PHYSICS DIVISION PROGRESS REPORT FOR OCTOBER 1, 1957 TO DECEMBER 31, 1957
The study of the decay scheme of Bi/sup 208/ is continuing. The only mode of decay identified is K-electron capture to the 2.62-Mev first-excited state of Pb/sup 208/. The measurements of the absorption ratios for the Na/sup 23/(n, gamma )Na/sup 24/ reaction have been completed. The Fong-Newton approach has been re-evaluatad using improved nuclear level densities and performing full integrations over the distributions of kinetic and excitation energies of the fragments for all modes in the fission of U/sup 235/ with thermal neutrons. It is confirmed that the predictions of yield and kinetic energy distributions are in violent disagreement with observation. The study of longitudinal polarization of beta rays from P/sup 32/, Y/sup 90/, Pr/sup 144/, Au/sup 198/, and Bi/sup 210/ by the Moller scattering technique has continued. The experimental results are equal to or somewhat less than that expected for full-v/c polarization. Following the measurements of the 110-v a-c line frequency stability, a tuning fork frequency standard with a stuied accuracy of one part in 10/sup 5/ has been installed. This unit is used in conjunction with a 60-cycle power amplifier to drive the synchronous motors of two AEP auto control units, one a master control for the 4 pi BETA coincidence unit, the other is used for measureanents with the high pressure 4 pi counter. A calculation has been performed to determine the width and average value of the fission-fragment excitation energy distribution that is required to give the observed neutron multiplicity distribution. For U/sup 235/ masses 95-151 a halfwidth of 12.9 Mev and average total excitation of 17.7 Mev, and for Cf/sup 252/ masses 107-145 a half width of 17.7 Mev and average total excitation of 29.8 Mev were found. The rates of change of < nu > with excitation energy were found to be 0.166 and 0.148 Mev/ sup -1/ for U/sup 235/ and Cf/sup 252/, respectively. Gamma rays from the long- lived isomer of Ho/sup 166/ were found at 420 and 540 Mev. A decay scheme is presented. A brief study was made of the protons from the reaction N/sup 14/(He/ sup 3/,p)O/sup 16/, and two groups were observed corresponding to an excitation near 11 Mev in O/sup 16/. The measured values correspond to excitations of 11.22 plus or minus 0.10 Mev and 11.10 plus or minus 0.10 Mev which may be somewhat high owing to thick target effects. Two resonances in the reaction C/sup 14/( alpha , gamma )O/sup 18/ were discovered at alpha-particle energies of 1.13 and 1.78 Mev corresponding to levels in O/sup 18/ at 7.12 and 7.62 Mev. Measurement of the branching ratio of the radiation from the reaction O/sup 16/(He/sup 3/,p)F/ sup 18/ shows that the F/sup 18/ excited state 3.1 Mev de-excites to the ground state 25% of the time and to the 0.94 Mev state 75% of the time. The wavelength ddstribution of neutrons scattered from liquid helium at angles of 90 deg and 45.5 deg for liquid helium at temperatures down to 1.25 deg K has been measured. The neutron dfraction pattern of solid argon at 4.2 deg K was measured and the lattice parameter (5.257 plus or minus 0.02 A), density (1.83 g/cc), and separation of nearest neighbors (3.72 A) were calculated. The analysis of the low-energy U/sup 235/ cross sections for neutrons by the complete Wigner-Eisenbud theory was completed. The theoretical calculations of the total and the partial cross sections agree with the experimental cross sections to within one or two percent everywhere up to a neutron energy of 2 ev. (For preceding period see PR- P-35.) (W.D.M.)
- Research Organization:
- Atomic Energy of Canada Ltd. Chalk River Project, Chalk River, Ont.
- NSA Number:
- NSA-12-009862
- OSTI ID:
- 4344894
- Report Number(s):
- PR-P-36; AECL-567
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-58
- Country of Publication:
- Canada
- Language:
- English
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