Measurement of the S(n,α) cross-section at n_TOF(CERN): Applications to BNCT

Abstract

Aim

The main purpose of this work is to present a new (n,α) cross-section measurement for a stable isotope of sulfur, ³³S, in order to solve existing discrepancies.

Background

³³S has been studied as a cooperating target for Boron Neutron Capture Therapy (BNCT) because of its large (n,α) cross-section in the epithermal neutron energy range, the most suitable one for BNCT. Although the most important evaluated databases, such as ENDF, do not show any resonances in the cross-section, experimental measurements which provided data from 10[[ce:hsp sp="0.25"/]]keV to 1[[ce:hsp sp="0.25"/]]MeV showed that the lowest-lying and strongest resonance of ³³S(n,α) cross-section occurs at 13.5[[ce:hsp sp="0.25"/]]keV. Nevertheless, the set of resonance parameters that describe such resonance shows important discrepancies (more than a factor of 2) between them.

Materials and methods

A new measurement of the ³³S(n,α)³⁰Si reaction cross-section was proposed to the ISOLDE and Neutron Time-of-Flight Experiments Committee of CERN. It was performed at n_TOF(CERN) in 2012 using MicroMegas detectors.

Results

In this work, we will present a brief overview of the experiment as well as preliminary results of the data analysis in the neutron energy range from thermal to 100[[ce:hsp sp="0.25"/]]keV. These results will be taken into account to calculate the kerma-fluence factors corresponding to ³³S in addition to ¹⁰B and those of a standard four-component ICRU tissue.

Conclusions

MCNP simulations of the deposited dose, including our experimental data, shows an important kerma rate enhancement at the surface of the tissue, mainly due to the presence of ³³S.