HRIBF NEWS


Edition 11, No. 1 January 2003 Price: FREE

Breaking News Feature Articles Regular Articles

Editors: C.-H. Yu, C. J. Gross, and W. Nazarewicz

Feature contributors: C. Baktash, J. R. Beene, J. C. Blackmon, D. J. Dean, C. J. Gross, T. Papenbrock, G. R. Young
Regular contributors: C. J. Gross, M. R. Lay, M. J. Meigs, P. E. Mueller, D. W. Stracener, B. A. Tatum


A. Double-Stripped 132Sn Beams at 105 Ions/sec Level!

October saw the completion of our first experiment with pure 132Sn beams at energies above the Coulomb barrier. Sub-barrier fusion cross-section measurements have been taken using doubly stripped 132Sn beams from 453-560 MeV. Beam intensity averaged 20,000 ions/sec (i/s) and peaked at 30,000 i/s. With a new target-ion source this record was eclipsed in December and January when 100,000 i/s were achieved and for two 10-hour periods, 120,000-140,000 i/s were reached. In these later measurements, the beam energy was 475-495 MeV and used for a Coulomb excitation measurement.

More work is needed to understand all the factors involved in this exciting development. The later measurement used a new uranium-carbide target material manufactured at ORNL and used hydrogen-sulfide gas to chemically select Sn isotopes. The primary beam was approximately 10 uA of 42-MeV protons. In addition, a different beam tune through the second-stage mass separator was used which is applicable to beams with poor emittance and beams which do not require the high mass resolution of the the second-stage separator.

More details and reports on the experiments should be available in the next newsletter.

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1. HRIBF Update and Near-Term Schedule

The last six months has been a remarkably productive period at HRIBF. During the last quarter of FY02, the HRIBF produced about 780 hours of beam on target for research, including 340 hours of radioactive fluorine beam. Following this successful fluorine campaign, which included such highlights as the first use of the DRS with radioactive ion beams, a campaign of neutron-rich RIB experiments was initiated. This campaign is still underway. During the first quarter of FY03, we recorded 1149 hours of beam on target for research, including 396 hours of radioactive beam. Since the end of December, we have added about 50 hours so that for the last six months we have logged in excess of 1900 research hours with almost 800 hours of this being radioactive beam. Experiments during the neutron-rich campaign have concentrated primarily on taking advantage of our pure tin capability. Highlights include the remarkable achievement of a measurement of the 132Sn + 64Ni evaporation residue excitation function extending to subbarrier energies and Coulex measurements on 128,130Sn. An effort to measure the B(E2) to the 4.04 MeV first excited state in 132Sn using the 150-crystal ORNL-MSU-TAMU BaF2 array is now in progress. During the course of this campaign, double-stripped 132Sn beams with a purity in excess of 99% have been produced with an intensity in excess of 140,000 ions per second on target. The corresponding single-stripped beam intensity should be greater than 600,000 ions per second on target. This is well over an order of magnitude improvement beyond the intensities we were advertising six months ago.

We hope to extend the present neutron-rich campaign until around mid-February. At that time, we will shut down for a major maintenance period of about ten weeks, which will involve substantial work on the tandem, including installation of a new and much improved gas stripper. Following the shutdown, a period of several weeks of stable beam running is planned, primarily for outside user experiments and equipment development and testing. In midsummer, we will initiate our next radioactive beam campaign. These plans are somewhat tentative because of considerable budget uncertainty and the constraints of the Continuing Resolution that we are now operating under. It is possible that the current campaign will have to be terminated early and the shutdown extended due to these budgetary constraints.

In the last issue of the newsletter, a brief discussion of the DOE Operations Review of the HRIBF in June of 2002 was provided. This review was quite favorable in most respects and recommended a substantial immediate increase in HRIBF funding to allow us to provide more hours of radioactive beam. It was also partially responsible for a modest reorganization of HRIBF management and the appointment of a new advisory committee. Alan Tatum has been appointed to the newly created position of Group Leader for RIB Production Systems, supported by Ray Juras who continues to be responsible for day-to-day operation of the HRIBF and ORELA. Darryl Dowling is now responsible for accelerator systems development and Dan Stracener is responsible for ISOL systems development. Cyrus Baktash continues as Group Leader for Experimental Systems. In this role he is responsible for the development of research equipment at the HRIBF and oversees the work of research support technical staff and equipment mentors. Jim Beene continues as HRIBF Director, Witek Nazarewicz as Scientific Director, and Carl Gross as User Liaison.

