Ion source developments for the production of radioactive isotope beams at TRIUMF.

At the ISAC facility at TRIUMF radioactive ions are produced by bombarding solid targets with up to 100 µA of 500 MeV protons. The reaction products have to diffuse out of the hot target into an ion source. Normally, singly charged ions are extracted. They can be transported either directly to experiments or via an ECR charge state breeder to a post accelerator. Several different types of ion sources have to be used in order to deliver a large variety of rare isotope beams. At ISAC those are surface ion sources, forced electron beam arc discharge (FEBIAD) ion sources and resonant laser ionization sources. Recent development activities concentrated on increasing the selectivity for the ionization to suppress isobaric contamination in the beam. Therefore, a surface ion rejecting resonant laser ionization source (SIRLIS) has been developed to suppress ions from surface ionization. For the FEBIAD ion source a cold transfer line has been introduced to prevent less volatile components from reaching the ion source.

A test stand for off-line laser ion source development at TRIUMF.

A test stand for ion source development and laser resonance ionization spectroscopy was built and commissioned at TRIUMF. The test stand is needed to develop efficient ion sources that can function reliably in the hostile, high temperature, high radiation environment of TRIUMF's isotope separator on-line (ISOL) production target ion source. In addition, it enables laser resonance ionization spectroscopy to develop laser excitation schemes suitable for the solid-state laser systems used with TRIUMF's resonant ionization laser ion source . Also, it allows for possible improvement of current ion sources and validation of new designs. The test stand employs a copy of the ion optics used on-line, so that results can be transferred directly to radioactive ion beam production. Due to space restrictions and the need for rapid mass scans, a quadrupole mass spectrometer is used as a mass separator. One of the first experiments conducted on the laser ion source test stand (LIS STAND) was resonant ionization spectroscopy of gallium to improve on the ionization scheme previously used on-line, so that low yield isotopes (e.g., (62)Ga) become available for experiments. Different Rydberg series in gallium were observed and autoionizing states were searched for. The overall LIS STAND system performance, characteristics, and the first resonant ionization spectroscopy are described.

Recent developments of the ion sources at Tri University Meson Factory/Isotope Separator and ACcelerator Facility.

This paper describes the recent progresses concerning the on-line ion source at the Tri University Meson Factory/Isotope Separator and ACcelerator (TRIUMF/ISAC) Radioactive Ion-Beam Facility; description of the new design of the surface-ion-source for improved stability of the beam intensity, description of the transport path to the east target station at ISAC, description of the new brazing techniques that solved recurrent problems with water leaks on the target/ion source assembly in the vacuum system, finally, recent developments concerning the Forced Electron Beam Induced Arc Discharge (FEBIAD) ion source are reported. In particular, a study on the effect of the plasma chamber volume on the ionization efficiency was completed.

Charge state breeding for the acceleration of radioactive ions at TRIUMF.

A 14.5 GHz electron cyclotron resonance ion source (PHOENIX from Pantechnik) has been set up at the Isotope Separation and ACceleration (ISAC) facility at TRIUMF for the charge state breeding of radioactive ions. After extensive testing and optimization on a test bench it has been moved on-line and put into operation. During a first test in 2008 a beam of (80)Rb(14+) was successfully created from (80)Rb(1+) and accelerated by the ISAC postaccelerator. Further tests with different stable and radioactive isotopes from the ISAC on-line sources and from a test source with stable Cs have been carried out. Until now an efficiency of 1.4% for (124)Cs(20+) has been obtained.

First Penning-trap mass measurement of the exotic halo nucleus 11Li.

In this Letter, we report a new mass for 11Li using the trapping experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived nuclide, t_{1/2}=8.8 ms, for which a mass measurement has ever been performed with a Penning trap. Combined with our mass measurements of ;{8,9}Li we derive a new two-neutron separation energy of 369.15(65) keV: a factor of 7 more precise than the best previous value. This new value is a critical ingredient for the determination of the halo charge radius from isotope-shift measurements. We also report results from state-of-the-art atomic-physics calculations using the new mass and extract a new charge radius for 11Li. This result is a remarkable confluence of nuclear and atomic physics.

Direct mass measurement of the four-neutron halo nuclide 8He.

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.

The ECRIS charge state breeding project at TRIUMF.

The performance of charge state breeding with an electron cyclotron resonance (ECR) ion source intended to increase the charge state of online produced radioactive ions at the ISAC facility at TRIUMF has been investigated. A 14 GHz PHOENIX from PANTECHNIK has been setup on a test bench. Singly charged ions have been produced with several ion sources typical for the on-line operation and were injected into the charge breeder. The main purpose of the tests has been the optimization of the efficiency for the charge breeding into the desired charge state. Maximum efficiencies reached so far with the standard one step deceleration of the ions in front of the plasma are up to about 6% for noble gas ions and about 3.5% for alkalines. As ion optics simulations show, the acceptance can be increased by a two step deceleration. In order to meet the velocity acceptance of the accelerator at different A/q values a similar two gap acceleration system for the highly charged ions has been installed to allow the source to run at different voltages. For the further beam transport to the accelerator, cross sections for charge exchange of the highly charged ions with the residual gas have been determined.

