HRIBF Newsletter, Edition 18, No. 1, February 2010

 


Feature Articles

  1. HRIBF Update and Near-Term Schedule
  2. Recent HRIBF Research - Deviations from U(5) Symmetry in 116Cd
  3. Update of the IRIS2 Project
  4. Summary of the HRIBF Workshop, Upgrade for the FRIB Era
  5. The HRIBF Cyclotron Replacement Project

Regular Articles

    RA1.  RIB Development
    RA2.  Accelerator Systems Status
    RA3.  Users Group News
    RA4.  Suggestions Welcome for New Beam Development
    RA5.  HRIBF Experiments, July-December, 2009



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

In many respects, the prospects for HRIBF look extremely favorable. There are certainly good reasons for optimism. The IRIS2/HPTL upgrade project is essentially complete (see IRIS2 update in this newsletter). Improved operational efficiency due to the availability of two RIB production stations, as well as the impact of new beam production and purification capabilities, should soon be evident. The near-term budget outlook for the facility is more favorable than it has been for many years. Finally, we are free of the direct impact of the July 2008 Operational Emergency which crippled facility operation for more than a year.

In spite of a Continuing Resolution that extended deep into fiscal year (FY) 2009, the final 2009 budget for the facility was very favorable. This upward trend was continued in the FY 2010 appropriation, and, at a reduced rate, in the FY 2011 President's budget. The 2009 budget for the HRIBF was the first to exceed the inflation adjusted FY 2005 allocation since the large cuts imposed in FY 2006. These favorable budgets have enabled us to replenish badly depleted materials, supplies, and maintenance budgets. Even more important we have finally been able to proceed with the hire of two new accelerator operators, Justin Leach and Andrew Barclay. These two hires are the first elements of an HRIBF staff enhancement plan that was developed more than five years ago, but has been delayed due to funding. Once Justin and Andrew have completed necessary training, we will finally be in a position to operate the facility in a seven-day twenty-four hour mode for extended periods.

One of the indirect legacies of the extended shutdown period during the recovery from the July 2008 Operational Emergency has been a series of ORIC failures as we attempt a restart of routine operations. Chronic unreliability of this fifty year old cyclotron is the most important issue we face. Continuous operation should certainly help these chronic problems, but by far the best solution would be replacement of ORIC with a commercial accelerator. In November 2009, more than 150 scientists attended a two-day HRIBF users workshop devoted to discussions related to upgrade of the facility by addition of a commercial cyclotron. A Summary of the workshop is available in this Newsletter. Addition of an accelerator with capabilities similar to those of the IBA C70 cyclotron would dramatically improve efficiency, reliability and scientific reach of HRIBF. Annual operating costs could be reduced by well over $1M per year. We could take full advantage of the capabilities of IRIS2, and we should easily achieve 4000 hours of RIB delivered to experiments. Most important, we could take advantage of higher driver accelerator beam currents coupled with the developments in ISOL technology we have made in recent years to deliver neutron-rich beams with baseline intensities in excess of one thousand times greater than are now available.

ORNL has made an investment worth approximately $5M in the HRIBF utilities infrastructure by replacing the fifty year old cooling tower and many of our electrical substation circuit breakers. These improvements will have a direct impact on HRIBF reliability.

Experiments with neutron-rich beams are a centerpiece of our science program. The Operational Emergency ended our last successful neutron-rich campaign in July 2008, and the associated facility shutdown has exacerbated the accumulation of a substantial backlog of important neutron-rich beam experiments. Consequently, our highest priority is to initiate an extended (up to six month long) neutron-rich campaign as soon as we are able to do so.


2. Recent HRIBF Research - Deviations from U(5) Symmetry in 116Cd
[J. C. Batchelder (UNIRIB), spokesperson]

The cadmium isotopes near their mid-neutron shell, i.e., N=66, exhibit one of the well-known examples of shape coexistence [1]. In addition to the spherical quadrupole vibrational levels (hereafter referred to as normal phonon states), which are described within the Interacting Boson Model (IBM) by the U(5) limit, they possess intruding proton particle-hole configurations that give rise to additional states in the low-lying spectrum of levels [2].

