[en] Long-lived ⁴¹Ca isotope (t1/2 = 1.04 x 10⁵ yr) with an abundance of 10^-10 % has been suggested for radiochemical dating, determination of cosmic ray flux and is used as a medical tracer isotope. However, useful measurements in these applications require isotopic selectivity in the range of 10¹⁰-10¹⁶ against the predominant stable isotope ⁴⁰Ca. Resonance ionisation mass spectrometry (RIMS) is used in applications where large sensitivities are desired along with extremely high selectivities. In the present work, spectral simulation (SS) method has been used to calculate selectivities of calcium isotopes for double resonance photoionisation scheme and the results have been compared with that reported earlier

[en] The hyperfine structure of the ground state 4f⁷6s²(⁸S_7/2^o) and the excited 4f⁷6s6p(⁸P_9/2) state for both the isotopes ¹⁵¹Eu and ¹⁵³Eu has been measured using the laser induced fluorescence spectroscopy from an effusive atomic beam. The isotope shift for the 4f⁷6s²(⁸S_7/2^o)→^601.8154nm4f⁷6s6p(⁸P_9/2) transition of Eu I has also been measured. The precision in the measurement of the isotope shift of this transition and the hyperfine structure constants for both the isotopes of Eu has been improved using a radio-frequency modulation technique based on EOM side band generation as well as by frequency locking technique. The experimentally determined isotope shift between the ¹⁵¹Eu and the ¹⁵³Eu isotopes for the 4f⁷6s²(⁸S_7/2^o)→^601.8154nm4f⁷6s6p(⁸P_9/2) transition is 3549.3 (5) MHz. The values of the magnetic dipole constant (A) and the electric quadrupole coupling constant (B) for the ¹⁵¹Eu and ¹⁵³Eu isotopes for the 4f⁷6s²(⁸S_7/2⁰) ground state have been found to be consistent with the values reported by the atomic beam magnetic resonance (ABMR) technique. The hyperfine coupling constants for both the isotopes of Eu for the excited 4f⁷6s6p(⁸P_9/2) state are measured to be A(¹⁵¹Eu)=664.73 (9) MHz and B (¹⁵¹Eu)=290 (3) MHz; A(¹⁵³Eu)=295.15 (7) MHz and B (¹⁵³Eu)=727 (2)MHz. -- Highlights: • Precision measurement of isotope shift and hyperfine structure constants of europium for the 4f⁷6s²(⁸S_7/2⁰)–4f⁷6s6p(⁸P_9/2) transition. • Hyperfine separations of the ground and excited states have been measured by the laser induced fluorescence technique. • The hyperfine separations of the ground state have measured using the EOM technique. • The hyperfine separations of the excited state have measured using the AOM locking technique. • The hyperfine anomaly has been estimated to be 0.56 (3)%

[en] Seven schemes are studied theoretically for Doppler-free two-photon excitation of rare 41Ca isotope using single-mode continuous-wave lasers. The ionization efficiencies and optical selectivities for all the schemes are calculated for various powers of the excitation and ionization lasers and for various focusing conditions of the two lasers. To maximize the ionization efficiencies and the optical selectivities, wavelength-dependent Stark compensation is used. Certain laser wavelengths of the ionization step termed as magic wavelengths are identified for compensating the Stark shift induced by the excitation laser. The effects of the Stark-shift-induced asymmetry and its reversal by selecting the appropriate magic wavelength for the ionization step for various excitation and ionization laser intensities are investigated. The ionization efficiency and optical selectivity for the best scheme after Stark compensation are found to be 8.4x10-4 and 9x103, respectively

[en] The feasibility of isotope enrichment of ¹⁵⁵Gd and ¹⁵⁷Gd isotopes using relatively broadband lasers within the tuning range of rhodamine-6G dye has been studied. A new set of photoionization schemes have been proposed for using in the industrial scale enrichment of these isotopes. These photoionization schemes result in better photon economy compared to the photoionization schemes reported earlier. The enriched isotopic mixture results in a 50% increase in the neutron absorption cross-section and a 70% reduction in the residual neutron absorption. The degree of enrichment of the odd isotopes is adequate for using the enriched mixture as an efficient burnable poison. The effect of linewidth of the excitation laser and Doppler width of the atom source on the degree of enrichment have been theoretically evaluated and experimentally verified. The computed selectivities were in good agreement with the experimental results. (orig.)

[en] The efficiency of the two photoionization schemes, scheme 1: 4f¹⁴6s²¹S₀ (0 cm^-1) → (555.648 nm) 4f¹⁴6s6p ³P₁^o (17 992.007 cm^-1) → (581.027 nm) 4f¹³6s²6p(7/2, 3/2)₂ (35 196.98 cm^-1) → (582.79 nm) autoionization state (52 353 cm^-1) → Yb⁺ and scheme 2: 4f¹⁴6s²¹S₀ (0 cm^-1) → (398.8 nm) 4f¹⁴6s6p ¹P₁^o(25 068.222 cm^-1) → (<394 nm) Yb⁺ has been studied by a spectral simulation approach for the isotope-selective excitation of the ¹⁶⁸Yb isotope. Isotopic selectivities have been computed for 4f¹⁴6s²¹S₀-4f¹⁴6s6p ³P₁^o (555.648 nm), ³P₁^o-(7/2, 3/2)₂ (581.027 nm) and 4f¹⁴6s²¹S₀-4f¹⁴6s6p ¹P₁^o (398.8 nm) transitions for various laser bandwidths of the excitation lasers. The degree of enrichment of the low-abundant ¹⁶⁸Yb isotope has been computed using the obtained isotopic selectivity values. Results obtained for scheme 1 are in good agreement with the results reported earlier. The abundance of ¹⁶⁸Yb isotope has been computed for various laser linewidths of the excitation laser and Doppler widths for scheme 2. Comparison of the two photoionization schemes for isotope-selective photoionization of the ¹⁶⁸Yb isotope has been made. The present computational method has been examined for computation of degree of enrichment for the photoionization schemes under consideration. (author)

