Ionization quenching in LSC.

Ionization quench function Q(E) introduces an important correction in the CIEMAT/NIST tracing method. In this paper we present a detailed analysis of the equations used to compute the counting efficiency of 55Fe. The counting efficiency of this radionuclide is very sensitive to the shape and values of Q(E) for this method. We demonstrate that the Birks equation and stopping power are not adequate to obtain low discrepancies between the experimental and computed efficiencies. An empirical procedure to compute accurate Q(E) functions is also given.     

The LSC efficiency for low-Z electron-capture nuclides.

In this paper, we apply the CIEMAT/NIST method to the three low-Z electron-capture nuclides 54Mn, 55Fe and 65Zn by using the KLM and KL1L2L3M atomic rearrangement models, respectively. The counting efficiencies are computed with the new code EMILIA, which comprises an improved model for the interaction of low-energy X-rays with the scintillation cocktail. The calculated counting efficiencies are compared with experimental results.     

The evaluation of uncertainty in low-level LSC measurements of water samples.

The uncertainty in measurements of gross alpha and beta activities in water samples by liquid scintillation counting with alpha/beta discrimination has been evaluated considering the problems typical of low-level measurements of environmental samples. The use of a pulse shape analysis device to discriminate alpha and beta events introduces a correlation between some of the input quantities, and it has to be considered. Main contributors to total uncertainty have been assessed by specifically designed experimental tests. Results have been fully examined and discussed.     

Half-life determination of 40K by LSC.

The long-lived radioisotope 40K is one of the isotopes applied by geologists to date rocks hundreds or even thousands of millions of years old. Knowing the half-life of 40K, the potassium-argon (K-Ar) method gives an estimate of the date of the rock's formation by measuring the quantity of the daughter stable isotope 40Ar. As in the case of other radiometric methods, the results of the K-Ar dating method are generally accompanied by an error estimate, which includes the counting process, the uncertainty in the half-life of 40K and the beta to capture branching ratio. The objectives of this paper are basically three. First, we describe a procedure to incorporate the largest amount of the potassium cations into the liquid scintillator cocktail. This time, gels are able to provide much higher counting rates than the background. Second, Cerenkov counting gives the best shapefactor for 40K beta-ray transitions. Third, the CIEMAT/NIST method determines the activity of the samples and an averaged half-life for the radionuclide.     

LSC measurements of the half-life of 40K.

Liquid scintillation counting techniques combined with the CIEMAT/NIST method have been applied to measure the specific activity of natural potassium salts. Samples have been prepared with three different scintillators. The individual atomic composition as well as the density of the cocktails have been taken into account for the efficiency calculation. With the specific activity the half-life is calculated to be T1/2 = 1.248(3) x 10(9) a. The result is in reasonable agreement with other measurement results provided the same isotopic concentration of 40K is used.     

Standardization of 18F by coincidence and LSC methods.

The nuclide 18F disintegrates to 18O by beta+ emission (96.86%) and electron capture (3.14%) with a half-life of 1.8288 h. It is widely used in nuclear medicine for positron emission tomography (PET). A radioactive solution of this nuclide has been standardized by two techniques: coincidence measurements with a pressurized proportional counter and liquid scintillation counting using the CIEMAT/NIST method. One ampoule containing a solution calibrated in activity was sent for measurement at the International Reference System maintained by the BIPM. Results are in excellent agreement with SIR values.     

Determination of the 32P activity in angioplastic balloons by LSC.

The determination of the 32P activity in angioplastic balloons involves two problems: the extraction of 32P, which is covered with plastic foils, and the determination of the 33P impurity. At PTB the active balloons are destroyed by combustion in an oxygen stream. The active phosphorus is extracted quantitatively from the tube. The activities of 32P and 33P are determined by measurements performed over a period of one month or more by a subsequent data fit.     

The effect of vial type and cocktail quantity on tritium measurement in LSC

The effect of sample vial type and cocktail quantity on tritium measurement in liquid scintillation counting is studied in this paper. With both high and low level tritium samples, glass vials allow higher counting rates than plastic vials do. We also present detailed analysis of the way to obtain the optimal counting condition by dispensing different quantity of cocktail into sample vials. Results indicate that the optimal counting condition has little relationship with tritium concentration in the sample. The main factor which influences the counting is the quantity of cocktail added into samples. Figure of merit is employed to access the results, which increases as the quantity of cocktail increasing. But when the ratio of cocktail and sample reaches 2.0, increase of ratio makes little contribution to the counts, and the disintegrations per minute comes nearly to be a constant.     

