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Achievements 2003 - 2013
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One of the most prominent RPL results is the development of the odd-odd 194Ir nucleus level scheme using data obtained in the (n,γ), and (d,p) reaction measurements. This is the heaviest A~190 region nucleus for which one could perform classification of low-energy states using mean field Nilsson single-particle orbits. A study has been carried out in collaboration with our colleagues from the ILL reactor (Grenoble, France) and the Munich Tandem accelerator (Germany). Based on this RPL 194Ir level scheme, a new U(6/12)U(6/4) supersymmetric nuclear quartet has been developed. 

During the last years, in collaboration with partners from other nuclear research centers, RPL physicists have developed level schemes of the odd tungsten isotopes 183,185,187W using the (n,γ), (d,p) and (dpol,p) reaction measurement data, as well as level scheme of the odd-odd nucleus 188Re using thermal neutron capture reaction γγ-coincidence measurement data obtained with big volume Ge detectors in the Rež reactor (Czech Republic), and single γ-ray spectrum in the energy range from 105 to 1860 keV registered by the high resolution crystal-diffraction spectrometer GAMS5 in Grenoble. The established level scheme of 188Re nucleus includes more than 190 levels up to 1585 keV excitation energy. The results obtained indicate coexistence of axially-symmetric and non-axial states in decay schemes of the studied nuclei. Of particular interest has been identification of quasi bands with inverse spin sequence in odd tungsten isotopes. In 2012 the study of the odd-odd 186Re nucleus structure has been started. There are plans to perform new experimental studies of the odd-odd 192Ir nucleus in order to support the theoretical level scheme earlier proposed by RPL physicists.

Experimental nuclear studies in RPL are performed in close association with theoretical nuclear structure calculations using both collective (rotor plus particles) and algebraic (interacting boson) nuclear models. These calculations allow to determine the application limits of traditional nuclear models in critical regions when quantum phase transitions from the prolate nuclear shape to oblate and from the deformed shape to spherical are observed. Model calculations performed in the case of odd-odd nuclei allow to obtain information about residual interaction of valence nucleons in a nuclear mean field and to study isotopic dependence of the NN-interaction potential. Also, because of the high density of excited levels, transitional region nuclei are interesting objects for the studies of quantum chaos and their relationship to nuclear shape phase transitions.

In the domain of nuclear physics methods applications, RPL physicists work on monitoring of the artificial radionuclides: Cs-137 and Sr-90 in soils and conifer needles and tritium in ground and surface waters of potentially polluted territories in Latvia. Data about radionuclide accumulation and migration have been collected over a longer period of time depending on seasonal and climate conditions. Monitoring has been carried out in areas surrounding the decommissioned Salaspils Nuclear Reactor and the radioactive waste repository. Detailed studies have also been performed about the Ra-226 and the pollution caused by its decay products in soils, drains and rooms of the potentially polluted object – territory of the former laboratory producing radon solution from Ra-226 salts for radon baths used in balneology in the past. We have also studied the impact of cement-to-water mass ratio on hardening of concrete used for storage of liquid radioactive waste as well as diffusion of radionuclides, tritium and Cs-137, in water using cement compound plus water.

Drinking water used in the food industry has been checked for the radionuclide content throughout the whole territory of Latvia to meet EU regulations. Based on the results obtained in the measurements of natural radionuclide concentration in building materials, it is planned to perform a study on natural radionuclide (40K, 226Ra, 232Th, 235U) content in clay based building materials produced by different companies.

In addition to carrying out practical activity measurements of environmental and technological samples RPL physicists are involved in development of new applied nuclear physics methods for detecting radionuclides in various matrices using gamma and beta spectrometry. Also, prerequisites are being drafted for re-establishing activation analysis measurements in Latvia to be performed at the future cyclotron center.