HRIBF NEWS


Edition 6, No. 3 October 27, 1998 Price: FREE

Contents:

Editor: Carl J. Gross

Contributors: J. R. Beene, J. D. Garrett


1. Call for Proposals

Proposals are now being accepted for the next series of experiments at the HRIBF. Proposals are solicited for experiments with beams of radioactive 66Ga and 67Ga with energies between 3.4 and 360 MeV and 69As and 70As with energies between 3.4 and 380 MeV. Users desiring higher or lower beam energies or beams of heavier gallium or arsenic isotopes or beams of radionuclides of selenium should contact Jerry Garrett.

About 106 ions per second (i/s) of 66Ga, 67Ga, 69As, and 70As are now available. Somewhat more intense beams of these isotopes might be available during the scheduling period. The 70As beam is highly contaminated with its isobar 70Ge. Fluorine and 56Ni beams are still being developed. Users should anticipate up to about 107 i/s of 56Ni and 106 i/s of 17F or 18F. The 56Ni beam will be contaminated with 56Co.

As in the past, users should provide information on the minimum beam intensity required to obtain useful results from their proposed study. Such information is crucial for evaluating the requests for early experiments and should be carefully substantiated in the experimental writeup. The past policy of accepting proposals for specific experiments, and not for ongoing scientific programs, will be continued.

Requests for measurements using stable beams will be considered for:

Arguments substantiating that stable beam work falls into one of these categories should be contained in the experimental writeup. However, projects involving radioactive beams will be given preference over those based on purely stable beams. A list of stable beams which have been accelerated is given on the HRIBF web site. If other stable beams are desired, please contact Jerry Garrett or Carl Gross.

PAC-accepted proposals for experiments submitted previously, which have not been run due to the unavailability of the beam or experimental equipment, may be revised at the discretion of the authors.

THE DEADLINE FOR THE RECEIPT OF THESE PROPOSALS IS FRIDAY, DECEMBER 4, 1998. Twelve copies of each proposal should be sent to:

U.S. Mail Address Courier Service Address
Jerry Garrett
Oak Ridge National Laboratory
Bldg. 6000, Mail Stop 6368
P.O. Box 2008
Oak Ridge, TN 37831-6368
Jerry Garrett
Oak Ridge National Laboratory
Bldg. 6000, Mail Stop 6368
Bethel Valley Road
Oak Ridge, TN 37831-6368

The status of experimental equipment available has been discussed in articles in previous HRIBF newsletters and on our web site. Up to date information can be obtained from Carl Gross, the HRIBF Liaison.

The cover pages of the HRIBF proposals and guidelines for their preparation are available on the HRIBF web site (http://www.phy.ornl.gov/hribf/hribf.html).

2. Call for Letters of Intent for Neutron-rich Beams

The development of neutron-rich radioactive beams produced as fission fragments from the reaction of 40-MeV protons and 238U has started. It may be possible to provide RIBs for isotopes of volatile elements with halflives greater than a few seconds. Energies near the Coulomb barrier may be available for fission fragments up to A ~ 90. Additional information on the possible availability of these neutron-rich beams is given in the following newsletter article. Users are invited to submit letters of intent for experiments based on these neutron-rich RIBs. These letters of intent will be used to help determine which of these beams to develop. The minimum intensity requirements for obtaining useful experimental results should be explicitly stated.

THE DEADLINE FOR THE RECEIPT OF THESE LETTERS OF INTENT IS ALSO FRIDAY DECEMBER 4, 1998. Twelve copies of each letter should be sent to:

U.S. Mail Address Courier Service Address
Jerry Garrett
Oak Ridge National Laboratory
Bldg. 6000, Mail Stop 6368
P.O. Box 2008
Oak Ridge, TN 37831-6368
Jerry Garrett
Oak Ridge National Laboratory
Bldg. 6000, Mail Stop 6368
Bethel Valley Road
Oak Ridge, TN 37831-6368

3. Neutron-rich Beam Development

We have begun on-line development of neutron-rich radioactive beams produced as fission fragments in proton-induced fission of 238U. Initial tests were done with 10 nA of 30-MeV protons from the Tandem, in a standard HRIBF EBP ion source, mounted at UNISOR. A high permeability target consisting of an 8- to 12-um layer of uranium carbide deposited on a reticulated vitreous carbon matrix, with a total density of 1.2 g/cm2, was used. Production runs will employ proton energies in the 40-50-MeV range, which will enhance the yield of most isotopes by a factor of two to three compared to the 30-MeV tests.

The yields of a variety of neutron-rich isotopes have been measured in the range of elements from Cu to Sr and from Ag to Ba, for target temperatures up to 2100 degrees Celcius. Favorable examples in the mass 90 region are the Br isotopes. The measured positive ion yield at UNISOR was 1.9x107, 6x106, and 2x106 ions/sec/uA for 84,87,90Br, respectively. This would correspond to accelerated beams at ~5 MeV per nucleon of less than or equal to 107 i/s for 84,87Br and approximately 3x106 i/s for 90Br, assuming a production proton beam of 20 uA at 40 MeV.

A number of neutron-rich beams in the mass ~120 region were produced with positive ion intensities approaching 108 i/s/uA. Accelerated beams with intensities on the order of 107 i/s can be produced from these species up to energies of ~3.5 MeV/amu. Acceleration to 5 MeV/amu requires double stripping and, consequently, more than an order of magnitude loss in intensity.

Our work to date on neutron-rich beams has been of a survey nature. We require guidance from the research community as to beams on which to concentrate our development efforts. We expect to have approval for using U targets in high-intensity proton beams soon, and beam development to proceed rapidly afterward.

4. Web Site Describing the Next-generation ISOL Facility at ORNL's SNS Site

A new web site describing what a Next-generation ISOL (NISOL) Facility might look like at the Spallation Neutron Source (SNS) site in ORNL has recently been established. It can be found at: (http://www.phy.ornl.gov/nisol/).

A $130 million "construction line item" appropriation for the SNS for fiscal year 1999 has been approved by the US Congress and signed into law by the President. Additional information on the SNS can be obtained from their web site (http://www.ornl.gov/sns/).





Additional copies of the newsletter and more information about HRIBF can be found on the World Wide Web at www.phy.ornl.gov. You may contact us at the addresses below.

Jerry D. Garrett Carl J. Gross
Scientific Director Scientific Liaison
Mail Stop 6368 Mail Stop 6371
garrett@mail.phy.ornl.gov cgross@mail.phy.ornl.gov
+1-423-576-5489 +1-423-576-7698

Holifield Radioactive Ion Beam Facility
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37831 USA
Telephone: +1-423-574-4113
Facsimile: +1-423-574-1268