Neutron Capture Cross Sections in the keV Region for 154Sm, ¹⁶⁰Gd, ¹⁶⁴Dy, and ¹⁶⁵Ho

Neutron capture cross sections for ¹⁵⁴Sm, ¹⁶⁰Gd, ¹⁶⁴Dy, and ¹⁶⁵Ho (ground state) have been investigated in the energy range from 5 to 160 keV. Capture cross section data in this energy region that are currently available for ¹⁶⁵ Ho varies by approximately a factor of two between different workers and for ¹⁵⁴Sm, ¹⁶⁰Gd, and ¹⁶⁴Dy little or no previously published data are available in this energy range. The present work represents an attempt to remove some of the uncertainty in the case of ¹⁶⁵ Ho and to provide original data for the other three isotopes over the 5 to 160 keV region. This work was done by activation of metal samples of the above mentioned rare earths and counting the decay products with a well type plastic scintillator. Samples were activated by neutrons generated by the ⁷Li(p,n)⁷ Be reaction with the samples being placed at 90 deg with respect to the neutron target. The 0.820 b capture cross section of ¹²⁷I at 25 keV was used as the standard for normalization along with the thermal neutron capture cross sections of the isotopes. From the experimental cross section curves the γ-ray strength functions, the s-wave neutron strength functions, and the p-wave neutron strength functions were determined. These parameters are the first to be determined for samarium and dysprosium over an energy region this broad while for gadolinium, only one other comparable set exists.