Investigation of Analogs of M1, E1 and M2 Transitions in ¹⁰B, ¹²C and ¹⁴N Through Radiative Pion Capture

Abstract

For the selfconjugate nuclei ¹⁰B, ¹²C and ¹⁴N some of the most convincing evidence was compiled, which demonstrated the potential of the radiative pion capture reaction^1,2. The reasons for this are twofold. Firstly the level spacing in the bound state region in the final nuclei ¹⁰Be, ¹²B and ¹⁴C is sufficiently large, that even with a resolution of 2 MeV certain transitions can he isolated experimentally. Secondly the observed transition strength is concentrated into a few levels, mainly analogs to strong isovector M1-transitions in the target nucleus. In addition a considerable fraction of the reaction proceeds through spin-isospin dipole states with prominent J^π=1⁻ and 2⁻ structures observed in ¹²C. In view of the impact of these findings for future radiative pion capture experiments, it seemed appropriate to remeasure these photon spectra with improved resolution (900 keV FWHM at 129.4 MeV) and statistics in our pairspectrometer at SIN³. Figure 1 shows the result, where only the important part of the spectrum above 100 MeV is displayed. In Table I we present the photon energies, excitation energies and branching ratios for the different transitions.

Work supported by BMFT, Bonn, W. Germany and Swiss National Science Foundation.