
    Qaim SM (1965) J Inorg Nucl Chem 27:759CrossRefGoogle Scholar
  5. 5.
    Butement FDS, Qaim SM (1965) J Inorg Nucl Chem 27:907CrossRefGoogle Scholar
  6. 6.
    Qaim SM (1966) Nucl Phys 84:411CrossRefGoogle Scholar
  7. 7.
    Qaim SM (1970) Nucl. Phys. A154:145Google Scholar
  8. 8.
    Szelecsènyi F, Blessing G, Qaim SM (1993) Appl Radiat Isot 44:575CrossRefGoogle Scholar
  9. 9.
    Hilgers K, Stoll T, Skakun Y, Coenen HH, Qaim SM (2003) Appl Radiat Isot 59:343CrossRefGoogle Scholar
  10. 10.
    Qaim SM, Bisinger T, Hilgers K, Nayak D, Coenen HH (2007) Radiochim Acta 95:67CrossRefGoogle Scholar
  11. 11.
    Hohn A, Coenen HH, Qaim SM (2000) Radiochim Acta 88:139CrossRefGoogle Scholar
  12. 12.
    Qaim SM, Hohn A, Bastian Th, El-Azoney KM, Blessing G, Spellerberg S, Scholten B, Coenen HH (2003) Appl Radiat Isot 58:69CrossRefGoogle Scholar
  13. 13.
    Qaim SM (1995) Radiochim Acta 70/71:163Google Scholar
  14. 14.
    Qaim SM, Stöcklin G (1973) J Inorg Nucl Chem 35:19CrossRefGoogle Scholar
  15. 15.
    Qaim SM, Stöcklin G (1976) Nucl Phys A257:233Google Scholar
  16. 16.
    Qaim SM (1974) J Inorg Nucl Chem 36 (1974), 239; Erratum p. 3886Google Scholar
  17. 17.
    Qaim SM, Wölfle R, Stöcklin G (1974) J Radioanalyt Chem 21:395CrossRefGoogle Scholar
  18. 18.
    Qaim SM (1978) Radiochim Acta 25:13Google Scholar
  19. 19.
    Qaim SM, Wölfle R, Stöcklin G (1974) J Inorg Nucl Chem 36:3639CrossRefGoogle Scholar
  20. 20.
    Wu CH, Wölfle R, Qaim SM (1979) Nucl Phys A329:63Google Scholar
  21. 21.
    Qaim SM (1982) Nucl Phys A382:255Google Scholar
  22. 22.
    Biró T, Sudàr S, Miligy Z, Dezsö Z, Csikai J (1975) J Inorg Nucl Chem 37:1583CrossRefGoogle Scholar
  23. 23.
    Sudár S, Csikai J (1979) Nucl Phys A319:157Google Scholar
  24. 24.
    Csikai J, Szalay A (1965) Nucl Phys 68:546CrossRefGoogle Scholar
  25. 25.
    Hussain L, Bari A, Kuroda PK (1968) J Inorg Nucl Chem 30:3145CrossRefGoogle Scholar
  26. 26.
    Molla NI, Qaim SM (1977) Nucl Phys A283:269Google Scholar
  27. 27.
    Grimes SM, Haight RC, Alvar KR, Barschall HH, Borchers RR (1979) Phys Rev C19:2127Google Scholar
  28. 28.
    Haight RC, Grimes SM, Johnson RG, Barschall HH (1981) Phys Rev C23:700Google Scholar
  29. 29.
    Qaim SM, Wölfle R, Rahman MM, Ollig H (1984) Nucl Sci Eng 88:143Google Scholar
  30. 30.
    Qaim SM, Uhl M, Molla NI, Liskien H (1992) Phys Rev C46:1398Google Scholar
  31. 31.
    Qaim SM (1984) Radiochim Acta 35:5Google Scholar
  32. 32.
    Qaim SM (1986) Nucl Phys A458:237Google Scholar
  33. 33.
    Qaim SM, Klapdor HV, Reiss H (1980) Phys Rev C22:1371Google Scholar
  34. 34.
    Qaim SM, Wölfle R (1985) Phys Rev C32:305Google Scholar
  35. 35.
    Qaim SM, Wölfle R, Strohmaier B (1989) Phys Rev C40:1993Google Scholar
  36. 36.
