Beta spectra deconvolution for liquid scintillation counting

This study presents the first results of a deconvolution method for Liquid Scintillation complex spectra. The method has been developed by means of the software MATLAB and is based on the utilization of Fourier Transforms. Its main target is to obtain a fast calculation procedure capable to unfold complex spectra without requiring any preliminary knowledge of the peak shapes of the component nuclides. Experimental tests have been carried out by means of a Perkin Elmer Wallac Quantulus 1220. Distinctive features of Quantulus have not been used, the instrument was only utilized to generate spectra in numerical form that subsequently were uploaded to a PC and analyzed by MATLAB. Results show acceptable capabilities of the method both for fitting convoluted spectra and for unfolding single nuclide shapes. Further experimentation is scheduled, in order to take account of quenching effects; it will be carried out by adding to the calculation algorithm another step, capable of performing a self-choice of the number of harmonics. The final aim is to fit any kind of beta spectra also when quenching influences the shape deeply.     

Alpha-radiometry of seawater by liquid scintillation counting

Summary Liquid scintillation counting of the alpha-radionuclides after pre-concentration by cation-exchange represents a simple and robust method for the determination of total alpha-radioactivity in seawater. The total efficiency and the minimum detectable activity were calculated to be 95% and 30 mBq, respectively, for a liter sample and 1000-minute measuring time. The method has been applied successfully for the determination of alpha-radioactivity in seawater from five different coastal areas in Cyprus. The average alpha-radioactivity and uranium concentration were found to be 124±8 mBq ^. l^-1 and 3.2±0.2 mg ^. l^-1, respectively.     

Alpha-liquid scintillation counting for the determination of plutonium

Liquid scintillation counting is useful and extensively employed for -activity measurement. However, quenching is observed and erroneous results are obtained when the size of the solution aliquot and its acidity exceed certain limits. A simple procedure has been developed to overcome the quenching effect of volume and acidity on -counting.     

Radon surveys with charcoal and liquid scintillation counting

A detection system for indoor radon using vials with activated charcoal adsorbant and liquid scintillation spectrometry for measurement has been tested thoroughly for months during different seasons. Deviation in the results of two days of exposure from the mean value were at most about ±30%. This system was chosen for a pilot project for large area surveillance in Mühlviertel, a granitic area in the federal state of upper Austria. The distribution system of the detectors is described. The measurement of more than 1200 vials within about two weeks was possible by using ultra low-level liquid scintillation counters (Quantulus). The highest value observed so far was 3150 Bq/m³. Comparing the ratios of the results from the three different measurement systems (charcoal, track etch, electret) significant but acceptable differences were found not only between track etch (3 months exposure) and activated charcoal (3 days exposure), but also between track etch and electret, which both had been exposed for three months. The data are discussed regarding the dose to the population.Note: This paper reflects the personal opinions of the authors.     

An efficient inexpensive multisleeve liquid scintillation counting system

This paper reports a method that conserves greatly on the cost of counting radioactive samples for liquid scintillation counting. It accomplishes this by using several glass sleeves that are much more inexpensive than conventional counting and/or minivials, and because volumes of counting fluid are reduced the cost of the counting fluid is also markedly reduced. The usual vial system (A) uses 15 ml of counting fluid with 37% efficiency for tritum; the minivial uses .75 ml with 37% efficiency while 0.15 and 30 μl volumes gave approximately 21% efficiency. Another feature of this system is the capacity to reuse the outer sleeve(s) and dispose of the smaller counting vessel. This means that less counting fluid and glass will have to be disposed of in the environment.     

Liquid scintillation counting of low activity63Ni

A simple and versatile method was developed to detect low specific-activity⁶³Ni with a liquid scintillation counter. High counting efficiency was obtained for a sample containing up to 220 mg of nickel using a mixture of a violet solution of nickel ammine complex and an emulsifier liquid scintillator. The detection limit was 0.06 Bq g^–1 Ni /1.6 pCi g^–1 Ni/ assuming the counting for 1000 min and 95% confidence level.     

