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Progress towards trapping {sup 82}Rb in an optical trap

Ralf Guckert, V. D. Sandberg, D. Tupa, David J. Vieira, Xin Guo Zhao

Published Dec 31, 1997• 0 citations
OpenAlex

Abstract

The efficient coupling of an optical trap to a mass separator is being developed to undertake high-precision electroweak interaction measurements. The use of an ion implantation and subsequent heated foil release method is being pursued as a suitable way of introducing radioactive samples into the ultra high vacuum region of the optical trap without gas loading. The batchwise trapping and cooling of one million {sup 82}Rb atoms is envisioned with overall efficiencies of 1% or more. The cloud of cold radioactive atoms ({approximately}1 mm in diameter) will than be spin polarized and transferred to a second optical trap, repolarized, and loaded in a magnetic trap in which a beta-asymmetry measurement will be performed. The latest developments towards undertaking this experiment will be presented.

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The authors describe the coupling of a magneto-optical trap to a mass separator for the ultra-sensitive detection of selected radioactive species. As a proof of principle test, they have demonstrated the trapping of {approximately} 6 million {sup 82} Rb (t{sub 1/2} = 75 s) atoms using an ion implantation and heated foil release method for introducing the sample into a trapping cell with minimal gas loading. Gamma-ray counting techniques were used to determine the efficiencies of each step in the process. By far the weakest step in the process is the efficiency of the optical trap itself (0.3%). Further improvements in the quality of the nonstick dryfilm coating on the inside of the trapping cell and the possible use of larger diameter laser beams are indicated. In the presence of a large background of scattered light, this initial work achieved a detection sensitivity of {approximately} 4,000 trapped atoms. Improved detection schemes using a pulsed trap and gated photon detection method are outlined. Application of this technology to the areas of environmental monitoring and nuclear proliferation are foreseen.

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Trapping radioactive Rb82 in an optical dipole trap and evidence of spontaneous spin polarization

D. Feldbaum, H. Wang, Jonathan D. Weinstein +2 more

Optical trapping of selected species of radioactive atoms has great potential in precision measurements for testing fundamental physics such as the electric dipole moment, atomic parity nonconservation, and parity-violating $\ensuremath{\beta}$-decay correlation coefficients. We report on the trapping of ${10}^{4}$ radioactive $^{82}\mathrm{Rb}$ atoms $({t}_{1∕2}=75\phantom{\rule{0.3em}{0ex}}\mathrm{s})$ with a trap lifetime of $\ensuremath{\sim}55\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ in an optical dipole trap. Transfer efficiency from the magneto-optical trap is $\ensuremath{\sim}14%$. We further report evidence of spontaneous spin polarization of the atoms in optical dipole trap loading. These advancements are an important step toward a new generation of precision nuclear-spin--$\ensuremath{\beta}$-emission direction correlation measurements with polarized $^{82}\mathrm{Rb}$ atoms.

