Isotope Separator And Accelerator Research Articles

High-precision half-life determination of $$^{14}$$O via direct $$\beta $$ counting

The half-life of the superallowed Fermi $\beta^+$ emitter $^{14}$O was determined to high precision via a direct $\beta$ counting experiment performed at the Isotope Separator and Accelerator (ISAC) facility at TRIUMF. The result, $T_{1/2}$($^{14}$O) = 70619.2(76) ms, is consistent with, but is more precise than, the world average obtained from 11 previous measurements. Combining the $^{14}$O half-life deduced in the present work with the previous most precise measurements of this quantity leads to a reduction in the overall uncertainty, by nearly a factor of 2. The new world average is $T_{1/2}$($^{14}$O) = 70619.6(63) ms with a reduced $\chi^2$ value of 0.87 obtained from 8 degrees of freedom.

High-precision branching ratio measurement and spin assignment implications for Ga62 superallowed β decay

A high-precision branching ratio measurement for the superallowed Fermi $\beta^{+}$ emitter $^{62}$Ga was performed with the Gamma-Ray Infrastructure for Fundamental Investigations of Nuclei (GRIFFIN) spectrometer at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. The high efficiency of the GRIFFIN spectrometer allowed 63 $\gamma$-ray transitions, with intensities down to $\approx$1 part per million (ppm) per $^{62}$Ga $\beta^{+}$ decay, to be placed in the level scheme of the daughter nucleus $^{62}$Zn, establishing the superallowed $\beta$ branching ratio for $^{62}$Ga decay to be 99.8577$^{+0.0023}_{-0.0029}\%$, a factor of 4 more precise than the previous world average. For several cascades, $\gamma-\gamma$ angular correlation measurements were performed to assign spins and/or determine the mixing ratios of transitions. In particular, the spin of the 2.342 MeV excited state in the daughter nucleus $^{62}$Zn was definitively assigned as $J = 0$. This assignment resolves a discrepancy between previous measurements and has important implications for the isospin symmetry breaking correction, $\delta_{C1}$, in $^{62}$Ga superallowed Fermi $\beta$ decay.

Remote handling systems for the ISAC and ARIEL high-power fission and spallation ISOL target facilities at TRIUMF

TRIUMF, Canada’s particle accelerator centre, is constructing a new high-power ISOL (Isotope Separation On-Line) facility called ARIEL (Advanced Rare IsotopE Laboratory). Thick porous targets will be bombarded with up to 48 kW of 480 MeV protons from TRIUMF’s cyclotron, or up to 100 kW of 30 MeV electrons from a new e-linac, to produce short-lived radioisotopes for a variety of applications, including nuclear astrophysics, fundamental nuclear structure and nuclear medicine. For efficient release of radioisotopes, the targets are heated to temperatures approaching 2000 °C, and are exposed to GSv/h level radiation fields resulting from intended fissions and spallations. Due to these conditions, the operational life for each target is only about five weeks, calling for frequent remote target exchanges to limit downtime. A few days after irradiation, the targets have a residual radiation field producing a dose rate on the order of 10 Sv/h at 1 m, requiring several years of decay prior to shipment to a national disposal facility. TRIUMF is installing new remote handling infrastructure dedicated to ARIEL, including hot cells and a remote handling crane. The system design applies learnings from multiple existing facilities, including CERN-ISOLDE, GANIL-SPIRAL II as well as TRIUMF’s ISAC (Isotope Separator and ACcelerator).

Fast radio frequency quadrupole envelope computation for model based beam tuning

Efficient tuning of complex accelerator chains requires automated procedures, themselves reliant upon beam physical models. The Isotope Separator and ACcelerator (ISAC) facility at TRIUMF requires frequent changes of beam species (isotope), mass to charge ratio and beam energy tailored to experiment requirements, which demands rapid beam tuning. In addition, emergent effects such as long term changes of energy or energy spread require beam optimization that must be based on a complete model of the accelerator. Using an envelope code to build an end-to-end simulation of the accelerator facility for operational purposes reduces computing times by 3 or 4 orders of magnitude, when compared to particle tracking codes, so that the requisite simulations may be carried out in real time, by polling control system data. Herein described is the second order Hamiltonian for an radio frequency quadrupole (RFQ), presented within the framework of the envelope code transoptr. To benchmark the transoptr model, envelope simulations of the TRIUMF-ISAC RFQ have been performed and compared with the multiparticle code parmteq.

