J.F. García

Mixed waste reduction in radioactivity determination by using plastic scintillators

Abstract In this work, we tested whether plastic scintillation (PS) is a suitable alternative to liquid scintillation (LS) and Cerenkov techniques for beta emitter detection. The main advantage of this alternative is the reduction of mixed waste produced as consequence of the measurement process. In addition, the quality parameters obtained with PS are as reliable as those obtained with LS and allow determination, with a relative error 90 Sr / 90 Y in low level activity aqueous samples. Gamma and alpha emitters were also measured with plastic scintillators using linear and logarithmic amplified scintillation detectors.

Simultaneous determination of plutonium alpha emitters by liquid scintillation counting using multivariate calibration

Abstract In this study a new method is presented for the simultaneous determination of plutonium alpha emitters by liquid scintillation counting using multivariate calibration. The prediction errors obtained for 239+240Pu and 238Pu activities are around 8%. With the procedure proposed, the measurement of the blank spectrum is no longer required.

Uranium-series isochron dating at El Castillo Cave (Cantabria, Spain): The “Acheulean”/“Mousterian” question

Abstract A massive flowstone layer, Level 23, near the base of the stratigraphic sequence in El Castillo Cave (Cantabria, Spain), is dated by the uranium-series isochron method to 89+11/−10 ka bp. The flowstone separates cultural layers traditionally labelled “Mousterian” (above) and “Acheulean” (below). The date reported here, in association with other recent age determinations for “Mousterian” and “Acheulean” artifact assemblages in Western Europe, calls into question the temporal significance of these archaeological designations. In addition, it further underlies the importance of the Castillo cultural sequence and allows tentative discussion of changing rates of sedimentation in the vestibule of the cave, where some 18 m of cultural and geological deposits were laid down during the course of the Upper Pleistocene.

Radiostrontium separation and measurement in a single step using plastic scintillators plus selective extractants. Application to aqueous sample analysis.

This study describes a new protocol for (90)Sr determination in water samples based on the use of a selective extractant (DtBuCH18C6) and plastic scintillator microspheres. The proposed procedure unifies chemical separation and sample measurement preparation in a single step to reduce the effort, time and reagents required for analysis. In addition, the final measurement does not produce mixed waste. The minimum activity detectable for 10 mL of sample solution is 0.46 Bq L(-1). Relative errors for the determination of (90)Sr activity in drinking, sea and river waters are less than 4%.

Plastic vs. liquid scintillation for 14C radiotracers determination in high salt matrices.

The use of radiotracers is a common procedure for better understanding of the dynamics of oil reservoirs. Several molecules and radionuclides are implemented for this purpose; one of these is (14)C labelled thiocyanate. Samples taken from fluids in production wells require a pre-treatment step in order to purify and concentrate the activity of the radiotracer before measurement. Pre-treatment is based on ionic exchange and the solution eluted includes a high concentration of salt that can be a serious drawback for the development of a stable emulsion when the liquid sample and the scintillation cocktail are mixed for Liquid Scintillation (LS). The objective of this study is to evaluate the capability of Plastic Scintillation (PS) to determine the activity of radiotracers in salt matrices. For this purpose, an initial comparative study of the influence of salt and coloured matrices on the detection efficiency for PS and LS was performed. Results indicate that in both techniques colour quenching produces the same effects: efficiency decrease and spectra shift, whereas salt quenching produces different effects for PS and LS, ionization quenching for PS and chemical quenching for LS. As a result of this divergence, the calibration required for each counting method is different: two steps for PS and a single step for LS. After system study and procedure optimization, radiotracer activities in real samples taken from oil reservoirs have been determined. The results indicated that PS shows similar capability to the classical LS to determine the activity in these salt matrix samples with the additional advantages that no separation of the phase can appear and no mixed waste is produced after measurement.

Determination of oil reservoir radiotracer (S14CN-) in a single step using a plastic scintillator extractive resin.

