HRIBF NEWS

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   Edition 4, No. 2               April 30, 1996            Price: FREE

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Contents:

Editor:  Carl J. Gross

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1. Call for First Proposals for the HRIBF (J. D. Garrett)

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.

It is planned that about 10**8 69As and 70As ions per second will be available late in the scheduling period (see the following article on beam development). However, users should provide information on the minimum beam 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. Priority for early experiments will be given to those proposals providing the greatest probability of producing interesting publishable results with the low-intensity radioactive beams available during the initial operation. 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: (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. Arguments substantiating that stable beam work falls into one of these categories should be contained in the experimental writeup. 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.

The cover pages of the HRIBF proposals and guidelines for their preparation will soon be available on the HRIBF web site, "www.phy.ornl.gov".

2. HRIBF Status (J. R. Beene)

At the end of September 1995, the Accelerator Improvement Project to convert the HHIRF into a radioactive ion beam facility was completed. At that time, the main components of the new RIB Injector were intact. We immediately began an intensive commissioning effort which led to successful production of a stable Cu beam from material in the target position in the RIB Injector ion source. The beam was extracted from the source, passed through the first-stage mass analysis system, converted to a negative beam by charge exchange, accelerated off the injector platform, passed through the second-stage mass analysis system, and accelerated by the 25 MV tandem. In spite of this quick success, a substantial amount of work remains to be done in commissioning and improving the performance of equipment on the RIB Injector. From November 1995 through March 1996, this commissioning work was interrupted by shielding reconfiguration and installation and testing of the remote radioactive materials handing facility. The continuing effort to upgrade the reliability and extraction efficiency of ORIC and the completion of the commissioning of the RIB Injector hardware are the major hardware related tasks remaining before routine operation of HRIBF.

These accelerator- and beam transport-related tasks are essential, but the keys to the success of HRIBF are beam development and associated target and ion source issues. The resources available to us are increasingly being concentrated in these areas. At this time we have three development teams working in close collaboration on different aspects of these problems. A target and ion source research team works on the design of high-power targets and the development and initial testing of new ion source concepts. An in-beam testing, evaluation, and experimentation team uses low-power proton and deuteron beams from the 25 MV tandem to do target and ion source tests and activation release studies. They also use heavy-ion beams for implantation release studies. This experimental work is centered on the UNISOR separator. The third team, which includes members of both the other development teams, is responsible for commissioning and operation of the RIB Injector and the development of beams for research.

The near-term plans for beam development at HRIBF are to concentrate all our efforts on the production of 69,70As beams for nuclear structure research and a 17F beam for nuclear astrophysics. The arsenic RIB will be our demonstration beam, as well as our first beam for research. We will produce 69,70As with the 70Ge(p,n) and 70Ge(p,2n) reactions on an isotopically enriched liquid 70Ge target with a thickness of about 2 g/cm**2. This combination was chosen because of the large cross section (~600 mb at the peak for 70As production and ~350 mb for 69As), and the comparative simplicity and robustness of the liquid metal target, as well as the long and successful experience at ISOLDE with liquid metal targets (including Ge). The production rate of As isotopes is known from experimental data; for each uA of p beam incident on the target, we will make 10**10 70As ions/s and ~6 x 10**9 69As ions/s (with the beam energy optimized for each case). We do not yet have firm experimental estimates of the overall efficiency with which we will be able to convert these ions into an accelerated beam suitable for physics experiments. A reasonable estimate is 2 x 10**7 ions/s/uA and 1 x 10**7 ions/s/uA for mass 70 and 69, respectively. Our facility design goal is for proton driver beams of 50 uA. A reasonable goal for the early stages of operation is for proton beams in the 10-20 uA range. These numbers suggest that we should be able to produce beams of roughly 10**8 As ions per second for both mass 69 and 70. Several factors may limit the performance of the second-stage mass analysis system to less than its design performance of 1/20,000 mass resolution. Since the masses of 70Ge and 70As differ by ~1/10,000, it is likely that the initial 70As beam will contain a significant 70Ge component.

Work with the liquid Ge target is now being carried out by the development team on the UNISOR separator with low-intensity proton beams. We plan to measure release and transport time profiles and the overall efficiency of the target ion source for As beam production. We hope to complete this work around the end of May 1996. As soon as successful As RIB production is demonstrated at UNISOR, the As beam development program will move to the RIB Injector, and the target development group will shift their emphasis to 17F beam production. The ion source research team has been working for some time on ion source concepts optimized for F beam production; we believe this aspect of the problem is well in hand. The rapid release of this extremely chemically active element from target material and timely transport to the ionization region is a much more challenging problem. Many promising ideas have been proposed, which can be evaluated quickly and efficiently on our test facilities. By the end of the summer we should be in a position to make an educated judgment on whether we should continue an all-out effort on 17F beam production, or based on input from our astrophysics user community, move (at least temporarily) to a more tractable first beam for astrophysics.

