| 1. |
- Birgersson, Evert, et al.
(författare)
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Binary fission-fragment yields from the reaction 251Cf(nth, f)
- 2005
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Ingår i: Nuclear fission and fission-product spectroscopy. - : American Institute of Physics. - 0735402884 ; , s. 349-352
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Konferensbidrag (refereegranskat)abstract
- The recoil mass spectrometer LOHENGRIN of the Laue-Langevin Institute, Grenoble has been used to measure the light fission-fragment mass yield and kinetic energy distributions from neutron-induced 252Cf*, using 251Cf as target material. ©2005 American Institute of Physics
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| 2. |
- Birgersson, Evert, 1974-
(författare)
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Determination of binary fission-fragment yields in the reaction 251Cf(nth, f) and Verification of nuclear reaction theory predictions of fission-fragment distributions in the reaction 238U(n, f)
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Neutron-induced fission has been studied at different excitation energies of the compound nucleus by measurements on the two fissioning systems, 252Cf* and 239U*.For the first time, the light fission fragment yields from the reaction 251Cf(nth, f) have been measured with high resolution. This experiment was performed with the recoil mass spectrometer LOHENGRIN at ILL in Grenoble, France. When the results from this work, where the compound nucleus is at thermal excitation, are compared to the spontaneous fission of 252Cf, enhanced emission yields as well as an increased mean kinetic energy is observed around A = 115. This suggests the existence of an additional super-deformed fission mode in 252Cf.The reaction 238U(n, f) was studied using the 2E-technique with a double Frisch grid ionization chamber. Fission fragment mass, energy and angular distributions were determined for incident neutron energies between 0.9 and 2.0 MeV. The experiments were performed at the Van de Graaff accelerator of IRMM in Geel, Belgium. This is the first measurement of the mass distribution for incident neutron energies around 0.9 MeV. The motivation for studying 238U(n, f) was to verify theoretical predictions of the mass distribution at the vibrational resonance in the fission cross section at 0.9 MeV. However, the predicted changes in fission fragment distributions could not be confirmed.A precise modelling of the fission process for the minor actinides becomes very important for future generation IV and accelerator driven nuclear reactors. Since fission fragment distributions depend on the excitation of the fissioning system, so does the number of delayed neutrons, which are one of the safety parameters in a reactor.
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| 3. |
- Birgersson, Evert, et al.
(författare)
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Light fission-fragment mass distribution from the reaction 251Cf(nth, f)
- 2007
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Ingår i: Nuclear Physics A. - Amsterdam : Elsevier. - 0375-9474 .- 1873-1554. ; 791:1-2, s. 1-23
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Tidskriftsartikel (refereegranskat)abstract
- For mass numbers A = 80 to 124 the recoil mass spectrometer LOHENGRIN of the Institute Laue-Langevin in Grenoble was used to measure with high resolution the light fission-fragment mass yields and kinetic energy distributions from thermal-neutron induced fission of 252Cf* for the first time, using 251Cf as target material. The obtained mean light fragment mass AL = (107 ± 2) and the corresponding mean kinetic energy Ek,L = (103±2) MeV are within the expected trend. Emission yields around A = 115 are enhanced and the corresponding mean kinetic energy is higher compared to spontaneous fission of 252Cf. This could be explained by the existence of an additional super-deformed fission mode.
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| 4. |
- Birgersson, Evert, et al.
(författare)
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Properties of the reaction 238U(n, f) at the vibrational resonances
- 2009
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Ingår i: Nuclear Physics A. - Amsterdam : Elsevier. - 0375-9474 .- 1873-1554. ; 817:1-4, s. 1-34
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Tidskriftsartikel (refereegranskat)abstract
- Recent fission cross-section calculations for the reaction 238U(n, f ), based on an extended statistical model, predict a significant change of fission fragment properties, such as the mean mass by A = 1.5 and a notable increase in total kinetic energy in the region of the vibrational resonance at an incident neutron energy En = 0.9 MeV. This model includes individual fission cross-sections by the asymmetric standard 1 (S1) and standard 2 (S2) as well as the symmetric super-long (SL) mode. In order to verify the model predictions, a dedicated experiment on 238U has been carried out to measure fission-fragment mass yield distributions for incident neutron energies from En = 2.0 MeV down to 0.9 MeV, where the fission characteristics at the vibrational resonance at En = 0.9 MeV were investigated for the first time. The previously reported distinct structure in the angular anisotropy around En = 1.2 and 1.6 MeV wasobserved at En = 0.9 MeV as well. The predicted large changes in fission fragment mass yield and total kinetic energy could not be confirmed. In the resonance the mean total kinetic energy is only about 0.5 MeV higher than at En = 1.8 MeV. At the same time, a slight decrease of the mean heavy fragment mass was observed, probably indicating a slightly increased contribution of the S1 fission mode.
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| 5. |
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| 6. |
- Oberstedt, Andreas, et al.
(författare)
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Recent results on the neutron-induced fission cross-section of 231Pa
- 2005
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Ingår i: Proceedings of the 3rd international workshop on nuclear fission and fission-product spectroscopy. - : American Institute of Physics. - 0735402884 ; , s. 27-30
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Konferensbidrag (refereegranskat)abstract
- The cross-section for the neutron-induced fission of 231Pa has recently been measured from the threshold to En = 3.5 MeV. The experimental results are described in terms of extended statistical model calculations.
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| 7. |
- Oberstedt, S., et al.
(författare)
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First results on the neutron-induced fission cross-section of Pa-231 for incident neutron energies E-n > 17 MeV
- 2012
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Ingår i: Annals of Nuclear Energy. - : Elsevier. - 0306-4549 .- 1873-2100. ; 43, s. 26-30
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Tidskriftsartikel (refereegranskat)abstract
- First results on the neutron-induced fission cross-section of Pa-231 for incident neutron energies E-n > 17 MeV are presented. The experiments were carried out with quasi mono-energetic neutrons produced in the reaction T(d, n)He-4. Corrections for low-energy neutron background produced in this reaction at incident deuteron energies E-d > 2 MeV are taken into account and based on experimental data obtained by two different techniques. Despite the relatively large error bars at the higher neutron energies, the new cross-section values meet the accuracy requirements set by the IAEA and will allow to remove the hitherto existing large spread between different previously published data. Recent cross-section calculations describe well the new experimental results, which are in consistency with cross-section values obtained in a particle-transfer reaction at excitation energies corresponding to neutron energies E-n < 10 MeV.
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