Measurement of the lunar neutron density profile

Woolum, D. S.; Burnett, D. S.; Furst, Marian; Weiss, J. R.

doi:10.1007/bf00577879

Cited by 45 publications

(44 citation statements)

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“…This is a larger reduction than was suggested by Woolum et al (1975) based upon discrepancies between the neutron energy spectrum calculated by LCH (1972) and the actual energy spectrum in the regolith inferred by experiments.…”

Section: Discussionmentioning

confidence: 57%

“…The Cd ratio was greater at 373 g cm -2 than at 180 g cm-2 , indicating a shift in the neutron energy spectrum to lower energies with increasing depth. Woolum et al (1975) studied the differences between the calculated energy spectrum of LCH and the properties of the energy spectrum as measured by the LNPE and the isotopic measurements. They concluded that the divergence may be an indication that the 158 Gd production rate as calculated by LCH is too large by about a factor of two.…”

Section: The Lunar Neutron Energy Spectrummentioning

confidence: 99%

“…the LCH neutron spectrum and the properties of the lunar neutron spectrum which has been inferred from experiments (Woolum et al, 1975). Table VII is the low energy neutron capture rate (A).…”

Section: · ---· · ----mentioning

confidence: 99%

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Apollo 17 neutron stratigraphy ?Sedimentation and mixing in the lunar regolith

Curtis

Wasserburg

1975

The Moon

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Abstract. We have measured shifts in the isotopic abunctances 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 produced 126 Xe 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 x 10 16 n cm-2 , (2) a poorly mixed zone extending from I 00 g cm-2 to at least 500 g cm-2 with an average fluence of 3.5 x 10 16 n cm-2 , and (3) a deep layer of lightly irradiated materials ( < 10 16 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 true 157 Gd capture rate is t of the value calculated by Lingenfelter et al. (I 972).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.

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Section: Discussionmentioning

confidence: 57%

Section: The Lunar Neutron Energy Spectrummentioning

confidence: 99%

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Apollo 17 neutron stratigraphy ?Sedimentation and mixing in the lunar regolith

Curtis

Wasserburg

1975

The Moon

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“…these cal culated neutron fluxes at a lunar'depth of 4 g/cm2 , the ratio. of the total 117 "1/v" capture rate to that for neutrons with energies below 3 eV was deter mined to be 1.31, which is 0.74 of the factor used in RAT.The best measurement of the neutron density in the moon was made by the Apollo 17 Lunar Neutron Probe Experiment -LNPE- Burnett, 1974, andWoolum et al, 1975). From tracks produced by the 1 OB(n,a)-and 23 5 U(n,f) reactions, the lunar fluxes of low-energy neutrons were determined and com pared with the theoretical fluxes of LCH.…”

mentioning

confidence: 99%

“…From tracks produced by the 1 OB(n,a)-and 23 5 U(n,f) reactions, the lunar fluxes of low-energy neutrons were determined and com pared with the theoretical fluxes of LCH. Woolum et al (1975) concluded that the actual lunar neutron density was 0.8 of that used by LCH.To convert the Apoll.o 17 LNPE results to a solar-cycle average, Woolum and Burnett (1974) derived a solar-cycle correction factor based on neutron fluxes measured in the Earth's atmosphere and on neutron-monitor counting rates. Since the neutron-monitor counting rate was greater at the time of the Apollo 17 mission than that averaged over a solar cycle, the Apollo 17 flux of neutrons was estimated to be a factor of 1.21 greater than the aver age flux of neutrons (Woolum and Burnett, 1974).…”

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confidence: 99%

Gamma-ray spectroscopy in astrophysics

Ramaty

Kline

Weaver

1978

Nature

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This was the first symposium devoted entirely to spectroscopy in gamma ray astronomy. Its purposes were to bring together most of the scientists contributing to all the aspects, experimental and theoretical, of this new field and to discuss and compare ideas, measurements, calcu lations and technical experience in what we confidently expect to be a very important new discipline in high energy astrophysics.This goal was achieved, we feel, in that a very large fraction of all that is known about gamma ray spectroscopy in astrophysics was indeed presented or discussed at the Symposium, yet many of these results are new, presented here for the first time. Further, the discipline is on the brink of moving to the next level of development within the coming year, with a number of satellite experiments and major balloon experiments in gamma ray spectroscopy and in related astrophysical sciences about to be launched. We therefore felt that we should publish the Proceedings as soon as possible, without the delays involved in reformatting the manuscripts and extensive editing. We hope that the information that will thus become available will prove to be useful to all workers in these fields.We have ordered the papers approximately as presented, with experimental and theoretical papers combined in each session. The introductory session is followed by the sessions on solar, stellar, and planetary gamma ray spectroscopy, and on cosmic gamma ray spectroscopy, with the technical discussions and previews of new experiments in the last two sessions.The Symposium was organized by the editors of these proceedings, T. L. Cline and R. Ramaty. We wish to thank the Symposium Session Chairmen, D. D. Clayton, and M. M. Shapiro, and the Workshop Session Chairmen, G. J. Fishman and N. S. Wall, for their assistance. We are grateful to R. C. Reedy for supplying us the manuscript on Planetary Gamma Ray Spectro scopy which was not presented at the Symposium. This paper is taken from the Proceedings of the Ninth Lunar and Planetary Science Conference (Pergamon Press 1978, with permission). We are also indebted to R. W. Bussard and R. P. Weaver for their help in running the conference. We thank F. B. McDonald for his continued support of this Symposium, and R. S. Cooper for his interest and his contribution. We thank Barbara Pratt in particular for her excellent secretarial help with both the organization of the Symposium and the preparation of this document. It is a pleasure for me to be here and welcome you all to the Goddard Space Flight Center. I noticed from the agenda that we have speakers from all the major groups that are interested in high energy astronomy and in particular in gamma ray astronomy virtually in the entire free world. The agenda is particularly interesting to me and I intend to spend as much of my time here over the next day as I can. I would like to make a couple of points. The people here at Goddard know that when they give me an oppor tunity to come and welcome you, the potential is always there for me to say something...

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2009

Handbook of Spallation Research

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Measurement of the lunar neutron density profile

Abstract: capture rate is about one half of that calculated theoretically.

Cited by 45 publications

References 14 publications

Apollo 17 neutron stratigraphy ?Sedimentation and mixing in the lunar regolith

Apollo 17 neutron stratigraphy ?Sedimentation and mixing in the lunar regolith

Gamma-ray spectroscopy in astrophysics

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