Becker, O

Brand, L

Enders, K

CERN Document Server

,2a.E§¢?;5Keyword: Paul-Trap OCR Outputmagnetic octupole and electric hexadecapole interactions have been observed.interaction constants A have been obtained with 10*8 precision and moreover electric quadrupole,available for chains of isotopes. In similar measurements on stable Eu+ isotopes magnetic dipoledetailed understanding of the distribution of magnetization over the nuclear volume, if they areobtained. This leads to reliable and accurate hyperfine anomalies, which may be useful for a moreresonance experiments precision values of hyperfine separations and nuclear moments can bethe ions are confined in a r.f. ion trap for extended periods of time. In laser-microwave doublenumber of 10- 10particles is sufficient to perform off line experiments: After surface ionisation11 12Radioactive Eu isotopes produced at the ISOLDE facility shall be collected on metal foils. A totalSUMMARYContactman: G. HuberSpokesman: G. WerthInstitut fiir Physik, Universitat MainzO. Becker, K. Enders, L. Brand, G. WerthHYPERFINE SPECTROSCOPY OF UNSTABLE EU+ ISOTOPES IN AN ION TRAPPROPOSAL TO THE ISOLDE COMMITTEESCO000025507.05.1993I W nI 3$'2¤ISC / P51CERN LIBRARIES, GENEVAc ERM ~ 1% C, CERN/1SC 93*20P *‘i?.e'”.(>T\\] EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH{’·iQ;. 15;%S = ¤/ui, OCR Outputdoes not exist so far. An empirical rule by Moskowitz and Lombardi I9Iatomic states. It ranges typically between l0‘and 10. A general model to understand these data2 *4stable nuclei and some unstable ones by measurements in neutral atoms, sometimes in differentby Biittgenbach ISI. 43has been determined with reasonable accuracy ($10%) for the pairs of odd12The experimental and theoretical status of the magnetic hfs anomaly has been most recently reviewedeffect) |6,7I.of Ais the change in the distribution of magnetization over the nuclear volume (Bohr-WeisskopfI2wavefunction ur for the two isotopes (Breit-Rosenthal-effect) has been neglected. The physical originwhere the subscripts 1,2 refer to two different isotopes. Here the change in the electronicg (1+82)2; = g%.....(1*€1L.. % (1+1AZ)It follows, A = T Tc si ua I\v(¤)I16A = A'(1+e)value A' for a point like nucleusThese arise from the deviation of a measured magnetic hfs coupling constant A from the calculatedwould yield accurate values of differential hyperfine anomalies.become known to better than 1 part in 106. A detemiination of these quantities in different isotopesuncertainties as low as a few parts in 10I5I and nuclear magnetic moments can be expected to11A isotopes. Experiments of hyperfine-splittings of stable ions using the ion storage method resulted ininvestigations to precise measurements of hyperfine separations and nuclear moments of chains ofWe propose, to make use of the favourable properties of ion traps to extend this kind ofintensity of the shortlived isotopes was in some cases as low as 105 atoms per second.magnetic state selection I3|, and collinear laser spectroscopy I4!. In these experiments the beamfluorescences spectroscopy lll, atomic beam magnetic resonance |2|, laser optical pumping andstability. A variety of methods has been employed in these experiments like Doppler limitedhas substantially increased our knowledge of nuclear properties in the region outside the valley ofparticles produced by high energy reactions on accelerators and nuclear reactors during the past yearsThe measurement of spins, nuclear magnetic moments and isotope shifts in a large number