A. Grau Carles

Half-life determination of 40K by LSC.

Abstract 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 rocks 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 β-ray transitions. Third, the CIEMAT/NIST method determines the activity of the samples and an averaged half-life for the radionuclide.

EMI2, the counting efficiency for electron capture by a KL1L2L3M model

Abstract The program EMI2 computes the liquid-scintillation counting efficiency for pure electron capture, single isomeric and electron capture-gamma nuclides. In this second version, the atomic rearrangement process subsequent to electron capture is described in terms of a more sophisticated KL 1 L 2 L 3 M model of 264 different pathways. The addition of Coster–Kronig transitions improves the accuracy of the method, especially for nuclides of low atomic numbers. A Monte Carlo method is applied to simulatethe photoelectric and Compton interactions of X- and γ -photons with the scintillator inside the vial geometry.

Precision measurement of the RaE shape factor

Abstract We apply to RaE a new method to determine the shape factor coefficients of pure beta transitions with energies over the Cherenkov threshold of water. This method is based on the precision measurement of one observable, the ft-value, and two quasi-observables, the Cherenkov counting efficiency and the position of the maximum point of the liquid-scintillation logarithmic pulse-height spectrum. We found for the revised shape factor function that the ground state wave function |210Bi, 1−1〉 is the combination of the three wave functions | 1h 9 2 2g 9 2 〉 , | 1h 9 2 1i 11 2 〉 and | 1h 9 2 2g 7 2 〉 . This result is also confirmed by the excellent agreement we obtain with experiment for the longitudinal electron polarization.

New methods for the determination of β-spectra shapefactor coefficients

Abstract The maximum point of a logarithmic β-decay distribution is a quite well-defined point, which can be used for the calibration of liquid scintillation logarithmic spectrometers. It is observed that maximum points of several β-ray nuclides with forbidden transitions, such as 204Tl, 36Cl, 137Cs, 89Sr and 90Y, lie outside of this calibration curve, indicating the presence of inaccuracies in the current shapefactors of these nuclides. For β-ray nuclides below the Cherenkov threshold in the scintillation mixture, such as 129I, the CIEMAT/NIST method can be used for the accurate determination of the shapefactor coefficients.

Standardization of 125I, 85Sr and 109Cd by CIEMAT/NIST method

Abstract We applied the CIEMAT/NIST method to the standardization of 125 I, 85 Sr and 109 Cd in liquid scintillation counting. The effects of the chemical nature of the quencher on the standardization curves for these nuclides and the convenience of using CH 3 NO 2 instead of CCl 4 for quenching samples were studied. Monte Carlo simulations were used to compute the energy spectrum of the electrons produced in the interaction of the KL- and KM-photons with the liquid scintillator. We demonstrated that photons with energies in the range between 20 and 40 keV create both Compton and photoelectric electrons. These Monte Carlo simulations also permitted us to determine accurately the x-ray contribution to the counting efficiency for 125 I, 85 Sr and 109 Cd.

A new linear spectrum unfolding method applied to radionuclide mixtures in liquid scintillation spectrometry

Abstract The classical spectrum unfolding method has been successfully used in simultaneous standardizations of radionuclide mixtures carried out in liquid-scintillition spectrometers with logarithmic pulse-height spectra outputs. However, this method is not applicable to linear spectra. The reason for this inapplicability is essentially the very important spectral shape difference between the logarithmic and the linear spectra. This article introduces a new linear spectrum unfolding method, and studies in detail the diverse aspects that must be modified on the classical method. Mixtures of 14C+3H, 45Ca+35S and 204Tl+36Cl, with different activity ratios have been used to test this new linear spectrum unfolding method.

Spectrum unfolding and double window methods applied to standardization of 14C and 3H mixtures

Abstract A spectrum unfolding method for beta-ray emitters is applied to double-label counting of 3 H and 14 C. Twenty-two samples with counting rate rati

Extension of the TDCR model to compute counting efficiencies for radionuclides with complex decay schemes.

The triple-to-double coincidence ratio (TDCR) method is frequently used to measure the activity of radionuclides decaying by pure β emission or electron capture (EC). Some radionuclides with more complex decays have also been studied, but accurate calculations of decay branches which are accompanied by many coincident γ transitions have not yet been investigated. This paper describes recent extensions of the model to make efficiency computations for more complex decay schemes possible. In particular, the MICELLE2 program that applies a stochastic approach of the free parameter model was extended. With an improved code, efficiencies for β(-), β(+) and EC branches with up to seven coincident γ transitions can be calculated. Moreover, a new parametrization for the computation of electron stopping powers has been implemented to compute the ionization quenching function of 10 commercial scintillation cocktails. In order to demonstrate the capabilities of the TDCR method, the following radionuclides are discussed: (166m)Ho (complex β(-)/γ), (59)Fe (complex β(-)/γ), (64)Cu (β(-), β(+), EC and EC/γ) and (229)Th in equilibrium with its progenies (decay chain with many α, β and complex β(-)/γ transitions).

The ionization quench factor in liquid-scintillation counting standardizations

Abstract We present a new detailed analysis of the ionization quench function Q ( E ) used in calculating the counting efficiency in liquid-scintillation counting (LSC), which shows that Q (0)=1, and permits one to derive Q ( E ) as a function of the electron energy and the parameter kB . The coefficients are tabulated by applying a new empirical formula of Q ( E ) for kB values in the range between 0.001 and 0.20 gMeV −1 cm −2 . We demonstrate the convenience of applying 3 H and 54 Mn for β-ray and electron capture standardizations, respectively.

Radioactivity determination of 90Y, 90Sr and 89Sr mixtures by spectral deconvolution

Abstract The measurement of 90 Y, 90 Sr and 89 Sr in environmental samples has received considerable attention since the advent of the nuclear era. These three radionuclides are pure beta-ray emitters and a nondestructive sample analysis procedure is not available. It is necessary to use complex radiochemical separation procedures to isolate these radionuclides prior to counting. The result is a significant delay between the sample treatment and the activity determination. A rapid analytical procedure is required to obtain the activity of these radionuclides and would appear to be an important goal. A deconvolution method has been applied to logarithmic spectra obtained with a liquid scintillation spectrometer. In a previous paper, this procedure was applied to samples in which 90 Y and 90 Sr were in equilibrium. Samples have been assessed in which 90 Y activity was higher or lower than 90 Sr activity, and medium and low activities were considered. Samples with count rates below ba-ckground were analyzed, and the limits of detection of the procedure were determined. The effects of chemical quench and the different activity ratios were studied. It was shown that this treatment of the beta spectra is adequate and represents a rapid method of determining these radionuclides.