******************************************************************************* Edition 3, No. 2 March 6, 1995 Price: FREE *******************************************************************************Contents:
Editor: Carl J. Gross Contributors: Fred Bertrand, David Olsen******************************************************************************* *******************************************************************************1. Holifield Radioactive Ion Beam Facility
Oak Ridge National Laboratory
Physics Division
With the need to develop the 1995 Long Range Plan (LPR), the HRIBF facility was requested to produce a summary of its activities in the past five years and its outlook for the future. The summary was presented to the Facilities Subgroup of the Nuclear Science Advisory Committee Long Range Plan Working Group on February 23, 1995 in Washington, D.C. It was to follow this outline:
In the Scientific Frontiers Section of the 1989 NSAC Long Range Plan for Nuclear Science in the United States it is written, "Wholly new vistas would be opened by a radioactive nuclear beam (RNB) accelerator. Already, experiments with radioactive beams at the Bevalac facility have given evidence for neutron halos in neutron-rich nuclei, and provide tantalizing hints that nuclei with regions of nearly pure neutron matter can be produced. A RNB facility would also provide critical information for nuclear astrophysics, give access to entirely new nuclei even further from stability, and enable the investigation of novel phenomena such as massive isospin transfer, or of new forms of multiparticle radioactivity. Last but not least, it may lead us closer to the long-sought superheavy island of nuclear stability."
In 1992 the Department of Energy, Nuclear Physics Program Office, provided funds at ORNL for the construction of an Isotope Separation On-Line (ISOL)-type radioactive-ion beam (RIB) facility in order to exploit the new physics opportunities described in the 1989 long range plan. ORNL had proposed that such a facility could be constructed quickly and at modest cost because the required driver- and post-accelerators were already operational and no new civil construction would be needed for shielded areas for the target/ion source platform. A total of $2.6 million of Accelerator Improvement Project (AIP) funds was provided over fiscal years 1992, 1993, 1994, and 1995 for the needed reconfiguration. The experimental research program on the Holifield Heavy Ion Research Facility 25 MV tandem was ended in June of 1992, and reconfiguration was begun for the new Holifield Radioactive Ion Beam Facility (HRIBF) when AIP funds became available in FY 1993.
The Physics Division research and facility staff has committed itself to providing the nuclear physics community with the first RIB facility capable of producing beams with sufficient intensity and energy to be useful for nuclear physics and nuclear astrophysics. In addition to the preparation of the accelerator facility for RIB production, the Physics Division has obtained major new equipment for use in RIB physics and has started new experimental and theoretical programs in nuclear structure and nuclear astrophysics that will exploit the new physics opportunities that will be presented by radioactive ion beams. In December 1993 the HRIBF was designated by the DOE as a User Facility. There are currently ~ 300 members of the user group, and a Program Advisory Committee has been established. We anticipate that the first radioactive beam will be accelerated by the tandem in August 1995.
The facility reconfiguration is currently on schedule and within budget. All major components are either in house or have firm delivery dates. The new 300 kV target/ion source platform is completed, and a stable beam has been extracted from the ion source and accelerated off the platform. Plans have been approved for handling of the radioactive target/ion sources, and the construction of that capability has begun. Two new recoil mass spectrometers, one for nuclear structure, the other for astrophysics, have been delivered and are being installed. One large, new experimental hall has been built to house the nuclear structure recoil mass spectrometer. A significant upgrade to our existing Compton-suppressed Ge system is under development, and a prototype Clover Ge detector has been ordered. Safety documentation has been written and approval has been granted for low-intensity commissioning of the facility. It is planned to have a low-intensity radioactive beam out of the tandem by August 31, 1995.
