Low-background Beta Research Articles

A small-volume and low-background digital anticoincidence beta counting system for C-14 dating using a gas counter combined with tiled CdTe wall detectors

A low-background anticoincidence beta counting system has been developed by integrating an internal gas proportional counter with CdTe detectors to decrease the volume of the anticoincidence gas counter. Digital signal processing was incorporated according to the characteristics of CdTe detectors and a small-volume, low-background digital anticoincidence beta counting system has been developed for C-14 dating.

Determination of technetium-99 in soils and radioactive wastes using ICP-MS

AbstractThree methods have been used for the determination of 99Tc in soils and solid radioactive wastes using 99mTc as a yield monitor. In the method one and three the samples were leached in low concentrated nitric and sulphuric acid. Many contaminants were then co-precipitated with Fe(OH)3 in alkali media and Tc in the supernatant was separated using anion-exchange extraction chromatography. There were made also some studies how to improve the chemical recovery of 99mTc in the process of chromatography. In the method two the sample was ashed and then leached in 8 mol dm−3 HNO3 and after iron precipitation, technetium was separated on chromatographic column. The chemical recovery of 99mTc was optimized in the process of chromatography and leaching. Typical recoveries of technetium determined with 99mTc tracer for all these methods were in the range 39 %–87 %.The 99Tc activity was measured using proportional low-background beta detector after one week of staying to allow decay of 99mTc activity. 99Tc was also determined by the non-radiometric method using inductively coupled plasma mass spectrometer.

Intake and excretion of 99Tc in a common sea alga, hijiki (Hizikia fusiforme), as ingested in the daily diet--a measurement in an adult male.

Ingestion and excretion of environmental 99Tc was measured in an adult male who ingested 'hijiki' food in his diet that contained a sub-bequerel activity per kg, and which was prepared from a marine alga, Hizikia fusiforme, or hijiki in Japanese, traditionally eaten in the Japanese diet. Harvested hijiki was boiled, dried and cooked. This was eaten at each meal five times over 2 d. All faeces and 24-h urine samples were collected during the 3 d before and subsequent 11 d starting from the day when the intake began. The ingestion intake was measured by analysing the dried hijiki material. 99Tc was determined by using liquid-liquid extraction and low-background beta ray spectrometry. The excreta were also analysed for minerals by atomic absorption spectrometry. The apparent absorption rate in the gastrointestinal tract for 99Tc under these conditions was calculated to be approximately 0.5. The present result from a single subject indicates the need for further studies.

Radioactivity of Radon and Thoron Daughters in Romania

The radioactivity values of 222Rn and 220Rn daughters presented in this paper were obtained as a result of the measuring programme systematically performed within the national network for environmental radioactivity surveillance over a 9 year period (1980–1988). In order to determine filter activity use is made of a low background beta global measuring facility, of the Nuclear Enterprises type with G-M counter tubes with 2 counts.min-1 background in anti-coincidence. The reference standard was 90Sr/90Y.

Determination of228Ra in drinking water

A procedure for the analysis of228Ra in drinking water has been developed. The procedure involves separation of radium by an initial coprecipitation with lead sulfate. The isolated Pb(Ra)SO4 is then dissolved in sodium diethylenetriamine pentaacetate (DTPA). Radium-228 is co-precipitated from this solution with barium sulfate while the DTPA supernate which contains pre-existing228Ac is discarded. The purified Ba(Ra)SO4 precipitate is then allowed to ingrow, generating228Ac, which is then dissolved in DTPA, isolating both226Ra and228Ra in the precipitate while228 Ac remains in the aqueous supernate. The supernate is partitioned against di-(2-ethylhexyl phosphoric acid), HDEHP, dissolved in n-heptane, which retains the228Ac. Actinium-228 is then stripped from the organic phase by partitioning against 1M HNO3. Finally, the228Ac is coprecipitated onto cerium oxalate. The precipitate is collected on a filter and counted in a low-background beta counter. Radium-228 standards with concentrations ranging from 0.044 to 1.6 Bq were used to establish the detector counting efficiency for228Ac in cerium oxalate samples, as well as monitoring the chemical yield and absorption factors. The resultant average value of 30.3±2.1 cpm/Bq (uncertainty given at 95% level of confidence) was obtained. Various228Ra cross checks from U. S. Environmental Protection Agency (EPA) with concentrations of 0.063–0.52 Bq/l were analyzed in order to assess the performance of the procedure. The minimum detectable concentration (MDC) of228Ra in water with this procedure is 0.015 Bq/l. This is based on a one liter aliquot of sample, a 100 min couting period, and a 3 hour decay interval between the end of228Ac ingrowth and midpoint of counting. Decontamination factor studies were performed to determine the extent of the carry-over of238U,226Ra,210Po, and90Sr into the final fraction.

