Biological Irradiation Facility
Instrument responsible: Balázs Zábori
The Biological Irradiation Facility of the Budapest Neutron Centre provides a versatile platform for biological irradiation studies. 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 remotely controlled filter holder at a distance of 262 cm from the core which has six windows with the following materials: four Bi disks of 5, 10, 15 and 20 cm thick and one Pb disk of 20 cm, the 6th one is an open hole. At the orifice of the beam tube two cylindrical tanks were constructed of alumina to serve as a water shutter and its emergency water storage, respectively. The water can be pumped up from and released to a larger buffer tank located outside of the reactor shielding block by pressurized air. 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 situated 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 (rolling 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 a useful diameter of 10 cm. It is possible to use this collimator 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 intensity 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 is movable on a rail. The samples to be irradiated can be rotated to achieve a uniform, homogeneous irradiation. Cadmium or Boron carbide filters are used, if required, for decreasing the thermal neutron contribution.
Three levels of the dosimetry system were developed: real time, active beam monitors; passive activation, track-etch and TL detectors and computer codes for spectrum and dose calculations. Each exposure is individually planned and continuously monitored during the procedure. Some typical dose and flux values are presented in 1. Table and the schematic view of the system is presented in 1. Figure.
The irradiation facility is applicable to study the effects of the neutron and gamma radiation and high dose rate on the living animals, cells, etc.
Figure 1. Schematic view of the Biological Irradiation Facility.
Table 1. Presently existing minimum and maximum dose and flux values.