We have measured shifts in the isotopic a bundances of Gd and Sm in soils from the Apollo 17 deep drill stem and calculated the neutron fluence from these measurements. The measurements show two well defined regions of nearly constant fluence: (1) a thick deep section with a very large neutron fluence, and (2) a thinner shallow region with a small fluence. This depth dependence is most plausibly described by a model of rapid accumulation in the last 100–200 m.y., the layered structure reflecting accumulations of isotopically homogeneous source material. This interpretation is compatible with a variety of other characteristics of the soils, including the spallation produced126Xe normalized to target element abundances.
An alternative model of deposition, followed by irradiation without mixing, followed by shallow mixing will quantitatively describe the data. The model yields an age of 1.25 AE for the bottom of the drill stem. This model was rejected because of the implausible requirement that the soils from the drill stem be accumulated from a source of unirradiated material.
The uniformity of various properties of soils provides criteria for defining major stratigraphic intervals in the drill stem which differ from those identified by the Preliminary Examination Team.
Neutron fluences measured on shallow and deep soils from all lunar landing sites have been normalized to irradiation in an arbitrary standard chemical environment. We infer from histograms of the normalized fluences that there is a distinct difference in neutron fluence between shallow and deep samples which implies a general vertical stratification of neutron fluence in the lunar regolith.
The regolith can be divided into three vertical regions: (1) a well mixed surface layer, ∼100 g cm−2 thick, with an average fluence of 2.3 × 1016 n cm−2, (2) a poorly mixed zone extending from 100 g cm−2 to at least 500 g cm−2 with an average fluence of 3.5 × 1016 n cm−2, and (3) a deep layer of lightly irradiated materials (<1016 n cm−2). Analysis of this stratification, using a vertical mixing model, indicates that the probability of mixing to several hundred g cm−2 is comparable to the probability of mixing to several kg cm−2. This is in contrast to the depth-cratering rate models which have been inferred from crater size frequency distributions using a power law. Alternatively, this discrepancy can be resolved if the true157Gd capture rate is 1/3 of the value calculated by Lingenfelteret al. (1972). The most plausible interpretation is that vertical mixing models are not an adequate description of relatively rare deep cratering events which result in significant lateral heterogeneity and addition of unirradiated material to the lunar surface.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Tax calculation will be finalised during checkout.
Apollo 17 Lunar Sample Information Catalog: 1973, Lunar Receiving Laboratory (MSC 03211).
Apollo 17 Preliminary Examination Team: 1973,Science 182, 659–672.
Armstrong, T. W. and Alsmiller, R. G., Jr.: 1971,Proc. Second Lunar Sci. Conf. 2, 1729–1745.
Bogard, D. C., Nyquist, L. E., Hissek, W. C., and Moore, D. R.: 1973,Earth Planetary Sci. Letters 21, 52–69.
Brunfelt, A. O., Heier, K. S., Nilssen, B., Steinnes, E., and Sundvall, B.: 1974,Lunar Science V, 92–94.
Burnett, D. S. and Woolum, Dorothy, S.: 1974,Proc. Fifth Lunar Sci. Conf. 2, 2061–2074.
Burnett, D. S., Huneke, J. C., Podosek, F. A., Russ, G. Price, III, and Wasserburg, G. J.: 1971,Proc. Second Lunar Sci. Conf. 2, 1671–1679.
Crozaz, G., Drozd, R., Hohenberg, C., Morgan, C., Ralston, C., Walker, R., and Yuhas, D.: 1974,Proc. Fifth Lunar Sci. Conf. 3, 2475–2499.
Duke, M. B. and Nagle, J. S.: 1974, Lunar Core Catalog (JSC 09252), 16–17.
Duncan, A. R., Erlank, A. J., Willis, J. P., and Sher, M. K.: 1974,Lunar Science V, 184–186.
Eberhardt, P., Eugster, O., Geiss, J., Graf, H., Grogler, N., Guggisberg, S., Jungch, M., Maurer, P., Morgeli, M., and Stettler, A.: 1974,Lunar Science V, 197–199.
Eugster, O., Tera, F., Burnett, D. S., and Wasserburg, G. J.: 1970a,J. Geophys. Res. 75, 2753–2768.
Eugster, O., Tera, F., Burnett, D. S., and Wasserburg, G. J.: 1970b,Earth Planetary Sci. Letters 8, 20–30.
Gault, D. E., Horz, F., Brownlee, D. E., and Hartung, J. B.: 1974,Proc. Fifth Lunar Sci. Conf. 3, 2365–2386.
Heiken, Grant and McKay, David S.: 1974,Proc. Fifth Lunar Sci. Conf. 1, 843–860.
Huneke, J. C., Podosek, F. A., Burnett, D. S., and Wasserburg, G. J.: 1972,Geochim. Cosmochim. Acta 36, 269–301.
Helmke, Philip A., Blanchard, Douglas P., Jacobs, Jeffrey W., Telander, Karen M., and Haskin, Larry A.: 1973,EOS 54, 595.
Kornblum, J. J., Fireman, E. L., Levine, M., and Aronson, A.: 1973,Proc. Fourth Lunar Sci. Conf.,2, 2171–2186.
Lingenfelter, R. E., Canfield, E. H., and Hess, W. N.: 1961,J. Geophys. Res. 66, 2665–2671.
Lingenfelter, R. E., Canfield, E. H., and Hampel, V. E.: 1972,Earth Planetary Sci. Letters 16, 355–369.
Lugmair, G. W. and Marti, K.: 1971,Earth Planetary Sci. Letters 13, 32–42.
Nagle, J. S.: 1974, (personal communication).
Pepin, R. O., Basford, J. R., Dragon, J. C., Coscio, M. R., Jr., and Murthy, V. R.: 1974,Proc. Fifth Lunar Sci. Conf. 2, 2149–2182.
Philpotts, J. A., Schumann, S., Schnetzler, C. C., Kouns, C. W., Doan, A. S., Jr., Wood, F. M., Jr., Bichel, A. L., and Lum Staab, R. K. L.: 1973,EOS 54, 603–604.
Russ, G. P., III: 1972,Earth Planetary Sci. Letters 13, 384–386.
Russ, G. P., III: 1973,Earth Planetary Sci. Letters 19, 275–289.
Russ, G. P., III: 1974,Neutron Stratigraphy in the Lunar Regolith, Ph.D. Thesis, California Institute of Technology.
Russ, G. P., III, Burnett, D. S., and Wasserburg, G. J.: 1972,Earth Planetary Sci. Letters,15, 172–186.
Russ, G. P., III, Burnett, D. S., Lingenfelter, R. E., and Wasserburg, G. J.: 1971,Earth Planetary Sci. Letters 13, 53–60.
Shoemaker, E. M., Hart, M. H., Swann, G. A., Schleicher, D. L., Dahlem, D. H., Schaber, G. G., and Sutton, R. L.: 1970,Science 167, 452–455.
Soderblom, Laurence A. and Lebovsky, Larry A.: 1972,J. Geophys. Res. 77, 279–294.
Williams, M. M. R.: 1966,The Slowing Down and Thermalization of Neutrons, North-Holland, p. 93.
Woolum, Dorothy, S., Burnett, D. S., Furst, Marion, and Weiss, J. R.: 1975,The Moon, (in press).
About this article
Cite this article
Curtis, D.B., Wasserburg, G.J. Apollo 17 neutron stratigraphy —Sedimentation and mixing in the lunar regolith. The Moon 13, 185–227 (1975). https://doi.org/10.1007/BF00567515
- Landing Site
- Lunar Surface
- Drill Stem
- Neutron Fluence
- Size Frequency Distribution