James S. Eldridge

Petrogenetic relationship between Allan Hills 77005 and other achondrites

Allan Hills (ALHA) 77005 is a newly discovered, unique achondrite from Antarctica. Petrologic similarities with the shergottites in terms of mineralogy, oxidation state, inferred source region composition, shock metamorphic effects and shock ages suggest a genetic relationship. Volatile to involatile element ratios (e.g. K/U, Rb/U, Cs/U, Tl/U) and abundances of other trace elements support this hypothesis. ALHA 77005 may be a cumulate that crystallized from a liquid parental to those from which the shergottites crystallized; alternatively it may be a sample of the type of source peridotite from which shergottite parent liquids were derived by partial melting. Chemical similarities with terrestrial ultramafic rocks suggest that this unique meteorite provides an additional sample of the only other solar system body known to have basalt source regions chemically similar to the upper mantle of the Earth.

Meteorite Fail at Pueblito de Allende, Chihuahua, Mexico: Preliminary Information

Specimens from the meteorite fall at 1:05 a. m., on 8 February 1969 at Pueblito de Allende, Chihuahua, Mexico, have been recovered. The meteorite is a chondrite (C3 and C4) with both opaque and microcrystalline matrices. Specimens were brought to a low background gamma counter less than 4 � days after the fall, and gamma rays from short-lived isotopes have been observed.

Elemental Compositions and Ages of Lunar Samples by Nondestructive Gamma-Ray Spectrometry

A gamma-ray spectrometry system with low background was used to determine the radioactivity of crystalline rocks, breccias, and fine material. Nuclides identified were 40K, 232Th, 238U, 7Be, 22Na 26A1, 44Ti, 46Sc, 48V, 52Mn, 54Mn, and 56Co. Concentrations of K, Th, and U ranged between 480 and 2550, 1.01 and 3.30, and 0.26 and 0.83 parts per million, respectively. Concentrations of thorium and uranium were those of terrestrial basalts, while the potassium concentrations were near values for chondrites. Products of low-energy nuclear reactions showed pronounced concentration gradients at rock surfaces. Concentrations of K and of 22Na determined here were combined with concentrations of rare gases to estimate gas-retention ages and cosmic-ray exposure ages with ranges of 2200 to 3200 and 34 to 340 million years, respectively, for three rocks.

Primordial radioelements and cosmogenic radionuclides in lunar samples from apollo 15.

Two basalts, two breccias, and two soils from Apollo 15 were analyzed by nondestructive gamma-ray spectrometry. The concentrations of potassium, thorium, and uranium in the basalts were similar to those in the Apollo 12 basalts, but the potassium: uranium ratios were somewhat higher. Primordial radioelements were enriched in the soils and breccia, consistent with a two-component mixture of mare basalt and up to 20 percent foreign component (KREEP). The abundance patterns for cosmogenic radionuclides implied surface sampling for all specimens. The galactic cosmic-ray production rate of vanadium-48 was determined as 57 � 11 disintegrations per minute per kilogram of iron. Cobalt-56 concentrations were used to estimate the intensity of the solar flare of 25 January 1971.

Non-destructive determination of radionuclides in lunar samples using a large low-background gamma-ray spectrometer and a novel application of least-squares fitting☆

Abstract Dual-parameter γ-ray spectrometer systems with large-volume NaI(Tl) crystals and ultra-low backgrounds have been used for the non-destructive determination of K, Th, U, and cosmic-ray produced radionuclides in 60 lunar samples. The total mass of samples measured with these systems is ∼28 kg, and the individual sample masses varied from 2 to 2300 g. Samples from Apollo 11, 12, 14, 15, and 16 missions have been measured. Operation of the spectrometers in a coincidence mode and analyzing singles- and coincidence-spectra permits the simultaneous determination of 8–10 radionuclides in each lunar sample.