HRIBF NEWS

Edition 11, No. 2	July 2003	Price: FREE

Breaking News

• A. ORIC Improvement Should Enhance n-Rich RIB Yields
• B. Coulomb Excitation of Very Neutron-Rich Sn Isotopes

Feature Articles

• 1. HRIBF Update and Near-Term Schedule
• 2. Recent HRIBF Research - Fusion of the ¹³²Sn Beam on ⁶⁴Ni Target
• 3. Recent HRIBF Research - Study of the Single-Particle Transfer Reaction ²H(⁸²Ge,p)
• 4. Recent HRIBF Research - Mass Measurements of Neutron-Rich Fission Fragments
• 5. High Power Target Laboratory
• 6. Decay Spectroscopy Workshop to be Held at ORNL
• 7. PAC-9 Meeting Scheduled for August 21-22
• 8. Workshop on the Experimental Equipment for RIA Held in Oak Ridge, TN
• 9. 15^th National Nuclear Physics Summer School Held in Knoxville, TN
• 10. Second RIA Summer School on Exotic Beam Physics to be Held at MSU

Regular Articles

• RA1 - RIB Development
• RA2 - Accelerator Systems Status
• RA3 - User Group News
• RA4 - Suggestions Welcome for New Beam Development
• RA5- HRIBF Experiments, August-December 2002

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

Feature contributors: C. Baktash, J. R. Beene, J. C. Blackmon, C. J. Gross, P. A. Hausladen, J. Liang, W. Nazarewicz, A. Tatum, J. Thomas, K. Rykaczewski
Regular contributors: C. J. Gross, M. R. Lay, M. J. Meigs, P. E. Mueller, D. W. Stracener, B. A. Tatum

A. ORIC Improvement Should Enhance n-Rich RIB Yields

ORIC proton beam energy has been increased from 42 MeV to greater than 50 MeV during an extremely productive beam development period in June 2003.  The expected result is that the fission-fragment yield for neutron-rich RIB production may as much as double due to the increase in proton energy.

The original design for ORIC called for a maximum proton energy of 75 MeV.  In practice, the top energy extracted for experiments was limited to about 65 MeV.  Higher energy protons could not be achieved because the entrance of the electrostatic deflector (usually running at about 29 to 29½ inches) could not be moved towards full radius (32 inches) without the complete loss of beam.  In the late 1970’s, ORIC was converted to a heavy-ion booster for the 25MV Tandem as part of the Holifield Heavy Ion Research Facility (HHIRF).  As part of this modification, the rf structure of ORIC was modified to shift the rf frequency range downward by approximately 3 MHz.  These modifications are still in place today, and the general belief has been that proton beams above 50 MeV would not be possible without undoing them, particularly the change in dee-to-dee liner capacitance.  Thus, the ORIC proton beam in recent years has been limited to the mid-40 MeV range (again with the deflector entrance at about 29½ inches).

In recent years, Merrit Mallory, an accelerator physicist and former staff member who worked with ORIC over 30 years ago, has been visiting annually and working with present and former HRIBF staff members to understand the problem of extracting 42-50 MeV protons.  During beam development studies in June these efforts paid off, solving a problem that has existed for over 40 years.  Earlier in these studies, it became apparent that the exit of the electrostatic deflector septum was interfering with the last circulating beam turns, thus limiting the radius at which the beam could be extracted and, hence, the beam energy.  ORIC light ion beams are normally extracted with radial betatron oscillation frequencies greater than the nu-r = 1 resonance.  When the nu-r value decreases, the betatron amplitude completely interferes with the septum.  This year, the interference point in the carbon septum was machined away and permitted operator tuning of the beam out near the nu-r = 1 resonance and to maximum extraction radius, gaining more than 70 turns.  Once the interference point was passed, the extraction efficiency increased to around 55%, with beam energy increased to at least 50 MeV, and the deflector entrance positioned at its mechanical out limit.  Adjustments to allow further motion in the deflector entrance position are expected to result in further increases in the beam energy and extraction efficiency.

Our staff greatly appreciates the efforts of Merrit Mallory, as well as former staff members Jim Ball, Dick Lord, and Ed Hudson who also contributed to this success.  Thanks also to Darryl Dowling, Alan Tatum, and the HRIBF operations and development staff who made the necessary modifications and set up the machine for this work.  In particular, our two most experienced operators, Mike Dinehart and Cliff LeCroy, were the ones who patiently and skillfully tuned the beam to greater than 50 MeV and maximized the extraction efficiency to 55%.