Radioactive and stable cobalt concentrations in mussel in Kyushu islands, Japan

Two kinds of mussel, Septifer virgatus and Mytilus edulis, were collected from Kyushu island, Japan, in order to elucidate a background level of 60Co, which is one of the most significant radionuclide for environmental monitoring around a nuclear power plant. The mussels were collected from 7 locations in 1983 and classified 2 or 3 groups depending on their shell size at each location. Activities of 60Co were measured by a low-background beta counter after purified by means of chemical separation and electrodeposition. Stable cobalt concentrations were determined by colorimetric method. The concentrations of cobalt in Septifer virgatus are one order higher level than that in Mytilus edulis. There are not so large difference in cobalt content depending on shell size so long as comparing them at the same location. The radioactivities in mussels show the same trend as stable cobalt. It has become apparent that Septifer virgatus has a tendency to concentrate cobalt with growing but Mytilus edulis is opposite. The cobalt-60 introduced to sea from nuclear explosions seems to be relatively constant in coastal seawater since specific activities are distributed in a narrow range in spite of kind, shell size and location.

Determination of total activity by liquid scintillation counting and its application to aqueous effluent samples

An analytical method for determining total activity in water samples is described. The method depends on the direct relationship between the average energy deposited in a liquid scintillator solution and the channels ratio recorded for two different portions of the total energy spectrum. Calibration curves are constructed using single energy beta emitters. Samples are first counted at low gain for medium to high energy activity, followed by a second count at high gain to record total activity. Results obtained by this method for both synthetic and reactor effluent samples were quantitative (3–7%) compared with results obtained by low-background beta counting (42–100%).

Measurement of210Pb from a sediment core off the coast of California

Measurements of210Pb at various dephts in a sediment core from the Santa Cruz Basin off the coast of California have been made. The radiochemical separation of210Pb was carried out after ashing the sediment at 400 °C. The activities of the purified210Pb was assayed in a low background beta counter by counting the 1.17 MeV betas of its daughter product210Bi. The method for the chemical separation of210Pb and the results are discussed in the paper.

An extremely low background beta-gamma-gamma coincidence spectrometer with GMGe(Li)NaI(Tl) counter combination

An extremely low background betagammagamma coincidence spectrometer has been constructed for the measurement of cosmic ray produced radionuclides carried by extraterrestrial matter accreted on the Earth. The detectors used in this work are a large volume Ge(Li) detector, a pair of GM counters of thin layer type for beta counting, a large volume NaI(Tl) well scintillator and liquid scintillator for guard counter. Six counting modes are applicable; gamma only, gammagamma coincidence, Compton suppression, betagamma, (beta+gamma)gamma and betagammagamma counting modes. The absolute counting efficiency of the betagammagamma mode is slightly lower than that of the betagamma mode, however the figure of merit in the betagammagamma mode becomes better than that in the betagamma mode at higher energies.

Low Background Beta Counting with CaF2(Eu) in a Phoswich Configuration

Low Background Beta Counting with CaF2(Eu) in a Phoswich Configuration

A low-background beta counting arrangement

An improved low-background counter suitable for the measuring of beta samples has been described in the present paper. For eliminating the background radiation there has been used a liquid scintillation detector. The anticoincidence stage is carried out by diodes. As a result of series measurement there has been measured a background rate of 0.3 pulse/minute.

