Neutron capture effects on samarium, europium, and gadolinium in Apollo 15 deep drill-core samples

Hiroshi Hidaka, Mitsuru Ebihara, Shigekazu Yoneda

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

The isotopic compositions of Sm and Gd in seven lunar samples from the Apollo 15 deep drill core were determined to discuss the effects of neutron capture near the lunar surface. Large isotopic deviations of 150Sm/149Sm, 156Gd/155Gd, and 158Gd/157Gd derived from neutron capture effects were observed in all samples. Although neutron capture products in lunar samples were investigated extensively in the 1970s, our precise isotopic measurements resulted in several new findings. The neutron fluence in the Apollo 15 drill core is a function of depth with a symmetric peak at 190 g/cm2 depth from the surface, confirming the results of earlier investigations. Neutron fluence values calculated from the isotopic shifts by comparison to artificially irradiated standard reagents were (5.16-7.49) x 1016 n/cm2. These values are 1.3 to 1.4x larger than those previously reported. Variations of ε(Sm)/ε(Gd) with depth are interpreted as being due to variations in the neutron energy spectrum. Here ε(Sm) and ε(Gd) are defined as in previous studies of lunar neutron stratigraphy. Our data suggest that the neutron is more thermalized at the lower layers than it is at the upper layers. In addition to large isotopic shifts for 149Sm, 150Sm, 155Gd, 156Gd, 157Gd, and 158Gd, isotopic enrichments of 152Gd and 154Gd derived from neutron capture for 151Eu and 153Eu, respectively, were also observed in all samples.

Original languageEnglish
Pages (from-to)581-589
Number of pages9
JournalMeteoritics and Planetary Science
Volume35
Issue number3
DOIs
Publication statusPublished - 2000 Jan 1
Externally publishedYes

Fingerprint

capture effect
samarium
gadolinium
europium
neutrons
isotopic composition
stratigraphy
fluence
isotopic enrichment
lunar surface
energy
effect
shift
neutron spectra
reagents
energy spectra
deviation

ASJC Scopus subject areas

  • Geophysics
  • Space and Planetary Science

Cite this

Neutron capture effects on samarium, europium, and gadolinium in Apollo 15 deep drill-core samples. / Hidaka, Hiroshi; Ebihara, Mitsuru; Yoneda, Shigekazu.

In: Meteoritics and Planetary Science, Vol. 35, No. 3, 01.01.2000, p. 581-589.

Research output: Contribution to journalArticle

@article{a6b598ba831145bd9a10a67adb00c031,
title = "Neutron capture effects on samarium, europium, and gadolinium in Apollo 15 deep drill-core samples",
abstract = "The isotopic compositions of Sm and Gd in seven lunar samples from the Apollo 15 deep drill core were determined to discuss the effects of neutron capture near the lunar surface. Large isotopic deviations of 150Sm/149Sm, 156Gd/155Gd, and 158Gd/157Gd derived from neutron capture effects were observed in all samples. Although neutron capture products in lunar samples were investigated extensively in the 1970s, our precise isotopic measurements resulted in several new findings. The neutron fluence in the Apollo 15 drill core is a function of depth with a symmetric peak at 190 g/cm2 depth from the surface, confirming the results of earlier investigations. Neutron fluence values calculated from the isotopic shifts by comparison to artificially irradiated standard reagents were (5.16-7.49) x 1016 n/cm2. These values are 1.3 to 1.4x larger than those previously reported. Variations of ε(Sm)/ε(Gd) with depth are interpreted as being due to variations in the neutron energy spectrum. Here ε(Sm) and ε(Gd) are defined as in previous studies of lunar neutron stratigraphy. Our data suggest that the neutron is more thermalized at the lower layers than it is at the upper layers. In addition to large isotopic shifts for 149Sm, 150Sm, 155Gd, 156Gd, 157Gd, and 158Gd, isotopic enrichments of 152Gd and 154Gd derived from neutron capture for 151Eu and 153Eu, respectively, were also observed in all samples.",
author = "Hiroshi Hidaka and Mitsuru Ebihara and Shigekazu Yoneda",
year = "2000",
month = "1",
day = "1",
doi = "10.1111/j.1945-5100.2000.tb01438.x",
language = "English",
volume = "35",
pages = "581--589",
journal = "Meteoritics and Planetary Science",
issn = "1086-9379",
publisher = "The University of Arkansas Press",
number = "3",