Our longer-term beam development program is driven by the wishes of our user community, tempered by the physical and chemical realities of production release and ionization time scales and efficiencies. Reasonable near-term possibilities for nuclear structure include (63),64Ga and 70,71Se. For astrophysics, isotopes of S and Si will be considered next, subject to the priorities of the research community. Within a year to two years of beginning operation, we will begin to produce neutron-rich beams from proton induced fission of actinide targets. For the most part, beam development issues are much better understood for this system than for those used to produce proton-rich beams. However, use of actinide targets will present more severe regulatory and radiation handing problems.

It must be realized that development of each beam is a research project in itself, involving diverse aspects of metallurgy, surface physics, high-temperature chemistry, etc. We are moving aggressively to enhance our capabilities to do target ion source and beam development research, including collaboration with groups external to ORNL as well as members of the Chemical and Analytical Sciences Division and the Metals and Ceramics Division at ORNL who bring unique knowledge and talent to bear on our problems.

2a. Late Breaking Beam Development News

During the week of 22 April, we completed our first on-line studies of arsenic RIB production and a study of the release of radioactive fluorine from aluminum oxide (Al2O3).

Experiments were carried out to investigate the release of radioactive fluorine produced in a low-density mesh (~0.16 mg/cm**3) made of 3-micron-diameter fibers of aluminum oxide. Samples of the mesh were exposed to a low-intensity 20 MeV proton beam to produce 18F with the 18O(p,n) reaction on the naturally occurring 18O in the sample. Irradiated samples were counted to determine the 18F content, and then heated for controlled periods to temperatures ranging from 900 C to 1750 C. Essentially all (>80%) of the 18F was released from the aluminum oxide mesh for all samples heated to 1400 C or higher. Essentially no release was observed for samples heated less than 1000 C. No detailed information on release times was obtained, but nearly complete release was seen for a sample held at 1400 C for less than 5 minutes.

In the arsenic study we successfully generated a beam 70As using a low-intensity (7 nA) proton beam on a liquid Ge target in the HRIBF electron beam plasma ion source. The As ions were analyzed with the UNISOR mass separator. The very preliminary results indicate a very long holdup time in the target or ion source and a low efficiency for As beam production, implying an As beam intensity about an order of magnitude lower than the estimates given in articles 1 and 2.

3. Radiation Handling System Has Arrived (P. E. Mueller)

The Remote Handling System (RHS) was installed by PaR SYSTEMS, Inc. of Shoreview, Minnesota, during March 1996. The RHS consists of three major components: (1) a robotic arm that is mounted on the 300 kV source platform next to the Target Ion Source (TIS); (2) a conveyor that extends from the source platform room, through the cyclotron vault, and into a shielded storage room; and (3) a robotic gantry crane in Rad Lab II (formerly the BRS room).

The robotic arm (GALILEO) is a PaR Model 6350 Telerobotic Manipulator which has six degrees of freedom (the human arm has seven degrees of freedom). GALILEO is driven by electric motors and steel reinforced polyurethane belts. GALILEO is designed to withstand 10^8 RAD total dose and, with periodic replacement of the motors and belts, 10^9 RAD total dose.

The RHS will only operate when there is no cyclotron beam and when there is no high voltage. The TIS will remotely disengage from the RIB Injector vacuum system and move to a retracted fiducial position on the 60 kV table. GALILEO will pick the TIS up and place it in a stainless steel Contamination Control Box (CCB) which will sit on the end of the conveyer, that will temporarily extend into the gap between the source platform and the wall. GALILEO will then put a dust-tight cover on the CCB. The end of the conveyer and the CCB will retract into the wall and the motor-driven rollers of the conveyor will move the CCB through ORIC's vault to Rad Lab II where the robotic gantry crane (PICASSO) will pick the CCB up off the conveyor and place it inside a lead cask. PICASSO will then put a lead lid on top of the cask. The RHS will also reverse this sequence to install a new TIS on the RIB Injector.

The RHS successfully performed 50 consecutive repetitions of moving a 250 lb TIS mock-up (twice the weight of a nominal TIS) from the cask position in Rad Lab II to the fiducial position on the 60 kV table and then back again to the cask position. Each repetition took 41 minutes to complete. The RHS performed all 50 repetitions over a 34-hour period without any human intervention.

The PaR SYSTEMS, Inc. supplied control system for the RHS is fully programmable and includes manual options for both GALILEO and PICASSO. The RHS control system will communicate with the RIB Injector VISTA-based control system.

4. Users Group News

John D'Auria and Mark Riley have been elected to the HRIBF Users Group Executive Committee. Over 150 ballots were counted out of 350 which were sent to the membership. Retiring from the Committee are Ed Zganjar and Rick Casten. Continuing members are Art Champagne (chairperson), Cary Davids, Joe Hamilton, and Carrol Bingham. We thank Ed and Rick for their service to the community and hope they will continue to be active at HRIBF.

