«ANNUAL REPORT Riga 2012 Annual Report 2011, Institute of Solid State Physics, University of Latvia. Editor: A.Krumins. Composed matter: A.Muratova. ...»
3. University of Latvia, Institute of Chemical Physics (Dr. G. Kizane)
4. Institute of Wood Chemistry ( Dr. hab. G. Dobele, Dr.hab. G. Telesheva, Dr.hab.T.Dizbit)
5. Riga Technical University, Faculty of Material Science and Applied Chemistry (Dr.Berzina-Cimdina r).
6. Institute of Technical Physics, Rīga Technical University (Dr.J.Ruža).
7. Riga Technical University, Faculty of Material Science and Applied Chemistry (Prof. J.Dehtjar,).
1. Mississippi University (Prof. A.Afanasjev).
2. Brookhaven National Laboratory, Upton (Prof. R.F. Casten).
1. Technical University Munich (Prof. T. von Egidy, Dr. H.-F. Wirth) France
1. Institute Laue-Langevin, Grenoble, France ( Dr. W. Urban, Dr. M. Jentchel).
1. Memorial University of Newfoundland, Newfoundland (Dr.A.Aleksejevs)
2. Department of Physics, Acadia University, Wolfville, NS (Dr.S.Barkanova) Czech Republik
1. Nuclear Research Institute, Ŕež (Dr. J.Honzatko, Dr. I.Tomandl).
1. Institute of Physics, Tartu ( Prof. Ch.Luschik, Prof. A.Luschik, Dr. A.Sildos, Dr.T.Kärner).
1. R&D Institute of Materials RPA “ Carat”, Lviv ( Dr. D.Sugak, Dr. S.Ubizskii).
1. Ural State University, Ekaterinburg (Prof. A. Nikiforov).
2. Ural Technical University, Ekaterinburg (Prof. B.Shulgin)
3. St.Petersburgh Nuclear Physics Institute, Gatchina (Dr.V.Bunakov, Dr.A.Sushkov)
4. Institute of Metal Physics, Urals Division of Russian Academy of Sciences, 620219 Yekaterinburg, Russian Federation (Ac. Dr. Sc B.N.Goscickii, Dr. V.Voronin).
Denmark Riso National Laboratory, Roskilde, (Dr. S. Nielsen)
Our previous study of the doubly odd transitional 188Re nuclear structure  was based on γγ-coincidences measured following the 187Re(n,γ)188Re reaction with thermal neutrons at the nuclear reactor in Řež (Czech Republic). The level scheme of 188Re was established up to 800 keV excitation energy, considerably extending and correcting the earlier level scheme of Shera et al. .
Due to extreme level density, characteristic to nuclei belonging to the transitional A~190 region, development of the 188Re level scheme above 400 keV requires high precision data about γ-transition energies and intensities. Such data have been obtained via thermal neutron capture measurements with the same enriched 187Re target at ILL (Grenoble, France), employing the high precision crystal-diffraction spectrometer GAMS5. Additional energy and angular γγ-coincidence measurements have been performed as well. Obtained spectra provided data about more than 800 γ-transitions in the energy range from 105 to 1860 keV.
These data have essentially higher resolution above 350 keV energy than those of earlier crystal-diffraction measurements .
Analysis of obtained new and previous  spectroscopic information allowed establish confidently the depopulation data for 122 levels of 188Re in the energy range from 800 to 1585 keV: 79 of these levels are populated by primary γ-rays. Five new levels have been established also in the energy range 600-800 keV. As a result, the level scheme of 188Re now includes 190 levels: 115 levels of negative parity and 75 levels of positive parity. The level scheme is strongly supported by observed high-low and low-low γγ-coincidences.
In our earlier work , the most of 188Re levels below 800 keV energy have been interpreted in terms of rotational bands based on Nilsson two-quasiparticle configurations.
Now, in addition to already known 7 negative parity and 6 positive parity rotational bands, associated with proton orbits 5/2 and 9/2, and neutron orbits 1/2, 3/2, 7/2, 9/2 and 11/2, we propose three new tentative negative parity structures above 500 keV energy: the Kπ=0- rotational band with 0- level at 611.5 keV, 1- level at 582.2 keV, and 2- and 3- members at 723.4 and 782.8 keV, respectively; the Kπ=1- rotational band at
735.2 keV with 2- level at 813.2 keV and 3- level at 925.2 keV; and the Kπ=4- band with 4member at 558.3 keV and 5- member at 739.8 keV. These rotational bands are interpreted using two-quasiparticle configurations involving proton orbit 7/2. The earlier proposed  Kπ=1- rotational band with bandhead level 582.2 keV has been taken apart.