These intruding excitations may mix with the normal states, perturbing their properties. However, once this mixing is accounted for [3], the underlying normal phonon states have been claimed to be very close to the U(5) limit, and, in fact, are often cited as the best examples of U(5) nuclei [4] and are often used in textbooks to illustrate quadrupole vibrational spectra in nuclear systems [5,6]. These nuclei span the "bottom of the parabola" that is characteristic [1] of intruding particle-hole configurations that underlie shape coexistence. The low-lying levels of 112,114Cd have been explained [3] as mixtures of vibrational and intruder configurations. Experimental studies of 110Cd [7,8,9], 112Cd [10,11,12,13], 114Cd [14] and116Cd [15,16] have supported this description. An intruder band structure has also been well established [7,15,17] in 110-116Cd, with enhanced intraband B(E2) values observed.

In the cases of 110,112,114Cd, it is the lowest excited 0+ states that have large B(E2) values for decay to the one-phonon 2+ states (and also the 2+ intruder states decay to them with enhanced B(E2) values), whereas the second excited 0+ states have much smaller B(E2) values for their decay [10,12,14]. This pattern can be explained well within the strong mixing approach as outlined in [3], and shown in [17,18], although the weak mixing approach can also explain the B(E2) pattern in 114Cd [14]. In 116Cd, it is the second excited 0+ state, rather than the first, which has the enhanced B(E2) value for decay to the one-phonon 2+ level [19], and it is also this level that is fed by the strong B(E2) value from the 2+intruder level [20], a pattern that remains unexplained [18,20].

In order to better understand the behavior of 116Cd and all of the Cd isotopes, we reinvestigated the decay of levels in 116Cd populated via the beta-decay of 116Ag. Silver-116 was produced via the proton-induced fission of 238U at the Holifield Radioactive Ion Beam Facility (HRIBF). The proton induced fission products were then mass-separated by the OLTF and deposited on a moving tape collector (MTC). The collected samples were subsequently moved to the counting position located at the center of the CARDS array (Clover Array for Radioactive Decay Spectroscopy), which consisted of three segmented-clover Ge detectors, plastic scintillators, and a high-resolution (FWHM 1.5 keV at 44 keV) Si conversion-electron spectrometer [21]. The BESCA detector had an efficiency for conversion electrons of ~2%, while the clovers had a summed efficiency of ~5% for 344-keV 152Eu gamma rays.

Figure 2-1: A comparison of experimental and IBM-2 B(E2) calculations for the 3+1 and 6+1 levels in 116Cd. All level lifetimes and mixing ratios are taken from [20] and transition strengths are quoted in W.u.

Figure 2-2: Experimental versus IBM-2 calculations for the 4+1 levels in 116Cd.

The results of our experimental observations confirm the existence and placement in the decay scheme of the five levels (1869.8, 1916.0, 1928.6, 1951.4, and 2026.7 keV) assigned in [22] to be the complete three-phonon state quintuplet. However, while the experimental B(E2) values for decay of the 3+, 4+ and 6+ levels (see Figs. 2-1 and 2-2) compare well with the calculations, the decay of the 0+ and 2+ levels is not consistent with this picture.

The experimental B(E2) values for the decay of the 2+4 state are completely different than those predicted by the IBM2 for a vibrational phonon state. As mentioned above, the decay pattern is different with the IBM2 predicting decays to the 2+2, 4+1, 0+2, 0+3, and 2+3 states. Of these states, only the decay to the 0+2 state is observed, along with decays to the 2+1 and 0+1 states. For the one transition that is observed (2+4 → 0+2), the experimental B(E2) value is 61 W.u. compared to the calculated value of 4.2 W.u. For comparison, the experimental and calculated B(E2) for decay of this level are shown in Fig. 2-3. The decay pattern of this level is not consistent with a three-phonon interpretation and the 1951.4-keV, 2+ level is more consistent with an isolated weakly-deformed band structure in view of the strength of the connecting 668.8-keV transition.