}

TY - JOUR

T1 - Neutron capture effects on samarium, europium, and gadolinium in Apollo 15 deep drill-core samples

AU - Hidaka, Hiroshi

AU - Ebihara, Mitsuru

AU - Yoneda, Shigekazu

PY - 2000/1/1

Y1 - 2000/1/1

N2 - The isotopic compositions of Sm and Gd in seven lunar samples from the Apollo 15 deep drill core were determined to discuss the effects of neutron capture near the lunar surface. Large isotopic deviations of 150Sm/149Sm, 156Gd/155Gd, and 158Gd/157Gd derived from neutron capture effects were observed in all samples. Although neutron capture products in lunar samples were investigated extensively in the 1970s, our precise isotopic measurements resulted in several new findings. The neutron fluence in the Apollo 15 drill core is a function of depth with a symmetric peak at 190 g/cm2 depth from the surface, confirming the results of earlier investigations. Neutron fluence values calculated from the isotopic shifts by comparison to artificially irradiated standard reagents were (5.16-7.49) x 1016 n/cm2. These values are 1.3 to 1.4x larger than those previously reported. Variations of ε(Sm)/ε(Gd) with depth are interpreted as being due to variations in the neutron energy spectrum. Here ε(Sm) and ε(Gd) are defined as in previous studies of lunar neutron stratigraphy. Our data suggest that the neutron is more thermalized at the lower layers than it is at the upper layers. In addition to large isotopic shifts for 149Sm, 150Sm, 155Gd, 156Gd, 157Gd, and 158Gd, isotopic enrichments of 152Gd and 154Gd derived from neutron capture for 151Eu and 153Eu, respectively, were also observed in all samples.

AB - The isotopic compositions of Sm and Gd in seven lunar samples from the Apollo 15 deep drill core were determined to discuss the effects of neutron capture near the lunar surface. Large isotopic deviations of 150Sm/149Sm, 156Gd/155Gd, and 158Gd/157Gd derived from neutron capture effects were observed in all samples. Although neutron capture products in lunar samples were investigated extensively in the 1970s, our precise isotopic measurements resulted in several new findings. The neutron fluence in the Apollo 15 drill core is a function of depth with a symmetric peak at 190 g/cm2 depth from the surface, confirming the results of earlier investigations. Neutron fluence values calculated from the isotopic shifts by comparison to artificially irradiated standard reagents were (5.16-7.49) x 1016 n/cm2. These values are 1.3 to 1.4x larger than those previously reported. Variations of ε(Sm)/ε(Gd) with depth are interpreted as being due to variations in the neutron energy spectrum. Here ε(Sm) and ε(Gd) are defined as in previous studies of lunar neutron stratigraphy. Our data suggest that the neutron is more thermalized at the lower layers than it is at the upper layers. In addition to large isotopic shifts for 149Sm, 150Sm, 155Gd, 156Gd, 157Gd, and 158Gd, isotopic enrichments of 152Gd and 154Gd derived from neutron capture for 151Eu and 153Eu, respectively, were also observed in all samples.

UR - http://www.scopus.com/inward/record.url?scp=0034083075&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0034083075&partnerID=8YFLogxK

U2 - 10.1111/j.1945-5100.2000.tb01438.x

DO - 10.1111/j.1945-5100.2000.tb01438.x

M3 - Article

AN - SCOPUS:0034083075

VL - 35

SP - 581

EP - 589

JO - Meteoritics and Planetary Science

JF - Meteoritics and Planetary Science

SN - 1086-9379

IS - 3

ER -