Suche nach Signaturen der Supersymmetrie in 193Pt und gemischt-symmetrischer Zustände in 194Pt mittels Gamma-Spektroskopie

Nach der Kernsanierung des Beschleunigerbereichs des Instituts für Kernphysik Köln wurde im Rahmen dieser Arbeit das HORUS-Spektrometer wieder aufgebaut. Anschliessend wurden zwei Experimente für eine Gamma-Gamma-Winkelkorrelationsanalyse durchgeführt. Die Ergebnisse dieser Experimente an den Kernen 194Pt und 193Pt werden in dieser Arbeit vorgestellt. Beide zu untersuchenden Kerne wurden in Beta-Zerfallsexperimenten untersucht. Der Mutterkern wurde mittels einer Fusionsverdampfungsreaktion erzeugt. Im Falle von 194Pt handelt es sich dabei um eine (p,n) Reaktion. Nach dem Beta-Zerfall von 194Au konnten mit Hilfe der Gamma-Gamma-Winkelkorrelationsanalyse der Spin von zehn Zuständen zum erstenmal experimentell bestimmt werden. Außerdem konnten 57 Multipolmischungsverhältnisse bestimmt werden. Bei 193Pt wurde mit einer (p,2n) Reaktion 193Au erzeugt. In diesem Experiment konnten drei Spins angeregter Zustände in 193Pt zum erstenmal determiniert werden. Nach der Kernsanierung wurde ein neues Datenaufnahmesystem zur Messung kernphysikalischer Experimente aufgebaut. Bei der Messung an 194Pt wurden zwei Datenaufnahmesysteme verwendet. Zum einen die ''alte'' Datenaufnahme und zum anderem die ''neue'' Datenaufnahme des Instituts. Ein kurzer Vergleich der beiden Systeme bei einem kernphysikalischen Experiment wird gezeigt. Ziel ist es, das neue System zur Aufnahme und Auswertung kernphysikalischer Daten dauerhaft einzusetzen. In der Massenregion der Gold- und Platinisotopen existieren gerade-gerade Kerne, die sich mit Hilfe des Interacting-Boson-Models (IBM) und des Interacting-Boson-Model-2 (IBM-2) beschreiben lassen. Kerne mit ungerader Nukleonenzahl können mit dem Interacting-Boson-Fermion-Model (IBFM) veranschaulicht werden. Eine spezielle Anwendung des IBFMs ist die sogenannte U(6/12) x U(6/4) Supersymmetrie. In der Supersymmetrie liegen Supermultipletts, welche aus Kernen bestehen, die sich mit dem gleichen Hamiltonian und einem Satz von Parametern beschreiben lassen. Um Vorhersagen in 194Pt und 193Pt zu überprüfen, wurden Multipolmischungsverhältnisse einiger Gamma-Übergänge und Spins von Zuständen bestimmt. Das IBM beschreibt die komplexe Natur stark vereinfacht, so konnten erstaunlich gute Fits von 194Pt und 193Pt gemacht werden. Des Weiteren werden IBM Rechnungen der gerade-gerade Platinisotope der Massen 192 bis 198 gezeigt und die Systemtik wird diskutiert

Quasideuteron states with deformed core

The M1 transitions between low-lying T=1 and T=0 states in deformed odd-odd N=Z nuclei are analyzed in the frames of the rotor-plus-particle model. Using the representation of an explicit coupling of angular momenta we show that strong coupling of the quasideuteron configurations to the axially deformed core results in a distribution of the total 0+ --> 1+ strength among a few low-lying 1+ states. Simple analytical formulae for B(M1) values are derived. The realization of the M1 sum rule for the low-lying 1+,T=0 states is indicated. The calculated B(M1) values are found to be in good agreement with experimental data and reveal specific features of collectivity in odd-odd N=Z nuclei.Comment: 11 pages, 1 figure, LaTe

Application of the extended P+QQ force model to N≈ZN \approx Z fp shell nuclei

To study collective motion, the extended pairing plus $QQ$ force model proposed recently is applied to $A$=46, 48 and 50 nuclei in the $fp$ shell region. Exact shell model calculations in the truncated model space $(f_{7/2},p_{3/2},p_{1/2})$ prove the usefulness of the interaction. The simple model with the pairing plus quadrupole pairing plus $QQ$ force and $J$-independent isoscalar proton-neutron force reproduces unexpectedly well observed binding energies, energy levels of collective (yrast) states and reduced $E2$ transition probabilities in $^{46}$Ti, $^{46}$V, $^{48}$V, $^{48}$Cr, $^{50}$Cr and $^{50}$Mn. The correspondence between theory and experiment is almost comparable to that attained by the full $fp$ shell model calculations with realistic effective interactions. Some predictions are made for energy levels and variations of $B(E2)$ in the yrast bands, in these nuclei. Characteristics of the interaction are investigated by comparing with the realistic effective interactions.Comment: 34 pages including 14 figure

