INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS B: ATOMIC, MOLECULAR AND OPTICAL PHYSICS
J. Phys. B: At. Mol. Opt. Phys. 37 (2004) L305–L311 PII: S0953-4075(04)82253-3
LETTER TO THE EDITOR
Lifetime and hyperfine structure of the
3
D
2
state of
radium
Jacek Biero ´ n
1,4
, Charlotte Froese Fischer
2
, Stephan Fritzsche
3
and
Krzysztof Pachucki
4
1
Instytut Fizyki imienia Mariana Smoluchowskiego, Uniwersytet Jagiello´ nski, Krak´ ow, Poland
2
Vanderbilt University, Nashville, TN 37235, USA
3
Fachbereich Physik, Universit¨ at Kassel, D-34109 Kassel, Germany
4
Instytut Fizyki Teoretycznej, Uniwersytet Warszawski, Ho˙ za 69, 00-681 Warszawa, Poland
Received 14 June 2004
Published 17 August 2004
Online at stacks.iop.org/JPhysB/37/L305
doi:10.1088/0953-4075/37/17/L01
Abstract
The energy and lifetime of the metastable
3
D
2
level of radium play an important
role in planned experimental investigations of parity and time reversal violation.
The multiconfiguration Dirac–Hartree–Fock (MCDHF) model was employed
to compute the oscillator strengths of the
1
P
1
–
1
S
0
and
3
D
2
–
1
S
0
transitions, and
the hyperfine structures of the
1
P
1
and
3
D
2
states of radium. The calculations
yield the
3
D
2
lifetime τ = 4 s.
Parity and time reversal violation effects in atoms are enhanced by various nuclear and atomic
mechanisms, and in the last decade several atoms (as well as molecules) were considered
as candidates for experimental searches [11]. Recent advances in trapping and spectroscopy
of minuscule amounts of atoms make it possible to extend the search into the domain of
radioactive elements, of which francium [22] and radium [15] are currently considered the
most promising ones. The advantage of radium lies in octupole deformations of nuclei in
several isotopes [9], simple electronic structure [Kr]4d
10
4f
14
5s
2
5p
6
5d
10
6s
2
6p
6
7s
2
as well as
in the coincidental proximity of two atomic levels of opposite parity, 7s7p
3
P
1
and 7s6d
3
D
2
,
which are separated by a very small energy interval of 5 cm
−1
. In the present letter, we
calculated the energy and the electric quadrupole oscillator strength of the
3
D
2
–
1
S
0
transition,
the only significant decay channel of the metastable state
3
D
2
. The data for the
3
D
2
state
are necessary for setting up the experiment [15], in which the enhancement of the weak
interaction coupling between the 7s7p
3
P
1
and 7s6d
3
D
2
states will be exploited to detect a
possible permanent electric dipole moment of the radium atom. The energy and the electric
dipole oscillator strength of the
1
P
1
–
1
S
0
‘allowed’ transition were calculated for the purpose of
calibrating the method and tailoring an appropriate MCDHF model for the
3
D
2
level, which is
the main objective of the present letter. The hyperfine structures of the
1
P
1
and
3
D
2
levels were
also evaluated, using the same wavefunctions as for the transition rates. The experimental
0953-4075/04/170305+07$30.00 © 2004 IOP Publishing Ltd Printed in the UK L305