|Edition 10, No. 3||Summer Quarter 2002||Price: FREE|
- 1. HRIBF Update and Near-Term Schedule
- 2. Recent HRIBF Research - The 18F(d,p)19F Reaction at 6 MeV/u
- 3. Recent HRIBF Research - Fine Structure in Proton Emission from 141Ho
- 4. Recent HRIBF Research - Thoretical Astrophysics Research and HRIBF Science
- 5. First RIA Summer School on Exotic Beam Physics
- 6. PAC-8 Meeting Delayed
- 7. Dr. Glenn R. Young Became the New Director of the Physics Division
- RA1 - RIB Development
- RA2 - Accelerator Systems Status
- RA3 - Experimental Equipment - New Storage Media for Data Acquisition
- RA4 - User Group News
- Workshop on Transfer Reactions using RIBs at HRIBF
- Executive Committee Election to be Held in September and Annual Users Group Meeting at October's DNP Meeting
- RA5 - Suggestions Welcome for New Beam Development
- RA6- HRIBF Experiments, May - July 2002
Editors: C.-H. Yu, C. J. Gross, and W. Nazarewicz
Feature contributors: D. Bardayan, J. R. Beene,
C. J. Gross, R.L. Kozub, M.S. Smith, K. Rykaczewski
Regular contributors: J.C. Blackmon, C.J. Gross, M. R. Lay, M. J. Meigs, P. E. Mueller, D. W. Stracener, B. A. Tatum, R.L. Varner
Our trouble-prone and often interrupted fluorine RIB campaign for 2002 is nearing completion. In spite of the difficulties, this campaign has produced some notable results, including the first use of the DRS with a radioactive beam. We will soon shut down the RIB injector for the changeover to the target and ion source system for production of neutron-rich RIBs. Part of the tandem column structure was let up to air to effect repairs since the last time the tandem was operated at high voltage. It will therefore be necessary to devote time (~ one week) to conditioning before the terminal potentials required for the neutron-rich experiments can be achieved. Following this conditioning and stable-beam running required to prepare and test experimental setups, we will begin our campaign of neutron-rich RIB experiments, with emphasis on experiments with pure tin beams.
After the neutron-rich campaign, a major accelerator maintenance period is scheduled (~ seven weeks) in November and December. The work to be done includes refurbishing all ion pumps in the tandem, installing the new gas stripper, and moving the foil stripper to a position downstream (in the sense of beam travel) of the gas stripper.
On June 13 and 14, 2002, a DOE review of HRIBF operations was carried out. The outside review panel consisted of Derek Lowenstein, Brookhaven National Laboratory; Paul Schmor, TRIUMF; Bradley Sherrill, NSCL; Christoph Tschalaer, MIT-BATES Linac; Roy Whitney, Jefferson Laboratory. DOE Nuclear Physics program office staff who attended included Dennis Kovar, Steve Steadman, Jehanne Simon-Gillo, and Gene Henry. We have not yet received the final written report from the panel, so it is not appropriate to comment in much detail on the content of the report. In general terms, we can expect both favorable comments on our accomplishments and suggestions for improving the operation of the facility. The report is likely to suggest changes in the way the ORNL low-energy nuclear physics program as a whole is managed in order to improve the integration of facility operations with research and the user program, and to improve our ability to develop a coherent long-range plan. In addition the report will recommend the creation of additional advisory panels to supplement the existing HRIBF Program Advisory Committee (PAC). A more detailed discussion of the findings of the review panel will be provided after the official report is available.
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Understanding the synthesis of nuclei in nova explosions depends critically on knowing the properties of the 18F(p,gamma)19Ne and 18F(p,alpha)15O reactions at temperatures ~1-4 x 108K. Further, since 18F is a long-lived observable by-product of novae, the abundance of 18F may provide insights about nova mechanisms. It is thus important to know the degree to which the (p,gamma) and (p,alpha) reactions destroy 18F in such explosions. The levels of interest are low-lying 19Ne resonances just above the 18F+p threshold (6.411 MeV excitation energy), six of which seem to be missing based on what is known about the 19F mirror spectrum [Ut98, Bu98]. Some of the 19Ne levels relevant to nova temperatures are inaccessible through traditional resonance scattering experiments, and difficult to observe via proton transfer reactions in reverse kinematics using a radioactive ion beam. Thus, in order to provide further insights about these resonances, the inverse (d,p) reaction has been used at the HRIBF to selectively populate neutron single-particle states in the corresponding region of the 19F mirror spectrum.
