Edition 9, No. 4 Summer Quarter 2001 Price: FREE

Breaking News Feature Articles Regular Articles

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

Feature contributors: R. L. Auble, D. C. Radford, M. S. Smith, C.-H. Yu
Regular contributors: M. R. Lay, M. J. Meigs, P. E. Mueller, D. W. Stracener, B. A. Tatum

A. New 17F Beam Intensity Record of 107 Ions per Second on Target

In a recent experiment (RIB-086), a 17F beam was provided to the Enge spectrometer which achieved a record high 17F beam-on-target intensity for the HRIBF. The beam of 122-MeV 17F from the 25-MV tandem electrostatic accelerator was post stripped to the 9+ charge state to remove any 17O contaminant, and the intensity of the beam was monitored by a carbon foil/MCP detector located 1 meter before the target. The beam intensity consistently exceeded 8.5x106 particles per second (pps) with peak intensities of 107 pps (1.6 pA).

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B. Deadline for Special Call for Proposals Requiring Pure Sn Beams Extended Two Weeks

In light of the upcoming NSAC Review of the nuclear structure and astrophysics research program, we have been asked, and have agreed to extend the deadline for our special call for proposals requiring pure neutron-rich Sn RIBs. The new deadline for receipt of the proposals is September 17. Intensities of the 132Sn beams on target are in excess of 104 ions/second for energies below the Coulomb barrier and approach 5 x 103 ions/second above the barrier. We have provided a beam intensity estimator on our website. This large table lists beams and their intensities into the tandem as a function of ORIC beam current. The calculator predicts the charge state fraction, terminal voltage, and estimated intensity of RIB on target per uA of ORIC beam. Additional details on the special call for proposals are available. The next regular meeting of the PAC will occur in mid-January with a proposal deadline in mid-December.

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C. Personnel Changes; Jim Beene Resumes Directorship of HRIBF

During the past year Jim Beene was asked to lead a Task Force to investigate the possibility of constructing a neutrino facility at the Spallation Neutron Source (ORLaND) and temporarily stepped down as Director of the HRIBF. The Task Force is nearing completion of its duties, and Jim has been able to return as Director. In his absence, Ron Auble served as Acting Director and Ray Juras served as Acting Head of Operations as well as continuing to lead the HRIBF Engineering Group. Ron will resume his duties as Head of Operations and Ray will devote his time to the Engineering Group. We thank Ron and Ray for their extra service during this period and note the many HRIBF successes achieved during their service.

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1. HRIBF Update and Near-term Schedule

At the end of the last reporting period, the tandem was shut down due to failure of a bearing, and subsequent failure of the stator windings, in one of the 400Hz generators which provide power to electronics in the tandem. An attempt to rebuild the generator in-house was unsuccessful, requiring that the generator be returned to the manufacturer. The rebuilt generator was reinstalled the week of May 7, and the n-rich RIB program was resumed on May 14.

The uranium carbide target and EBP ion source used for n-rich RIB production have worked remarkably well and have allowed completion of several experiments which are described elsewhere. The only malfunction was a problem in the control system that resulted in an external water leak on the target/ion-source assembly. Fortunately, a method was devised which allowed the leak to be repaired in-situ, thus minimizing down time and allowing the n-rich RIB campaign to be completed. The UC2 target-EBPIS was removed in June and is currently in storage for subsequent use in future n-rich RIB experiments.

Following removal of the n-rich target-ion source assembly, the RIB injector was reconfigured for installation of a hafnia target Kinetic Ejection Negative Ion Source (KENIS) for the production of 17,18F. During the changeover, the tandem accelerator was used to provide stable ion beams.

The 17,18F campaign is in progress and is expected to run through August or early September. Following completion of the 17,18F campaign, stable ion beams will be provided for detector development, optimization of pure Sn n-rich beams, nuclear structure experiments, and ion source development. At present, the tandem is scheduled to be shut down for maintenance from mid-September until mid-October. During the shutdown, the KENIS will be removed and the UC2 target-EBPIS will be reinstalled to provide pure Sn RIBs using the elementally selective formation of the sulfide.

During the next several months, on-line testing of positive- and negative-surface ionization sources is expected to be completed. These ion sources are being developed to enhance our capability for providing pure beams of the group VIIA elements (negative source), in particular isotopes of Cl, Br, I, and group IA elements (positive source).

