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Performance of francium ion sources

Sergey Nikitich Atutov, R. Calabrese, L. Corradi, A. Dainelli, C. de Mauro, Alen Khanbekyan, E. Mariotti, P. Minguzzi, L. Moi, Stefano Sanguinetti, G. Stancari, L. Tomassetti, Stefano Veronesi

Published Jan 1, 2006• 0 citations

Abstract

A cold cloud of rare atoms is desirable in several fields. High-resolution spectroscopy of poorly-known atomic levels and tests of the Standard Model in atomic systems are examples of studies pursued in laboratories around the world [1]. Francium is particularly suitable because it is the heaviest alkali metal and it has several isotopes with relatively long lifetimes. Also, one expects enhanced parity-violating effects and reduced theoretical uncertainties from isotope comparisons. By accumulating atoms in a trap, one partially compensates for their scarcity. Our group and the one at SUNY Stony Brook, who pioneered the field [2], are focusing on the isotopes with mass numbers in the range 208–211. A production target, a beam transport line and a magneto-optical trap (MOT) are operating at INFN’s National Laboratories in Legnaro. An overview of our work is given in Refs. [3, 4]. Here we summarize the performance of the Fr sources.

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Dec 22, 2008•5 citations

A cold cloud of rare atoms is desirable in several fields. High-resolution spectroscopy of poorly-known atomic levels and tests of the Standard Model in atomic systems are examples of studies pursued in laboratories around the world [1]. Francium is particularly suitable because it is the heaviest alkali metal and it has several isotopes with relatively long lifetimes. Also, one expects enhanced parity-violating effects and reduced theoretical uncertainties from isotope comparisons. By accumulating atoms in a trap, one partially compensates for their scarcity. Our group and the one at SUNY Stony Brook, who pioneered the field [2], are focusing on the isotopes with mass numbers in the range 208–211. A production target, a beam transport line and a magneto-optical trap (MOT) are operating at INFN’s National Laboratories in Legnaro. An overview of our work is given in Refs. [3, 4]. Here we summarize the performance of the Fr sources.

Summary form only given. We have constructed a new apparatus for on-line magneto-optical trapping of radioactive francium atoms at the Stony Brook Superconducting LINAC. An ion beam with an energy of /spl sim/100 MeV from the accelerator strikes a target of gold or isotopically enriched platinum mounted on the end of a tungsten rod. A heavy-ion fusion reaction [/sup 16,18/O(/sup 197/Au,xn) or /sup 19/F(/sup 198/Pt,xn)] selectively produces the isotopes /sup 208-212/Fr in the target room of the accelerator. The beam power and an auxiliary heater heat the target, allowing the francium to diffuse rapidly to the surface. The target ionizes the francium as it diffuses out. We then transport the francium as ions to a different room for subsequent neutralization and capture in a magneto-optical trap (MOT). Since the transport system is electrostatic, it is mass independent, allowing us to transport any isotope of Fr or even other alkalis. We have delivered over 3/spl times/10/sup 6/ Fr/sec to a Faraday cup in front of the trap, and tests show greater than 90% transport efficiency from the target. A small constriction in the vacuum system separates the target and transport region from the trap, permitting differential pumping of the trap.

A magneto-optical trap for francium radioactive atoms has been set up at the Istituto Nazionale di Fisica Nucleare, Legnaro laboratories, and its characterization and optimization are under way. The main features of the Fr+ beam line, of the target, and of the magneto-optical trap are described in detail. Measurements of the Fr-ion production rate as a function of the target temperature, the primary beam intensity, and energy have been made. Preliminary tests with other stable alkali atoms aimed at an improvement of the magneto-optical trap collection efficiency are reported. Fast and efficient trap loading of rubidium has been obtained through the light-induced atomic desorption from an organic coating. A larger number of sodium atoms, as compared with a monochromatic trapping laser, has been trapped by use of a broadband laser.

Francium is the least studied of the alkali atoms because it has no stable isotopes. We have performed precision spectroscopy on cold Fr atoms in a magneto optical trap. We have determined the location of the first two excited states of the S series by two-photon spectroscopy. We have measured the lifetimes of the 7p levels with a precision better than 0.5%. Our measurements test the many-body perturbation theory ab initio calculations of the dipole matrix element to very high accuracy in this relativistic alkali.