Liquid Scintillation Cocktail Research Articles

Standardization of 63Ni by 4πβ Liquid Scintillation Spectrometry With 3H-Standard Efficiency Tracing.

The low energy (Eβmax = 66.945 keV ± 0.004 keV) β-emitter 63Ni has become increasingly important in the field of radionuclidic metrology. In addition to having a low β-endpoint energy, the relatively long half-life (101.1 a ± 1.4 a) makes it an appealing standard for such applications. This paper describes the recent preparation and calibration of a new solution Standard Reference Material of 63Ni, SRM 4226C, released by the National Institute of Standards and Technology. The massic activity CA for these standards was determined using 4πβ liquid scintillation (LS) spectrometry with 3H-standard efficiency tracing using the CIEMAT/NIST method, and is certified as 50.53 kBq ·g−1 ± 0.46 Bq · g−1 at the reference time of 1200 EST August 15, 1995. The uncertainty given is the expanded (coverage factor k = 2 and thus a 2 standard deviation estimate) uncertainty based on the evaluation of 28 different uncertainty components. These components were evaluated on the basis of an exhaustive number (976) of LS counting measurements investigating over 15 variables. Through the study of these variables it was found that LS cocktail water mass fraction and ion concentration play important roles in cocktail stability and consistency of counting results. The results of all of these experiments are discussed.

Systematic effects of total cocktail mass (volume) and H 2O fraction on 4πβ liquid scintillation spectrometry of 3H

Detection efficiencies ϵ of 3H by 4πβ liquid scintillation (LS) spectrometry systematically vary as a function of both total cocktail mass m and cocktail composition (such as the H 2O mass fraction f). Quench indicating parameter (QIP) determinations, such as for the Horrocks number H, are also dependent on m and f. These systematic effects were investigated with a matrix of 33 LS cocktails covering a broad array of m and f values: 3.0 g ⪯ m ⪯ 21.4 g and 0.002 ⪯ f ≤ 0.52. The effects of m and f on the LS background counting rates of matched blanks are also treated in detail. The uncertainties associated with these m- and f-dependent effects on ϵ and on H are particularly given close scrutiny. The systematics clearly demonstrate that efficiency changes cannot be adequately monitored by quench indicating parameters when the quench changes are induced by multiple causal factors (e.g. simultaneously varying cocktail sizes and compositions). The experimental results presented here have significant implications on the critical importance of understanding the systematics of these variable effects for a given LS system (combination of cocktails and spectrometer), and of very closely matching LS cocktail volumes and compositions in order to achieve reproducible and accurate LS counting results.

Simultaneous determination of 210Pb and 212Pb progenies by liquid scintillation counting

A time efficient method has been developed for separation and measurement of 210Pb and 212Pb and its progenies in aerosol samples. After leaching, transferring to a sulphate system and adding a certain amount of HCl, Po and Bi isotopes are extracted into a liquid scintillation cocktail and measured simultaneously using pulse shape analysis. 210Pb is measured from the ingrown 210Bi after ca 2 weeks or measured directly in the aqueous phase. The lower limits of detection are 0.2 mBq for 210Po and 212Bi, and 0.5 mBq for 210Bi.

Comparison of the French and U.S. National 3H (tritiated H 2O) standards by 4πβ liquid scintillation spectrometry

Radioactivity standards of tritiated water ( 3H 2O)—disseminated by the Laboratoire Primaire des Rayonnements Ionisants (LPRI) and the National Institute of Standards and Technology (NIST), the national radionuclidic metrology and standardization laboratories of France and U.S.A., respectively— have been intercompared by liquid scintillation (LS) spectrometry. The ratio of the certified massic activities for the two standards was compared to that obtained from direct measurements on matched sets of LS cocktails prepared from the standards. Seven experimental trials (involving a total of 21 counting sources for each standard) were performed for the comparison. The trials were performed under a wide range of experimental conditions, including use of two different LS spectrometers and three series of LS cocktail compositions (with systematically varied 3H detection efficiencies). The results exhibited an apparent mean disagreement between standards of < 0.4% on a relative basis. For contrast, the relative combined standard uncertainty on the massic activity ratio for the two standards, as obtained from their respective certified uncertainty assessments, is about 0.7%.

