Towards the experimental validation of a small Time-Projection-Chamber for the quasi-absolute measurement of the fission cross section

Abstract

To accurately measure neutron-induced fission cross sections, to characterize neutron-beam lines or to make dosimetric investigations, it is necessary to have high accuracy measurements of neutron fluence. It is possible to perform independent and precise neutron flux measurements with respect to the 1H(n,n)p elastic scattering cross section. The use of a silicon detector is recommended from 1 to 70 MeV neutron energy. However, it has been observed that a high electrons background forbids its use below 1 MeV. Hence, a new gaseous proton-recoil telescope is developed and characterized to overcome this limit. It should provide quasi-absolute neutron flux measurements with an accuracy around 3% and is not sensible to gamma and electrons background. It consists in two ionization chambers read by a segmented micromegas technology detection plane. The gas pressure inside is adjustable to the proton range in the detector and therefore to the neutron energy. This detector is described in details below and the newest results of its characterization are presented. A special attention is paid to detection efficiency measurements.

Development of a small Time-Projection-Chamber for the quasi-absolute neutron flux measurement

“…All the details of the intrinsic efficiency measurements can be found in [14,15]. The intrinsic efficiency has first been studied with an alpha source delivering 4.5 alphas/s inside the GPRT.…”

“…Even if other proton recoil detectors have been developed as plastic scintillator [6][7][8][9][10] or proportional counters [11][12][13], the inaccuracy of their efficiency makes these detectors not suitable for our goal (see [2,14,15] for details).…”