For the case of the 0+4 state in 116Cd, the experimental decay of this state is completely different than what is predicted by the IBM-2 calculations. The experimental relative B(E2)'s versus the predicted values are shown in Fig. 2-4 (the lifetime of the 0+4 state has not been measured, so the experimental B(E2) is unknown). From the IBM-2 calculations one would expect that the state should decay strongly to the 2+2 state (B(E2) = 43.5 W.u.) and very weakly to the 2+1 state. In fact the opposite is true, as we only observe a single transition de-exciting this state to the 513.5-keV 2+ state and an upper limit for the relative B(E2) to the 2+2 of 14%.

Figure 2-3: A comparison of experimental and IBM-2 B(E2) calculations for the 2+4 levels in 116Cd.

Figure 2-4: A comparison of experimental and IBM-2 B(E2) calculations for the 0+0 level in 116Cd.

The deviations in the experimental B(E2) values from IBM-2 calculations that are observed in 116Cd for the phonon-states cannot be explained through considered mixings with the intruder excitations or mixed-symmetry states. Along with the inability to explain the decays of the 0+2 and 0+3 levels, the present results for the proposed three-phonon levels show that the description of 116Cd as a vibrational nucleus with well understood mixing between normal and intruder states is inadequate.

A careful analysis of the other known even-even Cd isotopes (110-120) reveals that the discrepancy in the decay of the three-phonon 0+ and 2+ states with the U(5) description is a consistent feature in all these nuclei. Fig. 2-5 shows the decays of the 0+ and 2+ members of the three-phonon quintuplet for110Cd [23],112Cd [24,25], 114Cd [26],116Cd [this work], 118Cd [27], and 120Cd [27]. In the U(5) description of the normal states, the 2+ three-phonon state would be expected to strongly decay to all three of the two-phonon states (0+, 2+, 4+). The decay of this state in 112,114,116Cd is to the 2+ two-phonon and 2+ one-phonon states, while in 110,118,120Cd, this state is only known to decay to the 2+ one-phonon state. (In Ref. [28], the 1915.8-keV state was labeled as a three-phonon state decaying to the 2+ two-phonon state, while Ref. [27] labels this state as an intruder state based on energy systematics). The three-phonon 0+ states in 110,112,114,116,118Cd decay only to either intruder states or the 2+ one-phonon state.

In all the neutron-rich even-even Cd nuclei from 110-120, none of the observed 0+ and 2+ states previously assigned as three-phonon states decay in a manner consistent with a three-phonon state. This discrepancy is unaccounted for to date in calculations that incorporate mixing between normal and intruder states. Further, the consistent decay pattern across the Cd isotopes, regardless of level spacings that would cause significant differences in energy denominators for mixing amplitudes, is suggestive that the deviations from the expected harmonic vibrator or U(5) selection rules are not due to mixing.

Figure 2-5: Comparison of the decays of the 0+ and 2+ members of the three-phonon levels in 110,112,114,116,118,120Cd. Relative B(E2)s are shown. Intruder states are circled to distinguish them from N-phonon states.

To continue this investigation, we have recently taken data with high statistics (1.4X108 events in the 2+1 → 0+1 gamma transition) on the beta-decay of 120Ag. This data is currently being analyzed.

References:

