EFFECTS OF NUCLEAR SHELL ON THE DISTRIBUTION OF KINETIC ENERGY FRAGMENTS IN FAST NEUTRON FISSION (in Russian)
A double ionization chamber was used in finding the complete kinetic energy distribution of U/sup 238/ fragments produced by 14.9-Mev neutron fission The obtained data were plotted and compared to the data on the kinetic energy distribution of fragments from the U/sup 235/ fission by 14.1-Mev neutrons and to the calculated dispersion It was found that E and DELTA E have the highest magnitudes with the fragment mass ratio 1.25 to 1.3. A diagram is also included of changes in the kinetic energy distribution in the U/sup 235/ fission by thermal neutrons and in the spontaneous fission of Cf/sup 252/ measured by the time-of-flight method. It was observed that in all events . the kinetic energy values are highest when the heavy fragment has a mass number near 132. This probably represents a filled shell nucleus with 50 protons and 82 neutrons. A break in the curve was found at the fragment mass ratio corresponding to a light fragment with the mass number 82 to 84, which indicates a closed shell with 50 neutrons. A similar closed shell effect was also observed in the dispersion energy ( DELTA E) relation to the fragment mass ratio which was determined for U/ sup 233/ and U/sup 235/ by D. C. Brunton et al. (Phys. Rev. 75, l8568 Reactions of N/sup 14/ and bismuth involving the production of alpha -active isotopes were studied at ~ 102 Mev. A luminescence alpha counter, insensitive to BETA and gamma background was used for investigating the bismuth decay activity. The alpha energy was measured with an ionization chamber, and the characteristics of the alpha radiation formed are tabulated. Alpha activities were attributed to Rn/sup 212/ (T 1/2 = 16 hours, E/sub alpha / = 5.82 Mev), in equilibrium with At/sup 2/(T /1/2 = 7.5 hours, E/sub alpha / = 5.89 Mev) and Po/ sup 211/ (T 1/2 0.5 sec, E/sub alpha /= 7.43 Mev), and Ra/sup 212/ (T 1/2 = 23 min E/sub alpha / = 6.23 Mev). The relation of Rn/sup 212/ and Rn/sup 211/ production cross sections to the nitrogen ion energy is presented graphically, as well as the fission cross section sigma /sub f/ of the constituent nucleus Th/ sup 223/ which practically coincides with the cross section of its formation. Isotopes Rn/sup 213/ and Rn/sup 211/ can appear as the result of (N, 3n) and M, 4n) reactions as well as in alpha emission reactions (N, x alpha 3n) and M, x alpha 4n), x = 1.2. The more probable reaction may be determined from the dependence of Rn/sup 212/ and Rn/sup 211/ production cross sections on the energy of the nitrogen nuclei. The cross sections for the reactions (N, 3n) and (N, 4n) are presented. A comparison of experimental and theoretical curves leads to the conclusion that (N, 3n) and M, 4n) reactions contribute (>50%) to the yield of Rn/sup 212/ and Rn/sup 211/ only with a nitrogen ion energy below 78 and 56 Mev, respectively. At higher energies the yield of these isotopes is determined by (N, x alpha 3n) and (N, x alpha 4n) reactions. The isotope with a half life ~ 150 days is Po/suip 210/ which is produced by various reactions (N, x alpha n), (N, p4n) (N, N/sup 13/), etc. The cross section of Po/sup 210/ production increases with energy. reaching the magnitude ~ 10/sup -25/ cm/sup 2/ at E = 100 Mev. (R.V.J.)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-13-018567
- OSTI ID:
- 4228711
- Journal Information:
- Zhur. Eksptl'. i Teoret. Fiz., Vol. Vol: 36; Other Information: Orig. Receipt Date: 31-DEC-59
- Country of Publication:
- Country unknown/Code not available
- Language:
- Russian
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CHEMISTRY DIVISION SEMIANNUAL REPORT FOR DECEMBER 1957 THROUGH MAY 1958