HRIBF NEWS

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   Edition 3, No. 5               October 17, 1995            Price: FREE

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Contents:

Editor:  Carl J. Gross

Contributors:  J.D. Garrett, C. Baktash, M.S. Smith

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1. HRIBF Users Meeting

The Annual Users Meeting of the HRIBF will be held during the Fall Meeting of the Division of Nuclear Physics in Bloomington, Indiana. The meeting is scheduled for 18:00 (just after the DNP Town Meeting) on Friday, October 27, 1995, in the Oak Room of the Indiana University Memorial Union.

Preliminary Agenda: Joe Hamilton, presiding

Fred Bertrand Opening remarks Jim Beene Operations startup Carl Gross Availability of experimental equipment Matthew Brinkman Germanium and particle arrays Jerry Garrett Letters of intent and proposals Cary Davids Announcement of election results for new Executive Committee members

2. Facility Update.

The construction of the RIB injector system has been completed on time and within budget. The high-voltage injection platform on which the radioactive ions are produced, ionized, and charge exchanged and where the first-stage isotope selection is made is operational and has been tested with beams of stable ions. Likewise, the beam lines for delivering the light ion beams from ORIC to the high voltage platform and the radioactive ions from the platform to the 25 MV tandem are complete, as are modifications to the ORIC and tandem accelerators. Stable negative-ion beams, prepared on the high-voltage platform, have been delivered to the exit of the isobaric separator in the beam line to the Tandem, and they should soon be accelerated in the Tandem.

A program for developing the first radioactive ion beams is underway. Recently samples of NiO, ZnO, and Ge have been irradiated with 25 MeV protons to study the release of radioisotopes of Cu, Ga, and As, respectively. Preliminary analysis indicates that As is released from molten Ge when heated to about 1100 degrees C.

Construction of the beam line to the Recoil Mass Separator (RMS) is underway and is expected to be completed in late November.

A more complete discussion of the facility status will be given at the HRIBF User's Meeting during the Bloomington DNP Meeting.

3. Staff Position in Experimental Nuclear Structure Physics

The Physics Division, Oak Ridge National Laboratory, invites applications for a staff position in experimental nuclear structure physics. Candidates are sought with several years experience beyond Ph.D., who have a distinguished research record in decay studies of nuclei on the limits of stability, and have a strong interest in research with radioactive-ion beams. The successful candidate will join the Experimental Nuclear Physics Group, whose primary objective is the development of a diverse research program for the Holifield Radioactive Ion Beam Facility. This unique facility, a new DOE program initiative now under development in the ORNL Physics Division, is scheduled to begin operation in 1996. General information about the HRIBF is available on the World Wide Web at http://www.phy.ornl.gov/hribf.

The Experimental Nuclear Physics Group offers an excellent environment for nuclear structure research which includes close collaborations with a leading nuclear structure theory group within the Physics Division and guests of the Joint Institute for Heavy Ion Research, as well as access to the resources of the Nuclear Data Project and state-of-the-art computational facilities.

Interested candidates should submit a curriculum vita, bibliography, a statement of research interest, and have four letters of reference sent directly to:

Dr. Cyrus Baktash Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge, TN 37831-6371 USA FAX: (423) 574-1268 E-mail: baktashc@ornl.gov.

Review of applications will begin in November 1995 and continue until the position is filled.

ORNL is a multi-program laboratory, managed by Lockheed Martin Energy Systems for the U.S. Department of Energy. ORNL is an Affirmative Action/Equal Opportunity Employer.

4. LDRD Funds Granted for Preparations for the National ISOL Facility at ORNL

ORNL Laboratory Director's Research and Development (LDRD) Funds have been granted for research toward and the preparation of a proposal for constructing the National ISOL RIB Facility at ORNL. The Nuclear Science Advisory Committee (NSAC) has recently identified the National ISOL Facility in its Long Range Plan for US Nuclear Science as the next major facility to be constructed under the auspices of DOE's Nuclear Physics Program Office. With the experience gained in constructing and operating the HRIBF, ORNL should be in a leading position to compete for this $100 million new facility whose construction could start as early as 1998.

5. 34 Letters of Intent Received

Thirty-four responses were received to the recent call for letters of intent for experiments at the HRIBF. The content of these letters of intent can be characterized as follows:

Nuclear Astrophysics 6 Nuclear Structure 21 Nuclear Reactions 7

The letters of intent also can be classified by the "lead" institution or collaboration:

ORNL 8 UNIRIB Collaboration 10 RIBENS Collaboration 6 Other U.S. Institutions 5 Non-U.S. Institutions 5

The letters of intent are presently being reviewed by the HRIBF PAC.

