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Hyperfine structure of metastable states of barium studied by atomic-beam magnetic-resonance with laser detection
Volume 62A, number 4
PHYSICS LETTERS
22 August 1977
HYPERFINE STRUCTURE OF METASTABLE STATES OF BARIUM STUDIED BY ATOMIC-BEAM MAGNETIC-RESONANCE WITH LASER DETECTION M. GUSTAVSSON, I. LINDGREN, G. OLSSON, A. ROSEN and S. SVANBERG Department of Physics, Chalmers University of Technology, Goteborg, Sweden Received 21 October 1977 An atomic-beam magnetic-resonance technique together with laser detection has been used to study the hyperfine 3D structure of the metastable states of the 6s5d configuration of barium. Preliminary results for the 1 state, which has not been studied previously, are given.
In order to make full use of the effective-operator fo’r’malism in analysing the hyperfine interaction, it is necessary to know the experimental splittings in several atomic states within the same configuration. Such data is available in comparatively few cases [1]. The atomic-beam magnetic-resonance (ABMR) technique has been applied for a long time in hyperfine investigations of atomic ground states, and various optical methods have been extensively used for studying short-lived excited states. The ABMR technique has also been used for measurements in a number of metastable atomic states [2]. Various techniques for populating such states have been used, e.g. thermal or electron-bombardment excitations. Recently, metastable states in connection with ABMR work have been chargeproduced [3]. more efficiently using a plasma disA major problem in ABMR work is the detection of the atomic beam. For radioactive isotopes the
radioactivity itself offers an efficient way of detection. For stable isotopes, on the other hand, no effective universal detector is available. For instance, electron-bombardment ionization and subsequent massseparation has a detection efficiency of the order of 1: 1000. The rapid development in the technology of tunable lasers opens here interesting possibilities. In this letter we describe an ABMR experiment on metastable states of barium, where a CW tunable dye laser has been used for the detection. Tunable lasers can also be used in atomic-beam experiments for polarizing the beam and/or inducing transitions, as demonstrated recently by groups at Orsay [4] and Bonn [5]. The experimental arrangement used in the present work1D onand barium is shown fig. 1. The metastable 3D states are in produced by means of an 6s5d
Ba 3D
-
6s5d 3D. —-~5d~p~
5d6p~P~
Oven
~
~/7;~zlZ7~.~_
E~~et.
I~O
rf loop beam Fig. 1. Schematic view of the set-up used in the ABMR experiment with laser detection.
250
i.b
1=0
2.0
=
1=
F=½F~
3.
4.0
5.0
(~Hz)
Fig. 2. DC-signals observed in a low-field frequency scan for the 6s5d 3D 3 state.
Volume 62A, number 4
PHYSICS LETTERS
22 August 1977
37Ba ‘ F=3/2 137Ba
133.0
134.0
135.0
136.0 (MHz)
Fig. 3. Signals for the 6s5d 3D 1 state observed in a high-field frequency scan using lock-in detection at B = 418.8 gauss.
intense plasma discharge in front of the atomic-beam oven. The ABMR apparatus is of the sixpole-focusing type [6]. The atoms are focused or defocused in the A and B magnets, depending on the sign of the éffective magnetic moment. Atoms will reach the detector region, only if they have undergone a transition from a focusing to a defocusing state in the homogeneous C-field region. Such atoms are detected by observing the fluorescent light following a laser excitation to the Sd6p configuration (see fig. 2). In this way,individual states can be studied without interference from other states. This is particularly advantageous for weakly populated levels. In our experiments we used a coherent radiation model 490 CW dye laser in multimode operation. The wavelength for the laser-induced transitions falls in a convenient wavelength region, 580—610 nm. 1D 3D 3D The hyperfine structure of the 2, 2 and 3 states of barium has been studied by Schmelling [7], using the ABMR technique with a surface-ionizing detector followed by a mass-separator. As an illustration of the strong signals we obtain for these states with the present technique,we 3D show in fig. 2 a lowfield frequency scan for the 3 level, obtained in straight DC detection. The strong I = 0 signal originates from the even isotopes with a total abundance of 82%. The odd isotopes with A = 135 (7%) and A = 137 (11%), having the same nuclear spin (1 3/2), give rise3D to weaker unresolved hyperfine resonances. state is considerably more difficult to I The with the ABMR technique, due to the small observe electronic magnetic moment (gj 0.5). The I = 0 Signal has been observed by the Bonn group for this state .
