Edition 4, No. 3 June 6, 1996 Price: FREE

Editor:  Carl J. Gross

1. Reminder of Proposal Deadline

Proposals are now being accepted for the first experiments at the HRIBF. Proposals are solicited for experiments with beams of radioactive 69As and 70As with energies between 20 and 345 MeV. Users desiring higher or lower beam energies should contact Jerry Garrett. It is anticipated that the HRIBF research program will begin this autumn. The deadline for the acceptance of proposals is Friday, June 14, 1996. Twelve copies of the proposals should be sent to:

Jerry Garrett
Bldg. 6000, Mail Stop 6368
Oak Ridge National Laboratory
P.O. Box 2008
Oak Ridge, TN 37831-6368.

The cover pages of the HRIBF proposals and guidelines for their preparation are available on the HRIBF web site, "" under the Call for Proposals.

Requests for measurements using stable beams will be considered for: (i) commissioning equipment; (ii) experimental measurements associated with a radioactive beam project; and (iii) measurements in which the experimental facilities at the HRIBF are uniquely suited for the proposed study.

2. Arsenic Yields at UNISOR Improve by Factor of 25 (J. R. Beene)

In the last issue of HRIBF News, we reported our expectation of between 10**7 and 10**8 particles per second for initial intensities of 69,70As RIBs from with a 20 uA proton driver beam. We also reported, as late-breaking news, the very preliminary results from our initial on-line test run at the UNISOR facility that fell far short of these expectations. During the week of May 20-24, a second on-line test run, again using 40 MeV protons on a liquid Ge target, was carried out at UNISOR. We were able to increase the 70As intensity extracted from the ion source by a factor of 25, implying an eventual RIB intensity in excess of 10**8 particles per second with a 20 uA proton beam. The observed intensity of 69As (T_1/2 = 15.2 m) was 32% of that of 70As (T_1/2 = 53 m); the production ratio is ~0.5. The gains were a result of changes in the geometry of the target (factor of more than 3) and an ~170 C increase in target temperature (factor of 7.5). Regular test runs aimed at optimization of target and ion source design and operation will continue with an on-line test run scheduled every other week. We will continue to concentrate on arsenic and flourine, and expect to make further significant improvements in arsenic intensity. The rapid development of our understanding of the liquid Ge target means that we should move it to the RIB injector platform for demonstration of RIB production soon.

Additional copies of the newsletter and more information about HRIBF can be found on the World Wide Web at

Jerry D. Garrett, Scientific Director    |Email:
Mail Stop 6368                           |Tel:   (423) 576-5489

Carl J. Gross, Scientific Liaison        |Email:
Mail Stop 6371                           |Tel:   (423) 576-7698

Holifield Radioactive Ion Beam Facility  |Tel:   (423) 574-4113
Oak Ridge National Laboratory            |Fax:   (423) 574-1268
Oak Ridge, TN 37831