Neutron spectroscopy from 1 to 15 MeV with Mimac-FastN, a mobile and directional fast neutron spectrometer and an active phantom for BNCT and PFBT

Daniel Santos,Olivier Guillaudin,Jean-François Muraz,Nadine Sauzet,F Ott,C Alba-Simionesco,A Menelle

doi:10.1051/epjconf/202023105003

Abstract

In the frame of direct dark matter search, the fast neutrons producing elastic collisions on the nuclei of the active volume are the ultimate background. The MIMAC (MIcro-tpc MAtrix Chambers) project has developed a directional detector providing the directional signature to discriminate them from the searched events based on 3D nuclear tracks reconstruction. The MIMAC team of the LPSC has adapted one MIMAC chamber as a mobile fast neutron spectrometer, the Mimac-FastN detector, having a wide neutron energy range (10 keV – 600 MeV) working with different gas mixtures and pressures. This presentation will be focused on the MeV range with 4He + 5% CO2 gas mixture at 700 mbar. A boron coating inside the active volume used for calibration purpose opens the possibility to use the active volume as an active phantom for Boron Neutron Capture Therapy (BNCT) and Proton Fusion Boron Therapy (PFBT).

Highlights

To perform a fast neutron spectroscopy without a time flight measurement or without many 3He counters is a real challenge and required in many different domains, such as neutron dosimetry, identification of fissile nuclear material and nuclear physics in general
The spectrometer Mimac-FastN was filled with a gas mixture of 95 % of 4He and 5 % of CO2 at 700 mbar
Using the same gas mixture, with a threshold on the neutron energy as low as 200 keV, this directional fast neutron spectrometer gives a complete polyenergetic neutron spectrum exploring the material and eventual pollutions of the target or neutron sources. This ability to provide polyenergetic neutron spectrum has already been applied to characterize the angular distribution of fast neutrons produced in a nuclear reaction proposed for a radiotherapy called Accelerator-Based Boron Neutron Capture Therapy (AB-BNCT) [13]

Summary

Introduction

To perform a fast neutron spectroscopy without a time flight measurement or without many 3He counters is a real challenge and required in many different domains, such as neutron dosimetry, identification of fissile nuclear material and nuclear physics in general. Some applications require measurements above 10 MeV and a large energy range. Among these applications, we can mention the secondary neutrons in radiotherapy, and the characterization of cosmic neutrons produced in the atmosphere by cosmic particles, going up to 100 MeV. Iterative moderation using neutron capture on converters leads to poor energy resolution and requires hypothesis on the expected neutron energy, the detection in solids through elastic collisions is limited due to the absorption of recoils in the converter, whereas detection in liquid scintillators results in a limited measuring range

Detection Principle

Energy Calibration

Experimental Results

Conclusions