The natural thermoluminescence of meteorites: I. Twenty‐three Antarctic meteorites of known ²⁶Al content

Abstract

The level of thermoluminescence (TL) naturally present in 23 Antarctic chondrites of known 26Al content has been measured as a means of exploring their thermal and radiation history. Antarctic meteorites tend to have lower natural TL than non‐Antarctic meteorites, presumably because of their generally longer terrestrial ages. Seventeen of the meteorites lie on a band of increasing natural TL and 26Al activity; meteorites with 26Al of 45–60 dpm/kg have natural TL values (normalized to the high temperature TL) of 2–4, whereas those with 26Al values of 30–45 dpm/kg have normalized natural TL values of 1–2, and ALHA 76008, with an 26Al content of 11 dpm/kg, has a TL value of 0.87 ± 0.01. This suggests that the “half‐life” for TL decay is comparable to that of 26Al. The six meteorites not lying on the TL‐26Al trend have much lower TL than others of comparable 26Al. For two of them (RKPA 79001 and RKPA 80202, which are tentatively paired) the low natural TL probably reflects a recent severe shock, while another (ALHA 77294) has previously been measured in this lab and had TL consistent with the TL‐26Al trend. The remaining three, ALHA 78006, ALHA 77296, and ALHA 77297 (of which the last two are probably paired), have suffered a recent reheating such as would be expected from orbits of unusually small perihelia.

The natural thermoluminescence of Antarctic meteorites and their terrestrial ages and orbits: A 2010 update

“…In 1987 the Antarctic Meteorite Working Group (MWG), an advisory group to NASA, NSF, and the Smithsonian Institution, added natural thermoluminescence (TL) measurements to the preliminary examination program for returned Antarctic meteorites. They did this on the basis of arguments summarized by Sutton and Walker (1986) and a pilot study by Hasan et al. (1987).…”

The Cali meteorite fall: A new H/L ordinary chondrite

“…Ending point (h = 17 km) Longitude Latitude Longitude Latitude 76.38 ± 0.05°W 3.85 ± 0.05°N 76.44 ± 0.05°W 3.63 ± 0.05°N 0.95 AU of the Sun (which would cause a factor of 10-100 lower natural TL; Hasan et al 1987) and have not recently (within the last 10 5 years) transferred to a near-Earth orbit (like the major ALH 85110 fall and its many paired fragments; Benoit and Sears 1993). These conclusions are consistent with the orbit calculated above from eyewitness observations.…”

The thermoluminescence of meteorites: A brief 2010 perspective

“…In the light of this scientific background (Sutton and Walker, 1986), and a pilot study in which samples of known 26 Al were analyzed (Hasan et al, 1987), the Antarctic Meteorite Working group of NASA, NSF, and the Smithsonian Institution arranged for the systematic determination of natural TL in newly recovered Antarctic meteorites. The data appeared in NASA's Antarctic Meteorite Newsletter (now online http://www.curator.jsc.…”

“…nasa.gov/antmet/amn/amn.cfm). Aluminum-26 is a cosmogenic isotope that decays at about the same rate as natural TL under Antarctic conditions (Hasan et al, 1987). Meteorites have been recovered from the Antarctica in a systematic way since 1978, on the order of a few hundred to a few thousand meteorites being returned each year (Cassidy et al, 1977;Cassidy, 2003).…”

“…The Hasan et al (1987) interpretation of the natural TL vs. 26 Al plot was that most meteorites plotted on a line governed by terrestrial age (those with natural TL values >5 krad), but a small number had low natural TL (<5 krad) and high 26 Al and had experienced small perihelia. These were assumed to be small meteorites where the enhanced solar energetic particle radiation had driven up 26 Al and the higher temperatures had reduced natural TL (Michel et al, 1996;Nishiizumi et al 1990).…”