    Qaim SM, Wölfle R, Liskien H (1986) Phys Rev C34:489Google Scholar
  37. 37.
    Qaim SM, Wölfle R (1991) Acta Phys Hung 69:137Google Scholar
  38. 38.
    Qaim SM, Wölfle R, Liskien H (1982) Phys Rev C25:203Google Scholar
  39. 39.
    Suhaimi A, Wölfle R, Qaim SM, Stöcklin G (1986) Radiochim Acta 40:113Google Scholar
  40. 40.
    Qaim SM, Wölfle R (1987) Nucl Sci Eng 96:52Google Scholar
  41. 41.
    Liskien H, Widera R, Wölfle R, Qaim SM (1988) Nucl Sci Eng 98:266Google Scholar
  42. 42.
    Suhaimi A, Wölfle R, Qaim SM, Warwick P, Stöcklin G (1988) Radiochim Acta 43:133Google Scholar
  43. 43.
    Wölfle R, Qaim SM, Liskien H, Widera R (1990) Radiochim Acta 50:5Google Scholar
  44. 44.
    Wölfle R, Khatun S, Qaim SM (1984) Nucl Phys A432:130Google Scholar
  45. 45.
    Wölfle R, Sudár S, Qaim SM (1985) Nucl Sci Eng 91:162Google Scholar
  46. 46.
    Wölfle R, Suhaimi A, Qaim SM (1993) Nucl Sci Eng 115:71Google Scholar
  47. 47.
    Qaim SM, Wölfle R (1978) Nucl Phys A295:150Google Scholar
  48. 48.
    Qaim SM, Wu CH, Wölfle R (1983) Nucl Phys A410:421Google Scholar
  49. 49.
    Scholten B, Qaim SM, Stöcklin G (1993) Radiochim Acta 62:107Google Scholar
  50. 50.
    Qaim SM (1985) Nucl Phys A438:384Google Scholar
  51. 51.
    Mannan A, Qaim SM (1988) Phys Rev C38:630Google Scholar
  52. 52.
    Qaim SM, Mushtaq A, Uhl M (1988) Phys Rev C38:645Google Scholar
  53. 53.
    Qaim SM, Majah MIbn, Wölfle R, Strohmaier B (1990) Phys Rev C42:363Google Scholar
  54. 54.
    Molla NI, Qaim SM, Uhl M (1990) Phys Rev C42:1540Google Scholar
  55. 55.
    Sudár S, Szelecsényi F, Qaim SM (1993) Phys Rev C48:3115Google Scholar
  56. 56.
    Cserpák F, Sudár S, Csikai J, Qaim SM (1994) Phys Rev C49:1525Google Scholar
  57. 57.
    Qaim SM (1994) In: Proceedings of international conference on nuclear data for science and technology, Gatlinburg, American Nuclear Society, La Grange Park, IL, p 186 (1994)Google Scholar
  58. 58.
    Birn I-G, Strohmaier B, Freiesleben H, Qaim SM (1995) Phys Rev C52:2546Google Scholar
  59. 59.
    Sudár S, Qaim SM (1996) Phys Rev C53:2885Google Scholar
  60. 60.
    Strohmaier B, Fassbender M, Qaim SM (1997) Phys Rev C56:2654Google Scholar
  61. 61.
    Dóczi R, Sudár S, Csikai J, Qaim SM (1998) Phys Rev C58:2577Google Scholar
  62. 62.
    Sudár S, Hohn A, Qaim SM (2000) Appl Radiat Isot 52:937CrossRefGoogle Scholar
  63. 63.
    Nesaraja CD, Sudár S, Qaim SM (2003) Phys Rev C68:024603Google Scholar
  64. 64.
    Qaim SM, Sudár S, Fessler A (2005) Radiochim Acta 93:503CrossRefGoogle Scholar
  65. 65.
    Sudár S, Qaim SM (2006) Phys Rev C73:034613Google Scholar
  66. 66.
    Al-Abyad M, Sudár S, Comsan MN, Qaim SM (2006) Phys Rev C73:064608Google Scholar
  67. 67.
    Hilgers K, Sudár S, Qaim SM (2007) Phys Rev C76:06401Google Scholar
  68. 68.
    Ihle H, Jordan HL, Stöcklin G (1973) Chem Ing Tech 45:621CrossRefGoogle Scholar
  69. 69.