The report of the DOE Operating Review Panel also resulted in the formation of a new advisory panel to the HRIBF Director, the Scientific Policy Committee (SPC). The first meeting of the SPC was held November 22-23, 2002. The members include Chairman Juha Aysto (University of Jyvaskyla, Finland), Bradley W. Filippone (California Institute of Technology), Thomas Glasmacher (Michigan State University), John Hardy (Texas A&M University), Karl E. Rehm (Argonne National Laboratory), Alan Shotter (TRIUMF, Canada), Friedrich-Karl Thielemann (Institut fur Physik, Basel, Switzerland). This panel will provide advice on both technical and scientific directions of the facility.

The presentations to the Operating Review Panel covered a broad range of topics including the scientific program; results from recent experiments and the planned program of future running; possible new scientific programs to pursue; the means we use to solicit and obtain user community input to decisions about development investments in new beams and detectors; status of detectors and endstations and plans for upgrades to existing devices and addition of new devices to the HRIBF; status of various beam development projects; operations costs as well as recent and planned improvements to achieve more efficient operation; resources needed to increase current operation to over 2000 hours of RIB per year; and a proposed suite of upgrades to the facility and its detectors to enable reaching as much as 4000 hours of RIB per year out of a total of 6000 hours total operation. The report from the Panel recommended targeted increases in funding to provide more RIB hours immediately, as noted above, and also recommended a specific plan be developed for capital improvements to both accelerators and detectors which could be achieved over the next 5 years. Input from the User Community, particularly on the scientific direction and resulting implications for capital and development investment, is vital to the formation of this plan. Overall guidance will also be sought from the SPC noted above. We encourage Users to make their views known via usual liaison channels and also to the management and SPC members listed above. While Proposals and Letters of Intent to the HRIBF PAC remain a favored method for formal input on specific physics topics, many issues facing HRIBF as it evolves are of a strategic nature and will benefit from broad community input.

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2. Recent HRIBF Research - New Neutron-Rich RIB Coulomb Excitation Results*

In the Summer 2001 newsletter, we reported the first results using neutron-rich radioactive ion beams (RIBs) from the HRIBF facility, including Coulomb excitation measurements of B(E2; 0+ --> 2+) in 126,128Sn and 132,134,136Te. The Te results have since been published [Radford et al., PRL 88,222501 (2002)]. Here we report on new experiments performed with neutron-rich RIBS during the Fall 2002.

The first experiments with isobarically pure tin radioactive beams were performed in the fall of last year, when we used Coulomb excitation to measure B(E2) values for 128,130Sn. Pure beams of 128,130Sn, with energies of 3 MeV per nucleon, were used to bombard a natural carbon foil at the target position of the Recoil Mass Spectrometer (RMS). Energetic carbon nuclei from target-beam collisions were detected at laboratory angles between 7 and 44 degrees in the HyBall. Gamma rays, detected by the segmented clover Ge detectors of CLARION, were recorded along with the HyBall data whenever they were in coincidence. Maximum beam intensities were about 3 x 106 s-1 (128Sn) or 5 x 105 s-1 (130Sn).

The purified beams were formed from molecular SnS+ ions from the target-ion-source. After selecting ions with the correct molecular weight, the sulfur is removed in a cesium vapor charge-exchange canal, and Sn- ions are mass analyzed in a second magnet for injection into the tandem accelerator. The Sn ions were primarily in their 0+ ground states, but 8.5% and 11% were in the metastable 7- state for 128Sn and 130Sn, respectively. Isobars of other elements made up less than 1% of these beams.

Spectra of gamma rays from 126,128Sn, gated by prompt coincidence with carbon recoils and Doppler-shift corrected, are shown in Figure 2-1. They are remarkably clean, due to the selectivity of the HyBall gate in discriminating against room background and decay of stopped beam particles. Also shown in this figure is a corresponding spectrum from an earlier experiment on 128Sn performed before the pure Sn beams were developed; the 128Sn made up about 14% of this A=128 beam.

[Spectra]
Figure 2-1: Spectra of gamma rays from Coulomb excitation of the radioactive ion beams, Doppler-shift corrected and gated by prompt coincidence with carbon recoils in the HyBall detectors. Peaks are all 2+ --> 0+ transitions, and are labeled by nuclide and energy.

Preliminary values for the B(E2; 0+ --> 2+) in Sn isotopes are listed in Table 1. They are also displayed together with the B(E2) systematics for this mass region in Figure 2-2. The quoted errors include contributions for systematic uncertainties in gamma-ray efficiencies, etc.

