Ultra-clean underground counting facility for low-level environmental samples

Conference · Wed Jan 01 04:00:00 EST 1986

OSTI ID:7025959

Winn, W G; Bowman, W W; Boni, A L

An underground counting facility with cleanroom environment has been designed and constructed to improve detection of low-level radioisotopes in the environment. The 3.0 m x 4.3 m x 2.4 m counting chamber is placed 14.3 m below ground, has 10.2-cm thick walls of pre-WWII naval armor plate, and is further shielded by a minimum of 1.2 m of specular hematite. The total overburden of shielding is equivalent to 31.7 m of water. Careful selection of building materials and a special air filtering system maintain a cleanroom environment with minimum contamination potential. Background improvements are noted relative to an earlier ground-level counting chamber with 30.5-cm-thick walls of pre-WWII naval armor plate. The gamma background continuum is reduced by a factor of 3 to 4 in the region of 0 to 10 MeV. A minimum of 10.2 cm of low-background lead around the detector optimizes this factor at 4 to 6. Discrete gammas from airborne natural radon daughters are eliminated by controlling the air near the detectors. Detectors constructed with low-level materials will further realize the improvements in background. A constant background is required for long counts of low-level samples, and the underground detectors are well shielded against surface operations. Performance appraisals of facility detectors include a large dual NaI(Tl) coincidence system, three smaller NaI(Tl) detectors, an HPGe well detector, and gas proportional and geiger counters. Major electronics for the detectors are located at a ground level control center to eliminate any associated backgrounds. Because an individual sample may be counted several days, uninterruptable power is used. An IBM PC/XT computer processes spectra from multichannel analyzers using custom-developed software.

• Research Organization: Du Pont de Nemours (E.I.) and Co., Aiken, SC (USA). Savannah River Lab.
• DOE Contract Number: AC09-76SR00001
• OSTI ID: 7025959
• Report Number(s): DP-MS-85-157; CONF-8610174-1; ON: DE87002657
• Country of Publication: United States
• Language: English

Related Subjects

510200 -- Environment
Terrestrial-- Chemicals Monitoring & Transport-- (-1989)
510300* -- Environment
Terrestrial-- Radioactive Materials Monitoring & Transport-- (-1989)
54 ENVIRONMENTAL SCIENCES
BIOLOGICAL MATERIALS
CONSTRUCTION
CONTAMINATION
DESIGN
ISOTOPES
LOW LEVEL COUNTERS
MATERIALS
MEASURING INSTRUMENTS
MONITORING
RADIATION DETECTORS
RADIATION MONITORING
RADIOACTIVITY
RADIOISOTOPES
SAMPLE PREPARATION
UNDERGROUND FACILITIES