1. J. L. Wood, et al., Phys. Repts. 215, 101 (1992).
2. A. Arima and F. Iachello, Phys. Rev. Lett. 35, 1069 (1975).
3. K. Heyde, et al., Phys. Rev. C 25, 3160 (1982).
4. J. Kern, et al. Nucl. Phys. A 593, 21 (1995).
5. K. Heyde, Basic Ideas and Concepts in Nuclear Physics, 3rd Ed., Institute of Physics Publishing, Bristol and Philadelphia, pp. 416-418 (2004).
6. R. F. Casten, Nuclear Structure from a Simple Perspective, 2nd Ed., Oxford University Press, p. 191 (2000)
7. J. Kern, et al., Nucl. Phys. A 512, 1 (1990).
8. F. Corminboeuf, et al., Phys Rev. C 63, 014305 (2000).
9. F. Corminboeuf, et al., Phys Rev. Lett. 84, 4060 (2000).
10. M. D'el`eze, et al., Nucl. Phys. A 554, 1 (1993).
11. S. Drissi, et al., Nucl. Phys. A614, 137 (1997).
13. R. Hertenberger, et al., Nucl. Phys. A574, 414 (1994).
12. H. Lehmann, et al., Phys. Lett. B387, 259 (1996).
14. R. F. Casten, et al., Phys. Lett. B297, 19 (1992).
15. S. Juutinen, et al., Phys. Lett. B386, 80 (1996).
16. R. M. A. L. Petit, et al., J. Phys. G 20, 1955 (1994).
17. M. D'el`eze, et al., Nucl. Phys. A551, 269 (1993).
18. P. E. Garrett, et al., Phys. Rev. C 78, 044307 (2008).
19. H. Mach, et al., Phys. Rev. Lett. 63, 143 (1989).
20. M. Kadi, et al., Phys. Rev. C 68, 031306(R) (2003).
21. J. C. Batchelder , et al.,Nucl. Instr. Meth. Phys. Res. B. 204, 625, (2003).
22. Y. Wang, et al., Phys. Rev. C 64, 054315 (2001).
23. D. de Frenne and E. Jacobs, Nuclear Data Sheets 89, 481 (2000) and references therein. 24. K. L. Green, et al., Phys. Rev. C 80, 032502(R) (2009).
25. P. E. Garrett, et al., Phys. Rev. C 75, 054310 (2007).
26. J. Blachot, Nucl. Data Sheets 97, 593 (2002) and references therein.




3. Update on Injector for Radioactive Ion Species 2 (IRIS2)
[B. A. Tatum, A.J. Mendez, spokespersons]

The IRIS2 Project completion date has been delayed until March 31, 2010, to allow additional time for documentation updates and new review requirements. In turn, this has delayed our ability to complete commissioning with radioactive beam.

From a technical perspective, the project continues to progress very well with most of the equipment installation and testing complete. Additional high voltage tests have been performed on the platform systems to identify and mitigate the effect of any remaining corona points. Handrails have been installed on both of the platform structures. The modular laser room has been installed, and laser safety system installation is nearing completion. Testing of the automated sequences of the remote handling system bridge crane has also been successfully completed, and we are now finalizing related procedures and lift plans.

As previously reported, both the injector and transport beamlines are fully assembled, tested and operational. In addition to the stable beam commissioning activities reported in the last newsletter, which focused on the setup of the 1st-stage mass separator, subsequent stable beam tuning exercises have been completed. A 2 μA, 40Ar+ beam was accelerated off the platform to 200 keV and tuned to LERIBSS. The focus of the exercise was to maximize transmission rather than mass resolution, and it was highly successful: transmission from the object point of the 1st-stage separator to the 1st cup on beamline 12 was essentially 100%, to within the accuracy of the Faraday cup calibrations. To state it another way, there were essentially no losses in transport through the entire IRIS2 system, comprising both the injector and transport beamlines. Total transmission from IRIS2 to the LERIBSS Faraday cup was approximately 85%, 1.7 μA out of 2 μA, with virtually all of the loss coming between the image point of the isobar magnet (FC_12_3) and LERIBSS. This will likely improve with experience and time.


4. Summary of the HRIBF Workshop, Upgrade for the FRIB Era
[HRIBF Users Executive Committee]

The HRIBF Users Executive Committee called a user workshop meeting on Friday and Saturday, November 13-14, 2009, at the Pollard Conference Center on the campus of Oak Ridge Associated Universities (ORAU) in Oak Ridge, Tennessee. The purpose of the workshop was twofold: (i) to solicit user input and support for a proposed new production driver, a 70-MeV variable-energy, light-ion cyclotron to replace the ORIC; (ii) to solicit user input to update the HRIBF strategic plan. The result of the meeting was a user-driven White Paper that contains a strong science case for a modern, reliable ISOL facility at ORNL. A description of the proposed upgrade is also available. The discussion in the White Paper and throughout the workshop assumed that the upgrade is based on a commercial cyclotron with specifications equivalent to or exceeding those of the recently developed IBA C70. The C70 specifications can be found here.

By any measure, the workshop was a resounding success. In all, there were 151 participants representing 44 institutions from 10 countries, and many suggestions and proposals for exciting work at HRIBF were made by this group. This high level of participation is clear evidence that user interest in a cyclotron upgrade for the HRIBF is both widespread and intense.

