Simultaneous determination of 226Ra, 233U and 237Np by liquid scintillation spectrometry

Determination of the response for the National Ignition Facility particle time of flight (PTOF) detector using single particle counting

The Particle Time of Flight (PTOF) detector is a chemical vapor deposition diamond-based detector used to measure bang times in low-yield (≲ 1015 neutrons) experiments at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). Historically, the impulse response for PTOF diamond detectors has been obtained from x-ray timing shots on the NIF and shots on the MegaRay pulsed electron accelerator at LLNL. The impulse response may alternatively be obtained using single particle interactions with the detector, at substantially less cost and higher frequency compared to NIF timing shots, which typically occur months apart. Here, the response of a PTOF detector setup is characterized by statistically averaging a large number of single particle waveforms. A high fidelity instrument response function can be constructed in this way. This is confirmed by comparison of the single particle counting-constructed response to the impulse response function measured for the same detector at LLNL's MegaRay facility.

DECLAB: a software for liquid scintillation spectra deconvolution

The deconvolution of liquid scintillation (LS) spectra is meaningful in several scenarios like supporting incomplete radiochemical separations, for screening purposes and determining different isotopes of the same element, which is explored in this paper for the case of 89Sr/90Sr. In this paper DECLAB, an online application for liquid scintillation spectra analysis is presented. The software considers the classical calibration modes like constant efficiency and quenching curve and furthermore, the deconvolution of multicomponent spectra by means of Partial Least Square Regression. DECLAB is designed to analyse Perkin Elmer Wallac Quantulus 1220 spectra. However, in further upgrades, the applicability of this tool will be extended to other LS spectrometers.

Study of liquid scintillation alpha spectral properties

Alpha spectra were acquired with Quantulus 1220 liquid Scintillation Counter (LSC) and correlations among parameters, such as alpha particle energy, sample quenching, peak's centroid and resolution were established. The effect of quenching and factors such as types of counting vials, extractive reagents and composition of extractive scintillation cocktail on alpha spectral resolution, was experimentally studied.

Simultaneous determination of specific alpha and beta emitters by LSC-PLS in water samples

Liquid scintillation counting (LSC) is a commonly used technique for the determination of alpha and beta emitters. However, LSC has poor resolution and the continuous spectra for beta emitters hinder the simultaneous determination of several alpha and beta emitters from the same spectrum. In this paper, the feasibility of multivariate calibration by partial least squares (PLS) models for the determination of several alpha (^natU, ²⁴¹Am and ²²⁶Ra) and beta emitters (⁴⁰K, ⁶⁰Co, ⁹⁰Sr/⁹⁰Y, ¹³⁴Cs and ¹³⁷Cs) in water samples is reported. A set of alpha and beta spectra from radionuclide calibration standards were used to construct three PLS models. Experimentally mixed radionuclides and intercomparision materials were used to validate the models. The results had a maximum relative bias of 25% when all the radionuclides in the sample were included in the calibration set; otherwise the relative bias was over 100% for some radionuclides. The results obtained show that LSC-PLS is a useful approach for the simultaneous determination of alpha and beta emitters in multi-radionuclide samples. However, to obtain useful results, it is important to include all the radionuclides expected in the studied scenario in the calibration set.

Deconvolution of liquid scintillation alpha spectra of mixtures of uranium and radium isotopes

A method for the determination of uranium and radium isotopes in water samples is proposed. Liquid scintillation techniques were used for collecting alpha spectra, which were then analyzed by fitting the alpha peaks with overlapping Gaussians. The analysis can quantify the observed isotopes with accuracy depending on the activity of each isotope. In order to simulate the peaks with Gaussian normal distribution functions, the centroid of each peak as well as the full width at half maximum (FWHM) are required, as they depend on the quenching of the sample. For this purpose, samples with known activities of 226Ra and its decay products and also of the uranium isotopes 238U and 234U, at various quenching levels, were used to establish the correlation of the peaks' shift with the quench effect. In addition, the correlation of the FWHM with the centroid of a peak was determined, using the same procedure. Following the above analysis technique, an average of 97+/-2% of detection efficiency and a lower limit of detection of 8.2 mBq kg(-1) for alpha isotopes were achieved.