    Qaim SM, Wölfle R, Stöcklin G (1976) Atomki Közlemények 18:335Google Scholar
  70. 70.
    Qaim SM, Wölfle R, Stöcklin G (1976) J Radioanalyt Chem 30:35CrossRefGoogle Scholar
  71. 71.
    Qaim SM (1978) In: Proceedings of international conference on neutron physics and nuclear data for reactors and other applied purposes, Harwell, September 1978 (OECD-NEA, Paris, 1978), p 1073Google Scholar
  72. 72.
    Qaim SM, Graca C (1975) Nucl Phys A242:317Google Scholar
  73. 73.
    Qaim SM (1976) Radiochem Radioanalyt Lett 25:335Google Scholar
  74. 74.
    Qaim SM, Molla NI (1976) In: Proceedings of 9th symposium on fusion technology, Garmisch-Partenkirchen, Germany, June 1976, EUR 5602, Pergamon Press, p 589Google Scholar
  75. 75.
    Rahman MM, Qaim SM (1985) Nucl Phys A435:43Google Scholar
  76. 76.
    Wölfle R, Mannan A, Qaim SM, Liskien H, Widera R (1988) Appl Radiat Isot 39:407CrossRefGoogle Scholar
  77. 77.
    Liskien H, Wölfle R, Widera R, Qaim SM (1990) Appl Radiat Isot 41:83CrossRefGoogle Scholar
  78. 78.
    Majah MIbn, Qaim SM (1990) Nucl Sci Eng 104:271Google Scholar
  79. 79.
    Molla NI, Qaim SM, Liskien H, Widera R (1991) Appl Radiat Isot 42:337CrossRefGoogle Scholar
  80. 80.
    Molla NI, Qaim SM, Kalka H (1992) Phys Rev C45:3002Google Scholar
  81. 81.
    Birn I, Qaim SM (1994) Nucl Sci Eng 116:125Google Scholar
  82. 82.
    Bostan M, Qaim SM (1994) Phys Rev C49:266Google Scholar
  83. 83.
    Klopries RM, Dóczi R, Sudár S, Csikai J, Qaim SM (1997) Radiochim Acta 76:3Google Scholar
  84. 84.
    Fessler A, Wattecamps E, Smith DL, Qaim SM (1998) Phys Rev C58:996Google Scholar
  85. 85.
    Fessler A, Qaim SM (1991) Radiochim Acta 84:1Google Scholar
  86. 86.
    Nesaraja C, Linse K-H, Spellerberg S, Sudár S, Suhaimi A, Qaim SM (1999) Radiochim Acta 86:1Google Scholar
  87. 87.
    Majah MIbn, Chiadli A, Sudár S, Qaim SM (2001) Appl Radiat Isot 54:655CrossRefGoogle Scholar
  88. 88.
    Reimer P, Avrigeanu V, Plompen AJM, Qaim SM (2002) Phys Rev C65:014604Google Scholar
  89. 89.
    Reimer P, Hult M, Plompen AJM, Johnston PN, Avrigeanu V, Qaim SM (2002) Nucl Phys A705:265Google Scholar
  90. 90.
    Reimer P, Avrigeanu V, Chuvaev SV, Filatenkov AA, Glodariu T, Koning A, Plompen AJM, Qaim SM, Smith DL, Weigmann H (2005) Phys Rev C71:044617Google Scholar
  91. 91.
    Semkova V, Reimer P, Altzitzoglu T, Plompen AJM, Quétel C, Sudár S, Vogl J, Koning AJ, Qaim SM, Smith DL (2009) Phys Rev C80:024610Google Scholar
  92. 92.
    Kneff DW, Oliver BM, Farrar H IV, Greenwood LR (1986) Nucl Sci Eng 92:491Google Scholar
  93. 93.
    Qaim SM (1972) Nucl Phys A185:614Google Scholar
  94. 94.
    Qaim SM (1974) Nucl Phys A224:319Google Scholar
  95. 95.
    Qaim SM (1973) J Inorg Nucl Chem 35:3669CrossRefGoogle Scholar
  96. 96.
    Molnar GL, Belgya T, Révay Zs, Qaim SM (2002) Radiochim Acta 90:479CrossRefGoogle Scholar
  97. 97.
    Reimer P, Koning AJ, Plompen AJM, Qaim SM, Sudár S (2009) Nucl Phys A815:1Google Scholar
  98. 98.