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2. PAC-6 Results

The sixth Program Advisory Committee met on June 14-15, 2001. Of the 20 proposals received, 13 received at least some allocation of beam time. Approved experiments require the following RIBs: 17F, 18F, 126Sn, 130Sn, 134Te, and 135I. Titles and spokespersons of accepted experiments are available.

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3. Recent HRIBF Research - Physics with Heavy Neutron-rich RIBs at the HRIBF*

We report on recent experiments using neutron-rich radioactive ion beams (RIBs) from the HRIBF facility. We have performed successful Coulomb excitation measurements of B(E2; 0+ --> 2+) in 126,128Sn and 132,134,136Te, and have proven the feasibility of using fusion-evaporation reactions of RIBs on light targets to study evaporation residues with gamma-gamma-recoil coincidence spectroscopy. The experimental setup for these experiments consisted of the CLARION Ge detector array and the HyBall CsI charged-particle detector array at the target. Foil-plus-microchannel-plate (MCP) ion detectors were used both to count the beam and to detect recoiling reaction products. Thick (4-5 mg/cm2) metallic foils placed near the achromatic focus of the RMS [1] were also used to excite K vacancies in beam particles; detection of the resulting X rays provided a continuous measurement of the isobaric composition of the beam.

Coulomb excitation measurements have been performed using a natural carbon target of 0.83 mg/cm2. Carbon ions scattered out of the target were detected in the HyBall, and provided a very clean gate for coincident gamma rays. The C ions could be cleanly distinguished from other ions in the HyBall CsI detectors by means of pulse-shape analysis. The ratio of gamma-HyBall coincidences to HyBall singles gives an excellent measure of the excitation probability of the beam during the collision. In this way, measurements of the B(E2; 0+ --> 2+) have been obtained for the first time for the nuclides 126,128Sn and 132,134,136Te. Beam intensities of 3x105 to 107 ions/s and energies ~3 MeV/nucleon were used.

Fig. 3-1 - Gamma-ray spectra from Coulomb excitation of beams from the HRIBF, in prompt time coincidence with scattered carbon target ions detected in the HyBall CsI detectors. Some of the spectra have a small normalized random coincidence component subtracted. Unlabeled peaks in the spectra for masses 126 and 128 are believed to arise from Coulomb excitation of the odd-odd Sb isotopes to previously unobserved levels.

Gamma-ray spectra in prompt coincidence with carbons are shown in fig. 3-1 for the five different masses. The Sn isotopes of interest are strongly contaminated with the Sb and Te isobars, and the 134,136Te beams show significant components of the corresponding stable Ba nuclei. Analysis of the results to extract the final B(E2) values is in progress. Figure 3-2 shows very preliminary results together with the systematics for measured Sn, Te, Xe, Ba and Ce isotopes, taken from ref. [2]. The present results are shown as filled circles.

Fig. 3-2 - Preliminary values of B(E2; 0+ --> 2+) extracted from the spectra of fig. 3-1 (filled circles) together with systematics compiled in reference [2] (open symbols).

It is very interesting that our preliminary B(E2; 0+ --> 2+) value for 136Te is similar to, or perhaps even a little lower than, that for 134Te. This is contrary to expectations from the shell model, and from extrapolating the systematics of heavier N = 82,84 isotones. If this result stands after the final analysis, it could be interpreted as indicating that the shell-model parentage of the first 2+ state in 136Te is dominated by the two-neutron state, i.e., the corresponding level in 134Sn at 725 keV, with only a small component of the two-proton (134Te, 1279 keV) level. The weak mixing implied by this interpretation is somewhat surprising.

In another experiment, the inverse-kinematics transfer reaction 9Be(134Te,8Be) at about 4 MeV per nucleon was used to identify single-neutron states in 135Te. Unbound 8Be products were detected in the HyBall CsI detectors as a pair of alpha particles, and could easily be distinguished from other types of charged particles on the basis of the pulse shape. Gamma rays in coincidence with the alpha pairs produce a very clean spectrum, shown in the top portion of fig. 3-3. It is dominated by the single-neutron states of 135Te; our preliminary assignments are indicated in the lower part of fig. 3-3. The data shown were obtained in 16 hours with a beam current of about 4x105 i/s.

