Calibration of Fe activity with a lithium-drifted silicon detector

NMIJ participated in the CCRI (II) key comparison of ⁵⁵Fe activity measurement. A planar-type Si(Li) detector and a liquid-scintillation counter were used to calibrate the activity. The calibration result obtained by the Si(Li) detector agreed with that obtained by the liquid-scintillation counter using the CIEMAT/NIST method within uncertainty. The result was reported to the BIPM in 2006. The activity of ⁵⁵Fe was also measured by using a 2π pressurized proportional counter. The result obtained by the 2π pressurized proportional counter agreed with the above results within uncertainty. The measurement by the Si(Li) detector was very simple and its procedure was a combination of conventional methods. The measurement by the liquid-scintillation counter is most popular to calibrate the activity of ⁵⁵Fe. However the Si(Li) detector is also useful.     

Calibration of a radionuclide calibrator system as a Bulgarian standard for activity

A commercially available radionuclide calibrator of the type Curiementor 3 (PTW, Freiburg, Germany) was calibrated using activity standard solutions, from the Physikalisch-Technische Bundesanstalt (PTB), of a number of photon-emitting radionuclides, in particular those used in nuclear medicine: ¹⁸F, ⁵¹Cr, ⁶⁷Ga, ^99mTc, ¹¹¹In, ¹²³I, ¹²⁵I, ¹³¹I, ¹⁸⁶Re, ²⁰¹Tl, and for beta-emitting nuclides: ³²P, ⁸⁹Sr, ⁹⁰Y, ²⁰⁴Tl. An energy-dependent efficiency curve was established to calculate efficiencies for photon-emitting radionuclides. The differences between experimental and calculated radionuclide efficiencies of the measuring system are of the order of a few percent. The performance of the system was checked for instrument stability, using a long-lived ¹³⁷Cs source, and for linearity using the decay of a ^99mTc source. The calibration measurements were carried out with 2 g of solution in standard PTB-type glass ampoules. The dependence of efficiency with varying solution mass and changing ampoule geometry is studied for some of the radionuclides. For example, geometry correction factors are determined for various solution volumes or ampoules with different wall thickness. The measuring system will enable the National Centre of Metrology (NCM) of Bulgaria to provide calibration services for activity measurements, which are traceable to PTB standards, and to organize national comparisons in order to improve the quality of measurements for nuclear medicine in Bulgarian hospitals. Furthermore, it should enable NCM to declare Calibration and Measurement Capabilities (CMCs) and to submit radioactive solutions to the International Reference System (SIR) at the BIPM in order to compare the results with Key Comparison Reference Values (KCRVs).     

Measurement of Fe solution activity by LSC-TDCR method

A solution of ⁵⁵Fe was measured by using liquid scintillation counting (LSC)-TDCR method. The measurement was performed within the frame of the CIPM CCRI(II)-K2.Fe-55 comparison during the year 2006. Two computation codes were used for the calculation of detection efficiency, the difference between the results being analyzed. The photomultipliers asymmetry and its influence on the results, as well as the long-term stability are also analyzed. The influence of the variation of kB value over the activity value is compared with the case of ³H standardization.     

An inter-laboratory comparison of low-level measurements in ground-level aerosol monitoring

After the nuclear reactor accident of Chernobyl, the “Integrated Measurement and Information System (IMIS) for Monitoring the Environmental Radioactivity and Detecting Emissions from Nuclear Plants was implemented in Germany. IMIS is a nationwide comprehensive measuring system which permanently monitors the radioactivity in all important environment media in the whole federal territory. At approximately 40 sites, the activity concentration of radioactive substances is measured in air and precipitations. At least 14 of them are responsible for trace monitoring of radionuclides in the air. The legal bases of IMIS prescribe regular inter-laboratory comparison analyses in cooperation with the Physikalisch-Technische Bundesanstalt (PTB), with the use of reference materials prepared by the Federal Coordinating Laboratories. In order to fulfil this requirement in the field of trace survey measurements in ground-level air, the Federal Office for Radiation Protection (“Bundesamt für Strahlenschutz”, BfS) and the PTB have conducted a comparison with real, dust-loaded reference filters in 2005. The comparison was organized within the framework of a cooperation of trace survey stations from Austria, Germany and Switzerland. The paper describes the preparation of the real, dust-loaded reference filters, the procedure for spiking the filters with the activity standard solution containing ²²Na, ⁸⁸Y, ⁸⁹Sr, ⁹⁰Sr, ¹²⁵Sb, ¹³³Ba, ¹³⁴Cs, and ²⁴¹Am. Some results are discussed and conclusions are given.     

