Tuesday, January 1, 2019

Neutron Irradiated Dimes

Today you can get rocks, fossils, gems, meteorites, astronaut ice cream, gyroscopes, and magnets at any museum store. Irradiated dimes were sold at Oak Ridge National Laboratory from 1949 to 1967. They speak from the heart of the atomic age. On the one hand, Oak Ridge was a secret town that officially did not exist. On the other hand, the actual use of the atomic bomb proved impossible to miss. 

What we call “Oak Ridge” today (ZIP Codes 37830 and 37831) was built by the federal government as part of the Manhattan Project. The under-developed area of eastern Tennessee had small farming towns—Edgemoor, Elza, and Robertsville, among others—but was largely uninhabited. The purpose of the new city, which grew to 75,000, was to separate fissionable uranium (U 235) from the other isotopes, mostly U 238. It also produced plutonium. In addition, the site manufactured other isotopes that have industrial and medical uses such as antimony (Sb 124). 
Case legends on irradiated dimes.
(in black)
(in blue)
Not shown: 
(May be the earliest variety.)
The town was finally opened on March 19, 1949. The American Museum of Atomic Energy began the same year. It was re-dedicated as the American Museum of Science and Energy in 1978.  
UCNC is the Union Carbide Nuclear Company. 
The Union Carbide Corporation Nuclear Division operated 
the Y-12 separation plant at ORNL.  
The division apparently used the two names at different times. 
UCNC also operated a uranium mine in Emery County, Utah. 
See Western Mining History here.
This quote is most likely from a 1954 ORNL press release:
"One of the most popular exhibits in the American Museum of Atomic Energy is a “dime irradiator.” To date, more than 250,000 dimes have been irradiated, encased in plastic and returned to their owners as souvenirs. The irradiator works as follows: A mixture of radioactive antimony and beryllium is enclosed in a lead container. Gamma rays from the antimony are absorbed by the beryllium atoms and a neutron is expelled by the beryllium atom in the process.            
“These neutrons, having no electrical charge, penetrate silver atoms in the dime. Instead of remaining normal silver-109, they become radioactive silver-110. After irradiation, the dime is dropped out through a slot in the lead container and rests momentarily before a Geiger tube so that its radioactivity may be demonstrated. It is then encased in the souvenir container. Radioactive silver, with a half-life of 22 seconds, decays rapidly to cadmium-110 (In 22 seconds, half of the radioactivity in each dime is gone, in another 22 seconds half the remainder goes, and so on until all the silver-110 has become cadmium).  Only an exceedingly minute fraction of the silver atoms have been made radioactive." From “Irradiated Dimes - American Museum of Atomic Energy and New York World's Fair (1950s, 1960s)” At Oak Ridge Associated Universities website here. (ORAU operates the AMSE.)
Some typical eBay prices of the moment.
 The press release cites a figure of 250,000 dimes given out. By the time the program ended, the figure was close to 1,000,000. This summary from 9 November 2013 by CoinTalk user mrweaseluv was based on an article that I wrote for Coin World. (I visited ORNL twice in September 1999 to interview people and tour the museum and the city.). 
“A beryllium case was placed over small lump of [radioactive] antimony [Sb 124]. The antimony gave off gamma rays that excited the beryllium which emitted neutrons that struck the dimes. The half-life was 24.6 seconds. Some of the Ag-109 atoms became Ag-110. Giving off an electron, the Ag-110 became Cadmium (Cd-110), which is stable. Another 51.82% of the silver atoms became Ag-107, the remaining 41.18 of the silver remained Ag-109. Of the remaining 5% was comprised of other isotopes, the most stable of which is Ag-108 which remains radioactive for five years, though the amount in a dime is statistically unimportant at the human level. Dimes are also made of copper. Cu-63 and Cu-65 represent almost 69.17% and almost 30.83% of the mass and are stable. When they absorb a neutron, they become zinc. The remaining fraction of a percent is Cu-67 which is radioactive for two-and-half days. Only silver dimes could be used. When the government switched to cupro-nickel, it was only a matter of time before silver dimes became scarce. The program was discontinued in 1967. Ni-63 remains radioactive for 92 years, decaying much quicker than Ni-59 which has a half-life of 80,000 years.”  (Cited from CoinTalk dot com here. )
See also: 
By Pascal Brock, Harold Levi, Bruce Perdue, Ken Berger, 
The following is taken from the TAMS Journal, Vol.14, No. 1, February 1974.
“The Neutron Irradiated Dime, Atomic Energy Commission, New York World's Fair, 1964-1965” by Stephen P. Alpert, TAMS # 2134.
The E-Sylum: Volume 14, Number 52, December 18, 2011, Article 10

“Antimony-124 is used together with beryllium in neutron sources; the gamma rays emitted by antimony-124 initiate the photodisintegration of beryllium. The emitted neutrons have an average energy of 24 keV. Natural antimony is used in startup neutron sources.”

“Gamma rays are ionizing radiation and are thus biologically hazardous. Due to their high penetration power, they can damage bone marrow and internal organs. Unlike alpha and beta rays, they pass easily through the body and thus pose a formidable radiation protection challenge, requiring shielding made from dense materials such as lead or concrete.”

“The decay scheme is rather complex, as it includes more than 25 β− transitions and about 70 γ transitions with energies spread between 148 keV and 2807 keV. However, only about a tenth of them have probabilities greater than 1 %.”
124Sb – Activity measurement and determination of photon emission intensities Part A – COMMISSARIAT A L'ENERGIE ATOMIQUE ISSN 0429 3460

Title: A Study of the Nuclear Radiations from Antimony and Arsenic
Authors: Mitchell, Allan C.; Langer, Lawrence M.; McDaniel, Paul W.
Publication: Physical Review, vol. 57, Issue 12, pp. 1107-1117
Publication Date: 06/1940

 I find that date revealing. We have a poor sense of history or at least I do. Obviously, research into the physics and chemistry of radiation had been continuing for almost 50 years. But we too easily see Hiroshima and Nagasaki as the dawn of the Atomic Age. In fact, Wilhelm Röntgen announced x-rays in 1895, and by 1906 they found medical applications. Admittedly, the first decade was a period of uneven and sometimes tragic results. 


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