Program - Brookhaven National Laboratory

F. Mingrone, on behalf of the n TOF collaboration
Dipartimento di Fisica, Universitá di Bologna, and Sezione INFN di Bologna, Italy
The measurement of the 238 U radiative capture cross section falls within the NEA High Priority Request
List [1] for the most relevant isotopes to be investigated in more detail for improving the design of different
advanced nuclear systems [2] and nuclear fuel cycles [3]. According to the European Strategic Energy
Technology Plan, in fact, nuclear energy appears as an unavoidable source of energy for the future, and to
achieve a long term sustainability of nuclear energy an improvement in the accuracy and precision of the
present basic nuclear data is crucial. Although there are lots of 238 U(n, γ) measurements, inconsistencies
are still present in the cross section. Therefore there is a proposal for a series of joined measurement of this
reaction cross section in order to reach an uncertainty below 2% in the range from a few eV to hundreds of
keV, both at the EC-JRC-IRMM facility GELINA and at the n TOF facility at CERN. The preliminary
results of the 238 U capture cross section measurement using C6D6 detectors are presented. This measurement
has been performed in April 2012 at the n TOF facility, in an energy range from the thermal point
to about 500 keV. The very high instantaneous neutron flux, the excellent energy resolution and the low
repetition rate characteristic of the facility allowed us to reach the desired precision.
[1] http://www.nea.fr/html/dbdata/hprl/. [2] OECD/NEA WPEC Subgroup 26 Final Report: ”Uncertainty
and Target Accuracy Assessment for Innovative Systems Using Recent Covariance Data Evaluations”,
http://www.nea.fr/html/science/wpec/volume26/volume26.pdf. [3] Report of the Numerical results
from the Evaluation of the nuclear data sensitivities, Priority list and table of required accuracies for
nuclear data. FP-7 IP-EUROTRANS.
HA 4 4:40 PM
Measurement of the 240,242Pu(n,f) Cross Section at the CERN n TOF Facility
A. Tsinganis, CERN, Geneva, Switzerland and National Technical University of Athens, Greece. M.
Calviani, S. Andriamonje, C. Guerrero, V. Vlachoudis, CERN, Geneva, Switzerland. E. Berthoumieux,
F. Gunsing, Commissariat á l’ Énergie Atomique (CEA) Saclay - Irfu, Gif-sur-Yvette, France. N.
Colonna, Istituto Nazionale di Fisica Nucleare, Bari, Italy. C. Massimi, Dipartimento di Fisica,
Università di Bologna and Sezione INFN di Bologna, Italy. R. Vlastou, National Technical University of
Athens, Greece. The n TOF collaboration, Various.
The sustainable use of nuclear energy as a means of reducing reliance on fossil-fuel for energy production
has motivated the development of nuclear systems characterised by a more efficient use of nuclear fuels, a
lower production of nuclear waste, economic viability and competitiveness and minimal risk of proliferation
of nuclear material is being pursued by international collaborations [1]. The accurate knowledge of relevant
nuclear data is crucial for feasibility and performance studies of advanced nuclear systems, including Accelerator
Driven Systems (ADS). These data include neutron cross sections of a variety of plutonium isotopes
and other minor actinides, such as neptunium, americium and curium. In this context, the 240,242 Pu(n,f)
cross sections were measured relative to the well-known 235 U(n,f) cross section. These isotopes are included
in the Nuclear Energy Agency (NEA) High Priority List [2] and the NEA WPEC Subgroup 26 Report on
the accuracy of nuclear data for advanced reactor design [3]. The measurements were performed at the
CERN n TOF facility [4], taking advantage of the wide energy range (from thermal to GeV) and the high
instantaneous flux of the n TOF neutron beam. These characteristics mitigate the adverse effects of the
strong α-particle background produced by the samples and the low fission cross section below the fission
threshold. The measurements were carried out with the innovative Micromegas (Micro-MEsh GAseous
Structure) gas detector [5]. The gas volume of the Micromegas is separated into a charge collection region
(several mm) and an amplification region (tens of µm) by a thin “micromesh” with 35 µm diameter holes
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