HRIBF Newsletter, Edition 13, No. 2, Aug. 2005

   


Feature Articles

Regular Articles



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

Fiscal 2005 has been a challenging time for everybody working at HRIBF, but especially for our engineering staff who have borne the brunt of the intense effort required to finish the HPTL project on schedule while continuing to deliver beam to experiments. The replacement and conditioning of the power supply for the 180o bending magnet in the tandem terminal, and the fabrication and replacement of coils on the Isobar Separator dipoles [see the February 2005 Newsletter] have added to an already heavy workload. We are nevertheless on schedule to begin commissioning of HPTL by the end of August. We have recently completed a Readiness Review and made necessary modifications in our Authorization Basis documents in preparation for this commissioning process. [see "HPTL Update" in this newsletter for a status report].

Our ability to deliver beams to experiments has been limited for much of the year. Even though it was planned well in advance, the loss of the ability to carry out RIB development at the On Line Test Facility (OLTF) for 10 months was particularly painful since it impacted our beam development program severely. The HRIBF is now fully operational once again and able to deliver our full range of beams to all experimental endstations. We are making up for lost beam development time by using the OLFT heavily, and we have added the capability of studying production using 3,4He beams to the OLTF repertoire. During the time that we could not deliver heavy beams because of the Isobar Separator limitations, we scheduled 7Be and fluorine campaigns. The 7Be campaign was an especially notable success, both in terms of beam delivery and physics output [see section 3 for details]. We are now in the process of preparing for an extended (8 to 10 week) neutron-rich RIB campaign, which will begin the week of August 15 and extend beyond the end of the fiscal year (September 30). It will be followed by stable beam runs and a campaign of radioactive fluorine runs. We will make a concerted effort to increase the intensity and purity of our fluorine beams during this campaign. Our next scheduled maintainance period will occur in late November.

Funding for physical sciences in general and nuclear physics in particular continues to be a critical issue. The recently passed comprehensive energy bill has many aspects favorable to the DOE Office of Science, and language that strongly supports low energy nuclear physics, especially RIA. However, this is not an appropriations bill: we still live by our annual appropriations. The FY 2005 budget was reasonably favorable for HRIBF operations, but very tough on the HRIBF research program. The FY2006 President's budget, announced in February 2005, contained cuts in both HRIBF programs, and if enacted would lead to significant contraction of the entire HRIBF program. Both the Senate and House have passed FY2006 budgets that are more favorable than the President's budget, but the bills have significant differences in other areas so a favorable outcome won't be assured until a final result is produced by a conference committee. The problems posed by the recent budget trends and the near-term budget outlook have made it painfully clear that the 2002 Long Range Plan cannot be implemented as written. Consequently, NSAC charged a committee under the chairmanship of Bob Tribble of Texas A&M University to produce a report providing guidance for implementing the 2002 Long Range Plan. A brief article discussing this report from the point of view of HRIBF appears later in this newsletter.




2. Beam Opportunities at HRIBF
(C.J. Gross)

Table 2.1 lists a sample of particularly interesting beams that have been used in experiments at HRIBF. These beams range in intensity from a few per hour (near 78Ni,136Sn) to more than 1 ppA (light ions, near 132Sn). A complete list of all our beams is available. The links lead to descriptions of the experiments from previous newsletters using the beam.



Table 2.1 - Beam intensities at HRIBF for selected isotopes

Beam

Intensity on Target
(ions/sec)

Stripping

Purity (%)

Experiments

7Be

2x107

single

50

capture

6x106

fully

100

scattering

17F

5x106

single

50

scattering

9x106

fully

100

breakup

78Cu

0.15

single

< 1

mass, decay

82Ge

3x104

single

80

(d,p), Coulex

86Ge

0.006

single

< 1

mass, decay

132Sn

9x105

single

96

Coulex

2x105

double

96

fusion, Coulex

134Sn

3x103

single

30

Coulex

3 x102

double

30

fusion

132Te

4x107

single

90

decay, Coulex, g factor

7x106

double

90

transfer, fusion


3. Recent HRIBF Research - Recent Progress with 7Be Beams
(J. C. Blackmon, A. E. Champagne, U. Greife, and D. W. Stracener, Spokespersons)

An intense beam of 7Be has been developed by a collaboration between the University of North Carolina,  the Colorado School of Mines, and the HRIBF.  Samples of lithium metal were activated at Triangle Universities Nuclear Laboratory (TUNL) using a 10-MeV beam of protons from the FN tandem accelerator, producing 7Be by the (p,n) reaction.  Up to 50 mCi of 7Be per day were produced using proton beam intensities of about 10 microAmps.  The activated lithium slugs were shipped to ORNL, where a simple wet chemical process was performed to separate the 7Be from the lithium.  The separated 7Be was added to a metal powder matrix, coverted to an oxide (7BeO), and pressed into a cathode designed for a multi-sample cesium sputter source.  The influence of the cathode geometry, chemical composition and ion source parameters on the production of 7BeO- beam was studied in a series of tests at the OLTF.  The 7BeO- beam currents measured as a function of time from two of the better cathodes are shown in Fig. 3-1.  Both cathodes contained 1 mCi of activity within a copper metal matrix. Average beam intensities of about 1-2 million 7BeO- /s/mCi were typical under good operating conditions, and a single cathode produced good beam output for about a week with a total efficiency of about 0.5-1.0% for production of 7BeO- beam.

