HRIBF NEWS

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   Edition 3, No. 1               February 28, 1995            Price: FREE

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Contents:
Editor:  Carl J. Gross

Contributors:  David Olsen, Paul Mantica

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1. HRIBF Users Workshop Set for June 2-3, 1995.

A workshop for all HRIBF Users and other interested persons is being organized for June 2-3, 1995, in Oak Ridge. The workshop will include short presentations on potential experiments which could be conducted in the first two years of operation. Ample time will be allowed for discussions and collaborator meetings. Presentations should involve physics to be studied with the anticipated initial beams: Gallium isotopes 63 and 64 with maximum intensity of 0.05 pnA; Fluorine isotopes 17 and 18 with maximum intensity of 0.1 pnA. Experimental equipment planned for the facility is shown below. Some of the equipment may not be available at the start of user operations.

Since most of us have had limited experience with using RIBs and/or recoil separators we would like to make the following observations. Thin targets are desirable to prevent undue background due to the decay of the stopped beam. Care must be taken to minimize mass near the target so that Rutherford scattered beam does not overwhelm your detectors. Multiple scattering reduces mass separator efficiencies---a good rule of thumb is that the target should be less than 0.5 mg/cm^2. Although very strongly reaction-dependent, typical efficiencies of the DRS and RMS are 20% and 35%, respectively. The meeting will be held at the Joint Institute for Heavy Ion Research which is located at Oak Ridge National Laboratory. Lunch will be provided on both days. Lodging ($50-$80) can be found in the City of Oak Ridge or in neighboring Knoxville which is a 20-30 minute drive from the Lab. Air transportation to Oak Ridge is through the Knoxville Airport (TYS) which is served by most major U.S. airlines. Since the lab is 10 miles from any motel, rental cars are strongly recommended. Information and maps of the area can be obtained from HRIBF's WWW node which can be accessed by the address www.phy.ornl.gov. Other dates to remember: April 18-21 Washington APS Meeting May 1-3 Physics Division Advisory Committee June 2-3 HRIBF Users Workshop June 18-23 Nuclear Chemistry Gordon Conference

2. Town Meeting on Radioactive Ion Beams.

The Nuclear Structure, Low Energy Nuclear Physics, and Radioactive Ion Beam Town Meeting was held in Durham, NC, on January 19-21, 1995. Approximately 200 scientists participated in order to provide input to the Nuclear Science Advisory Committee (NSAC) on the development of the next Long-Range Plan. The plan, which will be submitted to DOE and NSF in September, will outline the physics community's desires and priorities for the next 5-10 years. The organizers of the meeting were Richard F. Casten (BNL), Calvin Howell (Duke University/TUNL), and Witold Nazarewicz (University of Tennessee/ORNL).

The meeting consisted of planned presentations by interested parties during the day and six working groups during the evening hours. Questions and comments were solicited from the community at large throughout the meeting. In the individual working groups, priorities were established and communicated to the chairperson of each group. The chairpersons presented a ten-minute summary of each working group's activities which were used to develop six draft recommendations of the town meeting. Each recommendation is presented below as taken from the white paper of the town meeting.

Recommendation:

The highest priority is the construction of an advanced ISOL-based Radioactive Beam Facility with broad scientific capabilities as envisioned in the IsoSpin Laboratory (ISL) concept, and the immediate upgrade of the MSU cyclotron facility. These two complementary facilities are required in order to fully exploit the research opportunities with Radioactive Nuclear Beams (RNBs).

The nuclear physics opportunities afforded by RNBs open up entirely new frontiers in exotic nuclei extending from the proton to the neutron drip lines. There is every likelihood for new (and significantly different) nuclear physics in these exotic nuclei, and manifestations of shell structure, collective modes, structural evolution, exotic decay modes, and reaction processes unlike anything we have yet encountered. These nuclei are also the seat of numerous critical astrophysics phenomena. To exploit these opportunities in a comprehensive way requires a wide variety of beams, energies and intensities and is best served by the construction of an advanced projectile fragmentation facility represented by the MSU upgrade and by the construction of a powerful ISOL-based (Isotope Separator On-Line) facility to produce and accelerate a broad range of RNBs.

Recommendation:

A new-generation gamma-ray multidetector array, as envisioned in the GRETA concept, will have a profound impact on many areas of physics and should receive the highest priority for instrument development, design, and fabrication.

Based on the experience gained with the construction and use of Gammasphere and other multidetector arrays, it seems possible to develop a new gamma-ray detector system with about three orders of magnitude higher sensitivity. A novel concept, called GRETA, for Gamma Ray Energy Tracking Array, would achieve this through an effective three-dimensional segmentation of germanium crystals arranged in a 4-pi spherical shell. Because of the very large gain in sensitivity, this high-resolution, very efficient, and highly granular detector system would open a new window in nuclear structure and provide a resource for other areas of science that require the precise characterization of gamma rays. It is essential to establish as soon as possible the feasibility of such a detector system and then proceed with its fabrication.

Recommendation:

The advent of Radioactive Nuclear Beam physics and new detector arrays opens up new vistas in nuclear structure, reactions, and nuclear astrophysics. Success in this research will require a very active theoretical effort, and we therefore strongly recommend additional support for nuclear theory in this area.

As the scientific thrust of the field represented by this Town Meeting advances into new domains at the limits of nuclear physics, especially at high angular momentum and in exotic nuclei at extremes of N and Z, novel nuclear behavior will be encountered, and will require innovative theoretical approaches, both to understand and to guide further experiments. This entails an active and flexible effort in nuclear theory and calls for increased support for theoretical efforts in this area.