A 160 ug/cm2-thick [CD2]n target of 98% enrichment was bombarded with an isotopically pure, 108-MeV 18F+9 beam. Using a silicon strip detector array (SIDAR) [Ba01] of ~500 um thickness, light charged particles were detected in the laboratory angular range of ~118°-157°, corresponding to "forward" center-of-mass angles in the range ~8°-27°. The beam energy was selected to be high enough for direct reaction models, yet low enough to allow all the protons to be stopped in the SIDAR. A silicon strip detector at the focal plane of the Daresbury Recoil Separator (DRS) was used to detect particle-stable recoils having A=19 in coincidence with the SIDAR. A strip (angle) vs energy plot from one of the SIDAR detectors in coincidence with the focal plane is shown in Fig. 2-1. Other recoils, from higher, alpha-decaying states in 19F, were detected just downstream from the target with an annular strip detector. The on-line data reveal seven proton groups that can be identified with the 2H(18F,p)19F reaction, corresponding to approximate excitation energies in 19F of 0, 1.5, 4.4, 5.1, 6.5, 7.3, and 8.1 MeV. Preliminary analysis shows no evidence (S<0.03) for the 5/2+ state at 6.838 MeV excitation, which may be the mirror of the 287-keV proton resonance in 19Ne, a potentially important resonance at nova temperatures. This and other astrophysical and nuclear structure issues will be examined more closely in off-line analysis.
D. W. Bardayan, et al., Phys. Rev. C 63, 065802 (2001), and
[Ut98]S. Utku, et al., Phys. Rev. C 57, 2731 (1998), and references therein.
[Bu98] Yousaf Butt, et al., Phys. Rev. C58, R10 (1998).
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The studies on the 140mDy and 141gsHo decays lead to the interpretation of the observed 0.97-MeV proton line as the 0.7% transition to the 2+ state in the daughter nucleus 140Dy, with over 99% branching for 1.17-MeV protons populating the 0+ ground state. The weak branching of 0.7% translates into a cross section for the fine structure line of about 2 nanobarns.
Following Raman et al. , we can derive quadrupole deformation parameter beta-2=0.23-0.24 for 140Dy from the measured 2+ state energy of 202 keV. This result is somewhat smaller than the anticipated beta-2 values of 0.27-0.28 [9-11]. However, the beta-2 value of 0.23-0.24 is close to beta-2=0.25(4) derived for 141gs,mHo  from the observed level scheme. This constitutes first experimental evidence that there is no dramatic shape change during the proton emission process from 141Ho parent to the 140Dy daughter. The latter is a commonly used assumption during theoretical analyses of proton radioactivity.
Recent calculations [12,13] indicate that the main part (about 80%) of the 141gsHo wave function is composed of the proton h11/2 orbital, but the observed decay pattern is governed by a few percent admixture of the proton f7/2 component. However, the fine structure branching ratio is overestimated by a factor of three, and the total decay probability is underestimated by a factor of ten. Very likely, this disagreement is caused by the more complex shape, in comparison to the considered [beta-2=0.24,beta-4] deformation space. There are preliminary indications that calculations done with a triaxial shape of the tunneling potential improve greatly the agreement between the observed and theoretical decay rates for 141gsHo . This is consistent with the earlier conclusion of Ref.  based on the signature splitting in the 7/2 band.
 K. Rykaczewski, et al.,
Nucl. Phys. A682, 270c (2001).
 M. Karny, et al., submitted to Phys. Rev. Lett.
 D. Seweryniak, et al., Phys. Rev. Lett. 86, 1458-1461 (2001).
 W. Krolas, et al., Phys. Rev. C65, 031303R (2002).
 D. Shapira, et al., Nucl. Instrum. Methods. Phys. Res. A454, 409 (2000).
 B. Hubbard-Nelson, et al., Nucl. Instrum. Methods. Phys. Res. A422, 411 (1999).
 R.K. Grzywacz, Nucl. Instrum. Methods. Phys. Res. , in press.
 S. Raman, et al., At. Data Nucl. Data Tables, 78, 1 (2001).
 K. Rykaczewski, et al., Phys. Rev. C60, 011301 (1999).
 P. Moller, et al., At. Data Nucl. Data Tables, 59, 185 (1995).
 F.R. Xu, et al., Phys. Rev. C59, 731 (1999).
 A.T. Kruppa, et al., Phys. Rev. Lett. 84, 4549 (2000).
B. Barmore, et al., Phys. Rev. C62, 054315 (2000).
 A.T. Kruppa, and W. Nazarewicz, private communication (2002).
