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- Title
A comparison of aerial and ground level measurements of 137Cs in theMarshall Islands
- Authors
Graham, J. C.; Simon, S. L.
- Abstract
The purpose of this paper is to resent and compare two independent sets of environmental of 137Cs gamma spectrometry measurements Cs collected nearly 14 years apart. One set of data was collectedin 1978 by a contractor of the U.S. Department of Energy during an aerial radiological survey of the northern atolls of the Marshall Islands. That program used helicopter mounted sodium-iodide scintillationdetectors; measurements were made from an altitude of 38 m. The second measurement program was conducted from early 1990 through late 1994 by the Republic of the Marshall Islands Government in a survey of the entire nation. This latter program used ground level in situ gammaspectrometry with high-purity germanium detectors. In this comparison, we highlight differences between the findings of the two studies and probable reasons for those differences, though we also discuss theeffectiveness of the two techniques for monitoring the ionizing radiation environment. In the comparison of exposure rates from 137Cs, fair agreement was noted after accounting for radioactive decay during the intervening years. Though the distributions were statistically different over their entire range, they were nearly identical above 1 mu R h-1. There was considerable difference in the estimates of 137Cs inventory; the difference was greater at low activity levels with the NaI measurements consistently larger than the in situ measurements. Reasons for this difference is attributed to three factors which differed between the two studies: (1) the assumed penetration of the cesium into the soil column, (2) the assumption of soil density, and (3) differences in the ability of the two different detector systems to reject interfering spectral contributions. Precise measurement of the lowest levels has implications for determining those atolls that exceeded the deposition of 137Cs from global fallout. This issue is discussed in addition to a compar
- Subjects
CESIUM
- Publication
Environmental Monitoring & Assessment, 1998, Vol 53, Issue 2, p363
- ISSN
0167-6369
- Publication type
Article
- DOI
10.1023/a:1005876130072