21-29 July 2022
US/Pacific timezone

Fast neutron-induced fission cross section of $^{242}$Pu measured at nELBE and PIAF

28 Jul 2022, 09:40
Folsom ()



Toni Kogler


Precise neutron-induced fission cross-sections of actinides such as the plutonium isotopes are of relevance for the development of future transmutation technologies and 4$^\text{th}$ generation of nuclear reactors. In contrast to thermal reactors, these future technologies employ the fast-neutron spectrum.

For $^{242}$Pu current uncertainties of the fission cross section in the energy region between 500 keV and 2.23 MeV are of about 19 %. Sensitivity studies [1,2] show that the total uncertainty has to be reduced below 5 %, to allow for reliable neutron physics simulations.

This challenging task was tackled at the neutron time-of-flight facility nELBE of the Center for High Power Radiation Sources at HZDR, Dresden. A parallel-plate fission ionization chamber with novel, homogeneous, large-area $^{242}$Pu deposits on Si-wafer backings was used to determine the $^{242}$Pu(n,f) cross section relative to the IAEA neutron cross-section standard $^{235}$U(n,f) in the energy range of 0.5 to 10.0 MeV. A systematic uncertainty below 2.7 % and an average statistical uncertainty of 4.9 % was reached [3]. The results show an agreement of better than 1 % as compared to recently published data (e.g. [4] & [5]) and a good accordance to current evaluated data sets.

In the course of characterizing the actinide targets at the PIAF facility of PTB Braunschweig with 15 MeV DT-neutrons, not only the areal density of the $^{235}$U fission chamber used as reference detector could be precisely determined, but also a further data point for the $^{242}$Pu(n,f) cross section could be obtained. In contrast to the experiment at nELBE, PIAF provides an open neutron field where the whole housing of the chamber was irradiated by neutrons. Thus, the scattering corrections at PIAF were of considerable importance. The effects on the incident neutron fluence were corrected using Geant4-based particle transport calculations.

This work was supported by the EURATOM FP7 project CHANDA and by the German Federal Ministry of Education and Research (03NUK13A).

[1] Working Party on International Evaluation Co-Operation, OECD / NEA, The High Priority Request List for Nuclear Data (HPRL) (2011).
[2] WPEC, Uncertainty and Target Accuracy Assessment for Innovative Systems Using Recent Covariance Data Evaluations, Tech. Rep. (Working Party on International Evaluation Co-Operation, OECD / NEA, 2008).
[3] T. Kögler et al., Fast-neutron-induced fission cross section of $^{242}$Pu measured at the neutron time-of-flight facility nELBE, Phys. Rev. C 99, 024604 (2019).
[4] F. Tovesson et al., Neutron induced fission of $^{240,242}$Pu from 1 eV to 200 MeV, Phys. Rev. C 79, 014613 (2009).
[5] P. Salvador-Castineira et al., Neutron-induced fission cross sections of $^{242}$Pu from 0.3 MeV to 3 MeV, Phys. Rev. C 92, 044606 (2015)

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