Gamma Rays from keV Resonance Neutron Capture in Some (2s−1d)-Shell Nuclei

Abstract

The $\gamma$-ray spectra from radiative neutron capture in resolved resonances in F, Na, Mg, Al, S and from some unresolved resonances in Cl were measured with a NaI total-absorption spectrometer. Both positive-and negative-parity capturing resonances were studied, and from the simple spectra that were observed it was possible to obtain a number of branching ratios. On the basis of known final-state parities, $E1\mathrm{}$ and $M1\mathrm{}$ transition strengths were obtained. These were in good agreement with those of other nuclides in this region of atomic weight, thus establishing that with no outstanding exceptions, $M1\mathrm{}$ competes favorably with $E1\mathrm{}$ for these nuclides. An empirical rule, valid at least for neutrons of keV energy and lower, seems to operate in the case of the $s-d$-shell nuclides: The ratio of radiation strengths $\frac{M1\mathrm{}}{E1\mathrm{}}$ is greater for odd-$Z$-even-$N$ target nuclides ($\gtrsim {10}^{-1\mathrm{}}$) than it is for even-$Z$-even-$N$ target nuclides (∼${10}^{-2\mathrm{}}$).