Lunar composition from Apollo orbital measurements

Abstract

Several spectrometers carried in the Service Module of the Apollo 15 and Apollo 16 spacecraft were employed for the compositional mapping of the lunar surface. The observations involved the measurements of secondary (fluorescent) X-rays, gamma-rays and alpha particle emissions. A large scale compositional map of over 20 percent of the lunar surface was obtained for the first time. It was possible to demonstrate interesting chemical differences between the mare and the highlands, to find specific areas of high radioactivity and to learn something about the composition of the moon's hidden side. Further the same devices were used to obtain useful astronomical data during the return to earth.

Restless quiescence: thermonuclear flashes between transient X-ray outbursts

“…The event's peak rate is about 2450 and 8500 cts per 8 s in the 1-3 keV band and at >3 keV, respectively, while Sco X-1 varied between 1350-2050 and 2000-2750 cts per 8 s, respectively, as seen later on Aug. 5 (see Adler et al 1972b). This correspond to a total peak rate about 2.3-3.3 times that of Sco X-1.…”

“…Galactic X-ray observations were made during the trans-Earth coast for several periods of about an hour (e.g., Adler et al 1972b). Among the various other instruments were the Gamma-ray Spectrometer (500 keV-30 MeV; e.g., Arnold et al 1972) and the Alpha Particle Spectrometer (4.5-9.0 MeV; e.g., Gorenstein & Bjorkholm 1972).…”

“…Among the various other instruments were the Gamma-ray Spectrometer (500 keV-30 MeV; e.g., Arnold et al 1972) and the Alpha Particle Spectrometer (4.5-9.0 MeV; e.g., Gorenstein & Bjorkholm 1972). The X-ray Fluorescence Spectrometer was pointed towards various constellations over a period of about 3 days (1971, Aug. 5-7) with an attitude stability within a degree for approximately 1 h of observation (Adler et al 1972b). A large increase in the X-ray count rate for about 10 min was recorded on UT 1971, August 5, 00:34 (Gorenstein et al 1974).…”

“…A large increase in the X-ray count rate for about 10 min was recorded on UT 1971, August 5, 00:34 (Gorenstein et al 1974). The burst event occurred when the spacecraft was pointed towards the Centaurus constellation, for a period of about 65 min (Adler et al 1972b;Gorenstein et al 1974). According to the Apollo 15 Flight Journal 10 , it was aimed at Centaurus A.…”

Re-evaluation of Lunar X-ray observations by Apollo 15 & 16

“…The Mg and Al filter thickness is, for example, stated to be in the range of 5.08-12.7 µm in Adler et al (1972a), while values of 5.1 and 6.4 µm are given by Clark (1979) and Yin et al (1993), respectively. The Be window thickness is quoted as ∼25 µm in most work (e.g., Adler et al 1972a;Adler et al 1975;Clark 1979;Yin et al 1993;Clark & Trombka 1997); however, for example, it is 40 µm in Adler et al (1973). It should be noted that the resulting intensity ratios highly depend on the assumed window and filter thickness since this determines the amount of X-ray transmission.…”