H. Naik

Measurement of Absolute Fission Yields in the Fast Neutron–Induced Fission of Actinides: 238U, 237Np, 238Pu, 240Pu, 243Am, and 244Cm by Track-Etch-cum-Gamma Spectrometry

Abstract The absolute fission yields of 46 fission products in 238U (99.9997 at.%), 46 fission products in 237Np, 27 fission products in 238Pu (99.21 at.%), 30 fission products in 240Pu (99.48 at.%), 30 fission products in 243Am (99.998 at.%), and 32 fission products in 244Cm (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., 238Pu, 240Pu, 243Am, and 244Cm–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., 243Am-239Np), (b) activation products of the catcher foil [e.g., 24Na from Al(n,α)], and (c) activation products of the target [e.g., 238Np from 237Np(n,γ) and 239Np from 238U(n,γ)] 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 238U and 237Np) 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 239U* as compared to other U isotopes are explained on the basis of a higher neutron-to-proton ratio (N/Z) of 238U compared to lower-mass uranium isotopes. The [overbar]ν, full-width at tenth-maximum, and ĀL increase with increasing mass of the fissioning systems, whereas AH of ~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.

Systematics of fragment angular momentum in low-energy fission of actinides

Abstract Independent isomeric yield ratios for 128 Sb, 130 Sb, 132 Sb, 131 Te, 133 Te, 132 I, 134 I, 136 I, 135 Xe and 138 Cs in 229 Th(n th , f), for 136 I in 233 U(n th , f) and 239 Pu(n th , f), for 138 Cs in 235 U(n th , f), for 130 Sb, 136 I and 135 Xe in 241 Pu(n th , f), for 128 Sb, 130 Sb, 130 Sb, 132 Sb, 131 Te, 133 Te, 134 I, 136 I, 135 Xe and 138 Cs in 245 Cm(n th , f) and for 128 Sb, 130 Sb, 132 Sb, 136 I and 135 Xe in 252 Cf(S.F.) have been determined using radiochemical and gamma-ray spectrometric techniques. From the isomeric yield ratios, fragment angular momenta ( J rms ) have been deduced using spin-dependent statistical-model analysis. These data along with the literature data in the above fissioning systems as well as in 249 Cf(n th , f) show several important features. These features are: (i) Angular momenta for fragments with spherical 50-proton shell, 82-neutron shell and even- Z products are lower compared to the fragments with deformed 88-neutron shell, no shells and odd- Z products indicating the nuclear-structure effects. (ii) Fission fragment J rms has a nearly inverse correlation with elemental yield in fissioning systems from 230 Th ∗ to 252 Cf possibly due to coupling between the collective and intrinsic degrees of freedom. (iii) Although the percentage odd-even effect in the elemental yield decreases from 230 Th ∗ to 250 Cf ∗ and 252 Cf, the odd-even fluctuation on fragment J rms remains nearly the same in spite of the inverse correlation. This possibly indicates the effect of fragment deformation. (iv) Fission-product elemental yield as well as angular momentum have no definite correlation with fissionability since both are decided near the scission point.

Photo-neutron reaction cross-sections for natZr in the bremsstrahlung end-point energies of 12-16 and 45-70 MeV

Abstract.The natZr(

Systematics of charge distribution studies in low-energy fission of actinides

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Fission Product Yield in the Neutron-Induced Fission of 232Th with Average Energies of 5.42, 7.75, and 10.09 MeV

, xn) 89-86Zr reaction cross-sections were experimentally determined at the bremsstrahlung end-point energies of 12, 14, 16, 45, 50, 55, 60 and 70MeV by activation and off-line

Measurement of Neutron-Induced Reaction Cross Sections in Zirconium Isotopes at Thermal, 2.45 MeV and 9.85 MeV Energies

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Correlations of fission fragment angular momentum with collective and intrinsic degrees of freedom

-ray spectrometric technique using the 20 MeV electron linac (ELBE) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany, and the 100 MeV electron linac at the Pohang Accelerator Laboratory (PAL), Pohang, Korea. The natZr(

Effect of shell closure proximity on fragment angular momenta in241Pu/nth'f/

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Some important aspects of fragment angular momentum in medium energy fission of 238U

, xn) 89-86Zr reaction cross-sections as a function of photon energy were also calculated using the TALYS 1.4 computer code. The flux-weighted average cross-sections at the end-point energies of 12-16 and 45-70 MeV were obtained using the literature and the TALYS calculation data based on mono-energetic photons and are found to be in good agreement with the present data. It was also found that the present data and the flux-weighted literature and theoretical values for the natZr(

Fission fragment angular momentum in the spontaneous fission of 244Cm

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