Biological Irradiation Facility
Instrument responsible: Balázs Zábori
BIO provides a versatile platform for biological irradiation studies at BNC. The irradiation facility can be applied to study the effects of the neutron and gamma radiation and high dose rate on living animals, cells, etc. The physical parameters of the facility are described below.
The beam shutter consists of 3 steel and heavy-concrete segments turnable by an excentric axis to open and close the neutron beam. There is an internal remote-controlled filter holder at a distance of 2.62 m from the core which has six windows with: four Bi disks of 5, 10, 15 and 20 cm thick and one Pb disk of 20 cm thickness. Window no. 6 is an open hole. At the orifice of the beam tube two cylindrical tanks of alumina serve as a water shutter and an emergency water storage, respectively. Applying pressurized air, the water can be pumped up from and transported to a larger buffer tank located outside the reactor shielding block. The construction materials inside the beam tube work as internal, not removable filters with total thickness of 18 mm Pb and 15 mm Al.
The irradiation cavity is located outside the shielding block of the reactor at a distance of 1400 mm, thus its surface-to-reactor core distance is 3100 mm including the exchangeable core window (65 mm) made either of beryllium (used as the fast neutron reflector, too) or of aluminum. The use of the aluminum window results in a hard neutron spectrum. Between the shielding surface of the reactor and the cavity there is a borated-water-shielded collimator with an effective diameter of 10 cm. This collimator can be used as a holder for outer filters of about 800 mm length. Presently, filters of plexi-glass, polyethylene, iron, aluminum and lead are available to decrease the gamma and neutron transmission or to modify the neutron spectrum and the neutron-to-gamma ratio. There are two changeable filter disks of boron-carbide working as thermal and epithermal absorbers. The collimator can be moved on a rail. The samples to be irradiated can be rotated to achieve a uniform, homogeneous irradiation. If required to decrease the thermal neutron contribution, cadmium or boron carbide filters can be used.
Three levels of the dosimetry systems: real time, active beam monitoring; passive activation, track-etch and TL detectors are used for monitoring and computer codes are available for spectrum and dose calculations. Each exposure is individually designed and continuously monitored during the procedure. Some typical dose and flux values are presented in Table 1. The schematic view of the system is presented in Figure 1.
Figure 1. Schematic view of the Biological Irradiation Facility.
Table 1. Minimum and maximum dose and flux values at BIO.