A study of the crystal lattice effects in the ¹⁴⁹Sm(n, [alpha]) ¹⁴⁶Nd reaction using thermal neutrons

Abstract

The effect of chemical form and temperature on alpha decay rates of the excited states of ¹⁵⁰Sm produced from thermal neutron capture at 0.096 eV by ¹⁴⁹Sm were studied. Targets of enriched ¹⁴⁹Sm as samarium oxide, samarium iodide and samarium metal were each irradiated at temperatures of 100, 200 and 300°C in a water-moderated reactor. High resolution alpha spectra were obtained using an electrostatic particle guide to transport the alpha particles away from the reactor core to the detector. Ratios of the intensity of the 4⁻ --> 2⁺ alpha transition to the intensity of the 3⁻ --> 0⁺ alpha transition of ¹⁵⁰Sm to ¹⁴⁶Nd were determined for all permutations of temperature and target material. As the temperature was increased from 100 to 300°C, the intensity ratio increased approximately 2.2% due to Doppler broadening. A shift in the energy of the resonance feeding the 4⁻ --> 2⁺ transition caused by different binding energies of the oxide and metal targets resulted in a change in the ratio of approximately 1.9%. Experimental ratios were compared with ratios calculated using the effective temperature model proposed by Lamb, and agreed within experimental error.