title: Low-background gamma spectrometry for environmental radioactivity.
abstract: Development and performance of a low-background gamma-ray spectrometer are described. The spectrometer consists of a 131% efficient Ge detector in U-type configuration. The passive shielding consists of ultrapure lead of 6" thickness. A top muon guard is used as an active shielding. The spectrometer and shielding are positioned inside a steel room made of 6"-thick pre-World War II iron. The steel room is located underground with 33 m of water-equivalent overburden. The total integrated background rate in the energy range 50-2,700 keV was measured at 0.068 counts per second per 100 cm3 Ge volume. The spectrometer serves as a reference instrument for low-level and highly accurate environmental radioactivity measurements. One specific application of 228Ra determination in drinking water is described. With a 1 l water sample, 1-step chemical procedure, and 1,000 min counting time, a detection limit Ld = 20 mBq/l (0.55 pCi/l) was reached, which meets the EPA mandated limit of 1 pCi/l. Methods of upgrading the spectrometer as well as the predicted improvements in 228Ra detection, including direct counting of water without chemical processing, are discussed.
authors.affiliation: Wadsworth Center, New York State Department of Health, Albany 12201-0509, USA. semkow@wadsworth.org
authors.forename: T M
authors.initials: TM
authors.lastname: Semkow
authors.forename: P P
authors.initials: PP
authors.lastname: Parekh
authors.forename: C D
authors.initials: CD
authors.lastname: Schwenker
authors.forename: A J
authors.initials: AJ
authors.lastname: Khan
authors.forename: A
authors.initials: A
authors.lastname: Bari
authors.forename: J F
authors.initials: JF
authors.lastname: Colaresi
authors.forename: O K
authors.initials: OK
authors.lastname: Tench
authors.forename: G
authors.initials: G
authors.lastname: David
authors.forename: W
authors.initials: W
authors.lastname: Guryn