Pushpa M. Rao

Determination of the first ionization potential of actinide elements by resonance ionization mass spectroscopy

Abstract Resonance ionization mass spectroscopy (RIMS) in the presence of an external static electric field has been used for the determination of photoionization thresholds. Extrapolation of the thresholds obtained with different electric field strengths to zero field strength directly leads to the first ionization potential (IP). The ionization potentials of the transplutonium elements americium, curium, berkelium and californium could be measured for the first time. Due to the high sensitivity of RIMS, samples of only 1012 atoms have been used. The results are: IPAm = 5.9738(2)eV, IPCm = 5.9915(2)eV, IPBk = 6.1979(2)eV and IPCf = 6.2817(2)eV. The same technique was applied to thorium, neptunium and plutonium, yielding IPTh = 6.3067(2)eV, IPNp = 6.2655(2)eV and IPPo = 6.0258(2)eV. Plotted as a function of the number of electrons N, the actinide ionization potentials can be approximated by two straight lines joining at the half-filled shell when normalized to ionization from the lowest fN s2 level to the lowest fN s level.

Investigation of new odd-parity autoionization Rydberg levels of neutral europium

Abstract Transitions to the odd-parity autoionizing energy levels of europium atom from excited states are investigated by the method of two-step laser photoionization. Four new odd-parity autoionizing Rydberg series converging to the first excited ionic level 4f 7 6s 7 S 3 have been discovered in the energy region 45735–47404 cm −1 . Sixty-seven new autoionizing levels, which could not be assigned to any of these series, have also been reported. The quantum defects of the Rydberg series show small deviation for lower Rydberg levels indicating inter series interactions or perturbations.

Isotope shifts and electronic configurations of the odd parity energy levels of singly ionised samarium

Isotope shift ΔT (148–154) has been evaluated for twelve low-lying even and 89 odd parity levels of singly ionised samarium (Sm II) from the isotope shift (IS) studies in 182 spectral lines of Sm II in the 3890–4525 Å region. These studies were carried out on a recording Fabry-Perot spectrometer using eriched isotopes148Sm (96%) and154Sm (98%) excited in liquid nitrogen-cooled hollow-cathodes. Earlier data on isotope shifts are available for only eight lines in this region. It has been found that for a few spectral lines there are errors both in magnitudes and signs of isotope shifts, reported earlier. Most of the 89 odd parity levels of Sm II, for which ΔT values have been evaluated presently, have in literature either no electronic configuration assignments or only tentative assignments. We have suggested the leading configuration for most of these odd levels of Sm II on the basis of ΔT values evaluated in the present studies.

Loading Detection and Number Estimation of an Electron Plasma in a Penning Trap

A quadrupole Penning trap for spectroscopy and investigations of non-neutral plasmas was designed and built. In this work we provide details of the trap design and a discussion of a simple design and procedure for convenient electron loading from an aligned filament. Electrons from thermionic emission which form a low-energy diffuse beam are trapped in weak magnetic fields. They are detected through a non-destructive electronic detection scheme, the details of which are discussed. The detection signal is diminished when the electron beam energy is increased while the electron flux is kept constant. This is explained by considering the energy shift in the distribution function of electrons emitted from the filament and entering the trap. We present a calculation of the number of trapped electrons from the shape of the detection signal. This calculation, based on a model of a driven damped harmonic oscillator to describe the axial motion of the electrons, compares favourably with the numbers obtained by measurements of the space charge induced shift in the trap potential.

Determination of crossed-second-order field shift in8 F and6 F terms of 4f 6(7 F)6s configuration of sm+

We report here the experimental evaluation of crossed-second-order (CSO) effects in the field shift of8F and6F terms of 4f6(7F)6s configuration of singly ionised samarium. Our experimental value of CSO field shift difference between8F and6F terms for148Sm and154Sm is −11.8(3.2) mK, which is in good agreement with the theoretical value of −13.8 mK evaluated using known parameters.

Isotope shift studies and electronic configuration assignments to the energy levels of neutral erbium

Abstract Isotope shifts Δ T (170-166) have been evaluated for 54 even and 94 odd energy levels covering almost all the known configurations of the neutral erbium. These Δ T values have been derived from the isotope shift measurements carried out in 159 lines in the region 3900–4605 A using a Fabry-Perot spectrometer and liquid-air-cooled hollow cathode source with highly enriched 170 Er and 166 Er isotopic samples. Electronic configurations assigned to energy levels of Er I by earlier workers have been mostly confirmed and in few cases revisions have been suggested on the basis of observed Δ T values. Probable configurations have been also suggested for unassigned levels of Er I, and a large number of even levels could be assigned to 4 f 11 5 d 6 s 6 p configuration.

EVALUATION OF CHANGES IN MEAN-SQUARE NUCLEAR CHARGE RADII OF STABLE ISOTOPES OF ERBIUM

Isotope shifts involving all the stable even-A isotopes of erbium have been studied in four transitions using optical technique and highly enriched isotopes. The value of change in mean-square charge radii δ〈r2〉 deduced from our studies in 5806.05 Å (f12 s2-f12 sp) transition is in excellent agreement with muonic X-ray value. With negligible specific mass shift (SMS) in 5806.05 Å line, the SMS and field shifts in other lines are compared via King-Plot. In transitions involving change of 4f-electron (e.g., f12s2-f11ds2), large negative SMS value is obtained which is very close to the theoretically predicted value.

Trapping of relatively short-lived radioactive

A new technique has been developed wherein one of the relatively short lived isotopes of europium (, Half life days) has been generated by decay of parent atoms and the ions are confined in a Paul trap for spectroscopic studies. Studies of the mass dependent ion oscillation frequencies show that the ions trapped have a mass number 146 amu and this was confirmed by similar measurements carried out on trapped barium and potassium ions. From calculations of thermal ionization probabilities based on the Langmuir–Saha equation and the number of trapped ions estimated from ion response signal, the approximate number of the different isobars (of mass number 146) trapped, has been evaluated. We also present simulations of the evolution of laser-induced fluorescence photons of the trapped ions, wherein a pulsed laser is used to excite the resonance - transition, which rapidly decays to the metastable states emitting fluorescence photons.

{}^{146}{\rm Eu}

During the last two decades there has been tremendous progress in the technique of trapping and cooling ions using quadrupole ion traps. Using these trapping techniques one can have charged particles of a single species confined near the trap centre, which enables to carry out studies of these ions in a well-controlled environment. The long storage times of the ions, possible in these traps, results in the elimination of transit-time broadening making it possible to do precision spectroscopic measurements on these ions. Several important experiments with single electron or ion have been undertaken to address problems related to basic physics, such as the measurement of the electron radius, precision measurements of fundamental parameters and tests of the predictions of quantum mechanics.

in a Paul trap

Abstract Isotope shifts, Δσ ( 172 Yb– 176 Yb), in 29 spectral lines of neutral ytterbium (Yb I) are reported in the region 3405–4365 A. Earlier measurements in this region are available for five lines. The present measurements of isotope shift were carried out using the photoelectric recording Fabry–Perot spectrometer and highly enriched isotopic samples of 172 Yb and 176 Yb. Term isotope shifts, ΔT ( 172 Yb– 176 Yb), have been evaluated for 19 even and five odd parity high lying energy levels of Yb I, and the configurations assigned to these levels are discussed.