Experimental studies for the development of an online dosimetry method in BNCT based on Single Photon Emission Tomography

D,M. MINSKY; A.A. VALDA; A.J. KREINER; A.A. BURLON,

Birminghm, Reino Unido. Exposición oral, premiado con el Travel Award

Congreso; Young Researcher BNCT Meeting; 2007

School of Physics and Astronomy University of Birmingham

In 94% of neutron captures in boron, the resulting 7Li ion is emitted in an excited state and decays immediately through a characteristic 478 keV prompt gamma ray. The attenuation coefficient for this photon in tissue is about 0.1 cm-1, hence this g ray escapes from the body to a large extent. Its detection thus offers the possibility of a measurement of the boron dose and it does not depend on the great uncertainties in boron concentration determinations. In previous work, we have designed a prototype of a Single Photon Emission Tomography system for this purpose. After taking 20 projections of 41 bins the system can reconstruct boron dose maps of 21x21 voxels of 1 cm3 size each. In this work we show preliminary experimental results obtained at the RA6 nuclear reactor with a prototype consisting of four CdZnTe detectors and their collimators and shielding. The first measurements show the difficulties in quantifying the small 478 keV Doppler-broadened peak. Although the gamma ray background generated by the reactor is not significant to the dosimetry, it is very high for a spectroscopic measurement. The gamma-ray background was in fact reduced to a large extent but should be reduced even further. The thermal neutron field in the detectors has been reduced by means of a 6Li shielding until it did not show any significant induced background in the measurements. Detectors with higher efficiency are needed and, for this purpose, in future experiments we will employ LaBr3Ce scintillators. We kindly acknowledge valuable help received from Drs. J.Longhino, O.Calzetta Larrieu, H.Blaumann and the staff of the RA6 reactor.