M. A. Schumaker

TIGRESS: TRIUMF-ISAC gamma-ray escape-suppressed spectrometer

The TRIUMF-ISAC gamma-ray escape-suppressed spectrometer (TIGRESS) is a new γ-ray detector array being developed for use at TRIUMFs Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. TIGRESS will comprise 12 32-fold segmented clover-type HPGe detectors coupled with 20-fold segmented modular Compton suppression shields and custom digital signal processing electronics. This paper provides an overview of the TIGRESS project and progress in its development to date.

High-resolution γ-ray spectroscopy: a versatile tool for nuclear β-decay studies at TRIUMF-ISAC

High-resolution γ-ray spectroscopy is essential to fully exploit the unique, high-quality beams available at the next generation of radioactive ion beam facilities such as the TRIUMF isotope separator and accelerator (ISAC). The 8π spectrometer, which consists of 20 Compton-suppressed HPGe detectors, has recently been reconfigured for a vigorous research programme in weak interaction and nuclear structure physics. With the addition of a variety of ancillary detectors it has become the worlds most powerful device dedicated to β-decay studies. This paper provides a brief overview of the apparatus and highlights from recent experiments.

Lifetime of 19 Ne * (4.03 MeV)

The Doppler-shift attenuation method was applied to measure the lifetime of the 4.03 MeV state in {sup 19}Ne. By utilizing a {sup 3}He-implanted Au foil as a target, the state was populated using the {sup 20}Ne({sup 3}He, {alpha}){sup 19}Ne reaction in inverse kinematics at a {sup 20}Ne beam energy of 34 MeV. De-excitation {gamma} rays were detected in coincidence with {alpha} particles. At the 1{sigma} level, the lifetime was determined to be 11{sub -3}{sup +4} fs and at the 95.45% confidence level the lifetime is 11{sub -7}{sup +8} fs.

Lifetimes of states in 19Ne above the 15O+α breakup threshold

The 15 O(α, γ) 19 Ne reaction plays a role in the ignition of type I x-ray bursts on accreting neutron stars. The lifetimes of states in 19 Ne above the 15 O+α threshold of 3.53 MeV are important inputs to calculations of the astrophysical reaction rate. These levels in 19 Ne were populated in the 3 He( 20 Ne , α) 19 Ne reaction at a 20 Ne beam energy of 34 MeV. The lifetimes of six states above the threshold were measured with the Doppler-shift attenuation method. The present measurements agree with previous determinations of the lifetimes of these states and in some cases are considerably more precise.

Precision half-life measurement of 62Ga

A measurement of the half-life of 62Ga was made as part of a programme of high-precision superallowed Fermi β decay studies at the ISAC radioactive beam facility. The experiment was conducted by counting β+ particles from the decay of 62Ga in a 4π gas proportional counter. The half-life was measured to be 116.01 ± 0.19 ms. Several parameters were varied during the experiment to test for systematic effects, but no significant effects were found.

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.

Testing the integration of BaF2 detectors into the 8π array: fast-timing measurements at TRIUMF

BaF 2 detectors for picosecond gamma-ray decay lifetime measurements have been installed into the 8π gamma-ray spectrometer as a proof-of-principle for a possible installation of a full array of ten detectors. Using four detectors a test measurement of the half-life of the 2 + state in 152 Sm resulted in a value of 1.33(6) ns, compared with a published value of 1.396 ns. Measurements with a 26 Na stopped beam were performed with various master-trigger conditions. Using a master trigger of germanium-SCEPTAR-BaF 2 OR BaF 2 -BaF 2 , the FWHM of the BaF 2 -BaF 2 triggered events was found to be ∼290 ps compared with ∼ 1.9 ns for the germanium-SCEPTAR-BaF 2 triggered events. Simulations using GEANT4 of a suggested BaF 2 lifetime measurement system have been carried out. These illustrate the considerable gain in spectrum quality which can be expected using simple add-back protocols.

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.

Gamma‐Ray Transitions In the Decay of the Superallowed Beta Emitter 62Ga

A measurement of the ground state β‐decay branching ratio of 62Ga has been made as part of a program of high‐precision superallowed Fermi β decay studies at the ISAC radioactive beam facility. The experiment was conducted by detecting γ rays and β particles from the decay of 62Ga using the 8π γ‐ray spectrometer and the SCEPTAR plastic scintillator array.

Halo neutrons and the β-decay of 11Li

The β-decay of 11Li has been studied at ISAC/TRIUMF using the 8pi spectrometer, an array of 20 Compton-suppressed high-purity germanium detectors. Most of the 11Li β-decay strength is observed to proceed through unbound states in 11Be, which subsequently decay by one-neutron emission to 10Be. This results in the observation of a γ-spectrum dominated by the decay of the excited states in 10Be. These transitions exhibit characteristic Doppler broadened lineshapes, due to the the recoiling effect induced by the neutron emission. A Monte-Carlo simulation was developed to analyze the complex shape of these γ-lines. Both the half-lives of states in 10Be and the energies of the β-delayed neutrons feeding those states were obtained. It was also possible to determine the excitation energies of the parent states in 11Be. The present contribution was the subject of a publication in a scientific journal (F. Sarazin et al., Phys. Rev. C 70, 031302(R)(2004) )shortly before the conference. It was judged not appropriate to submit for peerreviewing a contribution with nearly the same content. The reader is therefore invited to read the original publication.