So far three experiments have been performed using accelerated 7Be beams from the HRIBF.  The 7Be(d,t)6Be reaction (RIB-129) was studied in the fall of 2004 by bombarding a 1 mg/cm2 CD2 target with a 100-MeV beam of pure 7Be.  A 30 mCi cathode was used producing an average beam intensity of about 1.5 million 7Be/s on target.  Tritons from the (d,t) reaction were detected and cleanly identified using the SIDAR array operated in telescope mode with a 100 micron layer backed with a 500 micron layer.  The energy spectrum of tritons is currently being analyzed to study the properties of possible unbound states in 6Be that might have important influences on the 3He(3He,2p)4He reaction.  This experiment is part of the Ph.D. dissertation of Andy Chae from the University of Tennessee.

The primary motivation for development of the 7Be beam was to improve our understanding of the 7Be(p,&gamma)8B reaction.  A very accurate value for the 7Be(p,&gamma)8B cross section is needed to interpret measurements of the solar neutrino flux because this reaction determines the ratio of neutrinos emitted from 7Be and 8B decay.  Excitation functions for 7Be+p elastic and inelastic scattering were measured in one set of measurements to help better constrain extrapolations of 7Be(p,&gamma)8B to solar energies (RIB-109).  Both the 7Be+p s-wave scattering lengths and broad resonances at higher energies could have small but still significant influences on the shape of the S-factor for 7Be(p,&gamma)8B.  In the HRIBF measurements 7Be beams at 19 different energies ranging between 4 and 27 MeV bombarded thin CH2 targets.  Reaction products were detected in the SIDAR array.  Targets with gold backing were used in some cases to obtain accurate absolute normalizations.   The data is currently being analyzed by Jake Livesay from the Colorado School of Mines as part of his Ph.D. dissertation.

We are also measuring the 7Be(p,&gamma)8B cross section directly at the HRIBF (RIB-049).  The development of the experimental technique and the initial measurements comprised the Ph.D. dissertation of Ryan Fitzgerald from the University of North Carolina (2005).  In our first measurement conducted in March, a 12-MeV beam of 7Be (with contamination of the 7Li isobar) was produced from a 130 mCi cathode achieving an average intensity of 15 million 7Be/s on target.  The 7Be beam bombarded the windowless hydrogen gas target, operating at a pressure of 5 Torr with a thickness equivalent to 10 micrograms/cm2.  Recoiling 8B nuclei were collected and separated from the 7Be beam by the Daresbury Recoil Separator.  The 8B recoils were detected by a gas ionization chamber at the focal plane and cleanly distinguished.  A particle identification spectrum from the ion chamber is shown in Fig. 3-2 for an accumulated time of 2.6 days of beam on target.  A total of 22 recoiling 8B ions were observed corresponding to a cross section of 1.1 microbarns.  The target thickness, incident beam current, and recoil detection efficiency were determined by independent techniques with a precision much less than counting statistics (21%).

We are currently working to improve the experimental setup to provide  even more robust control on potential systematic uncertainties.  Most importantly, we are currently implementing improvements to the ion source and cathodes that we expect will produce at least a factor 4 improvement in 7Be beam intensity.  At that level, we would be able to achieve a measurement of the 7Be(p,&gamma)8B cross section with a precision of about 5% in a 10 day experimental run.  We are currently constructing a new chamber that will allow for 7Be production using the ORIC cyclotron, and 7Be beams with intensities of up to 108 7Be/s on target should be routinely available at the HRIBF in the near future.  Look for future articles on the results from the measurements described here as they become available.

4. Recent HRIBF Research - Study of the 124,132Sn + 96Zr Reactions
(W. Loveland, Spokesperson)

One of the interesting aspects of the study of nuclear reactions induced by radioactive ion beams is the possibility of using neutron-rich projectiles to synthesize new, neutron-rich heavy nuclei. Also, large fusion cross section enhancement has been predicted for fusion reactions with massive neutron-rich radioactive nuclei by different authors. This is due to the lowering of the fusion barrier, excitation of the soft dipole modes and lowering of reaction Q values. However, previous experimental data with stable beams indicates fusion hindrance in the case of massive neutron-rich nuclei. We have measured the fission excitation functions of 96Zr reactions with neutron-rich short-lived 132Sn and stable 124Sn projectiles near the Coulomb barrier. The measurement was carried out at ORNL. The coincident fission fragments were detected using four Si strip detectors. The time of flight of the beam as well as the fragments were measured using two upstream timing MCP's and timing signal from strip detectors. Using different energy, time and position conditions, the fission events were separated from other reaction processes.

Preliminary excitation functions obtained for both systems (124Sn + 96Zr and 132Sn + 96Zr) are shown in Fig. 4-1. The results show drastic differences between stable beam and the radioactive beam data. At energies above the Coulomb barrier, both systems show some sort of cross section suppression, and below barrier show enhancement with respect to one-dimensional barrier penetration models(1D-BPM) and coupled channel calculations. However, neither differences between the two excitation functions nor fusion hindrance observed with respect to 1D-BPM are understood. At below barrier energies, more data is needed for the 132Sn reaction. The capture cross section calculations shown by Fazio et al. using the DNS model for the reaction of  96Zr with  124Sn, give better agreement with our measurements and suggest a large quasi fission component in the reaction.




