Neutron time of flight spectroscopy measurements were made for a range of sample thickness on the even separated Gd isotopes $A=154, 158, \mathrm{and} 160$. These include transmission measurements using 200 and 40 m flight paths and self-indication measurements using a 40 m flight path. Resonance parameters were obtained for 48 levels to 1 keV for ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$ and for 95 and 56 levels to 10 keV for ${}_{}{}^{158}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{160}{}_{}{}^{}\mathrm{Gd}$. The experimental $s$-wave strength functions were $10{}_{}{}^4{}_{}{}^{}S_0^{}{}_{}{}^{}=(2.0\mathrm{}\pm 0.3), (1.5\mathrm{}\pm 0.2), \mathrm{and} (1.8\mathrm{}\pm 0.4)$, respectively. For ${}_{}{}^{160}{}_{}{}^{}\mathrm{Gd}$, the $p$ strength function is $10{}_{}{}^4{}_{}{}^{}S_1^{}{}_{}{}^{}\approx 1.7\pm 0.3$. Essentially complete $s$-wave populations were obtained for the first 19 levels in ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$ with $〈D〉=14.5\mathrm{}\pm 1.5$ eV and ${\Delta }_{\exp }=0.22\mathrm{}$ (vs ${\Delta }_{\mathrm{DM}}=0.28\mathrm{}\pm 0.11$); 47 levels in ${}_{}{}^{158}{}_{}{}^{}\mathrm{Gd}$ with $〈D〉=86\mathrm{}\pm 4$ eV and ${\Delta }_{\exp }=0.29\mathrm{}$ (vs ${\Delta }_{\mathrm{DM}}=0.38\mathrm{}\pm 0.11$); and 20 levels in ${}_{}{}^{160}{}_{}{}^{}\mathrm{Gd}$ with $〈D〉=202\mathrm{}\pm 20$ and ${\Delta }_{\exp }=0.32\mathrm{}$ (vs ${\Delta }_{\mathrm{DM}}=0.30\mathrm{}\pm 0.11$). Comparison of the observed ${\Gamma }_n^0$ distributions with the Porter-Thomas theory and the observed level spacings with the Wigner theory and other statistical orthogonal ensemble tests gave good results for the energy intervals over which complete $s$ populations were observed. The average radiation widths were $〈{\Gamma }_{\gamma }〉=88\mathrm{}$ meV determined from $n=25\mathrm{}$ levels in ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$, $〈{\Gamma }_{\gamma }〉=105\mathrm{}$ meV ($n=27\mathrm{}$) in ${}_{}{}^{158}{}_{}{}^{}\mathrm{Gd}$ and $〈{\Gamma }_{\gamma }〉=11\mathrm{}$ meV ($n=4\mathrm{}$) in ${}_{}{}^{160}{}_{}{}^{}\mathrm{Gd}$.

NUCLEAR REACTIONS ${}_{}{}^{154,158,160}{}_{}{}^{}\mathrm{Gd}(n,n)$, ($n,\gamma$), $E=0\mathrm{}-10$ keV; measured ${\sigma }_t \mathrm{}\left(E\right)\mathrm{}$; deduced $E_0$, ${\Gamma }_n$, ${\Gamma }_{\gamma }$, $S_0$, $〈D_0〉$, $S_1$.

• Received 17 June 1974

DOI:https://doi.org/10.1103/PhysRevC.10.1904