Cocktail volume effects in 4πβ Liquid scintillation spectrometry with 3H-standard efficiency tracing for low-energy β-emitting radionuclides

The effect of total liquid scintillation (LS) cocktail volume (or mass) in the 4πβ LS spectrometry of β-emitting radionuclides has been investigated. The magnitude of such possible volume effects on the apparent activity of low-energy β-emitting radionuclides, as determined by the CIEMAT/NIST 3H-standard efficiency tracing method, as well as any systematic trends in the relative detection efficiencies of low-ebergy β-emitters were studied. The radionuclides chosen for the study, 63Ni and 36Cl, were traced against 3H. Detection efficiency losses, as a function of total LS cocktail volume, were found to be energy-dependent. Because of the low E βmax for the decay of 3H and 63Ni, systematic losses in efficiency with increasing cocktail mass, as well as at extremely low (< 5 g) masses were observed. The determination of quench-indicating parameters, even for cocktails of uniform composition, were also found to be volume-dependent. Despite a relatively large (17%) variation in the 3H counting efficiency over the volume range 1–20 mL in 22 mL vials and a corresponding 7% varition in the 63Ni counting efficiency, the CIEMAT/NIST method was able to trace the observed 63Ni activity to about 0.1%. No volume effect on the observed relative efficiency of 36Cl was found. The best condition for repeatability in the determination of the massic activity of a single sample was found to be when the volume is 8–12 mL in a 22 mL vial. The effect of total LS cocktail volume on the efficiency-traced massic activities was found to have no clear, consistent trend and proved difficult to quantify. Nonetheless, two approaches to estimating the magnitude of the effect are presented and indicate that it is extremely small (< 0.1%) and was within the statistical variation of the measurements.

Temperature effect in DIN- and pseudocumene-based liquid scintillation cocktails quenched with CCl 4 and CH 3NO 2

A temperature-dependent effect is reported which concerns only DIN-based liquid scintillation cocktails when they are quenched with CCl 4. The poor solubility of CCl 4 at concentrations over 0.3% causes a slow decrease of the quenching parameter, which may require more than 25 days to reach steady values when the samples are kept at 16°C. The problem can be overcome by use of either nitromethane for quenching or the use of a non-DIN-based cocktail, which can otherwise lead to typical efficiency distortions of 2.5% for 14C or up to 41% for 55Fe.

放射性有機廃液の焼却に関する総合的研究

液体シンチレーションカウンタは, β線放出核種の測定に広く利用されている。日本では3H, 14C, 32P, 35S, 45Caを含む測定済み廃液のみが, 指定された焼却装置で焼却することができる。放射線安全管理および環境安全の観点から, 現状の焼却装置の性能およびRIの挙動について調べた。3H, 14Cは, 焼却でほとんどがガス状になり粒子発生量が少ないために明確な粒径分布を求められなかった。32Pは1μm以下の粒子が多い分布, 35Sは0.1-1μmの範囲が谷となるU字型の分布, 45Caは1μmをピークとする分布をそれぞれ示した。3H, 14C, 32P, 35S, 45Caの排気・排水への移行率は, 2.2, 94, 27, 5.6, 33および96, 1.3, 35, 76, 34%となった。排水のpHは, 焼却中5.5, 焼却後7であった。焼却後の排水のCODは3ppm, 不溶性物質の量は5mg/L以下であった。HEPAフィルタの粒子状32P, 35S, 45Caに対する捕集効率は, 99.95±0.02, 99.62±0.27, 99.97±0.01%となった。

A new beaded carbon molecular sieve sorbent for 222Rn monitoring.