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B. Coulomb Excitation of Very Neutron-Rich Sn Isotopes

We have measured the B(E2;0⁺ --> 2⁺) for the first excited 2⁺ states in the double-closed shell nucleus ¹³²Sn and the two-neutron nucleus ¹³⁴Sn. The results, based on a preliminary analysis are shown in Fig. B-1 along with measurements on the stable Sn isotopes, and earlier HRIBF results on ^126,128,130Sn [1]. The experimental setup developed for the ^132,134Sn measurements was also employed in a successful measurement of B(E2;0⁺ --> 2⁺) for the closed-neutron-shell nucleus ⁸²Ge.

Figure B-1: B(E2;2⁺ --> 0⁺) for first excited 2⁺ states in Sn isotopes. The open circles are adopted values from stable-beam work. The solid red circles are measurements at HRIBF with radioactive beams. ^126,128,130Sn are from Radford et al. [1], while the ¹³²Sn and ¹³⁴Sn results are preliminary values from this experiment. The two blue curves are theoretical calculations from Refs. [2,3].

The availability of isotopically-enriched neutron-rich Sn beams at HRIBF presented us with the opportunity to make the first measurement of excitation matrix elements in a new double-closed shell nucleus¹³²Sn. The high-energy (4.04 MeV) of the 2⁺ state presented severe challenges for a low-energy Coulomb excitation experiment, leading to small excitation probabilities and the necessity of detecting a 4-MeV photon. A setup was developed which was optimized to deal with these issues. The ¹³²Sn experiment was performed using 470 MeV and 495 MeV ¹³²Sn ions incident on a 1.3 mg/cm^{2 48}Ti target. Scattered ¹³²Sn ions and target recoils were detected in a 7 cm diameter annular (CD-style) double-sided Si-strip detector mounted 8 cm downstream of the target. The detector has 48 radial strips and 16 azimuthal sectors, and covered the full range of center-of-mass angles relevant to the Coulex angular distribution (~25° to ~180°) with a total efficiency of almost 80%. Gamma rays were detected in an array of 152 BaF₂ crystals arranged in six blocks mounted in close proximity to the target. A total trigger efficiency of 55% and a full-energy efficiency of 30% was achieved for 4-MeV gamma-rays. In addition, a carbon-foil-MCP beam counter was employed 57 cm downstream of the target and a Bragg counter was mounted at the beam dump 2 m downstream of the target to monitor beam composition. Beam intensities in excess of 10^{5 132}Sn ions per second were achieved (double-stripped), with a purity of 96%. See the January 2003 Newsletter for further discussion. The bombarding energy employed (3.75 and 3.6 MeV/u) are higher than the conventional "safe-energy" limit, which is ~2.8 MeV/nucleon for 180° scattering of ¹³²Sn +⁴⁸Ti. The excitation rate of the 4.04-MeV 2⁺ would have been negligibly small at 2.8 MeV/nucleon. At the higher energies, we limit the distance of closest approach to safe values by limiting the range of center-of-mass scattering angles included in the analysis (maximum angle is ~85° at 3.75 MeV and ~90° at 3.6 MeV). The preliminary result shown in Fig. B-1 is B(E2; 0⁺ --> 2⁺)= 0.14 (6) e²b², which amounts to almost 15% of the isoscalar quadrupole energy weighted sum rule. This is similar to the sum rule strength exhausted by the ²⁰⁸Pb 2⁺ state. We expect the final analysis to produce an uncertainty of approximately 25%.

The large increase over the past year in the intensity of neutron-rich Sn beams available at HRIBF presented us with the opportunity to apply the highly-optimized setup to a measurement on the two-neutron nucleus ¹³⁴Sn. The beam intensity of A=134 isotopes after application of the sulfide purification technique was 9000 ions per second, which was determined to be 61.6% Te, 25.6% Sn, 12.3% Sb and 0.5% Ba. Without purification the beam is ~98% Te. In this case, a ⁹⁰Zr target with a thickness of 1.0 mg/cm² was employed along with a beam energy of 400 MeV, which is below the "safe" limit. The Si detector was moved to 4 cm from the target to accommodate the change in kinematics, but otherwise the setup was identical. The preliminary experimental result obtained was B(E2; 2⁺ --> 0⁺)= 0.029 (6) e²b², which, as can be seen from Fig.B-1, is very close to the value for the two-hole nucleus ¹³⁰Sn.

References

[1] Radford et al., Phys. Rev. Lett. 88, 22501 (2002).
[2] Terasaki et al., private communications and Phys. Rev. C66, 054313 (2002).
[3] Bortignon et al., private communications; Colo et al., presentation at the XXVII Zakopane School of Physics.

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1. HRIBF Update and Near-Term Schedule

After a successful year of running, including a remarkably productive neutron-rich campaign that ended in March, we have had a long scheduled shutdown for maintenance and for carrying out several improvements to the tandem. The start of the shutdown was delayed for several months by the success of the neutron-rich campaign. The improvements, which are discussed in more detail in a later article in this newsletter, should have a substantial impact on tandem operation and reduce maintenance requirements.