In a telephone conference earlier this year, the Executive Committee met and elected Joe Hamilton to be chairperson-elect. Joe will succeed Art Champagne as chair on January 1, 1997.

The Annual Users Meeting of the HRIBF was held during the Fall Meeting of the Division of Nuclear Physics in Bloomington, Indiana. Over 70 interested scientists and students attended the session which was presided over by Executive Committee Member, Joe Hamilton. Physics Division Director Fred Bertrand provided details on the start-up of operations (see first topic), Jerry Garrett summarized some statistics about the Letters of Intent, and Cary Davids announced the Executive Committee election results. In addition, Carl Gross and Matt Brinkman summarized the status of the experimental equipment which will be available in the first few months of user operations. An updated summary follows:

You may now register with the HRIBF Users Group via WWW. Simply access our homepage at http://www.phy.ornl.gov/ and fill out the form found under the Users Information section. The Users Group is open to all interested experimentalists and theorists at every level of their study.

5. Status of the Germanium Array Upgrade (C. Baktash)

The status of the upgrade of the Ge array is given below. Funding has been started and a completion is expected before FY98.

  1. Clover Ge detectors:
  2. The prototype clover detector was received and tested in July 1995. It met or exceeded all specifications. At that time, we learned that the manufacturer, Eurisys Mesures, had developed the capability of producing segmented Clovers. Since segmentation would allow the placement of the Clovers closer to the target position without loss of resolution, it would increase the photopeak efficiency of the array by approximately 25%. An order for five segmented clovers was placed in September 1995. The first unit is due May 1996. The remaining units will be delivered one per month thereafter. Funds have been requested for five more segmented Clovers in FY97. Full delivery will be completed approximately 9 months after the receipt of funds.

  3. BGO shield:
  4. The BGO shield design has been modified to allow the placement of the segmented Clovers closer to the target position. Requests for bids will be issued in early May. Delivery of the first unit is expected in September 1996. The remaining five units will be delivered one per month thereafter. Funds have been requested for five more shields in FY97. Full delivery will be completed nearly 9 months after the receipt of funds.

  5. Support structure:
  6. The order to spin the hemispherical shells was placed in March 1996. The time estimate to complete the spinning and machining is 7-8 months.

  7. Electronics module for Clovers:
  8. A subcontract has been signed with LBNL to design a prototype electronics module for segmented Clovers using the components developed for the Gammasphere. The target date for the completion of the prototype is January 1997.
For the initial experiments with the RMS and until November 1996 when the new support structure becomes available, we shall install the Compton Suppression Spectrometer (CSS) at the RMS target position. The array, consisting of 20 Ge detectors, will have a photopeak efficiency of ~0.6%. The changeover to the final support structure and the incorporation of five Clovers into the system (photopeak efficiency of 1.4%) is projected to begin in December 1996. From April 1997, when the Clover electronics modules become available, until the projected completion date of August 1997, we shall be adding approximately one Clover per month to the system. In its final configuration, the array will consist of 11 Clovers and 12 elements of the CSS with a total photopeak efficiency of about 3.4%.

6. Focal Plane Detector Equipment Has Arrived

A large portion of the University of Edinburgh electronics for the double-sided silicon strip detectors (DSSSD) has arrived. Two crates containing 256 channels of shaping amplifiers and constant fraction discriminators have been delivered, including many of the necessary cables and hardware associated with the system. Yet to arrive are the detector-specific preamplifiers and some miscellaneous parts. ORNL and the UNIRIB consortium has purchased two detectors for use in the initial experiments and many of the additional CAMAC modules needed to complete the system.

The Surrey-Daresbury-Vanderbilt ionization chamber has been recently delivered to Oak Ridge and awaits testing. Initial tests with beam should begin on the RMS in June.

7. Data Analysis Workshop (H.-Q. Jin)

A four-day workshop on data analysis was held at the Joint Institute for Heavy Ion Research in Oak Ridge from February 7 to 10, 1996. There were a total of 58 participants from 22 different institutions, including 6 national Labs and 16 universities. The workshop included 19 formal presentations in the mornings and intensive informal discussions and hands-on demonstrations in the afternoons. People from the nuclear structure research community and the nuclear data network as either users or "programmers" participated in discussions on four areas of interests:

David Radford from Chalk River gave four lectures on his prestigious software package, Radware, which is widely used by the nuclear structure community for analyzing coincident data. Visions on high-fold data analysis were presented by several people, together with intensive discussions on data representations and modeling. The importance of data compilation and data networking was realized and emphasized. A favorite quote from Mark Riley (FSU) is "Should I go home and e-mail you my .lvl files from the past ten years?"

It turned out that the active interaction between "programmers" and users from the afternoon hands-on demonstrations and discussions was very valuable. This was particularly true for many students in the workshop.

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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