High-Precision Branching Ratio Measurement for the Superallowed + Emitter 74Rb

A high-precision branching-ratio measurement for the superallowed β + decay of 74Rb was performed at the TRIUMF Isotope Separator and Accelerator (ISAC) radioactive ion-beam facility. The scintillating electronpositron tagging array (SCEPTAR), composed of 10 thin plastic scintillators, was used to detect the emitted β particles; the 8π spectrometer, an array of 20 Compton-suppressed HPGe detectors, was used for detecting γ rays that were emitted following Gamow-Teller and nonanalog Fermi β + decays of 74Rb; and the Pentagonal Array of Conversion Electron Spectrometers (PACES), an array of 5 Si(Li) detectors, was employed for measuring β-delayed conversion electrons. Twenty-three excited states were identified in 74Kr following 8.241(4) × 108 detected 74Rb β decays. A total of 58 γ -ray and electron transitions were placed in the decay scheme, allowing the superallowed branching ratio to be determined as B0 = 99.545(31)%. Combined with previous half-life and Q-value measurements, the superallowed branching ratio measured in this work leads to a superallowed f t value of 3082.8(65) s. Comparisons between this superallowed f t value and the world-average-corrected Ft value, as well as the nonanalog Fermi branching ratios determined in this work, provide guidance for theoretical models of the isospin-symmetry-breaking corrections in this mass region.IS

The structure of nuclei far from beta stability

This report discusses: shape coexistence and intruder states; the electric monopole transition in nuclei; gold isotopes; platinum isotopes; iridium isotopes; search for superdeformation in {sup 192}Hg; search for population of superformed states in {sup 194}Pb using {sup 194}Bi {beta}{sup +}-decay; detailed nuclear structure studies far from stability; prototype internal pair spectrometer; and picosecond lifetime spectrometer

Structure of neutron deficient odd-proton nuclei near the shell closure at Z = 82

The experimental data on neutron-deficient, odd-proton isotopes of Au(Z = 79), Tl(Z = 81), and Bi(Z = 83) relevant to core particle coupling schemes and the shell model intruder state phenomenon are presented. The data show that, near the Z = 82 closed proton shell, the unpaired necleon can be used to probe the structure of the core. It is demonstrated that the description of this process in terms of core-particle coupling models enables on to quantify and systematize a large body of experimental data and, consequently, to provide new insights into the relevant nuclear structure. The purity of the particle/hole configurations is discussed. Information on the mechanisms responsible for the disappearance of the Z = 82 shell model gap as the neutron number decreases is obtained from the spectrum of states which result from the coupling of the intruder particle and the even-even core. The observed band structure indicates that the instrusion of the extra shell proton (or proton hole) into the low-energy structure of the neutron-deficient odd-A Au, Tl, and Bi isotopes is not strongly related to the deformation of the core. 6 figures

The Structure of Nuclei Far from Stability

From among a number of important nuclear structure results that have emerged from our research program during the past few years, two stand out as being of extra significance. These are: (a) the identification of a diabatic coexisting structure in {sup 187}Au which arises solely from differences in proton occupation of adjacent oscillator shells, and (b) the realization of a method for estimating EO strength in nuclei and the resulting prediction that the de-excitation of superdeformed bands may proceed, in some cases, by strong EO transitions

Electric monopole transitions: What they can tell us about nuclear structure

A brief survey of E0 strength in a number of nuclei in different regions of the nuclear chart is presented. The connection between E0 strength and shape coexistence is reviewed. Nuclear structure information obtained from measurements of electric monopole transitions in {sup 184}Pt and {sup 187}Au is discussed. Plans for future experiments utilizing radioactive ion beams and E0 internal pair formation is presented

Behavior of intruder based states in light Bi and Tl isotopes: the study of {sup 187 Bi} {alpha} decay

Intruder state excitation energies in odd-mass nuclei just outside a closed proton shell plotted versus neutron number generally exhibit parabola-shaped curves with minima near neutron mid-shells. The Bi isotopes, however, do not seem to follow this trend. Recent experiments performed at Argonne National Laboratory have identified the previously unobserved {sup 187}Bi ground state (h{sub 9/2}) to {sup 183}TI ground state s{sub 1/2} {alpha} transition. Its energy when combined with those of two earlier known transitions, namely {sup 187}Bi (h{sub 9/2}) {yields} {sup 183m}Tl (h{sub 9/2}) and {sup 187m}Bi (s{sub 1/2}) {yields} {sup 183}Tl(s{sub 1/2}), establishes the excitation energies of the {sup 183m}Tl and {sup 187m}Bi to be 620(20) keV and 110(20) keV, respectively. This value for {sup 187m}Bi is 80 keV lower than the excitation energy of the same intruder level in {sup 189}Bi. Implications of this result with respect to intruder-state systematics are discussed

Electric monopole transitions: What they can tell us about nuclear structure

A brief survey of E0 strength in a number of nuclei in different regions of the nuclear chart is presented. The connection between E0 strength and shape coexistence is reviewed. Nuclear structure information obtained from measurements of electric monopole transitions in {sup 184}Pt and {sup 187}Au is discussed. Plans for future experiments utilizing radioactive ion beams and E0 internal-pair-formation is presented

Low Energy E0 Transitions in Odd-mass Nuclei of the Neutron Deficient 180 < A < 200 Region

The region of neutron-deficient nuclei near Z = 82 and N = 104 provides the most extensive example of low-energy shape coexistence anywhere on the mass surface. It is shown that E0 and E0 admixed transitions may be used as a fingerprint to identify shape coexistence in odd-mass nuclei. It is also shown that all the known cases of low energy E0 and E0 admixed transitions in odd-mass nuclei occur where equally low-lying O/sup +/ states occur in neighboring even-even nuclei. A discussion of these and other relevant data as well as suggestions for new studies which may help to clarify and, more importantly, quantify the connection between E0 transitions and shape coexistence are presented. 60 refs., 7 figs., 4 tabs