The semi-inclusive 40Ca(γ, p) reaction

γ rays from muon capture in natural Ca, Fe, and Ni

“…Note that, in Fig. 3, the peak at 1517.51 keV is from a level in 39 Ar, which has a long lifetime of 0.95 ns and the peak is narrow, whereas the peak 1642.71 keV is a transition from the 3810.1-keV level in 38 Ar, which has a short lifetime of 55 fs and is noticeably broadened. (The peak at 1612 keV is a mix of several γ rays.)…”

“…There are many other reactions in which a proton is knocked out of 40 Ca, such as (p,2p), (e, e'p), or high-energy (γ, p); these all give better agreement with the spectroscopic factors, though the energy resolution is not sufficient to be useful to us. An example of this frustrating situation is the (γ, p) experiment of van den Abeele et al [38], who used tagged photons of 60 MeV, but their energy resolution of 300 keV means that only a general comparison can be made, even though this is an excellent resolution for this type of experiment. Similarly, the experiment of Kramer et al [39] on 40 Ca(e, e'p) yielded a resolution of 130 keV, and the observed energy levels agree better with the spectroscopic factors.…”

“…The number of lines observed is about double that of previous experiments, especially at the higher energies. The only thing to note is that the 3938.8-keV transition to the ground state is very close to a 3936.4-keV transition in 38 Ar, and these lines are broadened to 20 keV by the neutron emission; thus we cannot separate the γ rays, but we can use the observed energy of the combined lines to estimate the relative yields.…”

“…The comparison to the reaction 40 Ca(d, α) 38 K is of uncertain value. The numbers are just the strength at one angle and energy, so they are probably a poor predictor for the yield in muon capture but may give a general indication.…”

“…1, which is a spectrum for calcium in the region of 2 to 3 MeV. The peak at 2167 keV is from 38 Ar and has a lifetime of 0.47 ps, which is an intermediate value.…”