The Nilsson particle-plus-rotor model calculations, performed with program package described in , have shown that below 400 keV one can reproduce most of 188Re levels assuming axially-symmetric core deformation with ε=0.18 and ε4=0.05. However, the observed density of levels in the 400-1000 keV range, especially those with spins 3+,4+, is about three times greater than predicted by the particle-plus-rotor model calculations in the case of axially-symmetric deformation. Also, the calculated energies of two-quasiparticle bands with proton orbit 7/2 are about 200-300 keV lower than their proposed experimental positions. It can indicate a coexistence of states with different shapes at energies above 400 keV. A possibility of non-axial deformation for nuclear states including neutron orbits with high orbital moment j values, e.g., 11/2 and 9/2, in transitional region tungsten and osmium isotopes has been indicated also in .
 M. Balodis, et al., Nucl.Phys.A 847 (2010) 121.
 E.B. Shera, et al., Phys.Rev.C 6 (1972) 537.
 S.E. Larsson, G. Leander and I. Ragnarsson, Nucl.Phys.A 307 (1978) 189.
 V. Bondarenko, et al, Nucl.Phys.A 856 (2011) 1.
One of the outstanding and to date largely unresolved problems in nuclear spectroscopy is a proton-neutron coupling in nuclei. Proton-neutron interaction is believed to be a major force causing nuclear deformation. Proton-neutron levels can be studied experimentally by measuring properties of odd-odd nuclei. However, excitation patterns of these nuclei are far more complex than the structure of even-even or odd-A nuclei. In odd-odd nuclei, protonneutron coupling results in many low-excitation levels, members of proton-neutron multiplets.
A large number of low-energy transitions between these levels resulting in very complex spectra has for years limited effectively their studies. However, constant progress in experimental techniques permits nowadays to access with more confidence this difficult field.
In the case of nuclei belonging to transitional deformation region at A~190, there are still very few data about confidently established two-quasiparticle Gallagher-Moszkowski (GM) doublets and Newby shifts in K=0 bands . Though the residual NN-interaction, and especially its tensor component, plays an essential role in the structure of low-lying levels of these γ-soft odd-odd nuclei due to considerably greater level density than in the stable deformation region, and also because the ΔK=0 mixing between two-quasiparticle states is most important due to large ΔΩ values of involved proton and neutron orbits, the behaviour of residual NN-interaction matrix elements in the case when initial and final single-particle states belong to different deformation modes is yet unstudied problem.
Importance of correct accounting of all residual proton-neutron interaction terms both diagonal and non-diagonal, in order to reproduce the observed low-lying level scheme of transitional doubly odd nuclei, have been demonstrated by detailed particle-plus-rotor model calculations in the case of 188Re. The values of corresponding Vnp matrix elements have been calculated using expressions and parameter values given in . It has been found that, in the case of 188Re, it is especially important to include core polarization effects, i.e., the low-lying levels are best reproduced when one takes into account the central Gauss interaction potential with both short and long-range components, and includes spin polarization of central forces as well. The tensor interaction parameters: VT=-32.5 MeV, VTM=3.3 MeV, were chosen so as to reproduce the empirical value ENewby=-57.47 keV of levels in the Kπ=0+ (p:9/2n:9/2) rotational band.
In order to study proton-neutron interaction in neighbouring transitional nuclei, the systematic of available experimental data about two-quasiparticle doublets and Newby shifts in odd-odd rhenium (Z=75) and iridium (Z=77) isotopes has been made. It has been found that for 190,192,194Ir nuclei there are data about 18 GM-doublets (of which 6, mostly in 192Ir, are questionable) and 7 Newby shifts. In the case of 186Re, there are 5 complete GM-doublets (one questionable). Therefore, for thorough study of proton-neutron interaction in A~190 transitional deformation region nuclei, one must obtain additional experimental information about 186Re and 192Ir structure. Corresponding measurement project, employing the advantages of high precision crystal-diffraction spectrometer GAMS5, has been submitted to ILL, and first thermal neutron capture measurements of 186Re nuclei have been performed.
