Radiochemical measurements of ¹⁰Be and ⁷Be formation cross sections in oxygen by 135 and 550 MeV protons

Abstract

Radiochemical measurements of the activities of ¹⁰Be and ⁷Be in oxygen due to the bombardment of water samples by protons of energies 135 and 550 MeV are reported. The ratios σ (¹⁰Be)/σ(⁷Be) of the cross sections in oxygen are found to be 0.19 ± 0.01 and 0.32 ± 0.02 for 135 and 550 MeV protons, respectively, based on f_½ (¹⁰Be) = 2.7 X 10⁶ y and f_¼ (⁷Be) = 53.6d. Using the best estimate of the excitation function of ⁷Be in oxygen, the formation cross sections for ¹⁰Bein oxygen are estimated to be 1.0 ± 0.06 and 2.9 ± 0.2 mb for protons of energies 135 and 550 MeV respectively. Cross sections for ¹⁰Be in oxygen, averaged over the energy spectrum of cosmic rays, and based on the observations of its activity in meteorites and deep-sea sediments are discussed. The implication of the present measurements for the use of the ¹⁰Be isotope as a "clock" to estimate the "age" of cosmic rays is briefly noted.