RA1. RIB Development
(D. W. Stracener)
Seven on-line experiments were performed at the OLTF during the last six months. This beam time was used to test two different uranium carbide targets, to optimize ion source performance for radioactive beams of Sr, and to test neutron detectors for the VANDLE array. A novel uranium carbide material with a density of 5.2 g/cm3 was tested with mixed results on the release rate. Also, a target of uranium carbide disks produced for the SPES project at Legnaro was tested using a 40-MeV proton beam from the Tandem. At three target temperatures (1600 C°, 1800 C°, and 2000 C°), we measured yields of fission fragments and release rates for comparison with other uranium carbide target geometries. These targets had an average density of 4.25 g/cm3 and the release rates compared quite favorably with our standard HRIBF uranium carbide targets.
Substantial efforts at the three off-line ion source test facilities have resulted in a number of improvements and better understanding of ion sources that will impact RIB production at HRIBF in the near future. At ISTF1 work continues on the design of the gas-filled RFQ negative-ion cooler that will be used to purify radioactive beams of F, Cl, and Ni at IRIS2. The design and fabrication of the deceleration and reacceleration regions need to be finished before the system will be implemented at IRIS2. At ISTF2, a campaign has been under way to better understand the design and operation of the HRIBF hot plasma ion source, the EBPIS (Electron Beam Plasma Ion Source). The extraction efficiency of Xe has been used to diagnose the effects of various hardware designs and operational modes. Investigations include the gap distance between the anode and cathode, the percentage of open area in the anode grid, the anode potential, the size of the source extraction aperture, and the strength and direction of the magnetic field of the solenoids that surround the plasma region. So far, Xe efficiencies of about 33% have been achieved when the parameters listed above are optimized. At ISTF3 a project is underway to develop a He-jet transport system to move radioactive atoms from an actinide production target to a Bernas-Nier ion source. Since the recoiling fission fragments are stopped in He and transported to the ion source without touching any surfaces, this is a chemically-independent ISOL technique and will allow refractory fission fragments to be ionized and post-accelerated for experiments. A modular room has been built in Bldg. 6010 and the assembly of equipment in this room has begun. While waiting for the room to be completed, the ion source chamber was designed, fabricated, assembled and tested, and it is now ready for use. Also, the He-recirculation cart has been refurbished and is now fully functional.
The laser system for the laser ion source was originally purchased and tested at ISTF2 in 2009 with a Nd:YAG pump laser and three tunable Ti:Sapphire lasers in a single package. We have decided to separate the system into three independent and identical packages each consisting of a Nd:YAG pump laser and a Ti:Sapphire laser with the ability to change the optics to deliver a beam of the fundamental wavelength or the frequency doubled, tripled, or quadrupled beams. These units will be interchangeable and a spare unit will be purchased to reduce downtime due to laser failure. A new laser table has been installed in the IRIS2 laser room and most of the optical components of the IRIS2 laser system have been ordered.
A new long-lived radioactive ion beam was developed during this
period. With maintenance activities on ORIC underway, a number of
beams of long-lived radioactive isotopes have been accelerated using
the multi-sample Cs-sputter ion source on IRIS1. These beams have
included Be-7, Be-10, and Al-26, and now Sr-82 (half-life is 25.4
days) has been extracted and delivered to an experiment. We purchased
10 mCi of Sr-82 from the DOE Isotopes Program. This isotope is
shipped with the Sr-82 atoms dissolved in weak hydrochloric acid.
This liquid is transferred to a metal powder sample and pressed to
form a solid sputter target. This first attempt resulted in beams
with low intensity, with a peak of about 2000 ions per second on
target and an average of about 1200 ions per second over a seven-day
period. Improvements in the transfer of activity to the cathode and a
different metal powder should result in higher quality beams
(intensity and purity). These improvements will be tested later this
year and we are also considering a similar process to deliver beams of
Fe-59 (half-life is 44.5 days).