Skip to main content
SpringerLink
Log in

Statistical emission of nucleons in reactions produced by 14 MeV neutrons

  • Published:
Il Nuovo Cimento (1955-1965)

Summary

We have analysed a certain number of nuclear reactions for medium and light nuclei (10<Z<40), particularly (n, p) reactions with 14 MeV neutrons. The expressionn(ɛ)/ɛσ*, which is proportional to the nuclear level density, is represented fairly well, forɛ in the range (4÷10) MeV, by an exponential law of the kinde ε/θ, beingθ=(1÷1.2) MeV for medium nuclei (20<Z<40) andθ=1.45 for lighter nuclei.σ* has been calculated assumingr 0=1.4·10−13 cm for neutrons andr 0=1.6·10−13 cm for protons. On such a basis the ratioσ(n, p)/σ(n, nI) is in good agreement with the evaporative model when one considers theQ values of the reaction and the fact that the residual nucleus is even-even or odd-odd. From such ratio, calculated for evenA nuclei, it is possible to obtain values of the pairing energyA in good agreement with that calculated by Cameron. Also for (n, 2n), (n, np) and (p, n) reactions on medium nuclei, the evaporative model gives satisfactory results for the interpretation of the cross-section variations.

Riassunto

È stato analizzato un certo numero di reazioni nucleari per nuclei medi e leggeri (10<Z<40) ed in particolare reazioni (n, p) prodotte da neutroni di 14 MeV. La espressionen(ɛ)/ɛσ* che è proporzionale alla densità dei livelli nucleari è abbastanza bene rappresentata per valori diɛ compresi tra 4 e 10 MeV, da una legge esponenziale del tipoe ε/θ conθ=(1÷1.2) MeV per nuclei medi conZ fra 20 e 40, eθ=1.45 MeV per nuclei più leggeri. Laσ*è stata calcolata assumendo per i neutronir 0=1.4·10−13 cm e per i protonir 0=1.6·10−13 cm. In questa ipotesi si ha che il rapportoσ(n, p)/σ(n, nI) è in buon accordo col modello evaporativo, quando si tenga conto del valore diQ della reazione e del fatto che il nucleo residuo sia pari-pari o dispari-dispari. Da tale rapporto, calcolato per i nuclei pari, si ottengono i valori della « pairing energy » Δ in buon accordo con quelli calcolati da Cameron. Anche nel caso della reazione (n, 2n), (n, np) e (p, n) per nuclei medi, il modello evaporativo spiega in modo soddisfacente le variazioni dei valori delle sezioni d’urto.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  1. L. Colli, U. Facchini, I. Iori, M. G. Marcazzan andA. M. Sona:Nuovo Cimento,13, 730 (1959).

    Article  Google Scholar 

  2. V. F. Weisskopf andD. H. Ewing:Phys. Rev.,57, 472 (1940).

    Article  ADS  Google Scholar 

  3. D. L. Allan:Nucl. Phys.,6, 464 (1958);10, 348 (1959).

    Article  Google Scholar 

  4. P. V. March andW. T. Morton:Phil. Mag.,3, 143 (1957);3, 577 (1958).

    Article  ADS  Google Scholar 

  5. I. Kumabe andR. W. Fink:Nucl. Phys.,15, 316 (1960).

    Article  Google Scholar 

  6. A. H. Amstrong andL. Rosen: to be published.

  7. B. L. Cohen andA. G. Rubin:Phys. Rev.,113, 579 (1959).

    Article  ADS  Google Scholar 

  8. H. W. Fullbright, N. O. Lassen andN. O. Roy Poulsen:Dan. Viden.,31, no. 10 (1959);N. O. Lassen andN. O. Roy Paulsen:Intern. Conf. on Low Energy Nuclear Physics in Paris (July 1958).