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Another thrust in astrophysics theory is to understand the synthesis of nuclei and energy generation occurring in nova explosions. These are violent thermonuclear outbursts on the surface of white dwarf stars which rapidly release enormous amounts of energy while forming elements up to Ca and beyond. Uncertainties in the rates of reactions on unstable nuclei which drive these explosions (in the Hot CNO cycle and rp-process) severely limit the ability of models to predict synthesized abundances. This is an especially serious limitation for long-lived radionuclides (e.g., 18F, 22Na, 26Al ... ) whose gamma-ray emission is the target of sophisticated satellite observatories (e.g., INTEGRAL). Some of the first precision measurements of reactions important for nova nucleosynthesis are being made with radioactive fluorine beams at HRIBF. Reaction rates based on these measurements are, in some cases, one to two orders of magnitude different than previous determinations. To ascertain the impact of these new rates on nova model predictions, a nucleosynthesis code (Hix et al. ) has been used to integrate the system of coupled ordinary differential equations (a "network") governing the temporal evolution of the nuclear abundances from the initiation of the outburst to its conclusion. We carried out separate nuclear reaction network calculations with the full complement of nuclei and reactions for many spherically symmetric shells or "zones" within the white dwarf envelope. These zones, which have different hydrodynamic histories , are ejected after the outburst. Our code uses the most current nuclear datasets optimized for nuclear astrophysics , and our simulation work is done is close collaboration with ORNL nuclear data efforts to improve these datasets.
Determining the astrophysical impact of a new reaction rate measurement involves comparing nucleosynthesis predictions using reaction rates based on HRIBF measurements to those using older reaction rates. The reactions considered to date are 17F(p,gamma)18Ne, 18F(p,alpha)15O, 18F(p,gamma)19Ne, 14O(alpha,p)17F, and 14O(alpha,2p)16O. We find that, for example, simulations using the 17F(p,gamma)18Ne reaction rate based on our 17F(p,p)17F measurement  predict that the produced abundances of some nuclides such as 17O are a factor of 4 times larger than calculations using previous rates. In the hottest zones of the explosions, the production is up to a factor of 15000 larger than previously estimated. This illustrates the impact that a detailed nuclear physics measurement can have on our understanding of cosmic phenomena. We are also using this approach to determine the importance of possible future measurements with RIBs at HRIBF.
Most predictions of the abundances synthesized in stellar explosions are given without uncertainties, making it difficult to compare model predictions to the new, incredibly detailed observations by the Hubble or Chandra observatories. We have developed a Monte Carlo technique  that enables, for the first time, the assignment of statistically robust uncertainties to explosion abundance predictions considering the uncertainty of all the input nuclear physics. This technique also enables us to determine the correlations between all synthesized abundances and all reaction rates, and therefore to make priority lists for measurements at radioactive beam facilities. While we are currently using this approach for novae, it is applicable for simulations of a wide variety of astrophysical phenomena.
These calculations are all done with the hydrodynamics decoupled from the changes in nuclear composition. However, the hydrodynamic histories at different locations within the envelope are intimately coupled to the nuclear burning because (i) the nuclear reactions generate the energy driving the outburst, and (ii) the reaction rate between any two nuclear species increases linearly with density and exponentially with temperature. A fully consistent description of an explosion therefore involves coupling a large reaction network to a multidimensional hydrodynamics calculation of the outburst. We have begun a NASA-funded project in collaboration with Arizona State University to perform this coupling using a piecewise parabolic method (PPM) hydrodynamics code coupled to a full nuclear reaction rate network.
Finally, we have recently made our first nucleosynthesis calculations for X-ray bursts, thermonuclear flashes on the surfaces of neutron stars. We are currently examining the influence of new 14O(alpha,p)17F, and 14O(alpha,2p)16O reaction rates (from HRIBF measurements) on the energy generation and nucleosynthesis in these violent explosions. This is another example of the valuable collaborative efforts between theoretical astrophysics and laboratory nuclear physics at HRIBF that is improving our understanding of the cosmos.
 M.S. Smith, K.E. Rehm, Ann. Rev. Nucl. Part. Sci.
51, 91 (2001)
 W.R. Hix and F.-K. Thielemann, J. Comput. Appl. Math. 109, 321 (1999)
 M. Politano et al., Astrophys. J. 448, 807 (1995); S. Starrfield, priv. comm. (2000)
 D.W. Bardayan et al., Phys. Rev. Lett. 83, 45 (1999)
 W.R. Hix et al., in Cosmic Explosions, eds. S. Holt & W.W. Zhang (Melville: AIP) 383; M. S. Smith et al., Proc. Int. Conf. on Classical Nova Explosions, Barcelona (New York: AIP), in press (2002)
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The first RIA Summer School on Exotic Beam Physics was held August 12-17, 2002, at the ORNL Holifield Radioactive Ion Beam Facility. An overwhelming response to the Summer School was received demonstrating the great interest in RIA physics. Forty-two students representing 22 institutions attended the Summer School. The Summer School was a huge success with a great deal of positive feedback being received from those who participated.
