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DETERMINATION OF THE ISOTOPE SHIFT OF 131Cs AND 132Cs BY SCANNING THE LEVEL
CROSSING SIGNAL
E.-W. Otten, S. Ullrich
To cite this version:
E.-W. Otten, S. Ullrich. DETERMINATION OF THE ISOTOPE SHIFT OF 131Cs AND 132Cs BY SCANNING THE LEVEL CROSSING SIGNAL. Journal de Physique Colloques, 1969, 30 (C1), pp.C1-24-C1-27. �10.1051/jphyscol:1969105�. �jpa-00213636�
JOURNAL DE PHYSIQUE Colloque C I , supplkment au no I , Tome 30, Janoier 1969, page C 1 - 24
DETERMINATION OF THE ISOTOPE SHIFT OF ' 31Cs AND 132Cs BY SCANNING THE LEVEL CROSSING SIGNAL
E.-W. O ~ E N AND S. ULLRICH
I. Physikalisches Institut der Universitgt Heidelberg
RCume. - En utilisant une nouvelle technique de balayage, nous avons determine les depla- cements isotopiques de 131Cs et 132Cs par rapport B 133Cs : ^i(l3lCs) - ';(133Cs) = - 0,95 (1,lO) mK, et ';(132Cs) - G(133Cs) = + 1.32 (0,60) mK.
Ces resultats joints ti ceux concernant d'autres isotopes de Cs, montrent que f'effet de volume nuclhire est presque nul.
Abstract. - The isotope shifts of 131Cs and 132Cs with respect to I33Cs were determined by a new scanning technique to be
v"(l3lCs) - F(133Cs) = - 0.95 (1.10) mK 3("2Cs) - T(133Cs) = -1- 1.32(0.60) mK .
In accordance with results from other Cs isotopes they show the nuclear volume effect to be almost zero.
Recently LC and DR experiments in the two first excited 2P312 states of the radioactive nuclei 1 3 1 ~ s ( z , 1 2 = 10 d) and 132Cs (7112 = 6 d) could be performed in order to determine the nuclear qua- drupole moments [I]. The LC experiments in the 6 2P,12 state offered the chance to determine the isotope shift of these nuclei, since the resonance line (I(Cs) = 8 521.10 A) almost coincides with the Argon line
Therefore the level crossing intensities could be scan- ned by a Zeeman component of this argon line (Fig. 1).
Similar methods which use the scanning of a highly resolved hfs signal for the determination of the iso- tope shift have been applied to Hg [2] and Cs [3]
isotopes. In these cases a double resonance or an atomic beam [pumping signal resp. have been scanned. One of the advantages of such methods is the high isotopic resolution in an isotopic mixture independent of the magnitude of the isotope shift itself.
The experiment was performed as follows : For the production of the radioactive isotopes and the pre- paration of the resonance vessels the same technique was used as described in the foregoing paper [I].
The vessels were filled with either 100 ng of almost
L i g h t Source Resonance C e l l
A r (1.0) c s I 3 ' ( t I l 2 = 9 . 7 d )
FIG. 1. - Part of the level schemes of 40Ar and 131Cs. The conditions -field at the light source HI.= 4.8 kG, field at
the resonance cell H, = 163 G - are chosen for an excitation of the LC signal ((3, - 3) = (3, - 2) x (4, - 4)) by the a+
component (1,O --t I, - 1) of the argon line.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1969105
DETERMINATION OF THE ISOTOPE SHIFT OF "'CS AND ls2Cs C 1 - 2 5 isotopically pure 13'Cs, which was produced in a
pile by the reaction
130Ba(ny) 131Ba - 13'Cs, or with 10 ng of a
8 +
mixture of Cs isotopes which contained 30 % each of l3'Cs and 132Cs among others. The latter sample was produced from a Xe target by deuteron irra- diation. The lightsource consisted of a glass bulb, 1 cm in diameter, filled with 1 mm Hg of Ar. The
discharge was driven by the microwave field of a cavity, excited by a magnetron at 2.4 GHz and a power level of about 100 W. The light source was placed into the air gap of a magnet, the field of which was calibrated by proton resonance. The precise analysis of the scanning signal asked for a permanent control of the light intensity. The light source turned out to be rather insensitive to the magnetic field ; the intensity varied about 5 % over the range from 4-12 kG (Fig. 2).