Recommendation:

To pursue the exciting new physics opportunities which continue to emerge from the base program, we recommend strong support of the technological infrastructure of university groups and an efficient utilization of the existing charged particle- and neutron-based facilities.

The base program, centered in good part in a number of university and smaller national laboratory facilities and in university research groups (at in-house facilities and as users), is a vital core resource for our field and needs to be supported and invigorated. Future success in our field depends on the prosperity of university groups and facilities as much as on the construction of new or upgraded forefront facilities. Recent infusions of funding for equipment and instrumentation support, especially at universities, have improved the technological base for this effort and now present an opportunity which should be exploited. Support is also encouraged for research groups using probes, such as neutrons, at facilities funded by other programs or agencies.

Recommendation:

We strongly support the activities of the nuclear data evaluation program and its initiatives in frontier research areas.

New approaches in the evaluation and dissemination of nuclear data, including the initiation of ``horizontal'' surveys of selected data over many nuclei, is of substantial value to emerging frontier areas of our field and should be encouraged.

Recommendation:

We recommend increased support for the national stable isotope program, to insure that a sufficient quantity and variety of enriched stable isotopes be available for the experiments of coming years.

The use of enriched stable isotopes is essential to advances in a number of areas. In recent years, the reduced availability of this resource has significantly impacted research, and needs to be ameliorated.

3. How Can HRIBF Satisfy Recommendation 1?

In order to fully access most neutron-rich RIBs as discussed in the ISL white paper and accelerate them above the Coulomb barrier, some equipment changes will have to be made. ORIC would have to be replaced with a more energetic cyclotron capable of delivering higher beam currents. A LINAC booster would have to be added after the tandem accelerator in order to accelerate all fission fragments above the Coulomb barrier. Some additional shielding and the construction of, at most, two new rooms will be needed. It is believed that the total cost of these upgrades, including engineering and contingency funds, would be less than 100 million dollars (FY 1995).

It is proposed that a K=200 cyclotron capable of delivering 0.2 mA of 200 MeV protons be purchased from a commercial vendor. This driver should also be capable of providing beams with charge/mass ratios of 0.5 and at energies of 50 MeV/A. In order to provide the additional shielding necessary for such beams, this cyclotron could be placed in Rm. C110 where the Broad Range Spectrograph currently resides. The RIB ion source platform and injector would move to the present ORIC vault with additional shielding of concrete and iron. Excess space in the ORIC vault and Rm. C111 (where the present platform is) will be used for handling of the ion sources.

The booster should be a superconducting LINAC capable of accelerating the heaviest fission fragments from the tandem accelerator up to 5.5 MeV/A without additional stripping. The characteristics of the proposed LINAC are 45 MV of acceleration voltage, 92 feet long, approximately 100 MHz, and a beta of 0.06-0.11. A 4000-sq.-ft. building addition would be required to house the LINAC.

One possible scenario of how the present physical structure of HRIBF could support a 200-MeV proton driver and LINAC booster can be viewed on our WWW node (www.phy.ornl.gov). A proposed additional experimental hall is not shown in this figure.

4. HRIBF Comments on the Town Meeting

We are very pleased that the community supports RIB physics so much that it commands the highest priority of all the recommendations which came out of our Town Meeting. Since several labs throughout the world are joining us in planning for the next-generation RIB facilities, we remain optimistic that HRIBF will be an unqualified success. We strongly support the other recommendations, all of which impact HRIBF. Our sister facility, MSU, will access new nuclei through fragmentation studies and be capable of exploring exotic nuclei in higher-energy regimes. New Ge detector development will improve our sensitivity and, therefore, extend our reach to even more exotic nuclei. Theory will blaze new trails as new predictions occur as the effects of the large isospin imbalance are explored as the neutron drip line is approached. The base program provides innovations and personnel that directly impact HRIBF through detector development, training of personnel, and the new ideas they bring with them. Often, the scarcity of data on the most exotic of nuclei require that phenomological arguments be used to deduce the physics observed. Evaluated data sets are instrumental in providing reliable systematic studies critical to the understanding of the data. As each RIB is a development project in itself, adequate supplies of enriched isotopes are critical to access the most exotic regions of the chart of the nuclides. Each of the recommendations have an impact on HRIBF, and we strongly encourage you to fully support them.

5. RMS Update

Conditioning of the electrostatic deflectors has commenced. Although a small vacuum leak has limited the amount of SF_6 insulating gas used, the deflector plates in one tank have been conditioned up to +/- 100 kV, which is suitable for many experiments. Further conditioning up to the rated 270 kV will take place upon repair of the vacuum leak. Conditioning of the other set of plates will occur as soon as a broken insulator has been replaced; the replacement is currently in progress. The position sensitive avalanche counter (PSAC) focal plane detector is being tested. It has been vacuum checked and 0.9 micron mylar windows have been tested under pressure. No problems have so far been detected. The design of the ionization chamber has been finalized at Daresbury Laboratory and the vacuum vessel is currently being fabricated. A delivery date of mid- to late summer is expected.

6. Chester Holifield Has Died at Age 91

Former Congressman Chester Holifield passed away on February 5 in Redlands, CA. He was 91. Representative Holifield served in the U.S. Congress for 32 years beginning in 1942. He was reknown as one of the few congressmen to protest the internment of Japanese-Americans during World War II. He went on to chair the Joint Committee on Atomic Energy and was influential in creating the civilian Atomic Energy Commission. The Holifield Heavy Ion Research Facility was formally dedicated in his honor in 1975 by an act of Congress.

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Additional copies of the newsletter and more information about HRIBF 
can be found on the World Wide Web at www.phy.ornl.gov.

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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