HRIBF Newsletter, Edition 14, No. 1, Feb. 2006

   


Feature Articles

Regular Articles




1. HRIBF Update and Near-Term Schedule
(J. R. Beene)

The August 2005 issue of the HRIBF Newsletter discussed the challenges presented to the HRIBF operations staff by the effort to continue normal running of the HRIBF science program while successfully completing the HPTL project. This trying combination of tasks has, indeed, been completed. The HRIBF staff deserves our thanks and admiration for this achievement, and for the sustained, intense, focused and effective effort they provided to get it done. The commissioning of the HPTL is now complete and it is fully ready for the experimental program to begin. The only missing detail is the delivery and installation of a bridge crane for handling activated target ion source assemblies. The crane, which is not needed for the initial round of experiments, will be delivered and installed by the end of February.

The DOE Office of Nuclear Physics (DOE-NP) held a closeout review of HPTL project at ORNL on October 23 and 24, 2005. This review also served as a baseline cost, schedule and technical review of the IRIS2 project. The closeout review was very favorable as was the IRIS2 baseline review. Initial funds for the three-year IRIS2 project are allocated in the FY2006 DOE budget, and it has now begun.

The HRIBF Program Advisory Committee (PAC) met on December 8 and 9, 2005, to consider a set of high-quality proposals. A total of 149 eight-hour shifts of beam-time were approved out of 370 shifts requested (see section 8). The Scientific Policy Committee (SPC) met with Physics Division management and HRIBF management and staff on December 10 and 11. The present membership of the SPC includes seven distinguished scientists from the U.S. and Europe: Juha Aysto (chair, Jyvaskyla), Brad Fillppone (Cal Tech), John Hardy (Texas A&M), Thomas Glasmacher (NSCL), K. E. Rehm (Argonne), A. Shotter (TRIUMF), and F-K. Thielemann (Basel). The SPC provides us with advice and counsel on a wide range of topics and issues. Substantial time was devoted at this meeting to a discussion of the draft HRIBF Strategic Plan which was developed at the behest of DOE-NP to serve as a framework for the effort to optimize the development of HRIBF and ensure that it is well aligned with the priorities of DOE-NP and the Office of Science. This Plan is discussed more in detail in a separate article in this newsletter.

In spite of this sustained effort on HPTL as well as other maintenance tasks, just over 1200 hours of RIB were delivered to experiments in FY2005 as a part of 3363 total research hours. Fiscal 2006 has so far been devoted to HPTL commissioning, stable beam experiments and scheduled maintenance. A major tandem tank opening began on December 5 and lasted six weeks through the holiday period. This was the first extended tank opening since May 10 (there was a one-day unscheduled opening in September). A variety of routine but pressing maintenance issues were addressed. The first quarter resulted in 932 research hours of beam, including a nuclear astrophysics experiment during which the 25 MV tandem was operated are a record low voltage of 1.245 MV. The range of voltage over which this machine can deliver beam stably is remarkable.

The schedule for the remainder of FY2006 will be devoted largely to neutron-rich RIBs. We expect to wage two nearly back-to-back n-rich campaigns of roughly three month duration each, with only brief interruptions for stable-beam runs. Several of the n-rich experiments call for relatively high tandem voltages. Our current inventory of SF6 is less than optimal for running at the highest voltages. Consequently we intended to purchase additional SF6 this fall. Unfortunately, hurricane Katrina resulted in a worldwide shortage of this material. It will not be possible to purchase enough to impact performance until May at the earliest. Following the n-rich campaigns, we will have another 4-week period of scheduled maintenance in late summer, and end the fiscal year with a proton-rich beam campaign (Al or F). A new feature of our schedule in FY2006 will be the inclusion of beam-development and target testing experiments utilizing ORIC beams at the HPTL




2. Recent HRIBF Research - Proton-Transfer Study of Unbound 19Ne States via 2H(18F,alpha + 15O)n
(C. R. Brune, Spokesperson)

The 18F(p,alpha)15O reaction in the temperature range (1-4)x108 K plays an important role in classical novae. The rate of this reaction affects the production of heavier elements and is also critical for calculating the flux of 511-keV gamma rays which result from 18F decay (a major target of gamma-ray observatories). In order to better determine this reaction rate, several measurements of the 18F(p,alpha)15O reaction have been undertaken or are planned for Ec.m. > 330 keV at ORNL and elsewhere in recent years (e.g., RIB-099). The neutron transfer reaction 18F(d,p)19F has also been studied at ORNL to determine properties of states in the mirror nucleus (RIB-044). While these studies have contributed significantly to our understanding of the situation, there remains considerable uncertainty in the extrapolation of the cross section to lower energies and the assignment of analog states between 19F and 19Ne. Of particular importance are the two 3/2+ states just above the proton threshold in 19Ne (potential 8- and 38-keV resonances): it is still not clear which state, if either, has a significant proton spectroscopic factor. The answer to this question can change the 18F(p,alpha)15O reaction rate by up to an order of magnitude, with an even larger potential change in the amount of 18F synthesized in novae.