Fig. 3-3 - (Top) Gamma-ray spectrum from the 9Be(134Te,8Be)135Te reaction in coincidence with 2-alpha clusters detected by the HyBall. (Bottom left) Particle identification spectrum for one of the CsI detectors. (Bottom right) Partial level scheme for 135Te, showing preliminary tentative configuration assignments.

The 1180 keV level was first observed in the decay of a 19/2- isomer populated by spontaneous fission, and the levels at 657, 1081, 1126 and 1180 keV have also been seen by Hoff et al. [3] in the beta decay of 135Sb. Our observations strongly support the assignments of p3/2 and p1/2 single-neutron structure to the first two excited states as suggested by Hoff et al. [3], but the position of the f5/2 single-neutron state is more ambiguous. Hoff et al. assign this as the 1126-keV level, but the systematics of N = 83 isotones suggest that our newly-observed state at 1400 keV could be a better candidate.

More details may be found at


* Collaborators include D.C. Radford, C. Baktash, A. Galindo-Uribarri, C.J. Gross, T.A. Lewis, P.E. Mueller, P.A. Hausladen, D. Shapira, D.W. Stracener, and C.-H. Yu, (ORNL); C. J. Gross (ORISE/ORNL); B. Fuentes and E. Padilla (UNAM, Mexico); D. J. Hartley (U. Tennessee); C. J. Barton, M. Caprio, and N. V. Zamfir (Yale U.).

[1] C. J. Gross et al., Nucl. Instrum. Methods Phys. Res. A450, 12 (2000).
[2] S. Raman et al., At. Data Nucl. Data Tables 78, 1 (2001).
[3] P. Hoff et al., Z. Phys. A332, 407 (1989).

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4. Recent HRIBF Research - Implications of the HRIBF 17F(p,p)17F Measurement for Nova Nucleosynthesis*

Nova explosions are among the largest explosions in the Universe, and are characterized by temperatures over 108 K and densities up to 104 g/cm3. They are responsible for producing much of the 13C, 15N, and 17O found on earth, and are powered by thermonuclear reactions on radioactive nuclei such as 17F(p,gamma)18Ne. The nuclear burning in novae is not dominated by equilibria or steady flow, thus individual reactions can influence both the energy generated and the abundances synthesized in the explosion. For example, the 17F(p,gamma)18Ne reaction rate is thought to influence, among other things, the amount of 15N, 17,18O, and 18F nuclides produced in nova explosions. The 17F(p,gamma)18Ne reaction is also part of a sequence of reactions that provide a possible transition from the hot CNO cycle to reactions in the rapid proton capture process (rp-process) in the most energetic novae [1].

Uncertainties in resonances in 18Ne which could dominate the 17F(p,gamma)18Ne reaction rate led to a rate uncertainty of more than a factor of 100 at stellar explosion temperatures. A measurement of the excitation function for the 1H(17F,p)17F reaction at HRIBF gave the first unambiguous evidence for a crucial, unnatural parity (3+) level in 18Ne and enabled a precision determination of its energy and total width [2-4]. This led to a new determination of the 17F(p,gamma)18Ne reaction rate [4], which differs slightly from two previous rate estimates [5,6] but differs by up to a factor of 30 from the rate [7] in the most widely-used reaction rate library [8].

The main objective of this measurement was to give a firmer experimental basis for the 17F(p,gamma)18Ne reaction rate. An additional objective was to determine if this new reaction rate changed our understanding of element synthesis in explosions such as novae and X-ray bursts. To determine the influence of the new rate in stellar explosions, the system of coupled ordinary differential equations governing the temporal evolution of the nuclear composition (a reaction "network") is integrated from the initiation of the outburst to its conclusion [9]. The hydrodynamic "trajectories" (temperature and density as a function of time) 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 - an approach which is computationally difficult at this time. This coupling can, however, be done in an approximate way by using a one-dimensional hydrodynamics calculation with a limited reaction network to generate different trajectories for shells ("zones") of the envelope at different radii which are ejected after the outburst. Then, separate nuclear reaction network calculations with the full complement of nuclei and nuclear reactions are carried out to study the nucleosynthesis details within each zone.

