Total and differential fission cross sections of uranium and thorium for low energy deuterons

Nemilov, Yu.A.; Павлов, В. В.; Selitskii, Yu.A.; Соловьев, С. М.; Eismont, V.P.

doi:10.1007/bf01116092

Cited by 4 publications

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“…Anisotropics slightly smaller than unity have been reported previous-ly for fission induced in U 235 by 80-keV neutrons 5 and 6-MeV deuterons. 6 In addition to this "anomaly," the fission threshold of the U 236 nucleus deduced from V 234: (t,pf) has been found 7 to be approximately 0.5 MeV lower than that deduced from \J 235 (d,pf).…”

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confidence: 88%

Fission-Fragment Angular Anisotropy in the ReactionsU235(d, pf)and
Specht¹,
Fraser²,
Milton³
1966
Phys. Rev. Lett.
21
0
2
0
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We have been studying (d,pf) reactions on targets of U 235 and Pu 239 in order to look for variations in the average total kinetic energy of fission with excitation energy and, in addition, for correlations between kinetic energy and fission fragment angular anisotropy. We feel that the anisotropy results obtained and the tentative conclusions presented in this Letter are of sufficient interest to be published separately from the kinetic energy results. 1 Four semiconductor detectors were arranged in a plane containing the beam (12.5-MeV deuterons from the Chalk River tandem Van de Graaff). A two-counter AE/E telescope distinguished protons from other particles, and the remaining two counters detected fission fragments in a back-to-back arrangement. With the proton angle set at either 100° or 110° with respect to the deuteron beam, data were taken for fragment directions parallel and perpendicular to the classical recoil axis. An on-line computer was used for data recording, mass identification of the protons, and digital stabilization of the four detector-amplifier-encoder systems. The over-all energy resolution of the proton system was -150 keV.The measured angular anisotropy of the fragments, defined as W(0°)/W(90°), is plotted in Fig. 1. The results for V 235 (d,pf) will be discussed first. No measurements of the anisotropy in this reaction have been reported. The random coupling of the neutron spin, and the high spin (|~) of the U 235 ground state, to the orbital angular momentum transferred was presumed to reduce the anisotropy to values near unity without significant fluctuations with excitation energy. Calculations based on the existing model of fragment angular distributions 2 " 4 lead to anisotropics of the order of 1.2-1.3 nearly independent of the projection K of the total spin on the deformation axis of the transition state nucleus for K^ 2. Experimentally, however, a nearly constant anisotropy of 1.2-1.3 is found only for excitation energies above the neutron binding energy (6.45 MeV); more than 1 MeV lower, where the fission probability is about ten times smaller, 1 an anisotropy as low as 0.6 has been found. Anisotropics slightly smaller than unity have been reported previous-ly for fission induced in U 235 by 80-keV neutrons 5 and 6-MeV deuterons. 6 In addition to this "anomaly," the fission threshold of the U 236 nucleus deduced from V 234: (t,pf) has been found 7 to be approximately 0.5 MeV lower than that deduced from \J 235 (d,pf).This shift in threshold suggests that fission via the K =0 + band, expected to be lowest in the transition-state spectrum, is strongly inhibited in the reaction \J 235 {d,pf). In what follows, we tentatively attribute this inhibition and the low value of the anisotropy in this excitation-energy region to the detailed characteristics of the (d,p) process. We suggest that the simple physical assumptions made previously, 2 which lead to an angular-momentum distribution of excited levels independent of excitation energy, might not be justified. We assume instead that ...

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confidence: 88%

Fission-Fragment Angular Anisotropy in the ReactionsU235(d, pf)and
Specht¹,
Fraser²,
Milton³
1966
Phys. Rev. Lett.
21
0
2
0
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(d, p) - (alpha, gamma)

Keller¹,

Lange²,

Münzel³

et al.

Excitation Functions for Charged-Particle Induced Nuclear Reactions

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Figs. 143 - 168 (d, p) - (d, f)

Keller¹,

Lange²,

Münzel³

et al.

Excitation Functions for Charged-Particle Induced Nuclear Reactions

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Total and differential fission cross sections of uranium and thorium for low energy deuterons

Cited by 4 publications

References 4 publications

Fission-Fragment Angular Anisotropy in the ReactionsU235(d, pf)and
Specht¹,
Fraser²,
Milton³
1966
Phys. Rev. Lett.
21
0
2
0
View full text Add to dashboard Cite

Fission-Fragment Angular Anisotropy in the ReactionsU235(d, pf)and
Specht¹,
Fraser²,
Milton³
1966
Phys. Rev. Lett.
21
0
2
0
View full text Add to dashboard Cite

(d, p) - (alpha, gamma)

Figs. 143 - 168 (d, p) - (d, f)

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Total and differential fission cross sections of uranium and thorium for low energy deuterons

Cited by 4 publications

References 4 publications

Fission-Fragment Angular Anisotropy in the ReactionsU235(d, pf)andSpecht1, Fraser2, Milton3 1966Phys. Rev. Lett.21020View full textAdd to dashboardCite

Fission-Fragment Angular Anisotropy in the ReactionsU235(d, pf)andSpecht1, Fraser2, Milton3 1966Phys. Rev. Lett.21020View full textAdd to dashboardCite

(d, p) - (alpha, gamma)

Figs. 143 - 168 (d, p) - (d, f)

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Fission-Fragment Angular Anisotropy in the ReactionsU235(d, pf)and
Specht¹,
Fraser²,
Milton³
1966
Phys. Rev. Lett.
21
0
2
0
View full text Add to dashboard Cite

Fission-Fragment Angular Anisotropy in the ReactionsU235(d, pf)and
Specht¹,
Fraser²,
Milton³
1966
Phys. Rev. Lett.
21
0
2
0
View full text Add to dashboard Cite