The 5 yen coin is one denomination of Japanese yen.

Following the Tokimura nuclear accident, physicists Masuchika Konho and Yoshnobu 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 <math>{}^{65}{\rm Zn}<math> 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.

(Nature 406, 693 (2000); doi:10.1038/35021138)

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.

See also

• List of nuclear accidents

External links

• The front sides of two five yen coins (http://205.243.100.155/frames/5Yen3.jpg).
• The back sides of two five yen coins (http://205.243.100.155/frames/5Yen1.jpg). The coin on the right was shrunk with a very strong magnetic field by an amateur scientist in the United States (unrelated to nuclear power).