In order to address these questions, an experiment was carried out to measure the proton transfer reaction 18F(d,n)19Ne at ORNL/HRIBF in summer 2005 (RIB-145). With this approach, it is possible to determine resonance energies and the distribution of proton strength in 19Ne without resorting to mirror symmetry. A 150-MeV 18F9+ beam was used to bombard a 720-μg/cm2 CD2 target. A total of 14 shifts of 18F beam were used for the measurements, with an average intensity of about 2.5x106/s on target. The 19Ne excited states of interest decay by breaking up into alpha + 15O. The alpha and 15O were detected in coincidence with six position-sensitive Si detector telescopes. The energy and position determination allowed the momenta of both reaction products to be reconstructed. The excitation energy of the decaying state relative to the alpha + 15O threshold (relative energy) and the momentum of the undetected neutron can then also be calculated. The resolution in the relative energy is only minimally broadened by the effects of energy loss in the target and finite beamspot size. A schematic diagram of the target and detector layout is shown in Fig. 2-1. Backgrounds from other reactions are strongly suppressed by utilizing the coincidence requirement and particle identification on the alpha and 15O.


Fig. 2-1. Schematic diagram of the experimental apparatus. Each position-sensitive Si detector telescope is 5 cm x 5 cm; they were located approximately 45 cm downstream from the target and covered lab angles between 2.5 and 17 degrees. The 15O recoils were detected in the inner telescopes while alphas were primarily detected in the outer telescopes.

A particle identification spectrum obtained from an inner telescope is shown in Fig. 2-2. In order to optimize the resolution and calibration of the relative energy, the position and energy calibrations of the detectors must be well known. We thus also carried out stable beam calibrations using the elastic scattering of alpha and 16O beams. The resolution for the relative energy achieved is approximately 70 keV. Backgrounds were measured from a carbon target (i.e., without deuterium) and found to be negligible. We have also simultaneously measured the mirror reaction 2H(18F,alpha + 15N)p. The comparison of these mirror reactions will be helpful for determining isospin mirror assignments. The analysis of these data is ongoing. This project is a part of the Ph.D. dissertation of Aderemi Adekola from Ohio University.


Fig. 2-2. Particle identification spectrum obtained from an inner telescope.




3. Recent HRIBF Research - Online Computational Tool Processes HRIBF Results into Astrophysical Predictions and Aids Proposal Preparation
(M. S. Smith, Spokesperson)

The Computational Infrastructure for Nuclear Astrophysics is a suite of computer codes, online at nucastrodata.org, that was developed to streamline the incorporation of the most recent measurements at HRIBF and other facilities into astrophysical simulations. The suite, which has registered users in 42 institutions in 16 countries, enables researchers to upload and modify (e.g., renormalize, gain shift, extrapolate) a laboratory cross section [Fig. 3-1], convert this into a thermonuclear reaction rate [Fig. 3-2], combine with other rates into a library, run a simulation with this rate library, and visualize the results [Fig. 3-3]. A user-friendly interface with on-line help and an email-type commenting feature makes the suite ideal for students and for non-experts who wish to determine the astrophysical impact of their recent measurements or calculations. Customizable animations of the time-dependence of abundances [Fig. 3-4] and reaction fluxes [Fig. 3-5] in stellar explosions can be created, viewed, and exported for use in presentations and in research. The suite also has other features such as a Mass Model Evaluator where theoretical mass models can be uploaded, visualized, and compared to experimental values [Fig. 3-6].

The suite can also be used to investigate the sensitivity of astrophysical simulation predictions on the input nuclear reaction rates. Users can quickly modify (e.g., scale up and down) or replace a reaction rate, rerun a simulation, and examine the ratios of simulation predictions using the original and the new rate. Used in this way, the suite can be an invaluable tool for writing proposals for future experiments at HRIBF and elsewhere that have a relevance for astrophysics.

The suite has been recently used, for example, to determine that measurements of 18F + p reactions at HRIBF (RIB-020, RIB-044, and RIB-066) increased the amount of 18F synthesized in nova by up to a factor of 6 in the hottest zone of the explosion and up to a factor of 1.6 when the entire exploding envelope is considered - compared to estimates made with the previous "best", larger reaction rates. When compared to simulations using the older, lower, most widely-used 18F + p reaction reaction rates, our new rate decreases the 18F production by factors of 10 and 2 for the hot region and the entire envelope, respectively. Our calculations also change the predictions (by factors of ~2) of how many novae will be imaged by hundred million dollar satellites such as INTEGRAL which are presently searching for the decay of 18F produced in the outbursts. When the analysis of two additional experiments [18F(p,alpha)15O and 18F(d,n)19Ne, RIB-099 and RIB-145] are completed, the suite will be used to determine their impact on the problem of 18F production in nova outbursts.

Our online system is freely available to all at nucastrodata.org. By registering access to the suite via a short online form, users receive a disk allocation to save their work and share it with other researchers.



4. Recent HRIBF Research - Discovery of the New Alpha Emitters 109Xe and 105Te
(R. Grzywacz, Spokesperson)

The island of alpha and proton radioactivity above 100Sn has attracted considerable interest over the years. In addition to the strong influence of the N=Z=50 double shell closure and the proximity of the proton drip line, this unique region has also recently been identified as the termination point of the rp-process. Furthermore "super-allowed" alpha decays could occur in this region where the valence nucleons occupy the same orbitals, although no conclusive evidence for this effect has so far been obtained.


Figure 4-1: An example of recorded double pulse induced in the DSSD front (black) and back (red) strips. First "step" of this pulse is due to alpha particle emitted from 109Xe, second "step" is due to 105 Te decay leading to 101Sn.