A new commercially available beaded carbon molecular sieve sorbent, Carboxen-564 (20/45 mesh), was tested and compared to Calgon-PCB (40/80) activated carbon for its adsorptive and desorptive characteristics under controlled conditions of temperature (25 degrees C) and relative humidity (RH). The amount of water vapor adsorbed by the beaded carbon molecular sieve material was typically a factor of 4 lower than the activated carbon, with a concomitant fourfold increase in the 222Rn adsorption coefficient, K(Rn). The maximum K(Rn) value for a thin layer of Carboxen-564, following a 2-d exposure at 40% RH, was 7.2 Bq kg(-1) per Bq m(-3). The K(Rn) or a 1-cm bed, following a 2-d exposure was 5.5 Bq m(-3), a 25% reduction. Under dynamic sampling conditions, where 0.4 g of the beaded carbon molecular sieve was contained in a 6 cm x 0.4 cm diameter tube, the maximum K(Rn) value was 6.5 Bq m(-3) after 2.5 h of sampling at 29% RH when the input flow rate was 4.2 x 10(-3) m3 h-1. Kinetic studies were also conducted under passive sampling conditions. The data show that the 222Rn buildup time-constant for a thin layer of the beaded carbon molecular sieve material was 1.3 h, whereas that of a 1 cm bed was 13 h. The 222Rn desorption time-constants, from gram amounts of the beaded carbon molecular sieve material into air and into a commercially available toluene based liquid scintillation cocktail, were 2 h and 3 h, respectively. Carboxen's high 222Rn adsorbing capacity, rapid kinetics, hydrophobicity and physical properties makes it an attractive alternative to other commercially available activated carbon used in passive and dynamic sampling devices.

Automated Analysis of Radionuclides in Nuclear Waste: Rapid Determination of 90Sr by Sequential Injection Analysis

A rapid, automated, microanalytical procedure for the determination of 90Sr in aged nuclear waste has been developed. It is based on a sequential injection analysis (SIA) system which rapidly separates 90Sr from 90Y, 137Cs, and other radionuclides. The isolated 90Sr is then detected on-line with a flow-through liquid scintillation counter. The separation is achieved using a sorbent extraction minicolumn containing a resin (EIChrom, Sr-Spec) that selectively binds 90Sr as a crown ether complex under acidic conditions. The 90Sr is eluted with water, mixed with liquid scintillation cocktail, and detected in the flow cell of the counter. Sample 90Sr activity can be quantified from peak areas, giving linear calibration curves. The instrument can also be operated in a stopped-flow mode for longer counting times. Analyses of aged nuclear waste samples from the Hanford site by the SIA method and a manual method were in excellent agreement: correlation coefficient R = 0.994. Sample analysis by the SIA method is c...

Electrolytical enrichment for liquid scintillation determinations of low tritium samples: A revised methodology

The current methodology in low level tritium measurement is discussed. The distillation step has been found as a source of large errors in the sample activity determination. With the aim to obtain more reliable results, an alternative methodology is proposed, which bypass the distillation process. A liquid scintillation cocktails mixture able to receive alcaline samples is realised and largely tested. The method is also tested with a large number of artificial samples.

Simultaneous determination of lead-210, gross beta and gross alpha activities of air filters by pulse shape discrimination liquid scintillation counting

A chemical procedure for transferring deposited solid matter from a cellulose filter into the liquid scintillation cocktail has been described. The influence of chemical and color quenching on alpha and beta detection efficiency, as well as on misclassification of beta and alpha pulses was corrected by an external standard method. Under the chosen pulse shape discrimination level (PSD), the alpha and beta detection efficiencies were above 85% and spillovers of alpha and beta pulses were below 10% and 2% respectively. Determination limits for samples containing up to 200 mg of mineral matter were 0.015 mBq m−3 for alpha, 0.055 mBq.m−3 for210Pb and 0.055 mBq.m−3 for beta activity (counting time 12000 s and volume of filtered air ∼ 1000 m3). The method has been applied for routine monitoring of210Pb as well as for gross alpha and beta activities of longer-living radionuclides (T1/2.>11 hrs) in suspended air matter.

