Study on measuring device arrangement of array-type CdTe detector for BNCT-SPECT

Abstract

Aim

To design the measuring device arrangement of array-type CdTe detector for BNCT-SPECT.

Background

In a boron neutron capture therapy, a very serious unsolved problem exists, namely that the treatment effect for BNCT cannot be known during irradiation in real time. Therefore, we have been developing a so-called BNCT-SPECT with a CdTe detector, which can obtain a three-dimensional image for the BNCT treatment effect by measuring 478[[ce:hsp sp="0.25"/]]keV gamma-rays emitted from the excited state of ⁷Li nucleus created by the ¹⁰B(n,α) reaction. However, no practical uses were realized at present, because BNCT-SPECT requires very severe conditions for spatial resolution, measuring time, statistical accuracy and energy resolution.

Materials and methods

The design study was performed with numerical simulations carried out by a 3-dimenaional transport code, MCNP5 considering the detector assembly, irradiation room and even arrangement of arrayed CdTe crystals.

Results

The estimated count rate of 478[[ce:hsp sp="0.25"/]]keV gamma-rays was sufficiently large being more than the target value of over 1000[[ce:hsp sp="0.25"/]]counts/h. However, the S/N ratio did not meet the target of S/N[[ce:hsp sp="0.25"/]]>[[ce:hsp sp="0.25"/]]1. We confirmed that deterioration of the S/N ratio was caused by the influence of Compton scattering especially due to capture gamma-rays of hydrogen. Theoretical calculations were thereafter carried out to find out whether anti-Compton measurement in an array-type CdTe detector could decrease the noise due to Compton scatterings.

Conclusions

The calculation result showed that the anti-coincidence would possibly increase the S/N ratio. In the next phase, an arrayed detector with two CdTe crystals will be produced to test removal possibility of the anti-coincident event.