Neutron study of medium transfer bystander effect for a human skin cell line

Neutron irradiations at the McMaster Nuclear Reactor have been performed to study direct and bystander effects for a human skin cell line. The neutrons are produced in the core of the swimming pool type reactor by nuclear fission; they are then partially moderated through water before exiting along a beam tube in the reactor wall. The resultant neutron spectrum has an energy distribution with an average of 1 MeV. The gamma contamination of the reactor neutron beam was designed to be less than 0.8% for a neutron dose of 2 Gy/h with the current design. Microdosimetric methods have been used to measure the neutron and gamma doses for the cell irradiations. It was found that there was no significant direct cell death occurring for a human skin cell line when the neutron dose was below 200 mGy. It was further found that neutrons did not significantly induce the medium transfer bystander effect when the pure neutron doses were kept below 200 mGy, which is much higher than the γ effective dose threshold of 3 mGy. The result is consistent with a published microdosimetric model.