Physical Review Letters

Radiative Lifetime of Metastable Li II 2S01

Michael H. Prior, Howard A. Shugart

Published Oct 4, 1971• 46 citations

Abstract

The radiative lifetime of Li II $2^{1}S_{0}$ has been measured by counting decay photons versus time from an ensemble of metastable Li ions stored in a simple electromagnetic trap of the Penning variety. The result is ${\ensuremath{\tau}}_{\mathrm{expt}}=503(26)$ \ensuremath{\mu}sec. The error represents one standard deviation from the mean of a series of 34 separate determinations. This result is in agreement with the theoretical value ${\ensuremath{\tau}}_{\mathrm{th}}=513$ \ensuremath{\mu}sec.

DOI: 10.1103/physrevlett.27.902

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Physical Review Letters

Radiative Lifetime of Metastable Li II 2S01

Michael H. Prior, Howard A. Shugart

Published Oct 4, 1971• 46 citations

Publisher

Abstract

The radiative lifetime of Li II

2^{1}S_{0}

has been measured by counting decay photons versus time from an ensemble of metastable Li ions stored in a simple electromagnetic trap of the Penning variety. The result is

{\ensuremath{\tau}}_{\mathrm{expt}}=503(26)

\ensuremath{\mu}sec. The error represents one standard deviation from the mean of a series of 34 separate determinations. This result is in agreement with the theoretical value

{\ensuremath{\tau}}_{\mathrm{th}}=513

\ensuremath{\mu}sec.

DOI: 10.1103/physrevlett.27.902

Related papers

Radiative lifetime of metastable 2S13 Li+

Randall D. Knight, Michael H. Prior

The radiative lifetime of $1s2s^{3}S_{1}$ ${\mathrm{Li}}^{+}$ ions has been measured by a comparison of the count rate of spontaneous decay photons (210 \AA{}) to a laser-induced fluorescence signal proportional to the total number of metastable ions. The ions were confined in a rf-quadrupole trap, and the fluorescence signal used was the intercombination transition $1s2p^{3}P_{1}$ to $1{s}^{2}^{1}S_{0}$ at 202 \AA{}. The $^{3}P_{1}$ state was populated from $^{3}S_{1}$ by absorption of laser photons at 5485 \AA{}. The result is ${\ensuremath{\tau}}_{r}=58.6\ifmmode\pm\else\textpm\fi{}12.9$ sec (95% confidence level); theory predicts ${\ensuremath{\tau}}_{r}=49.1$ sec.The radiative lifetime of $1s2s^{3}S_{1}$ ${\mathrm{Li}}^{+}$ ions has been measured by a comparison of the count rate of spontaneous decay photons (210 \AA{}) to a laser-induced fluorescence signal proportional to the total number of metastable ions. The ions were confined in a rf-quadrupole trap, and the fluorescence signal used was the intercombination transition $1s2p^{3}P_{1}$ to $1{s}^{2}^{1}S_{0}$ at 202 \AA{}. The $^{3}P_{1}$ state was populated from $^{3}S_{1}$ by absorption of laser photons at 5485 \AA{}. The result is ${\ensuremath{\tau}}_{r}=58.6\ifmmode\pm\else\textpm\fi{}12.9$ sec (95% confidence level); theory predicts ${\ensuremath{\tau}}_{r}=49.1$ sec.

