Isospin nonconserving proton decays ofN13(T=32) to negative parity states ofC12

Abstract

From a coincidence study of the $^{11}\mathrm{B}$($^{3}\mathrm{He}$,$\mathrm{np}$)$^{12}\mathrm{C}$ reaction we obtain branching ratios of (9.6\ifmmode\pm\else\textpm\fi{}1.4)% and (16.4\ifmmode\pm\else\textpm\fi{}3.6)% respectively for the isospin forbidden proton decays of the lowest $T=\frac{3}{2}$ level of $^{13}\mathrm{N}$ to negative parity levels of $^{12}\mathrm{C}$ at 9.64 and 10.84 MeV. The reduced widths for these $s$- or $d$-wave decays are much larger than those for the $p$-wave decays to the lower lying positive parity levels of $^{12}\mathrm{C}$. This establishes the importance of ${(2s1d)}^{2}1{p}^{7}$ configurations in the isospin impurity in $^{13}\mathrm{N}$($T=\frac{3}{2}$). We argue that isospin impurities containing pairs of particles excited into higher shells are a widespread phenomenon and present a qualitative explanation of this effect which has been ignored in essentially all isospin mixing calculations.NUCLEAR REACTIONS $^{11}\mathrm{B}$($^{3}\mathrm{He}$,$\mathrm{np}$)$^{12}\mathrm{C}$; ${E}_{^{3}\mathrm{He}}=7.0$ MeV; $^{13}\mathrm{N}$($T=\frac{3}{2}$) proton decays; isospin mixing