We have used this multi-zone, "post-processing" approach with nova trajectories from Starrfield and collaborators [10] combined with a reaction network from Hix and collaborators [9] and nuclear reaction rates from Thielemann and collaborators [8]. We considered nova outbursts on 1.25 and 1.35 solar mass white dwarf stars with a heavy concentration of O, Ne, and Mg [10]. The matter ejected into the interstellar medium in these models is divided into approximately 30 zones. The 1.35 solar mass model, representing less common explosions, is significantly hotter with peak temperatures of 4.3 x 108 K. The nucleosynthesis was calculated using the new ORNL 17F(p,gamma)18Ne reaction rate [4] and those of Refs. [5-7]. The ratio of the mass fractions (abundances) produced in each zone, and the weighted sum, using the ORNL rate to the mass fractions produced using a different rate was determined.

Fig. 4-1 - The ratio of mass fractions synthesized in the 1.25 solar mass ONeMg White Dwarf Nova Model (top) and 1.35 solar mass model (bottom) plotted against nuclide mass using the new reaction rate to the abundances using the rate from Ref. [7].

The results for the ratio summed over all zones for the 1.25 and 1.35 solar mass white dwarf models are plotted as a function of nuclide mass in the fig. 4-1. With the new rate, the mass fractions of some nuclei (including 17O, which is predominantly produced in novae, as well as 15N and others) averaged over the entire explosion envelope are as much as a factor of 2 larger than the mass fractions predicted using the rate from Ref. [7]. The mass fractions in the hottest (i.e., inner) zones of the explosion differ by up to a factor of 600 compared to the abundances predicted using the rate from Ref. [7] for isotopes such as 17O and 18O. For the 1.35 solar mass model, the ratios are up to a factor of 4 larger when averaged over the entire explosion envelope compared to the rate from Ref. [7], and up to a factor of 15000 larger in the hottest zones of the explosion. The differences in abundances predicted with the new rate indicate that the rates of Refs. [5,6] are much smaller - only a few percent - for both nova models. The results from the hottest zones may be particularly important when mixing between the zones is taken into account, which we plan to examine in a future study. Investigations have also been carried out for a nova explosion on a 1.0 solar mass CO white dwarf, and calculations for X-ray burst trajectories are underway.

These calculations demonstrate the influence that individual reactions can have on nucleosynthesis in nova outbursts, and illustrate the need for placing important nuclear reactions in explosive nucleosynthesis on a firm experimental basis.


* Collaborators include M. S. Smith, D. W. Bardayan, and A. Mezzacappa (ORNL); S. Parete-Koon and M. W. Guidry (U. Tennessee); W. R. Hix (ORNL, U. Tennessee); S. Starrfield (Arizona State).

[1] R. K. Wallace, S.E. Woosley, Astrophys. J. Suppl. 45, 389 (1981)
[2] D. W. Bardayan et al., Phys. Rev. Lett. 83, 45 (1999)
[3] Physical Review Focus, July 9,1999,
[4] D. W. Bardayan et al., Phys. Rev. C 62, 055804 (2000)
[5] R. Sherr and H. T. Fortune, Phys. Rev. C 58, 3292 (1998)
[6] A. Garcia et al., Phys Rev. C 43, 2012 (1991)
[7] M. Wiescher, J. Gorres, and F.-K. Thielemann, Astrophys. J. 326, 384 (1988)
[8] F.-K. Thielemann et al., (1995)
[9] W. R. Hix and F.-K. Thielemann, J. Comput. Appl. Math. 109, 321 (1999)
[10] M. Politano et al., Astrophys. J. 448, 807 (1995); S. Starrfield, priv. comm. (2000)
[11] M. S. Smith et al., in "International Conference on Physics with Radioactive Ion Beams - ISOL'01", eds. C. J. Gross, D. J. Dean, M. S. Smith, (2001).

