Within the ACCESS project, the researcher consolidated his knowledge and skills in the fields of crystal production and characterization as room-temperature scintillators, material purification and screening for low-background applications, and the investigation of forbidden beta decays of specific nuclei. In particular, the researcher focused on:
- Measurement of Indium-115 beta decay with indium iodine and indium oxide cryogenic calorimeters;
- new limit on Tantalum-180m beta decay, first with gamma-spectrometry and then with a lithium tantalate cryogenic calorimeter;
- new limit on Vanadium-50 beta decay, first with gamma-spectrometry and then with a yttrium vanadate cryogenic calorimeter;
- new limit on Zirconium-96 and Zirconium-94 beta decay, first with gamma-spectrometry and then cesium-zirconium-cloride low-temperature scintillator;
- measurement of Technetium-99 beta decay using tellurium dioxide and lithium molybdate crystals operated as cryogenic calorimeters.
Within the framework of the ACCESS project, new cryogenic calorimeters based on indium oxide and indium iodide have been developed, yielding one of the most precise measurements of the Indium-115 beta decay.
On the Technetium-99 side, we measured both samples of tellurium dioxide produced by SICCAS and doped with Technetium-99 using a mass spectrometer and cryogenic detectors. However, we encountered technical problems due to the segregation of Technetium-99 in the crystal. After several attempts to optimize the procedure, we decided to develop an innovative approach to introduce Technetium-99 into a crystal, activating Technetium-99 from Molybdenum-98 in a natural lithium molybdate crystal.
The ACCESS project significantly enriched the host institution, Queen’s University, by introducing advanced expertise in cryogenic calorimetry and nuclear spectral shape measurements. The researcher contributed to the development of new experimental protocols, introduced novel simulation and data analysis tools, and initiated interdisciplinary collaborations. This two-way transfer of knowledge not only advanced the researcher’s skills but also expanded the scientific capabilities of the host institutions in a new research field.
In the final year, the research activities focused on enhancing cryogenic infrastructure, testing new detector configurations, and continuing spectral shape measurements. Several detector prototypes were installed and tested using NTD sensors. A new mechanical support for the pulse-tube was developed to mitigate vibrational noise. TES readout has been installed, but is still under testing. Transition measurements were performed on superconducting films. Crucial experimental work was conducted on a range of crystals (PbWO4, Li2MoO4, Na2Mo2O7, NaCl, and Li2WO4), including irradiated samples aimed at embedding beta-emitting isotopes (e.g. Tc-99, Cl-36) for direct measurement. Although some of these tests are still ongoing and have faced technical delays, promising preliminary results have been achieved. Monte Carlo simulations were further developed to incorporate new detector designs, thus supporting detector development and data analysis.
The main scientific achievement remains the high-precision measurement of the In-115 beta decay spectrum, which was disseminated in a widely cited PRL publication. The spectral data were shared with theoretical groups and used for model comparison studies published in Phys. Rev. C.
Throughout the three years, ACCESS results were disseminated via presentations at major international conferences (e.g. NEUTRINO, LRT, LTD, TAUP, MEDEX), publications in peer-reviewed journals, and open-access data repositories. Outreach activities included seminars for schools, public events like Pint of Science and SHARPER, and a dedicated website.
