[en] The (7/2)[523] and (7/2)[404] bands are observed in ¹⁵⁹Tm to I = (61/2) and (43/2), respectively, well beyond the i/sub 13/2/ neutron backbend. Before the backbend, the (7/2)[523] band exhibits large signature splitting, the (7/2)[404] none, which is interpreted as resulting from the very different driving influences of the K = (7/2) h/sub 11/2/, and g/sub 7/2/ orbits, respectively, on the core triaxiality. The i/sub 13/2/ neutron alignment changes the signature splitting in each band as a result of its dominant driving force to positive values of γ. Measured B(M1;I→I-1)/B(E2;I→I-2) values increase dramatically after the backbend, and this is explained in terms of calculated increases in the M1 transition rates and decreases in the E2 rates

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[en] The spin-lattice relaxation time T₁ of ¹⁶⁹Tm nuclear spins in TmPO₄ has been measured at temperatures T between 50 mK and 2.2 K, in a magnetic field H perpendicular to the c-axis, ranging from 15 mtesla to 5.5 tesla. The results above 0.5 tesla are interpreted in terms of a direct process, strongly slowed down by phonon bottleneck. In very low fields (H < 0.1 tesla), T₁ varies like H²/T. We discuss the feasibility of producing a nuclear ordered state of the ¹⁶⁹Tm spins by ''brute force''

[en] The multipole mixing ratios for the 198 and 177 keV γ-ray transitions in ¹⁶⁹Tm are determined as δ(198)=-6.1_-0.6^+0.4 and δ(177)=-0.20_-0.03^+0.04 from new measurements of angular correlation of the 63-198 and 63-177 keV cascades in addition to measurements on the cascades passing through the 118 and 139 keV levels. The present value of δ(198) indicates an almost pure E2 character for the 198 keV γ ray while from earlier measurements an admixture of only 9% E2 was reported for this γ ray. For both the 198 and 177 keV transitions the results do not agree with the conversion electron measurements and indicate that the conversion processes in these transitions are not normal. From time-differential measurement on the 63-198 keV cascade, the relaxation constant λ₂=(0.31±0.21)x10⁷ sec^-1 is obtained using the source in acetic acid solution. The integral attenuation coefficients for the 316 keV level are found to be G₂=0.19±0.04 in liquid chloride source and G₂=0.57±0.06 in liquid acetate source

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[en] For the first time nuclear Bragg diffraction of synchrotron radiation at the 8.41 keV resonance of ¹⁶⁹Tm was observed. Time differential measurements were performed with the pure nuclear (424) reflection of a thulium iron garnet single crystal. The dynamical theory of Moessbauer optics is applied to evaluate the time spectra. The measurements reveal information about the hyperfine fields which has not been accessible before by conventional Moessbauer spectroscopy with polycrystalline samples

[en] Clauser and Moessbauer showed that the second order (in perturbation theory) magnetic hyperfine interaction, the so called 'pseudoquadrupole interaction', in the ¹⁶⁹Tm Moessbauer effect can produce apparent isomer shifts. While they assumed two isolated singlets and simplified the coupling, the authors show that the second order magnetic hyperfine coupling can be observed in general for any kind of crystalline electric field (CEF) wavefunctions, and that the coupling between many states must often be considered in calculating it. Furthermore since the first order magnetic coupling of the excited CEF states is important, the interaction is best accounted for by diagonalization of the full magnetic hyperfine and CEF Hamiltonian. Examples of the effects that may occur are presented. (Auth.)

[en] By use of optical hyperfine structure investigations in the Tm I spectrum the A-values of 20 levels of the configurations 4f¹³6s6p and 4f¹²5d6s² and the A-values of 4f¹³6s²²Fsub(5/2) were determined very accurately. (orig./WL)

[en] Full text: It has been shown recently that Yb and Er atoms from the lanthanides group can be efficiently laser-cooled using strong transitions near 400 nm. Degenerate Fermi gases of ytterbium have been also recently demonstrated using laser-cooling based technic. Our goal was to investigate the possibility of laser cooling of Tm atom. Among other lanthanides, thulium possesses relatively simple level structure.Moreover, it has only one stable isotope ¹⁶⁹Tm with a nuclear spin of I = 1/2 which makes possible to use schemes for sub-Doppler cooling. Laser-cooled thulium is a favorable candidate for optical clocks applications, since the forbidden transition between the fine structure sublevels (J_g 5=2) - (J'_g = 7/2) of the ground state 4f¹³6s² (λ = 1.14 micron) has a spectral width of approximately 1 Hz. The collisional shift of such kind of transitions in lanthanides is suppressed because of the outer closed 6s² shell, which allows for precision spectroscopy in a dense atomic cloud. We studied two candidates for cooling transitions from the ground state 4f¹³6s² (J_g 7/2) to the states 4f¹²(³H₅)5d_3/26s² (J_e = 9/2) at 410.6 nm and 4f¹²(³F₄)5d_5/26s² (J_e = 9/2) at 420.4 nm. By means of saturation absorption spectroscopy, we measured the hyperfine structure and rates of these transitions. We evaluated the life times of appropriate excited levels as 15.9(8) ns and 48(6) ns, respectively. Decay rates from these levels to neighboring opposite-parity levels were evaluated by means of Hartree-Fock calculations. The fraction of atoms which do not return to the ground state is about 10^-5 and 5 · 10^-4 for the 410.6 nm and 420.4 nm transitions respectively. We conclude that the strong transition at 410.6 nm with relative slow leakage rate can be used for the efficient cooling of Tm I. We also measured hyperfine structure of two nearby transitions from the ground state to the states 4f¹³(²F_7/2)6s6p(¹P₁) (J_e 5/2) at 409.4 nm and 4f¹²(³F₄)5d_5/26s² (J_e = 7/2) at 418.9 nm, which can be used for Λ-type excitation of λ = 1.14 μm transition. (author)