in their accurate gj determinations [8]. With the technique described here,we have been able to observe 3D also the very weak hyperfine signals from the 1 state. The result of a frequency scan for this state, obtamed with lock-in detection, is shown in fig. 3. The 3D preliminary values of the hyperfine constants for the 1 state are A (137) = —522(2) MHz, B(1 37) 17(2) MHz,A(135) = —466(2) MHz and B(135) = 12(2) MHz. The sign of the A-factors has been determined from a consideration of the transmission properties of the ABMR-apparatus. More accurate determinations are in progress. For a complete investigation of the hyperfine interaction in the 6s5d configuration, high-precision measurements of the other states will also be performed. The applicability of the technique described here is mainly limited by the wavelength region of the tunable laser. The CW laser used in this experiment can be replaced by a pulsed laser system, thus extending the available wavelength region considerably. Tests have shown that such an approach should be feasible in several cases. This work was supported in part by the Swedish Natural Science Research Council.
References . [1J I. Lindgren and A. Rosen, Case Studies in Atom. Phys. 4 (1974) 93. [2J W.J. Childs, Case Studies in Atom. Phys. 3(1973) 215. 131 M. Gustavsson et al., Phys. Lett. B, to be published.
251
Volume 62A, number 4
PHYSICS LETTERS
22 August 1977
[41 H. Duong et al., Opt.
Commun. 7 (1973) 371; G. Huber et al., Phys. Rev. Lett. 34 (1975) 1209. [5] W. Ertmer and B. Hofer Z. Physik A276 (1976) 9; W. Zeiske et a!., Phys. Lett. 55A (1976) 405.
ed. K. Siegbahn (North-Holland, Amsterdam 1965); M. Olsmats, B. Wannberg and I. Lindgren, Nucl. Instrum. Meth. 103 (1972) 27. [7] S.G. Schmelling, Phys. Rev. A9 (1974) 1097.
[6] W.A. Nierenberg and I. Lindgren in: o, j3, ‘y-spectroscopy,
[8] R. Aydin et al, Z. Phys. A273 (1975) 233.
.252
PHYSICS LETTERS
22 August 1977
HYPERFINE STRUCTURE OF METASTABLE STATES OF BARIUM STUDIED BY ATOMIC-BEAM MAGNETIC-RESONANCE WITH LASER DETECTION M. GUSTAVSSON, I. LINDGREN, G. OLSSON, A. ROSEN and S. SVANBERG Department of Physics, Chalmers University of Technology, Goteborg, Sweden Received 21 October 1977 An atomic-beam magnetic-resonance technique together with laser detection has been used to study the hyperfine 3D structure of the metastable states of the 6s5d configuration of barium. Preliminary results for the 1 state, which has not been studied previously, are given.
In order to make full use of the effective-operator fo’r’malism in analysing the hyperfine interaction, it is necessary to know the experimental splittings in several atomic states within the same configuration. Such data is available in comparatively few cases [1]. The atomic-beam magnetic-resonance (ABMR) technique has been applied for a long time in hyperfine investigations of atomic ground states, and various optical methods have been extensively used for studying short-lived excited states. The ABMR technique has also been used for measurements in a number of metastable atomic states [2]. Various techniques for populating such states have been used, e.g. thermal or electron-bombardment excitations. Recently, metastable states in connection with ABMR work have been chargeproduced [3]. more efficiently using a plasma disA major problem in ABMR work is the detection of the atomic beam. For radioactive isotopes the
radioactivity itself offers an efficient way of detection. For stable isotopes, on the other hand, no effective universal detector is available. For instance, electron-bombardment ionization and subsequent massseparation has a detection efficiency of the order of 1: 1000. The rapid development in the technology of tunable lasers opens here interesting possibilities. In this letter we describe an ABMR experiment on metastable states of barium, where a CW tunable dye laser has been used for the detection. Tunable lasers can also be used in atomic-beam experiments for polarizing the beam and/or inducing transitions, as demonstrated recently by groups at Orsay [4] and Bonn [5]. The experimental arrangement used in the present work1D onand barium is shown fig. 1. The metastable 3D states are in produced by means of an 6s5d
Ba 3D
-
6s5d 3D. —-~5d~p~
5d6p~P~
Oven
~
~/7;~zlZ7~.~_
E~~et.
