Measurement of the activity and determination of the half-life of 225Ac at POLATOM.

A method for absolute measurements of the 225Ac activity in equilibrium with its progeny was developed. Measurements were performed using the triple-to-double coincidence ratio (TDCR) method in two different TDCR counters. The activity concentration of an 225Ac solution was determined and the solution was sent to the SIR system for a comparison. The half-life of 225Ac was determined by one of the TDCR counters and found to be 9.9150(63) days.

Comparison of digital coincidence modules used at POLATOM and PTB for TDCR and 4πß(LS)-γ coincidence counters.

Activity measurements of 3H, 241Am and 60Co solutions were performed to compare digital coincidence modules used at PTB and POLATOM for TDCR and 4πß(LS)-γ coincidence counting. The activities determined with various coincidence modules connected in parallel to the same counter at PTB were found to be consistent. Observed discrepancies caused by differences in the coincidence resolving time did not exceed 0.14%. Accidental coincidences simulated by a frequency generator were registered, and the coincidence resolving time was determined.

A new coincidence module using pulse-mixing method applied in the 4π(LS)-γ coincidence system with TDCR detector.

Application of a new coincidence module using the pulse-mixing method in the 4π(LS)-γ coincidence system with TDCR detector in the beta channel (TDCRG) is presented. The pulse-mixing method extended for the TDCR system with gamma channel was compared with the classical coincidence method where the coincidence resolving time is introduced. The characteristics of the resolving and dead time of the above two methods were investigated. The level of accidental coincidences in the system was determined. The new developed coincidence module was validated by activity measurement of a set of 51Cr, 54Mn, 60Co, 65Zn, 85Sr and 134Cs standards.

Preparation method and quality control of multigamma volume sources with different matrices.

The aim of the work was to develop new radioactive standard sources based on epoxy resins. The optimal proportions of the components and the homogeneity of the matrices were determined. The activity of multigamma sources prepared in Marinelli beakers was determined with reference to the National Standard of Radionuclides Activity in Poland. The difference of radionuclides activity values determined using calibrated gamma spectrometer and the activity of standard solutions used are in most cases significantly lower than measurement uncertainty limits. Sources production method and quality control procedure have been developed.

Comparison of 131I activity measurements at the NCBJ RC POLATOM and the ENEA-INMRI linked to the BIPM SIR system.

A bilateral comparison between ENEA-INMRI (Italy) and NCBJ RC POLATOM (Poland) of 131I-solution activity measurements was organized in the year 2015 and piloted by POLATOM, which provided the sources for the comparison. The 131I master solution was standardized independently at both institutes by using Liquid Scintillation Counting and ionization chamber techniques. The 131I master solution was then sent by POLATOM to the BIPM International Reference System (SIR). The comparison was registered as an EURAMET.RI(II)-K2.I-131 key comparison allowing the ENEA-INMRI result to enter in the SIR database.

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.

Standardization of Sm-153 solution by absolute methods.

Standardization of (153)Sm by 4π(LS)-γ coincidence and anticoincidence counting and the CIEMAT/NIST method in three LS-counters is presented. This short half-life radionuclide is applied in tumor therapy and bone pain palliation. A simplified disintegration scheme of (153)Sm was applied in the calculation of the counting efficiency. Standard uncertainties of 0.4% for the (153)Sm measurements by the 4π(LS)-γ coincidence and anticoincidence techniques and 0.7% by the C/N method were evaluated, respectively. An agreement of the standardization results by both methods within the respective uncertainties was obtained. The half-life of (153)Sm of (1.92895±0.00024) days was determined during one month of measurements and correction for europium isotope impurities by the C/N method in the TriCarb 2910 LS-counter.

Standardization of a 85Sr solution by three methods.

A (85)Sr solution was measured in two liquid scintillation (LS) counters. Scintillation pulses from the delayed transitions in the (85)Sr decay were by and large lost as the dead time of the LS-counter was much longer than the lifetime of the (85)Rb excited level. The registration probability of these pulses has been defined and introduced into the counting efficiency calculation. The results of the (85)Sr solution standardization by the CIEMAT/NIST and the TDCR methods relative to the results from the 4π(LS)-γ coincidence and anticoincidence method were 0.997±0.012 and 0.971±0.019, respectively.

Comparison of triple-to-double coincidence ratio (TDCR) efficiency calculations and uncertainty assessments for 99Tc.