Two new alpha-emitting nuclides were discovered, 109Xe and 105Te, in an experiment performed at HRIBF using the Recoil Mass Spectrometer (RMS) in November 2005. The 109Xe nuclei were produced via the 3n evaporation channel in reactions of 58Ni with 54Fe and implanted into the Double-sided Silicon Strip Detector (DSSD) at the RMS focal plane. The subsequent alpha decay of the daughter 105Te nuclei was expected to occur within a few microseconds of the 109Xe alpha decay, so a new trigger and readout method had to be developed for the digital data acquisition system allowing the preamplifier traces containing the two closely spaced pulses to be recorded. A typical double trace is shown in the Fig. 4-1. From these traces, correlated with the recoil implantation signals, it is possible to extract the energies of both alpha particles and determine the half-lives of 109Xe and 105Te, see Fig. 4-2. An important discovery in the decay of 109Xe was that it exhibits fine structure, as shown in the upper panel of Fig. 4-2, which allows us to determine the relative energies of the d5/2 and g7/2 neutron states in 105Te.


Figure 4-2: Spectra of alpha particle induced pulse amplitudes extracted from measured pile-up pulses (like in Fig. 4-1), attributed to 109Xe (top) and 105Te (bottom) alpha decays. New pulse shape fitting routines were developed to obtained optimum resolution.




5. High Power Target Laboratory (HPTL) Project Completed Successfully
(B. A. Tatum)

We are pleased to report that the High Power Target Laboratory Project has been completed with the exception of the installation of the remote handling system bridge crane. The crane will be delivered by the end of January 2006 and installed during the first two weeks of February. In spite of a four month overrun by the facility modifications construction contractor, all of the technical equipment was installed prior to the end of September 2005. This was a tremendous accomplishment by the HRIBF technical staff and our incredible crafts team in spite of a very heavy HRIBF operations schedule! The entire Project Team is to be congratulated for a job well done!

Commissioning has also been completed in several stages. First, we tested the ion source and RIB analysis system in late September by extracting a stable ion beam and tuning it through the low energy analysis beamline to the diagnostics station above the target room. Secondly, a commissioning run with low intensity ORIC beam took place in October to demonstrate the performance of the ORIC beamline as well as the production of radioactive fluorine. Final commissioning of the entire system occurred on December 6, 2005 when a 1.8uA beam of 42-MeV deuterons was delivered from ORIC to the HPTL Target Station. A hafnium oxide target was coupled to an EBP ion source for the production of Al17F+ ions, and the measured beam intensity of Al17F+ on Faraday cup RA_3 (located at the end of the RIB Analysis beamline in Room C-212) was 8 x 106 pps. The measured yield was slightly better than the expected yield of 3 x 106 pps/uA, which had been measured in previous tests at the OLTF and on the RIB Injector. This improvement may be due to better transmission from the ion source to the diagnostics station. The background levels as measured by the Ge detector were quite low; less than 2 cps in the 511-keV peak during irradiation of the hafnium oxide target. The plot below shows the decay of activity deposited onto the Faraday cup. The data points are the number of 511-keV gamma-rays detected during 15-second counting periods after the collection was stopped. The fit to the data indicates a decay half-life of 64.2 seconds, while the half-life of 17F is 64.5 seconds.

Figure 5-1: Decay of the activity deposited on the Farady cup RA_3.The data points are the number of 511-keV gamma-rays detected during 15-second counting periods after the collection was stopped. The fit to the data indicates a decay half-life of 64.2 seconds, while the half-life of 17F is 64.5 seconds.




6. Update on Injector for Radioactive Ion Species 2 (IRIS2)
(B. A. Tatum)

The ORNL Physics Division submitted a proposal for the construction of a second RIB injector, known as IRIS2, to DOE-NP in September 2004. This proposal was reviewed for significance and scientific merit in that month by the same panel that was conducting the annual HPTL Review. A revised Proposal and a draft Project Management Plan were requested by the Panel, and these documents were both submitted to DOE-NP in October 2005 in preparation for a baseline Review. This Technical, Cost, Schedule, and Management Review of the proposed project was held at Oak Ridge on October 24-25, 2005. As of the end of the calendar year, we are pleased to report that this project has been funded and the PMP is being finalized. The project cost is approximately $4.7M and will span three years with completion scheduled by the end of February 2009.

IRIS2, with components shown in red in the figure below, will be co-located with the recently completed High Power Target Laboratory (HPTL), so no civil construction is required. The principal focus of the Project is associated with Technical Equipment. The primary components of the project are:

  • High Voltage Platform System in the Target and Instrumentation Rooms

  • Injector Beamline on the platform

  • Transport Beamline from the platform to existing beamline 12

  • Remote Handling and Localized Shielding in the Target Room

  • Target Room HVAC System for temperature and humidity control for high voltage operation

  • Laser Room to provide an operating venue for lasers employed in on-line resonance laser ion sources and in other beam purification schemes employing lasers

  • Utility systems will be expanded to accommodate the substantial addition of technical equipment

    Figure 6-1: Floor map of HRIBF with IRIS2 (shown in red).




    7. The FY2006 Budget
    (J. R. Beene)

    The budget for HRIBF operations and for the HRIBF-based low energy research program for fiscal 2006 has proved to be much more austere than was anticipated at the time of our last Newsletter. The FY2006 budgets for Nuclear Physics adopted by the Congress turned out to be at the level of the President's Budget, and therefore well below the levels in the bills initially passed by either the Senate or the House. The PresidentŐs Budget for Nuclear Physics as a whole was 8.4% below the FY2005 budget. A 1% across the board rescission has since been added. The HRIBF budgets fared slightly better than average, but the effect is still disastrous. The HRIBF operations budget is reduced by 7.8%, while the fixed costs of operations are up more than 6% compared to FY2005. Fixed costs include staff salaries, so-called "background" power costs, and a few other recurring contract costs, and amount to about 90% of the HRIBF operations budget for this year. These fixed costs do not include the direct costs of operating the accelerators for experiments, consequently the funds remaining after fixed costs are highly leveraged in terms of their impact on our ability to deliver beam to experiments. The funds remaining for operations after fixed costs are met will be on the order of half as large as in FY2004 and FY2005. Clearly this will have substantial impact. With adequate funding we expected to continue the steady increase in RIB hours delivered to experiments that we had achieved over the last several years (reaching ~1700 hours in FY2004 before the increase was interrupted by the impact of HPTL completion and maintenance issues). That will clearly not be possible. A more realistic goal under the limitations imposed by the FY2006 budget will be ~1200 hours of RIB on target, and even that will stress us to the limit.

