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RERF Glossary

Free-in-air kerma

This table shows the free-in-air dose (kerma dose) of gamma rays by distance from the hypocenter. Neutron doses range from 1/10th to 1/100th of the gamma dose, decreasing as the distance increases. These doses are for those persons who were not shielded; the dose decreases to less than half in the average Japanese wooden house due to absorption by the building. Organ doses decrease further to about 80% due to shielding by human body tissues.
Table. Free-in-air kerma dose of gamma rays
Distance from the hypocenter
(km)
Hiroshima
(Gy)
Nagasaki
(Gy)
0.5 35 79
1.0 3.9 7.8
1.5 0.49 0.89
2.0 0.071 0.13
2.5 0.012 0.021