5. Recent HRIBF Research - Approaching Neutron-Rich Nuclei Using the Shell Model Monte Carlo Approach in a Proton-Neutron Formalism
(D. J. Dean, Spokesperson)

The Shell model Monte Carlo (SMMC) method [1] was developed as an alternative to direct diagonalization in order to study low-energy nuclear properties.  It was successfully applied to nuclear problems where large model spaces made diagonalization impractical. One calculates the thermal canonical expectation values of observables of few-body operators by representing the imaginary-time many-body evolution operator as a superposition of one-body propagators in fluctuating auxiliary fields. Thus, one recasts the Hamiltonian diagonalization problem as a stochastic integration problem.

Cem Ozen, a University of Tennessee Depeartment of Physics and Astronomy graduate student, working with David Dean, recently developed an SMMC approach in the pn-formalism where isospin is explicitly broken.  This implementation of SMMCpn enables one to treat shell-model Hamiltonians that are not isospin invariant in the model space, or for which different model spaces are used for protons and neutrons.  The method presented in this work is general and may be used for realistic Hamiltonians, as well those of a more schematic variety. Formulation of the method, technical implementation, and initial results constitute Cem's Ph.D. thesis and are reported in a Phys. Rev. C submission [2].

As a first novel application of the new implementation, we performed SMMCpn calculations for the even-even 90-104Zr and 92-106Mo isotopic chains using a realistic effective interaction [3] derived with many-body perturbation theory techniques for the 1p1/20g9/2 proton and 1s0g7/20h11/2 neutron model spaces. Initial experimental studies [4] indicated that nuclei in this region have very large deformations, and that the transition from spherical shapes to highly deformed shapes occurs abruptly: 96Zr is rather spherical, while 100-104Zr nuclei are well deformed with a quadrupole deformation parameter of beta2=0.35 [5]. Furthermore, the spherical-to-deformed transition is more abrupt in the Zr isotopes than in the nearby elements Mo, Ru, and Pd. Generator-coordinate mean-field calculations in this region [6] are able to reproduce the shape transitions with particular Skyrme interactions. The region also exhibits significant shape-coexistence phenomena [7].

Shown in Fig.5-1 are calculations of the ground-state masses for the Zr isotope chain relative to the 88Sr core. Note that a very simple modification of the monopole part of the interaction (one that does not change the excitation spectrum) yields a reasonable description of masses along the isotope chains. Further work will be performed to understand the nuclear deformations in this region. Although nuclei above A=94 show significant deformation with this realistic interaction, there is still a factor of two difference between theory and experiment. We will investigate the origin of this problem in future work.


[1] S.E. Koonin, D.J. Dean, and K. Langanke, Phys. Reps. 278, 2 (1997)
[2] C. Ozen and D.J. Dean, submitted to Phys. Rev. C (2005).
[3] A. Holt et al., Phys. Rev. C 61, 064318 (2000).
[4] E. Cheifetz et al., Phys. Rev. Lett. 25, 38 (1970).
[5] M. A. C. Hotchkis et al., Phys. Rev. Lett. 64, 3123 (1990).
[6] J. Skalski et al., Nucl. Phys. A559, 221 (1993).
[7] P.-G. Reinhard et al., Phys. Rev. C 60, 014316 (1999); J.L. Wood et al., Phys. Rep. 215, 101 (1992).


6. High Power Target Laboratory (HTPL) Update
(B. A. Tatum)

Progress on the High Power Target Laboratory (HPTL) has been substantial. Modifications to building 6000 have been completed and include the heavily-shielded Target Room, the lightly-shielded Instrumentation Room, and considerable space above the Target Room for low energy RIB analysis.A new entrance was also added to the south side of the existing South Annex that includes double doors and a wide ramp for easier equipment access.

All major technical equipment components have been delivered including the high voltage platform, magnets for the ORIC beam line and RIB analysis system, power supplies, and vacuum components. ORIC beam line alignment and assembly has gone extremely well. The platform has been installed for many months and the target station and RIB analysis system are being installed on that structure. As with most projects, the details will consume the most time in the remaining months. Control system programming, wiring, alignment, and testing of individual components will require many more hours of effort.

An HPTL Readiness Review was conducted recently at ORNL. Following completion of a small number of identified tasks and signing of our revised Accelerator Safety Envelope (ASE), we expect to be granted approval to operate by Oak Ridge Operations.

Commissioning activities are expected to begin by the end of August, and the HPTL Project remains scheduled for substantial completion by October 1, 2005.


7. DOE S&T Review Results
(G. R. Young)

A scientific and technical review of the HRIBF was held November 22-23, 2004, at ORNL. This review was convened by the DOE Office of Nuclear Physics and is expected to be the first of a series of regular reviews conducted as part of their management of the national nuclear physics program. The external panel members were Prof. John d'Auria (Simon Fraser U), Prof. Ingo Weidenhoever (Florida State U), Dr. Erich Ormand (Lawrence Livermore National Lab), Dr. Derek Lowenstein (Brookhaven National Lab), Dr. Daniela Leitner (Lawrence Berkeley National Lab), and Dr. Christopher Lister (Argonne National Lab).  DOE attendees included Dr. Denis Kovar, Dr. Eugene Henry and Dr. Jehanne Simon-Gillo from HQ and Messrs. Wayne Lin and David Arakawa from the ORO Site Office.

