Part of the POLATOM Radioisotope Center operating at NCBJ is the Radioactivity Standards Laboratory (LWR – Laboratorium Wzorców Radioaktywności) accredited by the Polish Center for Accreditation. The technical competence of LWR employees is confirmed by the fact that the laboratory is the depositary of the State Standard for the Unit of Measurement of Radionuclide Radioactive Activity. Employees devote a significant part of their time to monitoring the activity and level of radioactive contamination (radionuclide purity) of radiochemical preparations and radiopharmaceuticals produced in OR POLATOM. They also calibrate dozens of activity meters located in hospitals and diagnostic centers throughout Poland.
Scientific and research work is also carried out at LWR. The latest published results concern precise measurements of the activity of 177Lu and 225Ac solutions and the half-life of these radionuclides.

These and other radionuclides with appropriately selected physical properties have been used in nuclear medicine for many years. Their nuclear transformations can, among other things, support the fight against cancer by destroying tumour cells or enable precise localisation of lesions. One such radioisotope is lutetium 177Lu, which decays with the emission of β and γ particles and is often used for therapy and imaging of neuroendocrine tumours. Another radioisotope delivered specifically to tumour cells is actin 225Ac, which is used in targeted alpha therapy. This is now an increasingly important treatment modality in nuclear medicine. 225Ac in radioactive equilibrium with its derivatives emits several α-particles that lose their energy over very short distances, destroying targeted cancer cells while minimising the impact on healthy tissues. In order to determine the dose a patient receives, it is necessary to know precisely both the activity of the radionuclide and its half-life.

In their latest publications, specialists from the LWR OR POLATOM at the NCBJ presented the results of 177Lu activity measurements using the CIEMAT/NIST method and the β-γ coincidence and anticoincidence method [1, 2]. These are absolute measurement methods that use the liquid scintillator technique (LSC).

"The CIEMAT/NIST method is based on an experimental 3H measurement yield curve in a scintillation spectrometer, which allows to determine the measurement yield of the radionuclide under investigation and, consequently, to determine its radioactivity," describes Dr Justyna Marganiec-Gałązka of LWR, first author of the article. "The β-γ coincidence and anti-coincidence method, on the other hand, allows direct determination of the activity of a radionuclide decaying with β and γ emission, by counting signals occurring separately in the beta and gamma recording paths and in an additional path of so-called coincidence, recording pulses appearing simultaneously in both paths."

The same 177Lu samples were measured by both methods. The relative difference in the 177Lu activity values obtained was only 0.013%, which shows very good agreement between the two methods and verifies them against each other. Such precise measurements allow the production of reference sources used for calibration of activity meters.

The scientists also determined the half-life of 177Lu and compared the result with data reported by research groups from other countries. Measurements lasted at OR POLATOM for more than two months in a special detector containing three photomultipliers, into which a 177Lu sample in a liquid scintillator was inserted. The count rates of coincidence pulses between the three photomultipliers and between pairs of photomultipliers were recorded. The half-life value of 177Lu, 6.6489 ± 0.0052 days, obtained with very high accuracy, is consistent within the measurement uncertainty with values reported in the literature.

Measurements of 225Ac activity were performed by a different absolute measurement method in the LSC technique, the so-called triple-double coincidence method (TDCR), using a detector with three photomultipliers. The measurement efficiency of β and γ emission was calculated theoretically from the recorded coincidence pulse count rates, and the measurement efficiency of α emission was virtually 100%. Using the International Reference System (SIR) in Sévres, France, the results of 225Ac activity measurements at the LWR and at the Physikalisch-Technische Bundesanstalt (PTB) in Germany were compared. The results were found to be in agreement and differed by only 0.75% [3].

Measurements such as for 177Lu and 225Ac are performed at the LWR laboratory for many radionuclides, e.g. 85Sr, 90Y, 131I. Often, activity measurements are performed as part of international comparisons to confirm the measurement competence of the laboratory. In recent years, the laboratory has participated in comparisons of measurements of 3H, 14C, 18F, 51Cr, 55Fe, 64Cu, 65Zn, 68Ge/68Ga, 99mTc, 109Cd, and 131I. Very good agreement of LWR results with those of other laboratories has been obtained [4, 5, 6, 7].

