Measurement of proton production cross sections of (sup 10)Be and (sup 26)Al from elements found in lunar rocks

摘要

Cosmic rays penetrate the lunar surface and interact with the lunar rocks to produce both radionuclides and stable nuclides. Production depth profiles for long-lived radionuclides produce in lunar rocks are measured using Accelerator Mass Spectrometry (AMS). For a particular radionuclide these production depth profiles can be interpreted to give an estimate for the solar proton flux over a time period characterized by the half life of the radionuclide under study. This analysis is possible if and only if all the cross sections for the interactions of all cosmic ray particles with all elements found in lunar rocks are well known. In practice, the most important cross sections needed are the proton production cross sections, because 98% of solar cosmic rays and (similar to)87% of galactic cosmic rays are protons. The cross sections for the production of long-lived radionuclides were very difficult to measure before the development of AMS and only in recent years has significant progress been made in determining these essential cross sections. Oxygen and silicon are major constituents of lunar rocks. We have reported already (sup 14)C production cross sections from O and Si for proton energies 25-500 MeV, and O(p,x)(sup 10)Be from 58 160 MeV(6). Here we present new measurements for the cross sections O(p,x)(sup 10)Be,O(p,x)(sup 7)Be, Si(p,x)(sup 7)Be,Si(p,x)(sup 26)Al, and Si(p,x)(sup 22)Na from (approximately)30 - 500 MeV.