The review took a wide-ranging look at all aspects of the HRIBF, including facility status, operations and plans, scientific program including experimental and theoretical work as well as instrumentation development in support of the HRIBF program, operating hours, beam development efforts and plans, the HPTL upgrade project status and future upgrade plans, the outside user program, publications and theses produced, implementation of a safe working environment, support from ORNL management, and the HRIBF's interactions with and development of its user community.

The report is organized as findings of fact, comments by reviewers and DOE, and the resulting recommendations of the DOE. The reviewers took note of the recent experiments using neutron-rich beams to study nuclear structure well away from stability, notably on the n-rich side, and of the first studies of nuclei near the pathway for the stellar r-process. They noted continued work using proton-rich beams and the physics results from this on rp-process nucleosynthesis, as well as recent additions to the theory staff at ORNL both in structure and astrophysics.

The reviewers also noted the 50% increase in RIB hours over the past two years and the concurrent large increases in beam intensity achieved over that period. The progress of the new High Power Target Lab project was noted, and encouragement was given for further upgrades to add a second target-ion source to HRIBF. Plans were examined for further upgrade projects to significantly expand the intensity and variety of beams, and the panel commented favorably about ongoing work to develop new beams and improve old ones. One new development garnering attention was the highly encouraging first studies using laser purification methods to improve beam purity either by photodetachment of negative ions in favorable cases or multi-step resonant ionization schemes in others.

The report gives five specific recommendations for the facility. These are discussed in turn below.

The first recommendation is to formalize a coordinated strategic plan for science, equipment and facility development, with input from the community. The facility is currently developing such a plan and will seek consultation from the user community.

The second recommendation is to communicate to users the strategy for development of new beams, in order to improve planning for experiments. The new HRIBF website (as well as this newsletter) contains links to this information, and a link to Dan Stracener's presentation to the review panel about beam development. We request and encourage your input to this.

The third recommendation is that the Physics Division and HRIBF management should strongly encourage timely publication of HRIBF results. There has been a great burst of activity the past few years with the newly developed beams, and many new ideas have been tried, with good success. We will work with the community to move these results to publication. To this end we also request users to notify HRIBF when students give talks and prepare, defend and publish theses, as these are also important aspects of communicating HRIBF science to the outside world.

The fourth recommendation is that HRIBF publish beam schedules on a regular basis and make them available to the user community. You will find links on the new HRIBF web page giving you access to these. Carl Gross will be happy to receive your comments as we develop this new page.

Finally, the panel recommends ORNL, HRIBF and the HRIBF Users' Group work together to increase the size of the user community. We regard this as a key element to ensuring success of present efforts and building for the future era when experiments at RIA become possible. We continue to encourage new users, from both here and abroad, to make proposals for beam time and help us explore this new world of radioactive ion beam physics.


8. The "Tribble Report" and Its Relevance to HRIBF
(J. R. Beene)

In March 2005 DOE and NSF requested that NSAC produce a strategic plan updating the priorities of the 2002 Long Range Plan in light of continuing pressure on the funding available to the field.The charge letter to NSAC from the agencies noted that "Since the issuance of the Long Range Plan, resources needed to implement the recommended program have not been identified by the agencies." It further noted that the essentially constant effort funding of 2002-2005, compounded by the FY2006 President's Budget Request for Nuclear Physics (8.4% below the FY2005 level), would leave existing user facilities operating at ~65% of optimum level, and result in a ~10% reduction in the number of researchers supported. This funding level, projected into the outyears, left no room for continued operation of the program's major user facilities, as presently conducted, and clearly could not accommodate new initiatives such as RIA. NSAC formed a subcommittee under the chairmanship of Bob Tribble, including ORNL staff members Michael Smith and Witek Nazarewicz, to "examine the existing research capabilities and scientific efforts, asses their role and potential for advancements in the context of international efforts and determine the time and resources...needed to achieve the planned program." The report of that subcommittee, titled "Guidance for Implementing the 2002 Long Range Plan" was delivered to NSAC on June 23, 2005, and is now available online at the NSAC website. It is a critically important document, that will have a significant impact on the future development of our field. I assume all HRIBF staff and users have read the document. The purpose of this article is entirely parochial. I will not attempt to review the conclusions and recommendations of the report, except those relevant to the future of HRIBF, except to note that among the seven findings of the subcommittee is the reaffirmation that "RIA remains the highest priority of our field for new construction."

The report does an excellent job of summarizing the intellectual content and scientific relevance of "The Physics of Nuclei and Nuclear Astrophysics" which form the primary basis of the research program at HRIBF. Work carried out at HRIBF was explicitly recognized in one of seven highlighted achievements of the field since the 2002 Long Range Plan was crafted: "Measurements at HRIBF and NSCL of nuclei far from stability that have properties deviating sharply from predictions, which have forced major changes in our understanding of nuclear structure." In agreement with several reviews of science in the low-energy program over the last several years, the report endorses the economic and scientific worth of the upgrade programs at existing low energy facilities, and their potential impact in the near term, while reiterating the importance of RIA: e.g. "Current facilities with modest upgrades will have a 5-10 year window to continue forefront science. While our existing first-generation radioactive-beam facilities and stable-beam facilities will provide exceptional targeted opportunities, the future of the program lies with RIA."