A comparison exercise for data analysis was recently conducted by the Liquid Scintillation Counting Working Group (LSCWG) of the International Committee on Radionuclide Metrology (ICRM) to evaluate the uncertainties involved in applying different analysis methodologies (including computer programs) for the triple-to-double coincidence ratio (TDCR) method. The goals of the comparison were to (1) study differences in calculation results from different TDCR analysis programs, (2) investigate differences in analysis techniques and uncertainty assessment philosophies between laboratories, and (3) study the effect of not taking asymmetry of photomultiplier tube (PMT) efficiencies into account on the calculated activity. To achieve this, a single set of TDCR data for the pure beta emitter (99)Tc, was distributed to the participants, who analyzed the data according to their normal procedures and report the activity concentration of the (99)Tc solution from their results. The results indicate that the presently used programs are generally able to calculate the same activity values, assuming that the correct input parameters are used and that not taking PMT asymmetry into account in the calculations can lead to significant (0.6% for (99)Tc) errors in reported results. The comparison also highlighted the need for a more rigorous approach to estimating and reporting uncertainties.

Comparison of 99Tcm and 131I in Polish hospitals, 2007.

The Radioisotope Centre (RC) has organized for the first time in Polish hospitals a comparison of activity measurements of (99)Tc(m) and (131)I. From the 58 Polish hospitals invited, 37 participated in the comparison. Each participant got about 4 mL of (99)Tc(m) eluate and two (131)I capsules, low- and high-activity. Sources were standardized in the RC before dispatch using a 4pi ionization chamber calibrated by standard solutions. Participants used their own radionuclide calibrators. The measurement results were evaluated using the E(n) criterion and the z'-score. From all 118 measurement results received from participants, 75 results (64%) lay within +/-5% of the RC value, and 99 results (84%) lay within +/-10.0%.

Lifetime measurements of the neutron-rich N = 30 isotones 50Ca and 51Sc: orbital dependence of effective charges in the fp shell.

The lifetimes of the first excited states of the N = 30 isotones (50)Ca and (51)Sc have been determined using the Recoil Distance Doppler Shift method in combination with the CLARA-PRISMA spectrometers. This is the first time such a method is applied to measure lifetimes of neutron-rich nuclei populated via a multinucleon transfer reaction. This extends the lifetime knowledge beyond the f_{7/2} shell closure and allows us to derive the effective proton and neutron charges in the fp shell near the doubly magic nucleus (48)Ca, using large-scale, shell-model calculations. These results indicate an orbital dependence of the core polarization along the fp shell.

Some remarks on photons statistics in the LS-counter.

The available experimental data relating to processes in the liquid scintillation (LS) detector that lead to fluorescence have been analysed and the evaluated number of photons created are given. The evaluated global distribution of photons emitted from the LS-vial in the case of low-energy emitters is presented. The global distribution of photons is well fitted by the Polya distribution.

The IFIN-HH triple coincidence liquid scintillation counter.

The paper summarizes the IFIN-HH triple coincidence liquid scintillation counter used for the implementation of the TDCR method. The electronic unit was recently extended to record the three individual double coincidence ratios to take into account the differences in the quantum efficiencies of the three-photomultiplier tubes. Some details of the electronic system and the data processing are given. The critical point of a TDCR counter is to adjust correctly the discriminator levels on the three channels under the single electron peak. The paper describes the method of adjustment based on the evolution of the dark counting rate versus the discriminator level. Also indicated is the influence of the discrimination level on the activity results as measured at IFIN-HH using a 3H standard. The performances of the IFIN-HH TDCR counter was checked against the measurement results of the TDCR counters of CSIR NML (South Africa), RC (Poland) and LNHB (France). A set of ready-to-measure 63Ni sources in liquid scintillator, in sealed counting vials, was prepared and dispatched for measurement to all these laboratories. The paper describes designs of the TDCR counters used. An analysis and discussion of the measurement results is given.

Lowest excitations in 56Ti and the predicted N=34 shell closure.

Recent experimental characterization of the subshell closure at N=32 in the Ca, Ti, and Cr isotones has stimulated shell-model calculations that indicated the possibility that the N=34 isotones of these same elements could exhibit characteristics of a shell closure, namely, a high energy for the first excited 2(+) level. To that end, we have studied the decay of 56Sc produced in fragmentation reactions and identified new gamma rays in the daughter N=34 isotone 56Ti. The first 2(+) level is found at an energy of 1127 keV, well below the expected position that would indicate the presence of an N=34 shell closure in 56Ti.