[en] In the present work the two-dimensional lineshapes were calculated and evaluated the optical isotopic selectivity that can be achieved in various double-resonance excitation schemes. The theoretical calculation of lineshapes is based on the density matrix formalism, which accurately describes the wide variety of coherent laser phenomena. The density matrix formalism is applied to realistic experimental situations. Since this involves rigorous calculations, these were carried on ANUPAM supercomputer

[en] Hyperfine structure constants using the least squares minimization method were obtained for ¹⁷¹Yb and ¹⁷³Yb isotopes. Evaluation of the hyperfine structure constants enabled to obtain isotope shifts of the odd isotopes for the second excitation step. The results of the present investigations are presented

[en] Isotope ratio enhancement factors and isotopic selectivities for ¹³⁸La in a natural abundance lanthanum sample as well as an enriched sample have been computed theoretically for the 5d6s²²D_3/2 -5d² 6p ²F5/2 ⁰ (593.068 nm), 5d6s²²D_5/2 -5d²6p ²F_7/1)⁰ (593.062 nm), 5d6s²²D_3/2 -5d₂ 6p ²D_3/2⁰ (550.134 nm), 5d6s²²D_5/2 -5d²6p ²D_5/2)⁰ (545.514 nm) and 5d6s²² D_3/2 -5d6s6p ⁴ F_3/2⁰ (753.923 nm) transitions for a narrow band laser excitation in a one-photon resonant two-photon ionisation scheme considering a Lorentzian atomic profile for simulation of the excitation spectrum. Simulations have been carried out for a laser bandwidth of 50 MHz. The coherence effects are ignored in the computation as the laser bandwidth (50 MHz) is much smaller than the largest separation between the hyperfine levels (i.e. γ_L << Δ_HFGS). The results obtained for the ² D_3/2 - ⁴ F_3/2⁰ (753.923 nm) transition are in excellent agreement with the experimental results obtained by Young et al, using diode laser initiated resonance ionisation mass spectrometry. The isotopic selectivities and isotope ratio enhancement factors computed for the ²D_5/2 -² D_5/2⁰ (545.514 nm) transition are about 19% higher than the ² D_3/2 -⁴ F_3/2)⁰ (753.923 nm) transition used by Young et al. This increased isotopic selectivity can be used for isotope selective excitation of ¹³⁸ La with improved detection sensitivity. This method demonstrates its usefulness in identifying the most efficient atomic lines in order to focus experimental effort on these transitions. (author)

[en] Ytterbium enriched in ¹⁷⁶Yb is used for the production of the ¹⁷⁷Lu radioisotope, which has applications in cancer treatment. We have theoretically studied the two-step resonant, three-step photoionization of the ¹⁷⁶Yb isotope using the density-matrix approach. To simulate experimentally realistic conditions, the Doppler averaging, magnetic sublevel degeneracy, time-varying Rabi frequencies, ionization rate, angular divergence, and laser bandwidth have all been incorporated into the theoretical model. Calculations have been carried out to identify the optimized Rabi frequencies for evaluating the separation factor. The effect of the laser line shape on the excitation profile has also been thoroughly studied. We could obtain large separation factors of ∼5000 for the ¹⁷⁶Yb isotope, and the excitation conditions identified in this work may be utilized in the separation of the desired isotope

[en] The ⁸⁷Sr isotope has an extremely complex hyperfine structure (HFS) as a consequence of simultaneous mixing of the ³F₂, ³F₃, ³F₄ and ¹F₃ fine structure components in the 5s32f state. The resultant hyperfine spectrum of the 5s4d ³D₃-5s32f ³F₄ (364 nm) transition consists of 74 hyperfine components. HFS constants A, B for both upper and lower levels have been derived from the single-electron contribution factors a_5s, a_4d3/2, a_4d5/2, b_4d3/2 and b_4d5/2 using Breit-Wills formalism. Isotope ratio enhancement factors have been computed for the 5s5p ³P₂-5s21s ³S₁ (325 nm), 5s4d ³D₃-5s32f ³F₄ (364 nm) and the 5s²¹S₀-5s5p ³P₁ (689.7 nm) transitions for isotope selective excitation/ionization of ⁸⁹Sr and ⁹⁰Sr isotopes in collinear fashion. The results obtained are comparable to that of the experimental results reported earlier. Simulations have been carried out for various laser linewidths and acceleration potentials considering appropriate abundances, HFS of the odd isotope and mass shifts of the constituent isotopes. This method can be used for optimization of experimental configurations with respect to acceleration potentials and appropriate laser linewidths in order to obtain better selectivities for the ⁸⁹Sr and ⁹⁰Sr isotopes which allows the long term monitoring of these isotopes in the environment. The present study shows that the HFS of the ⁸⁷Sr isotope has a significant effect on the isotope selective excitation of ⁸⁹Sr and ⁹⁰Sr isotopes. (author)