Gross alpha determination in drinking water using a highly specific resin and LSC.

Some results of experiments concerning a new highly specific resin for the extraction of alpha-emitting nuclides from drinking water samples are presented. The product used during these experiments is a new extraction chromatographic resin which consists of a combination of several reagents and extractants supported on inert polymeric substrates, called "Resin" hereafter. It shows strong affinity for Actinides in the tri-, tetra- and hexavalent oxidation state, as well as for radium, even in presence of large amounts of calcium. Gross-alpha activities were determined using alpha-/beta-discrimination liquid scintillation counting (alpha-/beta-LSC) by direct measurement of the dried resin after extraction. Counting conditions were optimised accordingly. A method for the determination of alpha-emitting nuclides in drinking water was developed and tested using intercomparison and spiked drinking water samples.     

Measurement of a 103Pd solution using the TDCR method by LSC.

Palladium 103 is a radionuclide used in brachytherapy sources for the treatment of prostate cancers and also for other medical applications. It decays through electron capture to excited levels of 103Rh. This paper describes the calculation method used to compute the detection efficiency in the framework of the triple to double coincidence ratio model. The calculation of the energy transferred to the scintillator is made by considering the various atomic events following the electron capture and the electron conversion. The energy deposited in the scintillator after the absorption of X-rays is calculated using the PENELOPE stochastic calculation code. The main contributors to the final uncertainty and their covariance matrix are discussed. As the calculation method cannot be reduced to an explicit function, this paper describes the Monte Carlo method used for the evaluation of uncertainties.     

Standardization of 222Rn by LSC and comparison with alpha- and gamma-spectrometry.

Liquid scintillation counting (LSC) was used for the measurement of 222Rn in equilibrium with its daughters, with detection efficiency close to 5. The appropriate corrections were considered, including one related to the probability that the 165-micros half-life 214Po decays during the dead time of the counter initiated by the disintegration of his parent nuclide, 214Bi. The dead-time determination of a commercial LS counter is also presented using a 222Rn standard source. The LSC 222Rn sources were prepared by transfer of 222Rn produced by a solid 226Ra source into LSC cocktail frozen at 77K, flame-sealed afterwards. They were measured using the LNHB triple coincidence counter with adjustable extending-type dead-time unit, between 8 and 100 micros; two different procedures were used to calculate an effective dead time and then to deduce the counting rate extrapolated to zero dead-time value. The LSC results were compared with those obtained by cryogenic alpha-particle spectrometry (LNHB system) and by gamma-ray spectrometry for the same radon source in the LSC vial; the geometry transfer coefficient was calculated using the ETNA software. Measurement results and uncertainties are discussed.     

Quality control assurance of strontium-90 in foodstuffs by LSC

A method based on the separation of Sr-90 by extraction chromatography and beta determination by Liquid Scintillation Counting (LSC) technique was used for strontium analysis in food samples. The methodology consisted in prior sample treatment (drying and incineration) followed by radiochemical separation of Sr-90 by extraction chromatography, using the Sr-resin. The chemical yield was determined by gravimetric method, adding stable strontium to the matrix. Beta activity (Sr-90/Y-90) was determined using a low background liquid scintillation spectrometer (Tri-Carb 3170 TR/SL, Packard). The accuracy and the precision of the method, was performed previously through recovery trials with Sr-90 spiked samples, using the same type of matrices (milk, complete meals, meat and vegetables). A reference material (IAEA_321) was now used to measure the accuracy of the procedure. Participation in interlaboratory comparison exercises was also performed in order to establish an external control on the measurements and to ensure the adequacy of the method.     

The need for energy equilibrium.

Human bioenergetics has been extensively assessed by means of field proxies (ie, cardiorespiratory fitness field tests) during the last two decades. A systematic review of the germane literature, however, suggests considerable controversy as to whether the present tests lead to valid measurements of energy expenditure/utilisation. The present paper suggests that current modalities of field testing being used as predictive models for bioenergetics may suffer from methodological limitations, stemming primarily from inappropriate design. A major weakness in the theoretical basis of proxies is that, although based on field measurements, it seeks to predict laboratory bioenergetics which, in turn, are used to provide information on field performance. Hence, it seems reasonable that the number of transformations increases the potential for error and may have significant impact on the prediction of bioenergetics. Recent studies asserted the importance of achieving 'energy equilibrium' between the reference standard and each proxy. The suggested approach involves designing proxies that closely simulate each laboratory protocol used as reference standard. The theoretical bases of previous and contemporary approaches are discussed in an attempt to increase the validity of current proxy assessments.     

