Use in Nuclear Accident Investigation
Following the nuclear accident at Tokai, Ibaraki in 1999, physicists Masuchika Kohno and Yoshinobu Koizumi showed how this coin could be used to estimate neutron dosage to the surrounding population, by measuring its zinc isotope ratios. They write:
- The Japanese 5-yen coin is about 22 millimeters in diameter and 1.5 mm thick, weighs 3.75 grams and has a central hole 5 mm wide. We chose this coin for monitoring neutron exposure because it is widely circulated, the zinc content is precisely controlled, and the generated has a convenient half-life (244.1 days) and gamma ray energy emission (1,115.5 keV). To obtain a record of the dosage of neutrons released as a result of the accident, we collected exposed coins from people's houses at distances 100–550 m from the facility.
They concluded that the coin could offer information about the total neutron effect during the accident, and about shielding by modern Japanese houses, given that the coins were recovered from indoors.
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