    As bad as the impact of the FY2006 budget is on HRIBF operations, the impact on the low-energy research program is much worse. The FY2005 low energy budget was not adequate to cover staff salaries. The existence of a modest carry-over from previous years, some support from HRIBF operations as well as several small addition sources of short-term funds made it possible for us to survive the year without loss of staff. The additional cut of 7% in FY2006, together with no carry-over funds and no hope of help from the already strapped operations budget leaves us in desperate shape. We are far short of meeting even our staff cost, even if optimistic assumptions are made concerning our ability to generate additional short-term funds. This is before any expenses for actually doing research are considered. At this point, a reduction in low energy research staff at HRIBF of at least 20% seems inevitable. This will not only severely impact our in-house research programs, but will also impact the level of service we can provide to outside users of the HRIBF.




    8. PAC-12 Results and PAC-13
    (C. J. Gross, HRIBF Scientific Liaison)

    PAC-12 met December 8-9, 2005, in Oak Ridge and considered 21 proposals and letters of intent which requested 227 shifts of radioactive beams (RIBs), 74 shifts of low intensity stable beams (SIB for RIBs), and 66 shifts of stable beams (SIBs). Of these, a total of 109 RIB shifts (18 provisionally), 19 SIB for RIB shifts, and 21 SIB shifts (+15 additional shifts depending on results) were approved.

    Approved experiments requested RIBs of 7Be, 17,18F, 25,26Al, 80Ge, and 132Sn. The total number of accepted proposals was 9, 7 of which were from outside organizations. A letter of intent requesting development of 10Be beams was also endorsed.

    Uwe Greife, previous chair of the Users Executive Committee represented the Users at the meeting.

    We wish to thank John Hardy for his service on the PAC; John served as chair of the committee throughout his years of service. He will be replaced on PAC-13 by Brad Sherrill of Michigan State University. We anticipate PAC-13 to occur in late October of this year with proposals due in early September.




    9. The HRIBF Strategic Plan
    (J. R. Beene)

    At the last S&T review of the HRIBF facility and research program, held in November 2004, it was recommended that HRIBF develop a Strategic Plan for the facility and its research program. We had actually begun the development of such a plan a few months earlier and have continued to work on it since. The initial draft was put together by HRIBF management and staff. Extensive comments and suggestions from research staff members and members of the HRIBF Users Executive Committee have also been incorporated. The resulting draft plan was presented to and discussed with the HRIBF Scientific Policy Committee at its meeting on December 9 and 10, 2005; their insights and concerns have helped us to refine the Plan further.

    The HRIBF Strategic Plan is intended to serve as a framework to guide the development of HRIBF and its science program and ensure that they are well aligned with the priorities of DOE-NP and the Office of Science. It is divided into three parallel but closely coupled parts, titled Science Opportunities, Experimental Systems, and Facility. The initial part of the Plan lists, in compact form, the overarching scientific goals we hope to achieve at HRIBF, and the corresponding goals for development of experimental hardware and accelerator systems required to enable the science goals. These strategic goals are followed by an "implementation plan" which lists a set of milestones in each of the three areas along a timeline running until 2013. The Science Opportunities, from which the elements in the other two areas derive, are coded to indicate their relationship to the DOE Nuclear Physics Program Milestones. At this point, we are still collecting input from the HRIBF user community and staff, as well as our advisory committees, so the Plan is still considered to be a draft. Even in the long term, however, we will regard this Plan as a living document which will undergo continuous modification to suit changing needs and circumstances.




    10. RIA Summer School to be Held at HRIBF
    (C. J. Gross, HRIBF Scientific Liaison)

    The fifth annual RIA Summer School will be held at HRIBF July 17-23, 2006. The school is organized by the HRIBF, ATLAS, 88-inch Cyclotron Facility, N-division/LLNL, and NSCL and rotates among four of the five laboratories (except LLNL). Between 40 to 50 students are expected to attend lectures in the morning and take part in hands-on demonstrations of experimental equipment and techniques in the afternoon. Time will also be provided for the students to present their research projects. The school hopes to raise sufficient funds so that all local expenses will be covered by the school. For more information go to the school website at www.orau.org/ria/schools.htm.

    The timing of the school was chosen so that students may also attend the Nuclear Structure 2006 conference which will also be in Oak Ridge the following week.




    11. Nuclear Structure '06 Conference to be Held in Oak Ridge in July 2006

    The Physics Division of the Oak Ridge National Laboratory will host the "Nuclear Structure '06" Conference during the week of July 24-28, 2006, in Oak Ridge, Tennessee. This conference is the next one in a series of biennial meetings that have been hosted by North American national laboratories for nearly 30 years. The goal of the conference will be to provide both a broad perspective of the latest progress in experimental and theoretical nuclear structure physics, and to point out the exciting opportunities that lie ahead in the next few years. Detailed information about the meeting will soon become available on the conference web site.