I~O
rf loop beam Fig. 1. Schematic view of the set-up used in the ABMR experiment with laser detection.
250
i.b
1=0
2.0
=
1=
F=½F~
3.
4.0
5.0
(~Hz)
Fig. 2. DC-signals observed in a low-field frequency scan for the 6s5d 3D 3 state.
Volume 62A, number 4
PHYSICS LETTERS
22 August 1977
37Ba ‘ F=3/2 137Ba
133.0
134.0
135.0
136.0 (MHz)
Fig. 3. Signals for the 6s5d 3D 1 state observed in a high-field frequency scan using lock-in detection at B = 418.8 gauss.
intense plasma discharge in front of the atomic-beam oven. The ABMR apparatus is of the sixpole-focusing type [6]. The atoms are focused or defocused in the A and B magnets, depending on the sign of the éffective magnetic moment. Atoms will reach the detector region, only if they have undergone a transition from a focusing to a defocusing state in the homogeneous C-field region. Such atoms are detected by observing the fluorescent light following a laser excitation to the Sd6p configuration (see fig. 2). In this way,individual states can be studied without interference from other states. This is particularly advantageous for weakly populated levels. In our experiments we used a coherent radiation model 490 CW dye laser in multimode operation. The wavelength for the laser-induced transitions falls in a convenient wavelength region, 580—610 nm. 1D 3D 3D The hyperfine structure of the 2, 2 and 3 states of barium has been studied by Schmelling [7], using the ABMR technique with a surface-ionizing detector followed by a mass-separator. As an illustration of the strong signals we obtain for these states with the present technique,we 3D show in fig. 2 a lowfield frequency scan for the 3 level, obtained in straight DC detection. The strong I = 0 signal originates from the even isotopes with a total abundance of 82%. The odd isotopes with A = 135 (7%) and A = 137 (11%), having the same nuclear spin (1 3/2), give rise3D to weaker unresolved hyperfine resonances. state is considerably more difficult to I The with the ABMR technique, due to the small observe electronic magnetic moment (gj 0.5). The I = 0 Signal has been observed by the Bonn group for this state .
in their accurate gj determinations [8]. With the technique described here,we have been able to observe 3D also the very weak hyperfine signals from the 1 state. The result of a frequency scan for this state, obtamed with lock-in detection, is shown in fig. 3. The 3D preliminary values of the hyperfine constants for the 1 state are A (137) = —522(2) MHz, B(1 37) 17(2) MHz,A(135) = —466(2) MHz and B(135) = 12(2) MHz. The sign of the A-factors has been determined from a consideration of the transmission properties of the ABMR-apparatus. More accurate determinations are in progress. For a complete investigation of the hyperfine interaction in the 6s5d configuration, high-precision measurements of the other states will also be performed. The applicability of the technique described here is mainly limited by the wavelength region of the tunable laser. The CW laser used in this experiment can be replaced by a pulsed laser system, thus extending the available wavelength region considerably. Tests have shown that such an approach should be feasible in several cases. This work was supported in part by the Swedish Natural Science Research Council.
References . [1J I. Lindgren and A. Rosen, Case Studies in Atom. Phys. 4 (1974) 93. [2J W.J. Childs, Case Studies in Atom. Phys. 3(1973) 215. 131 M. Gustavsson et al., Phys. Lett. B, to be published.
251
Volume 62A, number 4
PHYSICS LETTERS
22 August 1977
[41 H. Duong et al., Opt.
Commun. 7 (1973) 371; G. Huber et al., Phys. Rev. Lett. 34 (1975) 1209. [5] W. Ertmer and B. Hofer Z. Physik A276 (1976) 9; W. Zeiske et a!., Phys. Lett. 55A (1976) 405.
ed. K. Siegbahn (North-Holland, Amsterdam 1965); M. Olsmats, B. Wannberg and I. Lindgren, Nucl. Instrum. Meth. 103 (1972) 27. [7] S.G. Schmelling, Phys. Rev. A9 (1974) 1097.
[6] W.A. Nierenberg and I. Lindgren in: o, j3, ‘y-spectroscopy,
[8] R. Aydin et al, Z. Phys. A273 (1975) 233.
.252