Spectroscopy of Neutron-Rich Nuclei Produced in the Spontaneous

Sp ectroscopy of NeutronRich Nuclei Pro duced in the Sp ontaneous Fission of Cf by Michael Wilhelm Simon Submitted in Partial Fulllment of the Requirements for the Degree Do ctor of Philosophy Sup ervised by Professor Douglas Cline Department of Physics and Astronomy The College Arts and Sciences University of Ro chester Ro chester New York ii To myParents iii Curriculum Vitae The author was b orn in San Diego California on Octob er He attended the University of California Berkeley from to and worked at the UCB Earthquake Engineering Research Center and Fire Research Lab oratory from to He attended San Francisco State University from to and graduated with a Bachelor of Science degree in Physics in During his enrollmenthe per formed research on sup erconducting tunnel junctions under the direction of Professor Roger Bland He entered the graduate physics program at the UniversityofRochester in the fall of He was awarded the Graduate Student Teaching Award in and received the Master of Arts degree in Physics in His dissertation research was carried out at the Nuclear Structure Research Lab oratory under the direction of Professor Douglas Cline iv Acknowledgments The research presented in this thesis represents not only my eort but also the contributions of many p eople I would liketoextend thanks to all those involved Iwould like to thank rst my advisor Dr Douglas Cline for his continued supp ort and encouragement Iwould also like to thank Dr ChingYen Wu for his a continued interest in this work and for innumerable useful discussions Thanks are also due to the other memb ers of the research group Dr Rich Ibb otson and Dr Matt Devlin deserve thanks for their contributions and eorts in the Ho exp eriment The contributions of Rob ert Gray and Carl Welch in the development of CHICO and during exp eriments are also gratefully acknowledged Thanks are also due to the collab orators at LBNL and LLNL Dr Kai Vetter Dr A O Machiavelli Dr I Y Lee Dr Ken Gregorich Dr Steve Asztalos and Dr R W MacLeo d contributed signicantly by insuring that the CHICO plus GAMMASPHERE exp eriments were successful Iwould also like to thank Dr Jacob Gilat for his careful work with the data and for many discussions Discussions with Dr John Rasmussen are also gratefully acknowledged Dr Mark Sto yer deserves thanks for his eorts in suggesting the exp eriment providing the ssion source and assistance during the course of this research The supp ort oered by the sta at the Nuclear Structure Research Lab oratory was invaluable Thanks are due to Chris Long Clint Cross RayTeng Dave Munson and Eileen Pullara FinallyI would like to thank my family and many friends for their supp ort v Abstract A new exp erimental technique has b een develop ed for the sp ectroscopic investiga tion of the neutronrich pro ducts of CfSF The chargedparticle detector CHICO was coupled to the Gedetector array GAMMASPHERE and a thin ssion source was used allowing the collection of highstatistics highfold ray data in kinematic coincidence with the recoiling ssion partners The selectivity provided by this tech nique allows the rays to be assigned unambiguously to the heavy or light ssion partner The added sensitivity allows many rotational bands to b e extended to h and a sensitivity to nuclei pro duced with a yield of ssion was achieved by massgating the ray sp ectra The chargedparticle detector CHICO was develop ed for this exp eriment and for studies utilizing other binary reactions such as Coulomb excitation transfer and fusionssion reactions The detector covers a total solid angle of sr and has a time resolution of ps resulting in a mass resolution of mm for beam exp eriments or massunits for sp ontaneous ssion This technique was used to set limits in agreement with shell mo del predictions on the E decay of the level in I Rotational bands in Mo Ru Nd Sm were extended to higher spin Band crossings were observed in the ground and band in Mo The band of Ru shows continued tri axial behavior at higher spin The yrast rotational bands in Pd were extended and rotational bands built on the lowlying isomeric levels in Pd were newly identied The behavior of the observed band crossings in the ground and isomer bands of Pd when compared to the neighb oring Rh and cranked shell mo del calculations indicate that the predicted change from prolate to oblate shap es in the neutronrich Pd do es not o ccur b efore Pd ground band up to In a separate exp eriment the lifetimes in Ho of the K h and K h were measured by the recoildistance spin band up to spin metho d The extracted matrix elements conrm earlier Coulomb excitation results vibrational band has a deformation larger and indicate that the K than the ground band vi Contents List of Tables ix List of Figures x Intro duction Theory and Mo dels Microscopic Mo dels of the Nucleus Spherical Shell Mo del Deformed Shell Mo del Collective Rotations and Vibrations Coupling of Single Particle Motion and Rotations Band Crossings Phenomenological Classication of Rotational Bands Exp erimental Techniques and Equipment Intro duction GAMMASPHERE The CHICO Detector Design Requirements CHICO Description PPACs Electronics Position Measurement and Calibration Time Measurement and Particle Identication Performance of GAMMASPHERE with CHICO Summary Cf Sp ontaneous Fission Exp eriment Description Intro duction The Exp eriment The Fission Source vii Thick Source Data Analysis Mass Measurement Gammaray Analysis Gammaray Sp ectrum Analysis Selectivity Mass Gating SelectivityProvided by the Doppler Correction HK Measurement Observation of Levels at Higher Spins and Excitation Energy Summary Neutron h band structures in the neutronrich Pd Intro duction Pd Ground Bands Isomeric bands in Pd Pd Rh Discussion Summary Lifetime measurement of I Matrix Elements from Te level lifetime in I Shell Mo del prediction of the Measurement of the level lifetime in I High Spin Results Ru Mo Nd Sm Summary Conclusion Bibliography A Lifetime Measurement of lowlying levels in Ho A Intro duction A The Coulomb Excitation Exp eriments A Intrinsic Moments of Bands in Ho from InBand Matrix El ements A Motivation for the Lifetime Measurement Exp eriment viii A The RecoilDistance Lifetime Exp eriment A Exp erimental Metho d A Lifetime analysis A Matrix elements derived from the lifetime measurement A Ground Band Matrix Elements A K InBand Matrix Elements A K Band to Ground Band Matrix Elements A Summary B Gammasphere Calibration B Energy and Eciency Calibration ix List of Tables Logic tables programmed into the Programmable Logic Unit PLU used to dene the rst level trigger The Forward only section refers to exp eriments with inverse kinematics Forward and Back ward would be used for exp eriments with a pro jectile with less mass than the target A valid particle signal is given only if one of the conditions is met Contributions to the time resolution for MeV Dy on a gcm Sn target Selection criteria for a thin ssion source isotop e A Quadrup ole moments and deformations of the K ground band and bands of Ho measured by Coulomb excitation the K A Ho Ground Band Lifetimes A Ho K Band Lifetimes x List of Figures Nuclei p opulated in CfSF whichhave b een studied sp ectroscopically Schematic view of part of the GAMMASPHERE array from Sectional view of CHICO The target chamb er housing the PPACs and the pressure window is on the right The transmission lines carrying the signals from the PPACs to the amplier b oards can also be seen The length of the assembly is cm Crosssection view of the CHICO target chamb er The heavy lines show the v acuum envelop e containing the gas volume One half of CHICO coupled with one half of GAMMASPHERE Assembly of an individual PPAC The asymmetrically segmented an ode and the catho de b oard with the attached

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