The mornings of the summer school were devoted to lectures. The lecture topics and presenters were:
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The meeting of the eighth Program Advisory Commitee (PAC-8) has been delayed and will be held on Nov. 21-22 in Oak Ridge. A review of the proposals so far received indicated that only one proposal using neutron-rich RIBs could be scheduled prior to the November-December shutdown. This proposal will be handled electronically. We apologize for any inconvenience the delay may have caused. However, as a result of the delay, we have decided to accept additional proposals for PAC-8! Send proposals as email attachments in either pdf (preferred) or postscript format by Friday, October 18, 2002, to email@example.com. Complete instructions(including submission forms) as well as additional information may be found on our website at http://www.phy.ornl.gov/hribf/users/ and http://www.phy.ornl.gov/hribf/usersgroup/news/.
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Effective July 1, 2002, Dr. Glenn R. Young became the new Director of the Physics Division at Oak Ridge National Laboratory. Glenn succeeded Dr. Fred E. Bertrand, Jr., who retired following 33 years of distinguished service to the Physics Division and Oak Ridge National Laboratory.
Glenn Young has been the Group Leader of the Experimental Nuclear Physics Group in the Physics Division and Deputy Spokesman of the PHENIX experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. He joined the Physics Division as a Eugene P. Wigner Fellow in 1978 following completion of a Chaim Weizmann Fellowship at MIT. He is a 1973 graduate of the University of Tennessee, Knoxville, and received his Ph.D. in Nuclear Physics from MIT in 1977. Glenn has published more than 200 papers in heavy ion nuclear physics and has given more than 30 invited presentations at national and international conferences. He is a Fellow of the American Physical Society and has served on DOE's Nuclear Science Advisory Committee (NSAC) and numerous NSAC subcommittees, on the American Physical Society's Division of Nuclear Physics Executive Committee, and on numerous program and technical advisory committees for DOE and NSF.
Fred Bertrand received his Ph.D. in Physics in 1968 from Louisiana State University. He joined the research staff in the ORNL Physics Division in 1970 following the completion of research associate appointments at ORNL and the University of Southern California. Fred has published more than 200 papers in nuclear structure and giant resonances. He served the Physics Division as a Group Leader, Section Head, and Associate Division Director prior to being named Director in 1995. As Director, Fred oversaw the development of the Holifield Radioactive Ion Beam Facility into one of the world's leading low-energy nuclear physics research facilities. During his tenure, four members of the research staff in the Physics Division were awarded the Presidential Early Career Awards. Fred is a Fellow of the American Physical Society and has served on numerous DOE and NSF panels.
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On-line tests with 40-MeV proton and deuteron beams will be conducted soon to test this material for the release of radioactive isotopes produced in (p,alpha), (d,alpha) and (d,n) reactions. The more interesting isotopes that can be produced in this target are 33Cl and 29,30P with cross sections that peak at a few hundred millibarns for incident beam energies between 5 and 20 MeV. The on-line tests will measure the yields of the elemental beams of the nuclei mentioned above and will also include a search for various molecular beams.
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The coax power leads that failed were of a newer, more flexible design, and had been installed in March when the coax insert had to be replaced due to a water leak. The power leads are an assembly consisting of a main copper conductor which is surrounded by a water-cooled bronze bellows. An external bronze overbraid around the bellows is employed to prevent hyper-extension and associated water leaks. It is desirable to make these leads as flexible as possible due to movement of the coaxial channel during beam tuning and to facilitate easier maintenance. The original leads utilized a piece of coarsely-stranded 4/0 cable for the center conductor. This was changed to a highly-stranded piece of 2/0 cable in the new design, providing maximum flexibility. The 2/0 cable is more than adequate to carry the required current since it is water cooled. However, the smaller center conductor caused enough of an increase in current through the non-water-cooled overbraid to exceed the temperature rating of the electrical insulation surrounding it, thus causing the failure. Consequently, leads fabricated with 4/0 cable have been reinstalled.