During the shutdown, a significant improvement in our understanding of the extraction from ORIC was achieved by HRIBF operations staff under the guidance of ex-ORNL staff member and regular summer visitor Merrit Malory with contributions from Jim Ball, Ed Hudson and Dick Lord (all former Physics Division staff members and ORIC experts). See more details in "Breaking News A". This development may prove to have important applications to extraction from other cyclotrons, but the short-term importance to HRIBF is an increase in proton energy from 42 to approximately 52 MeV, which should almost double our neutron-rich beam intensities.

The scheduled maintenance and upgrade of the tandem is complete. Significant conditioning will be needed before experiments requiring high tandem voltages can be run. The initial schedule includes a calibration run for the mass measurements made at the end of the last campaign, as well as several equipment development runs, followed by a radioactive-beam run using a ⁷Be beam to study proton elastic scattering in inverse kinematics, and a short campaign of stable-beam experiments. The ⁷Be test run will be the first on-line attempt to produce this beam in preparation for the upcoming proton capture experiment. We plan to initiate the next neutron-rich radioactive beam campaign in late September, although we may not yet be fully conditioned to 24 MV.

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2. Recent HRIBF Research - Fusion of the ¹³²Sn Beam on ⁶⁴Ni Target

The first reaction study using accelerated unstable neutron-rich ¹³²Sn beams to measure fusion-evaporation cross sections was performed at HRIBF in October 2002. The ¹³²Sn ions were post accelerated to energies below and above the Coulomb barrier. The average beam intensity was 2x10⁴ particles per second (pps) with a maximum near 3x10⁴ pps. The evaporation residues (ERs) were detected along with beam particles by a timing detector and an ionization chamber at 0°. They were identified by their time-of-flight and energy loss in the ionization chamber.

Figure 2-1 shows the histogram of the energy loss in the first two segments of the ionization chamber for a beam energy of 536 MeV. As can be seen, the ERs are well separated from the beam. With this setup, measurement of ER cross sections less than 5 mb can be achieved.

Figure 2-1: Histogram of the energy loss of beam and ERs measured in the first two segments of the ionization chamber for 536 MeV ¹³²Sn+⁶⁴Ni.

Figure 2-2 presents the fusion-evaporation excitation function of ¹³²Sn+⁶⁴Ni measured in this work (solid circles) [Li03] and that of ⁶⁴Ni on even Sn isotopes measured by Freeman et al.[Fr83]. The effects of average nuclear size and barrier variation are removed with the reduced coordinates. It can be seen that at energies below the barrier the ER cross sections for ¹³²Sn+⁶⁴Ni are much enhanced compared to those of ⁶⁴Ni+^112-124Sn and a simple shift of the barrier height cannot account for the enhancement.

Figure 2-2: Fusion-evaporation excitation functions of ¹³²Sn+⁶⁴Ni (filled circles) from the present work [Li03] and ⁶⁴Ni on even ^112-124Sn[Fr83]. The open circle is our measurement using a ¹²⁴Sn beam.

Simplified coupled-channels calculations including inelastic excitations of the projectile and target and one-neutron transfer reaction reproduce the ER cross sections for ⁶⁴Ni+¹²⁴Sn near and below the barrier. Calculations coupling inelastic excitations and two- to six-neutron transfer channels and using the same potential parameters as in ⁶⁴Ni+¹²⁴Sn underpredict the ER cross sections for ¹³²Sn+⁶⁴Ni near and below the barrier. More realistic coupled-channels calculations considering sequentail transfer of nucleons may account for the differences between the ¹³²Sn data and the calculation.

References

[Hu91]M. S. Hussein, Nucl. Phys. A531, 192 (1991).
[De00]V. Yu. Denisov, Eur. Phys. J. A 7, 87 (2000).
[Ho00]S. Hofmann and G. Münzenberg, Rev. Mod. Phys. 72, 733 (2000).
[Li03]J. Liang et al., submitted to Phys. Rev. Lett.
[Fr83]W. S. Freeman et al., Phys. Rev. Lett. 50, 1563 (1983).

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3. Recent HRIBF Research - Study of the Single-Particle Transfer Reaction ²H(⁸²Ge,p)

Exotic nuclei on the neutron-rich side of the valley of stability are expected to exhibit a weakened shell structure and an increased influence of coupling to the continuum [Do96].  The distribution of single-particle strengths constrains the effective Hamiltonian and pairing interactions in these diffuse, weakly-bound systems.  It is, therefore, important to study neutron single-particle states near closed shells such as N=50.  The same structure information is also important for astrophysical studies of neutron-capture rates in the r-process.

Figure 3-1: Strip number vs. proton energy (chan.).  The protons are in coincidence with the Ge.