In addition to this, the LWR Laboratory performs precise measurements of radionuclide purity, i.e. the activity of radioactive impurities in relation to the basic radionuclide in a given material is determined. Spectrometric methods are used for this purpose. For example, in the case of technetium 99mTc solution, which is used in nuclear medicine, impurities 99Mo and 103Ru are detected when the technetium is derived from molybdenum produced in a nuclear reactor. The European Pharmacopoeia sets their permissible limits at 0.1% and 5*10-3% respectively. In the LWR, they can even be detected at levels of 0.001% and 10-6% respectively. When 99mTc produced in the cyclotron was measured, completely different radionuclide impurities were detected: 93Tc, 93mTc, 94Tc, 95Tc [8]. Researchers at the LWR laboratory also determined, among other things, the limits of detection of radionuclides of cosmic origin that come to Earth with meteorites [9].

Determining the activity of radionuclides is an important aspect of research in many different fields, from nuclear medicine, industry and environmental protection to meteorite-related studies. The apparatus, skills and experience of the Radioactivity Standards Laboratory team allow such measurements to be carried out with extreme precision, as their research results have shown for years.

[1] Marganiec-Gałązka J., Czudek M., Lech E., Listkowska A., Saganowski P., Tymiński Z., Ziemek T. Activity standardization and half-life measurement of ¹⁷⁷Lu. Appl. Radiat. Isot., Vol. 197, (2023) 110829. https://doi.org/10.1016/j.apradiso.2023.110829
[2] Marganiec-Gałązka J., Ziemek T., Broda R., Cacko D., Czudek M., Jęczmieniowski A., Kołakowska E., Lech E., Listkowska A., Saganowski P., Tymiński Z. Standardization of ¹⁷⁷Lu by means of 4π(LS)β-γ coincidence and anti-coincidence counting. J. Radioanal. Nucl. Chem., Vol. 331, (2022) 3283–3288. https://doi.org/10.1007/s10967-022-08330-0
[3] Coulon R., Michotte C., Courte S, Nonis M., Ziemek T., Marganiec-Gałązka J., Lech E., Saganowski P., Czudek M., Listkowska A. Update of the BIPM comparison BIPM.RI(II)-K1.Ac-225 of activity measurements of the radionuclide ²²⁵Ac to include the 2021 result of the POLATOM (Poland). Metrologia, Vol. 60, No 1 A, (2022) 06001.
[4] Cassette P., Arinc A., Capogni M., DeFelice P., Dutsov C., Galea R., Garcia-Toraño E., Kossert K., Liang J., Mitev K., Nähle O., Nedjadi Y., Oropesa Verdecia P., Takács M., Ziemek T. Results of the CCRI(II)-K2.H-3 key comparison 2018: measurement of the activity concentration of a tritiated-water source. Metrologia,[70] Vol. 57, No 1 A, (2020) 06004.
[5] Ziemek T., Broda R., Listkowska A., Lech E., Dziel T., Saganowski P., Tymiński Z., Kołakowska E. Standardization of 55Fe solution using the TDCR method in POLATOM as a part of the CCRI(II)-K2.Fe-55.2019 key comparison. J. Radioanal. Nucl. Chem., (2022). https://doi.org/10.1007/s10967-022-08338-6
[6] Ziemek T., Lech E., Tymiński Z. Standardization of ⁹⁰Y solution by mean of a Cherenkov counting in comparison with a liquid scintillation counting technique. J. Radioanal. Nucl. Chem., Vol. 331, (2022) 3327–3333. https://doi.org/10.1007/s10967-022-08341-x
[7] Ziemek T., Capogni M., Ratel G., Broda R., Dziel T., Fazio A., Listkowska A. Comparison of ¹³¹I activity measurements at the NCBJ RC POLATOM and the ENEA-INMRI linked to the BIPM SIR system. Appl. Radiat. Isot., Vol. 134, (2018) 380-384. https://doi.org/10.1016/j.apradiso.2017.09.040
[8] Tymiński Z., Saganowski P., Kołakowska E., Listkowska A., Ziemek T., Cacko D., Dziel T. Impurities in Tc-99m radiopharmaceutical solution obtained from Mo-100 in cyclotron, Appl. Radiat. Isot., Vol. 134, (2018) 85–88. https://doi.org/10.1016/j.apradiso.2017.10.021
[9] Tymiński Z., Burakowska A., Tymińska K., Kołakowska E., Saganowski P., Ziemek T., Dziel T., Kotowiecki A. Pomiary izotopów gamma promieniotwórczych w trynitytach. Rocznik Polskiego Towarzystwa Meteorytowego, Vol. 9, (2018).