    12. Astrophysics Workshop to be Held at HRIBF
    (Dan Bardayan)

    The Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL) will hold a workshop on nuclear measurements for astrophysics with a special emphasis on the applications of radioactive beams to such studies on October 23-24, 2006.

    The purpose of this workshop, hosted by the HRIBF users' executive committee and the Joint Institute for Heavy Ion Research, is to bring together scientists who wish to study nuclear astrophysics with radioactive and stable beams and to acquaint participants with HRIBF's beams and experimental facilities available for such experimental studies.

    We plan to organize approximately six sessions discussing nuclear measurements of interest for studying Big Bang Nucleosynthesis, solar burning, hot CNO and rp-process nucleosynthesis in novae and X-ray bursts, and supernovae and the r-process. It is envisioned that the program will be made up of invited and contributed talks. The final session will include an open discussion of future directions for the HRIBF program in nuclear astrophysics and possible collaborative efforts. We welcome your suggestions, both for topics that should be discussed and for speakers. Further, if you would like to make a short contributed presentation, please contact Dan Bardayan. Further details will be announced on the workshop website.




    13. Reaction Workshop Held at HRIBF
    (D. Shapira)

    A workshop on "Near and Sub-barrier Fusion of Radioactive Ions with Medium and Heavy Targets" was held at the ORNL on December 2-3, 2005. There were 32 participants evenly devided between active users and visitors from other institutions in the US and abroad. The idea was to make the community interested in this subject of nuclear physics aware of our capabilities (beams and experimental facilities). A panel at the end of the workshop was convened by the organizers seeking input/consensus on how to best utilize HRIBF resources and cabapabilites to make advances in this field.

    Known practicitioners in the field made presentations and served on the panel. These included experimentalists (D. Hinde from ANU, E. Rehm form ANL) as well as theoreticians (B. Balantekin from U. of Wisconsin, P. Moller from LASL, M. Hussein from U. of Sao Paulo).

    As expected there is no clear consensus on how to proceed with our local program here, but several ideas were noteworthy. As a result of this workshop contact with future collaborators was established. There were two groups interested in the 7Be cababilities at HRIBF. One group was interested in transfer reaction studies and will probably end up doing them at ANL. The other group from INFN-Naples is interested in the quasileastic scattering and breakup of 7Be on heavy targets and will submit a proposal to PAC13.

    Our local collaboration is expanding and now includes active collaborators from U. of Notre Dame (Kolata), Univ. of Michigan (Becchetti, Amro), Oregon State U. (W. Loveland & co.), UNAM-Mexico (E. Chavez), ANU-Australia (D. Hinde ) and occasional participants from other colleges and universities.

    More details about the workshop can be found at its web site.




    Feature Articles

    RA1. RIB Development
    (D. W. Stracener)

    Experiments with high-intensity production beams from the ORIC will begin soon at the recently commissioned High Power Target Laboratory (HPTL). The first set of tests will be focused on the production of 25Al and 26Al beams from reactions on silicon. The targets that we plan to test include SiC fibers and pressed pellets of metal silicide powders, such as tungsten silicide and niobium silicide. Other target tests that will be made in the next few months include, thin liquid Ge for production of Se beams, different geometries for the fluorine production target, and high intensity tests on uranium carbide targets with densities that are significantly higher than those presently used.

    In the last newsletter we reported on the first experiments with a laser ion source using Ti:sapphire lasers. Another series of tests were recently completed where beams of Cu, Sn, and Ni were produced. This was the first demonstration of three-photon resonant ionization of Cu in a hot-cavity laser ion source using Ti:Sapphire lasers. The ionization efficiency for Cu was 2.4% and, for the first time, frequency quadrupling of the Ti:Sapphire laser was successfully utilized. In addition, we measured the emittance of laser-generated and surface-ionized ion beams, and made measurements of the temporal structures of laser ions with respect to the laser pulse at different source temperatures. The temporal structures of laser ions generated from hot cavities of three different lengths were also measured. These measurements were made in collaboration with Klaus Wendt and his group from Mainz who brought the Ti:sapphire lasers and successfully operated them. A 100 W, 10 kHz Nd:YAG pump laser has been purchased by the ORNL Physics Division and a order for a Ti:sapphire lasers has been placed.

    On-line measurements at the On-Line Test Facility (OLTF) during the last few months have included, alpha-particle beams on a liquid Ge target for the production of neutron deficient Se beams, proton-induced fission in a thorium oxide target, release of Re beams from a tungsten oxide target, and measurements of yields of fission fragments from three different UC targets that varied in density and porosity. Analysis of these data sets is continuing and the results will be reported later.



    RA2. Accelerator System Status

    ORIC Operations and Development (B. A. Tatum)

    ORIC provided proton, deuteron, and alpha beams to the RIB injector through the end of September for the production of radioactive ion beams required by the experimental program. In late October and early December, ORIC was utilized for commissioning of the new High Power Target Laboratory. Details of the project and commissioning are presented in a separate article.

    The latter part of the year was particularly challenging due to considerable problems with the ORIC rf system. Due to a chain reaction of problems, the system would not operate stably at the 19 MHz frequency required for proton acceleration. With some careful nurturing, we were successful in operating around 12 MHz which is required for both deuteron and alpha acceleration. The difficulties centered on the failure of major components in the rf tuning circuit. Four glass-envelope tunable vacuum capacitors are utilized in the plate circuit of the power amplifier tube. These fragile plate capacitors began to fail with age as some have in the past. Unfortunately, our spare units all showed signs of vacuum degradation due to deteriorated bellows seals. Most of these had never been used but deteriorated on the shelf after many years.