Compensation by the CIEMAT/NIST-method of long-term effects in LSC measurements of beta emitters

A systematic evaluation of activity concentrations of ³H, ⁶³Ni and ¹⁴C by using the CIEMAT/NIST method has been carried out over time intervals of 4, 2.4 and 2.3 years, respectively. It proves that the CIEMAT/NIST method can compensate, with no need for additional checking sources or procedures, for count losses and quench parameter reduction in long-term measurements with LSC spectrometers and allows one to obtain very accurate activity concentration values by using a quench curve close to the nuclide measurements. If this requirement of the method is not fulfilled, significant discrepancies, up to 5.6% for ³H, 1.5% for ⁶³Ni and 0.35% for ¹⁴C, can be obtained in only 1-year time difference.     

The energy cost of an 80 km run.

Data was collected from two men who attempted an 80 km run. Measurements of aerobic power (VO2 max) and determinations of heart rate (HR) and submaximal oxygen consumption (VO2) during treadmill running were carried out one week before the run. Throughout the 80 km run, HR was recorded by telemetry and used together with the laboratory data to estimate VO2 as a percentage of VO2 max. One subject completed the 80 km distance at 58% of VO2 max, the other subject, operating at 74% of VO2 max, was obliged to retired after 55 km. The data in this and other studies indicate that the high energy costs reported for the marathon (70-85% of VO2 max) cannot be sustained over the 80 km distance but that about 60% of VO2 max can be continued for seven hours and longer.     

Determination of Pu in nuclear waste slurries: A comparative study using LSC and ICP-MS

²⁴¹Pu was determined in slurry samples from a nuclear reactor decommissioning project at the Paul Scherrer Institute (Switzerland). To validate the results, the ²⁴¹Pu activities of five samples were determined by LSC (TriCarb and Quantulus) and ICP-MS, with each instrument at a different laboratory. In lack of certified reference materials for ²⁴¹Pu, the methods were further validated using the ²⁴¹Pu information values of two reference sediments (IAEA-300 and IAEA-384). Excellent agreement with the results was found between LSC and ICP-MS in the nuclear waste slurries and the reference sediments.     

Implementation of CIEMAT/NIST LSC efficiency tracing method in KRISS: T1 standardization

The CIEMAT/NIST efficiency tracing method has been widely used for radionuclide standardization. The method consists of the theoretical calculations of counting efficiencies and the experimental data obtained from a commercially available double photomultiplier detector. We have recently implemented the technique using ³H as a tracer. Our implementation of the method was validated by participating into an international comparison of activity measurements of a solution of ²⁰⁴T1. We report in this paper the procedure employed to implement the technique and compare our measurement result of ²⁰⁴T1 activity with that of the international comparison.     

Evaluating practicability of an LSC method for routine monitoring gross alpha and beta activities in water samples in Taiwan

A procedure using liquid scintillation counting for the monitoring of gross alpha and beta activities in environmental water was implemented to improve the conventional procedure using GFPC adopted in Taiwan. The new procedure was acquired through calibration and validation, and then was applied to the monitoring of surface water in Taiwan. This procedure can improve 2-4 times of detection efficiencies and takes only 70-80% of analysis time with reliable accuracy. With these features, the newly developed procedure is favorable during emergency situations.     

The distribution of anaerobic energy in 1000 and 4000 metre cycling bouts.

In sprinting events of short duration, performance depends not only on the mean external power output and the frictional losses but also on the distribution of energy over the race. To investigate the optimal distribution of anaerobic energy during cycling the 1000 m time trial and the 4000 m pursuit, we simulated a power equation which contains expressions for the production of aerobic and anaerobic power, for frictional losses and for the rate of change of kinetic energy. Parameters for air- and rolling resistance were derived from the literature and the equations for aerobic and anaerobic power production were based on supra-maximal bicycle ergometer tests. Simulated lap and final times were compared to those realized by the best four athletes during the 1990 World Championships. The mean final times of these athletes of 64.1 s and 272.6 s for the 1000 m and 4000 m respectively were closely approximated by the simulated times of 63.7 s and 281.3 s. The simulations show that performance in the 1000 m race depends to a great extent on a large power output at the onset of the race. Moreover, it is demonstrated that this distance should be cycled in an all out fashion and not with a uniform velocity after the start despite the higher air frictional losses. For the 4000 m pursuit it appears to be more effective to perform a short but powerful start and then continue the race with a constant or only slightly decreasing power output.