Current HRIBF Schedule
Radioactive Ion Beam extracted from Platform March/April 1995
Radioactive Beam from Tandem - low intensity August 1995
First Possible RIB experiments Nov./Dec. 1995
Start Routine User Operation May 1996
Figure 1 shows the first-floor layout of the facility. The ORIC cyclotron is used as the primary driver for production of RIBs. Proton, deuteron, 3-He, and alpha-particle beams will be used for reactions with selected targets to produce the RIB species of interest. The target/ion source is placed in a shielded room on an insulated platform system that can be operated to 300 keV. RIBs are extracted from the ion source and mass analyzed in the first-stage separator on the platform and delivered to a second-stage mass separator prior to injection into the tandem accelerator. The overall resolving power of the mass separation system is one part in twenty thousand. RIB beams are accelerated in the tandem using a potential up to 26 MV on terminal.
The two primary research programs of the facility will be in nuclear structure physics and nuclear astrophysics. The nuclear structure physics will be largely carried out with the new RMS and an upgraded version of the Oak Ridge Ge array. The RMS and the room in which it is located are designed to accommodate the GAMMASPHERE when it comes to ORNL. The astrophysics program will use the recoil mass spectrometer shown in room T109. That spectrometer, formerly located at the Daresbury facility in the United Kingdom, was transferred to ORNL by the British government upon the closure of Daresbury. This device, valued at ~ $3 million, has been delivered to ORNL and is currently being installed.
ION MAX ENERGY MAX CURRENT (microampere) protons 65 MeV 50 deuterons 50 MeV 50 3-He 133 MeV 200 alphas 100 MeV 200 heavy ions 25 MeV/A (Q/A=1/2) variable
The most crucial phase of any ISOL facility is the production of the radioactive atoms and their release from the target and transportation to the ion source. A great deal of effort has been devoted to developing the necessary target and ion source expertise for producing the variety of beams necessary to accomplish the scientific program outlined herein. The various beams that have been selected for development and their uses are shown in Table 1. The projected intensities, ranging from a few times 1E+9 particles per second (p/s) for fluorine to about 1E+8 p/s for the most proton-rich heavier beams such as 63-Ga, should be sufficient for detailed nuclear structure studies as well as for the measurement of cross sections relevant to stellar processes. (For reference, 1 particle nanoamp equals 6E+9 p/s.)
The tabulated neutron-rich beams are obtained from proton-induced fission of 238-U. It is planned that the neutron-rich capability will become available in 1997 or 1998. Estimated intensities of selected neutron-rich beams are given later in this report.
Table 1
Initial beams and anticipated uses:
17,18-F Astrophysics and Reactions 34-Cl Astrophysics 63,64-Ga Nuclear Structure 69,70-As Nuclear StructureLater proton-rich beams:
14,15-O Astrophysics and Reactions 30,31-S Astrophysics and Nuclear Structure 58-Cu Nuclear Structure 73,74-Br Nuclear StructureNeutron-rich beams:
76-86-As Astrophysics and Nuclear Structure 83-88-Se Astrophysics and Nuclear Structure 82-90-Br Astrophysics and Nuclear Structure 110-122-Ag Nuclear Structure 125-134-Sn Nuclear Structure 124-135-Sb Nuclear Structure 131-138-Te Nuclear Structure 128-140-I Nuclear Structure 134-144-Cs Nuclear Structure
The present User Group consists of approximately 300 members and is composed of 45% U.S. University, 24% National Laboratory, 4% U.S. Government and Industry, and 27% Foreign. The corresponding percentages for the utilization of accelerated beams during the last three years of the operation of the Holifield Heavy Ion Research Facility were: 63% U.S. University, 18% National Laboratory, 1% U.S. Government and Industry, and 18% Foreign. The users elect an Executive Committee that meets quarterly with the HRIBF Program Director and the HRIBF Scientific User Liaison. A Program Advisory Committee has been appointed. Currently the PAC is serving as a Scientific Advisory Committee. Meetings of the entire User Group are held every year at the Fall meeting of the DNP of the APS. Additional meetings and workshops are held in Oak Ridge on selected topics concerning preparation for RIB experiments.
