Gamma Residual Radioactivity Measurements on Rats and Mice Irradiated in the Thermal Column of a Triga Mark II Reactor for BNCT

Abstract

The current Boron Neutron Capture Therapy (BNCT) experiments performed at the University of Pavia, Italy, are focusing on the in vivo irradiations of small animals (rats and mice) in order to evaluate the effectiveness of BNCT in the treatment of diffused lung tumors. After the irradiation, the animals are manipulated, which requires an evaluation of the residual radioactivity induced by neutron activation and the relative radiological risk assessment to guarantee the radiation protection of the workers. The induced activity in the irradiated animals was measured by high-resolution open geometry gamma spectroscopy and compared with values obtained by Monte Carlo simulation. After an irradiation time of 15 min in a position where the in-air thermal flux is about 1.2 × 10(10) cm(-2) s(-1), the specific activity induced in the body of the animal is mainly due to 24Na, 38Cl, 42K, 56Mn, 27Mg and 49Ca; it is approximately 540 Bq g(-1) in the rat and around 2,050 Bq g(-1) in the mouse. During the irradiation, the animal body (except the lung region) is housed in a 95% enriched 6Li shield; the primary radioisotopes produced inside the shield by the neutron irradiation are 3H by the 6Li capture reaction and 18F by the reaction sequence 6Li(n,α)3H → 16O(t,n)18F. The specific activities of these products are 3.3 kBq g(-1) and 880 Bq g(-1), respectively.

Neutron spectrometer for fast nuclear reactors

“…These strips were used to read out the anode signals. On top of the Chromium layer in between the Gold strips a further layer of 3 mm  2:2 mm  100 nm of 6 LiF was then deposited on the contact. The LiF compound was chosen as a neutron converter because of its chemical neutrality.…”

“…The LiF compound was chosen as a neutron converter because of its chemical neutrality. The selected LiF was enriched with 6 Li isotope to 96%. The LiF layer is deposited on the top of the metallic anode in such a way that α and t can easily penetrate into the intrinsic diamond depletion layer with minimal loss of energy.…”

“…This allows for an event-byevent neutron energy measurement with the advantages of a solid state detector. Moreover, the 6 Li(n,α)t reaction is highly exothermic with Q¼ 4.7 MeV, which permits to reduce the background by imposing a high detection threshold. The coincidence between two crystals further suppresses noise and competing reactions.…”

“…However, both the reactor dynamics and the burn-out of fuel and actinides depend on the Li converter sandwiched between two CVD diamond detectors. The energy of the incident neutron converts completely into the energy of charged particles through the 6 Li(n,α)t reaction. This allows for an event-byevent neutron energy measurement with the advantages of a solid state detector.…”

“…The spectrometer is based on the conversion of neutrons impinging on 6 Li into α and t whose total energy comprises the initial neutron energy and the reaction Q-value. The 6 LiF layer is sandwiched between two CVD diamond detectors, which measure the two reaction products in coincidence.…”