Abstract
We tried to confirm the previous findings that growth of Paramecium tetraurelia and mouse leukemia cells was suppressed by shielding the natural background radiation and that the growth suppression of the cells was restored by compensatory radiation from a low dose gamma-ray source. We used a radiation-shielding box surrounded with iron (15cm) and paraffin (10cm) walls, which can reduce the gamma-ray and neutron doses to 1/50 and 1/4 of the background levels, respectively. We found no effect of the background radiation-shielding on the growth of P. tetraurelia cells for 10 days. We also found no effect of additional low dose gamma-ray irradiation on the growth of the cells.As there was no effect of background radiation-shielding on the growth for 10 days, we conducted long term shielding experiment. The cumulative fission number of the P. tetraurelia was reduced by shielding the background radiation during the whole life span of the cells. Now, we are conducting the further experiment to confirm the result.We conducted the same experiment using mouse leukemia L5178Y cells. We found that the growth of the mouse cells was suppressed by shielding the background radiation for 5-7 days. We also found that the growth suppression of the cells was restored by compensatory radiation from a low dose gamma-ray source in the shielding box. These results were not found in the M10 cells that are the radiation hypersensitive mutant of L5178 cells. We are investigating the mechanism of these phenomena by a molecular method.