チャコールディテクタを用いた空気中｀２２２´Ｒｎ濃度の瞬時値の測定

The concentration of 222Rn in air sampled within a very short period of time was measured using activated charcoal as the adsorber. The detector is the plastic canister containing mixture of the activated charcoal and the silica gel. The radon gas was adsorbed in the charcoal in the radon chamber at the temperature of 25°C. A little amount of liquid scintillation cocktail was added into the vial of liquid scintillation counter with the canister. The radon in the charcoal was extracted in the liquid scintillation cocktail. Alpha particles emitted from radon and its daughter nuclei in the cocktail were detected using the liquid scintillation counter. Present method has advantages of not only short sampling time of air but also adsorption of radon in charcoal under a constant temperature. The concentration of radon in air down to 2Bq/m3 could be detected. A kinetic model for adsorption of radon in the charcoal is also presented. The ratio of radon concentration in the charcoal to that in air under the equilibrium state of adsorption was estimated to be from 6.1 to 6.8m3/kg at the temperature of 25°C.

Direct activity measurement of pure beta-emitting radionuclides by the TDCR efficiency calculation technique

The activities of a number of pure beta-emitting radionuclides have been directly determined by the triple-to-double coincidence ratio (TDCR) efficiency calculation technique. The nuclides were 3H, 14C, 63Ni and 99Tc, which were prepared in a variety of commercial liquid scintillation cocktails. The method enables the counting efficiency associated with a given source to be determined from just two observables: the double-tube and triple-tube counting rates. This information allows the source activity to be extracted irrespective of the chemical quenching state of the sample. There is no need for quench curves, extrapolation or efficiency tracing measurements.

36Cl/Cl Accelerator-Mass-Spectrometry Standards: Verification of Their Serial-Dilution-Solution Preparations by Radioactivity Measurements.

A consortium of accclerator-mass-spectrometry (AMS) laboratories recently prepared a series of 36Cl/Cl isotopic ratio AMS standards by an eight-step serial gravimetric dilution scheme. Of the resulting nine solutions, only the latter six could be assayed by AMS to confirm the gravimetric dilution factors. This paper provides the results of relative radioactivity measurements on the first four solutions to verify the first three dilution factors. The fourth solution was the only dilution capable of being directly measured by both AMS and radionuclidic metrology of 36Cl, and therefore its assay by radioactivity counting was deemed of considerable importance. Assays were performed by 4πβ− liquid scintillation (LS) counting of gravimetric aliquots of the solutions, with confirmatory measurements by 2πβ− gas-flow proportional counting of gravimetrically-prepared solid sources. The radioactivity measurements on the fourth solution were complex and difficult because of the conflicting combination of a low activity concentration (0.036 Bq · g−1) and high salt content (146 mg NaCl per g of solution). These conditions necessitated independent studies of the 36Cl LS efficiency as a function of NaCl loading in the LS cocktails and of the feasibility of LS counting of precipitated samples, both of which are also reported here. The results of the radioactivity measurements confirmed the dilution factors for the first three solutions to absolute differences of about 1%, and that for the fourth solution to about 1% to 2%. The overall uncertainties for these verification measurements, at a relative three standard deviation uncertainty interval, were of comparable magnitude, i.e., in the range of ±1% to ±2% for the first three solutions and roughly ±3% for the fourth solution.

The development of an alpha/beta separation liquid scintillation cocktail for aqueous samples

Scintillation cocktail components were studied with regard to their impact on pulse decay discimination (PDD) and hence the separation of alpha from beta activity, using a Packard 2250 CA α/β. Di-isopropyl naphthalene (DIN) was found to be the most suitable solvent, both from safety considerations and also the fact that it acts in a very similar manner to naphthalene in stretching the pulses produced at the photomultiplier tube anode and hence enhancing the separation. Increasing the surfactant concentration and the use of dimethylanthracene (DMA) as secondary fluor degraded the cocktail's performance. PMT anode pulse shapes were found to be a useful indicator of PDD efficiency but could not give a quantitative guide.