    Qaim SM, Cserpák F, Csikai J (1992) Appl Radiat Isot 43:1065CrossRefGoogle Scholar
  99. 99.
    Qaim SM, Cserpák F, Csikai J (1996) Appl Radiat Isot 47:569CrossRefGoogle Scholar
  100. 100.
    Qaim SM, Spellerberg S, Cserpák F, Csikai J (1996) Radiochim Acta 73:111Google Scholar
  101. 101.
    Sudbrock F, Herpers U, Qaim SM, Csikai J, Kubik RW, Synal H-A, Suter M (2000) Radiochim Acta 88:829CrossRefGoogle Scholar
  102. 102.
    Qaim SM (1982) Radiochim Acta 30:147Google Scholar
  103. 103.
    Qaim SM (2001) Radiochim Acta 89:189CrossRefGoogle Scholar
  104. 104.
    Qaim SM (2001) Radiochim Acta 89:223CrossRefGoogle Scholar
  105. 105.
    Qaim SM (2001) Radiochim Acta 89:297CrossRefGoogle Scholar
  106. 106.
    Qaim SM, Rusheed A, Stöcklin G, Wölfle R (1977) Int J Appl Radiat Isot 28:585CrossRefGoogle Scholar
  107. 107.
    Michael H, Wölfle R, Qaim SM (1984) Int J Appl Radiat Isot 35:813CrossRefGoogle Scholar
  108. 108.
    Zaidi JH, Karim HMA, Qaim SM (1985) Radiochim Acta 38:123Google Scholar
  109. 109.
    Zaidi JH, Karim HMA, Arif M, Qureshi IH, Qaim SM (1990) Radiochim Acta 49:107Google Scholar
  110. 110.
    Spahn I, Coenen HH, Qaim SM (2004) Radiochim Acta 92:183CrossRefGoogle Scholar
  111. 111.
    Al-Abyad M, Spahn I, Sudár S, Morsy M, Comsan MNH, Csikai J, Qaim SM, Coenen HH (2006) Appl Radiat Isot 64:717CrossRefGoogle Scholar
  112. 112.
    Zaidi JH, Qaim SM, Stöcklin G (1983) Int J Appl Radiat Isot 34:1425CrossRefGoogle Scholar
  113. 113.
    Scholten B, Qaim SM, Stöcklin G (1989) Appl Radiat Isot 40:127CrossRefGoogle Scholar
  114. 114.
    Scholten B, Kovács Z, Tárkányi F, Qaim SM (1995) Appl Radiat Isot 46:255CrossRefGoogle Scholar
  115. 115.
    Tárkányi F, Qaim SM, Stöcklin G, Sajjad M, Lambrecht RM, Schweickert H (1991) Appl Radiat Isot 42:221CrossRefGoogle Scholar
  116. 116.
    Qaim SM, Weinreich R, Ollig H (1979) Int J Appl Radiat Isot 30:85CrossRefGoogle Scholar
  117. 117.
    Kovács Z, Tárkányi F, Qaim SM, Stöcklin G (1991) Appl Radiat Isot 42:329CrossRefGoogle Scholar
  118. 118.
    Szücs Z, Hamkens W, Takács S, Tárkányi F, Coenen HH, Qaim SM (1998) Radiochim Acta 80:59Google Scholar
  119. 119.
    Kovács Z, Scholten B, Tárkányi F, Coenen HH, Qaim SM (2003) Radiochim Acta 91:185CrossRefGoogle Scholar
  120. 120.
    Kettern K, Shubin YN, Steyn GF, Van Der Walt TN, Coenen HH, Qaim SM (2004) Appl Radiat Isot 60:939CrossRefGoogle Scholar
  121. 121.
    Hess E, Takács S, Scholten B, Tárkányi F, Coenen HH, Qaim SM (2001) Radiochim Acta 89:357CrossRefGoogle Scholar
  122. 122.
    Qaim SM, Steyn GF, Spahn I, Spellerberg S, Van Der Walt TN, Coenen HH (2007) Appl Radiat Isot 65:247CrossRefGoogle Scholar
  123. 123.
    Probst HJ, Qaim SM, Weinreich R (1976) Int J Appl Radiat Isot 27:431CrossRefGoogle Scholar
  124. 124.
    Weinreich R, Qaim SM, Michael H, Stöcklin G (1976) J Radioanal Chem 30:53CrossRefGoogle Scholar
  125. 125.
