Decay spectroscopy using the HRIBF recoil mass spectrometer

DecaySp ectroscopUsingtheHRIBFRecoilMassSp ectrometerC. J. Gross1;2,T.N.Ginter3, J. J. Ressler4, J. C. Batchelder, R. Grzywacz5, A. Piechaczek6, W.B.Walters,M. Wiescher7, K. Rykaczewski2, A. Aprahamian, C. R. Bingham;5, Z. Janas8, B. D. MacDonald9, E. F. Zganjar61Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 37831 USA2Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 USA3Department of Physics and Astronomy, Vanderbilt University, Nashvil le, TN 37235 USA4Department of Chemistry, University of Maryland, Col lege Park, Maryland 20742, USA5Department of Physics and Astronomy, University of Tennessee, Knoxvil le, TN 37996, USA6Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA7Department of Physics, Notre Dame University, Notre Dame, IN 46556, USA8Joint Institute for Heavy Ion Research, Oak Ridge, Tennessee 37831 USA9School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA(January 28, 2000)Two decay sp ectroscopy exp eriments p erformed with the Recoil Mass Sp ectrometer at the Ho-li eld RadioactiveinBeamFacility aredescrib ed.Utilizing theMovingTap eCollector,the+decay half-life of80Zr has b een measured to b e 4:1+0:80:6s.The resulting decrease in mass 80 pro duc-tion during the rapid proton capture pro cess, suggests that80Zr may not b e a signi cantwaitingp oint and the pro cess may pro ceed to heavier masses.The observation of proton ne structure isrep orted for the rst time in spherical nuclei.Three new decay branches, apparently from the twopreviously known statesin146Tm,have b eenobserved using double-sided silicon strip detectors.Arising from the complex con guration mixing common to o dd-o dd nuclei, our preliminary resultssuggest relative energy di erences and spins and parities in the146Tm parent and145Er daughterisotop es.KEYWORDS:Recoil Mass Sp ectrometer, moving tap e collector, proton and b eta radioactivityPACS:23.50.+z, 26.30.+k, 27.60.+j, 27.50.+eThestudyofradioactivity from nuclei farfrom stability is critical toourunderstanding ofnuclei andtheworldaroundus.Thesenuclei provide stringent testsofthepredictivepoweruclear mo dels develop ed from dataonnucleimuchclosertostability.Lyingattheextremesof,smallchangesinenergylevelscausedbsucphenomena as neutron-proton pairing or coupling to neighb oring states including those in the continuum, can lead todrastic changes in decay branchings, energies, and half-lives.These e ects can inuence the rate of nucleosynthesis[1] and can result in valuable prob es into the nuclear wavefunction [2].The nucleosynthesis pro cess in explosive stellar events is governed by capture and decay rates which are, in manycases, unknown.We still do not have a go o d understanding of how the natural abundances of the lightest stable Moand Ru are enhanced.These nuclei may b e pro duced through the rapid proton capture pro cess (rp-pro cess) whichcano ccurinX-ray bursts.yburstsareformedwhenmatterfromanearbstarispulled ontoneighb oringneutron star.The environments in these phenomena havevery high temp eratures (T109K) and proton densities.The rp-pro cess [3], governed by the proton capture rates and+decay rates, follows the proton drip line from56Nitowards100Sn.The progression toard higher masses can b e stopp ed at critical p oints or waiting p oints where nucleiwith long+half-lives are immediately b elow a proton unstable nucleus.The waiting p oints allow the temp eraturesto co ol and thus, terminate the pro cess of nucleosynthesis. One p ossible waiting p ointis80Zr and the proton unstable81Nb [4].We rep ort on the half-life of80Zr and its p ossible implications to the rp-pro cess.This study has also b eenrep orted in ref. [5].The study of nuclei b eyond the proton drip line can test nuclear structure mo dels and p erhaps detect the e ectsofcouplingtounb oundcontinuumstateswhichwouldmo difythenuclearavefunctions.Protonradioactivitystudies have b een shown [6{9] to provide information on the waefunctions of the parent state through the "simpleWKB"relationship [10]betweenitsangular momentum, decayenergy,andhalf-life.Therecentobservation [2]in131Eu of proton radioactivity with a decay branch to an excited state indicates a mixing of the wavefunction throughdeformation.Wehavundertakenasearch formultiple protondecaybranchesino dd-o dd,spherical nuclei wherecomplex wavefunctions should exist through the con guration mixing of manylow-lying states inolving b oth protonand neutron single-particle states.Such decays p opulate excited neutron states in the even-Z, o dd-N daughter whichCorresp onding author, Tel:+1-865-576-7698; Fax:+1-865-574-1268; email:cgross@mail.phy.ornl.gov1