    We have recently purchased and installed a set of modern tunable capacitors with ceramic envelopes. Testing of the system with these units has been quite successful, and the rf system appears to be running reliably again following an extended maintenance shutdown.

    RIB Injector Operations and Development (P.E. Mueller)

    During the period from 1 July 2005 to 1 October 2005, the 25 MV Tandem Electrostatic Accelerator delivered beams of

    • 2.7 Mpps [18.7 MV 7+/9+ terminal foil/post foil stripped] 150 MeV pure 18F,

    • 240 kpps [4.58 MV 2+ terminal gas stripped] 14.0 MeV 20:1 18F, and

    • 100 kpps [5.57 MV 2+ terminal gas stripped] 17.0 MeV 23:1 18F to the astrophysics endstation in Beam Line 21, and

    • 2 kpps [22.4 MV 14+/25+ terminal foil/high energy foil stripped] 500 MeV 0.36 134Sn,

    • 20 kpps [22.14 MV 14+/25+ terminal foil/high energy foil stripped] 489 MeV 0.9 132Sn, and

    • 17 kpps [21.90 MV 13+/24+ terminal foil/high energy foil stripped] 465 MeV 0.9 132Sn to the time-of-flight endstation in Beam Line 23.

    The 18F beams were produced via the 16O(4He,pn) 18F reaction by bombarding a fibrous HfO2 target coupled to a Kinetic Ejection Negative Ion Source (KENIS) with 2-3 uA of 85-MeV 4He from the Oak Ridge Isochronous Cyclotron (ORIC).

    The tin beams were produced via deuteron induced fission of 238U by bombarding a uranium carbide coating on a reticulated vitreous carbon fiber target coupled to an Electron Beam Plasma (positive) Ion Source (EBPIS) with 5-6 uA of 43 MeV 2H and passing the positive tin sulfide beam through the recirculating cesium jet charge exchange cell and selecting the negative tin beam resulting from molecular breakup.

    Tandem Development (M. Meigs)

    The Tandem Accelerator was operated for almost 3000 hours since the last report.   The machine ran at terminal potentials of 1.52 to 24.34 MV and the stable beams 1H, 4He, 16O, 17O, 40Ca, 54Fe, 58Ni, 80Se, 88Sr, 90Zr, 124Sn, 124Te, 126Te, 130Te and 197Au were provided.  This is the first time He has been accelerated at our facility.  Radioactive beams of 18F, 132Sn, 134Sn, and 134Te accounted for 559 hours of beam on target.  Only two tank openings were necessary during this period with one being a scheduled maintenance opening.  The other tank opening was a quick one-day to replace a failed power supply on the column base quadrupole.  The regular maintenance period allowed replacing bad bearings in the power shafts, replacement of foils in the terminal, refurbishing an ion pump in the terminal, and other minor maintenance and cleaning.  About 195 hours were spent on conditioning with the goal of operation up to 24.5 MV for the neutron-rich program.




    RA3. Experimental Equipment - A New Experimental Setup Optimized for (d,p-gamma) Reactions
    (M. Johnson, Spokesperson)

    A new setup for proton-gamma coincidence measurements in (d,p) reactions has been constructed and tested at HRIBF. One motivation for proton-gamma measurements is to extract neutron capture information for astrophysically important nuclei such as neutron-rich species which may lie on the so-called r-process path. The reactions are performed at the HRIBF by accelerating a nuclear species of interest and impinging the beam onto a deuterated polyethylene target (CD2). The energy loss of these heavy ions in the target and the unfavorable kinematics results in a practical limit to the achievable energy resolution by detection of charged particles alone. By adding high-resolution gamma-ray detectors, the energy resolution can be improved by almost an order of magnitude.

    The (d,p-gamma) setup is pictured in Fig. RA3-1, mounted to the CARDS array. The overall length of the (d,p-gamma) setup is about 3 feet. Additional space is needed on both ends to access the Si detectors within the chamber (discussed below). In all, 5 feet is required for the (d,p-gamma) assembly and accessibilty. Once the Si detectors have been assembled, the access space can be filled using KF-40 pipe for the upstream section and 4" pipe on the downstream section.


    Figure RA3-1: Photograph of the (d,p-gamma) setup looking upstream. Seen here is the CARDS array, four Ge clovers, and the vacuum chamber (center of clovers), which house the Si detectors and targets. Preamp modules for the Si telescopes described in the text are mounted (not shown here) on the aft section of the chamber (nearest the photographer). See text for more details.

    The (d,p-gamma) setup was designed to use four Ge clovers. In the geometry shown in Fig. RA3-1, the absolute gamma-ray efficiency was measured to be 6.9% at 1.33 MeV. The fronts face of the clovers are approximately 6 cm from the target. The central axis of the clover is perpendicular to the beam axis and is in-line with the target plane. With the use of high-resolution Ge detectors and the close geometry, the largest contribution to the energy resolution comes from Doppler broadening. The Doppler broadening was measured to be 32 keV (FWHM) in each crystal of the clover for recoils of 4-MeV/u A~90 beams onto a CD2 target.

    Protons are detected in a number of Si detectors, mounted within the vacuum chamber. Surrounding the target location is a set of four Si telescopes, configured in a box-like geometry as shown in Fig. RA3-2. The thin transmission detectors closest to the target are 5x5 cm position-sensitive strip detectors. Thick Si 5x5 cm pad detectors back up the thin detectors. The telescope array covers angles from 90 degrees to 135 degrees. The angular resolution is about 2 degrees for this geometry. The preamps are mounted on an additional chamber piece and are attached downstream of the central part of the chamber (visible in Fig. RA3-1).