  9. J. Benveniste:Int. Conf. of Geneva, P/2494 (1958).

  10. P. C. Gugelot:Phys. Rev.,81, 51 (1951).

    Article  ADS  Google Scholar 

  11. H. Feshbach, M. M. Shapiro andV. F. Weisskopf: NYO-3077 (1954).

  12. J. M. Blatt andV. F. Weisskopf:Theoretical Nuclear Physics (New York, 1952), p. 352.

  13. T. Ericson:Nucl. Phys.,11, 481 (1959).

    Article  Google Scholar 

  14. P. C. Gugelot:Phys. Rev.,93, 425 (1954).

    Article  ADS  Google Scholar 

  15. R. Britten:Phys. Rev.,88, 283 (1952).

    Article  ADS  Google Scholar 

  16. G. Igo:Phys. Rev.,106, 256 (1957).

    Article  ADS  Google Scholar 

  17. B. L. Cohen:Phys. Rev.,116, 426 (1959).

    Article  ADS  Google Scholar 

  18. L. Colli, I. Iori, M. G. Marcazzan, F. Merzari, A. M. Sona andP. G. Sona:Nuovo Cimento, to be published.

  19. H. Feshbach:Ann. Rev. Nucl. Sic.,8, 49 (1958).

    Article  ADS  Google Scholar 

  20. J. A. Evans:Proc. Phys. Soc.,73, 33 (1958).

    Article  ADS  Google Scholar 

  21. E. R. Graves andL. Rosen:Phys. Rev.,89, 343 (1953).

    Article  ADS  Google Scholar 

  22. D. B. Thompson andL. Cranberg:Bull. Am. Phys. Soc. (April 30, 1959), p. 258.

  23. D. L. Allan:Proc. Phys. Soc., A70, 195 (1957).

    Article  ADS  Google Scholar 

  24. In studying the n, p spectrum on Zn with neutrons of 7 MeV obtained byRosen (6), as also the pp′ spectra ofCohen andRubin (7) obtained at 11.3 and 13.5 MeV for values ofɛ corresponding to lower emission energies ((2÷3) MeV), it should be noted that the curves undergo an appreciable displacement from the usual exponential of pendency:θ ≈ (1÷1.2) MeV. This displacement results in greater steepness of the curve which reminds us of the effect of secondary protons observed earlier above. Inversely, in these reactions the energy is too low to produce protons due to nnp or pnp reactions. The hypothesis that this displacement is due to insufficient knowledge ofσ* is supported by the fact that in the three examined cases the displacement occurs not by reason of aE determined value but rather by reason of different values ofE in the three cases and a determined value ofɛ around 3 MeV.

  25. L. Colli, U. Facchini, I. Iori, M. G. Marcazzan, A. Pignanelli andA. M. Sona:Nuovo Cimento,7, 400 (1958).

    Article  Google Scholar 

  26. L. Colli, F. Cvelbar, S. Micheletti andM. Pignanelli:Nuovo Cimento,13, 868 (1959);14, 1220 (1959).

    Article  Google Scholar 

  27. L. Colli, M. G. Marcazzan, F. Merzari, P. G. Sona andF. Tonolini: to be published inNuovo Cimento.

  28. L. Colli, F. Cvelbar, S. Micheletti andM. Pignanelli:Nuovo Cimento,14, 81 (1959).

    Article  Google Scholar 

  29. F. L. Ribe:Fast Neutron Physics: to be published.

  30. I. L. Preiss andR. W. Fink:Nucl. Phys.,15, 326 (1960).

    Article  Google Scholar 

  31. L. Colli, S. Micheletti andM. Pignanelli: to be published.

  32. M. H. MacGregor, W. P. Ball andR. Booth:Phys. Rev.,108, 726 (1957).

    Article  ADS  Google Scholar 

  33. J. Cameron:Can. Journ. Phys.,36, 1040 (1958).

    Article  ADS  Google Scholar 

  34. A. H. Wapstra:Physica,21, 378 (1955).

    Article  Google Scholar 

  35. H. G. Blosser andT. H. Handley:Phys. Rev.,100, 1340 (1955).

    Article  ADS  Google Scholar 

  36. H. A. Howe:Phys. Rev.,109, 2083 (1958).

    Article  ADS  Google Scholar 

Download references

Author information

Authors and Affiliations

  1. Istituto di Fisica dell’Università, Torino

    U. Facchini

  2. Laboratori CISE, Milano

    U. Facchini

  3. Laboratori CISE, Milano

    I. Iori & E. Menichella

Authors
  1. U. Facchini
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. I. Iori
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. E. Menichella
    View author publications

    You can also search for this author in PubMed Google Scholar

Rights and permissions

Reprints and permissions

About this article

Cite this article

Facchini, U., Iori, I. & Menichella, E. Statistical emission of nucleons in reactions produced by 14 MeV neutrons. Nuovo Cim 16, 1109–1131 (1960). https://doi.org/10.1007/BF02860393

Download citation

  • Received:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/BF02860393

Search

Navigation