Effects of neutron scattering and absorption ofshort-range particles in cells and macromolecules

Inactivation through atomic or electronic collisions in thin targets of enzyme or viral DNA exposed to slow protons was studied theoretically. A method was developed, by which intermediate energy neutrons may be produced at useful fluence rates essentially without contributions from fast neutrons. Employing the new technique, it became possible to study, experimentally, effects due to slow particles in living cells with neutrons of as low as 8.5 keV mean energy. Experimental studies of the significance of atomic collisions, particle range and linear energy transfer for induction of chromatid aberrations were performed by exposing Chinese hamster fibroblasts in vitro to neutrons in the energy interval 8.5-500 keV. Our findings indicate that bond-breaking atomic collisions lead to inactivation in on the average four of ten events and that inactivation through electronic collisions is relatively inefficient in enzyme or viral DNA exposed to slow protons. Some physico-chemical phenomena associated with transmutation, particularly the decay of 3H, are similar to those seen in bond-breaking atomic collisions. Therefore, as certain transmutation events in cellular DNA are known to be mutagenic, this should be expected to be the case also for atomic collisions. Intermediate energy neutrons are considered optimal for treatment of certain tumour diseases. They may also be responsible for the major fraction of dose absorbed from neutrons in superficial tissue, at some sites outside the shielding at nuclear installations. As lymphoid, hemopoietic and testicular tissues should be within effective 'range' of intermediate energy neutrons, the possible specific health-hazard of such exposures must be considered. (author)