Band termination in the N=Z Odd-Odd Nucleus 46V

High spin states in the odd-odd N=Z nucleus 46V have been identified. At low spin, the T=1 isobaric analogue states of 46Ti are established up to I = 6+. Other high spin states, including the band terminating state, are tentatively assigned to the same T=1 band. The T=0 band built on the low-lying 3+ isomer is observed up to the 1f7/2-shell termination at I=15. Both signatures of a negative parity T=0 band are observed up to the terminating states at I = 16- and I = 17-, respectively. The structure of this band is interpreted as a particle-hole excitation from the 1d3/2 shell. Spherical shell model calculations are found to be in excellent agreement with the experimental results.Comment: 5 pages, 4 figure

Transition Rates between Mixed Symmetry States: First Measurement in 94Mo

The nucleus 94Mo was investigated using a powerful combination of gamma-singles photon scattering experiments and gamma-gamma-coincidence studies following the beta-decay of 94mTc. The data survey short-lived J^pi=1+,2+ states and include branching ratios, E2/M1 mixing ratios, lifetimes, and transition strengths. The mixed-symmetry (MS) 1+ scissors mode and the 2+ MS state are identified from M1 strengths. A gamma transition between MS states was observed and its rate was measured. Nine M1 and E2 strengths involving MS states agree with the O(6) limit of the interacting boson model-2 using the proton boson E2 charge as the only free parameter.Comment: 9 pages, 3 PostScript figures included, ReVTeX, accepted for publication in Physical Review Letters, tentatively scheduled for August 9, 199

Experimental evidence for 56Ni-core breaking from the low-spin structure of the N=Z nucleus 58Cu

Low-spin states in the odd-odd N=Z nucleus 58Cu were investigated with the 58Ni(p,n gamma)58Cu fusion evaporation reaction at the FN-tandem accelerator in Cologne. Seventeen low spin states below 3.6 MeV and 17 new transitions were observed. Ten multipole mixing ratios and 17 gamma-branching ratios were determined for the first time. New detailed spectroscopic information on the 2+,2 state, the Isobaric Analogue State (IAS) of the 2+,1,T=1 state of 58Ni, makes 58Cu the heaviest odd-odd N=Z nucleus with known B(E2;2+,T=1 --> 0+,T=1) value. The 4^+ state at 2.751 MeV, observed here for the first time, is identified as the IAS of the 4+,1,T=1 state in 58Ni. The new data are compared to full pf-shell model calculations with the novel GXPF1 residual interaction and to calculations within a pf5/2 configurational space with a residual surface delta interaction. The role of the 56Ni core excitations for the low-spin structure in 58Cu is discussed.Comment: 15 pages, 7 figures, submitted to Phys. Rev.

Lifetime measurements in the tungsten isotopes <math><mmultiscripts><mi mathvariant="normal">W</mi><mprescripts/><none/><mrow><mn>176</mn><mo>,</mo><mn>178</mn><mo>,</mo><mn>180</mn></mrow></mmultiscripts></math>

International audienceLifetimes of yrast states in the rare-earth midshell isotopes W176,178,180 have been measured with fast-timing methods using the Cologne iron-free Orange spectrometer and the Cologne HORUS spectrometer and with the recoil distance Doppler shift method using the Cologne coincidence plunger setup. Different fusion evaporation reactions have been used to populated excited states in the investigated nuclei. Lifetimes of the 21+, 41+, 61+, and 81+ yrast states were measured in all three tungsten isotopes and in addition the lifetime of the 101+ state was measured in W176. Quadrupole deformation parameters, reduced transition probabilities, and B4/2 ratios are extracted and discussed in the context of interacting boson model 1 calculations. The results with newly determined signatures largely confirm the investigated tungsten isotopes to be deformed prolate rotors

Low-spin excitations in

The low-spin excitations of the nucleus 146Sm which is just two neutrons and two protons away from the N = 82 shell and Z = 64 subshell closures have been investigated by means of the 143Nd (α, n) and 144Nd (α, 2n) fusion-evaporation reactions. We established 47 hitherto unknown energy levels up to 4.7MeV and 75 new transitions. In addition, 7 spin assignments were possible from the γ-γ angular correlation analysis. The structure of the possible candidates for a 2+ ⊗ 3− quadrupole-octupole multiplet are first discussed in terms of the harmonic vibrational model. A comparison of these states with the corresponding ones in the neighboring N = 84 isotones is also presented. Finally, the structure of the 146Sm nucleus is interpreted in terms of the IBA-spdf model. It is shown that the model is able to reproduce the experimental relative transition strengths of the 2+ ⊗ 3− quadrupole-octupole multiplet and also a series of collective properties such as the proposed double-octupole excitations