The analysis of radiotracers is important in the study of oil reservoir dynamics. One of the most widely used radiotracer is S(14)CN(-). Prior to activity measurements by Liquid Scintillation (LS), routine determinations require the pretreatment steps of purification and concentration of the samples using anion exchange columns. The final elution media produces samples with high salt concentration that may lead to problems with phase separation during the LS measurement. Plastic Scintillation (PS) is an alternative technique that provides a solid surface that can be used as a platform for the immobilisation of selective extractants to obtain a PS resin. The proposed procedure unifies chemical separation and sample measurement preparation in a single step, serving to reduce the number of reagents needed and manpower required for the analysis while also avoiding mixed waste production by LS. The objective of this study is to develop a PS resin for the determination of (14)C-labelled thiocyanate radiotracer in water samples. For this purpose, the immobilisation procedure was optimised, including optimisation of the proportion of PS microspheres:extractant and the use of a control blank to monitor the PS resin immobilisation process. The breakthrough volume was studied and the detection and quantification limits for 100 mL of sample were determined to be 0.08 Bq L(-1) and 0.31 Bq L(-1), respectively. The established procedure was applied to active samples from oil reservoirs and errors lower than 5% in the sample determinations were obtained.

Alpha/beta pulse shape discrimination in plastic scintillation using commercial scintillation detectors.

Activity determination in different types of samples is a current need in many different fields. Simultaneously analysing alpha and beta emitters is now a routine option when using liquid scintillation (LS) and pulse shape discrimination. However, LS has an important drawback, the generation of mixed waste. Recently, several studies have shown the capability of plastic scintillation (PS) as an alternative to LS, but no research has been carried out to determine its capability for alpha/beta discrimination. The objective of this study was to evaluate the capability of PS to discriminate alpha/beta emitters on the basis of pulse shape analysis (PSA). The results obtained show that PS pulses had lower energy than LS pulses. As a consequence, a lower detection efficiency, a shift to lower energies and a better discrimination of beta and a worst discrimination of alpha disintegrations was observed for PS. Colour quenching also produced a decrease in the energy of the particles, as well as the effects described above. It is clear that in PS, the discrimination capability was correlated with the energy of the particles detected. Taking into account the discrimination capabilities of PS, a protocol for the measurement and the calculation of alpha and beta activities in mixtures using PS and commercial scintillation detectors has been proposed. The new protocol was applied to the quantification of spiked river water samples containing a pair of radionuclides ((3)H-(241)Am or (90)Sr/(90)Y-(241)Am) in different activity proportions. The relative errors in all determinations were lower than 7%. These results demonstrate the capability of PS to discriminate alpha/beta emitters on the basis of pulse shape and to quantify mixtures without generating mixed waste.

Synthesis of plastic scintillation microspheres: alpha/beta discrimination.

Plastic scintillation microspheres (PSm) have been developed as an alternative for liquid scintillation cocktails due to their ability to avoid the mixed waste, besides other strengths in which the possibility for alpha/beta discrimination is included. The aim of this work was to evaluate the capability of PSm containing two combinations of fluorescence solutes (PPO/POPOP and pT/Bis-MSB) and variable amounts of a second organic solvent (naphthalene) to enhance the alpha/beta discrimination. Two commercial detectors with different Pulse Shape Discrimination performances (Quantulus and Triathler) were used to evaluate the alpha/beta discrimination. An optimal discrimination of alpha/beta particles was reached, with very low misclassification values (2% for beta particles and 0.5% for alpha particles), when PSm containing PPO/POPOP and between 0.6 and 2.0 g of naphthalene were evaluated using Triathler and the appropriate programme for data processing.

Determination of mixtures of alpha emitting isotopes (242Pu, 239+240Pu, 238Pu) by using liquid scintillation–moving curve fitting

Abstract A new method for the simultaneous determination of alpha emitting plutonium isotopes based on liquid scintillation spectrometry and moving curve fitting (LS–MCF) is presented. This method overcomes the instability of the spectrum position by introducing in the model some freedom in the band location. The method proposed has a higher detection efficiency than that of the classical semiconductor alpha spectrometry. Therefore, it can be used to process smaller samples and has the additional advantage of being a relatively quick procedure. With regard to the use of multivariate calibration, LS–MCF reduces the data treatment time because it does not require a previous spectrum position correction. LS–MCF can also be applied to samples with low activity levels.

Classical versus multivariate calibration for a beta emitter (14C) activity determination by liquid scintillation counting

Abstract Liquid Scintillation (LS) is a radiochemistry technique mainly used to quantify beta emitters. It is time consuming when low activity samples are determined. Using 14 C as an example, classical procedures of counting efficiency and activity determination are compared with Multivariate Calibration (MVC, PLS), for a series of solutions of different activities and compositions. The predicted activities have precisions in accordance with the theoretical uncertainties, accuracies for a single determination of 0.1 dpm and detection limits of 0.1 dpm in both approaches. The MVC approach does not need background information and therefore total counting time is reduced. Moreover, in this approach, the factors found can be clearly attributed to physical causes: 14 C content, quenching and lack of spectra reproducibility.