    Qaim SM, Probst HJ (1984) Radiochim Acta 35:11Google Scholar
  126. 126.
    Weinreich R, Probst H-J, Qaim SM (1980) Int J Appl Radiat Isot 31:223CrossRefGoogle Scholar
  127. 127.
    Al-Abyad M, Comsan MNH, Qaim SM (2009) Appl Radiat Isot 67:122CrossRefGoogle Scholar
  128. 128.
    Comparetto G, Qaim SM (1980) Radiaochim Acta 27:177Google Scholar
  129. 129.
    Qaim SM, Döhler H (1984) Int J Appl Radiat Isot 35:645CrossRefGoogle Scholar
  130. 130.
    Denzler F-O, Rösch F, Qaim SM (1995) Radiochim Acta 69:209Google Scholar
  131. 131.
    Scholten B, Lambrecht RM, Cogneau M, Vera Ruiz H, Qaim SM (1999) Appl Radiat Isot 51:69CrossRefGoogle Scholar
  132. 132.
    Takács S, Tárkányi F, Qaim SM (1996) Appl Radiat Isot 47:303CrossRefGoogle Scholar
  133. 133.
    Sahakundu SM, Qaim SM, Stöcklin G (1979) Int J Appl Radiat Isot 30:3CrossRefGoogle Scholar
  134. 134.
    Qaim SM, Sutisna MS, Ollig H (1988) Appl Radiat Isot 39:479CrossRefGoogle Scholar
  135. 135.
    Tárkányi F, Kovács Z, Qaim SM, Stöcklin G (1992) Appl Radiat Isot 43:503CrossRefGoogle Scholar
  136. 136.
    Klein ATJ, Rösch F, Qaim SM (2000) Radiochim Acta 88:135CrossRefGoogle Scholar
  137. 137.
    Fessler A, Alfassi ZB, Qaim SM (1994) Radiochim Acta 65:207Google Scholar
  138. 138.
    Zaman MR, Qaim SM (1996) Radiochim Acta 75:59Google Scholar
  139. 139.
    Reimer P, Qaim SM (1998) Radiochim Acta 80:113Google Scholar
  140. 140.
    Spahn I, Steyn G, Nortier MF, Coenen HH, Qaim SM (2007) Appl Radiat Isot 65:1057CrossRefGoogle Scholar
  141. 141.
    Mushtaq A, Qaim SM, Stöcklin G (1988) Appl Radiat Isot 39:1085CrossRefGoogle Scholar
  142. 142.
    Mushtaq A, Qaim SM (1990) Radiochim Acta 50:27Google Scholar
  143. 143.
    Qaim SM, Stöcklin G, Weinreich R (1977) Int J Appl Radiat Isot 28:947CrossRefGoogle Scholar
  144. 144.
    Kovács Z, Blessing G, Qaim SM, Stöcklin G (1985) Int J Appl Radiat Isot 36:635CrossRefGoogle Scholar
  145. 145.
    Qaim SM, Blessing G, Ollig H (1986) Radiochim Acta 39:57Google Scholar
  146. 146.
    Tárkányi F, Kovács Z, Qaim SM (1993) Appl Radiat Isot 44:1105CrossRefGoogle Scholar
  147. 147.
    Qaim SM, Stöcklin G (1993) Appl Radiat Isot 44:1443CrossRefGoogle Scholar
  148. 148.
    Hassan HE, Qaim SM, Shubin YN, Azzam A, Morsy M, Coenen HH (2004) Appl Radiat Isot 60:899CrossRefGoogle Scholar
  149. 149.
    Spahn I, Steyn GF, Vermeulen C, Kovács Z, Szelecsèny F, Coenen HH, Qaim SM (2009) Radiochim Acta 97:535CrossRefGoogle Scholar
  150. 150.
    Youfeng He, Qaim SM, Stöcklin G (1982) Int J Appl Radiat Isot 33:13CrossRefGoogle Scholar
  151. 151.
    Kovács Z, Tárkányi F, Qaim SM, Stöcklin G (1991) Appl Radiat Isot 42:831CrossRefGoogle Scholar
  152. 152.
    Tárkányi F, Qaim SM, Stöcklin G (1988) Appl Radiat Isot 39:135CrossRefGoogle Scholar
  153. 153.
