A precise determination of the {sup 222}Rn half-life by 4{pi}-{alpha}{beta} liquid scintillation measurements
- National Institute of Standards and Technology, Gaithersburg, MD (United States)
The half-life for {sup 222}Rn radioactive decay was determined by 4{pi}-{alpha}{beta} liquid scintillation (LS) measurement using gravimetrically-determined aliquants from the National Institute of Standards and Technology (NIST) radon-in-water standard generator. The decay of {sup 222}Rn in six matched samples, contained in flame-sealed glass LS vials, was followed for approximately 15 days (about four half-lives) with normalizations to a common similarly-prepared {sup 226}Ra reference source. With the {sup 218}Po-{sup 214}Pb-{sup 214}Bi-{sup 214}Po subseries following the {sup 222}Rn in transient equilibrium, the overall LS detection efficiency for {sup 222}Rn was very nearly 5 counts {center_dot} s{sup -1} {center_dot} Bq{sup -1}. Instrument nonlinearity tests over the entire range of measured activities (roughly 100 to 5 Bq) were also performed with a series of {sup 226}Ra reference LS samples. All {sup 226}Ra reference sources contained {sup 222}Rn in secular equilibrium. The LS measurement results for the six decay curves, each having 120 data values, were fitted by both weighted and unweighted least-squares exponential regressions. The relative uncertainties in the weighted regressions for the six half-life determinations and ranged from 0.049 to 0.060 percent. The six determinations had values ranging from T=3.8200 to 3.8259 d, with a weighted mean (weighted by the reciprocal variance) of T = 3.82248 {+-} 0.00086 d ({+-}0.022 percent uncertainty on a relative basis); and with an unweighted mean of T=3.82252, having a standard deviation of 0.00247 d ({+-}0.065 percent) and a standard deviation of the mean of 0.00086 d ({+-}0.026 percent). Based on a detailed uncertainty analyses, an adopted value of T = 3.8224{+-} 0.0018 is justified.
- OSTI ID:
- 160343
- Journal Information:
- Radioactivity and Radiochemistry, Vol. 6, Issue 1; Other Information: PBD: 1995
- Country of Publication:
- United States
- Language:
- English
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