Table 1: Preliminary B(E2) values for even-even Sn isotopes from the present work.
NuclideB(E2; 0+ --> 2+) (e2b2)
126Sn0.10(3)
128Sn0.073(6)
130Sn0.023(5)

[B(E2) Systematics]
Figure 2-2: Values of B(E2; 0+ --> 2+) for even-even Sn, Te, Xe, Ba and Ce isotopes around neutron number N=82. Open symbols are adopted values, while filled symbols are from our work.

The B(E2) value for 130Sn is remarkably small, corresponding to only 1.2 single-particle units. Due to the high excitation energy and low B(E2) for the 2+ level in this nucleus, the cross section for excitation of the level is only 1 millibarn. Clearly, without the isobarically pure beams, this measurement would have been extremely difficult.

*Collaborators include D. C. Radford, C. Baktash, J. R. Beene, A. Galindo-Uribarri, C. J. Gross, P. A. Hausladen, D. Shapira, D. W. Stracener and C.-H. Yu (ORNL); B. Fuentes and E. Padilla (UNAM, Mexico); Y. Larochelle (U. Tennessee); A. Piechaczek (Louisianna State U); and J. A. Cizewski, M. Johnson and J. Thomas (Rutgers U)

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3. Recent HRIBF Research - Theoretical Nuclear Structure

Realistic nuclear structure problems are difficult to solve due to the complexity of the nucleon-nucleon interaction and the sheer sizes of the model spaces. In recent years, several approximations have been developed that truncate the model space while obtaining highly accurate approximations to low-lying states. Most truncation schemes are based on physical insights or random searches but do not really yield the optimal truncations. Exceptions are the density matrix renormalization group and the factorization method  (See Ref. 1 for details) which we will describe here.

Let us expand the shell-model ground-state in terms of products of proton (p) and neutron (n) states as

.
This expansion is  a "factorization" of the ground-state in terms of  (not necessarily normalized) proton and neutron states. One can always find a factorization such that the optimal factors are orthogonal to each other and such that the norms
decrease with increasing index j.  Figure 3-1 shows these norms for some sd- and pf-shell nuclei. (We used the UDS interaction for the sd-shell nuclei and the KB3 interaction for the pf-shell nucleus).

Figure 3-1

Note that the norms decrease exponentially fast. This suggest that the factorization converges exponentially in the number K of retained states. Note that this exponential decay has also been observed in other systems ranging from spin-chains to lattice models in condensed matter to molecules in quantum chemistry. While the origin of this behavior is not well understood, it seems to be an empirical fact for many systems of physical interest.

We want to determine the optimal proton and neutron states for fixed number K of retained factors. The optimal factors are obtained from a variation of the energy and are the solution of a coupled eigenvalue problem:

The dimension of these eigenvalue problems is rather small (K times dimension of proton space and K times the dimension of neutron space opposed to the product of the dimensions of proton and neutron space).  To solve these eigenvalue equations we start with a random set of K neutron states and solve the first eigenvalue equation for the proton states with the lowest energy E. These solutions are then input to the second eigenvalue equations which yields improved neutron states and an improved energy E. The whole procedure is iterated until the energy E converges, typically 5-20 times.  It is straightforward to include symmetries into this formalism. Our calculations are done in m-scheme.

As an example we computed the ground-state and low-lying excitations for the sd-shell nucleus 24Mg.  Figure 3-2 shows the energy spectrum versus the dimension of the eigenvalue problem (relative to the dimension of the full m-scheme diagonalization, which is 28503).  The energies converge exponentially quickly as the number of retained factors is increased. A good approximation to the exact spectrum (dashed lines) results already from the solution of an eigenvalue problem that has 30% of the full m-scheme dimension. We also studied pf-shell nuclei.  For  48Cr, our method yields the ground-state energy within 100 keV by solving an eigenvalue problem with a dimension of only  8% compared to the full m-scheme diagonalization. This constitutes a reduction of the dimensionality by more than an order of magnitude and clearly demonstates the capability of the factorization method.

Figure 3-2

These first results are very encouraging, and we are currently examining the spin- and isospin structure of the computed ground states and low-lying excitations.  Note that the exponential convergence of the factorization is at the heart of another numerical method, the density matrix renormalization group (DMRG). ORNL's nuclear theory group is presently developing this method to solve nuclear structure problems and has applied DMRG to compute critical exponents of spin-chains.  The DMRG has the potential to explore exponentially large Hilbert spaces without ever letting the problem size getting out of hand. Its implementation to nuclear structure problems is, however, more cumbersome than the factorization method and also has led to some problems which are not yet fully understood. These truncation methods are rather new numerical tools. Related efforts of  the nuclear theory group are the application of coupled cluster theory to nuclear structure and the delay of the minus sign problem in shell-model Monte Carlo methods.