ofI. Physics MotivationTable 1: Hypertine splitting of ionic ground states measured ion traps. OCR Output12 968 180 601.61 (0.22) X. Feng, G.Z. Li and G. Werth, Phys.Rev.A (in press)207Pb+40 507 347 997.8 (1.0) F.G. Major and G. Werth, Phys.Rev.Lett. Q 1155(1977)199Hg+10 491 720 239.55 (0.09) A. Miinch, M. Berkler and G. Werth, Phys.Rev. @@ 4l47(l987)173Yb+12 642 812124.3 (1.4) R. Blatt. H. Schnad and G. Werth, Z.Phys. ALQ4 143(1983)171Yb+8 037 741 667.69 (0.36) R. Blatt and G. Werth, Phys.Rev. Ag; 1476(1982)137Ba+7 183 340 234.90 (0.57) W. Becker and G. Werth, Z. Phys. All], 41(1983)13583.+9 925 453 554.59 (0.10) H. Knab, M. Schupp and G. Werth, Europhys.Lett. 4, 136l(1987)133Ba+9 107 913 698.97 (0.50) H. Knab, M. Schupp and G. Werth, Eur0phys.Lett. 4, 1361(l987)13138+5 m2 368 354 (24) H. Sanaoshi et al., Abstr. IX. Int. Conf. on Hyperf. Interactions, (Osaka 1992)87Sr+1 788 763 128 (162) W.M. Itano and DJ. Wineland, Phys.Rev. @4, 1364(l98l)25Mg+l 250 017 674.096 (0.008) JJ. Bollinger et al., Laser Spccu. VI, Springer 1983,9Bc+[HZ]Ion ReferenceHyperfine separationany case superseedes the required precision of 10-6.Ba+ (rm = 11d) where the results are of the same order in precision as with the stable ones and in131the measurements to unstable isotopes I14I was succesful in the cases of B a+ (*:1/2 = 10a) and133given in Table 1. They have been restricted in the past to alkali-like systems. A first attempt to extendfrequency reference. Results of ion traps experiments, performed at Boulder, Sendai and Mainz, arespectral resolutions up to 1 ~ 1011 have been obtained, limited sometimes only by the availabletransitions. Due to the virtual absence of perturbations and the long observation times ( > 1 h) in trapstrap technique. These experiments use lasers for optical pumping and microwaves to drive hyperfineFor a number of stable isotopes precision hypertine measurements have been performed using the ion(a) Hyperfine Suucture measurements in ion trapsII. Status of Research- |l3l.approach, using the atom beam resonance method on alkali atoms, is presently under way at ISOLDEwhich would be sufficient to determine small (10*4) values of A with 1% accuracy. A similarfor a determination of magnetic hfs splitting constants A and nuclear g-values with 10-6 precision,a long chain of isotopes with accuracies in the 1% range. This is the subject of this proposal. It aimsA contribution to a better tmderstanding might be a systematic study of the Bohr-Weisskopf effect indeformed odd nuclei |l2| give predictions in selected areas of the nuclear chart.excitation model for non-deformed odd nuclei Il ll, or the collective Nilsson model for stronglynear doubly closed shell nuclei. Nuclear models like the single particle shell model llOI, the corewhcrc on is a parameter of the order of IO-! mq, depending on the element, gives reasonable resultsthe Zeeman-effect on Ba+ ions in such a trap, located in a 6 Tesla B-field. We have measured the OCR Outputthem by observation of the nuclear Zeeman-effect in a Penning-trap experiment. At present we studyThe gr-factors of the unstable isotopes are not known with sufficient accuracy. We plan to measure(b) gy-factor measurementsexperimental prerequisits.microwave induced hyperiine transitions, but we have demonstrated the feasibility of theto isotope contamination with 15lEu and due to failure of our laser system we could not perform theabout 1012 150Eu+ at Isolde and observed the optical spectrum with sufficient resolution (fig. 2). DueA first attempt to extend