The dependency of fast neutron flux and spectra on the collimation-field size and geometry for fast neutron therapy purposes

Abstract

The aim of this work is to optimize and investigate the relationship between the collimation-filed size and their geometries and the fast-neutron intensity and their energy-spectrum. Advantageously for these purposes, a prototype of collimator was designed and constructed to simulate different geometrical and materials compositions. Beams of fast neutrons generated by the reaction ⁹Be(d, n) with 13.6 MeV deuteron energy were investigated. The average energy of the emitted neutrons is about 6–7 MeV. The maximum intensity was at neutron energy of 4–5 MeV. In the process of the study, experimental works were carried out with Al, Fe, Cu and Cd foils which positioned on the collimator aperture as neutron detectors. The neutron activation method and Gamma-spectrometer were deployed to determine the neutron intensities within the energy-range from thermal energies to 14 MeV. Experiments were conducted for ten different combinations of materials and geometries which can be adjusted by the removable-polyethylene collimator parts and the metal parts. It was concluded that the thermal and fast neutron flux were depended on the collimation-field size and materials, where the fast neutron flux output was about 100% more for bigger collimator 9 × 9 cm² comparing with the smaller ones 5 × 5 cm² . And more than 60% in case of adding Lead layers into the collimator. These results could have influential implications on the fast neutron intensities and improvement of collimation systems for fast neutron therapy. Also, it could enhance the irradiation fluxes in the irradiation channels in nuclear reactors for medical isotopes productions and material testing and other applications.

KEYWORDS:

• Fast neutron therapy
• cyclotron
• neutron spectrum
• dose rate
• collimator

Acknowledgements

The authors greatly appreciated the help by the workers at the laboratory of radioactive materials at the School of Nuclear Science & Engineering.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work is supported by the National Research Tomsk Polytechnic University.

Notes on contributors

A. M. Shehada

A. M. Shehada, a PhD student at Tomsk Polytechnic University. Engaged in radiation physics and radiation protection research.

V. P. Krivobokov

V. P. Krivobokov, Professor, Doctor of Physical and Mathematical Sciences, Head of the Department of Scientific and educational center B.P. Weinberg, Tomsk Polytechnic University. Engaged in magnetron sputtering and ion interactions with matter.