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Measurement of the 235U(n, f) cross section relative to the 6Li(n, t) and 10B(n,α) standards from thermal to 170 keV neutron energy range at n_TOF
Ist Teil von
The European physical journal. A, Hadrons and nuclei, 2019, Vol.55 (7), p.1-19, Article 120
Ort / Verlag
Berlin/Heidelberg: Springer Berlin Heidelberg
Erscheinungsjahr
2019
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
.
The
235
U(n, f ) cross section was measured at n_TOF relative to
6
Li(n, t) and
10
B(n,
α
) , with high resolution (
L
=
183
.
49
(
2
)
m) and in a wide energy range (25meV-170keV) with 1.5% systematic uncertainty, making use of a stack of six samples and six silicon detectors placed in the neutron beam. This allowed us to make a direct comparison of the yields of the
235
U(n, f ) and of the two reference reactions under the same experimental conditions, and taking into account the forward/backward emission asymmetry. A hint of an anomaly in the 10-30keV neutron energy range had been previously observed in other experiments, indicating a cross section systematically lower by several percent relative to major evaluations. The present results indicate that the cross section in the 9-18keV neutron energy range is indeed overestimated by almost 5% in the recently released evaluated data files ENDF/B-VIII.0 and JEFF3.3, as a consequence of a 7% overestimate in a single GMA node in the IAEA reference file. Furthermore, these new high-resolution data confirm the existence of resonance-like structures in the keV neutron energy region. The results here reported may lead to a reduction of the uncertainty in the 1-100keV neutron energy region. Finally, from the present data, a value of
249
.
7
±
1
.
4
(
stat
)
±
0
.
94
(
syst
)
b·eV has been extracted for the cross section integral between 7.8 and 11eV, confirming the value of
247
.
5
±
3
b·eV recently established as a standard.