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4. PAC-8 Results

The members of PAC-8 met in Oak Ridge on November 21-22, 2002. Sixteen proposals and letters of intent requesting 122 shifts of RIBs, 66 shifts of SIBs for RIBs, and 28 shifts of SIBs were considered. Of these, 11 received some allocation of beam time and 3 were deferred for more information and discretionary time. The titles and spokespersons may be viewed on our website. A total of 168 shifts (114 RIB, 44 SIB for RIB, and 10 SIB) were accepted requesting beams of radioactive Be, F, Ga, Ge, and Te. Notice that a new beam category has been added: SIB for RIBs. This category is for those experiments which use SIBs in preparation for RIBs - i.e., RIB-intensity SIBs to explore reactions and techniques which will be used for future RIB experiments.

We expect to issue the next Call for Proposals in May with PAC-9 tentatively scheduled for August 21-22. A new member, Alan Shotter from TRIUMF, will replace I-Yang Lee. We thank I-Yang for his service to the HRIBF.

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5. Venue for ENAM'04 Chosen

The Fourth International Conference on Exotic Nuclei and Atomic Masses, ENAM'04, will be held at Callaway Gardens, September 12-16, 2004. The conference is held every three years with previous meetings held in Arles, France, Shanty Creek, MI, and Hämeenlinna, Finland. The conference originated by merging two other well-established conferences in 1995: Nuclei Far From Stability and the Atomic Masses and Fundamental Constants.

The conference is organized by Oak Ridge National Laboratory with Witek Nazarewicz and Carl Gross as co-chairs. The website is located at http://www.phy.ornl.gov/enam04/. The conference site is a well-known resort in the pine forests of Georgia about an hour southwest of Atlanta. The meeting will be held at the new Southern Pines Conference Center and lodging will be in neighboring two-bedroom cottages. The Gardens encompass 14,000 acres with nature and bicycle trails, golf and tennis, butterfly pavillon, and much more.

We anticipate sending the first announcement shortly. Please reserve these dates in your calendars!

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6. Workshop on the Experimental Equipment for RIA Will be Held in Oak Ridge, TN

A Workshop to discuss the equipment needed to perform experiments at the Rare Isotope Accelerator (RIA) will be held during March 18-22, 2003 in Oak Ridge, Tennessee. Construction of RIA was recommended with highest priority in the 2002 Report of the "Long Range Plan for Nuclear Physics" by the Nuclear Science Advisory Committee. The purpose of this Workshop, which follows the one held in 1998 at the Lawrence Berkeley National Laboratory, is to discuss the performance requirements, designs, manpower and cost estimates, as well as R&D schedules for the experimental equipment needed to fully exploit the exciting new physics opportunities that may be addressed at RIA. The Workshop is being sponsored by Argonne National Laboratory, Lawrence Berkeley National Laboratory, National Superconducting Cyclotron Laboratory, Oak Ridge National Laboratory, RIA Steering Committee, Oak Ridge Associated Universities, and Joint Institute for Heavy Ion Research. Please go to the Workshop web site for complete details (including the scope of the Workshop and deadlines for registration and accommodation) and future updates about the Workshop. You can also download the first announcement of the Workshop in PDF format.

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7. National Nuclear Physics Summer School to be Held in Knoxville, TN

The 15th National Nuclear Physics Summer School is being organized by Oak Ridge National Laboratory and the University of Tennessee.   The school will be held on the campus of the University of Tennessee in Knoxville from June 16-27, 2003.    Please bring the school to the attention of advanced graduate students and beginning postdoctoral research scientists at your institution.

The school is sponsored by the National Science Foundation, the Department of Energy's Institute for Nuclear Theory, Oak Ridge National Laboratory, and the University of Tennessee. Partial scholarships will cover most local expenses for participants.

The Lecturers will be:

Peter Parker Yale University Nuclear astrophysics
Erich Ormand Lawrence Livermore National Laboratory Nuclear structure
Raju Venugopalan Brookhaven National Laboratory High energy nuclear physics in the collider era
Eric Swanson University of Pittsburgh Structure of hadrons
Alejandro Garcia University of Washington Weak interactions in the nucleus
Gail McLaughlin North Carolina State University Neutrino physics

There will be 3 additional seminars:

Glenn Young Oak Ridge National Laboratory Results from RHIC
Rocco Schiavilla Old Dominion Univ. and TJNAF Electromagnetic structure of light nuclei
Geoff Greene Univ. of Tennessee and ORNL Fundamental physics with neutrons

The program also includes opportunities for student presentations, open discussion sessions, and social activities.  The on-line application form and further information can be found at the school's website:
http://www.phy.ornl.gov/npss03/

Inquiries may also be directed by email to npss03@mail.phy.ornl.gov. The application deadline is March 15, 2003.  However, because attendance is limited to about 50 participants, applications should be made as soon as possible.