On the first day of the workshop, introductory talks covered the following topics:

  • Overview of proposed 70-MeV cyclotron upgrade
  • Performance of upgraded HRIBF for neutron-rich and proton-rich beams
  • Implementation and technical details of the upgrade
  • FRIB
  • ISOL facilities
  • Radioisotope production
  • This was followed on Friday afternoon and Saturday morning by parallel, breakout discussion sessions in working groups on nuclear structure (in-beam and decay), reactions, astrophysics, applications, and ISOL technology. During the breakout sessions, there were lively discussions on the unique capabilities the HRIBF would have in the future FRIB era to perform complementary research in support of FRIB science. Most sessions included a series of presentations illustrating the type of research the users would like to do with the new beams and higher intensities that would be available with the new cyclotron driver. The ancillary equipment needs were discussed in detail. Theoretical perspectives were offered on the specific type of data needed to impact the development of models for nuclear structure, reactions, and astrophysics. A brief outline of the presentation and discussion topics is given here:

  • Upgraded HRIBF

    - Technical aspects of a commercial turnkey 70-MeV cyclotron
    - HRIBF and its relation to other ISOL facilities in the world
    - Isotope research opportunities with the cyclotron

  • Research areas
    - Nuclear structure by in-beam spectroscopy
    - Nuclear structure by decay spectroscopy
    - Nuclear astrophysics
    - Nuclear reactions
    - Applications with radioactive ion beams
    - ISOL technologies
  • Associated areas

    - Instrumentation
    - Coupling between nuclear theory and experiment
    - World-wide context
    - Coupling between FRIB and HRIBF
    - Education and outreach

    The majority of the proposed research centered on neutron-rich beams from proton-induced fission. In addition, proton-rich beams important for astrophysics and unique 56Ni beams with low 56Co contamination were highlighted. Major research thrusts discussed included studies of the following:

  • Single-particle strengths using light-ion transfer
  • Collectivity and g-factors of excited states using Coulomb excitation
  • Heavy-ion fusion
  • Radioactivity, encompassing level structure, beta-delayed neutrons, and beta strengths
  • (n,gamma) surrogate reactions
  • Low-energy resonance and proton capture reactions of importance for understanding explosive astrophysical processes.

    Separate sessions were devoted to laser and electromagnetic techniques for producing and enhancing radioactive beams and to various applications of radioactive beams at the HRIBF, especially in the context of new, unique opportunities associated with the proposed upgrade. Examples of the latter included isotope research and development, fission-fragment data of interest to nuclear reactor operations, stockpile stewardship, medical wear studies, and accelerator mass spectrometry.

    Working group summaries were presented later on Saturday morning, and the workshop closed early Saturday afternoon. The conveners of the working groups were responsible for writing drafts of their respective sections of the White Paper. They were recruited from the user community and included both non-HRIBF scientists and local personnel.

    Apart from soliciting user input and support for the upgrade proposal, the rich information collected during the workshop will be used to update the HRIBF strategic plan. As usual, the facility management will do this, in close consultation with the HRIBF Users Executive Committee, HRIBF Program Advisory Committee (PAC), and HRIBF Scientific Policy Committee (SPC). We are pleased that 13 of the 18 members of these HRIBF advisory bodies attended the meeting and were actively involved in discussions and the actual production of the White Paper.

    In conclusion, it is very clear that a very strong, compelling science case has been made in each of the main research areas by the HRIBF Users Group for a cyclotron driver upgrade. The White Paper which details those cases was submitted to DOE on January 22, 2010.

    The HRIBF Users Executive Committee would like to thank all those who made the workshop and the White Paper possible, including the ORNL central administration and Physics Division staff, ORAU, and the many conveners from various institutions who contributed to this process.


