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Neutron-induced fission cross sections for 242,243Cm and 241Am obtained with the surrogate reaction method

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Neutron-induced fission cross sections for 242,243Cm and 241Am have been obtained with the surrogate reaction method. Previous results for the neutron-induced cross section of 243Cm were questioned by these new data. For the first time, the 242Cm cross section has been determined up to the onset of second-chance fission. The good agreement at the lowest excitation energies between these new results and the existing neutron-induced data indicates that the distributions in spin and parity of states populated with both techniques are similar.

To determine the (n,f) cross sections for 242,243Cm and 241Am, we used the surrogate reactions 243Am(3He,t)243Cm*, 243Am(3He,d)244Cm*, and 243Am(3He,α)242Am*, respectively. The 243Am(3He,p)245Cm channel couldn’t be investigated due to parasitic single protons occuring from breakup reactions. The measurements were carried out at Tandem accelerator at IPN Orsay with a 3He beam at 24 MeV and 30 MeV. We had two 243Am targets, each of approximatively 100μg/cm2 on a 75μg/cm2 carbon backing, prepared at Argonne National Laboratory.

Set-up used at IPNO consisting of 4 telescopes to detect the ejectile for identification of the formed nucleus and 15 solar cells to count the fission products.

The target 243Am allowed to simultaneously produce three isotopes of Curium and an isotope of Americium via four open channels: 243Am(3He,p)245Cm, 243Am(3He,d)244Cm, 243Am(3He,t)243Cm and 243Am(3He,α)242Am. These four reaction channels are visible on the ΔE-E plot of the events measured by one of the Si telescopes (left part of the following figure).

The excitation energy of the compound nucleus is deduced from the Q value and the kinematics of the reaction. On the right part of the figure the excitation energy spectrum is shown for the proton channel (245Cm*) for single events and events in coincidence with a fission detected in one of the cells. The fission probability is obtained by the ratio of these two spectra taking account of the fission detection efficiency.

The following figures show the resulting neutron induced fission cross section determined via the surrogate method for 241Am (α channel), 242Cm (t channel) and 243Cm (d channel). Our results are compared to the (few) existing data and available evaluations: JEFF-3.1 (Europe), JENDL-3.3 (Japan) and ENDF-B-VII (USA), with emphasis on the low neutron energy part on the last picture.

The experiment and the results are presented and discussed in G. Kessedjian et al..

Related publications:

Mesures de sections efficaces d’actinides mineurs d’intérêt pour la transmutation
G. Kessedjian, PhD, Université Bordeaux 1, Nov 2008
Neutron-induced fission cross sections of short-lived actinides with the surrogate reaction method
G. Kessedjian et al., Phys. Lett. B 692, 297-301 2010
Fission probabilities of 242Am, 243Cm, and 244Cm induced by transfer reactions
G. Kessedjian et al., Phys. Rev. C 91, 044607 (2015)  

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