Quantification aspects of patient studies with Fe in positron emission tomography

Quantification accuracy in positron emission tomography (PET) using non-pure positron emitters, such as ⁵²Fe, may be influenced by gamma radiation emitted in the decay of these isotopes. High-energy positrons, emitted in the decay of the ⁵²Fe-daughter ^52mMn, also affect the quantification accuracy. A specific problem of the ⁵²Fe/^52mMn decay chain in vivo is that the kinetics of iron and manganese are different, and that PET cannot discriminate between the two nuclides. The effect of the decay properties of ⁵²Fe/^52mMn on the performance of PET was investigated using phantoms. Minor degradation in PET performance was found for ⁵²Fe/^52mMn compared to the pure low-energy positron emitter ¹⁸F. A method is presented to obtain a correction factor for the ^52mMn radioactivity in blood. A model for correction of ^52mMn-radioactivity in organs, based on existing data on manganese kinetics, is given. The presented corrections are discussed and illustrated in a patient study.     

The absolute counting of 125I

The Institute of Nuclear Energy Research (INER) participated in a comparison of activity organized by the Electrotechnical Laboratory (ETL, Japan). At this occasion, ¹²⁵I was measured. Seven laboratories of the Asia Pacific region carried out measurements and ETL, at the same time, took part in BIPM SIR measurements. Two measurement methods developed by INER, the sum-peak coincidence counting with two 76×76 mm NaI(Tl) detectors and the 4πe-X coincidence counting technique with efficiency extrapolation, were used to standardize the activity of ¹²⁵I. The results from the two methods are 2.6% different. INER's results agree with the results of the regional comparison and the BIPM SIR.     

Standardization of Fe by tracing method

This work describes the procedure followed by the Laboratório de Metrologia Nuclear (LMN) for the standardization of ⁵⁵Fe by the tracing method. This technique was applied using two radionuclides, which decay by the electron capture process followed by a prompt gamma-ray, namely ⁵¹Cr and ⁵⁴Mn, as tracers. The calibration was performed in a 4πβ–γ coincidence system. The efficiency was obtained by selecting a gamma-ray window set at the 320 keV total absorption peak for ⁵¹Cr and at 834 keV for ⁵⁴Mn.     

A new TDCR-LS Counter using Channel photomultiplier tubes

A new Triple to Double Coincidence Ratio (TDCR) liquid scintillation (LS) counter using recently available photodetectors, the Channel photomultiplier (CPM) tubes, was constructed and tested in the framework of a scientific cooperation between IFIN-HH and LNHB. The prototype LS counter uses 3CPM tubes arranged symmetrically in an optical chamber around a standard LS vial. The behavior of the prototype was first evaluated with a light emitting diode (LED) light pulser. The counter was then compared against a TDCR counter using conventional photomultiplier tubes, by measuring ⁵⁵Fe, ³H, ⁶³Ni and ⁹⁰Sr/⁹⁰Y LS sources prepared in commercial liquid scintillation cocktails. Although the observed detection efficiency was significantly lower than the one achieved with the traditional counter, we found a remarkable agreement on the activity determination using the two counters. Details on the prototype and the measurement results obtained are discussed in this paper.     

