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 65Zn 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.
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).
The 5 yencoin is one denomination of Japanese yen.
Five-yen coins date to 1870 (when, due to the much higher value of the yen, they were minted in gold).
The front of the coin depicts a rice plant growing out of the water, with "fiveyen" written in kanji; the back is stamped with "Japan" and the year of issue, also in kanji, separated by sprouts of a tree.
Coins are usually used for lower-valued units, and banknotes are usually used for the higher values; also, in most money systems, the highest value coin is worth less than the lowest-value note.
Some coins have coin orientation, where the coin must be flipped vertically to see the other side; other coins, such as British coins, have medallic orientation, where the coin must be flipped horizontally to see the other side.
Coins are popularly used as a sort of two-sided die; in order to choose between two options with a random possibility, one choice will be labeled "heads" and the other "tails," and a coin will be flipped or "tossed" to see whether the heads or tails side comes up on top.
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