Photodisintegration of C13

Barnett C. Cook
Phys. Rev. 106, 300 – Published 15 April 1957
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Abstract

The neutron yield functions of C12 and C13 from bremsstrahlung up to 41 Mev have been measured by using direct neutron detection. The photoproton yield function for C13 has also been measured by detecting the B12 activity. These yield functions were converted into cross sections (σ) by a slightly modified standard method.

σ for C13(γ, xn) 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 [Γ1210 Mev] in contrast to C12 with Γ123 Mev.

σ for C13(γ, p)B12 exhibits a broad (Γ126 Mev) giant resonance peak of 8.8 mb at 25.5 Mev. This large pn 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 γ-absorption cross section, σabs. σabs of C12 is also discussed. Both show a giant resonance peak but Γ12(C13)Γ12(C12) whereas the integrals of σabs 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 C12 and C13, 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 C13(γ, n) is still present in σabs and hence is not due to competition, but represents a "pygmy resonance."

During this work a new half-life for B12 was obtained: (181.3+1.5) msec.

  • Received 9 November 1956

DOI:https://doi.org/10.1103/PhysRev.106.300

©1957 American Physical Society

Authors & Affiliations

Barnett C. Cook*

  • The Enrico Fermi Institute for Nuclear Studies, The University of Chicago, Chicago, Illinois

  • *Present address: Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania.

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Issue

Vol. 106, Iss. 2 — April 1957

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