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A facility with a horizontal beam for radiobiological experiments with heavy ions has been designed and constructed at the Heavy Ion Laboratory in Warsaw University. The facility is 36 optimal to investigate the radiobiological effects of charged heavy particles on a cellular or molecular level as the plateau of the Bragg curve as well as in the Bragg peak. The passive beam spread out by a thin scattering foil provides a homogeneous irradiation field over an area of at least 1x1 cm 2 . For in vitro irradiation of biological samples the passive beam spreading combined with the x-y mechanical scanning of the irradiated sample was found to be an optimum solution. Using x-y step motor, the homogenous beam of ions with the energy loss range in the cells varied from 1 MeV/µm to 200 keV/µm is able to cover a 6 cm in diameter Petri dish that holds the biological samples [1]. Moreover on-line fluence monitoring based on single-particle counting is performed to determine the dose absorbed by cells. IntroductionThe use of heavy ion accelerators has enjoyed extensive interest for biophysical experiments over the past years. The radiobiological effects of charged heavy particles on a cellular or molecular level are of fundamental importance in the field of biomedical applications, especially in hadron therapy and space radiation biology.The study of the influence of high linear energy transfer (LET) ions on the DNA in the cell nucleus yields a basic information to the models describing the effects of radiation of different cells, the track structure of projectiles passing in the cell and the DNA geometry [2]. The use of heavy ions in radiotherapy ("hadrontherapy") could result in effective treatment due to a very good depth dose profile ("Bragg curve") and the high relative biological effectiveness (RBE) for cell inactivation. Nowadays, there are some clinical centers and research facilities performing treatments with protons and heavy ions. Therefore the study of biological characteristics of different particles has to be known to avoid therapy-induced side effects. The knowledge of radiation-induced DNA-breaks is also the base to estimate the risk from radiation exposure during long-manned space flights. There is also increasing interest in learning the influence of ionizing particles on the apoptosis or cell membrane damage.The main aim of the work was to set up a facility for radiobiological experiments for different ionizing particles in the region of the Bragg peak. The special attention has been concentrated on the information concerning the effectiveness of the low-energy ions, where the dosimetry of slow particles around the Bragg peak is a technical challenge. The V79 Chinese hamster cells were used for the first radiobiological experiments with carbon ions.

Gamma spectra were measured and activities of the detected isotopes were analyzed for 206 high-activity particles (hot particles, HPs) found in northeastern Poland after the Chernobyl accident. The isotopic composition of HPs observed in gamma-activity is compared with that of the general fallout and core inventory calculations. Particle formation and a process of depletion in Ru and Cs isotopes are discussed. On the basis of a search performed a year later, some comments on the behavior of HPs in the soil are made.