L. Rodríguez Barquero

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.

41Ca standardization by the CIEMAT/NIST LSC method

Abstract A procedure for the liquid scintillation counting standardization of the electron-capture nuclide 41 Ca has been successfully developed and applied with 41 CaCl 2 and 41 Ca-(HDEHP) n samples synthesized in the laboratory from 41 CaCO 3 supplied by Oak Ridge National Laboratory. Six scintillators were tested: the organic samples were stable in toluene—alcohol, Ultima-Gold™ and HiSafe III™ for 30 d, whereas the inorganic samples were only stable in toluene—alcohol and HiSafe III™ for the same period of time. Despite of the low counting efficiencies (1%–13%) due to the very low-energy of less than 3.6 keV of the X-rays and Auger electrons of 41 Ca, the stable samples were standardized by the CIEMAT/NIST method to a combined uncertainty of 2.4% over a range of figures of merit of 1.75 to 7.25 ( 3 H equivalent efficiency of 40% to 7%).

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.

Standardization of 134Cs by three methods.

The nuclide 34Cs decays by beta-emission followed by gamma-deexcitation to 134Ba with a half-life T(1/2) = 2.065 a. It has been standardized by three methods: liquid scintillation counting (LSC), 4pi beta-gamma coincidence counting and 4pi gamma counting. In the LSC measurements, the CIEMAT/NIST method was used to calculate the efficiency. For the coincidence measurements, a conventional 4pi beta (proportional counter)-gamma(NaI) system was used. For the 4pi gamma standardization, a well-type Nal(Tl) detector was modeled with the Monte Carlo package PENELOPE, and the counting efficiency obtained by calculation. Results of the three methods agree within 0.65%.

Standardization of 14C and 35S mixtures

Abstract This article examines the applicability of a newly developed method to standardize 14 C and 35 S mixtures in liquid scintillation spectrometry, which is an unsolved problem in the usual double window method. An improved spectrum unfolding method is applied and the spectral components and activities for 14 C and 35 S computed. Twenty eight assays with activity ratios for 14 C and 35 S between 0.1 and 12 and quench intensities which make the 35 S efficiency vary from 95% to 85% are analysed.

Simultaneous standardization of 90Sr90Y and 89Sr mixtures

Abstract A deconvolution method is applied to liquid-scintillation spectra of 90Y + 90Sr and 89Sr mixtures in equilibrium. Samples of medium, low and very low activities have been tested for activity ratios in the range between 1 10 and 8 1 . A chemical quench equivalent to a counting efficiency for tritium of 4.8% has been reached. Discrepancies

Cherenkov radiation effects on counting efficiency in extremely quenched liquid scintillation samples

Abstract The CIEMAT/NIST tracer method has successfully standardized nuclides with diverse quench values and decay schemes in liquid scintillation counting. However, the counting efficiency is computed inaccurately for extremely quenched samples. This article shows that when samples are extremely quenched, the counting efficiency in high-energy beta-ray nuclides depends principally on the Cherenkov effect. A new technique is described for quench determination, which makes the measurement of counting efficiency possible when scintillation counting aproaches zero. A new efficiency computation model for pure beta-ray nuclides is also described. The results of the model are tested experimentally for 89 Sr, 90 Y, 36 Cl and 204 Tl nuclides with independence of the quench level.

Standardization of 110mAg by liquid scintillation and 4πβ–γ coincidence counting

Abstract The nuclide 110m Ag is a β–γ emitter with a very complex decay scheme, including more than 50 γ-rays. It has been standardized by two methods: liquid scintillation counting (LSC) and 4πβ(pc)-γ coincidence measurements. In the LSC measurements the CIEMAT/NIST method was used, with 3 H being used as a tracer for efficiency calculations. In the 4πβ(pc)-γ standardization, Monte Carlo calculations have been made to determine the optimal measurement conditions. Results obtained with both methods for the activity concentration of the solution are in good agreement.

LSC standardization of 45Ca by the CIEMAT/NIST efficiency tracing method

Abstract A commercial solution of 45 CaCl 2 and two organic compounds, 45 Ca-2-ethylhexadecanoate and 45 Ca-HDEHP complex, synthesized in the laboratory, have been used to produce appropriate sources for LSC measurements. A toluene-based scintillator and three commercial cocktails (Hisafe II, Ultima Gold and Instagel) were used for measuring the samples. Their concentration quenching, time stability, and spectral behaviour were studied over a 30-day period. The stable samples were used to standardize the radioactive solutions by the CIEMAT/NIST efficiency tracing method. Experimental quench curves for 3 H were measured with each scintillator to cover the range of figure of merit between 1 and 4, corresponding to 3 H equivalent efficiency between 52 and 12%. Experimental and computed efficiencies were in good agreement, with individual discrepancies lower than 0.6% in all cases; high efficiency values, better than 95%, were obtained with unquenched samples. A combined uncertainty of 0.4% was obtained for the activity concentration estimation of each radioactive solution.

STANDARDIZATION OF MULTI-NUCLIDE MIXTURES BY A NEW SPECTRUM UNFOLDING METHOD

A new spectrum unfolding method has been applied to double-labeled mixtures with excellent results, while the CIEMAT/NIST method has been used for gels. The convenience of applying both methods has been demonstrated with mixtures containing more than three components.90Sr+90Y,89Sr,204TI,45Ca and35S nuclides were combined as three, four and five components, and the different quench values and activity ratios were assayed. The discrepancies between computed and experimental activities were also obtained. Mixtures with some of their components below background have been prepared in order to test low-level activities.