An autopsy of the HfO2 target/kinetic ejection negative-ion source that was used for our very successful 17,18F run last year, revealed that a stainless steel target heater lug had melted completely through. An autopsy of the first target/ion source used this year revealed that the same heater lug had also lost significant amounts of metal. While no heater lug damage was observed during the autopsy of the second target/ion source used this year, there was a light grey coating throughout the inside of the vacuum enclosure consistent with stainless steel deposition. In addition, blackening of the white boron nitride ceramic insulators for the surface ionization cone and the repelling grid seen during the autopsies of the first two target/ion sources used this year suggests cesium compound buildup as the cause of their premature failure.
As a result of these observations, the HfO2 target/kinetic ejection negative-ion source that is presently in use and that produced the beams reported above has been modified. The stainless steel target heater lugs have been replaced with niobium lugs. The standard stainless steel nuts and washers that fastened the target heater lugs to the 3/4" threaded copper rod vacuum feedthroughs have been replaced with 1" long, 1 3/8" diameter copper nuts. We did not load cesium during the target/ion source testing process until just before the actual installation on the high-voltage platform in C111S.
We removed the failed beam position monitors at the object and image of the first stage magnetic mass separator on the high voltage platform in C111S. We also replaced the manually operated rotational image slit system with a more robust remotely operated air actuator system that inserts either a 2 mm by 1 cm slit or a 1.2 cm by 2 cm hole.
The cesium oven, external line, and internal line heaters have been interlocked to the target/ion source cooling water flow switches. The cesium oven heater has also been interlocked to the transfer tube power supply (>100 amps required) in order to reduce cesium flow into a cooling ion source after a fault trips the power supply.
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The HRIBF data acquisition systems are moving to new storage media for experimental data. Event data will be saved onto the local hard disk of the acquisition computer. Periodically the user will transfer the data from the hard disk to DVD disks for permanent recording. DVD disks offer reliable random access storage. Writing data to DVD is at about the same speed as writing to Exabyte tapes, and the DVD we use, DVD-RW, is about the same size as one Exabyte tape. The advantage of this scheme is that DVD drives are more widely available than Exabyte tape drives, the Exabyte drives we use are nearly obsolete, and disk files are somewhat easier to control and manipulate than the tape files.
The DVDs will be written using the UDF file system, which is the industry standard file system for DVDs. Files on a DVD using the UDF file system are readable on most modern operating systems, including recent versions of Windows and MacOS, and on many of the currently available DVD drives. The DVDs are written with a DVD-RW drive on write-once DVD media.
The DVDs are created via a Graphical User Interface (GUI). The process involves three steps:
For more detailed information on this new data recording option, email firstname.lastname@example.org.
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About 60 scientists participated in a workshop on transfer reactions at the HRIBF on June 21 and 22. Organized by Ray Kozub, Jolie Cizewski, Jeff Blackmon and Felix Liang, the transfer workshop served the purpose of bringing together those interested in doing transfer-reaction experiments at HRIBF, acquainting them with HRIBF capabilities for such experiments, and addressing issues related to acquiring and interpreting transfer-reaction data. In the near future, a number of transfer-reaction experiments are expected to be carried out using radioactive ion beams at HRIBF.
The scientific program of the workshop was opened by John Schiffer, who presented an overview of transfer reactions studies and the nuclear structure that they can reveal. Wilton Catford then discussed the challenges encountered in measuring these reactions with radioactive ion beams. A more detailed analysis of both the experimental and theoretical aspects of transfer reactions was guided by 15 presentations that followed. Much discussion centered on novel experimental techniques directed towards addressing the particular problems presented by measurements with radioactive ion beams. The workshop was closed with a working session led by Ray Kozub. Most of the presentations from the workshop (and the conference photograph) can be downloaded from the conference website.
It is time to hold the annual election for the Users Executive Committee.
A nomination committee has selected four nominees:
|Uwe Greife||Colorado School of Mines|
|Daryl Hartley||United States Naval Academy|
We will hold the annual HRIBF Users Meeting at this year's DNP Meeting in East Lansing, Michigan, October 9-12. The meeting will be held jointly this year along with the users groups of the 88-Inch, ATLAS, NSCL, GAMMASPHERE, GRETA, and RIA. The meeting will be held on Thursday, October 10. The agenda of the meeting has not been finalized.
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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 email@example.com. 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.
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Schedules may be found by choosing the following links: May, June, and July.
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|Witek Nazarewicz||Carl J. Gross||Chang-Hong Yu|
|Deputy Director for Science||Scientific Liaison||Newsletter Editor|
|Mail Stop 6368||Mail Stop 6371||Mail Stop 6371|
|Holifield Radioactive Ion Beam Facility|
|Oak Ridge National Laboratory|
|Oak Ridge, Tennessee 37831 USA|