A critical aspect of the report is the recommendations it makes for dealing with the three budget scenarios laid down in the DOE charge to NSAC. These three scenarios concerned the five year period FY 2007-2011, and were based on the $370.4M President's Budget Request for FY 2006:

1) Flat-flat funding at $370.4 million, actual dollars

2) Constant effort funding (starting with $370.4 million in FY 2006), inflated dollars

3)Funding levels needed to restore research capabilities and scientific programs to mount an optimized program and to address the scientific opportunities identified in the 2002 Long Range Plan in order of their priority.

The basic conclusion of the report is that any scenario that falls significantly below constant effort funding built on a FY 2007 base of $430M would have "disastrous consequences for our field." The first two of DOE's scenarios both fall in this category (the base funding in FY 2007 for the second scenario is almost $50M or ~12% below the $430M figure). The report details some of the dire consequences, including the inevitable closure of one of the field's two major accelerator facilities (CEBAF or RHIC). For the third and rosiest of DOE's scenarios, the subcommittee identified a constant effort budget starting from a FY 2007 base of $475M (i.e. a 28% increase above the FY 2006 President's Budget Request) as being necessary to restore capabilities and mount an optimized program. In this scenario, timely initiation of RIA construction is possible, and support for carrying out upgrades at the HRIBF and ATLAS is explicitly noted. Because the impact of the first two scenarios is so dire the subcommittee considered two additional scenarios involving constant effort budgets but with FY 2007 base levels between those of scenarios 2 and 3. A budget based on $450M in FY 2007 would "slow considerably the execution of the basic program outlined in the LRP", but would still support the program of upgrades at HRIBF and ATLAS. A budget based on $430M in FY 2007 "seriously impacts the program. But basic priorities remain the same." In particular upgrades of HRIBF and ATLAS would proceed, but at a slower pace.

Thus, on the whole both the flavor and content of this report are extremely favorable to nuclear science with radioactive beams and to HRIBF. However, it is important to realize that it will take a significant effort by our community to get funding levels for the nuclear physics program even up to the minimum level identified in the Tribble Report ($430M in FY 2007). Both the House and Senate have passed Energy and Water appropriations bills larger than the $370.4M President's Request for FY 2006 ($408.3M for the House and $419.7M for the Senate). If the larger of these is enacted intact, a further 13% increase will be needed to reach the level required for the "optimized program" scenario.


9. PAC 12 Call for Proposals
(C. J. Gross)

The HRIBF will accept proposals for consideration at the next meeting of the Program Advisory Committee (PAC-12) until October 24, 2005. The PAC, which meets on December 8-9, 2005 in Oak Ridge, will consider and prioritize proposals for any of the many radioactive ion beams now available for research. More information will be posted on our website in September and a reminder will be sent closer to the due date.


10. Summer School and Workshop on RIB Production Targets and Ion Sources Took Place in May
(H. K. Carter)

The first U.S. "Radioactive Ion Beam-Targets and Ion Sources" summer school and workshop took place in Oak Ridge, May 23-27.

The summer school portion of the program intrduced 23 young researchers from a variety of scientific disciplines to the research field of radioactive ion beam production. Following the school, students joined more than 40 other scientists for a two-day workshop to discuss emerging trends and techniques in the field.

The purpose of the school was to introduce young researchers - ranging from advanced undergraduates to post doctoral students - to a field of study that was entirely new to many of them. An additional goal is to attract researchers from disciplines other than nuclear physics into target/ion source development. By bringing together scientists from a broad cross section of disciplines (from chemistry to material sciences), the school and workshop provided a chance to introduce future scientists to the growing field of radioactive ion beams, and to gain perspectives from outside experts.

The summer school's morning sessions were dedicated to lectures from experts from all over the world covering topics from motivations for making radioactive ion beams to diffusion/effusion in the target-ion source system and ion beam optics. In the afternoon, participants divided into five groups where docents and HRIBF staff and researchers guided students through hands-on experiments in the laboratory. The afternoon experiments included measuring the release rate of arsenic out of proton-irradiated germanium target material at different temperatures and different times. Using the online isotope separator, the students measured the time-profile of the release of stable arsenic implanted in a catcher in the target position of a target-ion source. Additionally, students were given an introduction to different computer programs for thermochemistry and nuclear physics. At the ISTF2 the students were introduced to another isotope separator as well as beam emittance measuring equipment. Students also had a chance to assemble ion sources and view different kinds of target materials.

The workshop following the school changed the focus and level of the science as experienced scientists joined the school participants at a conference center in downtown Oak Ridge. The workshop, which was organized by John D'Auria of Simon Fraser University, focused on the production of new radioactive ion beams that are presently not available, as well as improving existing beams in intensity and purity. The two-day workshop consisted of presentations followed by discussions. The presentations focused on seven topics in the general area of Isotope Separator On-Line (ISOL) targets and ion sources, and these were discussed by key experts from various laboratories around the world.