When the Holifield Facility ceased to operate in 1992, the budget for operation was substantially reduced. Now that the HRIBF is preparing to commence routine operation in June 1996, the operating budget is being increased. The budget required for operation is based on the assumptions: 1) that FY 1997 will be the first full year of routine operation, and 2) that 2400 hours of radioactive ion beam will be delivered on target in addition to some tandem stable beam operation and accelerator and beam development. The FY 1995 budget, the President's request for FY 1996, and our request for FY 1997 are, respectively, $4,000K, $5,000K, and $6,500K. The budget for FY 1996 is $350K low for optimal facility development and utilization.
It is important to briefly discuss two other types of budget, capital and Accelerator Improvement Project (AIP). The HRIBF is a newly reconfigured facility with a new DOE mission to carry out a radioactive beam nuclear physics program. This charge requires development of new apparatus both for the research program and for accelerator development, especially target/ion sources. The capital budget for the facility in FY 1995 is about $1225K, which is lower than needed to allow equipment development to proceed at the desired pace. There are indications that the capital budget in FY 1996 will be increased. We have also requested $400K of AIP funds in each of the fiscal years 1996 and 1997. Those funds will be used to upgrade the reliability and high-intensity operation of the cyclotron.
The research program at the Holifield Facility ended in 1992 in order to begin reconfiguration for production of radioactive beams. For this reason, many of our recent scientific accomplishments were extensions of work initiated at Holifield but completed at other facilities.
Much of what is asked for in this section is discussed elsewhere in this report. Presented here is a list of some of the major accomplishments.
We live in a portion of the universe that has equilibrated more than four billion years. Thus, our current knowledge of nuclear physics is confined to nuclei that can be produced with beams and targets having lifetimes that are comparable to this equilibration time. Not only does this restriction limit the number of nuclei accessible to experimental study, it also excludes nuclei with "exotic," and therefore less stable properties. For example, nuclei with extreme ratios of protons to neutrons cannot be studied using terrestrial isotopes. We know, however, less equilibrated sites have existed, and still exist, in the cosmos: e.g., the early universe, galactic centers, supernovae, cataclysmic binary stars, and stellar interiors. Many of the nuclear reactions that power such stellar processes are not accessible to experimental study with stable beams and targets. The HRIBF will provide a unique opportunity to address important scientific issues concerning nuclei that have heretofore been inaccessible to experimental study.
Among the important nuclear structure and nuclear astrophysics issues that will be addressed with the proton-rich exotic beams in the first two years of HRIBF operation are:
In order to expand the physics opportunities at HRIBF, we plan to accelerate neutron-rich radioactive beams with the existing facility beginning in 1997 or 1998. These beams would be produced using the proton-induced fission reaction on actinide targets and will require no modifications to the accelerators. Examples of interesting scientific topics that can be addressed using the neutron-rich beams include:
The ORNL Physics Division is devoting a major part of its resources to establishing the field of ISOL-type radioactive beam physics in the United States. It is clear that the experience gained in our current effort in accelerator development, target/ion source development, radioactivity handling, safety procedures and approvals, design of specialized RIB experimental apparatus, development and carrying out of a RIB research program, and, most importantly, collaboration with a user group that is dedicated to the physics of radioactive beams, should be used to continue to ensure that the U.S. capability in this exciting new area of research remains forefront. To that end, we have begun to develop a plan for the next-generation RIB facility at ORNL. We believe that facility should: 1) provide a clear advance over the current U.S./ORNL capabilities, 2) take full advantage of the knowledge gained in creating the "first-generation" facility, the HRIBF, 3) be built at a cost that is as low as possible but still provide a clearly new capability, and 4) be capable of carrying out most of the physics detailed in the ISL white papers. During the past few years a large group of our colleagues formed the ISL User Group to investigate the construction of the next-generation RIB facility. That group has provided an important blueprint for the RIB science to be carried out at the next-generation facility. However, any facility that would be capable of providing beams that would cover 100% of the ISL physics would have to be a "green field" construction project at a cost that may be unrealistic in today's funding climate.