the measurements to unstable isotopes was partially succesful. We collectedproduction area.longer than a few days (table 3). These isotopes may be subject to our measurements off line from the.... quadrupole moments |16|. It has a chain of 9 different isotpes with non—zero nuclear spin, which liveexceptionally 'large isotope shift and in a large difference in nuclear magnetic dipole and electricmass 151 and 153 are a prominent example of a nuclear shape transition which manifest itself in anEu+ seems to be an interesting candidate for the proposed investigations. The two stable isotopes ofthe two stabile isotopes 151Eu+ and 153Eu+.octupole (C) and electric hexadecapole (D) interaction in the ground state 4f7(8S)6s; 984 ofTable 2: The hfs coupling constants for the magnetic dipole (A), electric quadrupole (B), magnetic-6(5) -5(2) 1.2(1.2)26(23) 3(7) 9(28)-660 862(231) -1 752 868(84) 0.37702(19)1 540 297 394(l3) 684 565 993(9) 2.2500349(6)hrs constant Eu+ [Hz]151 153Eu+ [Hz]are listed in table 2.quadrupole (B), the magnetic octupole (C) and the electric hexadecupole (D) interactions. The resultsthe coupling constant A for the magnetic dipole interaction and moreover those for the electricmeasurement. From the measured frequencies and extended second order hfs correction we derivedthe Zeeman splitting in a residual stray field of 270 mG in our trap. Fig. 1 shows an example of theto-noise ratio. In spite of this difficulties the complete hyperfine structure has been resolved includingliving metastable states exist, where population trapping of the ions occurs, which reduces the signalcoupling of the electronic total angular momentum J = 4 to the nuclear spin of I = 5/2. Many longcomplex level structure |15|. The ground state is split into many hyperfine sublevels due to theMost recently we have extended our measurements to the stable Eu+ isotopes, which have a ratherwith high precision. OCR Outputradioactive 151Ba+ ions I14I showed, that 10 days lifetime is sufficient to complete an experimentimplanted into an UHV-apparatus, which requires a few days of bakeout. Previous experiments onThe minimum lifetime is given by the fact, that the isotopes have to be transported to Mainz andgives a minimum of 10collected atoms at ISOLDE.11estimate that about 100 trap fillings are needed to complete the measurements for one isotope, whichtrapping efficiency of 10-4 then would require a total number of 109 atoms per trap filling. Wepresent the minimum number for an uncooled ion cloud to get sufficient high si gnal-to-noise ratio. AThe number of atoms required for such an experiment can be estimated: About 105 ions in a trap is at4.9a155Eu+8.8a154Eu+ 108 s-1stableA 153Eu+13a152Eu+ 108 s-1stable151Eu+36a150Eu+ 108 s-193. 1d149Eu+ 108 s-154d148Eu+ 108 s-I24.6a147Eu+ 108 s-14.6a146Eu+ 108 s—15.6d145Eu+ 108 s-1Isotopes ISOLDE vieldNuclear Spin LifetimeTable 3shows the experimental setupoptical system, amplified by a photomultipliertube and counted in a multichannel analyzer. Fig. 4intensity from the ions, which is monitored through a mesh electrode, an interference filter and anby a microwave field after optical pumping by a laser beam is observed by the change in fluorescencebeen obtained. The storage time in many cases exceeds several hours. A hyperHne transition, drivenslowed down by buffer gas collisions at about 10-5 mbar. Trapping efficiencies of 10-4 - 10-5 haveSurface ionisation, sputtering or laser desorbtion produces a cloud of low energetic ions, which areIons are implanted on metal