5 yen coin

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The 5 yen coin is one denomination of Japanese yen. The current design was first minted in 1959 using Japanese characters knows as the "new script", and were also minted from 1949-1958 using "old-script" Japanese characters. 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 "five yen" written in kanji; the back is stamped with "Japan" and the year of issue, also in kanji, separated by sprouts of a tree. The three graphic elements of the coin represent agriculture, forestry and fisheries, the key elements of the Japanese first-sector economy.

Contents 1 Cultural significance 2 Use in nuclear accident investigation 3 References 4 External links

[edit] Cultural significance

The Japanese for "five yen," go en (五円) is a homophone with go-en (ご縁), a word for karma. As a result, five-yen coins are commonly given as donations at Shinto shrines, and superstitious Japanese often insert a single five-yen coin into a new wallet before inserting any other money.

[edit] Use in nuclear accident investigation

Following the nuclear accident at Tokai, Ibaraki in 1999, 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 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.^[1]

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.

[edit] References

1. ^ Kohno, Masuchika, and Yoshinobu Koizumi (2000). "Tokaimura accident: Neutron dose estimates from 5-yen coins". Nature 406: 693. DOI:10.1038/35021138.

[edit] External links

• The front sides of two five yen coins.
• The back sides of two five yen coins. 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).

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