Purification and activity standardisation of a Ho solution

As part of a project to use the long-lived (T_1/2=1200a) ^166mHo as reference source in its reference ionisation chamber, IRA standardised a commercially acquired solution of this nuclide using the 4πβ–γ coincidence and 4πγ (NaI) methods. The ^166mHo solution supplied by Isotope Product Laboratories was measured to have about 5% Europium impurities (3% ¹⁵⁴Eu, 0.94% ¹⁵²Eu and 0.9% ¹⁵⁵Eu). Holmium had therefore to be separated from europium, and this was carried out by means of ion-exchange chromatography. The holmium fractions were collected without europium contamination: 162 h long HPGe gamma measurements indicated no europium impurity (detection limits of 0.01% for ¹⁵²Eu and ¹⁵⁴Eu, and 0.03% for ¹⁵⁵Eu). The primary measurement of the purified ^166mHo solution with the 4π (PC) β–γ coincidence technique was carried out at three gamma energy settings: a window around the 184.4 keV peak and gamma thresholds at 121.8 and 637.3 keV. The results show very good self-consistency, and the activity concentration of the solution was evaluated to be 45.640±0.098 kBq/g (0.21% with k=1). The activity concentration of this solution was also measured by integral counting with a well-type 5″×5″ NaI(Tl) detector and efficiencies computed by Monte Carlo simulations using the GEANT code. These measurements were mutually consistent, while the resulting weighted average of the 4π NaI(Tl) method was found to agree within 0.15% with the result of the 4πβ–γ coincidence technique. An ampoule of this solution and the measured value of the concentration were submitted to the BIPM as a contribution to the Système International de Référence.     

Application of X-ray fluorescence spectrometry in multielement analysis of rubber samples

Elemental analysis of rubber samples is rather difficult, but XRF spectrometry offers some advantages relative to other more popular chemical instrumental techniques due to relatively simple sample preparation. For the excitation annular radionuclide photon sources of ⁵⁵Fe and ¹⁰⁹Cd were used. The analyses of metal content in samples of natural latex have been performed in order to investigate the relation between the low specific resistivity of the latex and the respective metal content. The results are presented and discussed.     

Absolute activity of (133)Ba by liquid scintillation coincidence counting using the 4pi(e,X)-gamma extrapolation technique.

The Technical Committee for Ionizing Radiation (TCRI) of the Asia Pacific Metrology Programme (APMP) recently organized a regional key comparison of activity measurements of the radionuclide ¹³³Ba. This paper reports on absolute measurements made at the National Metrology Institute of South Africa (NMISA) by the coincidence extrapolation technique, with liquid scintillation counting (LSC) comprising the 4π channel. A detection efficiency analysis was undertaken to predict the maximum efficiency likely to be achieved and to confirm that the method does indeed provide the source disintegration rate for ¹³³Ba. Various experimental and data analysis difficulties to be aware of are discussed in the paper.     

CCD saturation in high-background environments

Charge-coupled devices (CCDs) are nowadays preferred X-ray detectors in environments with high-background radiation. The maximum number of X-ray counts per exposure in a CCD-detector is limited by saturation. The simulation of this effect reproduces well the measurements with a ⁵⁵Fe source. In an accelerator area, where a large amount of charged particles is present, a strong reduction of X-ray recognition efficiency with increasing occupancy (percentage of hit pixels) is observed which depends only weakly on the specific distribution of cluster sizes.     

Activity standardization of Na

The activity of a ²²Na solution was measured by means of two 4πβ−γ coincidence-counting techniques. The first method corresponds to the classical 4πβ−γ coincidence counting and requires the β⁺-branching ratio. The second procedure is based on a variation of the distance between source and gamma detector. The efficiency for detecting the sum peak is then extrapolated to zero, giving the total source activity. The combination of both methods yields the β⁺ branching ratio. In addition, liquid scintillation counting using the CIEMAT/NIST-method as well as a secondary standardization by means of calibrated ionization chambers were used for activity determination. The results were checked for consistency and an ampoule was submitted to the BIPM to have the activity result entered into the database of the International Reference System (SIR).     

