Photofission of 232Th near threshold

doi:10.1016/0375-9474(86)90353-2

Nuclear Physics A

Volume 458, Issue 2, 6 October 1986, Pages 217-224

https://doi.org/10.1016/0375-9474(86)90353-2 Get rights and content

Abstract

Measurements are presented of the photofission cross section and the mean number $ν$ of neutrons per fission for ²³²Th made using bremsstrahlung from the Harwell electron linear accelerator HELIOS and a high efficiency neutron detector to record neutron multiplicity distributions. The cross section is interpreted in terms of a fission barrier with shallow wells in two separate outer barriers. Interesting structure is observed in $ν$ as a function of photon energy.

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Cited by (16)

Study of the 232Th fission barrier by electron-induced fission
1996, Nuclear Physics A
Fission fragment angular distributions and the electrofission cross section of ²³²Th were measured in the electron energy region 4.5–7.9 MeV. Below 5.20 MeV two distinct shelves were observed in the isotropic component of the total electrofission cross section, indicating the presence of resonances in the photofission cross section at 4.55 [(2⁺, 0) channel] and at 4.95 MeV [(1⁻, 0) channel]. These resonances are interpreted as associated to vibrational levels in the second well of the ²³²Th fission barrier. Moreover, a resonance observed at 5.65 MeV in both channels is interpreted as a signature for a vibrational level in the third well of the triple-humped fission barrier deduced for this nucleus.
Mass and kinetic energy distributions for the photofission of 232Th with 6.44 to 13.15 MeV bremsstrahlung
1993, Nuclear Physics, Section A
Post- and preneutron-emission mass and kinetic energy distributions of the fragments emitted in the photofission of ²³²Th with 6.44, 7.33, 8.35, 9.31, 11.13 and 13.15 MeV have been studied. Energy correlation and γ-spectrometric measurements were performed. Sb, Ru and Cd were separated chemically to determine postneutron yields in the symmetric mass region. The ²³²Th system predominantly splits in an asymmetric way with a maximum yield for heavy fragments in the region of mass 140. An enhanced yield around heavy mass 134 is observed, becoming of increasing importance with increasing compound nucleus excitation energy. For 6.44 and 7.35 MeV bremsstrahlung induced fission no symmetric component in the mass distribution could be observed. For the higher endpoint energies symmetric fission becomes more and more evident. From the symmetric fission yields at different excitation energies, using barrier penetration calculations, the height of the symmetric fission barrier is estimated to be of the order of 7.5 to 7.7 MeV. The total fragment kinetic energy shows a minimum for symmetric splits and a maximum for splits with heavy mass in the vicinity of mass 132. It increases with increasing excitation energy of the ²³²Th compound nucleus. This effect is especially pronounced in the energy region just above the barrier. It is observed for all masses, but mass splits with heavy mass in the vicinity of mass 132 show the strongest effects. The fragment mass distributions for ²³²Th(γ, f) show a clear difference when compared with those for α-particle accompanied fission of ²³⁵U. Our results are interpreted in the framework of the Brosa fission channels model and in the scission point model. They also provide information concerning the dissipation of collective energy into the intrinsic degrees of freedom during the transition from saddle to scission point.
Photofission and photoneutron measurements on 241Am between 5 and 10 MeV
1992, Nuclear Physics, Section A
Measurements are presented of the photofission and photoneutron cross sections of ²⁴¹Am and of the mean number $v$ of neutrons per fission between 5 and 10 MeV. The measurements were carried out using a bremsstrahlung beam generated by the Harwell electron linear accelerator HELIOS and a 1.5 g metallic ²⁴¹Am target. Neutron multiplicity distributions were recorded using a high-efficiency neutron detector. Yield measurements made in steps of 50 keV show possible evidence for a resonance at 6.1 MeV in the photofission cross section, but the statistical significance is not high.
Experimental electron beam irradiation of food and the induction of radioactivity
1992, International Journal of Radiation Applications and Instrumentation. Part
Samples of chicken, prawns, cheeses and spices were irradiated on the Harwell electron linear accelerator HELIOS at 20 MeV to assess mechanisms for the induction of radioactivity. The induced radioactivity was measured using a lead shielded Ge(Li) γ-ray spectrometer, and the results were compared with activities calculated on the basis of photoneutron and photoproton reactions induced by real and virtual photons. In general, there was good agreement. Bounds were also placed on the induction of radioactivity by capture of neutrons produced in the food samples themselves. Further, the data were used to assess the effects of a gross malfunction of an electron beam irradiation facility; after 1 day, the specific activity of food samples irradiated to 10 kGy at 20 MeV was ∼0.01 Bq g⁻¹. In addition, food samples were also irradiated at 10 MeV, and irradiated and control samples were analysed for microbiological burden. Reductions in the microbiological burden of the food samples by factors consistent with those found in previous measurements were found.
Giant dipole resonance photofission and photoneutron reactions in U 238 and Th 232
2024, Physical Review C
Giant Dipole Resonance photofission and photoneutron reactions in 238U and 232Th
2024, arXiv

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^☆: Work described in this paper was undertaken as part of the Underlying Research Programme of the UKAEA.

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Nuclear Physics A

Abstract

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Cited by (16)

Study of the <sup>232</sup>Th fission barrier by electron-induced fission

Mass and kinetic energy distributions for the photofission of <sup>232</sup>Th with 6.44 to 13.15 MeV bremsstrahlung

Photofission and photoneutron measurements on <sup>241</sup>Am between 5 and 10 MeV

Experimental electron beam irradiation of food and the induction of radioactivity

Giant dipole resonance photofission and photoneutron reactions in U 238 and Th 232

Giant Dipole Resonance photofission and photoneutron reactions in <sup>238</sup>U and <sup>232</sup>Th

Photofission of 232Th near threshold☆

Abstract

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Photofission of ²³²Th near threshold☆