The first study of a single-particle transfer reaction with the neutron-rich ⁸²Ge RIB was completed earlier this year at HRIBF to populate excitations in ⁸³Ge, about which only the half-life was previously known [Wi88].  A 430 ug/cm²-thick deuterated polyethylene target (CD₂) was bombarded with a mass-82 mixed beam (85% Se, 14% Ge, 1% As) at 4 MeV/u.  The beam and beam-like recoils were detected by a gas ionization counter (IC) at 0° which enabled Z identification by dE-E energy loss.  Protons were detected in a silicon detector array (SIDAR) [Ba01], mounted in lampshade configuration, subtending a laboratory angular range of 105°-150° (13°-40° in the c.m.).  Proton-Ge coincidences between SIDAR and the IC reveal the states in ⁸³Ge populated in the reaction, displayed in Fig. 3-1.

Q value (channels)

Figure 3-2: A fit of the Q-value spectrum of ⁸³Ge.  The first-excited state is ~260 keV above the ground state.

Preliminary analysis of the ⁸³Ge data suggests that the ground and first-excited states are not completely resolved.  A fit to the Q-value spectrum of the ²H(⁸²Ge,p)⁸³Ge reaction, with the assumption of ~300 keV resolution determined from the (d,p) reaction with the stable ⁸²Se contaminant, is shown in Fig. 3-2. Preliminary analysis of the angular distributions for the ground and first-excited state are shown in Fig. 3-3. The results are consistent with the systematics of the other odd, N=51 isotones with a 5/2+ ground state and a 1/2+ first-excited state.  However, the excitation energy of the 1/2+ state is only about 260 keV above the 5/2+ state, compared to over 1 MeV separation in stable N=51 isotones.  This measurement would not have been possible without the recent developments that enhanced the purity of the Ge RIBs.

Figure 3-3: Angular distributions (arb. units) for the ground and first-excited states.  The solid curves are DWBA calculations normalized to the data.

We are continuing the analysis to deduce spectroscopic factors for the low-lying states and working with theorists to understand the dramatic decrease in the s_1/2-d_5/2 energy spacing in the neutron-rich N=51 isotones.  We plan to continue the study of neutron-rich N=51 isotones by measuring the ²H( ⁸⁴Se,p)⁸⁵Se reaction.
 

References
[Do96] J. Dobaczewski, et al., Phys. Rev. C 53, 2809 (1996).
[Wi88] J.A. Winger, et al., Phys. Rev. C 38, 285-294 (1988).

[Ba01] D. W. Bardayan, et al., Phys. Rev. C 63, 065802 (2001), and references therein.

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4. Recent HRIBF Research -- Mass Measurements of Neutron-Rich Fission Fragments

In March of 2003, mass measurements were performed on a number of short-lived, neutron-rich fission products produced at the HRIBF, including ^77-79Cu, ^83-86Ge, and ^84-86As. The measurements were performed using a simple setup consisting of a position-sensitive channel plate and an ion chamber mounted near the focus of the energy-analyzing magnet of the 25-MV tandem accelerator. The idea of the measurements is simply that two isobars of different mass passing through the tandem simultaneously will have the same energy but different momenta, and will be bent to different locations at the focus of the energy analyzing magnet. This can be written quantitatively as dy = 2*rho*dM/M, where dy is the position difference, rho is the magnet radius, and dM the mass difference.  By measuring an unknown mass difference relative to a known mass difference, it is not necessary to know the magnet radius.  Measurements of mass differences can therefore be performed by measuring the position and Z of each ion in a mixed beam composed of unknown- and known-mass isobars. In this way, the characteristics of HRIBF beams, that is, accelerated and isobarically mixed, are used to maximum advantage.

Position sensitive channel plates and ion chambers are routinely used to characterize radioactive ion beams at the HRIBF, and these detectors were simply borrowed and installed as close to the magnet focus as possible for the purpose of the mass measurements. A picture of the arrangement of detectors can be seen in Fig. 4-1.
 

Figure 4-1: The position sensitive MCP and ion chamber used in the mass measurements.

Initial measurements on Cu and Ge were chosen because, in the case of Cu, the nonformation of the Zn^- ion makes clean identification of Cu easier, and in the case of Ge, extraction from the ion source as GeS⁺ substantially purifies the beam, and shortens the time for ions to migrate out of the target and reach the ion source.
 

Figure 4-2: (a) Ion chamber range vs. deposited energy used to identify  Z for the A=78 mass. measurement. (b) Position measurement in the MCP where position has been determined element by element. Peaks are normalized to the same area, and do not represent the actual relative intensities.