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RA1 - RIB Development

Recent tests of new target materials have resulted in the measurement of two new proton-rich beams at the On-Line Test Facility (OLTF), namely, 34Cl and 27Si. In addition, a Cs-sputter type ion source has been modified and is now ready for its first tests with 7Be/Cu cathodes at the OLTF. Pure beams of Sn isotopes (including 132Sn) and Ge isotopes have been delivered to experiments. A surface-ionization ion source for positive ions is being modified and tested at the Ion Source Test Facility (ISTF1) and is almost ready for on-line tests. Another ion source development project was recently started to couple a He-jet target to a modified electron-beam-plasma (EBP) ion source. This system will be used to ionize fission fragments that are produced via photofission using 150-MeV electrons from the Oak Ridge Electron Linear Accelerator (ORELA) facility. The following paragraphs will provide more details of these projects.

New Beams

Using an EBP ion source, we have measured beam intensities of 34Cl (half-life is 32.2 min) that were produced in a CeS target material using both (p,n) and (d,2n) reactions on 34S. The extracted radioactive beam intensities were in the range of 104 ions per second per microampere of production beam current with a target temperature of about 1900° C. The CeS target material (described in the previous Newsletter) showed no damage when inspected after the tests. The CeS was made from natural abundance material so the intensity of the 34Cl beam can be easily increased by a factor of twenty if the CeS targets were made from sulfur enriched in 34S. The 34Cl atoms were observed both as singly-charged positive ions and also as molecular ions such as AlCl+, which is similar to the fluorine case. The aluminum vapor concentration in the target was quite low during the measurement, but the yield of the aluminum chloride ions was slightly higher than the yield of the chlorine ions. This leads us to believe that the beam intensity of the molecular ions can be significantly increased if more aluminum atoms are added to the system. We plan to accomplish this by adding a sheath of aluminum oxide fiber around the target since this has worked well in the fluorine production target. Using molecules to transport the radioactive chlorine atoms should significantly shorten the effusion time and allow us to observe the much shorter lived 33Cl (half-life is 2.5 s) that is produced in a (d,n) reaction on 32S. Once we have maximized production and transport of chlorine atoms, we will couple this target to a negative ion source similar to the source used for the fluorine beam production.

Recent tests with an aluminum oxide fiber target have resulted in radioactive beams of 27Si (half-life is 4.14 s) from the (p,n) reaction on 27Al. The measured beam intensities in the initial tests are quite low (about 2000 ions per second per microampere of production beam) but there are several ideas for ways to increase the yield. As in the previous case, most of the observed activity was found in a molecular-ion channel, specifically, silicon sulfide. This is not too surprising since Si is in the same chemical family as Ge and Sn, which can be extracted from this EBP ion source as sulfide molecular ions with high efficiencies. In this test, the sulfur vapor concentration was very low, so we hope to increase the yields by increasing the amount of sulfur in the target. The target was operated at temperatures up to 1750° C and the target material showed no damage when inspected after the on-line tests. The target temperature can be increased to at least 1900° C if a hafnium oxide sheath is placed between the tantalum target holder and the aluminum oxide, and this should decrease the diffusion and effusion time which will reduce the losses due to radioactive decay during transport from the target to the ion source.

Recent efforts by the astrophysics group have resulted in the availability of 7Be atoms (half-life is 53.3 d) in the form of cathodes that can be used in a Cs-sputter type ion source. The 7Be was produced at the TUNL facility on the Duke University campus using 8-MeV protons from their FN tandem to irradiate a lithium pellet. About 30 mCi of 7Be was delivered to ORNL where the beryllium was separated from the lithium using wet chemical techniques in a hood at the ORELA facility. The 7Be activity was mixed with copper powder and pressed into aluminum holders that are designed to fit into a multi-sample target wheel to be used with a Cs-sputter ion source. Six such cathodes were made and are ready for testing. The ion source is also ready for testing, and the initial tests will be conducted in January 2003 at the OLTF. The ion source was developed and optimized at the ISTF1 and then modified slightly to fit onto the front end of the separator at the OLTF, which is identical to the front end of the RIB production platform. Once testing is completed, cathodes with about ten times the activity will be prepared for use on the RIB production platform.

