Measurements of 10Be and 26Al production cross sections with 12 GeV protons by accelerator mass spectrometry.

Abstract

The formation cross sections of $^{10}\mathrm{Be}$ and $^{26}\mathrm{Al}$ from Al, Fe, Co, Ni, Cu, Zn, Ag, and Au targets irradiated with 12 GeV protons were measured by accelerator mass spectrometry. The obtained cross sections were consistent with the excitation functions predicted from the literature values measured at other proton energies within the experimental uncertainties. The $^{10}\mathrm{Be}$ cross sections increased with an increase in the target mass. On the other hand, the $^{26}\mathrm{Al}$ cross sections decreased from Al to Ag targets, but increased somewhat from Ag to Au. The formation mechanisms of $^{10}\mathrm{Be}$ and $^{26}\mathrm{Al}$ including $^{7}\mathrm{Be}$, $^{22}\mathrm{Na}$, and $^{24}\mathrm{Na}$ are discussed with respect to fitting of the experimental results to the calculated values using the universal formula of Campi et al. During the course of the discussion, we introduce a new parameter, the degree of neuton excess (N-Z)/A, in order to classify light fragments more clearly.It is found that the production of $^{10}\mathrm{Be}$ and $^{24}\mathrm{Na}$ with positive values for the degree of neutron excess can be well reproduced by the formula, indicating that fragmentation is a dominant process for $^{10}\mathrm{Be}$ production from Fe to Au targets and for $^{24}\mathrm{Na}$ from Ag to Au. However, the values calculated by the formula overestimate the yields of $^{7}\mathrm{Be}$, $^{22}\mathrm{Na}$, and $^{26}\mathrm{Al}$ with negative values or zero for the neutron-excess parameter. Through a comparison of the calculated and experimental data it is also found that the cross section ratios of $^{10}\mathrm{Be}$${/}^{7}$Be, $^{24}\mathrm{Na}$${/}^{26}$Al, and $^{24}\mathrm{Na}$${/}^{22}$Na are linearly correlated with the degree of neutron excess of the targets. This suggests that the production of $^{7}\mathrm{Be}$, $^{22}\mathrm{Na}$, and $^{26}\mathrm{Al}$ with negative or zero (N-Z)/A by a fragmentation process from Ag to Au targets is suppressed relative to those of $^{10}\mathrm{Be}$ and $^{24}\mathrm{Na}$ with positive values of the neutron-excess parameter.