Use of extractive scintillation and pulse shape analysis for environmental alpha-assay

Extractive liquid scintillation cocktails with trioctylphosphineoxide (TOPO) and trioctylamine (TOA) as extractant, 2,5-diphenyloxazole (PPO) and napthalene as scintillator and toluene as solvent have been developed. Their application for the selective separation and measurement of 226Ra, 222Rn, 218,214,210Po as well as natural U and Th isotopes from HBr-solution in one step is described. Electronic pulse shape discrimination and window setting to reject beta- and gamma-radiation enables the detection of 214Pb and 214Bi as accompanying beta-emitters simultaneously. Radon together with the alpha-emitting daughter nuclides can be assayed similarly after extraction from natural water samples. All procedures are rapid with recoveries of >90% and counting efficiencies between 95 and 100%.

Liquid scintillation sample analysis in microcentrifuge tubes.

Local regulations prohibiting drain disposal of "biodegradable" liquid scintillation cocktails prompted investigation of volume reduction for these materials. Microcentrifuge tubes were used with aqueous and filter media samples of 3H, 14C, 32P, and 125I. Backgrounds, counting efficiencies, figures of merit, and spectral distributions obtained for microcentrifuge tubes compared favorably to conventional vials. Differences in 32P spectra for solid support samples appeared related to filter material and sample volume. Decreases in sample costs and waste volume and disposal costs were approximately 50-75%.

The measurement of222Rn in drinking water by low-level liquid scintillation counting

Radon-222 (Rn) has universally been found in well water. Non-stagnant ground water is collected at the well head while the well is pumping. The water is adjusted to a slow, non-aerated, steady flow through a clear tube, and a 500 ml glass bottle is filled. The sample is tightly capped after a high meniscus has developed. In the laboratory, standard 22 ml glass vials are filled with 10 ml of a toluene based mineral oil LS cocktail. Then, two 5 ml sample aliquots are pipetted into the vial. Vials are capped tightly, shaken vigorously, and placed in the liquid scintillation (LS) counter. Secular equilibrium is established in approximately 4 hours, after which samples are counted for 100 minutes each. The counting efficiency for Rn and progeny ranges between 315 to 345 percent depending on the chosen spectral window. The average background is about 6 cpm. A total of 28 wells were tested for Rn in the Carefree-Cave Creek, Arizona, USA area. The area's geometric average Rn concentration was found to be 46.5 Bq·l−1. The associated estimated lung dose is 0.51 mSv·y−1.

Aqueous Effluent Tritium Monitor Development

The development of a low-level tritium monitor for aqueous effluents has explored several potential techniques. In one method, a water-immiscible liquid scintillation cocktail was ultrasonically mi...

Investigation of radioactive counting samples of selected radionuclides in various liquid scintillators

This article presents some results of the investigation of radioactive counting samples prepared with the use of liquid scintillators. Liquid scintillation cocktails Atomlight (NEN) and Opti-phase HiSafe II (LKB) in standard glass vials of 20 ml volume were used. The counting efficiencies for several radionuclides in the above scintillators were compared. Two different experimental methods for measurement of the samples were applied: 1.(1) The 4πβ−γ coincidence method with a liquid scintillator in the beta channel (for β−γ and EC−γ emitters). In this case the counting efficiency was calculated according to the formula εβ = NcNγ.2.(2) The triple-double coincidence ratio (TDCR) method (for pure β or EC emitters). In this case the counting efficiency was calculated as εD = NDNO, where ND - the total number of double coincidences, NO - the number of disintegrations in the sample. The effect of the complexing agents HDEHP (diethylhexyl phosphoric acid) and EDTA (ethylenediaminetetraacetic acid) on the quality of the counting samples was studied. The application of the water solution of EDTA to prepare the counting samples of a few radionuclides improved both the counting efficiency and the stability of the samples. A slight quenching effect of HDEHP was observed.