Current developments with TRIUMF’s titanium-sapphire laser based resonance ionization laser ion source

Developments at TRIUMF’s isotope separator and accelerator (ISAC) resonance ionization laser ion source (RILIS) in the past years have concentrated on increased reliability for on-line beam delivery of radioactive isotopes to experiments, as well as increasing the number of elements available through resonance ionization and searching for ionization schemes with improved efficiency. The current status of these developments is given with a list of two step laser ionization schemes implemented recently.

Development of a new RFQ beam cooler and buncher for the CANREB project at TRIUMF

A new radiofrequency quadrupole (RFQ) based ion beam cooler and buncher is under development for the CANadian Rare-isotope facility with Electron Beam ion source (CANREB) project at TRIUMF. The CANREB project requires an RFQ buncher that will efficiently accept continuous beams of rare isotopes from either the Advanced Rare IsotopE Laboratory (ARIEL) or Isotope Separator and ACcelerator (ISAC) target by way of a high resolution magnetic spectrometer, with energies up to 60keV and deliver bunched beams to an electron beam ion source (EBIS) for charge breeding. The energy of the bunched beam delivered to the EBIS will be adjustable to match the requirements of the existing post acceleration infrastructure. The CANREB RFQ incorporates design considerations to facilitate ease of use over a wide range of ion masses, and is intended to accommodate incident beam rates as high as 108pps, delivering beam bunches at 100Hz. An overview of the CANREB RFQ design concept will be presented, informed by results from both ion optical simulations as well as commissioning efforts with other beam cooler and buncher devices. Simulation results indicate that the design is well suited to deliver high quality bunched beams with high efficiency with as many as 106 ions per bunch.

ARIEL E-linac Cryogenic System: Commissioning and First Operational Experience

The Advanced Rare IsotopE Laboratory (ARIEL) is a major expansion of the Isotope Separator and Accelerator (ISAC) facility at TRIUMF. A key part of the ARIEL project is a 10 mA 50 MeV continuous-wave superconducting radiofrequency (SRF) electron linear accelerator (e-linac). The 1.3 GHz SRF cavities are operated at 2 K. HELIAL LL helium liquefier by Air Liquide Advanced Technologies (ALAT) with a tuneable liquid helium (LHe) production was installed and commissioned in Q4’2013 [1]. It provides 4 K liquid helium to one injector and one accelerator cryomodules that were installed and tested in 2014. The 4 K to 2 K liquid helium transition is achieved on-board of each cryomodule. The cryoplant, LHe and LN2 distributions, sub-atmospheric (S/A) system and cryomodules were successfully commissioned and integrated into the e-linac cryogenic system. Required pressure regulation for both 4 K cryoplant in the Dewar and 2 K with the S/A system was achieved under simulated load. Final integration tests confirmed overall stable performance of the cryogenic system with two cryomodules installed. The paper presents details of the cryogenic system commissioning tests as well as highlights of the initial operational experience.

Precision Penning-trap measurement to investigate the role of theCr51(e−,νe)V51Qvalue in the gallium anomaly

A direct $Q$-value measurement has been made at TRIUMF's Ion Trap for Atomic and Nuclear Science (TITAN) for the $^{51}\mathrm{Cr}$(${e}^{\ensuremath{-}}$,${\ensuremath{\nu}}_{e}$)$^{51}\mathrm{V}$ reaction. This electron capture (EC) reaction was used in calibration measurements at the solar neutrino experiments SAGE and GALLEX, and the observed event rate differed from predictions creating the so-called gallium anomaly. Using isotopes delivered by the Isotope Separator and Accelerator (ISAC) facility at TRIUMF and charge breeding them to charge states 5+ and 6+, a $Q$ value of 751.86(55) keV was determined. This represents a 1.3$\ensuremath{\sigma}$ deviation from the result in the Atomic Mass Evaluation 2012 (AME12) and the value used in the calculated event rate. This deviation is found to be insignificant in context of the gallium anomaly, thus confirming that the predicted event rate has not been overestimated as the result of an erroneous $^{51}\mathrm{Cr}$ EC $Q$ value. Additionally, the absolute masses of each $^{51}\mathrm{Cr}$ and $^{51}\mathrm{V}$ have been independently determined and are in agreement with the AME12 values.