Statistics of the LS-detector in the case of low counting efficiency.

In the case of high-quenched 3H and 63Ni sources a distinct incompatibility of theoretical and experimental detection efficiency in the triple liquid scintillation (LS) detector was observed (Appl. Radiat. Isot. 52 (2000) 643). The authors concluded, that the Poisson distribution does not properly describe the detection process, when less than one photoelectron is expected in one of the photomultipliers. Application of other distributions of photoelectrons, e.g. binomial, does not solve the observable problem of incompatibility. Measurements of a set of 55Fe sources have been performed with phototubes defocusing and grey filters for decreasing the counting efficiency of the TDCR detector. Differences between counting results of the 55Fe source and the light emitting diode (LED), simulating the scintillation source, excited by a pulse generator have been observed. Various distributions (Poisson, binomial and Polya) were used for the determination of the theoretical counting efficiency in both cases. The Poisson law gave a good result in the case of the LED but the Polya law had to be applied in the case of 55Fe. The results were independent of the scintillator volume. It seems that the validity of the Polya law in the case of LS-sources is related to the scintillator itself. Measurements of the 3H solution confirmed that conclusion.

A review of the triple-to-double coincidence ratio (TDCR) method for standardizing radionuclides.

This paper gives a review of the development of the triple-to-double coincidence ratio (TDCR) method for standardizing pure beta- and pure electron capture (EC)-radionuclides. The initial idea of Schwerdtel and practical realization and elaboration of the TDCR method by Pochwalski is presented. The main aspects and theoretical principle of the method are summarized and progress on the development of the theoretical model is presented. The details of the activity determination of pure beta- and pure EC radionuclides are discussed, along with specific details in the application of the method in each case. The enhanced TDCR method based on the MAC3 electronic system developed in France is also discussed. Different applications of the TDCR method in metrology laboratories around the world are also pointed out.

Study of the influence of the LS-cocktail composition for the standardisation of radionuclides using the TDCR model.

The influence of the LS-cocktail on the value of the ionisation quenching kB factor was investigated. Sets of 3H and 63Ni standard sources in some commercial and home-made scintillators of different compositions were prepared and measured using the TDCR method. The Birks kB factor was determined for each LS-cocktail and the results are discussed. A model of anisotropy of the triple counter caused by PM-tubes defocusing was applied for calculation.

Multi-method of standardization of radionuclides with "triangular scheme" of disintegration.

The new system of absolute methods of measurement of activity is presented in the paper. This system could be named a new generation of methods particularly for standardization of radionuclides with "triangular-scheme" of disintegration. The system is based on multi-parametric coincidence and anti-coincidence 4pi(LS)-gamma methods. Theoretical considerations and experimental data of 51Cr-activity measurement using the above methods are presented. Finally, determination of the uncertainty for all the components in the multi-method system and the overall uncertainty for the system is presented.

Effective charge of the (pi)h(11/2) orbital and the electric field gradient of Hg from the Yrast structure of 206Hg.

The gamma-ray decay of excited states of the two-proton hole nucleus, 206Hg, has been identified using Gammasphere and 208Pb+238U collisions. The yrast states found include a T(1/2) = 92(8) ns 10(+) isomer located above the known 5(-) isomer. The B(E2;10(+)-->8(+)) strength is used to derive the quadrupole polarization charge induced by the h(11/2) proton hole. Also, the implied quadrupole moment has been used to provide an absolute scale for the electric field gradient of Hg in Hg metal.

Magic nucleus 132Sn and its one-neutron-hole neighbor 131Sn.

Prompt and delayed gamma-ray cascades in doubly magic 132Sn and its neighbor 131Sn have been studied at Gammasphere using a 248Cm fission source. Isotopic assignments of unknown gamma rays were based on coincidences with known transitions in A = 112-116 Pd fission partners. The yrast level spectra of both tin nuclei are interpreted using empirical nucleon-nucleon interactions from the 132Sn and 208Pb regions. Results include identification of the (nuf(7/2)h(-1)(11/2))9(+) aligned state in 132Sn and of extensive (nuf(7/2)h(-2)(11/2)), (nuf(7/2)d(-1)(3/2)h(-1)(11/2)) and (nuh(-1)(11/2)x3(-)) multiplets in 131Sn. The previously reported beta(-) decay of an unusual 131In high-spin isomer to levels in 131Sn is also elucidated.