We are currently in the early stages of preparation of a proposal for a next-generation upgrade of the HRIBF, including a conceptual study funded by ORNL Laboratory Director's Planning Funds. Some very PRELIMINARY parameters of the upgrade and costs are provided below, including a layout of the upgraded facility in Figure 2.
We propose to replace the ORIC with a K = 200 cyclotron that can deliver at least 200 microamps of 200-MeV protons to a RIB production target. The cyclotron would also have a mode to accelerate Q/A = 1/2 ions to produce proton-rich RIBs from fusion reactions. This cyclotron would be based on commercial designs for proton therapy machines and can be placed in the existing shielded areas, thus avoiding costly civil construction. A new target/ion source platform, using many of the existing platform components, will be built in the current cyclotron vault. It will also be necessary to construct a linac to serve as an energy booster following the tandem. This booster will accelerate the heaviest fission fragments above the Coulomb barrier with no additional stripping. The booster will be a superconducting linac with independent phase cavities using existing technology, will have an effective accelerating voltage of 53 MV, and will be about 108 feet long. Preliminary estimates indicate this upgrade can be provided for between $85 million and $100 million, including engineering and 25% contingency costs. Furthermore, we believe this upgrade will provide beams that can provide for most of the physics detailed in the ISL reports.
Table 2 provides, for several radioactive beam species, the intensity expected from the existing facility, using an actinide target, and those expected from the upgraded facility.
Table 2 - Preliminary Production Yields for Various HRIBF Acceleration Schemes
60 MeV Protons 200 MeV Protons ORIC + Tandem + Tandem + Booster Ion Single Stripping Double Stripping (1*E+8 p/s) (1*E+7 p/s) (1*E+9 p/s) 88-Se 1 a) - 2 90-Br 6 a) - 8 122-Ag 3 b) 1 a) 3 132-Sn 3 b) 1 a) 2 135-I 20 b) 9 a) 20 140-I 9 b) 4 a) 8 a) 5 MeV/nucleon b) 3.5 MeV/nucleon For reference, the heaviest stable isotopes are 82-Se, 81-Br, 109-Ag, 124-Sn, and 127-I.
The Holifield Facility has long been a source of excellent hands-on training for students at all levels. It is fair to say "small science" is still practiced here, but with the most forefront of equipment. The availability of no-cost lodging next to the facility is of special benefit to university users who wish to bring students, but whose budgets will not permit long periods of stay in commercial facilities. The Physics Division participates in many educational programs offered through ORNL. These include programs for high school, undergraduate, and graduate students. The Division also has a strong Research Associate program. Currently, the nuclear physics research programs, including the HRIBF, have 10 research associates on site. In the ten-year period from 1983 to 1993, which covers most of the time the Holifield Facility was operational, there were in the Physics Division 211 undergraduate students, 284 graduate students, and 75 research associates. During the four-year period from 1987 through l990, 64 Ph.D. theses were granted based on work carried out at the Holifield Facility.
****************************************************************************** ****************************************************************************** Additional copies of the newsletter and more information about HRIBF can be found on the World Wide Web at www.phy.ornl.gov. Figures referred to in the text may be viewed on our WWW site. ****************************************************************************** ****************************************************************************** Jerry D. Garrett, Scientific Director |Email: garrett@orph01.phy.ornl.gov Mail Stop 6368 |Tel: (615) 576-5489 Carl J. Gross, Scientific Liaison |Email: cgross@orph01.phy.ornl.gov Mail Stop 6371 |Tel: (615) 576-7698 Holifield Radioactive Ion Beam Facility |Tel: (615) 574-4113 Oak Ridge National Laboratory |Fax: (615) 574-1268 Oak Ridge, TN 37831