In-source spectroscopy on astatine and radium for resonant laser ionization

At on-line isotope separator facilities, rare isotopes of radioactive elements such as astatine, radium or polonium are demanded for fundamental research on nuclear structure. These elements are generally suitable for a resonance ionization laser ion source, but more data on the atomic structure is necessary to develop efficient laser ionization schemes. Due to the missing stable reference isotopes spectroscopic investigation of the atomic structure can only be performed during on-line operation. At the Isotope Separator and ACcelerator (ISAC) facility at TRIUMF, the elements astatine and radium were investigated by in-source laser spectroscopy to optimize the laser ionization efficiency. For astatine, laser spectroscopy was performed to search for high lying bound states as well as for auto-ionizing resonances. This led to the identification of four new high lying bound states of odd parity, while no auto-ionizing resonances were observed in the investigated region. Furthermore, the feasibility and the impact of laser ionization on the yield of radium isotopes was investigated using an activated target after proton irradiation.

High-precision half-life and branching-ratio measurements for superallowed Fermiβ+emitters at TRIUMF – ISAC

A program of high-precision half-life and branching-ratio measurements for superallowed Fermi emitters is being carried out at TRIUMF's Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. Recent half-life measurements for the superallowed decays of 14 O, 18 Ne, and 26 Al m , as well as branching-ratio measurements for 26 Al m and 74 Rb are reported. These results provide demanding tests of the Standard Model and the theoretical isospin symmetry breaking (ISB) corrections in superallowed Fermi decays.

High-Statistics Study of theβ+/EC-Decay of110In

A study of the 110In β+/EC decay was performed at the TRIUMF Isotope Separator and Accelerator (ISAC) facility to probe the nuclear structure of 110Cd. The data were collected in scaled-down γ-ray singles, γ − γ coincidence, and γ-electron coincidence mode. The data were sorted and a random-background subtracted γ − γ matrix was created containing a total of 850 million events. We expanded the level scheme of 110Cd significantly by identifying 75 levels under 3.8 MeV, including 12 new ones, and increased the number of previously observed transitions from these levels to 273. The γ-ray branching intensities have been extracted through an analysis of the coincidence intensities. The branching ratios were combined with a reanalysis of lifetimes measurements obtained in an (n, n'γ) reaction with monoenergetic neutrons for the calculation of B(E2) values and these results have lead to the proposal of a γ-soft rotor, or O(6) nucleus, rather than a vibrational, or U(5) pattern for the nature of the low-lying, low-spin levels in 110Cd.

High-precision branching-ratio measurement for the superallowedβ+emitter74Rb

A high-precision branching-ratio measurement for the superallowed ${\ensuremath{\beta}}^{+}$ decay of ${}^{74}$Rb was performed at the TRIUMF Isotope Separator and Accelerator (ISAC) radioactive ion-beam facility. The scintillating electron-positron tagging array (SCEPTAR), composed of 10 thin plastic scintillators, was used to detect the emitted $\ensuremath{\beta}$ particles; the 8$\ensuremath{\pi}$ spectrometer, an array of 20 Compton-suppressed HPGe detectors, was used for detecting $\ensuremath{\gamma}$ rays that were emitted following Gamow-Teller and nonanalog Fermi ${\ensuremath{\beta}}^{+}$ decays of ${}^{74}$Rb; and the Pentagonal Array of Conversion Electron Spectrometers (PACES), an array of 5 Si(Li) detectors, was employed for measuring $\ensuremath{\beta}$-delayed conversion electrons. Twenty-three excited states were identified in ${}^{74}$Kr following $8.241(4)\ifmmode\times\else\texttimes\fi{}{10}^{8}$ detected ${}^{74}$Rb $\ensuremath{\beta}$ decays. A total of 58 $\ensuremath{\gamma}$-ray and electron transitions were placed in the decay scheme, allowing the superallowed branching ratio to be determined as ${B}_{0}=99.545(31)%$. Combined with previous half-life and $Q$-value measurements, the superallowed branching ratio measured in this work leads to a superallowed $ft$ value of 3082.8(65) s. Comparisons between this superallowed $ft$ value and the world-average-corrected $\overline{\mathcal{F}t}$ 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.

Resonant Ionization Laser Ion Source (RILIS) off-line developments on Ga, Al and Ca

The Resonant Ionization Laser Ion Source (RILIS) is an element selective, highly efficient and versatile tool for generation of radioactive ion beams at on-line mass separator facilities. Parallel to TRIUMF’s on-line RILIS at the Isotope Separator and ACcelerator (ISAC) facility, an off-line Laser Ion Source test stand (LIS STAND) is operated for systematic laser resonance ionization spectroscopy, ionization scheme and ion source development. Three titanium sapphire (Ti:Sa) lasers optionally equipped with harmonic frequency generation units are used to resonantly step-wise excite and ionize elements of interest. A grating tuned Ti:Sa laser allows continuous laser wavelength scans of up to Δ≈200nm. With this laser inventory and the LIS STAND, atomic Rydberg series and auto-ionizing levels can systematically be studied. The LIS STAND has been in use since 2009 and so far the spectroscopy on Ga, Al and Ca has been performed. The development of efficient laser resonant ionization schemes, their investigation and comparison using the LIS STAND are discussed.