11. The Fourth Annual RIA Summer School Held at LBNL
(C. J. Gross)

The Fourth Annual RIA Summer School was held at Lawrence Berkeley National Laboratory July 31 - August 6. Forty-seven students participated in morning lectures by Robert Grzywacz (Nuclear Structure), Guy Savard (Fundamental Symmetries), Hendrik Schatz (Astrophysics), James Vary (Theory), Sherry Yanello (Reactions), Larry Ahle (RIA Applications), Cody Folden (Heavy Elements), Daniela Leitner (Accelerator Physics), and Augusto Macchiavelli (Gamma-ray Tracking). In the afternoon hands-on activities included work on the BGS, Coulomb excitation, ECR ion sources, gamma-ray tracking, low background counting, neutron activation analysis, neutron-gamma pulse shape discrimination, nuclear theory, and a weak interactions experiment.

The aim of the summer school is to nurture future RIA scientists so that the community will have sufficient manpower to effectively use RIA when it comes on-line. The RIA Summer School is jointly organized by the ATLAS, 88-Inch Cyclotron, HRIBF, NSCL, and LLNL/N-division. The school is an annual event that rotates among the organizations, excluding LLNL.

The next RIA summer School will be held July 17-21, 2006, at the HRIBF. Note that this is the week prior the Nuclear Structure Conference which will also be held in Oak Ridge. We hope that many of the students will be able to participate in both events.


12. Workshop on Fusion of Radioactive Ions to be Held in December

The Holifield Radioactive Ion Beam Facility will hold a workshop on the study of fusion reactions using radioactive nuclei with medium and heavy mass targets at energies near and below the Coulomb barrier. The workshop will be held at ORNL on December 2-3, 2005.

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 fusion and fission reactions in the radiaoctive ion beam (RIBs) environment and acquaint participants with HRIBF's beams and experimental facilities available for such experimental studies. The RIBs available from the HRIBF span a large range of neutron- and some proton-rich isotopes at energies suitable for these studies. In addition, plans for future measurements and related beam- and instrument development will be addressed. Theoretical approaches to deal with the quantity and quality of data from such experiments will also be part of the intended discussions.

For more details about the workshop, please visit the workshop website.


13. Nuclear Structure '06 to be held in Oak Ridge 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.


RA1. RIB Development
(D. W. Stracener)

In the last few months, a significant effort was made to improve the 7Be beam intensity, including finding the best matrix for the sputter target and improving the reliability of the ion source. The 7Be atoms are separated from the lithium production target using chemical separation techniques and then added to a sputter target containing a metal powder. Tests at the OLTF with different metal powders show that the best integrated yield of 7Be was achieved using copper powder (slightly better than silver powder). Further improvements to the ion source have been made and should result in better reliability and a decrease in the downtime due to problems with the cesium delivery system. Also, changes in the geometry of the sputter target holder should result in higher 7Be concentrations in the target matrix. Recently completed experiments using a Be beam are described in a separate article in this Newsletter.

A couple of candidate target materials for RIB production targets were tested off-line to ensure compatibility with the target holder and ion source materials and to determine the optimum operating temperature. With the goal of making proton-rich vanadium beams, titanium oxide powder was pressed into pellets and tested in a hot-plasma ion source. The maximum target temperature was 1700° C and above this temperature the ion source efficiency dropped dramatically. An on-line test showed that the release efficiency of vanadium atoms from this target at 1650° C is small, resulting in low beam intensities. Also, no activity was found in molecular sidebands (e.g. oxides, chlorides, or sulfides). Thorium oxide powders were also pressed into pellets and tested off-line. The maximum operating temperature for this target material was 1950° C. The pellets were slightly denser (about 10%) after operating at this temperature for about three days, which may indicate that the release efficiency will decrease during the lifetime of these targets. The yields of radioactive fission fragments from this target will be compared to those achieved using uranium carbide targets.

In September, we will have another development run using a laser ion source in collaboration with a group from the University of Mainz. The goal of this work is to develop a RIB production ion source using all solid-state lasers. Specifically, during this run, ionization schemes for Sn, Ni, Ge, Cu, and Sr will be investigated. The results of these tests will be reported in the next Newsletter. Also, in the next Newsletter, we will report on the recently completed on-line tests for proton-rich Se beams from a liquid Ge target and the yields of fission fragments from the thorium oxide target.


RA2. Accelerator System Status

ORIC Operations and Development (B. A. Tatum)

ORIC did not operate for most of the reporting period due to a combination of several factors: the Beryllium RIB campaign with the batch-mode ion source, stable ion beam runs, maintenance activities, a tandem tank opening, and HPTL construction.  Maintenance activities included the replacement of the deflector high voltage electrode which developed an extremely small water leak, but one large enough to prevent stable operation of the device.  Control system and RF improvements were also made

ORIC operation resumed in June for 17F astrophysics experiments and the machine performed quite well with only the normal frequent cathode change-outs that are associated with helium beams.  This was the first operation of ORIC on the EPICS control system and we are pleased with the performance to date.

