Concentrations of ^113mCd in the marine environment

Abstract

Reports on the detection of ^113mCd in any type of environmental sample have been rare. The 113 mass chain yield is small relative to other longer-lived fission products, such as ⁹⁰Sr and ¹³⁷Cs, produced from uranium, plutonium and thorium fissions¹. Also, only a small fraction of the 113 chain yield decays to ^113mCd (ref. 2). Salter³ estimated that the ^113mCd/⁹⁰Sr activity quotient in thermonuclear fission should be 0.003. He stated that “this ratio is in good agreement with data from a few samples measured in the northern hemisphere prior to 1962 which have no ¹⁰⁹Cd”. This, to our knowledge, was the first report of the detection of fission-produced ^113mCd in the environment. Salter³ also calculated that 0.062 MCi of ^113mCd and 0.25 MCi of ¹⁰⁹Cd were produced by activation during the atmospheric detonation of the 1.4-megaton Starfish device on 9 July 1962 over Johnston Atoll. As both ¹⁰⁹Cd and ^113mCd are produced during neutron activation of stable cadmium, and ¹⁰⁹Cd is not a fission product, the last part of Salter's statement is significant. The absence of ¹⁰⁹Cd in samples collected before 1962 indicates that all nuclear testing before this time, which included all tests conducted at Enewetak and Bikini Atoiis in the Marshall Islands, could have generated ^113mCd only as a fission product. It is therefore important to recognize that ^113mCd could be present in other environments contaminated with fission product wastes discharged to the aquatic environment from other nuclear facilities. ^113mCd has a half life⁴ of 14.6 ± 0.1 yr and decays predominantly by beta-particle emission. We present here a preliminary report of ^113mCd concentrations measured in sediment and tissue samples of marine organisms collected around different atolls in the Marshall Islands.