Dioctyl sulfoxide as a stabilizer for scintillation counting

The use of dioctyl sulfoxide (DOSO) as a stabilizer for scintillation counting of uranium(VI), plutonium(IV) and americium(III) has been investigated. It has been observed that the addition of 2% DOSO to the scintillator solution results in a decrease in count rate of Am(III), which is about one third of that obtained with 2% TOPO. Uranium(VI) could be counted with almost the same efficiency with DOSO, TOPO, or as such without any stabilizer. The counting efficiency of plutonium(IV), however, is inferior for DOSO as compared to TOPO.     

Study on quench effects in liquid scintillation counting during tritium measurements

Quench effects can cause a serious reduction in counting efficiency for a given sample/cocktail mixture in liquid scintillation counting (LSC) experiments. This paper presents a simple experiment performed in order to test the influence of quenching on the LSC efficiency of ³H. The aim of this study was to investigate the behavior of several quench agents with different quench strengths (nitromethane, nitric acid, acetone, dimethyl-sulfoxide) added in different amounts to tritiated water in order to obtain standard sets for quench calibration curves. The OptiPhase HiSafe 2 and OptiPhase HiSafe 3 scintillation cocktails were used in this study in order to compare their quench resistance. Measurements were performed using a low-level LS counter (Wallac, Quantulus 1220).     

Liquid scintillation and Cherenkov counting characteristics of109Cd

When¹⁰⁹Cd is placed in a liquid scintillation counter, 146±1 counts are obtained for every 100¹⁰⁹Cd nuclides which undergo decay. Thus, the average efficiency for each of the two steps in the decay process is 73%. In examining the distribution of energy among the windows available, it was noted that the distribution pattern is quite similar to that of¹⁴C. An average Cherenkov counting efficiency, in water, was found to be 0.0258±0.0005%. Both 0.010M K₂Cr₂O₇ and CHCl₃ quench the count rate, particularly in the lower energy channel, where count rates are suppressed by up to a factor of 20.     

Liquid scintillation counting of radionuclides emitting high-energy beta radiation

Liquid scintillation counting of radionuclides emitting beta radiation with E_max>2 MeV has been investigated. Fluor volume effects were similar to those for low energy beta radiation, and pulse height spectra broadened in a predictable manner with no pulse clipping up to 4.913 MeV. Large changes in sample channels ratio due to color quenching resulted in progressively smaller losses of counting efficiency as beta energy increased. Counting efficiences were estimated to be near 100 percent for³⁴Cl^m,³⁶Cl,³²P and³⁸Cl. Cerenkov counting of³⁸Cl by liquid scintillation counter was volume dependent for both counting efficiency and pulse height spectrum. Counting efficiencies for³⁴Cl^m,³⁶Cl,³²P and³⁸Cl were estimated to be 57.0, 7.5, 42.7 and 66.3%, respectively. Pulse height spectra were shifted to greater pulse heights as a function of beta E_max, supporting the possibility of energy discrimination for beta emitters by Cerenkov pulse height spectrum analysis. The advantage of singles Cerenkov counting over coincidence Cerenkov counting was greatest for³⁶Cl and least for³⁸Cl; this advantage was amplified more for samples of³⁶Cl which had been color quenched than for similarly quenched samples of³⁸Cl or³²P.     

Recent progress and application of low level liquid scintillation counting

The use of an ultra low level liquid scintillation counter with extremely low background, MCA technique, storage and software evaluation of pulse height spectra has given very low LLD's, the possibility of - and -spectrometry to some extent and time saving optimization of counting conditions. Quick and very simple but yet accurate analytical methods could be worked out worked out for environmental measurements: Environmental levels of tritium,¹⁴C in several assimilation products,²²²Rn and²²⁶Ra in water without any sample pretreatment. Suggestions for possible further applications in environmenial monitoring and low level counting are given.     

