G. A. Demand

Far from 'Easy' Spectroscopy with the 8π and GRIFFIN Spectrometers at TRIUMF-ISAC

The 8 pi spectrometer, installed at the TRIUMF-ISAC facility, was the worlds most sensitive gamma-ray spectrometer dedicated to beta-decay studies. A description is given of the 8 pi spectrometer and its auxiliary detectors including the plastic scintillator array SCEPTAR used for beta-particle tagging and the Si(Li) array PACES for conversion electron measurements, its moving tape collector, and its data acquisition system. The recent investigation of the decay of Cs-124 to study the nuclear structure of Xe-124, and how the beta-decay measurements complemented previous Coulomb excitation studies, is highlighted, including the extraction of the deformation parameters for the excited 0(+) bands in Xe-124. As a by-product, the decay scheme of the (7(+)) Cs-124 isomeric state, for which the data from the PACES detectors were vital, was studied. Finally, a description of the new GRIFFIN spectrometer, which uses the same auxiliary detectors as the 8 pi spectrometer, is given.

Gamma‐Ray Spectroscopy at TRIUMF‐ISAC: the New Frontier of Radioactive Ion Beam Research

High‐resolution gamma‐ray spectroscopy is essential to fully exploit the unique scientific opportunities at the next generation radioactive ion beam facilities such as the TRIUMF Isotope Separator and Accelerator (ISAC). At ISAC the 8π spectrometer and its associated auxiliary detectors is optimize for β‐decay studies while TIGRESS an array of segmented clover HPGe detectors has been designed for studies with accelerated beams. This paper gives a brief overview of these facilities and also presents recent examples of the diverse experimental program carried out at the 8π spectrometer.In this article we prove the bivariate uniqueness property for a particular “max-type” recursive distributional equation (RDE). Using the general theory developed in [5] we then show that the corresponding recursive tree process (RTP) has no external randomness, more preciously, the RTP is endogenous. The RDE we consider is so called the Logistic RDE, which appears in the proof of the ζ(2)-limit of the random assignment problem [4] using the local weak convergence method. Thus this work provides a non-trivial application of the general theory developed in [5]. AMS 2000 subject classification : 60E05, 60J80, 60K35, 62E10, 82B43.

Coulomb excitation of the proton-dripline nucleus 20Na

The low-energy structure of the proton dripline nucleus {sup 20}Na has been studied using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. A 1.7-MeV/nucleon {sup 20}Na beam of {approx}5x10{sup 6} ions/s was Coulomb excited by a 0.5-mg/cm{sup 2nat}Ti target. Scattered beam and target particles were detected by the BAMBINO segmented Si detector while {gamma} rays were detected by two TIGRESS HPGe clover detectors set perpendicular to the beam axis. Coulomb excitation from the 2{sup +} ground state to the first excited 3{sup +} and 4{sup +} states was observed, and B({lambda}L) values were determined using the 2{sup +}{yields}0{sup +} de-excitation in {sup 48}Ti as a reference. The resulting B({lambda}L){down_arrow} values are B(E2;3{sup +}{yields}2{sup +})=55{+-}6 e{sup 2} fm{sup 4} (17.0{+-}1.9 W.u.), B(E2;4{sup +}{yields}2{sup +})=35.7{+-}5.7 e{sup 2} fm{sup 4} (11.1{+-}1.8 W.u.), and B(M1;4{sup +}{yields}3{sup +})=0.154{+-}0.030 {mu}{sub N}{sup 2} (0.086{+-}0.017 W.u.). These measurements provide the first experimental determination of B({lambda}L) values for this proton dripline nucleus of astrophysical interest.

Superallowed Fermi β decay studies at TRIUMF-ISAC

A program of high-precision superallowed Fermi β decay studies is being carried out at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. Recent high-precision branching ratio measurements for the superallowed decays of 74Rb and 26Alm, as well as a half-life measurement for 26Alm that is the most precise half-life measurement for any superallowed emitter to date, are reported. These results provide demanding tests of the theoretical isospin symmetry breaking corrections in superallowed Fermi β decays.

Mapping quadrupole collectivity in the Cd isotopes: The breakdown of harmonic vibrational motion

The stable Cd isotopes have long been used as paradigms for spherical vibrational motion. Extensive investigations with in‐beam γ spectroscopy have resulted in very‐well‐established level schemes, including many lifetimes or lifetime limits. A programme has been initiated to complement these studies with very‐high‐statistics β decay using the 8π spectrometer at the TRIUMF radioactive beam facility. The decays of 112In and 112Ag have been studied with an emphasis on the observation of, or the placement of stringent limits on, low‐energy branches between potential multi‐phonon levels. A lack of suitable 0+ or 2+ three‐phonon candidates has been revealed. Further, the sum of the B(E2) strength from spin 0+ and 2+ states up to 3 MeV in excitation energy to the assigned two‐phonon levels falls far short of the harmonic‐vibrational expectations. This lack of strength points to the failing of collective models based on vibrational phonon structures.

Structure of the Kπ = 4+bands in 186,188Os

The structures of 3+ states in Os have been debated over several decades. Based on measured B(E2) values they were interpreted in 186–192Os as Kπu2009=u20094+ two‐phonon vibrations, whereas inelastic scattering, and (t,α) work imply a hexadecapole phonon description. To clarify the nature of these Kπu2009=u20094+ bands in 186,188Os, we performed a (3He,d) reaction on 185,187Re targets using 30 MeV 3He beams and a Q3D spectrograph. Absolute cross sections were obtained for excited states up to 3 MeV at 9 angles from 5° to 50°. Results indicate a significant 52+[402]π+32+[402]π component in agreement with quasiparticle phonon model predictions for a single hexadecapole phonon structure.

First Results with TIGRESS and Accelerated Radioactive Ion Beams from ISAC: Coulomb Excitation of 20,21,29Na

The TRIUMF‐ISAC Gamma‐Ray Escape Suppressed Spectrometer (TIGRESS) is a state‐of‐the‐art γ‐ray spectrometer being constructed at the ISAC‐II radioactive ion beam facility at TRIUMF. TIGRESS will be comprised of twelve 32‐fold segmented high‐purity germanium (HPGe) clover‐type γ‐ray detectors, with BGO/CsI(Tl) Compton‐suppression shields, and is currently operational at ISAC‐II in an early‐implementation configuration of six detectors. Results have been obtained for the first experiments performed using TIGRESS, which examined the Au2009=u200920, 21, and 29 isotopes of Na by Coulomb excitation.

Nature of the Kπ = 4+ bands in the Os isotopes

Levels in 186,188Os have been investigated using the (3He,d) reaction with 30 MeV 3He beams. Absolute level‐population cross sections have been determined, and angular distributions measured between 5° and 50°. The 43+ levels are observed to be some of the strongest populated states below 2 MeV excitation energy, and the magnitudes of the 5/2+[402]π+3/2+[402]π configuration extracted are in line with quasiparticle‐phonon model predictions which state that the lowest‐lying Kπu2009=u20094+ band is predominantly a hexadecapole excitation.