Gamma-ray spectroscopy at TRIUMF-ISAC: recent highlights and future plans

High-resolution gamma-ray spectroscopy is essential to fully exploit the unique scientific opportunities at the next generation radioactive beam facilities such as TRIUMF Isotope Separator and Accelerator (ISAC). At ISAC the 8π spectrometer and its associated auxiliary detectors is optimized for β-decay studies while TIGRESS, an array of segmented clover HPGe detectors has been designed for reaction studies with accelerated radioactive ion beams. This paper gives a brief overview of these facilities, recent results from the diverse program of nuclear structure and fundamental interaction studies they support and future plans.

Canada's ISAC Radioactive Beam Facility - At the Nexus of Past and Future Triumphs

TRIUMF, Canada's national laboratory for particle and nuclear physics (Figure 1), marked several milestones in 2009—the 40-year anniversary of its official commemoration, 35 years of main cyclotron operation, and 10 years since the primary in-house physics program shifted to rare isotope beams at the ISAC (Isotope Separator and ACcelerator) facility [1]. The year 2010 is now a year of milestones for ISAC—the 15th anniversary of the facility's funding and the 10th anniversary of beam through the first linear post-accelerator. As well, 2010 will be about looking forward to new triumphs as the laboratory embarks on a major new initiative to expand its core capabilities.

A multicharge ion source (Supernanogan) for the OLIS facility at ISAC/TRIUMF

The Off-Line Ion Source (OLIS) [K. Jayamanna, D. Yuan, T. Kuo, M. MacDonald, P. Schmor, and G. Dutto, Rev. Sci. Instrum. 67, 1061 (1996); K. Jayamanna, Rev. Sci. Instrum. 79, 02711 (2008)] facility consists of a high voltage terminal containing a microwave cusp ion source, either a surface ion source or a hybrid surface-arc discharge ion source [K. Jayamanna and C. Vockenhuber, Rev. Sci. Instrum. 79, 02C712 (2008)], and an electrostatic switch that allows the selection of any one of the sources without mechanical intervention. These sources provide a variety of +1 beams up to mass 30 for Isotope Separator and ACcelerator (ISAC) [R. E. Laxdal, Nucl. Instrum. Methods Phys. Res. B 204, 400 (2003)] experiments, commissioning the accelerators, setting up the radioactive experiments, and for tuning the beam lines. The radio frequency quadrupole (RFQ) [M. Marchetto, Z. T. Ang, K. Jayamanna, R. E. Laxdal, A. Mitra, and V. Zvyagintsev, Eur. Phys. J. Spec. Top. 150, 241 (2005)] injector accelerator is a constant velocity machine designed to accept only 2 keV/u and the source extraction energy is limited to 60 kV. Further stripping is then needed downstream of the RFQ to inject the beam into the drift tube linac [M. Marchetto, Z. T. Ang, K. Jayamanna, R. E. Laxdal, A. Mitra, and V. Zvyagintsev, Eur. Phys. J. Spec. Top. 150, 241 (2005)] accelerator that requires A/q up to 6. Base on this constraints a multicharge ion source capable to deliver beams above mass 30 with A/q up to 6 was needed in order to reach full capability of the ISAC facility. A Supernanogan [C. Bieth et al., Nucleonika 48, S93 (2003)] multicharge ion source was then purchased from Pantechnik and was installed in the OLIS terminal. Commissioning and performance of the Supernanogan with some results such as emittance dependence of the charge states as well as charge state efficiencies are presented.