Tandem Operations and Development (M. J. Meigs)

The Tandem Accelerator was operated for approximately 2600 hours since the last report.   The machine ran at terminal potentials of 2.44 to 23.22 MV and the stable beams 1H, 2H, 7Li, 10B, 12C, 16O, 18O, 23Na, 24Mg, 28Si, 32S, 54Fe, 58Ni, 75As, 124Sn, and 172Yb were provided.  This is the first time Yb has been accelerated at our facility.  Radioactive beams of 7Be, and 18F accounted for about 600 hours.  Six tank openings were necessary during this period with one being a scheduled maintenance period.  Two of the other five were to fix vacuum leaks of which one was caused by maintenance activities and the other was failure of a Faraday cup bellows.  The other three were to fix damage to the terminal communications and the terminal bending magnet power supply, which was caused by sparks.  During the regular maintenance period it was discovered that the terminal CAMAC crate box cover was not tight which would allow spark energy to enter and cause failures.  Since this problem was fixed, we have had no terminal communications failures.  About 290 hours were spent on conditioning with the goal of operation at 24.5 MV for the neutron-rich program.

During this period, beam lines 31 to the RMS and 16 to the OLTF were reinstalled and beams were delivered to these two areas.  No beam had been delivered to either area for about eight months due to the High Power Target Laboratory construction.

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

During this reporting period, we delivered beams of

  • 6.5 Mpps 1+/ 4+ terminal gas / post foil stripped 12 MeV pure 7Be and

  • 30 Mpps 1+ terminal gas stripped 12 MeV 7Be to the Daresbury Recoil Separator, and

  • 1 Mpps 1+/ 4+ terminal gas / post foil stripped 14 MeV pure 7Be and

  • 400 kpps 7+/ 9+ terminal foil / post foil stripped 150 MeV pure 18F to the astrophysics endstation in Beam Line 21.

The 7Be beams were produced with a cesium sputter negative ion source with 126 mCi 7BeO in Ag powder in a Cu holder. The 18F beam was 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 euA of 85 MeV 4He from the Oak Ridge Isochronous Cyclotron (ORIC). This is the first operation of a KENIS with permanent magnets installed around the beam line upstream of the first quadrupole multiplet to sweep away electrons and with the recirculating cesium jet charge exchange cell removed to maximize transmission. The KENIS cesium oven heater, external line heater, and internal line heater were controlled by MICROMEGA CN77000 Series Controllers in a modified controller chassis. During the 18F campaign there were NO failures of these new heater controllers. We plan to implement these controllers for the new recirculating cesium jet charge exchange cell for the upcoming neutron rich fission product campaign. The previously used OMEGA controllers failed frequently.

High voltage transient protection circuitry was installed for the (cathode and target heater) high current power supplies at target ion source potential in C111N. The increasing vibration of the platform potential motor-generator shaft was reduced by replacing both coupling bearings, both coupling elements, the flange bearing, and the pillow block bearing. The target ion source potential motor-generator shaft pillow block bearing failed (motor decoupled from shaft) and was replaced. The upper and lower coils for the second dipole of the second stage (isobar) mass separator (BM_12_1) were replaced with ONLY two days of rigging after extensive preparation of the work area.




RA3. HRIBF Users Group News
(C. J. Gross)

The HRIBF has decided not to hold a users group meeting at this year's DNP meeting. In place of the meeting, we are in the process of updating our web site to provide updated information about our equipment and capabilities. This information should be available by October 1. In addition, the website has been reorganized; if you have bookmarked pages they have probably changed. We look forward to receiving your ideas for any additional improvements.

The Users workshop on Fusion-Fission has been rescheduled for December 2-3, 2005. See the accompanying article for more information.


RA4. 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.



RA5. HRIBF Experiments, January through June 2005
(M. R. Lay)

