The radioactivity of atmospheric krypton in 1949?1950
Anthony Turkevich*,
Lester Winsberg?,
Howard Flotow?, and
Richard M. Adams?
- Author Affiliations
Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439
Abstract
The chemical element krypton, whose principal source is the atmosphere, had a long-lived radioactive content, in the mid-1940s, of less than 5 dpm per liter of krypton. In the late 1940s, this content had risen to values in the range of 100 dpm per liter. It is now some hundred times higher than the late 1940 values. This radioactivity is the result of the dissolving of nuclear fuel for military and civilian purposes, and the release thereby of the fission product krypton-85 (half-life = 10.71 years, fission yield = 0.2%). The present largest emitter of krypton-85 is the French reprocessing plant at Cap-de-la-Hague.
It is generally known that the chemical element krypton, isolated from the atmosphere in 1996, is radioactive. For example, Wilhelmova et al. (1) quote the air in Prague, Czechoslovakia, as having an average krypton-85 content of 0.8 Bq per cubic meter of air in the period 1983?1988. This radioactivity is the result of the dissolving of nuclear fuel both from past military and civilian programs and from present civilian power programs.
The largest current producer of radioactive krypton is the French reprocessing plant at Cap-de-la-Hague, which released 1.8 ? 1017 Bq of krypton radioactivity in 1994.? If diluted by the whole world?s atmosphere, this would produce a radioactivity of krypton of 2,400 dpm per liter (STP).‖ Cap-de-la-Hague?s output may represent about half of the present input into the atmosphere of this radioactive nuclide.
The present paper provides the earliest known measurements of the krypton radioactivity in the United States, relates them to the output of the Hanford reactors and of the nuclear explosions that occurred before the samples were collected, and points out the special characteristics of krypton-85 for studying atmospheric mixing on a planetary and subplanetary scale.
The nuclear fission product krypton-85 was discovered independently by Thode and Graham in Canada (ref. 2; ref. 2 was based on ref. 3) and by Hoagland and Sugarman in the United States (4) in the mid-1940s. It was found to have a half-life of about 10 years [the presently listed value is 10.70 years (5)], to decay primarily by beta emission [a branch emitting a half million electronvolt (MeV) gamma ray was later found (6)], and to be formed in about 0.23% of the thermal neutron induced fissions of uranium-235.
Soon after the World War II, while writing up the fission product research of the war, A.T. pointed out the special characteristics of this fission product for, among other uses, tracing air masses on a worldwide scale (letter from A.T. to P. Morrison, Argonne National Laboratory, July 19, 1946).
Preliminary measurements made in a screen-wall counter by W. F. Libby (in 1947; unpublished work) and A.T. and W. F. Libby (in 1948; unpublished work) gave indications that these predictions were correct. The present report describes the technique that was used soon afterward to establish more precisely that atmospheric krypton in the late 1940s was much more radioactive than it had been, and gives the results of some early measurements of krypton samples isolated from the atmosphere at that time.**
Accepted April 10, 1997.
Copyright ? 1997, The National Academy of Sciences of the USA