Results from APMP comparisons on radioactivity measurements of 58Co, 88Y and 166mHo.

International comparisons on radioactivity measurements of 55Co, 88Y and 166mHo were carried out within the framework of the Asia-Pacific Metrology Programme. Radioactive sources were also sent to the International Reference System (SIR) at the Bureau International des Poids et Mesures (BIPM) in order to link the results of these regional comparisons to the BIPM key comparison-reference values. The arithmetic mean for the activity results of 166mHo was in good agreement with the SIR reference value, but some disagreements were found for 58Co and 88Y results. The mean values for 58Co and 88Y were both higher than the existing SIR values by about 1.5% and 0.9%, respectively. Although there were some disagreements, it was successfully demonstrated that these regional comparisons could be linked to other international key comparisons through the SIR. The present results were also evaluated to estimate a reasonable uncertainty level for each laboratory, which is very important in the establishment of an adequate traceability scheme for radioactivity standards.     

Absolute activity measurement of the electron-capture-based radionuclides 139Ce, 125I, 192Ir and 65Zn by liquid scintillation coincidence counting.

Four radionuclides with electron-capture-based decay schemes have been directly measured by a liquid scintillation coincidence extrapolation technique. 125I, 192Ir and 65Zn were measured as part of international key comparisons held under the auspices of the International Bureau of Weights and Measures (BIPM). The 139Ce measurements formed part of a regional comparison organized by the Asia Pacific Metrology Programme (APMP). Since 139Ce decays purely by electron-capture, the basic method is described for this radionuclide. Results and difficulties encountered are discussed and uncertainty budgets are presented.     

Implementation of CIEMAT/NIST LSC efficiency tracing method in KRISS: T1 standardization

The CIEMAT/NIST efficiency tracing method has been widely used for radionuclide standardization. The method consists of the theoretical calculations of counting efficiencies and the experimental data obtained from a commercially available double photomultiplier detector. We have recently implemented the technique using ³H as a tracer. Our implementation of the method was validated by participating into an international comparison of activity measurements of a solution of ²⁰⁴T1. We report in this paper the procedure employed to implement the technique and compare our measurement result of ²⁰⁴T1 activity with that of the international comparison.     

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.     

Comparisons of activity measurements with radionuclide calibrators

The correct administration to a patient of the prescribed activity of a radiopharmaceutical is an important factor to ensure the confidence in the diagnosis or the therapeutic efficiency, while at the same time keeping the unnecessary human exposure as low as possible.

Comparisons of activity measurements for ¹³¹I, ²⁰¹Tl and ^99mTc with radionuclide calibrators were organized the first time in Cuba during 2002 with the aim of obtaining information about the quality of administration of radiopharmaceuticals. Ten Cuban nuclear medicine departments and the laboratories involved in the production of these kinds of compounds participated in the comparison runs. The results presented in this paper facilitated the identification of several problems and initiated corrective actions. In addition, they indicate the necessity of establishing Quality Systems in nuclear medicine in Cuba.     

Proficiency tests in the determination of activity of radionuclides in radiopharmaceutical products measured by nuclear medicine services in 8 years of comparison programmes in Brazil

Proficiency tests were applied to assess the performance of 74 nuclear medicine services in activity measurements of ¹³¹I, ¹²³I, ⁹⁹Tc^m, ⁶⁷Ga and ²⁰¹Tl. These tests produced 913 data sets from comparison programmes promoted by the National Laboratory for Ionizing Radiation Metrology (LNMRI) from 1999 to 2006.

The data were evaluated against acceptance criteria for accuracy and precision and assigned as Acceptable or Not acceptable accordingly. In addition, three other statistical parameters were used as complementary information for performance evaluation which related to normative requirements and to radionuclide calibrators.

The results have shown a necessity to improve quality control procedures and unsatisfactory performances of radionuclide calibrators, which incorporate Geiger–Müller detectors.