6. HRIBF Users Group Charter Approved

The new charter of the HRIBF Users Group has been overwhelmingly approved by the membership. Out of a total of 116 votes cast, 113 supported the new charter. The charter now reflects the transition from the Holifield Heavy Ion Research Facility to the Holifield Radioactive Ion Beam Facility. The text of the charter can be found soon on our WWW site. We thank those who participated in the vote.

7. DRS Update

The installation of the Daresbury Recoil Separator is proceeding well. A number of important tasks have been completed, including: the positioning and alignment of the 14 magnets; the construction and installation of the velocity filter electrode box handling assembly; and the modification and testing of power supplies (to run on U.S. power). A number of tasks are currently in progress, including: the wiring of magnet power supplies; the installation of magnet power supply and magnet cooling water systems; the installation of DRS Control System hardware; the assembly of velocity filter high- voltage electrode sub-assemblies; and the design of beam current monitoring devices. In the near future, we will begin assembly of the velocity filter electrode boxes. A number of projects are continuing off-site, including - at TUNL - the construction of the target chamber and velocity slit chambers, and - at Yale - the testing of focal plane assembly components and detectors and the design of the vacuum control system.

8. RMS Update

The first electric dipole has been conditioned to +/- 220 kV. After 40 hours, the dipole was again energized and conditioning was observed to begin at +/- 215 kV. The dipole was then pushed towards its maximum rated voltage (+/- 275 kV) when a small vacuum leak in the ceramic was detected. Upon inspection it was decided that corona was produced in the power supply (stack) which caused a spark to the ceramic. Conditioning of the second dipole was halted due to this development. Modifications to the high-voltage stack were done, and the leak has been repaired. With the modified stacks, the second electric dipole has been conditioned to +/- 200 kV, which is sufficient for presently planned experiments. Conditioning to higher voltages will be done when time permits.

The focal plane detector, PSAC, has been tested and has been found to achieve the desired position resolution. After some modifications of the high-voltage boards (1 mm wire spacing instead of 2 mm), the position resolution has been measured to be less than 2.0 mm in the x (A/Q) direction and approximately 2.5 mm in vertical direction.

Silena peak-sensing ADCs have been purchased for use with the Edinburgh silicon strip detector electronics. Over 160 channels may be used. The Edinburgh electronics have been constructed and used in experiments performed at the FMA. Delivery to Oak Ridge should be completed in the fall. Two 40 x 40 (4 cm x 4 cm) double-sided silicon strip detectors have been ordered by the University of Tennessee and have arrived.

The RMS ionization chamber is currently being fabricated at Daresbury Laboratory. Its vessel has been vacuum tested, and it should also be delivered in January.

9. Ge Upgrade Funded

An array of Compton-suppressed germanium detectors consisting of 12 existing ORNL detectors with BGO shields and 11 Compton-suppressed (BGO) "Clover" germanium detectors has been funded by DOE with contributions from UNIRIB, the University of Tennessee, Vanderbilt University, and the State of Tennessee. This array will be the centerpiece of in-beam gamma-ray spectroscopy at HRIBF and will be located at the target position of the RMS.

10. First Ge Clover Arrival

The first Clover detector was received in late July. This Clover detector is a slightly modified version of the Eurogam-II detectors. It consists of four cylindrical Ge crystals, each 8 cm long, which share a common cryostat. Test measurements with a Co-60 source indicate that the detector meets or exceeds the specifications. The results are:

(1) a total efficiency of 99.6% in the singles mode and better than 150% in the "add-back" mode; (2) an average energy resolution (FWHM) of about 2.1 keV at 1332 keV; and (3) a timing resolution of better than 6 ns.

The Ge upgrade project calls for a total of 11 Clover detectors. Since in the last few months Eurisys Mesures, the manufacturer of these detectors, has developed the technical capability of segmenting Clover detectors, we have placed an order for five segmented Clover detectors. The shipment of the first segmented Clover is expected in March 1996. With segmentation, the lateral position information regarding the interaction of gamma rays within the detector will improve from 4 cm to 2 cm. The improved position information would permit a better correction for Doppler broadening, which in turn allows the placement of the segmented detectors closer to the target position without loss of energy resolution.

The design of the BGO suppression shields is now complete. Requests for quotes will be issued later this calender year when the capital funds for FY 1996 are received. The design of the support structure for the Ge array has been completed, and requests for bids were issued in mid-September.

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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:    (423) 576-5489

Carl J. Gross, Scientific Liaison         |Email:  cgross@orph01.phy.ornl.gov
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