These measurements represent the least intense RIBs to be studied at the HRIBF, only 20 counts per hour in the case of ⁷⁹Cu and ⁸⁶Ge, and also the shortest half-lives, each less than 0.2 seconds.   In addition to being successful in themselves, the measurements are leading the way toward other uses of weakly produced but far-from-stability RIBs, such as decay studies with accelerated beam where the contaminating isobars may be largely eliminated by range discrimination.

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5. High Power Target Laboratory

The first phase of a planned series of upgrades to the HRIBF is about to begin! In February of this year, a proposal was submitted to DOE-NP for funding of a $4.7M addition to the HRIBF known as the High Power Target Laboratory, or HPTL. Two reviews, including Technical, Cost, and Schedule considerations, have been completed. DOE-NP concluded that the project "has high scientific merit and significance" and will fund the project beginning in August of this year. Completion of the HPTL is planned for September 2005.

The HPTL project consists of a new ORIC beam transport line to a second high voltage platform system and target station. Addition of a second target station effectively decouples high-power target and ion source testing from the present production system. The intent is to provide a location where new and existing target geometries can be tested with the high power light ion beams provided by ORIC, yielding crucial information on RIB target design and providing a location for development of new beam species of interest to the user community. Thin and liquid targets can be accommodated due to the downward angle of the incident ORIC beam line, and beam rastering techniques will be employed to optimize target lifetime and RIB yields. Additionally, the HPTL will be designed to accommodate a laser ion source development program.

Facility modifications are required at the beginning of the project to accommodate the HPTL technical equipment, including reconfiguration of shielding in the south high bay area near the On-Line Test Facility, and demolition/rebuild of the west end of the south annex to provide additional lightly-shielded space. The location was chosen to minimize project cost and optimize use of existing space. Future newsletters will provide status updates on the project.

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6. Decay Spectroscopy Workshop to be Held at ORNL

The workshop format will consist of a few talks to introduce a topic followed by short contributed talks about planned or possible experiments at HRIBF. Generous time will be allocated for discussion.

Speakers include:

H. Grawe (GSI)
J. H. Hamilton (Vanderbilt University)
P. Mantica (Michigan State U.)
U. Koester (CERN)
W. Nazarewicz (U. Tennessee/ORNL)
P. H. Reagan (Surrey)
L. Trache (Texas A&M)
W. B. Walters (U. Maryland)
M. Wiescher (Notre Dame)
J. A. Winger (Mississippi State University)
J. Wood (Georgia Tech.)

• Beta decay studies with accelerated and non-accelerated RIBs
• Production and detection of excited states produced in deep-inelastic/nucleon transfer collisions using neutron-rich RIBs
• Particle emission around the proton drip line

For more detailed and updated information, please visit the workshop website.

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7. PAC-9 Meeting Scheduled for August 21-22

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8. Workshop on the Experimental Equipment for RIA Held in Oak Ridge, TN

A Workshop to discuss the equipment needed to perform experiments at the Rare Isotope Accelerator (RIA) was held on March 18-22, 2003 in Oak Ridge, Tennessee. The Workshop was attended by more than 150 researchers from the U.S. and abroad.

The purpose of the workshop was 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 new physics opportunities that may be addressed at RIA.

The program of the workshop consisted of overview talks, short presentations on specific experimental techniques and detectors, and parallel sessions of six Working Groups. The overview talks served as the general introduction for the subsequent discussions of the detector systems by the Working Groups. Nearly half of the available time at the meeting was devoted to the technical discussions and evaluations of the proposed detectors by the Working Groups.

The program for the Workshop and other information about the workshop may be found at the workshop website. Copies of the oral presentations may be viewed or downloaded from the following searchable database.

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9. 15^th National Nuclear Physics Summer School Held in Knoxville, TN

Students were housed on the campus of the University of Tennessee-Knoxville.  Lectures were primarily held in the Science and Engineering Research Facility at UT, but also in the Joint Institute for Heavy Ion Research at ORNL.  Peter Parker (Yale Univ.), Raju Venugopalan (BNL), Eric Swanson (Univ. Pittsburgh), Erich Ormand (LLNL), Alejandro Garcia (Univ. Washington), and Gail McLaughlin (North Carolina State Univ.) were lecturers.  Special seminars were given by Glenn Young (ORNL), Rocco Schiavilla (Old Dominion Univ./TJNAF), Geoff Greene (UT/ORNL), and Ian Anderson (SNS).  Excellent scientific presentations were also given by 21 of the student participants.  The complete program for the school is available online, including links to many of the lectures.

While at ORNL, students received a guided tour of the HRIBF and were able to climb inside the world's largest tandem accelerator.  Ian Anderson and Geoff Greene nicely summarized the scientific opportunities at the Spallation Neutron Source, and Al Ekkebus led them on a tour of the SNS site. The students also visited the graphite reactor and enjoyed a history lesson by Marilyn McLaughlin.  In addition to the very full academic program, students made time for a riverboat ride on the Tennessee River, hiking in the Great Smoky Mountains National Park, and rafting on the Ocoee River.