    Figure RA3-2: Photograph of the target location looking downstream. Seen here is a CD2 target extended into the beam axis. Three other target manipulators are retracted. The bottom manipulator holds a phosphor for beam tuning. Surrounding the target are four Si telescopes. The Ge clovers are on the outside of the chamber walls adjacent to the Si telescopes. Short cables (seen) connect the Si telescopes to the feedthrus to the preamp modules downstream.

    For more backward angles, SIDAR is used (Fig.RA3-3a), covering the angular range covered by SIDAR is from 142 degrees to 165 degrees. It is mounted on a flange and slid into the vacuum chamber on two precision slide-rails (Fig. RA3-3b). The preamps for SIDAR are mounted on the flange on which it sits. The solid angle coverage of the entire Si array is estimated at 28% of 4-pi. Also, the SIDAR flange has a viewport which is in-line with the target location, and can be used to tune the beam using a phosphor (see Fig. RA3-2).

    Figure RA3-3a: Photograph of SIDAR mounted on the flange. The cables connect the detector wedges to feedthrus to preamp modules which are attached (not shown) on the other side of the flange. In this photograph, the upstream direction is into the plane of the page.

    Figure RA3-3b: Photograph of SIDAR being inserted into the vacuum chamber. The feedthrus for the preamp modules can be seen on the left side (exterior) of the flange. Also seen is the viewport (on top of the beamline) for beam tuning. Atop the vacuum chamber is a gate valve which can be connected to a cryo-pump. (No cryo-pump was attached here for the feasibility test discussed in the text.)

    Recently, a test run (RIB-131) was performed in which different stable beams were accelerated by the tandem accelerator to test the performance of the (d,p-gamma) setup described above. Fig RA3-4 shows a preliminary plot of excitation energy (derived from proton measurements) versus gamma-ray energy for a run with a 90Zr beam onto a 1000 microgram/cm2 CD2 target. One of the benefits of proton-gamma measurements is demonstrated by this plot: for each gamma-ray transition it can be seen at which excitation energy the nucleus was formed. Also, a number of directly populated states are visible, clearly separated in gamma-ray energy, which are not resolved in proton energy alone.


    Figure RA3-4: Preliminary results taken from RIB-131. The x-axis is gamma-ray energy (spectrum dispersion is 8 keV/channel), the y-axis is excitation energy extracted from proton energy deposited in the Si array and lab angle (spectrum dispersion is 20 keV/channel). The groupings at x~150, 255, and 325 are proton-gamma coincidences for populating the 1.21-, 2.04- and 2.56-MeV levels. The elongation along the y-axis is due to the comparatively poor resolution of the protons.

    Currently, the test runs are being analyzed to determine the full capabilities of the (d,p-gamma) setup. Plans are being made to make new proposals for (d,p-gamma) measurements.




    RA4. HRIBF Users Group News
    (C. J. Gross)

    The HRIBF Users Executive Committee met on December 8, 2006 and elected Robert Grzywacz (University of Tennessee/ORNL) as this year's chair. We thank Uwe Greife (Colorado School of Mines) for his service this past year. During this meeting, the committee discussed the HRIBF strategic plan which shows the integration of science with the facility and instrumentation upgrades into a timeline. This plan, requested by DOE, illustrates how the goals of HRIBF match the goals of DOE.

    Letters from the outgoing and new HRIBF Users Executive Committee chairs can be viewed online.

    The next users workshop will be on Nuclear Astrophysics and is scheduled for October 23-24, 2006.




    RA5. Suggestions Welcome for New Beam Development

    HRIBF welcomes suggestions for future radioactive beam development. Such suggestions may take the form of a Letter of Intent or an e-mail to the Liaison Officer at liaison@mail.phy.ornl.gov. In any case, a brief description of the physics to be addressed with the proposed beam should be included. Of course, any ideas on specific target material, production rates, and/or the chemistry involved are also welcome but not necessary. In many cases, we should have some idea of the scope of the problems involved.

    Beam suggestions should be within the relevant facility parameters/capabilities listed below.

    • The tandem accelerates negative ions only.
    • Positive ions may be charge-exchanged or used directly off the platform (E < 40 keV).
    • ORIC presently produces up to 52-MeV of 1H (12 uA); 49-MeV 2H (12 uA); 120-MeV 3He (not yet attempted, costly); 100-MeV 4He (3 uA). Higher currents may be possible.
    • Typical reactions required to produce more than 106 ions per second are n, 2n, pn, and alpha-n fusion-evaporation reaction channels and beam-induced fission products. More exotic reactions are possible if extremely low beam currents are all that is needed.
    • Species release is strongly related to the chemistry between the target material and the beam species. It is best when the properties are different and the target is refractory. Thin, robust targets (fibrous, liquid metals, a few grams per square centimeter) must be able to withstand 1500 degrees Celsius or more.
    • Minimum half-life is seconds unless chemistry is very favorable.
    • Very long-lived species (T1/2 > 1 h) are probably best done in batchmode, i.e., radioactive species are produced with ORIC beams and then transported to the ion source where beams are produced via sputtering. Sputter rates of the species and target substrates are important.
    • Isobaric separation is possible for light beams (fully stripped ions), while isobaric enhancement may be possible for heavy beams.
    • Beware of long-lived daughters or contaminant reaction channels.