Purified beams of Ge (~95%) and Sn (>99%) isotopes have been delivered to experiments using the technique where the isotope of interest is extracted as a sulfide molecular ion and then the negative ion is produced when the beam is passed through a Cs-vapor charge exchange cell. This process removes the isobaric contamination very efficiently allowing essentially pure beams to be delivered to experiments. The intensities and purities of the beams that were delivered are given in another article in this newsletter.

Ion Source Development

Development and testing of ion sources for production of radioactive ion beams is done at the ISTF1 and then on-line tests are made at the OLTF using low-intensity beams from the tandem electrostatic accelerator. A fairly simple positive surface-ionization source is being modified to fit in the standard ion source enclosure for the facility and will be ready for on-line tests at the OLTF in the near future. The ionization surface will be either a high-porosity carbon matrix with an iridium coating or a tubular surface of tantalum or tungsten depending on which design has the highest efficiency for Rb ions. The efficiency measurements for stable Rb ions and ion source emittance measurements are now being made at the ISTF1. This ion source will be coupled to a uranium carbide target to provide purified beams of neutron-rich isotopes of rubidium that are produced via proton-induced fission using 40-MeV protons.

All of the accelerated neutron-rich beams that are presently available at the HRIBF are produced using low energy (40 MeV) protons to induce fission in a uranium carbide target. Another way to produce beams of these fission fragments is being investigated. This involves photofission in uranium foils using the 150-MeV electron beam from ORELA. Calculations suggest that the production rates for some selected isotopes will be significantly higher using photofission than when using the low energy proton beam that is presently available. For example, the production rate of 82Ge in the target will increase by a factor of about 80 and the production rate of 132Sn will increase by about a factor of 800. The questions that must now be addressed are how efficiently can the fission fragments be transported to the ion source and what is the ionization efficiency.

The fission fragments will recoil out of the thin uranium foil, be stopped in a high pressure atmosphere of He gas that contains an aerosol, and then be transported to an ion source through a few meters of tubing. The aerosols, with the attached fission fragments, will be injected into the ion source with as little He gas as possible. The He will be removed using skimmers and side-jets but a significant flow rate (~0.03 liters/min) of He will still be injected into the ion source. Modifications to our standard EBP ion source have been made, and the measurements indicate that an unacceptable reduction in the efficiency of the ion source occurs at He flow rates that are greater than 0.02 liters/min, indicating that further development efforts are necessary. Continuing efforts will focus on development of the ion source to handle larger He flow rates and improved skimmer designs to more efficiently remove the He before it enters the ion source.

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RA2 - Accelerator Systems Status

ORIC Operations and Development

ORIC operated from the first week of August through the middle of September. In August a 3uA, 85-MeV alpha beam was used for 18F production. The only difficulty during this period occurred in late August when the electrostatic deflector began experiencing high drain current. The septum was found to have a small hole burned through it, and replacement of the septum corrected the problem with minimal downtime. In September, the experimental program shifted back to neutron-rich beam experiments, and ORIC provided 10uA of 42-MeV protons for this effort through the end of the calendar year. This was a very smooth operational period for ORIC, with the only major problem being a brief period of instability in the rf system tuning loop. In particular, ORIC operation resulted in 396 hours of RIB beam on target in the first quarter of FY03.

Regarding development, Tony Mendez has been exploring potential design changes to the ORIC ion source which have the potential to increase cathode lifetimes for helium operation. Several experiments are planned for the February-March time frame during the tandem accelerator tank opening. Additionally, new extraction system channels are being fabricated to assure a full complement of spares which incorporate small design changes made in recent months.

Tandem Operations and Development

The Tandem Accelerator has operated for more than 2100 hours since the last report with almost 40% of the beam on target being RIB beams of 18F, 80Ge, 128Sn, 130Sn, 132Sn, and 132Te. The machine ran at terminal potentials of 2.33 to 23.73 MV and the stable beams 1H, 2H, 12C, 18O, 28Si, 32S, 48Ti, 58Ni, 80Se, 90Zr, 116Sn, 124Sn, 130Te, 138Ba, and 197Au, were also provided. The tandem ran for almost five months without opening for maintenance, when a lull in the schedule and excessive noise from the tank caused the machine to be opened. Two rotating shaft bearings were found to be failing and were replaced. Unfortunately, this was not the cause of the noise and a second tank opening was necessary. The noise was coming from a bearing on the column base chain sheave, but there was also a failure of the middle chain sheave bearing in the terminal. The column base bearing had been in service since being put in the tank more than twenty years ago and the terminal bearing had been replaced seventeen years ago. It is very lucky that we found the terminal bearing before complete failure since it could have caused a chain to break. About 170 hours were used to condition the machine for operation up to 24 MV. A good deal of the conditioning time was taken to correct problems in units 17 and 18 which had been causing ticking when the machine was above 22 MV.

