Audi, G

De Saint-Simon, M

Doubre, H

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LL¤%t ispectrometer [6]. OCR Outputmeasurement of the mass of 1*Li with an accuracy better than 10 keV with a L. G. Smith type massdifficult in Perming traps. We therefore propose the following experiment at ISOLDE aiming at theit almost inaccessible to precise measurements in storage rings requiring a cooling process and veryhighly desirable. No simple reaction Q-measurement is possible and its very short half-life (9 ms) makesconsistency among them. A precise mesurement of the mass of * ‘Li, with a better accuracy, is thereforein 1988 [5] and a later determination leading to a weighted average of 3l5(40) keV with only roughspectrometric measurement at CERN by Thibault et al. in 1975 [4]; one measurement by Wouters et al.mass of *1Li is poorly known, and only little progress has been recorded since the on-line masslow value of S appears to be the key parameter for the existence and the extension of the halo. Yet, thekey to the size of the halo is its separation energy S, as the halo size scales directly with 1/ JE . Thus asensitivity with respect to the HLi binding energy. For example, in the quasi-molecular model [3], themomentum correlations, potential geometry and depth". These parameters have various degrees ofseparation energy, two-neutron removal cross-section, momentum distributions and possible n-ndescription of all the parameters implied in the observations: matter distribution, halo size, haloknowledge of HLi has considerably increased, one still misses a model that would give a coherentyears, as outlined by around 100 experimental and theoretical investigations [2]. Although our»-·- The observation [I] of a spatially extended neutron halo in *’Li has found a large interest in the lastPHYSICAL INTERESTA. C. Mueller, D. Guillemaud—MuellerOrsay, IPN—IN2P3, France:R. B. MooreMontreal, Foster Radiation Laboratory, McGill University, Canada:H. - J. Kluge, G. BollenMainz, Institut tiir Physik, Universitat Mainz, Germany:B. Jonson, G. NymanGoteborg, Department of Physics, Chalmers University of Technology, Sweden:G. Lebée,._ CERN, Geneva, Switzerland:C. BorceaBucharest, Institute for Atomic Physics, Romania:P. G. Hansen, K. RiisagerAarhus University, Institute of Physics and Astronomy, Demnark:M. de Saint Simon, G. Audi, H. Doubre, C.ThibaultYy 8 Orsay, CSNSM-IN2P3, France:CGRA — FSC,Accurate mass measurement of halo nuclei_§C.P \</O,gaC.]:LETTER OF INTENTapril 23, 199330000C} ?;}i.%$ERN 93- ssc 8l \\||\\|\\|1I\\1||l\\\1||\l|\|l\|\||1|\|1Illll P1¤ 14812Jl 12 A CERN LIBRARIES, GENEVmany checks and cross-checks. Some of these will use other alkali isotopes, lithium and sodium, where OCR Outputobtained in a mere 4 hours for the HLi case, it is clear that a high-precision experiment will requireAlthough the conditions for the proposed experiment are so favourable that sufficient statistics can beREQUEST FOR MACHINE TIMEproduced at ISOLDE.species. The RPMS could advantageously be used for mass measurement of very short—lived candidatesislands" [9]. It is therefore important to investigate the binding energy of the most neutron-rich lightpossibly couple with a stable core to a system which could be very slightly bound, leading to "stablein [3], halo nuclei have very unusual structures and clusters of neutrons (close to be bound) maya function of the neutron number for the light nuclei close to the neutron drip-line flattens out. As shownMore generally, it has been observed that the dependance of one- and two-neutron separation energies asOUTLOOK- Am/m = 2 104.resulting in a resolving power of 5 104 and the enhancement factor has been measured to be 108 forcommunity is interested in getting very pure beams. The transmission could be optimized to 10 %spectrometer at the location of the second magnet of the High Resolution Separator if the ISOLDEexperimental hall could be selected (RA2, RA3, RB2, RB3...). Another possibility would be to instal theISOLDE more compact. Several possibilities for the layout of the experiment (figure 2) in the ISOLDEIn contrast to the layout at LEAR, the use of the energy filters is not required, rendering the setup atPOSSIBLE LOCATIONS OF THE EXPERIMENTnecessary.for fine tuning of the trajectory in the