Date Exp. No. Spokesperson Title of Experiment
1/1-2 Scheduled shutdown
1/3 RIB-129 Bardayan/ORNL Single-particle states in the neutron-rich 85Se nucleus near the N=50 closed shell
1/3-4 RIB-037 Meigs,Juras/ORNL Tandem development
1/4 RIB-012 Liang/ORNL As + Ti sub-barrier fusion
1/4-5 RIB-037 Meigs,Juras/ORNL Tandem development
1/5-10 RIB-129 Bardayan/ORNL Searching for resonances in the unbound 6Be nucleus
1/11-14 Unscheduled maintenance
1/15-17 Scheduled shutdown
1/18-19 Unscheduled maintenance
1/19-22 RIB-129 Bardayan/ORNL Searching for resonances in the unbound 6Be nucleus
1/22-23 Scheduled shutdown
1/24-28 Unscheduled maintenance
1/29-30 Scheduled shutdown
1/31 RIB-129 Bardayan/ORNL Searching for resonances in the unbound 6Be nucleus
1/31 RIB-037 Meigs,Juras/ORNL Tandem development
2/1-2 RIB-013 Blackmon/ORNL DRS commissioning
2/3 RIB-037 Meigs,Juras/ORNL Tandem development
2/3-4 RIB-012 Liang/ORNL As + Ti sub-barrier fusion
2/5-6 Scheduled shutdown
2/7-10 RIB-142 Kozub/TN Tech University Test of (7Li,6He) as a proton transfer reaction for inverse kinematics
2/10-11 RIB-012 Liang/ORNL As + Ti sub-barrier fusion
2/12-13 Scheduled shutdown
2/14 RIB-141 Kronenberg/ORISE Off-line RIB development at the OLTF
2/14 RIB-037 Meigs,Juras/ORNL Tandem development
2/15 RIB-012 Liang/ORNL As + Ti sub-barrier fusion
2/16 RIB-013 Blackmon/ORNL DRS commissioning
2/17 RIB-037 Meigs,Juras/ORNL Tandem development
2/17-19 RIB-049 Champagne/UNC-Chapel Hill Proposal to measure the 1H(7Be,gamma)8B reaction
2/19-20 Scheduled shutdown
2/21-23 RIB-049 Champagne/UNC-Chapel Hill Proposal to measure the 1H(7Be,gamma)8B reaction
2/24-25 RIB-013 Blackmon/ORNL DRS commissioning
2/26-27 Scheduled shutdown
2/28-3/2 RIB-120 Liang/ORNL Fusion of 132Sn and 64Ni above the Coulomb barrier
3/2 RIB-012 Liang/ORNL As + Ti sub-barrier fusion
3/3-9 RIB-049 Champagne/UNC-Chapel Hill Proposal to measure the 1H(7Be,gamma)8B reaction
3/9 RIB-039 Mueller/ORNL High voltage injector development
3/9-11 RIB-049 Champagne/UNC-Chapel Hill Proposal to measure the 1H(7Be,gamma)8B reaction
3/11 RIB-141 Kronenberg/ORISE Off-line RIB development at the OLTF
3/12-13 Scheduled shutdown
3/14-15 RIB-109 Greife/CO School of Mines Measurement of the 7Be+p elastic excitation function
3/15-18 RIB-039 Mueller/ORNL High voltage injector development
3/19-20 Scheduled shutdown
3/21-23 RIB-109 Greife/CO School of Mines Measurement of the 7Be+p elastic excitation function
3/24 RIB-120 Liang/ORNL Fusion of 132Sn and 64Ni above the Coulomb barrier
3/25-27 Scheduled shutdown
3/28-31 RIB-120 Liang/ORNL Fusion of 132Sn and 64Ni above the Coulomb barrier
3/31-4/1 RIB-054 Bardayan/ORNL Study of (p,t) reactions with the SIDAR detector array
4/2-3 Scheduled shutdown
4/4 RIB-037 Meigs,Juras/ORNL Tandem development
4/4-8 RIB-045 Hausladen/ORNL Identification of the decay the Tz=+1/2 nucleus 113Ba
4/9-10 Scheduled shutdown
4/11 RIB-037 Meigs,Juras/ORNL Tandem development
4/12-14 RIB-045 Hausladen/ORNL Identification of the decay the Tz=+1/2 nucleus 113Ba
4/15 RIB-014 Stracener/ORNL Target ion source development
4/15 RIB-037 Meigs,Juras/ORNL Tandem development
4/16-17 Scheduled shutdown
4/18 RIB-120 Liang/ORNL Fusion of 132Sn and 64Ni above the Coulomb barrier
4/19-20 RIB-141 Kronenberg/ORISE Off-line RIB development at the OLTF
4/20-21 RIB-014 Stracener/ORNL Target ion source development
4/21 RIB-147 Karny/University of Warsaw Search for pi-nu mirror components in the wave function of a third proton emitting state in 150Lu
4/22 Unscheduled maintenance
4/23-24 Scheduled shutdown
4/25-29 Scheduled maintenance
4/30-5/1 Scheduled shutdown
5/2-6 Scheduled maintenance
5/7-8 Scheduled shutdown
5/9-11 Unscheduled maintenance
5/11-12 RIB-141 Kronenberg/ORISE Off-line RIB development at the OLTF
5/12-13 RIB-014 Stracener/ORNL Target ion source development
5/13 RIB-141 Kronenberg/ORISE Off-line RIB development at the OLTF
5/14-15 Scheduled shutdown
5/16 RIB-141 Kronenberg/ORISE Off-line RIB development at the OLTF
5/17 Setup
5/17-23 RIB-147 Karny/University of Warsaw Search for pi-nu mirror components in the wave function of a third proton emitting state in 150Lu
5/23-25 RIB-014 Stracener/ORNL Target ion source development
5/26-27 RIB-121 Shapira/ORNL Subbarrier fusion of 134Sn with 64Ni
5/28-30 Scheduled shutdown
5/31-6/6 RIB-133 Karny/University of Warsaw Structure of the wave function of the unbound resonance state 141mHo studied via thefine structure in proton emission
6/6-9 RIB-013 Blackmon/ORNL DRS commissioning
6/9-10 RIB-014 Stracener/ORNL Target ion source development
6/10 Unscheduled maintenance
6/10 RIB-014 Stracener/ORNL Target ion source development
6/11-12 Scheduled shutdown
6/13-14 RIB-014 Stracener/ORNL Target ion source development
6/15-17 RIB-013 Blackmon/ORNL DRS commissioning
6/18-19 Scheduled shutdown
6/20-22 RIB-013 Blackmon/ORNL DRS commissioning
6/23-24 RIB-000 Gross/ORNL RMS development
6/25-28 RIB-145 Brune/Ohio University Proton-transfer study of unbound 19Ne states via 22H(18F,alpha+15O)n
6/28-30 RIB-037 Meigs,Juras/ORNL Tandem development