Standardization of 237Np

The standardization of ²³⁷Np was investigated. The certified massic activity for ²³⁷Np was obtained by 4παβ liquid scintillation (LS) counting with correction for the ²³³Pa daughter using the CIEMAT/NIST efficiency tracing method using a ³H standard. Confirmatory measurements were also performed by high-resolution HPGe gamma-ray spectrometry, and by 4παβ(LS)-γ(NaI) anticoincidence counting. All results agree within the respective method's uncertainties. It was confirmed that the ²³⁷Np/²³³Pa radioactive equilibrium is disturbed when making dilutions and/or removing aliquots.     

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.     

Half-life measurements of Rb by liquid scintillation counting

The specific activity of natural ⁸⁷Rb was measured by means of 4πβ liquid scintillation counting in a two-photomultiplier-tube spectrometer. ³H-efficiency tracing was used together with the CIEMAT/NIST method to obtain the detection efficiency. For this purpose a new parameterization of the shape factor for the third forbidden non-unique β-transition was performed. The hygroscopic behaviour of the salts used for sample preparation was studied. The half-life of ⁸⁷Rb was found to be T_1/2=4.967(32)×10¹⁰ y.     

jStudy of a Monte Carlo rearrangement model for the activity determination of electron-capture nuclides by means of liquid scintillation counting

A new Monte Carlo approach for the computation of the electron spectra of electron-capture nuclides is applied to obtain efficiencies in liquid scintillation counting for CIEMAT/NIST applications. The new method is applied to the radionuclides ¹⁰⁹Cd and ¹²⁵I by using a stochastic atomic rearrangement model, taking into account rearrangement processes including L-, M-, and N-subshells. The counting efficiencies were computed with the new code MICELLE which also comprises an approach for calculating the counting efficiency of a radionuclide in a gel phase sample. The calculated counting efficiencies are compared with experimental results.     

Development of a primary standard for calibration of Cu activity measurement systems

A ⁶⁴Cu national primary standard, was developed by the National Institute for Ionising Radiation Metrology (INMRI) of the ENEA (ENEA-INMRI) using the CIEMAT/NIST method of 4πβ liquid scintillation spectrometry with ³H-standard efficiency tracing. Relatively short ⁶⁴Cu half-life is required for the work to be performed at the production site. It was produced at the Scanditronix MC40 Cyclotron of the Joint Research Centre (JRC) of the European Commission (Ispra, Italy) through the ⁶⁴Zn(d,2p) ⁶⁴Cu reaction. Significant efforts were made to identify and quantify the impurities of ⁶¹Cu and ⁶⁵Zn in the mother solution, which were activated through the ⁶⁴Zn(d,n) ⁶¹Cu and ⁶⁴Zn(d,p) ⁶⁵Zn reactions, respectively. To this purpose, a new procedure for the determination of pure β-emitter impurities by the CIEMAT/NIST method has been applied. A transfer standard portable well-type ionisation chamber was also calibrated with minimum uncertainty.     

Comparative study of different methods for the activity quantification of H and C radionuclides in dual labeled samples using liquid scintillation analyzer

Different methods such as full spectrum DPM (FSDPM), dual isotope estimation and inclusion methods were studied for the activity quantification of ³H and ¹⁴C in dual beta labeled samples using liquid scintillation analyzer. A standardized Packard tritiated water was used as tritium source and ¹⁴C activity was standardized by CIEMAT/NIST method and compared with the results obtained by the above three methods. Minimum detectable activity was 2100 dpm/l for ³H and 1200 dpm/l for ¹⁴C with a counting time of 300 min. The accuracy of the results obtained was found to be within ±10% for ³H: ¹⁴C activity ratios 1:1, 1:2, 2:1, 6:1, 9:1, 13:1 and 18:1.     

The Compton source efficiency tracing method in liquid scintillation counting: A new standardization method using a TDCR counter with a Compton spectrometer

We describe a new standardization method in liquid scintillation counting based on the use of a temporary virtual tracer source created inside the scintillator by Compton interaction. The Compton tracer source is measured by the triple coincidence liquid scintillation counter after selection of the Compton events by a gamma-ray detector. The paper describes the principle of the method, the experimental setup and presents the results obtained by this method for the standardization of a ³H solution. These results are compared with those obtained using the classical triple to double coincidence ratio method. Possible application of this new method for international comparisons is addressed.     

Further investigations of a simple counting technique for measuring mixtures of two pure beta-emitting radionuclides

A simple liquid scintillation counting technique to measure the activity composition of a mixture containing two known pure β-emitting radionuclides was recently developed at the NMISA. The method has been applied to various two-component mixtures of ³²P, ³³P and ³⁵S, primarily to gauge the effect of spectral energy differences on the method's ability to extract the individual activities. Excellent results were obtained for mixtures of ³³P and ³⁵S, radionuclides with similar, low β energies. Mixtures containing the high-energy β-emitter ³²P were more difficult to resolve, although quenching of the counting sources with CHCl₃ improved mixture resolution.     

Further investigations of a simple counting technique for measuring mixtures of two pure β-emitting radionuclides

A simple liquid scintillation counting technique to measure the activity composition of a mixture containing two known pure β-emitting radionuclides was recently developed at the NMISA. The method has been applied to various two-component mixtures of ³²P, ³³P and ³⁵S, primarily to gauge the effect of spectral energy differences on the method's ability to extract the individual activities. Excellent results were obtained for mixtures of ³³P and ³⁵S, radionuclides with similar, low β energies. Mixtures containing the high-energy β-emitter ³²P were more difficult to resolve, although quenching of the counting sources with CHCl₃ improved mixture resolution.