Much of the recognition for a very successful school goes to Gay Henegar (UT) and Ally Wright (ORNL/ORAU) who served as the school's secretariat.

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10. Second RIA Summer School on Exotic Beam Physics to be Held at MSU

The second annual RIA Summer School on Exotic Beam Physics will be held at Michigan State University from August 4-9, 2003, at the National Superconducting Cyclotron Laboratory. The aim of the Summer School is to nurture and encourage future RIA scientists. The RIA Summer School is jointly organized by ANL, HRIBF/ORNL, LBL, and the NSCL. The School is an annual event, rotating among these laboratories.

Speakers and topics include:

The School will be attended by about 45 participants. The afternoons will provide opportunities for "hands-on" learning of experimental techniques useful in RIA research. On the final day, the students will produce and identify a rare-isotope beam. In the late afternoons, participants will have the opportunity to present 10-minute talks on their research. Details are posted at: http://www.orau.org/ria/ria03/.

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RA1 - RIB Development

For several reasons, the beam development efforts have been limited to off-line tests during this period. As is reported elsewhere in this newsletter, there was a very successful run in the first few months of the year with a UC target, followed by a scheduled shutdown period for accelerator maintenance. Also, several beam lines in the facility, including the beam line from the tandem to the On-Line Test Facility (OLTF), have been modified to remove unnecessary complexity and to accommodate the newly-funded High Power Target Laboratory (HPTL). This also necessitated a modification of the position of the target station at the OLTF that should be completed very soon.

We have made some initial off-line tests of several uranium carbide targets manufactured at Argonne National Laboratory from pressed powder of uranium oxide together with graphite powder. These were then heated to temperatures up to 1800° C to convert the oxide to the carbide. The density of these targets is higher than our normal UC/RVC targets and is part of a joint effort to develop higher density UC targets that may be useful at RIA. Results of release measurements and performance will be presented in future newsletters.

In the last Newsletter, we reported the production of ⁷Be sputter targets. The targets were tested in a multi-sample, Cs-sputter ion source and we have produced negative-ion beams of ⁷Be with intensity up to 4x10⁶ ions/second. Three different batches of ⁷Li have been irradiated at the TUNL facility at Duke and the ⁷Be was chemically separated from the ⁷Li here at ORNL. The ⁷Be is mixed with Cu or Nb powder and pressed into sputter targets that are used to generate negative-ion beams using a Cs-sputter process. Up to four such pellets can be placed into the target holder and rotated into the ion source as needed. Targets from the first two batches have been tested at the OLTF and targets from the third batch are expected to be used on the RIB Injector Platform to produce accelerated ⁷Be beams for experiments.

In the first batch, the total activity in the sputter targets at the time of testing (half-life of ⁷Be is 53.3 days) was 0.6 mCi. The best intensity achieved with these pellets was 2x10⁵ ions/second with an efficiency of 0.4% (the integrated beam intensity divided by the total number of atoms present in the pellet). This beam intensity was sustained over a period of five days from a single sputter target having an initial activity of 0.09 mCi. The total activity in four sputter targets produced in the second batch was 4.4 mCi at the time of testing. One of the samples with an initial activity of 1.6 mCi yielded a beam intensity of 4x10⁶ ions/second measured over a period of about six days. This represents an efficiency of about 0.5%. The ⁷Be activity from the third batch of irradiated material will be concentrated in a single pellet and is expected to have an activity level of about 20 mCi which should result in beams of 6x10⁷ ions/second from the ion source and about 6x10⁵ ions/second of accelerated ⁷Be beam at the experimental target for a period of at least five days.

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RA2 - Accelerator Systems Status

ORIC Operations and Development

ORIC experienced another very successful operating period from January through March 2003, providing approximately 1000 hours of operation in support of the experimental program and machine development activities.  There were no major machine problems during that time.  ORIC was in scheduled shutdown during April and May.  In June, ORIC operation resumed for development of higher-energy proton beams and higher extraction efficiencies.   This effort proved to be tremendously successful and is discussed in detail in the Breaking News A of this newsletter.