foils which then are placed inside an aperture of an ion trap electrode.HI. Experimental Methodl17I. We expect a similar precision in the gy-factor detem1ination, which is under preparation.cyclotron frequency of electrons stored in the same trap. The total accuracy of the gy-value is 5 — 10-73 · 10-8 (fig. 3). The B-field strength at the ions position was determined by a measurement of theZccman splitting of thc clcctronic groundstatc of thc cvcn isotopes at 163 GHz with an uncertainty ofSum: 14 OCR OutputTa-mu w-stmce 2 each155Eu+ ..... 147Eu+ 108Beam Min. Intensitv Target Material Ion source ShiftsTarget requirements:of 14 shifts over a period of two years.case of approval we would ask for beam time of two shifts per unstable isotope, which gives a totalsupport from ISOLDE would be restricted to the production of the resp. isotope separated beam. Inseveral days would be investigated after collection on a foil at ISOLDE and transport to Mainz. TheIn the first stage of the experiments for hypertine measurements isotopes with lifetime extendingIV. Support from ISOLDEbars. OCR Outputthe different hyperfine components are indicated by thick (*50Eu*) and thin dashed (l5lEu+)Optical 954-9P5 exitation spectrum of a mixture of 150Eu+ and *5*Eu+ ions. The positions ofLaserdeturiing [GHZ]20 :20 4010Fig_ 2Q 5003/2gg 1000G tis13/2:1::::::11:¤¤ 1500 "’ fii??H7:=¤/2N l 9P E 5 u,i....10 E :.1F 9p ,,.;...15/21*51 +150 ' E+ Finset shows the two innermost Zeeman-resonances with higher resolution.hyperfine level in *5lEu+. The residual magnetic field at ions position was 270 mG. TheAmF=O part of the Zeeman transitions between the F=l3/2 and F'=11/2 ground statertf. Frequency + 10 017 200 [kHz]Fig. 1:0 100 200 300 400 500 600800900*1000u/2 Am.=01100M11/2 +11/21200Ml1300-15/2r=1a/21400+13/20 1 20 12:1:1 uz am ”*magnetic Held OCR OutputMicrowave inducees Amy=l transition between groundstate Zeeman levels in Ba+ in a 6 TFig. 4 Frequency [MHZ + 163400 MHZ]9.4 9.6 9.810010.2D° ow a1.0 I- °%°2-0T co Jl3.04.05.06.07.0Setup for laser-microwave double resonance experiment on Eu+ in a Paul ion trap.Fig. 3Rb clocksynthesiser[' ° Attenuator drivirigvoltagepc _5_ t lpr.f. Amp1ifier/vacuum chamberAttenuatorApertureInterference FilterB Ar+Las&r Dye LaserShutterLensHeNe Laserstabilized W Wavemeter· Counter r-—1D1sc.’—`?—1 tubePM§mP·] cooled|17I H. Knab, K.H. Knoll, F. Scheerer and G. Werth, Z.Phys._IQ§, 205(l993)|16| S.A. Ahmad et al., Z.Phys. QQ, 35(l985)I15I O. Becker, K. Enders, J. Dembcynski and G. Werth, Phys.Rev.A (submitted)|14l H. Knab, M. Schupp and G. Werth, Eu1·ophys.Lett. Q, l36l(1987)|13I H.'I`. Duong, ISOLDE Exp. IS 306612l S.G. Nilsson, Dan.Mat.Fys.Medd. QZ, No 16(1955)I1 ll A. de Shalit, Phys.Rev. IQ, 1530(l961)l10| H.H. Stroke, RJ. Blin-Stoyle and U. Jaccarino, Phys.Rev. QQ, l326(l96I)|9l P.A. Moskowitz and M. Lombardi, Phys.Lett. g6_B, 334(l973)|8| S. Biittgenbach, Hyperfine Interactions QQ, 1(1984)I7| HJ. Rosenberg and H.H. Stroke, Phys.Rev. AQ, 1992(1972)l6| A. Bohr and V.W. Weisskopf, Phys.Rev. Q/_7_, 94(1950)____ I5! G. Werth, Comm.At.Mol.Phys. _2_§, 229(l993)l4| J. Bonn, W. Klempt, R. Neugan, E,W. Otten, B. Schinzler, Z.Phys. 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Hyperfine spectroscopy of unstable Eu $^{+}$ isotopes in an ion trap

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Hyperfine spectroscopy of unstable Eu+^{+}+ isotopes in an ion trap

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Hyperfine spectroscopy of unstable Eu $^{+}$ isotopes in an ion trap