arXiv:0708.3826•Physical Review A•Nov 20, 2007•12 citations
The efficient coupling of an optical trap to a mass separator is being developed to undertake high-precision electroweak interaction measurements. The use of an ion implantation and subsequent heated foil release method is being pursued as a suitable way of introducing radioactive samples into the ultra high vacuum region of the optical trap without gas loading. The batchwise trapping and cooling of one million {sup 82}Rb atoms is envisioned with overall efficiencies of 1% or more. The cloud of cold radioactive atoms ({approximately}1 mm in diameter) will than be spin polarized and transferred to a second optical trap, repolarized, and loaded in a magnetic trap in which a beta-asymmetry measurement will be performed. The latest developments towards undertaking this experiment will be presented.
We report the successful trapping of $6\ifmmode\times\else\texttimes\fi{}{10}^{6}$ 82Rb{}^{82}\mathrm{Rb}82Rb (t1/2=75s){(t}_{1/2}=75\mathrm{s})(t1/2​=75s) atoms with a trap lifetime of $\ensuremath{\sim}30\mathrm{s}$ in a magneto-optical trap that is coupled to an off-line mass separator. Efficient sample introduction is achieved by implanting 82Rb{}^{82}\mathrm{Rb}82Rb ions into a small yttrium catcher foil located inside the trapping cell. Upon heating, the radioactive atoms are released from the foil and trapped without significant gas loading. This advancement makes a variety of high-precision electroweak interaction experiments possible, including the measurement of \ensuremath{\beta}-decay correlations associated with spin-polarized 82Rb{}^{82}\mathrm{Rb}82Rb nuclei.
The authors describe the coupling of a magneto-optical trap to a mass separator for the ultra-sensitive detection of selected radioactive species. As a proof of principle test, they have demonstrated the trapping of {approximately} 6 million {sup 82} Rb (t{sub 1/2} = 75 s) atoms using an ion implantation and heated foil release method for introducing the sample into a trapping cell with minimal gas loading. Gamma-ray counting techniques were used to determine the efficiencies of each step in the process. By far the weakest step in the process is the efficiency of the optical trap itself (0.3%). Further improvements in the quality of the nonstick dryfilm coating on the inside of the trapping cell and the possible use of larger diameter laser beams are indicated. In the presence of a large background of scattered light, this initial work achieved a detection sensitivity of {approximately} 4,000 trapped atoms. Improved detection schemes using a pulsed trap and gated photon detection method are outlined. Application of this technology to the areas of environmental monitoring and nuclear proliferation are foreseen.
The use of an optical trap for the quantitative detection of small numbers of radioactive atoms is featured. Presently under construction is a system consisting of a high-efficiency magneto-optical trap (MOT) coupled to a mass separator. Mass-separated samples will be implanted into a thin platinum foil, subsequently released from the foil by heating, and resonantly trapped in the MOT. The number of atoms in the trap will be quantitatively deduced from the amplitude of the fluorescence signal. Measurements for different isotopes are planned by appropriately shifting the trapping and repumping laser frequencies of the optical trap. Our initial investigations will concentrate on the determination of trace amounts of 135Cs and 137Cs.
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.
Precision measurement of atomic and nuclear polarization is an essential step for beta-asymmetry measurement of radioactive atoms. In this paper, we report the polarization measurement of Rb atoms in an yttrium-aluminum-garnet (YAG) far-off-resonance optical dipole trap. We have prepared a cold cloud of polarized Rb atoms in the YAG dipole trap by optical pumping and achieved an initial nuclear polarization of up to 97.2(5)%. The initial atom distribution in different Zeeman levels is measured by using a combination of microwave excitation, laser pushing, and atomic retrap techniques. The nuclear-spin polarization is further purified to 99.2(2)% in 10 s and maintained above 99% because the two-body collision loss rate between atoms in mixed spin states is greater than the one-body trap loss rate. Systematic effects on the nuclear polarization, including the off-resonance Raman scattering, magnetic field gradient, and background gas collisions, are discussed.
Optical trapping of selected species of radioactive atoms has great potential in precision measurements for testing fundamental physics such as the electric dipole moment, atomic parity nonconservation, and parity-violating $\ensuremath{\beta}$-decay correlation coefficients. We report on the trapping of 104{10}^{4}104 radioactive 82Rb^{82}\mathrm{Rb}82Rb atoms (t1∕2=75s)({t}_{1∕2}=75\phantom{\rule{0.3em}{0ex}}\mathrm{s})(t1∕2​=75s) with a trap lifetime of $\ensuremath{\sim}55\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ in an optical dipole trap. Transfer efficiency from the magneto-optical trap is $\ensuremath{\sim}14%$. We further report evidence of spontaneous spin polarization of the atoms in optical dipole trap loading. These advancements are an important step toward a new generation of precision nuclear-spin--$\ensuremath{\beta}$-emission direction correlation measurements with polarized 82Rb^{82}\mathrm{Rb}82Rb atoms.