HELMHOLTZ-COIL
I IRON-MAGNET
RESONANCE RESONANCE PROBE
FIG. 2. - Schematic diagram of the experimental setup. P = prism, PM 1 = photomultiplier for investigation of the resonance light, PM 2 = photomultiplier for control of thelamp intensity.
L, - Lq = lenses, IF = interference filter (D2 filter), PF = polarization filter, 0 = oven, MC = modulation coil.
The difference between the center of gravity of the Ar line and the Cs line is quoted to be
in the spectral tables [4]. The Cs can be excited, there- fore, by the two a + components of the Ar line which correspond to g factors g, = 0.8 19 and g, = 1.102 [4]
of the upper (4p) and the lower (4 s) state resp.
The latter one, predominantly used for scanning, meets the (F = 4) hfs component of the 133Cs ground- state a t = 5.8 kG, the (F = 3) component at = 1 1.5 kG.
Similar values hold for the other Cs isotopes.
The scanning signals were taken point by point by recording the derivative of the LC signal at each fixed scanning field (Fig. 3). The (Am = 2) crossings suit especially the purpose of scanning. Because they are excited only from groundstate sublevels with
SCANNING FIELD
I I I I I I I I I
122 124 12.6 12B 13.0 132 13.4 136 13B 14.0 W KILO-GAUSS FIG. 3. - Intensity of LC signals of 131Cs as scanned by a o+ component of the argon light source. The solid curves are Gaussians, fitted numerically to the experimental points
a Levelcrossing (F = 2, rnF = - 2) z
@ Levelcrossing ( F = 2, mr = - 2) z
2 ( F = 4 , mF = - 3 ; F = 3, rnr = - 1) 169,9 gauss.
C 1 - 2 6 E.-W. OTTEN AND S. ULLRICH one definite m value, they occur at exactly one exci-
tation energy for each of the two F values of the groundstate. But since the hfs splitting of the latter is large compared to the doppler width, the two compo- nents are excited completely separated at different scanning fields. Any difficulties in the analysis, which arise from the superposition of unresolved hfs compo- nents, are avoided by this technique. The absorption -
as well as the emission spectrum are simple, symmetric gaussians (the Ar line is not expected to be selfre- versed, since the lower state is short lived). Therefore the scanning signal could be fitted numerically always to a gaussian. The linewidth of the signals varied between 50 mK and 60 mK depending on the condi- tions of the lightsource. In table I the scanned cros- sings are listed. The measurements were extended to
LC-partners center of the center of gravity averaged (*) other ground state excited state 1
~~~~~~
scanned signal of Cs isotope shift measure- (F, ma) * (F', m;) x ( F , mg)1
[ ~ a u s s ]1
to A m1
lm.11
mints-
(*) With respect to 133Cs with the definition : I. S .- T' (lighter isotope) - '3 (heaver isotope).
134, 135, 137cs in order to prove, how accurately the already known shifts (column 7) of these isotopic lines are reproduced by this technique. For a deter- mination of the isotope shift from the scanning signals the shift of the excitation energy from the centers of gravity had to be calculated by diagonalizing the hfs matrices of the upper and lower state at the point of the LC field. For reasons of accuracy, moreover, the g factor of the argon line as well as its relative position with respect to the 133Cs line were redeter- mined by introducing these quantities together with the isotope shifts as free parameters in a least square fit of all data of 1 3 3 s 134, 1 3 7 C ~ . Assuming pure linear Zeeman effect of the Ar line it yielded :
g, = 1.091 (1) and the isotope shifts listed in column 6 of table I. The final values in column 6 are weighted averages of the individual measurements in column 5.
