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 4πβ(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 4πβ(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.

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.

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.

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.

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.

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.

Analysis of detection-efficiency variation techniques for the implementation of the TDCR method in liquid scintillation counting

Detection efficiency variation is often used in liquid scintillation counting in order to evaluate a parameter in the detection efficiency calculation model. The aim of this paper is to compare the effects of three different detection efficiency variation methods in the activity measurement of three pure-beta radionuclides: 3H, 63Ni and 14C. Some general conclusions concerning the TDCR method are drawn.

Radioactive contamination of forests in Poland

Partial results of a large survey of radioactive contamination in Polish forests are presented. All measurements were performed with low-background gamma spectrometers. The measurement method is briefly described. Activities of 137Cs, 134Cs, 125Sb, 106Ru, 144Ce, 154Eu, 155Eu, and 60Co in A0 and A1 layers of forest litter from all over Poland are determined. The geographical distribution of contamination as well as its origin is discussed. Nonuniform composition of the Chernobyl fallout over Poland is confirmed and documented.