RIB Injector Operations and Development

During this reporting period, we delivered pure beams of

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 3 euA of 85-MeV 4He from the Oak Ridge Isochronous Cyclotron (ORIC). In the case of the pure 18F beam, the 18O contamination was eliminated by passing the beam from the 25-MV Tandem Electrostatic Accelerator through a thin carbon foil and selecting the 9+ charge state. The KENIS failed due to a short between the cone, grid, and ground. This failure mode occurred in the previous two ion sources of this type.

The heavy neutron-rich beams were produced via proton induced fission of 238U by bombarding a uranium carbide coating on both a reticulated vitreous carbon matrix target and a graphitic foam target coupled to an Electron Beam Plasma (positive) Ion Source (EBPIS) with 10 uA of 42-MeV 1H. The pure tin beams were produced by passing a positive tin sulfide beam through the recirculating cesium jet charge exchange cell and selecting the negative tin beam resulting from molecular breakup. Fortunately, there are no contaminating beams of the sulfides of tin isobars. Sulfur is introduced into the uranium carbide target by flowing hydrogen sulfide gas through a dedicated variable leak valve into the EBPIS internal gas feed line. A special gas manifold was installed on the third floor to accommodate the very hazardous hydrogen sulfide.

This is the first time that this technique has been used to produce pure heavy neutron rich beams accelerated to a few A-MeV.

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RA3 - User Group News

The annual Users Executive Committee Election was held this fall. We would like to welcome Jeff Blackmon and David Radford to this committee. They will serve for three years and will replace Peter Parker and Krzysztof Rykaczewski. We thank Peter and Krzysztof for their service to the HRIBF. The committee membership is:

HRIBF Users Group Executive Committee for 2003
Ani Aprahamian Notre Dame University
Jeff Blackmon Oak Ridge National Laboratory
Paul Mantica (chair) Michigan State University
David Radford Oak Ridge National Laboratory
Demetrios Sarantites Washington University
Ed Zganjar Louisiana State University

The new Chair of the Users Executive Committee has the following message for HRIBF users:


``The Users Executive Committee would like to continue to encourage strong interactions between the on-site ORNL staff and outside users through workshops on special topics. The goals of the workshops are to enhance the available capabilities and provide an outside voice on developmental direction at HRIBF. Last year, a very successful transfer reactions workshop was hosted by ORNL and organized by Jolie Cizewski and Ray Kozub. If you have interest in organizing a workshop this year, please contact one of the members of the Users Executive Committee.

The HRIBF and the Users Executive Committee will also be considering ways to enhance the presence of outside users on future RIB experiments. The fact that RIB experiments present a host of challenges that may discourage potential users must be addressed. I would appreciate receiving comments from users on ways to foster a more active user group.'' -- Paul Mantica, Chair, Users Executive Committee.


The annual HRIBF Users Group Meeting was held at the Fall DNP Meeting in East Lansing this year. More than 80 people attended a joint session of Users Groups from HRIBF, 88-Inch, ATLAS, MSU, GAMMASPHERE, and RIA. Our session was chaired by Ani Aprahamian and presentations on the facility and recent research were given by Carl Gross and Witek Nazarewicz, respectively. The next meeting will be held at October's DNP meeting in Tucson, AZ.

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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.

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RA5 - HRIBF Experiments, August-December 2002

