The total 'Be(n, p)'Li cross section has been measured from 25 meV to 13.5 keV. These energies correspond to temperatures of T =2.9)& 10 ' to 0.16 GK. For thermal neutrons the cross sections to the ground state (po) and the first excited state (p, ) of 'Li are 38400+800 b and 4202120 b, respectively. This result for the total 'Be(n, p)'Li thermal cross section is about 25%%uo lower, and is approximately a factor of 10 more precise than previous published measurements. For energies above 100 eV, a significant departure from a 1/u shape for the total cross section is observed. The data were analyzed using a single-level approximation, and were also analyzed together with other data using multilevel-multichannel R-matrix theory. Results are presented for the properties of the 2 threshold state and for a possible nearby 2 state. The astrophysical reaction rate, N~(nv ), was calculated from the measured cross sections for the combined po and pl transitions. The resulting reaction rate is approximately 60-80% of the rate currently in use. This reduction in the Be(n,p) Li reaction rate could result in a calculated increase in the production of 'Li during the big bang by as much as 20%.

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The y rays following the P decays of 'Kr, 'Rb, and 'Sr have been studied, using Ge(Li) detectors for singles and coincidence measurements. A level scheme for "Y is reported which contains 36 excited levels and 143 of the 162 observed y rays in the decay of "Sr. For the decay of "Rb, 243 y rays were observed, with 231 placed in a level scheme for "Sr consisting of 74 excited levels. The decay of 'Kr was observed to have 217 y rays, 203 of which are placed in a level scheme for Rb comprising 56 excited levels. Over 98% of the observed yray intensity is contained in each of the level schemes. Spin and parity assignments are proposed, whenever possible, on the basis of y-ray transition probabilities and deduced logft values. A comparison is made with available reaction data for the Y level scheme, and some of the levels in each decay scheme are interpreted in terms of the nuclear shell model. RADIOACTIVITYKr, Rb, Sr [from U(n, f)]; measured Eyp Iy y-y coin.Ge(Li) detectors. 3Rb, 3Sr, 93Y deduced levels, J, r, log ft. Mass-separated Kr activity.

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A system for the precision study of the nuclear decays of shortlived nuclei produced by neutron irradiation is described. The system a s envisioned will employ continuous introduction of irradiated material into the ion source of an electromagnetic isotope separator and subsequent operation of the separator i n connection with nuclear decay analysis apparatus. The results of a n empirical study a r e presented regarding the characteristics of a vapor transport line used for the extraction of irradiated material from the vicinity of the reactor c 6 r e and Lrdrrspol-t to t h o isotope eeparator ion source. Of particular interest in this study a r e the transit times achieved with the system and properties ol tlre system associated with the presence of electrical mn-A discharge i n the vapor transport line. Extensions of the results of : %', ib this study to an actual system a r e discussed.'present address :

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