Escape and spreading widths of the isobaric analog states of Sn and Te isotopes

Abstract

The escape widths for direct proton decay from isobaric analog states in Sb and I nuclei have been obtained by combining calculated single-particle widths with experimental spectroscopic information for neutron pickup reactions on the respective Sn and Te target nuclei. They display a pronounced odd- A/even- A staggering effect with very small widths for the even- A isotopes due to the lower proton decay energies. Only data for odd- A nuclei are available, and there is good agreement. Combining the calculated escape widths with the known experimental total widths yields values for the spreading widths. As expected, and in agreement with theoretical predictions, the spreading widths are essentially constant and dependent only weakly on neutron excess. Interestingly, the spreading widths are independent of whether statistical isospin-violating neutron decay is energetically possible or not, as is the case for the isobaric analog states of the light Sn isotopes with A < 116. The branching ratios for the isospin-forbidden neutron decays from the isobaric analog states average about 95% for the heavier even- A Sb isotopes, and about 60% for the odd- A isotopes. Gamma-ray deexcitation and direct and statistical proton decay compete in the decays of the IAS of the light Sn isotopes, and a branching ratio of about 90% for gamma-ray deexcitation is expected for the IAS in 112Sb.