Dates Experiment Energy Beam Beamline Spokesperson/Institute
8/1 RIB-039 Conditioning
8/2 RIB-044 108 MeV 18O DRS R. Kozub/Tennessee Tech University
8/5-6 RIB-039 Conditioning
8/7-15 RIB-044 108 MeV 18F DRS R. Kozub/Tennessee Tech University
8/16 RIA School 235 MeV 58Ni RMS
8/17-18 Scheduled Shutdown
8/19 RIB-099 11 MeV 18O DRS D. Bardayan/ORNL
8/20-23 RIB-039 Conditioning
8/24-25 Scheduled Shutdown
8/26 RIB-104 250 MeV 58Ni SCAT J. Liang/ORNL
8/27 RIB-082 110 MeV 32S APB C. Gross/ORNL
8/28 RIB-105 140 Mev 58Ni BL17 P. Hausladen/ORNL
8/29 RIB-068 135 MeV 32S RMS A. Galindo-Uribarri/ORNL
8/30 12 MeV 1H
8/31-9/2 Shutdown (Labor Day)
9/3-4 RIB-076 200 MeV 48Ti Von Hamos C. R. Vane/ORNL
9/5 RIB-082 250 MeV 58Ni APB C. Gross/ORNL
9/6 RIB-084 550 MeV 130Te RMS J. Gomez del Campo/ORNL
9/9-11 RIB-090 500-600 MeV 138Ba RMS D. Radford/ORNL
9/12-13 RIB-092 550 MeV 138Ba APB J. Cizewski/Rutgers University
9/14-15 Scheduled Shutdown
9/16-18 RIB-088 390 MeV 130Te RMS D. Radford/ORNL
9/19-25 130Sn
9/26-29 RIB-077 179 MeV 80Ge RMS A. Galindo-Uribarri/ORNL
9/30-10/4 RIB-095 396 MeV 132Te RMS N.-V. Zamfir/Yale University
10/5-6 Scheduled Shutdown
10/7 RIB-093 8 MeV 1H SCAT J. Beene/ORNL
10/8 RIB-068 22 MeV 124Sn SCAT A. Galindo-Uribarri/ORNL
10/9 446 MeV 12C RMS
10/10 RIB-014 40 MeV 2H OLTF D. Stracener/ORNL
10/11 33 MeV 1H
10/12-13 Scheduled Shutdown
10/14 RIB-039 Tandem/Beam Development
10/15 RIB-091 550 MeV 124Sn APB J. Liang/ORNL
10/16 RIB-014 33 MeV 1H OLTF D. Stracener/ORNL
10/17-18 RIB-100 496 MeV 124Sn DRS R. Kozub/Tennessee Tech University
10/19-20 Scheduled Shutdown
10/21 RIB-091 550 MeV 124Sn APB J. Liang/ORNL
10/22 560 MeV Mass 132
10/22-28 452-536 MeV 132Sn
10/29 RIB-088 384 MeV 128Sn RMS D. Radford/ORNL
10/30 RIB-091 480-506 MeV 132Sn APB J. Liang/ORNL
10/31 RIB-097 550 MeV 132Sn RMS E. Zganjar/Louisiana State University
11/1 124Sn
11/2-3 Scheduled Shutdown
11/4-5 RIB-093 8.175 MeV 1H SCAT J. Beene/ORNL
11/6-7 RIB-097 550 MeV 126Te RMS E. Zganjar/Louisiana State University
11/8 12 MeV 1H
11/9-10 Scheduled Shutdown
11/11-12 RIB-068 8.175 MeV 1H SCAT A. Galindo-Uribarri/ORNL
11/13 RIB-013 110 MeV 58Ni DRS J. Blackmon/ORNL
11/13 RIB-105 110 MeV 58Ni BL35 P. Hausladen/ORNL
11/14 RIB-039 Conditioning
11/14-15 RIB-013 9.6 MeV 12C DRS J. Blackmon/ORNL
11/16-17 Scheduled Shutdown
11/18 RIB-068 8.175 MeV 1H SCAT A. Galindo-Uribarri/ORNL
11/19-20 RIB-097 550 MeV 124Sn RMS E. Zganjar/Louisiana State University
11/21-22 RIB-093 270 MeV 90Zr SCAT J. Beene/ORNL
11/23-24 Scheduled Shutdown
11/25-26 RIB-084 550 MeV 130Te RMS J. Gomez del Campo/ORNL
11/27 RIB-039 Tandem/Beam Development
11/28-12/1 Scheduled Shutdown (Thanksgiving)
12/2 RIB-039 Tandem/Beam Development
12/3-6 Scheduled Maintenance
12/7-8 Scheduled Shutdown
12/9 Scheduled Maintenance
12/10-11 RIB-093 270-370 MeV 90Zr RMS J. Beene/ORNL
12/12-13 Unscheduled Maintenance
12/14-15 Scheduled Shutdown
12/17-23 RIB-093 495 MeV 130Te, 132Sn RMS J. Beene/ORNL
12/24-31 Scheduled Shutdown

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Witek Nazarewicz Carl J. Gross Chang-Hong Yu
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witek@mail.phy.ornl.gov cgross@mail.phy.ornl.gov chy@mail.phy.ornl.gov
+1-865-574-4580 +1-865-576-7698 +1-865-574-4493

Holifield Radioactive Ion Beam Facility
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Telephone: +1-865-574-4113
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