a Measurement of the Single Positive Helium Ion(doublet -2S(1/2)-DOUBLET-2P(1/2)) Lamb Shift.

Jagdish S. Patel

Published Jan 1, 1986• 0 citations

Abstract

A beam of unpolarized metastable He('+) 2s(, 1/2) ions, quenched by a static electric field, (')E has an anisotropy in the emitted radiation that can be used to determine the He('+) 2('2)s(, 1/2)-2('2)p(, 1/2) Lamb shift. A high precision measurement of this anisotropy for a field strength of (VBAR)(')E(VBAR) = (370.97 (+OR-) 0.06) V/cm has been made. The value of the field-free anisotropy, A('(0)), adjusted by small corrections is (0.1178082 (+OR-) 0.0000086), where the uncertainty is the statistical one standard deviation. Using much improved apparatus over Drake, Goldman and van Wijngaarden, our values for both the anisotropy A('(0)) and the Lamb shift, S = (14022.67 (+OR-) 1.06) MHz lie lower by 17 standard deviations from theirs. The great discrepancy is not understood, and may be attributed to the inherent difficulties of measuring light intensities by photon counting techniques. Source: Dissertation Abstracts International, Volume: 47-09, Section: B, page: 3817. Thesis (Ph.D.)--University of Windsor (Canada), 1986.

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a Measurement of the Single Positive Helium Ion(doublet -2S(1/2)-DOUBLET-2P(1/2)) Lamb Shift.

Jagdish S. Patel

Published Jan 1, 1986• 0 citations

OpenAlex

Abstract

Related papers

He+ Lamb-shift measurement by the quenching-radiation anisotropy method

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Lyman-α radiation of a metastable hydrogen beam to measure electric fields

A. Lejeune, Laurence Chérigier-Kovacic, F. Doveil

The interaction between a metastable H(2s) atomic hydrogen beam and an external electric field leads to the emission of the Lyman-α line. It originates in the Stark mixing of the near-degenerate 2s1/2 and 2p1/2 levels separated by the Lamb shift. The quenched radiation proportional to the square of the electric field amplitude is recovered in vacuum by using such an atomic probe beam. We observe the strong enhancement of the signal when the field is oscillating at the Lamb shift frequency. This technique is applied in a plasma, offering an alternative way to measure weak electric fields by direct and non-intrusive means.The interaction between a metastable H(2s) atomic hydrogen beam and an external electric field leads to the emission of the Lyman-α line. It originates in the Stark mixing of the near-degenerate 2s1/2 and 2p1/2 levels separated by the Lamb shift. The quenched radiation proportional to the square of the electric field amplitude is recovered in vacuum by using such an atomic probe beam. We observe the strong enhancement of the signal when the field is oscillating at the Lamb shift frequency. This technique is applied in a plasma, offering an alternative way to measure weak electric fields by direct and non-intrusive means.

Applied Physics LettersOct 31, 20117 citations

The Lamb shift of

{\mathrm{He}}^{+}

is derived from the measured anisotropy in the electric-field-induced quenching radiation of the metastable

2{s}_{\frac{1}{2}}

state. The results demonstrate that the anisotropy method can be applied with high precision to one-electron ion beams, as well as neutral beams. We find a Lamb shift of 14040.2\ifmmode\pm\else\textpm\fi{}2.9 MHz (1 standard deviation). The sources of error and difficulties encountered in working with ion beams are discussed in detail.

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

2^{1}S_{0}

metastable state of helium by a static electric field. Neutral ground-state helium atoms effusing from a cooled source slit are immediately excited to the

2^{1}S_{0}

and

2^{3}S_{1}

metastable states by a pulse of antiparallel magnetically focused electrons. The metastable beam is collimated before passing through a uniform electric field region 0.5 m long and is then preferentially detected at the end of the time-of-flight region, 1.825 m from the electron gun. The time-of-flight distribution for the

2^{1}S_{0}

state is separated from that of the

2^{3}S_{1}

state by illuminating the beam before the electric field region with an rf-discharge helium lamp. The

2^{1}S_{0}

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

2^{1}P_{1}

state, which then decays 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

2^{1}S_{0}

time-of-flight distribution is therefore obtained from the difference between the full beam and the quenched beam. The number of

2^{1}S_{0}

atoms arriving at the detector in specific velocity intervals with the electric field off is compared to the number with the field on to determine the quenching rate (

=k{E}^{2}

). The result for the quenching constant

k

for both

{\mathrm{He}}^{3}

and

{\mathrm{He}}^{4}

with

E

in kV/cm is $k=0.933\ifmmode\pm\else\textpm\fi{}0.005$; this value is in good agreement with theory and with an earlier less accurate experiment. The error in the present experiment arises from a 0.5% uncertainty in the effective length of the electric field region.

The static dipole polarizability of helium atoms in the metastable

2^{3}S_{1}

and

2^{1}S_{0}

states has been determined by measuring the deflection of a beam of excited helium atoms that is caused by an inhomogeneous electric field of known properties. The necessary velocity distribution information is obtained from time-of-flight measurements, and a resonance quenching technique made it possible to distinguish the singlet and triplet components of the beam. The results, $\ensuremath{\alpha}(2^{3}S_{1})=(44.6\ifmmode\pm\else\textpm\fi{}3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$

{\mathrm{cm}}^{3}

and $\ensuremath{\alpha}(2^{1}S_{0})=(108\ifmmode\pm\else\textpm\fi{}13)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$

{\mathrm{cm}}^{3}

, agree with the theoretical value that has been used to calibrate earlier polarizability measurements of the alkali metals and the heavier noble gases.