Abstract
The neutron yield functions of and from bremsstrahlung up to 41 Mev have been measured by using direct neutron detection. The photoproton yield function for has also been measured by detecting the activity. These yield functions were converted into cross sections () by a slightly modified standard method.
for exhibits a peak of ∼3.7 mb at ∼13.5 Mev and the "giant resonance" peak of ∼10 mb at ∼24 Mev. This latter peak is broad [ Mev] in contrast to with Mev.
for exhibits a broad ( Mev) giant resonance peak of 8.8 mb at 25.5 Mev. This large emission ratio cannot be accounted for by statistical considerations.
After a reasonable allowance is made for multiple processes, these two measurements are combined to give the total -absorption cross section, . of is also discussed. Both show a giant resonance peak but whereas the integrals of over the resonance are approximately equal. The idea that core excitation is responsible for the giant resonance is supported by the approximate equality of the resonance energies of and , but the remarkable difference in the width of these resonance peaks suggests a strong dependence of the absorption process on the ground-state configurations. The peak at 13.5 Mev found in is still present in and hence is not due to competition, but represents a "pygmy resonance."
During this work a new half-life for was obtained: () msec.
- Received 9 November 1956
DOI:https://doi.org/10.1103/PhysRev.106.300
©1957 American Physical Society