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5. HRIBF Well Represented at ENAM 2001; Selected to Host Next ENAM Conference

At the 3rd International Conference on Exotic Nuclei and Atomic Masses held on July 2-7, 2001 (ENAM 2001) in Hameenlinna, Finland, three invited talks were given on recent experimental results from HRIBF. Krzysztof Rykaczewski (ORNL) gave a review talk on progress in proton-decay studies, highlighting the HRIBF results [1] of fine structures in proton decays of 145,146Tm. Chang-Hong Yu (ORNL) presented a talk on "Physics with Neutron-Rich Radioactive Ion Beams at HRIBF," reporting preliminary results from experiments using neutron-rich Ag, Sn and Te beams for Coulomb excitation, transfer, and fusion-evaporation reactions [2]. Robert Grzywacz (U. Tennessee) gave a talk on spectroscopic applications of the digital-signal processing technique that was first commissioned at HRIBF [3], and now successfully tested for fragmentation-based experiments. All three talks were well received and provided an update on recent activities at HRIBF. Conference attendees were especially interested in the technical aspects of running experiments with radioactive ion beams at HRIBF, as well as the pure Sn beams that HRIBF is now ready to deliver.

The 3rd ENAM Conference International Advisory Committee also passed a resolution allowing the Physics Division of Oak Ridge National Laboratory to organize the 4th ENAM conference to be held in 2004 or 2005. Hosting the next ENAM will give HRIBF an opportunity to showcase its world-class equipment and RIB capabilities to the low-energy nuclear physics community. The organization of the 4th ENAM conference will be chaired by Witek Nazarewicz, and more details about the conference will be announced in the future.


[1] HRIBF Newsletter, Spring Quarter 2001, and HRIBF Newsletter, Winter Quarter, 2000.
[2] HRIBF Newsletter, Fall Quarter, 2000; and this newsletter.
[3] HRIBF Newsletter, Spring Quarter, 2001.

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6. UNIRIB Workshop Held August 22

The UNIRIB Consortium held a 1-day workshop, August 22, preceded by an Executive Committee Meeting on August 21. Ed Zganjar was elected Chairman of the Executive Committee succeeding Joe Hamilton while Paul Semmes was elected Vice-chair. Among the business accomplished, a new mission statement was drafted which emphasizes UNIRIB's unique role as a multi-university presence at HRIBF in addition to its research and training roles. During the workshop overview talks were heard from UNIRIB and HRIBF researchers concerning recent and developing research opportunities. The well-attended workshop elicited lively discussions on a wide variety of experiments and explored strategies for successful research programs at the HRIBF.

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RA1 - RIB Development

Early in this last quarter we tested two slightly different uranium carbide targets at the UNISOR Facility. These targets were made by the same manufacturer and consisted of a thin layer (10-12 um) of uranium carbide (UC) deposited onto a reticulated vitreous carbon (RVC) matrix. One of the targets was made at the same time as the original batch but included a layer of iridium between the UC and the RVC matrix in an effort to prevent the fission fragments produced in the UC layer from diffusing into the carbon matrix. This Ir layer lowered the production rates by about 15% due to the lower uranium density, and measured yields were found to be about 15% lower than the yields from the original UC/RVC targets. Thus, diffusion into the carbon does not appear to be a problem. The other target tested was made at a later time and turned out to be much more brittle than the original batch, requiring more careful handling. However, the measured radioactive ion beam intensities were quite similar to the original batch of UC/RVC targets. One of the trace contaminants in all of these targets is sulfur, and we found that pure beams of Sn isotopes could be extracted as positively-charged SnS molecules from the EBP ion source. The results of the measurements of these isobarically pure Sn beams were reported in the supplement to the last newsletter.

In the last few weeks we have made some hardware changes to the UNISOR separator to increase its reliability and versatility. Some minor changes were made to the front end to allow the batch-mode ion source to be mounted and tested at the UNISOR Facility, and testing of this source will begin in the next couple of weeks. A section of the beam line has been refurbished, which should result in more reliable operation. Two 25-year old Sargent-Welch turbo-pumps have been replaced (after one of them crashed) and many of the original (almost thirty years old) elastomer seals have been eliminated and replaced with metal gaskets. A new Faraday cup to measure the total beam current from the ion source will be installed, and the insulators for the optics elements (Einzel lens and steerers) have been cleaned or replaced.

Beam development during the next few months will focus on the following items:

Work has begun (or will begin shortly) on these projects, and we hope to report positive results in future newsletters.