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LIFETIME OF THE METASTABLE 23S1 STATE IN STORED Li+ IONS

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A laser-induced fluorescence technique combined with the observation of spontane ous magnetic dipole photons from the highly metastable 2 3 S t state of Li + has been used to measure the radiative lifetime of this state.The ions are created by electron impact on a lithium A. Direct Determination of the Spontaneous Decay Curve .... 18 B. Direct Determination of the Number of Remaining Metastables 20 C. Indirect Determination of the Radiative Lifetime 23 IV.Ion Trap Theory and Performance 29 A. The RF-Quadrupole Ion Trap 29 B. The Ion Detection System 36 C. Ion Trap Performance 43 1.Ion storage 43 2. Ion distribution 50 V.Experimental Methods 56 A. The Vacuum System 56 B. The Lithium Oven and Hot Wire Detector 60 C. The Ion Trap and Electron Gun 62 D. The Magnetic Field 66 1. Detector operation ..... 73 2. Detector calibration 76 6.The Laser and Optical System 81 H.The Computer System 84 1. Timing and control .84 2. Operating and analysis programs 88 VI.Experimental Results 93 A. The Detection of Spontaneous Ml Photons 93 B. The Detection of Laser-Induced Photons 96 C. The Metastable Lifetime and Nonradiative Quenching .... 99 D. Procedures in Measuring the Radiative Lifetime 104 E. Data Reduction and Error Analysis Ill VII.Conclusion 119 Appendix A. Optical Pumping Calculations .121 A. The Magic Angle 121 B. The Optical Pumping Equations 123 C. Results of the Calculations .126 Appendix B. Measurements of the Ion Density Distribution 128 A. The Laser Scanning Technique 128 B. Experimental Results 130 Acknowledgements ....A laser-induced fluorescence technique combined with the observation of spontane ous magnetic dipole photons from the highly metastable 2 3 S t state of Li + has been used to measure the radiative lifetime of this state.The ions are created by electron impact on a lithium A. Direct Determination of the Spontaneous Decay Curve .... 18 B. Direct Determination of the Number of Remaining Metastables 20 C. Indirect Determination of the Radiative Lifetime 23 IV.Ion Trap Theory and Performance 29 A. The RF-Quadrupole Ion Trap 29 B. The Ion Detection System 36 C. Ion Trap Performance 43 1.Ion storage 43 2. Ion distribution 50 V.Experimental Methods 56 A. The Vacuum System 56 B. The Lithium Oven and Hot Wire Detector 60 C. The Ion Trap and Electron Gun 62 D. The Magnetic Field 66 1. Detector operation ..... 73 2. Detector calibration 76 6.The Laser and Optical System 81 H.The Computer System 84 1. Timing and control .84 2. Operating and analysis programs 88 VI.Experimental Results 93 A. The Detection of Spontaneous Ml Photons 93 B. The Detection of Laser-Induced Photons 96 C. The Metastable Lifetime and Nonradiative Quenching .... 99 D. Procedures in Measuring the Radiative Lifetime 104 E. Data Reduction and Error Analysis Ill VII.Conclusion 119 Appendix A. Optical Pumping Calculations .121 A. The Magic Angle 121 B. The Optical Pumping Equations 123 C. Results of the Calculations .126 Appendix B. Measurements of the Ion Density Distribution 128 A. The Laser Scanning Technique 128 B. Experimental Results 130 Acknowledgements ....

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Radiative Lifetime of the 2 S01 Metastable State of Helium

Robert S. Van Dyck, C. E. Johnson, Howard A. Shugart

A time-of-flight technique has been used to measure the radiative lifetime of the $2 ^{1}S_{0}$ state of helium. After passing from a cooled source, helium atoms are excited by a pulsed anti-parallel electron beam. The atomic beam then contains not only ground-state helium atoms but also metastable atoms in both the $2 ^{3}S_{1}$ and the $2 ^{1}S_{0}$ states. The metastable atoms are detected at two positions, 1.9 and 6.7 m from the electron gun, by Auger ejection of an electron from a copper target, the first of which is a 60% transmitting mesh. Ground-state helium atoms cannot cause an electron to be ejected and hence are not detected. The time-of-flight distribution for the metastable $2 ^{1}S_{0}$ state is separated from that of the $2 ^{3}S_{1}$ state by illuminating the beam with an rf-discharge helium lamp. The $2 ^{1}S_{0}$ state is quenched by resonant absorption of a 20 581 - \AA{}A photon, raising the atom to the $2 ^{1}P_{1}$ state, which then decays preferentially to the $^{1}S_{0}$ ground state; the $2 ^{3}S_{1}$ state remains unaffected because it is the ground state for the triplet system. The time-of-flight distribution for the $2 ^{1}S_{0}$ atoms is therefore obtained from the difference between the full beam and the quenched beam. A comparison of the number of $2 ^{1}S_{0}$ metastables within a given velocity interval at the two detectors determines the number which decay in flight and yields a value for the two-photon radiative lifetime. The value of the singlet lifetime for both ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{4}$ is 19.7 \ifmmode\pm\else\textpm\fi{} 1.0 msec, agreeing with the theoretical value of 19.5 msec, but disagreeing with the value 38 \ifmmode\pm\else\textpm\fi{} 8 msec measured by Pearl using a movable detector. The 1.0-msec error is an estimate of the remaining systematic errors in the experiment.A time-of-flight technique has been used to measure the radiative lifetime of the $2 ^{1}S_{0}$ state of helium. After passing from a cooled source, helium atoms are excited by a pulsed anti-parallel electron beam. The atomic beam then contains not only ground-state helium atoms but also metastable atoms in both the $2 ^{3}S_{1}$ and the $2 ^{1}S_{0}$ states. The metastable atoms are detected at two positions, 1.9 and 6.7 m from the electron gun, by Auger ejection of an electron from a copper target, the first of which is a 60% transmitting mesh. Ground-state helium atoms cannot cause an electron to be ejected and hence are not detected. The time-of-flight distribution for the metastable $2 ^{1}S_{0}$ state is separated from that of the $2 ^{3}S_{1}$ state by illuminating the beam with an rf-discharge helium lamp. The $2 ^{1}S_{0}$ state is quenched by resonant absorption of a 20 581 - \AA{}A photon, raising the atom to the $2 ^{1}P_{1}$ state, which then decays preferentially to the $^{1}S_{0}$ ground state; the $2 ^{3}S_{1}$ state remains unaffected because it is the ground state for the triplet system. The time-of-flight distribution for the $2 ^{1}S_{0}$ atoms is therefore obtained from the difference between the full beam and the quenched beam. A comparison of the number of $2 ^{1}S_{0}$ metastables within a given velocity interval at the two detectors determines the number which decay in flight and yields a value for the two-photon radiative lifetime. The value of the singlet lifetime for both ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{4}$ is 19.7 \ifmmode\pm\else\textpm\fi{} 1.0 msec, agreeing with the theoretical value of 19.5 msec, but disagreeing with the value 38 \ifmmode\pm\else\textpm\fi{} 8 msec measured by Pearl using a movable detector. The 1.0-msec error is an estimate of the remaining systematic errors in the experiment.

