Standardization of (68)Ge/(68)Ga Using Three Liquid Scintillation Counting Based Methods.

A solution containing (68)Ge in equilibrium with its daughter, (68)Ga, has been standardized for the first time at the National Institute of Standards and Technology (NIST) using 3 liquid scintillation-based techniques: live-timed 4πß -γ anticoincidence (LTAC) counting, the Triple-to-Double Coincidence Ratio (TDCR) method, and (3)H-standard efficiency tracing with the CIEMAT(1)/NIST (CNET) method. The LTAC technique is much less dependent on level scheme data and model-dependent parameters and was thus able to provide a reference activity concentration value for the master solution with a combined standard uncertainty of about 0.3 %. The other two methods gave activity concentration values with respective differences from the reference value of +1.2 % and -1.5 %, which were still within the experimental uncertainties. Measurements made on the NIST "4π"γ secondary standard ionization chamber allowed for the determination of calibration factors for that instrument, allowing future calibrations to be made for (68)Ge/(68)Ga without the need for a primary measurement. The ability to produce standardized solutions of (68)Ge presents opportunities for the development of a number of NIST-traceable calibration sources with very low (<1 %) relative standard uncertainties that can be used in diagnostic medical imaging.

Measurement of absolute K X-ray emission intensities in the decay of 103mRh.

A new experiment was designed to measure the photon emission intensities in the decay of 103mRh. The rhodium samples were activated in the ISIS experimental nuclear reactor at CEA Saclay. The procedure includes an absolute activity measurement by liquid scintillation counting using the Triple-to-Double Coincidence Ratio method, followed by X-ray spectrometry using a high-purity germanium detector to determine the photon emission intensities. The new result (IX = 0.0825 (17)) is derived with a significant reduction of the uncertainty.

68Ga activity calibrations for nuclear medicine applications in Cuba.

The realization and dissemination of the 68Ga activity measurement unit in Cuba is presented. Firstly, the implementation of the Triple to Double Coincidence Ratio (TDCR) method is described for the calibration of the activity concentration of a 68Ga solution using a Hidex™ commercial liquid scintillation counter and a FORTRAN code developed for the calculation of the 68Ga counting efficiencies in the given measurement system. The relative expanded uncertainty (k = 2) associated with the 68Ga activity concentration obtained with the TDCR method is equal to 2%. With the aim to validate this measurement uncertainty estimate, the method is also applied to an Amersham standard solution of 22Na - a positron emitter with a similar decay mode to the 68Ga disintegration scheme from the point of view of type of emitted particles detected in the measurement system. The observed difference between the measured 22Na activity concentration by the TDCR method and the corresponding reference value traceable to NIST is equal to 0.16%. Outcomes of transferring the 68Ga activity standard, realized with the TDCR method, to the secondary standard radionuclide calibrator Capintec CRC™ 15R and to three radionuclide calibrators used for 68Ga PET applications in a hospital are also shown.

A new 4π(LS)-γ coincidence counter at NCBJ RC POLATOM with TDCR detector in the beta channel.

A new 4π(LS)-γ coincidence system (TDCRG) was built at the NCBJ RC POLATOM. The counter consists of a TDCR detector in the beta channel and scintillation detector with NaI(Tl) crystal in the gamma channel. The system is equipped with a digital board with FPGA, which records and analyses coincidences in the TDCR detector and coincidences between the beta and gamma channels. The characteristics of the system and a scheme of the FPGA implementation with behavioral simulation are given. The TDCRG counter was validated by activity measurements on (14)C and (60)Co solutions standardized in RC POLATOM using previously validated methods.

Method for rapid screening analysis of Sr-90 in edible plant samples collected near Fukushima, Japan.

A screening method for measuring (90)Sr in edible plant samples by focusing on (90)Y in equilibrium with (90)Sr is reported. (90)Y was extracted from samples with acid, co-precipitated with iron hydroxide, and precipitated with oxalic acid. The dissolved oxalate precipitate was loaded on an extraction chromatography resin, and the (90)Y-enriched eluate was analyzed by Cherenkov counting with a TDCR liquid scintillation counter. (90)Sr ((90)Y) concentration was determined in plant samples collected near the damaged Fukushima Daiichi Nuclear Power Plants with this method.

Primary standardization of SIR-Spheres based on the dissolution of the (90)Y-labeled resin microspheres.

The project "Metrology for molecular radiotherapy" is a collaborative European project initiated to bring together expertize in ionizing radiation metrology and nuclear medicine research. This project deals with the development of personalized dosimetry to individual patients who are undergoing molecular radiotherapy (also known as targeted radionuclide therapy). The general aim is to provide a metrological traceability to primary standards for individual dosimetry in the case of molecular radiotherapy. In particular, one objective is the standardization of (90)Y-labeled resin microspheres SIR-Spheres (Sirtex, Sydney, Australia) used for the treatment of liver cancer by radioembolization. The present paper describes the primary measurements carried out using the Triple to Double Coincidence Ratio (TDCR) method applied after the complete dissolution of the SIR-Spheres in the Sirtex vial. A method for the dissolution was developed to optimize the homogeneity of the solution to enable the primary measurements based on Cherenkov and liquid scintillation counting. A comprehensive description of the protocol implemented for the microsphere dissolution is reported. First calibration factors obtained with the reference ionization chambers at LNE-LNHB are also given.

A full digital approach to the TDCR method.

Current state of the art solutions based on the Triple to Double Coincidence Ratio method are generally large size, heavy-weight and not transportable systems. This is due, on one side, to large detectors and scintillation chambers and, on the other, to bulky analog electronics for data acquisition. CAEN developed a new, full digital approach to TDCR technique based on a portable, stand-alone, high-speed multichannel digitizer, on-board Digital Pulse Processing and dedicated DAQ software that emulates the well-known MAC3 analog board.

First TDCR measurements at low energies using a miniature x-ray tube.

Developed for radionuclide standardization using liquid scintillation, the Triple to Double Coincidence Ratio (TDCR) method is applied using coincidence counting obtained with a specific three-photomultiplier system. For activity determination, a statistical model of light emission is classically used to establish a relation between the detection efficiency and the experimental TDCR value. At LNE-LNHB, a stochastic approach of the TDCR modeling was developed using the Monte Carlo code Geant4. The interest of this TDCR-Geant4 model is the possibility to simulate the propagation of optical photons from their creation in the scintillation vial to the production of photoelectrons in photomultipliers. As an alternative to the use of radionuclide sources, first TDCR measurements are presented using a miniature x-ray tube closely coupled to the scintillation vial. The objective of this new set-up was to enable low-energy depositions (lower than 20 keV) in liquid scintillator in order to study the influence of both time and geometrical dependence between PMTs already observed with radioactive sources. As for the statistical TDCR model, the non-linearity of light emission is implemented in the TDCR-Geant4 model using the Birks formula which depends on the kB factor and the scintillation yield. Measurements performed with the x-ray tube are extended to the assessment of these parameters and they are tested afterwards in the TDCR-Geant4 model for activity measurements of (3)H.

Activity standardization of ¹³4Cs and ¹³7Cs.

The paper presents the results from a primary standardization of (137)Cs using two independent methods - efficiency tracing using PC-NaI coincidence and the TDCR method. The nuclides (60)Co and (134)Cs were used as the tracers. Primary standardization of the (134)Cs is also discussed. The efficiency extrapolation was carried out by measuring samples of varying mass and using the wet extrapolation method. The results obtained are in good agreement; the differences did not exceed 0.5%. The advantages, pitfalls and also possibilities for improvement of the procedures are discussed.