Alpha-beta discrimination liquid scintillation counting for uranium and its daughters

Advances in liquid scintillation counting (LSC) technologies, such as imporved scintillation cocktail formulations and alpha-beta radiation discrimination, make LSC suitable for applications in uranium process chemistry. Ease of use, low cost, and the huge dynamic range of LSC are distinct advantages for analytical support of actinide processing. All uranium isotopes decay primarily with alpha radiation emission. The immediate short-lived daughters of²³⁸U are²³⁴Th and²³⁴Pa. These nuclides are beta emitters having energy bands that overlap the uranium bands in a liquid scintillation spectrum. The resolution of these overlapping bands by alpha-beta radiation discrimination is useful for uranium quantification and purity verification. Protactinium-234 is a high-energy beta emitter that can be further identified and quantified from it's Cherenkov radiation. Energy spectra were collected on the Packard 2500AB liquid scintillator analyzer for uranyl solutions in diisopropylnaphthalene and pseudocumene based scintillator cocktails. Calibration curves were prepared for nitric, hydrochloric, and sulfuric acid media. Base titrations demonstrated the effect of acid quenching on those system. Ion exchange and water soluble polymer extraction studies are readily followed using liquid scintillation methods.     

Liquid scintillation counting of 55Fe applied to air-filter samples

A simple and rapid method has been improved for determination of low specific activity of 55Fe with a liquid scintillation counter. High counting efficiency was obtained for a sample containing up to 150 mg of iron using mixture of a colorless solution of phosphate iron complex and an emulsifier liquid scintillator. The detection limit was 0.31 Bq (8.4 pCi) per gram iron assuming the counting for 1000 minutes and 95% confidence level. This counting method was applied to determination of 55Fe in air-filter samples.     

Absolute liquid scintillation counting of35S and45Ca using a modified integral counting method

The disintegration rates of³⁵S and⁴⁵Ca samples were determined by the modified integral counting method, which extrapolates the integral count rate to the zero detection threshold of a liquid scintillation spectrometer. The agreement between the extrapolated value and the standardized disintegration rate of the sample is very satisfactory.     

Gross alpha/beta analyses in water by liquid scintillation counting

Summary The standard procedure for analyzing gross alpha and gross beta in water is evaporation of the sample and radioactivity determination of the resultant solids by proportional counting. This technique lacks precision, and lacks sensitivity for samples with high total dissolved solids. Additionally, the analytical results are dependent on the choice of radionuclide calibration standard and the sample matrix. Direct analysis by liquid scintillation counting has the advantages of high counting efficiencies and minimal sample preparation time. However, due to the small sample aliquants used for analysis, long count times are necessary to reach required detection limits. The procedure proposed consists of evaporating a sample aliquant to dryness, dissolving the resultant solids in a small volume of dilute acid, followed by liquid scintillation counting to determine radioactivity. This procedure can handle sample aliquants containing up to 500 mg of dissolved solids. Various acids, scintillation cocktail mixtures, instrument discriminator settings, and regions of interest (ROI) were evaluated to determine optimum counting conditions. Precision is improved and matrix effects are reduced as compared to proportional counting. Tests indicate that this is a viable alternative to proportional counting for gross alpha and gross beta analyses of water samples.     

Measurement of subnanosecond scintillation decay times by time-correlated single photon counting

A time-correlated single photon counting system for measuring scintillation decay times is described in which the system time response function has a FWHM less than 220 ps. This is a two-scintillator system in which a time-to-amplitude converter (TAC) is started by gamma-induced flashes from a bright 500-ps FWHM scintillator closely coupled to a 14-stage photomultiplier. The TAC is stopped by single-photon pulses from an amplified high-gain microchannel-plate photomultiplier viewing the sample. A ⁶⁰Co source is sandwiched between the start scintillator and the sample to be measured. The time correlation depends on the coincident excitation of both scintillators by the two γ rays from each nuclear disintegration.