Shipboard analysis of strontium-90 in seawater on Geosecs II

Strontium-90 in seawater samples was analyzed aboard the USS Knorr by direct extraction of the 90Y daughter. The extraction was made in two 17-gallon heavy-walled glass bottles. Yttrium carrier was added and the 90Y was extracted with HDEHP in toluene, back-extracted with HCl, and purified with a second HDEHP extraction. The Y was mounted as the oxalate and counted in a methane end window system. Check analyses were performed in a shorebased laboratory equipped with low background beta counters. The results of the sea and shore analyses were consistent within the limits of error. The test demonstrates that 90Sr analyses can be performed satisfactorily at sea, and that a better equipped laboratory and counting facility would improve the performance considerably.

Scintillation guard detectors for low-activity beta measurements with Geiger-M$uuml$ller counters

The design of compact plastic-scintillator guard detectors for low background beta measurement is described. Their performance is compared with other available guard detectors and background count-rate reductions are demonstrated. The demountable assemblies for 1 and 2 in window Geiger-Müller counters can be readily manufactured and are arranged to fit standard AERE photomultiplier housings. Typical backgrounds in 4 in lead shields are 0·5 counts per minute for the GM4LB and 4·9 counts per minute for the 2B2.

Transistorized nuclear counting instruments for a low-level counting laboratory

Simple transistorized circuits adoptable for low-level counting work have been described in this paper. These include: 1. a dekatron scaler with five decades; 2. a low background beta counting system with coincidence and anticoincidence circuits; 3. a single channel pulse height analyzer for gamma spectrometry. The performance of these circuits in low-level counting work has also been reported. The special features of the circuits described here are their simplicity, good long-term stability and reliability, with fastness adequate for most type of low-level counting work.

Low-background Beta Counters for Iodine-131 Sources

IN a recent article1 the use of two end-window Geiger counters (20th Century Geiger-Muller type EW2C) for scanning chromatograms containing iodine-131 was discussed. It was shown that using anti-coincidence techniques the background in the double-counter system was typically about 3.5 c.p.m. Furthermore, it was pointed out that significant fraction of this background arose from radioactive contaminants in the window material of the counters. The efficiency of detection for iodine-131 and Whatman No. 1 chromatography paper is about 50 per cent. Using the formula quoted in ref. 1 the total time (T) required to determine the presence of 2 µµc. with an accuracy of 10 per cent is 375 min. By carefully selecting Geiger counters, backgrounds lower than the typical one can be obtained, although it is doubtful if it is possible to do better than about 2.8 c.p.m. The above value of T would then be reduced to 316 min.

Improved Determination of Strontium-90 in Milk by an Ion Exchange Method.

An improved procedure is described for the determination of Sr/sup 90/ in milk by ion exchange. The procedure consists of storing the milk samples with formaldehyde preservative for the ingrowth of the Y/sup 90/ daughter of Sr/sup 90/ , adding Y carrier, and then passing the milk consecutively through cation and anion exchange resin columns. The alkaline earth ions in milk are replaced by sodium ions in the cation exchange column, after which the Y is retained as an anionic complex, sodium citrate, in the anion exchange column. The effluent milk is discarded and the Y complex on the anion exchange resin is destroyed with HCl. The Y, eluted with the acid, is precipitated as the oxalate, and the radiortrium is measured with a lowbackground beta counter. (P.C.H.)

A METHOD FOR THE DETERMINATION OF CAESIUM-137 IN SEA WATER.

A method has been developed for the determination of Cs137 in sea-water. The acidified sample, containing added ammonium nitrate and caesium carrier, is passed through a column containing ammonium 12-molybdophosphate (AMP) mixed with an equal weight of asbestos to give adequate porosity. The caesium is retained quantitatively on the AMP (which acts as a selective cation exchanger) together with a small fraction of the natural rubidium and potassium present in the original sample. After treatment to separate the rubidium and potassium (both of which contain natural beta-emitting nuclides) the Cs137 is counted. The principal advantage of this method is the high radiochemical purity of the separated Cs137 which may be assayed by beta counting. With the use of low-background beta counters, levels of approximately 0.1 pc/l. may be determined on a 25-I. sea-water sample with a 95 per cent confidence limit of ±0.015 pc/l. The results of measurements on sea-water samples collected from the North Atlantic and coastal waters round the British Isles during 1961 and 1962 are reported.

A Low Background Beta Counter with a Plastic Scintillator Anticoincidence Shield

The design and performance of a low background beta counter is described. The counter consists of a central gas flow proportional counter surrounded by a large plastic scintillator anticoincidence shield.