Physical Review AOct 1, 197199 citations

The radiative lifetime of Li II

2^{1}S_{0}

has been measured by counting decay photons versus time from an ensemble of metastable Li ions stored in a simple electromagnetic trap of the Penning variety. The result is

{\ensuremath{\tau}}_{\mathrm{expt}}=503(26)

\ensuremath{\mu}sec. The error represents one standard deviation from the mean of a series of 34 separate determinations. This result is in agreement with the theoretical value

{\ensuremath{\tau}}_{\mathrm{th}}=513

\ensuremath{\mu}sec.

The radiative lifetime of

1s2s^{3}S_{1}

{\mathrm{Li}}^{+}

ions has been measured by a comparison of the count rate of spontaneous decay photons (210 \AA{}) to a laser-induced fluorescence signal proportional to the total number of metastable ions. The ions were confined in a rf-quadrupole trap, and the fluorescence signal used was the intercombination transition

1s2p^{3}P_{1}

to $1{s}^{2}^{1}S_{0}$ at 202 \AA{}. The

^{3}P_{1}

state was populated from

^{3}S_{1}

by absorption of laser photons at 5485 \AA{}. The result is ${\ensuremath{\tau}}_{r}=58.6\ifmmode\pm\else\textpm\fi{}12.9$ sec (95% confidence level); theory predicts ${\ensuremath{\tau}}_{r}=49.1$ sec.

The radiative lifetime of the

{}^{1}{S}_{0}

metastable state of

{\mathrm{Xe}}^{2+}

has been measured with a different type of electrostatic ion trap. The ion trap stores ion beams of a few keV using purely electrostatic fields and provides a large field-free region where the stored ions oscillate. A photomultiplier working in the single-photon counting mode was used to observe the 380 nm photons arising from the magnetic dipole

(M1)

transition ${}^{1}{\stackrel{\ensuremath{\rightarrow}}{{S}_{0}}}^{3}{P}_{1}$ of

{\mathrm{Xe}}^{2+}.

The present measurement yields a value of $4.46\ifmmode\pm\else\textpm\fi{}0.08 \mathrm{ms},$ which is in good agreement with previous measurements, but is almost four times more accurate.

2^{1}S_{0}

state of helium is 20 \ifmmode\pm\else\textpm\fi{} 2 msec.

A time-of-flight technique has been used to measure the radiative lifetime of the

2 ^{1}S_{0}

state of helium. After passing from a cooled source, helium atoms are excited by a pulsed anti-parallel electron beam. The atomic beam then contains not only ground-state helium atoms but also metastable atoms in both the

2 ^{3}S_{1}

and the

2 ^{1}S_{0}

states. The metastable atoms are detected at two positions, 1.9 and 6.7 m from the electron gun, by Auger ejection of an electron from a copper target, the first of which is a 60% transmitting mesh. Ground-state helium atoms cannot cause an electron to be ejected and hence are not detected. The time-of-flight distribution for the metastable

2 ^{1}S_{0}

state is separated from that of the

2 ^{3}S_{1}

state by illuminating the beam with an rf-discharge helium lamp. The

2 ^{1}S_{0}

state is quenched by resonant absorption of a 20 581 - \AA{}A photon, raising the atom to the

2 ^{1}P_{1}

state, which then decays preferentially to the

^{1}S_{0}

ground state; the

2 ^{3}S_{1}

state remains unaffected because it is the ground state for the triplet system. The time-of-flight distribution for the

2 ^{1}S_{0}

atoms is therefore obtained from the difference between the full beam and the quenched beam. A comparison of the number of

2 ^{1}S_{0}

metastables within a given velocity interval at the two detectors determines the number which decay in flight and yields a value for the two-photon radiative lifetime. The value of the singlet lifetime for both

{\mathrm{He}}^{3}

and

{\mathrm{He}}^{4}

is 19.7 \ifmmode\pm\else\textpm\fi{} 1.0 msec, agreeing with the theoretical value of 19.5 msec, but disagreeing with the value 38 \ifmmode\pm\else\textpm\fi{} 8 msec measured by Pearl using a movable detector. The 1.0-msec error is an estimate of the remaining systematic errors in the experiment.