P. De Felice

Laboratory application of NaI(Tl) γ-ray spectrometry to studies of natural radioactivity in geophysics

We implemented a laboratory apparatus based on a NaI(TI) gamma-ray spectrometer for the assessment of naturally occurring radioactive materials. This apparatus is devoted to the quantitative determination of U, Th and K in rock and soil samples. We analysed the calibration procedures with particular emphasis to factors which affect accuracy and detection limits. A first series of measurements were compared to those obtained by means of high energy gamma-ray spectrometry. A discussion was made on factors restricting the approach based on scintillation spectrometry, such as secular equilibrium and radon encapsulation.

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.

Comparison of activity concentration measurement of 63Ni and 55Fe in the framework of the EUROMET 297 project

Abstract Eleven laboratories participated in an intercomparison of activity concentration measurements using liquid scintillation counting (LSC) for the standardization of 63Ni and 55Fe in the frame of the EUROMET project No. 297 and under the co-ordination of LPRI. The purpose of this action was to compare the main LSC activity concentration measurement methods currently used in radioactive metrology, and to exchange models and ideas on LSC. This paper presents a summary of the results reported by the participant laboratories and an overview of the measurement methods used.

Practical applicability of field γ-ray scintillation spectrometry in geophysical surveys

Abstract We discuss the problems and calibration procedures for a portable γ-ray scintillation spectrometer for determinations of potassium, uranium and thorium concentration in rocks. Particular emphasis was given to the evaluation of the background radiation. The apparatus was tested in the field at two selected areas in NW Italy. We found appropriate sites which could be used as reference targets to frequently check the γ-ray equipment. An area formed by serpentinitic rocks showed such a low measured radioactivity that it could be used as a reference for the local background effect. An anomalously high uranium amount against negligible potassium and thorium concentrations were found in outcrops of dolomitic rocks, which can be used to detect possible changes in the instrument calibration constants.

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.

The 222Rn Reference Measurement System developed at ENEA

Abstract A 222 Rn Reference Measurement System was recently developed at ENEA. The system is based on a radon transfer and counting system calibrated by a 226 Ra standard liquid solution. The reference counting instrument is a cylindrical electrostatic cell with a Si detector. It is used for the detection of the electrostatically collected 218 Po ions produced in the decay of 222 Rn. The activity of 222 Rn gas in a spherical glass bulb can be measured in the Reference Measurement System by a particular procedure that does not require volume determinations or any assumption of total radon removal from the liquid 226 Ra solution. The combined uncertainty estimated for the calibration of 222 Rn sources as in a typical gas transfer system is about 1% (one standard deviation). The Reference Measurement System and the operational procedure adopted by ENEA are described together with a short outline of the transfer instrument based on a NaI(Tl) well-type detector used for calibration purposes.

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.

Correction for radon distribution in solid/liquid and air phases in gamma-ray spectrometry.

The effect of radon diffusion and distribution between a (226)Ra matrix and the top air gap inside sample containers for gamma-ray spectrometry was studied. Containers filled at almost 100% or just 70% of total capacity yielded correction factors of about 7% and 20% respectively. Applying these correction factors allowed activity values calculated from (226)Ra or radon decay products to agree within 2%.

Field γ-ray spectrometry on the Vulcano island (Aeolian Arc, Italy)

Abstract In situ NaI(Tl) γ-ray spectrometric measurements on the Vulcano island show that the magmatic evolution of the main structural units is reflected by the uranium, thorium and potassium concentrations. The results allowed us to delineate two temporal and radiometric districts. The older district comprises lava flows and pyroclastics of mafic composition forming the whole southern part of the island, with an equivalent uranium concentration and an eTh/eU ratio ranging, on average, from 2.9 to 3.4 ppm and from 2.4 to 4.1, respectively. Rocks of the younger district, ranging from leucitic tephritic and trachytic to rhyolitic composition, show higher K contents (about 6%) and more variable eTh/eU ratios (2.4–6.1).

Homogeneity testing of spiked reference materials

As part of a EUROMET project to produce a range of γ-ray emitting radioactive spiked reference materials, a technique, based on analysis of variance, was developed to evaluate the uncertainties in characterising such materials. A particular concern was to ensure that users of these materials are properly informed regarding the consequences of any remaining inhomogeneities in them. A minimum of five random samples of each reference material were counted six times on a suitable γ-ray spectrometer. Once all of the data were collected and normalised, between-sample (MS BS ) and within-sample (MS WS ) variances were calculated. The quantity MS WS includes factors associated with sample measurement such as counting statistics, background stability, detector response stability, source-to-detector geometry and electronic stability. The quantity MS BS includes not only all of the terms in MS WS , but also includes terms for sample inhomogeneity, mass determination and density determination. These quantities enable the following calculation to be performed ; σ mat 2 = σ tot 2 - σ meas 2 where σ tot is the overall uncertainty, σ meas is the measurement uncertainty and σ mat is the uncertainty arising from sample inhomogeneity ; it is assumed here that the effects arising from mass and density determinations are negligible. The value of σ mat is only valid at the sample weight at which it was measured, and data are presented to show the variation of the uncertainty arising from sample inhomogeneity with changing sample weight.