M. Capogni

An intercomparison of Monte Carlo codes used in gamma-ray spectrometry

In an intercomparison exercise, the Monte Carlo codes most commonly used in gamma-ray spectrometry today were compared with each other in order to gauge the differences between them in terms of typical applications. No reference was made to experimental data; instead, the aim was to confront the codes with each other, as they were applied to the calculation of full-energy-peak and total efficiencies. Surprising differences between the results of different codes were revealed.

Intercomparison of methods for coincidence summing corrections in gamma-ray spectrometry

A comparison of the coincidence summing correction methods is presented. Since there are several ways for computing these corrections, each method has advantages and drawbacks that could be compared. This part of the comparison was restricted to point sources. The same experimental spectra, decay scheme and photon emission intensities were used by all the participants. The results were expressed as coincidence summing correction factors for several energies of (152)Eu and (134)Cs, and three source-to-detector distances. They are presented and discussed.

Intercomparison of methods for coincidence summing corrections in gamma-ray spectrometry—part II (volume sources)

The second part of an intercomparison of the coincidence summing correction methods is presented. This exercise concerned three volume sources, filled with liquid radioactive solution. The same experimental spectra, decay scheme and photon emission intensities were used by all the participants. The results were expressed as coincidence summing corrective factors for several energies of (152)Eu and (134)Cs, and different source-to-detector distances. They are presented and discussed.

Development of a primary standard for calibration of 64Cu activity measurement systems

A (64)Cu 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 4pibeta liquid scintillation spectrometry with (3)H-standard efficiency tracing. Relatively short (64)Cu 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 (64)Zn(d,2p) (64)Cu reaction. Significant efforts were made to identify and quantify the impurities of (61)Cu and (65)Zn in the mother solution, which were activated through the (64)Zn(d,alphan) (61)Cu and (64)Zn(d,p) (65)Zn reactions, respectively. To this purpose, a new procedure for the determination of pure beta-emitter impurities by the CIEMAT/NIST method has been applied. A transfer standard portable well-type ionisation chamber was also calibrated with minimum uncertainty.

A prototype of a portable TDCR system at ENEA

A prototype of a portable liquid scintillation counting system based on the Triple-to-Double Coincidence Ratio (TDCR) technique was developed at ENEA-INMRI in the framework of the European Metrofission project. The new device equipped with the CAEN digitizers was tested for the activity measurements of pure β-emitters ((99)Tc and (63)Ni). The list-mode data recorded by the digitizers were analyzed by software implemented in the CERN ROOT environment, which allows the application of pulse shape discrimination using the new device.

Results of an international comparison for the activity measurement of 177Lu

An international Key Comparison of (177)Lu has recently been carried out. Twelve laboratories performed assays for radioactivity content on aliquots of a common master solution of (177)Lu, leading to eleven results submitted for entry into the Key Comparison Database of the Mutual Recognition Arrangement. A proposed Comparison Reference Value (CRV) was calculated to be 3.288(4)MBq/g using all eleven results. Degrees of equivalence and their uncertainties were calculated for each laboratory based on the CRV. Most of the values reported by the participating laboratories were within 0.6% of the CRV.

Simulation of radioactive decay in GEANT Monte Carlo codes: Comparison between spectra and efficiencies computed with sch2for and G4RadioactiveDecay

Two CERN Monte Carlo codes, i.e. GEANT3.21 and GEANT4, were compared. The specific routine (sch2for), implemented in GEANT3.21 to simulate a disintegration process, and the G4RadioactiveDecay class, provided by GEANT4, were used for the computation of the full-energy-peak and total efficiencies of several radionuclides. No reference to experimental data was involved. A level of agreement better than 1% for the total efficiency and a deviation lower than 3.5% for the full-energy-peak efficiencies were found.

Implementation of a new low cost detector for low intensity light pulses produced by a radioactive gamma-source.

The readout of a cheap scintillating fibre was implemented by means of a new solid-state device (Silicon Photomultiplier, SiPM), able to detect very tiny light pulses. The GEANT3.21 code was adopted to simulate the counting detection efficiency and the energy deposited inside the scintillating fibre due to the radiation of a radioactive gamma source. The results obtained show the capability to detect gamma rays producing as few as 3-4 photoelectrons. The new devices may have many applications in radioactivity metrology.

Development of portable Liquid Scintillation counters for on-site primary measurement of radionuclides using the Triple-To-Double Coincidence Ratio method

The Triple-to-Double Coincidence Ratio (TDCR) method in Liquid Scintillation counting (LSC) is a primary radionuclide standardization method widely used in National Metrology laboratories and was primarily developed for the activity measurement of beta emitters. It is based on liquid scintillation: the light is detected by three photomultipliers (PM) and the detection efficiency is evaluated by using a model which uses the ratio of triple-to-double coincidences between the PM tubes. Up to now, most of current TDCR systems were locally-made metrology instruments neither aimed at nor suitable for in-situ measurements. In the framework of the European Metrofission project, a work package was dedicated to the realisation of miniature self-calibrated primary TDCR systems, which are state-of-the-art, for use on-site. The challenge was to develop a versatile portable, table-top designed instrument, from this metrology device. This implied improvements for the miniaturisation of the detection chamber, for the miniaturisation of electronic modules by exploring the possibilities of digital treatment, and for the validation of models and extension of them to nuclides with special beta spectrum shapes, to nuclides with complex decay schemes including many gamma-rays and to nuclides with higher atomic number decaying by electron capture. Four prototypes of counters were built by the Metrofission partners ENEA (Italy), LNHB (France), NPL (UK) and PTB (Germany) using various technical approaches. The paper describes these prototypes and provides some details on the choice of the technical options concerning the design of the optical chamber, of the photodetectors and of the acquisition system.

Comparison between two absolute methods used for 177Lu activity measurements and its standardization.

A (177)Lu primary standard was developed at the ENEA-INMRI in the frame of an international comparison organized by BIPM and piloted by NIST (USA). The CIEMAT/NIST method with (3)H standard source as tracer was used for standardizing a solution of (177)Lu. The activity value was compared also with the measurements of the same mother solution carried out by the 4πγ integral counting method. Particular efforts were made to identify and quantify the long-lived (177m)Lu impurity in the mother solution. The results obtained by the two methods are in good agreement within their standard uncertainties. The arithmetic mean of the two values is in good agreement with the Comparison Reference Value (CRV). By the new primary standard two well-type ionization chambers (ICs), one fixed and the other one portable, were calibrated with an uncertainty lower than 2%. These ICs are used for routinely applications in the activity measurements of short-lived radionuclides particularly useful for medical applications.