The Portales Valley meteorite fell as a large shower on 13 June 1998. About 50 specimens have been recovered. These various fragments located at different depth within the meteoroid provide an opportunity to study cosmogenic effects also as a function of shielding. Portales Valley was classified as a H6 ordinary chondrite. It consists of large silicate-rich regions crosscut by unusual thick veins of metallic Fe-Ni. We measured the gamma-activity and the nuclear tracks in a fragment weighing about 600 g. Twelve cosmogenic radioisotopes were revealed with high accuracy of counting. Measurements in other fragments are in progress. Cosmogenic 22Na (T1/2 = 2.6 y) shows an exposure to GCR during the last years of low solar activity, similar to those measured in our Laboratory in other chondrites which fell in similar phase of the solar activity.
Cosmic ray effects in the fresh-fall Portales Valley
CINI, Giuliana;BONINO, Giuseppe;TARICCO, Carla;
1999-01-01
Abstract
The Portales Valley meteorite fell as a large shower on 13 June 1998. About 50 specimens have been recovered. These various fragments located at different depth within the meteoroid provide an opportunity to study cosmogenic effects also as a function of shielding. Portales Valley was classified as a H6 ordinary chondrite. It consists of large silicate-rich regions crosscut by unusual thick veins of metallic Fe-Ni. We measured the gamma-activity and the nuclear tracks in a fragment weighing about 600 g. Twelve cosmogenic radioisotopes were revealed with high accuracy of counting. Measurements in other fragments are in progress. Cosmogenic 22Na (T1/2 = 2.6 y) shows an exposure to GCR during the last years of low solar activity, similar to those measured in our Laboratory in other chondrites which fell in similar phase of the solar activity.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