Limits of error of 0.6 mK are typical. It should be possible to narrow them by an improvement of data taking. The isotope shifts, obtained for 134, 135s 13'Cs are in good agreement with Hiihnermanns [8] values within these limits of error. The error of 0.12 mK, listed for 133Cs, means the final uncertainty in the position of the Ar line relative to 'j3Cs as calculated by the computer fit. Unfortunately the result for 131Cs is disturbed by the fact that the scanning result of the crossing, excited from the upper F = 3 level, deviates unusually much from the others. Only one crossing of 132Cs was scanned within the lifetime of the isotope. Therefore the typical error of 0.6 mK
DETERMINATION OF THE ISOTOPE SHIFT O F ~"CS AND 13ZC~ C 1 - 2 7 is overtaken. All data are preliminary. The fit is insen-
sitive to quadratic Zeeman effect. This stems from the fact, that all scanning signals fall into two narrow intervals around 5 000 and 12 000 gauss within which a curvature is not discernible.
From standard formulas [5] the normal nuclear volume effect for Cs is calculated to be 7.5 mK per additional nucleon. The mass effect is expected to be 0.34 mK per nucleon ; but following a calculation of Bauche [6] it is completely cancelled by the coupling effect. The experimental results show, that the volume effect is almost zero. These small values fit into the known series of Cs isotope shifts which reach from lZ7Cs to I3?Cs, [7], [El. They do not exceed 2.0 mK per nucleon. This can be interpreted as an increase of the surface difuseness and (or) deformation of the lighter nuclei. This behaviour is expected, when the closed neutron shell of 13'Cs (N = 82) is stripped.
We are grateful to Dipl.-Phys. F. Ackermann and Dr. A. Schenck for preparing the resonance vessels.
We appreciate the cooperation of Dr. Schatz in orga- nizing the cyclotron irradiations. We are indebted
to Prof. Seelmann-Eggebert, Dr. Grupe and Dr.
Wassilopoulos who supplied us with the pile produced 13'cs. This work was supported by the Deutsche Forschungsgemeinschaft.
References
[I] ACKERMAN (F.), OTTEN ,(E.-W.), PUTLITZ (G. ZU), SCHENCK (A.) and ULLRICH (S.), Phys. Letters, 1968, 26 B , 367.
[2] SAGALYN (P. L.), MELISSINOS (A. C.), and BmeR (F.), Phys. Rev., 1958, 109, 375.
[3] YELLIN (I.), MARRUS (R.), WANG (E.), BuU. Amer.
Phys. Soc., 1967, Series 11 Volume 12, 905.
[4] Atomic Energy Levels NBS. 467.
[5] KOPFERMANN (H.), Kernmornente, Akadernische Ver- lagsgesellschaft, Frankfurt, 1956.
[6] BAUCHE (J.), Lab. Aime Cotton, Orsay, unpublished.
[7] 1271 129Cs : MARRUS (R.), Orsay/Berkeley, priv.
communication.
[8] 13Sp 137C~ : H ~ ~ H N E R M A N N (H.), P h y ~ . Letters 1966,
21, 303.
[9] HUHNERMANN (H.) and WAGNER (H.)?Z. Physik, 1968, 215, Heft 1 (Abstracts).
TRANSVERSE OPTICAL PUMPING SIGNALS IN 3He
A. DONSZELMANN Laboratoire Zeeman, Amsterdam
RCsum6. - Le travail qui a Cte expos6 est une gCnCralisation de ceux qui ont it6 decrits par [I], [2] pour le cas de 3He. Les experiences sont en train de se rkaliser et les rCsultats seront publies dans Physica.
Abstract. - The work which is discussed is a generalisation of that described in [I], [2] in the case of 3He. The experiments are not finished and the results will appear in Physica.
Bibliographic Paris, 1966, 262, 37 ; C. R. Acad. Sci., Paris 1966, 262, 286.
[l] COHEN-TANNOUDJI (C.) et HAROCHE (S.), C. R. Acad. [2] PARTRIDGE (R. B.) et SEMES (G. W.), Proc. Phys. Soc., Sci., Paris, 1965, 261, 5400 ; C. R. Acarl. Sci., 1966, 88, 983.
