P. Bricault

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.

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

M. Smith, M. Brodeur, T. Brunner, S. Ettenauer, A Lapierre, R. Ringle, V. L. Ryjkov, F. Ames, P. Bricault, G. W. F. Drake, P. Delheij, D Lunney, and J. Dilling TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, Canada Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver BC, Canada Technische Universität München, E12, James Franck Strasse, Garching, Germany Department of Physics, University of Windsor, Windsor, Ontario, Canada and CSNSM/CNRS/IN2P3, Universite de Paris-Sud, F-91405, Orsay, France (Dated: July 21, 2008)

The proposed TITAN facility at ISAC for very precise mass measurements on highly charged short-lived isotopes

Abstract One of the necessary experimental quantities required for the test of unitarity of the fundamental Cabbibo–Kobayashi–Maskawa (CKM) quark mixing matrix can be gained from nuclear beta decay. However, the short-lived beta-decaying nuclei have to be produced on-line in order to provide a large enough sample to carry out the experiments. At the new ISAC (Isotope Separator and Accelerator) facility at the TRIUMF national laboratory in Vancouver, Canada, ideal conditions are provided for the production of some of the most interesting nuclides in that respect. The experimental information that is needed are branching ratio, half-life and Q-value of the specific beta decay. For the first two components experiments have already been carried out or are in preparation at ISAC (Ball et al., Phys. Rev. Lett. 86 (2001) 1454, and experiments E823 and E909 approved at TRIUMF), for the third one, we are proposing to set up a unique facility capable of high accuracy mass measurements δm/m⩽1×10−8 on very short-lived isotopes (T 1/2 ⩽50 ms ) employing a Penning trap spectrometer coupled to an electron beam ion trap (EBIT) for charge breeding. The main goal of TITAN is mass measurements, however, the unique combination of the systems will allow to carry out high precision measurements in other fields of nuclear and also atomic physics.

Commissioning and initial operation of a radioactive beam ion source at ISAC

In November of 1998, the ISAC radioactive beam facility at TRIUMF started delivering on-line isotope separated radioactive beams to experiments. A surface ionization source developed for ISAC has been used to commission the mass separator and beam transport systems and is providing radioactive beams to the first generation of ISAC experiments. The ion source is integral with the radioactive beam production target and is designed to be simple, radiation hard, inexpensive, and easily exchanged by remote-handling techniques. The ion source and its extraction column are suspended at the bottom of ∼2 m of steel shielding incorporated in the target module. The module is suspended in a vacuum tank with primary and secondary vacuum systems. All services for the target/ion source and beam extraction system are ducted through the module shielding. The first sets of beam transport elements and beam diagnostic devices are similarly suspended in vacuum at the bottom of two additional shielded modules. Ion beam charact...

Radioactive ion beams facility at TRIUMF

Abstract A radioactive ion beam (RIB) facility is being built at TRIUMF. A novel design for the target/ion source station will allow us to bombard a thick target with TRIUMFs 100 μA, 500 MeV proton bam, producing a variety of very intense beams of nuclei far from stability. After mass separation the beams can be sent to two different experimental areas. One uses the 60 keV energy beam and the second one will use the 0.15 to 1.50 MeV/u post-accelerated beam. Singly charged ion beams, with A ≤ 30 delivered from the on line mass separator, with an energy of 2 keV/u, will be accelerated in a two stage linac consisting of an RFQ and a post-stripper drift-tube linac up to 1.5 MeV/u. CW operation mode is required to preserve beam intensity. As a consequence of the low q/A ions a low operating frequency for the RFQ is required to achieve adequate transverse focusing. The main features of this accelerator are: 35 MHz RFQ, stripping at 150 keV/u, beam energy continuously variable from 0.15 to 1.50 MeV/u and CW operation.

High power target developments at ISAC

Abstract TRIUMF, Canada’s national research facility for particle and nuclear physics is currently operating the ISAC facility. A high-energy proton beam from the H - TRIUMF cyclotron is used to generate short-lived radioactive species in a thick target. An ion source at the target creates a radioactive beam, which is then injected into the ISAC beam lines and accelerator system. The ISAC facility is designed to accept proton beam intensity up to 100 μA at 500 MeV. At present our target design can only sustains 40 μA at maximum. Beyond this point the target has to be cooled. A new target equipped with fins has been developed that may sustain proton beam up to 100 μA. The fined target has been tested off-line and a thermal simulation using ANSYS ® has been conducted and the results are reported here.

ISAC target operation with high proton currents

Abstract The TRIUMF-ISAC facility target stations were designed for ISOL target irradiations with up to 100 μA proton beam currents. Since beginning operation in 1998, ISAC irradiation currents have progressively increased from initial values of ∼1 μA to present levels of up to 40 μA on refractory metal foil targets. In addition, refractory carbide targets have operated at currents of up to 15 μA for extended periods. The 1–40 μA operational regime is achieved by tailoring each target to the thermal requirements dictated by material properties such as beam power deposition, thermal conductivity and maximum operating temperature of the target material. The number of heat shields on each target can be varied in order to match the effective emissivity of the target surface for the required radiative power dissipation. Targets of different thickness, surface area and volume have been investigated to study the effect of diffusion and effusion delays on the yield of radioisotopes. For yields of short-lived products, believed to be dominated by diffusion delays, a consistent nonlinear increase of yield as a function of proton current has been observed. The nonlinear dependence is consistent with expectations from radiation enhanced diffusion.

Ion source developments for the production of radioactive isotope beams at TRIUMFa)

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.

Charge state breeding of radioactive ions with an electron cyclotron resonance ion source at TRIUMF

Efficient primary ion sources at ISOL facilities normally produce singly charged ions. This limits the usable mass range for postacceleration due to the A∕Q acceptance of the accelerator. At the ISAC facility at TRIUMF an A∕Q below 7 is desired to avoid further stripping. Thus, charge state breeding is necessary if higher masses are to be accelerated. A 14 GHz ECRIS “PHOENIX” booster has been chosen as a breeder. In order to investigate and optimize its performance under ISAC conditions it has been set up at a test bench equipped with a standard ISAC target-ion-source to produce singly charged ions. A series of measurements has been performed with the noble gases Ar, Kr, and Xe. Efficiencies of more than 6% in the maximum of the charge state distribution after mass separation have been obtained and the emittance of the extracted beam and breeding times have been measured. This article gives a status report on the ongoing measurements.

Evaluation of a prototype Isotope Separator Accelerator surface ionization source

A prototype surface ionization source coupled with a fixed-geometry extraction electrode system was commissioned on the Isotope Separator Accelerator (ISAC) ion source test stand at TRIUMF. The suitability of the ion source and extraction system for use in the ISAC facility was determined by a series of emittance measurements of the extracted beams. The test stand optics were successfully commissioned using the prototype ion source; emittance measurements of the mass-separated beams demonstrated that second- and third-order beam aberrations (introduced by the magnetic dipole mass separation) could be corrected by the use of multipole electrostatic optics elements. An upper limit of the root-mean-square-energy spread (2 eV) was deduced from the emittance measurements. Emittance measurements were performed at beam energies of 10–50 keV, as well as for ion masses ranging from Li+ to Rb+, to demonstrate the feasibility of the prototype for a variety of beam energies and masses.