spectrometer and for the investigation of systematic errors will betransmission and peak reconstruction process corresponds to a yield of 100 ions per pulse. Stable beamto ISOLDE at every PS supercycle. The lower limit of the sensitivity of the RPMS resulting from1Li/ pulse of the PS-booster should be approximately 4 hours in the case of 2 PS-booster pulses sendmaintained below 10*0 (Amw 10 keV). The duration of such a measurement with a production of 1400same order, finally, systematic errors should be investigated in the ISOLDE enviromnent andstatistical accuracy better than lO", magnetic field stability was measured to give uncertainties of the_,_ resolving power of 1.4 10* can be achieved. Accumulation of 10Li in the mass peak leads to a4 1lmode. Multi-particle simulations with HLi (figure 1) indicate that a transmission of a few percent and aexotic nuclei, to its good quality beam (low emittance) and to the availability of the slit—shaped beamThe ISOLDE facility is a production tool particularly well suited to the RFMS, due to its high yields forms.ISOLDE, the RPMS ideally complements the ISOLTRAP (IS302) in the half-live range from 1 to 100flight across the spectrometer). Thus, taking into account the diffusion time in the ion source ofvelocity allowing to handle any nucleus or nuclear state with half-live larger than l0j.ts (the time ofmasses of very short lived nuclear species. The cyclotron frequency measurement is performed at beamexperiment based on a transmission spectrometer is well suited to the accurate measurement of thefocusing properties (angle and velocities) and, particularly, a high level of isochronism. The proposedrotating on the same trajectory, in a very homogeneous magnetic field. Such field provides goodhelp of CERN. This technique relies upon the comparison of the cyclotron frequencies of ionic speciesthe antiproton-H' ion mass comparison at LEAR (CERN), has been built by CSNSM-IN2P3 with theinstance) will be performed with the RF mass-spectrometer (RPMS) [7, 8]. This setup, initially aimed atDirect mass comparison of 1lLi with a well known mass of a stable or long-lived isotope ( 7Li forEXPERIMENTAL PROCEDURE»- [9] A. S. Jensen and K. Riisager, Nucl. Phys. A537 (1993) 45. OCR Output[8] A. Coc, et al., Nucl. Instr. and Meth. A271 (1988) 512.[7] A. Coe et al., Rep LRB 85-Ol, CSNSM, Orsay (1985).Toronto, Canada, 1960) 418.[6] L. G. Smith, Proc. Int. Conf. on Nuclidic Masses, ed. H. E. Duckworth (univ. of Toronto Press,[5] J. M. Wouters et al., Z. Phys. A331 (1988) 229.[4] C. Thibault et al., Phys. Rev. C12 (1975) 644.[3] P. G. Hansen and B. Jonson, Europhys. Lett. 4(1987)409.P. G. Hansen, Nucl. Phys. A553 (1993) 89c.Rev. Nucl. Part. Sci., vol 43;"Nuclei at the limits of particle stability" by A. C. Mueller and B. M. Sherrill, to appear in Ann.Niigata,June 1991, ed. K. Ikeda and Y. Suzuki;[2] Proceedings of Intemational Symposium on Stmcture and Reactions of Unstable Nuclei,[1] 1. Tanihata et al., Phys. Rev. Lett. 55 (1985) 2676;REFERENCESweeks of beam on target. We shall submit a more precise request with our final proposal.the latter can be expected to give other new mass results. Such a programme is estimated to require 2power of 1.4 10’ and a maximum transmission of 6%. OCR OutputFigure 1. Simulation ofthe transmission ofthe RF mass spectrometer for **Li displaying a resolvingRF SCANChannel Numb.60 B0 100 120 140 160 180 20020 401020*30138000Resolv. Power =1917.5004Harm. N + 1/2 =30.5Error ct.(Hz) =40 499.6493Center (MHZ} =3600.1Peak FWHM (Hz)=1000Particle/chan. =50 ¤.00OE+0OGrad. (cm—1) =-2.5PDS external =2.5PDS internal =100.0Step (Hz/chan):GO499.648727Scan ctr(MHz) =0.260573Cyc.Fr. (MI-Iz) =0.223RF v0Itagc(kV) =0.18668Bzcra (Tesla) =1.00000Ampkcavity 4 =0.00273Beta1.00000AmpI.c¤vity 3 =28.0Moment(MeV/c) =1.00000AmpI.cavity 2 =38.2Kin.En. (keV) =1.00000AmpI.cavity 1 =Particle Q =Real modulator11Pcnrticle A =80°¤rticIc/chan.RPMS SIMULATIONchambers can be inverted.(4/5) beam injection/ejection, (6) inlet beam diagnostic chamber, (7) detector chamber. The latterFigure 2. Top view of the RFMS setup. (1) Magnet (25 tons), (2) RF modulator, (3) phase defining slit,even1 m··`·-£--H-___";l/_."~·"ha 5 4

Accurate mass measurement of halo nuclei

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