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 ^{75,76,77,78,79}Cu, ^{82,83,85,86,87}Ge, ⁸⁴Se, ⁹²Sr, and ^{132,133,134,135,136}Sn. The machine ran at terminal potentials of 4.5 to 23.7 MV and the stable beams ¹H, ⁵⁸Ni, ⁷⁶Ge, ^76,82Se, ⁹⁰Zr, ¹³⁰Te, and ¹³⁴Ba were also provided. The last three months of the period were spent doing scheduled maintenance and upgrades. This is the long anticipated shutdown, which only came after a cooling failure in the 180-degree magnet power supply forced the research period to close. The RIB source was also at the end of its useful life so the "scheduled" shutdown was started. The major maintenance done included rebuilding all ion pumps inside or just adjacent to the accelerator tank. Many of these ion pumps had been in service for more than twenty years and were beginning to struggle, especially after the accelerator tube had been let up to air. The major upgrade is the installation of a new recirculating gas stripper, which should allow equilibrium gas stripping of all beam species, whereas the old stripper system could not attain the high stripper tube pressure without compromising the accelerator tube pressure. Another advantage of the new stripper system is the elimination of the titanium sublimator pumps, which not only were a high maintenance item but also allowed titanium dust to be close to the accelerator tubes. The foil stripper was moved above the gas stripper so that molecular beams could be broken apart without degradation from coulomb explosion. Many other jobs, too numerous to mention here, were also done during the shutdown period.

RIB Injector Operations and Development

During this reporting period, we delivered beams of

• 97 kpps 14+/25+ foil/foil stripped 495 MeV pure ¹³²Sn to the Barium Fluoride Array in Beam Line 21,
• 150 kpps 14+/25+ foil/foil stripped 470 MeV pure ¹³²Sn to the Barium Fluoride Array in Beam Line 21,
• 860 kpps 14+ foil stripped 316 MeV pure ¹³²Sn to the Barium Fluoride Array in Beam Line 21,
• 50 kpps 14+ foil stripped 316 MeV 33% ¹³³Sn to the Barium Fluoride Array in Beam Line 21,
• 8500 pps 14+ foil stripped 316 MeV 38% ¹³⁴Sn to the Barium Fluoride Array in Beam Line 21,
• 75 kpps 11+ foil stripped 183 MeV 22% ⁸²Ge to the Barium Fluoride Array in Beam Line 21,
• 68 kpps 11+ foil stripped 220 MeV 20% ⁸²Ge to the Barium Fluoride Array in Beam Line 21,
• 5500 pps 16+ foil stripped 400 MeV 38% ¹³⁴Sn to the Barium Fluoride Array in Beam Line 21,
• 780 pps 16+ foil stripped 400 MeV mass 135 to the Barium Fluoride Array in Beam Line 21,
• 1350 pps 16+ foil stripped 400 MeV mass 136 to the Barium Fluoride Array in Beam Line 21,
• 105 kpps 13+ foil stripped 327 MeV 14% ⁸²Ge to the Daresbury Recoil Separator,
• 170 kpps 13+ foil stripped 327 MeV mostly ⁸³Se to the Daresbury Recoil Separator, and
• 600 kpps 13+ foil stripped 327 MeV 78% ⁸⁴Se to the Daresbury Recoil Separator.

Mass measurements of ^76-79Cu and ^82-87Ge and were performed with a MicroChannel Plate and BRAGG detector in Beam Line 17.

These heavy neutron-rich beams were produced via proton induced fission of ²³⁸U by bombarding a uranium carbide coating on a graphitic foam target coupled to an Electron Beam Plasma (positive) Ion Source (EBPIS) with 10 uA of 42-MeV ¹H. Monatomic beams were produced by passing the appropriate positive sulfide beam through the recirculating cesium jet charge exchange cell and selecting the desired negative beam resulting from molecular breakup. Fortunately, contaminating beams of the associated isobaric sulfides were greatly reduced. Sulfur was introduced into the uranium carbide target by flowing hydrogen sulfide gas through a dedicated variable leak valve into the EBPIS internal gas feed line.

During this campaign, the charge exchange cell was reloaded with cesium at a cost of 32 MAN-mREM. Also, a water leak on the target/ion source vacuum enclosure was repaired at a cost of 8 MAN-mREM in a 900 mREM/hr field!

The ion source finally failed due to an anode to ground electrical short.

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RA3 - User Group News

The Executive Committee of the Users Group has proposed large changes to the organization of the group. A new charter under which the group is to be organized has been posted on the HRIBF website and will be the subject of a Users Group Meeting to be held in Oak Ridge at 6:00 p.m. on August 18, 2003. If you wish to attend the meeting, register for the Decay Spectroscopy Workshop which is also to be held on August 18-19, 2003. The letter announcing the new charter details some of the structural changes proposed to modernize the organization. Send your comments to the members of the UEC at the email addresses below.

HRIBF Users Executive Committee

Ani Aprahamian	Ani.Aprahamian.1@nd.edu
Jeff Blackmon	blackmon@mail.phy.ornl.gov
Paul Mantica, chair	mantica@nscl.msu.edu
David Radford	radfordd@mail.phy.ornl.gov
Demetrios Sarantites	dgs@wuchem.wustl.edu
Ed Zganjar, vice-chair	zganjar@rouge.phys.lsu.edu

The new charter will be voted on by the membership immediately after the meeting in Oak Ridge. Paper ballots will be mailed to your address and you will have three weeks to ensure that we receive your vote. As the new charter proposes to shrink the Executive Committee from 6 to 4 members, we will delay this year's election until the results of the charter vote has been determined.