 A.K. Jain et al, Rev.Mod.Phys. 70 (1998) 843.
 J.P. Boisson, R. Piepenbring and W. Ogle, Phys. Rep. 26C (1976), 99.
The results of tritium content measurements in drinking and ground water are presented. The liquid scintillation counting (LSC) method has been used for determining tritium content in drinking water taken from 155 communal and 54 food manufacturer water sources in all regions of Latvia. Tritium concentration in all measured samples was 10 Bq/L. Monitoring of tritium in the ground waters near the shutdown Salaspils nuclear reactor and the radioactive waste repository “Radon” has been carried out since 1997. During this period, the concentration of tritium has decreased from 8900 to 100 Bq/l in “Radon” and from 7200 to 29 Bq/L in Salaspils. Quality assurance of the obtained results has been ensured according to the EN ISO/IEC 17025 standard.
CONFORMITY ASSESSMENT IN RADIOACTIVITY MEASUREMENTS
The role of conformity assessment in measurements of radioactivity is discussed. In our Laboratory of Radiation Physics there is carried out testing of natural as well as artificial radionuclides in different environmental samples (soil, precipitation, different types of water, needles, etc.), of various types of samples irradiated in the nuclear reactor and in the radioactive polluted objects. The credibility of obtained results is ensured by the quality assurance and control. The main requisitions involved in the quality assurance of the laboratory according to the requirements of ISO/IEC 17025:2005 /1/ are: 1) the use of calibrated equipment only; 2) the regular and long-time use of reference materials for the control of equipment; 3) the estimation of uncertainty sources and determination of uncertainties within the given interval of credibility; 4) the validation and verification. One of the most important requirements is a regular participation in the interlaboratory comparison exercises, which enables one to estimate and disclose possible sources of non-conformities as well as to carry out the corrective actions.
Natural spinel crystals from Ural and Pamir deposits and synthetic magnesium aluminium spinel single crystals with different stoichiometry (MgO.nAl2O3 ) grown by Verneuil method were used. The photoluminescence (PL), its excitation (PLE) and optical absorption of stoichiometric and nonstoichiometric magnesium aluminium spinel crystals containing the chromium and manganese ions and defects produced by fast neutron irradiation( fluence up to 1020cm-2, E0.1 MeV) are investigated. The broadening of R- and N-lines takes place in synthetic stoichiometric spinel. Structure of synthetic nonstoichiometric spinels (n1) has to be more disordered, since in addition to the site exchange the so called stoichiometric vacancies are present in the structure. The R- and N-lines broadening takes place after spinel crystals irradiation by fast neutron too. The neutron irradiation causes increasing of the spinel inversion. Furthermore the great deviation from stoichiometry leads to the local structure of α-Al2O3 formation around Cr3+ ions. The orange emission band at 570 nm is belonging to complex center “Mn2+-F+ (or F centre)”.
It is known that the absorption spectra of the neutron irradiated pure MgO consists of four bands with maxima 250, 357, 570 and 980 nm, associated with radiation defects [10-12]. In additional to above mentioned bands after irradiation by fast neutron at fluence 1018cm-2 are observed two week bands at maxima ~ 485 and 746 nm. Figure 1 gives the absorption spectra of MgO crystal after fast neutron irradiation and annealed at different temperature. The addition band with maxima 485 and 745 nm disappear at temperature above 700 K. These bands position coincide with band position observed in irradiated and annealed MncMg1-cO single solid solution , when band with maximum ~ 500 nm belongs to a complex Mn3+VMg. The lowest spin–allowed transition 5E → 5T2 of Mn3+ was observed in . Jahn-Teller effects modify the energy level scheme from the Tanabe-Sugano description. The band 745 nm coming from Mn3+. Appearance and disappearance take place in consequence the next reaction: Mn2+ + hν → Mn3+ +e─ ; Mn3+ + Fe2+ → Mn2+ + Fe3+. The absorption and luminescence spectra behaviour of magnesium oxide containing transition metal ions exposed to a fluence of fast neutrons up to 1018cm-2 (E0.1 MeV) and annealed are investigated. It is shown that the sharp lines after irradiation with fast neutrons in the 850-950 nm regions belong to exchange coupled Fe3+ - Fe3+ pairs. The absotption band 745 nm in irradiated MgO crystals coming from Mn3+.