A FACILITY FOR BIOMEDICAL EXPERIMENTS WITH THERMAL-NEUTRONS

The Studsvik thermal-neutron facility was originally designed for neut ron capture radiography (NCR) at high thermal-neutron fluence and low fast-neutron contamination. It has now been modified to permit irradia tion of living cells and animals without the need for stopping and res tarting the R2-0 reactor. Previous calculations of the thermal-neutron intensity at the NCR position were performed using the two-dimensiona l diffusion theory code DIXY. In this report the Monte Carlo program M CNP 3B is used to calculate the neutron fluence at the radiography pos ition, and neutron and photon fluences at the positions of the cell sp ecimens. The normalized neutron fluences from the calculations agree w ell with measured values and show that the contamination with high-ene rgy neutrons is low. The agreement between measured and calculated pho ton doses was reasonable. The thermal-neutron fluence rate is (2.3 +/- 0.1) x 10(9) cm-2 s-1 at 100 kW at the NCR position and (0.96 +/- 0.0 3) x 10(9) cm-2 s-1 at 100 kW at the front plate of the loading tube. The photon dose is about (1.6 +/- 0.2) x 10(-12) Gy per neutron. Survi val curves of V79 cells grown as monolayers and irradiated in the ther mal neutron beam, with and without boron, are presented.