The Executive Committee and HRIBF has agreed to take part in a joint users group meeting at this year's DNP Meeting in Tucson, Arizona. We expect the meeting to take place on Thursday, October 30, and will consist of the users groups from HRIBF, ATLAS, NSCL, GAMMASPHERE, and RIA. A reminder of the meeting will be sent when the times and location are known.

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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.

• 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 (T_1/2 > 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.

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RA5 - HRIBF Experiments, January - June 2003

Date	Exp. No.	Energy	Beam	Beamline	Spokesperson
1/1-2	Shutdown
1/2	RIB-093	470 MeV	130Te	SCAT	Beene/ORNL
1/3	Shutdown
1/3	RIB-093	470 MeV	130Te	SCAT	Beene/ORNL
1/4-15	Shutdown
1/6-12	RIB-093	470 MeV	130Te	SCAT	Beene/ORNL
1/13-15	Shutdown
1/15-16	RIB-093	470 MeV	132Sn	SCAT	Beene/ORNL
1/17-20	Shutdown
1/21	RIB-093	470 MeV	132Sn	SCAT	Beene/ORNL
1/21-22	RIB-117	350 MeV	82Se	DRS	Thomas
1/22-23	RIB-039	350 MeV	82Ge	DRS	Mueller/ORNL
1/23-25	RIB-117	327 MeV	82Ge,82Se	DRS	Thomas/Rutgers University
1/25-27	Shutdown
1/27-2/1	RIB-117	327 MeV	82Ge,82Se	DRS	Thomas/Rutgers University
1/27-28			82Ge
1/28-29			82Se
1/29-2/1			82Ge
2/1-2	Shutdown
2/3-5	RIB-117	327 MeV	82Ge	DRS	Thomas/Rutgers University
2/5	RIB-039	327 MeV	83,84Ge	DRS	Mueller/ORNL
2/6	RIB-093	495 MeV	130Te,132Sn	SCAT	Beene/ORNL
2/6-8		470 MeV	132Sn
2/9	RIB-039	316 MeV	133,134Sn	SCAT	Mueller/ORNL
2/9-12	RIB-110	183 MeV	82Ge	SCAT	Padilla/UNAM
2/12-15		220 MeV
2/15-16	Shutdown
2/17	RIB-110	220 MeV	82Se	SCAT	Padilla/UNAM
2/17-18		241 MeV	90Zr
2/19	RIB-093	9 MeV	1H	SCAT	Beene/ORNL
2/20	RIB-037	58 MeV	58Ni	DRS	Meigs/Juras
2/20	RIB-100	58 MeV	58Ni	DRS	Kozub/Tennessee Tech University
2/21	RIB-105	304 MeV	76Ge	Rotating	Hausladen/ORNL
2/22-23	Shutdown
2/24	RIB-105	304 MeV	76Ge	Rotating	Hausladen/ORNL
2/24	RIB-093	400 MeV	130Te	SCAT	Beene/ORNL
2/24-28			134Sn
2/28			136,135Sn
3/1			134Ba
3/1-3		450 MeV	92Sr	DRS	Mueller/ORNL
3/3				RIB Inj
3/3	000-Shutdown			Shutdown
3/4-5	RIB-105	304 MeV	76Se+76Ge	Rotating	Hausladen/ORNL
3/5		220 MeV	76Cu
3/6			75Cu
3/6			77Cu
3/7			78Cu
3/8-9	Shutdown
3/10-11	RIB-063	355 MeV	84Se	DRS	Cizewski/Rutgers University
3/11-13	Shutdown
3/13	RIB-063	355 MeV	84Se	DRS	Cizewski/Rutgers University
3/14	Shutdown
3/14	RIB-063	355 MeV	84Se	DRS	Cizewski/Rutgers University
3/14-16	Shutdown
3/17	RIB-105	220 MeV	82Se	Rotating	Hausladen/ORNL
3/17			82Ge
3/17			83Ge,84Ge
3/18			85Ge,82Ge
3/19-21			86Ge
3/21			87Ge
3/22-23	Shutdown
3/24-25	RIB-063	355 MeV	82Se	DRS	Cizewski/Rutgers University
3/25	RIB-105	220 MeV	76Ge/Se	Rotating	Hausladen/ORNL
3/26-6/30	Shutdown

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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
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
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37831 USA
Telephone: +1-865-574-4113
Facsimile: +1-865-574-1268