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RA2 - Accelerator Systems Status

ORIC Operations and Development
ORIC provided up to 7 uA of 42-MeV protons to the target-ion source on the RIB platform for neutron-rich RIB production during most of the operating period. Near the end of July, up to 3 uA of 44-MeV deuterons were delivered to the target-ion source for 17F production. The only major problem with ORIC operation during the period was a water leak on the upper rf trimmer capacitor. The leak occurred in a short bellows line connecting the trimmer body to the ground plane. Unfortunately, the leak caused instabilities in the rf system that resulted in other component damage, but the problems were corrected and the rf system is now running quite well.

Tandem Operations and Development
The Tandem Accelerator has provided more than 837 hours of beam on target since the last report with more than twenty percent of the time for radioactive beams. The machine ran at terminal potentials of 1.77 to 23.42 MV and 1H, 13C, 16,17O, 32S, 35,36,37Cl, 58Ni, 76Ge, 74,76,78,80,82Se, and 130Te, were provided from the stable injector while masses 17, 19, 78, 80, 128, 134, 136, and 138 were provided from the RIB injector. The tank remained open for the first two weeks of the period due to a failed Georator (alternator) at the lower major dead section. The two units that had been causing voltage-holding problems were carefully examined and nothing was seen externally. The ticking continued when the accelerator was operated at higher gradients. During the scheduled tank opening in September more work will be done to try to isolate or cure the problem.

The recirculating stripper was run for the first time, and it has been determined that reconfiguration of the terminal will be necessary to allow it to work properly without also using sublimation pumps. Sublimation pumps require considerable maintenance; elimination of the pumps would significantly increase research hours. In addition, sublimation pumps create titanium dust, which can cause voltage-holding problems. Unfortunately, the sublimation pump is not working now due to unknown reasons concerning the sublimation pellets themselves. New sublimation pellets will be installed during the shutdown, which should allow the gas stripper to be run at sufficient pressure for equilibrium stripping. At the moment only sub-equilibrium stripping can be done.

RIB Injector Operations and Development
During this reporting period, we delivered the following neutron rich beams to the Recoil Mass Spectrometer (RMS) in Robinson Hall using the uranium-carbide-target-electron-beam-plasma ion source:

Isotope Intensity
(ions per second)
Contaminant Intensity
(ions per second)
Energy (MeV) Charge State
78Ge 4.5x105 1.1x106 174.5 11
80Ge 1.8x105 1.6x106 179 11
134Te 1.7x106 7.2x105 396 16
134Te 3.9x105 1.6x105 530 14/26
134Te 1.8x105 7.5x104 560 15/28
136Te 2.5x105 2.5x105 396 16
138Te not observed 1.9x106 396 16

At the end of the neutron-rich beam campaign we measured isobarically pure beams of Sn isotopes with the tape system after the second stage mass analyzer before injection into the 25 MV tandem electrostatic accelerator. The results of these measurements were reported in the supplement to the last newsletter.

We have begun a month-long 17F/18F campaign with an HfO2 target-kinetic-ejection-negative ion source, initially delivering 5.1x105 i/s of 40.1 MeV 17F+5 ions per second to the nuclear astrophysics endstation. The 17O contaminate was of equal intensity.

During the neutron-rich campaign, two failures occurred in C111S. In both cases, repairs were made with the uranium-carbide-target-electron-beam-plasma ion source in place and with minimal radiation dose to HRIBF staff and demonstrate that we are able to effectively conduct maintenance in C111S even with elevated radiation dose rates.

After several years of operation, the mounting screws for the Faraday cup that measures ORIC light ion beam current just before the target (FC_RI9_1) loosened. Unfortunately, one of these four screws fastened the signal wire to the Faraday cup. The loose connection rendered the Faraday cup unusable. An unscheduled tandem accelerator maintenance period allowed us to wait two weeks until the radiation dose rate at 30 cm from the diagnostics vacuum box that contains the Faraday cup dropped to 340 mREM/hr. The Faraday cup was removed, repaired with a new design of locking screw, and reinstalled with a total of 25 mREM shared evenly among a physicist, a technician, a pipefitter, and a radiological control technician. Since the vacuum system was breached, all work was done in full anticontamination clothing including respirators.