    Tárkányi F, Qaim SM, Stöcklin G (1988) Radiochim Acta 43:185Google Scholar
  154. 154.
    Tárkányi F, Qaim SM, Stöcklin G (1990) Appl Radiat Isot 41:91CrossRefGoogle Scholar
  155. 155.
    Kastleiner S, Qaim SM, Nortier FM, Blessing G, Van Der Walt TN, Coenen HH (2002) Appl Radiat Isot 56:685CrossRefGoogle Scholar
  156. 156.
    Rösch F, Qaim SM, Stöcklin G (1993) Radiochim Acta 61:1Google Scholar
  157. 157.
    Rösch F, Qaim SM, Radiochim. Acta 62 (1993) 115; Erratum 75 (1996) 227Google Scholar
  158. 158.
    Fassbender M, Novgorodov AF, Rösch F, Qaim SM (1994) Radiochim Acta 65:215Google Scholar
  159. 159.
    Denzler F-O, Rösch F, Qaim SM (1995) Radiochim Acta 68 (1995), 13; Erratum 75 (1996), 227Google Scholar
  160. 160.
    Hohn A, Scholten B, Coenen HH, Qaim SM (1998) Appl Radiat Isot 49:93CrossRefGoogle Scholar
  161. 161.
    Hohn A, Coenen HH, Qaim SM (1998) Appl Radiat Isot 49:1493CrossRefGoogle Scholar
  162. 162.
    Bastian TH, Coenen HH, Qaim SM (2001) Appl Radiat Isot 55:303CrossRefGoogle Scholar
  163. 163.
    Hohn A, Nortier FM, Scholten B, Van Der Walt TN, Coenen HH, Qaim SM (2001) Appl Radiat Isot 55:149CrossRefGoogle Scholar
  164. 164.
    Hassan KF, Qaim SM, Saleh ZA, Coenen HH (2006) Appl Radiat Isot 64:101CrossRefGoogle Scholar
  165. 165.
    Kastleiner S, Coenen HH, Qaim SM (1999) Radiochim Acta 84:107Google Scholar
  166. 166.
    Stoll T, Kastleiner S, Shubin YN, Coenen HH, Qaim SM (2002) Radiochim Acta 90:309CrossRefGoogle Scholar
  167. 167.
    Kettern K, Linse K-H, Spellerberg S, Coenen HH, Qaim SM (2002) Radiochim Acta 90:845CrossRefGoogle Scholar
  168. 168.
    Kandil SA, Spahn I, Scholten B, Saleh ZA, Saad SMM, Coenen HH, Qaim SM (2007) Appl Radiat Isot 65:561CrossRefGoogle Scholar
  169. 169.
    Sudár S, Cserpák F, Qaim SM (2002) Appl Radiat Isot 56:821CrossRefGoogle Scholar
  170. 170.
    Skakun Ye, Qaim SM (2008) Appl Radiat Isot 66:653CrossRefGoogle Scholar
  171. 171.
    Hilgers K, Shubin YN, Coenen HH, Qaim SM (2005) Radiochim Acta 93:553CrossRefGoogle Scholar
  172. 172.
    Qaim SM, Spahn I, Kandil SA, Coenen HH (2007) Radiochim Acta 95:313CrossRefGoogle Scholar
  173. 173.
    Hilgers K, Coenen HH, Qaim SM (2008) Appl Radiat Isot 66:545CrossRefGoogle Scholar
  174. 174.
    Fassbender M, Scholten B, Qaim SM (1998) Radiochim Acta 81:1Google Scholar
  175. 175.
    Fassbender M, Shubin YN, Qaim SM (1998) Radiochim Acta 84:59Google Scholar
  176. 176.
    Fassbender M, Shubin YN, Lunev VP, Qaim SM (1997) Appl Radiat Isot 48:1221CrossRefGoogle Scholar
  177. 177.
    Qaim SM, Kettern K, Shubin YN, Sudár S, Coenen HH (in press) Radiochim ActaGoogle Scholar
  178. 178.
    Kettern K, Coenen HH, Qaim SM (2009) Radiat Phys Chem 78:380CrossRefGoogle Scholar

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© Akadémiai Kiadó, Budapest, Hungary 2010

Authors and Affiliations

  1. 1.Institut für Neurowissenschaften und Medizin, INM-5: NuklearchemieJülichGermany

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