    RA6. HRIBF Experiments, July through December 2005
    (M. R. Lay)

    Date Exp. No. Spokesperson Title of Experiment
    7/1 RIB-037 Meigs,Juras/ORNL Tandem development
    7/1 RIB-145 Brune/Ohio University Proton-transfer study of unbound 19Ne states via 22H(18F,α+15O)n
    7/2-5 Scheduled shutdown
    7/6 Unscheduled maintenance
    7/7-10 RIB-145 Brune/Ohio University Proton-transfer study of unbound 19Ne states via 22H(18F,α+15O)n
    7/11-15 RIB-037 Meigs,Juras/ORNL Tandem development
    7/15-16 RIB-145 Brune/Ohio University Proton-transfer study of unbound 19Ne states via 22H(18F,α+15O)n
    7/16-18 RIB-014 Stracener/ORNL Target ion source development (As & F)
    7/19/5 RIB-141 Kronenberg/ORAU Off-line RIB development at the OLTF
    7/19-22 RIB-145 Brune/Ohio University Proton-transfer study of unbound 19Ne states via 22H(18F,α+15O)n
    7/23 RIB-120 Liang/ORNL Fusion of 132Sn and 64Ni above the Coulomb barrier
    7/24-25 RIB-013 Blackmon/ORNL DRS commissioning
    7/25-26 Scheduled shutdown
    7/26 RIB-099 Bardayan/ORNL Measurement of the 18F(p,alpha)15O excitation function
    7/27 RIB-037 Meigs,Juras/ORNL Tandem development
    7/27-28 RIB-099 Bardayan/ORNL Measurement of the 18F(p,alpha)15O excitation function
    7/28-29 RIB-039 Mueller/ORNL High voltage injector development
    7/29-8/2 RIB-099 Bardayan/ORNL Measurement of the 18F(p,alpha)15O excitation function
    8/3 RIB-037 Meigs,Juras/ORNL Tandem development
    8/3-4 RIB-099 Bardayan/ORNL Measurement of the 18F(p,alpha)15O excitation function
    8/5 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    8/6-7 Scheduled shutdown
    8/8-10 Scheduled maintenance
    8/10 RIB-013 Blackmon/ORNL DRS commissioning
    8/11 RIB-037 Meigs,Juras/ORNL Tandem development
    8/12-16 RIB-131 Johnson/Rutgers University (d,pγ) measurements at HRIBF
    8/16 RIB-037 Meigs,Juras/ORNL Tandem development
    8/17-18 RIB-131 Johnson/Rutgers University (d,pγ) measurements at HRIBF
    8/19-20 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    8/20 RIB-039 Mueller/ORNL High voltage injector development
    8/20-26 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    8/27 Scheduled shutdown
    8/29 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    8/29-9/1 RIB-037 Meigs,Juras/ORNL Tandem development
    9/1 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    9/1-2 RIB-037 Meigs,Juras/ORNL Tandem development
    9/2 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    9/3-5 Scheduled shutdown
    9/6-7 Unscheduled maintenance
    9/7-8 RIB-013 Blackmon/ORNL DRS commissioning
    9/9/5 RIB-141 Kronenberg/ORAU Off-line RIB development at the OLTF
    9/9-10 RIB-037 Meigs,Juras/ORNL Tandem development
    9/10-14 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    9/14-16 RIB-012 Liang/ORNL As + Ti Sub-barrier fusion
    9/16-19 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    9/19-21 Unscheduled maintenance
    9/22-26 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    9/26-27 Unscheduled maintenance
    9/28-10/1 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    10/2 Scheduled shutdown
    10/3-6 RIB-000 Gross/ORNL RMS development
    10/6-7 RIB-013 Blackmon/ORNL DRS commissioning
    10/8-9 Scheduled shutdown
    10/10-11 RIB-141 Kronenberg/ORAU Off-line RIB development at the OLTF
    10/12-14 RIB-013 Blackmon/ORNL DRS commissioning
    10/15-16 Scheduled shutdown
    10/17-19 RIB-150 Rykaczewski/ORNL Fine structure in proton emission and isospin mixing to the N ∼ Z nuclei
    10/19-21 RIB-000 Gross/ORNL RMS development
    10/22-23 Scheduled shutdown
    10/24-26 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    10/26-27 RIB-014 Stracener/ORNL Target ion source development (As & F)
    10/27-28 RIB-013 Blackmon/ORNL DRS commissioning
    10/29-30 Scheduled shutdown
    10/31-11/1 RIB-101 Page/University of Liverpool Search for new alpha emitters above 100Sn
    11/1-2 Unscheduled maintenance
    11/2-4 RIB-101 Page/University of Liverpool Search for new alpha emitters above 100Sn
    11/5-6 Scheduled shutdown
    11/7-8 RIB-014 Stracener/ORNL Target ion source development (As & F)
    11/8-12 RIB-101 Page/University of Liverpool Search for new alpha emitters above 100Sn
    11/13-16 RIB-035 Stracener/ORNL Target ion source development (actinide targets)
    11/16-21 RIB-045 Hausladen/ORNL Identification of the decay the Tz=+1/2 nucleus 113Ba
    11/21-23 RIB-013 Blackmon/ORNL DRS commissioning
    11/24-27 Scheduled shutdown
    11/28 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
    11/29 RIB-013 Blackmon/ORNL DRS commissioning
    11/30-12/2 RIB-035 Stracener/ORNL Target ion source development (actinide targets)
    12/3-31 Scheduled shutdown and maintenance


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