Abstract
Neutron transmission and self-indication measurements have been made for two of the separated isotopes of Sm () and the separated isotopes of Eu () at the Nevis synchrocyclotron. The measurements used a 200-m path for transmission measurements and a 40-m path for self-indication measurements, covering an energy range from approximately 1 eV to greater than 5 keV. Since these isotopes are at a region of a peak in the strength function, mainly resonances are involved. The results for the even-even Sm isotopes show that essentially complete populations were obtained for the first 70 levels in and 27 levels in . Values of (or for Eu) were obtained for the observed resonances. Values of , obtained for 9, 3, 45, and 46 levels of , , , and , respectively, give values of 65, 79, 90.0, and 94.8 meV, respectively, with most of the individual values within 20% of . The strength function is for , , , and , where is the number of levels in the sample. Somewhat smaller values result for the Sm isotopes if a larger energy interval is used. Values of the mean level spacing for these isotopes of 51.8±1.5, 115±8, ∼0.7, and ∼1.1 eV, respectively, were found. Good fits are obtained with the Porter-Thomas theory for the reduced-neutron-width distributions and the Wigner formula for the nearest-neighbor level separation. Other statistical tests applied to and , respectively, are: (a) the Dyson-Mehta statistic, which is particularly sensitive to long-range order in the level spacings, versus ; (b) correlation coefficients of adjacent nearest-neighbor spacings are -0.26±0.10 and -0.32±0.18 versus -0.27 predicted for an orthogonal ensemble.
- Received 2 February 1972
DOI:https://doi.org/10.1103/PhysRevC.6.251
©1972 American Physical Society