High-precision branching ratio measurement for the superallowedβ+emitterGa62

A high-precision branching ratio measurement for the superallowed ${\ensuremath{\beta}}^{+}$ decay of $^{62}\mathrm{Ga}$ was performed at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. The 8\ensuremath{\pi} spectrometer, an array of 20 high-purity germanium detectors, was employed to detect the \ensuremath{\gamma} rays emitted following Gamow-Teller and nonanalog Fermi ${\ensuremath{\beta}}^{+}$ decays of $^{62}\mathrm{Ga}$, and the SCEPTAR plastic scintillator array was used to detect the emitted \ensuremath{\beta} particles. Thirty \ensuremath{\gamma} rays were identified following $^{62}\mathrm{Ga}$ decay, establishing the superallowed branching ratio to be $99.858(8)%$. Combined with the world-average half-life and a recent high-precision $Q$-value measurement for $^{62}\mathrm{Ga}$, this branching ratio yields an $\mathit{ft}$ value of $3074.3\ifmmode\pm\else\textpm\fi{}1.1$ s, making $^{62}\mathrm{Ga}$ among the most precisely determined superallowed $\mathit{ft}$ values. Comparison between the superallowed $\mathit{ft}$ value determined in this work and the world-average corrected $\overline{\mathcal{F}t}$ value allows the large nuclear-structure-dependent correction for $^{62}\mathrm{Ga}$ decay to be experimentally determined from the CVC hypothesis to better than 7$%$ of its own value, the most precise experimental determination for any superallowed emitter. These results provide a benchmark for the refinement of the theoretical description of isospin-symmetry breaking in $A\ensuremath{\geqslant}62$ superallowed decays.

Direct Mass Measurement of the Four-Neutron Halo NuclideHe8

A high-precision Penning trap mass measurement of the exotic 8He nuclide (T(1/2)=119 ms) has been carried out resulting in a reduction of the uncertainty of the halo binding energy by over an order of magnitude. The new mass, determined with a relative uncertainty of 9.2 x 10(-8) (deltam=690 eV) is 13 keV less bound than the previously accepted value. The mass measurement is of great relevance for the recent charge-radius measurement of 8He [P. Mueller, Phys. Rev. Lett. 99, 252501 (2007).10.1103/PhysRevLett.99.252501]. The 8He mass is the first result from the newly-commissioned Penning trap: TITAN (TRIUMF's Ion Trap for Atomic and Nuclear science) at the ISAC (Isotope Separator and Accelerator) radioactive beam facility at TRIUMF.

Electron capture branching ratio measurements in an ion trap for double beta decay experiments at TITAN

Double beta decay (ββ) is a nuclear decay mode expected to appear in at least two varieties, the double-neutrino (2ν) and the zero-neutrino (0ν) mode. The 0νββ-decay is of particular interest as it requires the neutrino to be a Majorana particle. The search for such a decay is presently being carried out or planned in a number of experiments, such as EXO, MAJORANA, GERDA, CUORE, COBRA, NEMO-III and SNO+. The 0ν-decay rate depends on the neutrino mass but, unfortunately, also on a rather complex nuclear matrix element, making the extraction of the mass heavily dependent on the underlying theoretical nuclear model. However, all theoretical models can readily be tested against the 2ν mode, which, unlike its 0ν counterpart, only involves simple Gamow–Teller nuclear matrix elements. These elements can be determined experimentally either through charge-exchange reactions or, for the ground-state transition, through the electron capture (EC) or single β-decay of the intermediate odd–odd nucleus. The present program is geared towards the measurement of the EC branching ratios (BR). In most cases, these ratios are poorly known or not known at all, because EC is usually suppressed by several orders of magnitude compared to the β-decay counterpart due to energy considerations. Traditional methods for measuring these ratios have so far suffered from overwhelming background generated by these high-energy electrons. Recently, a unique background-free method for measuring EC branching ratios was proposed using the TITAN ion trap at the TRIUMF ISAC (Isotope Separator and ACcelerator) radioactive beam facility. The measurements will make use of the EBIT (Electron Beam Ion Trap) operating in Penning mode where electrons from the β−-decay will be confined by the magnetic field. K-shell X-rays from EC will be detected by seven X-ray detectors located around the trap, thus providing orders of magnitude background suppression and thus ideal low-BR measurement environment.

The TRIUMF nuclear structure program and TIGRESS

The isotope separator and accelerator (ISAC) facility located at the TRIUMF laboratory in Vancouver, Canada, is one of the world’s most advanced isotope separator on-line-type radioactive ion beam facilities. An extensive γ-ray spectroscopy programme at ISAC is centred around two major research facilities: (i) the 8π γ-ray spectrometer for β-delayed γ-ray spectroscopy experiments with the low-energy beams from ISAC-I, and (ii) the next generation TRIUMF-ISAC gamma-ray escape suppressed spectrometer (TIGRESS) for in-beam experiments with the accelerated radioactive-ion beams. An overview of these facilities and recent results from the diverse programme of nuclear structure and fundamental interaction studies they support is presented.