Pierino De Felice

Fast procedures for coincidence-summing correction in γ-ray spectrometry

Abstract Simplified and fast procedures for coincidence-summing correction in γ-ray spectrometry were investigated. These procedures are based on the usual theoretical expressions of the correction factors, but differ in the determination of the total efficiency curve based on the following approximations: (a) replacement, below the knee efficiency value, of the total efficiency by the full-energy peak efficiency; and (b) use of linear interpolations (in log–log plot) between only two experimental points above the knee efficiency value; or (c) assumption of a peak-to-total efficiency ratio independent on the counting geometry; or (d) assumption of a constant relation between the peak-to-total efficiency ratios and the photoelectric-to-total cross section ratios. The above approximations were separately assumed for determination of the coincidence-summing correction factors for nuclides with complex decay scheme (133Ba, 134Cs, 152Eu) and for 60Co and 88Y measured on a 15% relative efficiency p-type coaxial HPGe detector, for three source-detector geometries: point source placed on top of and at 10 cm from the detector window, and 1 l Marinelli beaker filled with aqueous solution. The results were compared with those based on more accurate experimental determinations of the total efficiency curve from measurements of standard sources of eight different single-γ-ray emitters. The usefulness of each simplified procedure is evaluated with respect to its accuracy and to the reduction of the number of standard sources and measurement time.

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.

Radon gamma-ray spectrometry with YAP:Ce scintillator

The detection properties of a YAP:Ce scintillator (YAlO3:Ce crystal) optically coupled to a Hamamatsu H5784 photomultiplier with standard bialkali photocathode have been analyzed. In particular, the application to radon and radon-daughters gamma-ray spectrometry was investigated. The crystal response has been studied under severe extreme conditions to simulate environments of geophysical interest, particularly those found in geothermal and volcanic areas. Tests in water up to a temperature of 1001C and in acids solutions such as HCl (37%), H2SO4 (48%) and HNO3 (65%) have been performed. The measurements with standard radon sources provided by the National Institute for Metrology of IonizingRadiations (ENEA) have emphasized the non-hyg roscopic properties of the scintillator and a small dependence of the light yield on temperature and HNO3. The data collected in this first step of our research have pointed out that the YAP:Ce scintillator can allow high response stability for radon gamma-ray spectrometry in environments with large temperature gradients and high acid concentrations. r 2002 Elsevier Science B.V. All rights reserved.

(18)F primary standard at ENEA-INMRI by three absolute techniques and calibration of a well-type IG11 ionization chamber.

A new (18)F primary standardization carried out at ENEA-INMRI by three different absolute techniques, i.e. 4πγNaI(Tl)γ high-efficiency counting, TDCR and 4πβ(LS)-γ[NaI(Tl)] coincidence counting method, allowed the calibration of a fixed well-reentrant IG11 ionization chamber (IC), with an uncertainty lower than 1%, and to check the calibration factor of a portable well-type IC NPL-CRC model, previously calibrated. By the new standard the ENEA-INMRI was linked to the BIPM International Reference System (SIR) through the BIPM SIR Transfer Instrument (SIRTI).

14 MeV Neutrons for 99Mo/99mTc Production: Experiments, Simulations and Perspectives

Background: the gamma-emitting radionuclide Technetium-99m (99mTc) is still the workhorse of Single Photon Emission Computed Tomography (SPECT) as it is used worldwide for the diagnosis of a variety of phatological conditions. 99mTc is obtained from 99Mo/99mTc generators as pertechnetate ion, which is the ubiquitous starting material for the preparation of 99mTc radiopharmaceuticals. 99Mo in such generators is currently produced in nuclear fission reactors as a by-product of 235U fission. Here we investigated an alternative route for the production of 99Mo by irradiating a natural metallic molybdenum powder using a 14-MeV accelerator-driven neutron source. Methods: after irradiation, an efficient isolation and purification of the final 99mTc-pertechnetate was carried out by means of solvent extraction. Monte Carlo simulations allowed reliable predictions of 99Mo production rates for a newly designed 14-MeV neutron source (New Sorgentina Fusion Source). Results: in traceable metrological conditions, a level of radionuclidic purity consistent with accepted pharmaceutical quality standards, was achieved. Conclusions: we showed that this source, featuring a nominal neutron emission rate of about 1015 s−1, may potentially supply an appreciable fraction of the current 99Mo global demand. This study highlights that a robust and viable solution, alternative to nuclear fission reactors, can be accomplished to secure the long-term supply of 99Mo.

A national campaign for coincidence-summing correction in γ-ray spectrometry

A national campaign was carried out in Italy for the application of coincidence-summing correction in gamma-ray spectrometry. Twelve laboratories, belonging to the National Environmental Radioactivity Surveillance Network, took part in the campaign. They are equipped with gamma-ray spectrometry systems based on p- and n-type HPGe detectors with different relative efficiencies. A simplified procedure was used for coincidence-summing correction. This procedure requires a single-photon, single-nuclide source to measure the peak-to-total efficiency ratio at just one photon energy value. All the laboratories were given a 137Cs standard source for total efficiency determination, and a 134Cs source in the same geometry whose activity they had to determine. The results show the usefulness of the procedure. The average deviation of all the laboratory results from the ENEA-INMRI reference value was reduced from -12% before correction to +1% after correction. The paper gives a description of the different organisational aspects of the campaign, reports the results obtained and draws conclusions in which the gain in measurement accuracy is evaluated in the light of the effort required for each participant to perform the correction.

Half-life determination of 125I

Abstract The half-life of 125I was determined by measuring the activity of an initial 3 kBq source at several times. Over a period of two months, 96 absolute measurements were performed, using the sum-peak method to give a half-life of (59.38±0.03) d. A discussion is presented on the effect of correcting for accidental coincidences on the half-life measurements by comparing the results with and without this correction.

Evaluation of the radon interference on the performance of the portable monitoring air pump for radioactive aerosols (MARE)

A compact portable aerosol sampling and measurement device was developed at Jožef Stefan Institute (JSI). A CeBr3 scintillation detector is positioned centrally within a concertinaed filter assembly. It provides continuous and via network communications on-line monitoring of low levels of airborne radioactive particulates. The evaluation of the response of the device to the natural background at controlled conditions with elevated radon concentrations, performed at the National Institute of Ionizing Radiation Metrology of ENEA, is presented.

Recent results (1986–1989) on the ENEA quality assurance programme for the radioactivity surveillance network in Italy

A programme for the Quality Assurance of the Italian network for surveillance of radioactivity in foodstuff and environmental samples was started by the ENEA in 1983. The main purpose of this programme is to establish uniform levels of accuracy and reproducibility in measurement procedures routinely used by the laboratories belonging to the network. This paper describes the technical aspects relevant to the calibration and intercomparison campaigns carried out, in Italy, in the period 1986-1989. The relevant measurements include gamma spectrometry and beta-ray counting in liquid aqueous samples.