Off-line ion source terminal for ISAC at TRIUMF.

The off-line ion source (OLIS) terminal consists of a microwave cusp ion source, either a surface ion source or a hybrid surface-arc discharge ion source and an electrostatic switch that allows selecting any one of the sources without mechanical intervention. These sources provide variety of beams to ISAC experiments, for commissioning the accelerators, for setting up the radioactive experiments, and for tuning the beam lines. The microwave ion source has been operational since 1995 and provides singly and doubly charged beams from various stable isotopes for many ISAC experiments at high and low energy areas. Originally its prime goal was to provide beams from gaseous elements, but later two ovens and a sputtering system were added in order to provide beams from liquids and from solids. The surface ion source installed in 2002 can provide low energy spread beams from alkali and semialkali elements. It also has three separate ovens and an ionizer. Therefore, it can provide three different temperature regions simultaneously to provide different beams to ISAC. It is mainly used for laser spectroscopy experiments and other experiments, which require a finite beam quality. A hybrid surface-arc discharge ion source was also developed and installed in order to meet specific demands from experiments. This source terminal is now automated for start up and for mass selection. It is capable of providing stable beams for months without maintenance and it is also capable of providing negative ion beams if required. To date, over 40 different isotopes including many rear isotopes were delivered to various experiments from the OLIS source terminal. Performances of the ion sources and some of the results are discussed.

Precision branching ratio measurement for the superallowed beta+ emitter 62Ga and isospin-symmetry-breaking corrections in A>or=62 nuclei.

A high-precision branching ratio measurement for the superallowed beta+ decay of 62Ga was performed at the Isotope Separator and Accelerator radioactive ion beam facility. Nineteen gamma rays emitted following beta+ decay of 62Ga were identified, establishing the dominant superallowed branching ratio to be (99.861+/-0.011)%. Combined with recent half-life and Q-value measurements, this branching ratio yields a superallowed ft value of 3075.6+/-1.4 s for 62Ga decay. These results demonstrate the feasibility of high-precision superallowed branching ratio measurements in the A>or=62 mass region and provide the first stringent tests of the large isospin-symmetry-breaking effects predicted for these decays.

Nuclear charge radii of 9,11Li: the influence of halo neutrons.

The nuclear charge radius of 11Li has been determined for the first time by high-precision laser spectroscopy. On-line measurements at TRIUMF-ISAC yielded a 7Li-11Li isotope shift (IS) of 25 101.23(13) MHz for the Doppler-free [FORMULA: SEE TEXT]transition. IS accuracy for all other bound Li isotopes was also improved. Differences from calculated mass-based IS yield values for change in charge radius along the isotope chain. The charge radius decreases monotonically from 6Li to 9Li, and then increases from 2.217(35) to 2.467(37) fm for 11Li. This is compared to various models, and it is found that a combination of halo neutron correlation and intrinsic core excitation best reproduces the experimental results.

Scalar interaction limits from the beta-nu correlation of trapped radioactive atoms.

We have set limits on contributions of scalar interactions to nuclear beta decay. A magneto-optical trap provides a localized source of atoms suspended in space, so the low-energy recoiling nuclei can freely escape and be detected in coincidence with the beta. This allows reconstruction of the neutrino momentum, and the measurement of the beta-nu correlation, in a more direct fashion than previously possible. The beta-nu correlation parameter of the 0(+)-->0(+) pure Fermi decay of (38)K(m) is a =0.9981+/-0.0030+0.0032 / -0.0037, consistent with the standard model prediction a =1.

Novel search for heavy nu mixing from the beta+ decay of 38mK confined in an atom trap.

A new technique, full neutrino momentum reconstruction, is used to set limits on the admixture of heavy neutrinos into the electron neutrino. We measure coincidences between nuclear recoils and positrons from the beta decay of trapped radioactive atoms and deduce the neutrino momentum. A search for peaks in the reconstructed recoil time-of-flight spectrum as a function of positron energy is performed. The admixture upper limits range from 4 x 10(-3) to 2 x 10(-2) and are the best direct limits for neutrinos (as opposed to antineutrinos) for the mass region of 0.7 to 3.5 MeV.

Precise half-life measurement for the superallowed 0(+)-->0(+) beta emitter (74)Rb: first results from the new radioactive beam facility (ISAC) at TRIUMF.

Presently, the world data for superallowed beta decay leads to a result in disagreement (at the 98% confidence level) with the predictions of the minimal standard model for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Precise data for the superallowed 0(+)-->0(+) beta decay of (74)Rb would provide a critical test of the nucleus-dependent isospin symmetry-breaking corrections that must be calculated for these superallowed Fermi beta decays. The present work reports the first precise measurement of the half-life for (74)Rb ( t(1/2) = 64.761+/-0.031 ms). The data were obtained at the radioactive beam facility (ISAC) at TRIUMF using a beam of approximately 4000 (74)Rb ions s(-1).