The second failure occurred on the target-ion source itself. A control system error caused the electromechanical cooling water return valve for the target-ion source to continuously cycle. The two diaphragm flow switches in series with the valve failed to drop out with reduced cooling water flow. A plastic tube in the cooling water circuit on the exterior of the target-ion source vacuum enclosure developed a heat (steam) induced leak and drained the cooling water system. Fortunately, a flow switch finally dropped out, turning off the target-ion source high current power supplies. The lack of a vacuum leak indicated that there was probably no damage to the target-ion source. We therefore waited 12 days until the radiation dose rate at 30 cm from the front of the target-ion source dropped to 700 mREM/hr and then replaced the plastic tube. A total of 76 mREM was shared mainly between a physicist and a technician but also with a radiological control technician. No anticontamination clothing was worn during this job. In addition to control system changes, all four diaphragm flow switches were replaced with paddle wheel flow switches. This is the third type of flow switch that has been used. The first type, a plunger flow switch, did not always pick up.

We also measured the neutron radiation dose rate in C111N during delivery of neutron rich beams. Assuming a thermal neutron flux only, the activation of a 0.4-gm piece of gold foil measured a neutron radiation dose rate of 160 mREM/hr for 6.9 uA 42-MeV protons on the uranium carbide target. Assuming a standard epithermal neutron flux (252Cf moderated in a 15 cm radius sphere of D2O), a simultaneous measurement with a personal neutron dosimeter yielded a neutron radiation dose rate of 850 mREM/hr. Both of these measurements indicate that the neutron flux in C111N is not sufficient to induce acute radiation damage to electronics.

In order to ameliorate the continuing problem with spark-induced failure of Allen-Bradley control system components at source potential, all modules have been consolidated into one crate, the 5 VDC power supply for target-ion source limit switches has been replaced with a more robust 24 VDC power supply, and ferrite cores have been installed on critical power and signal cables.

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RA3 - User Group News --- Executive Committee Nominations and Upcoming Election

It is time to hold the annual election for the Users Executive Committee. A nomination committee has selected four nominees:

Dick Boyd Ohio State University
Daeg Brenner Clark University
Paul Mantica Michigan State University
Ed Zganjar Louisiana State University

Additional nominations may be submitted from the group at-large by collecting the support of 10 members (as of September 1) and forwarding the name of the nominee to the chairperson of the executive committee, Kris Rykaczewski, at Deadline for at-large nominations is September 15. More information may be found in the Users Group Charter. The two candidates receiving the most votes will replace I-Yang Lee and Bill Walters. They will join Ani Aprahamian (chair for 2002), Peter Parker, Kris Rykaczewski, and Demetrios Sarantites on January 1 and will serve for 3 years. Your ballots will be sent to you by e-mail at the end of September.

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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 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, May - July 2001

Experiment Title Spokesperson/Institute Dates*
RIB-000 Commissioning of the RMS Radford/ORNL
5/30-31 7/13
RIB-012 As+Ti Sub-barrier fusion Liang/ORNL 7/2
RIB-013 Commissioning of the DRS Smith/ORNL 6/21-22
RIB-035 Target ion source development (actinide targets) Stracener/ORNL 5/14(-16:00) 5/21
RIB-037 Tandem development Meigs/ORNL 7/3
RIB-040 Beam diagnostics development Shapira/ORNL 6/5
RIB-060 Accelerator mass spectrometry Galindo-Uribarri/ORNL 7/9-12
RIB-064 1H(17F,p')17F inelastic scattering cross section Blackmon/ORNL 7/16(08:00)-17
RIB-070 Study of the proton-drip line nucleus 69Br and the implications for the astrophysical rp process Batchelder/ORISE 6/25(14:00-)-29
RIB-073 Study of medium-spin excited states in neutron-rich N > 82 nuclei Radford/ORNL 6/12(16:00)-15
RIB-074 Coulomb excitation of neutron-rich Sn and Te isotopes Radford/ORNL 5/15-18
RIB-077 Coulex of neutron-rich Ge isotopes near the N=50 shell closure Galindo-Uribarri/ORNL 6/11(12:00)-12(02:00)
*Weekend operation is suspended due to financial considerations.

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You may contact us at the addresses below.

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
+1-865-574-4580 +1-865-576-7698 +1-865-574-4493

Holifield Radioactive Ion Beam Facility
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37831 USA
Telephone: +1-865-574-4113
Facsimile: +1-865-574-1268