Measurement of Absolute Fission Yields in the Fast Neutron-Induced Fission of Actinides: {sup 238}U, {sup 237}Np, {sup 238}Pu, {sup 240}Pu, {sup 243}Am, and {sup 244}Cm by Track-Etch-cum-Gamma Spectrometry
- Bhaha Atomic Research Centre (India)
The absolute fission yields of 46 fission products in {sup 238}U (99.9997 at.%), 46 fission products in {sup 237}Np, 27 fission products in {sup 238}Pu (99.21 at.%), 30 fission products in {sup 240}Pu (99.48 at.%), 30 fission products in {sup 243}Am (99.998 at.%), and 32 fission products in {sup 244}Cm (99.43 at.%) induced by fast neutrons were determined using a fission track-etch-cum-gamma spectrometric technique. In the case of highly alpha-active and sparingly available actinides - e.g., {sup 238}Pu, {sup 240}Pu, {sup 243}Am, and {sup 244}Cm - a novel recoil catcher technique to collect the fission products on a Lexan polycarbonate foil followed by gamma-ray spectrometry was developed during the course of this work. This completely removed interferences from (a) gamma rays of daughter products in secular equilibrium with the target nuclide (e.g., {sup 243}Am-{sup 239}Np), (b) activation products of the catcher foil [e.g., {sup 24}Na from Al(n,{alpha})], and (c) activation products of the target [e.g., {sup 238}Np from {sup 237}Np(n,{gamma}) and {sup 239}Np from {sup 238}U(n,{gamma})] reactions, making the gamma spectrometric analysis very simple and accurate. The high-yield asymmetric fission products were analyzed by direct gamma spectrometry, whereas the low-yield symmetric products (e.g., Ag, Cd, and Sb) as well as some of the asymmetric fission products (e.g., Br) and rare earths (in the case of {sup 238}U and {sup 237}Np) were radiochemically separated and then analyzed by gamma-ray spectrometry. The neutron spectra in the irradiation positions of the reactors were measured and delineated in the thermal to 10-MeV region using threshold activation detectors. The present data were compared with the ENDF/VI and UKFY2 evaluated data files. From the measured cumulative yields, the mass-chain yields have been deduced using charge distribution systematics. The mass yields, along with similar data for other fast neutron-induced fissioning systems, show several important features:1. Fine structure in the interval of five mass units in even-Z fissioning systems due to odd-even effects. The fine structure decreases from lighter to heavier even-Z actinides, in accordance with their odd-even effect.2. Higher yields in the mass regions 133 to 135, 138 to 140, and 143 to 145 and their complementary mass regions, depending on the mass of the fissioning systems due to the presence of 82n-66n, 86n-62n, and 88n-56n shells.3. For odd-Z fissioning systems having no odd-even effect, the fine structure is very feeble and is due only to shell effects.4. Unusually high yields observed in the mass region 133 to 139 in the fissioning system {sup 239}U* as compared to other U isotopes are explained on the basis of a higher neutron-to-proton ratio (N/Z) of {sup 238}U compared to lower-mass uranium isotopes. The {nu}-bar, full-width at tenth-maximum, and A{sub L}-bar increase with increasing mass of the fissioning systems, whereas A{sub H}-bar of {approx}139 {+-} 1 remains constant throughout due to the strong preference for the formation of the deformed 88n shell, which is also favorable from the N/Z point of view.
- OSTI ID:
- 20804647
- Journal Information:
- Nuclear Science and Engineering, Vol. 135, Issue 3; Other Information: Copyright (c) 2006 American Nuclear Society (ANS), United States, All rights reserved. http://epubs.ans.org/; Country of input: International Atomic Energy Agency (IAEA); ISSN 0029-5639
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ACTIVATION DETECTORS
AMERICIUM 243
CHARGE DISTRIBUTION
CURIUM 244
DAUGHTER PRODUCTS
FAST NEUTRONS
FINE STRUCTURE
FISSION
FISSION PRODUCTS
FISSION TRACKS
FISSION YIELD
GAMMA RADIATION
GAMMA SPECTROSCOPY
MEV RANGE
NEPTUNIUM 237
NEPTUNIUM 238
NEPTUNIUM 239
NEUTRON REACTIONS
NEUTRON SPECTRA
NUCLEAR DATA COLLECTIONS
PLUTONIUM 238
PLUTONIUM 240
PROTONS
SODIUM 24
URANIUM 238
URANIUM 239