    5. The HRIBF Cyclotron Replacement Project
    ( C. J. Gross & B. A. Tatum)

    The HRIBF is proposing to replace the nearly 50-year-old ORIC with a commercial 70-MeV cyclotron that can replace most of the abilities of ORIC as well as bring new features beneficial to RIB production. The new cyclotron provides higher and easily adjustable proton energy. Coupled with higher beam intensity, the new cyclotron would increase the yield of neutron-rich fission fragment beams by at least a factor of 8 and potentially much more through the use of a two-step target. The variable energy deuteron beam allows us to maintain our current (d,n) reactions at low-energy for proton-rich beam production, e.g., 17F. The 70-MeV alpha beam also adequately covers ORIC's beam energy and intensity capabilities while, at the same time, eliminating problems associated with running alphas on ORIC:

    • Mechanical reconfiguration and stresses (rf, ion source, extraction system)
    • Ion source cathode replacement every 24-48 hours of operation
    • Power consumption

    Figure 5-1 - A schematic layout of the HRIBF with the proposed location of the new cyclotron.

    In addition, a possible dual port extraction capability will allow us to simultaneously extract two beams of deuterons or protons at different energies. One beam can be used for normal RIB production while the other can be used for isotope production such as 7Be which we could use in our batch-mode ion source.

    Very large beam intensities are possible with a commercial cyclotron. This ability will allow us to develop two-step targets where neutrons generated on a Be or Ta target could be used to induce fission on a surrounding uranium target. This "cold fission" process will produce more neutron-rich radioactive species than our current proton-induced fission process resulting in orders of magnitude improvement of many of our beams.

    A more in-depth discussion of the commercial cyclotron possibilities may be found in two white papers:

    The next step will be to develop a proposal based on the above white papers which we hope to submit to DOE this summer.

    To summarize:

    • Scientific Benefits
      • Immediate >8x gain in neutron-rich beams from (p,f)
      • Employ (n,f) with n from (p,n) or (d,n) for bigger gains
      • Sample n-rich yields relative to present HRIBF
        • 132Sn x 50, 134Sn x 1100; class="style2" 136Sn x 1900; 133Sn x 8000
        • 82Ge x 460; 84Ge x 1790; 86Ge x 4300; 88Ge x 7300
      • Above yields attainable with only minor upgrades to existing infrastructure
      • Up to 3x more with infrastructure upgrades
      • Maintains and extends existing proton-rich capability
      • Produce long lived isotopes for batch mode operations very economically using dual port proton or deuteron beams
    • Facility/Operational Benefits
      • Fully replaces ORIC and expands on capabilities
      • Commercial accelerator sold for isotope production
      • Batch mode sample or isotope production while producing RIB
      • Much improved reliability (effect on both n-rich and p-rich)
      • Much reduced power cost (~15% of ORIC)
      • Use existing target rooms - no major civil construction
    • Machine specifications
      • Multiple beam capability, variable energy
      • 750 μA proton, variable energy up to 70 MeV
      • >50 μA deuterons, variable energy up to 35 MeV
      • ~50 μA alpha, fixed energy at 70 MeV




    Regular Articles

    RA1. RIB Development
    (D. Stracener)

    The last few months of 2009 were a busy period at the On-Line Test Facility (OLTF). Efforts included twelve on-line tests to i) measure yields from a variety of uranium carbide targets, ii) measure yields from an ion source that is specifically designed to provide Sr beams with greater purity, and iii) provide 120Ag to the CARDS array that was installed on a beamline after the OLTF separator. Specifics of the ion source projects were detailed in the last HRIBF Newsletter. Uranium carbide targets that were recently tested include UC targets produced at ORNL and several higher-density targets that were produced using a hot-press technique. The ORNL-produced UC targets are made by mixing graphite with a uranyl nitrate solution, which is then heated to make uranium dicarbide. This material is ground to a very fine powder (less then 3 micron diameter) and mixed with synthetic graphite powder before a pellet is formed using a cold-press technique. The resultant UC targets are quite uniform with an average density of 2.2 g/cm3. While these targets have been used for RIB production at the HRIBF since 2006, this is the first extensive survey of fission fragment yields. The other UC targets that were tested had densities up to 5.2 g/cm3 and are being studied in collaboration with Will Talbert. The release from these targets has been shown to be reasonably fast and the yields are comparable to yields from other UC target geometries that have been tested at the OLTF. In addition, the OLTF provided beams of 3He and 4He at 40 keV, which were implanted in thin aluminum foils. These successful tests were made in collaboration with Ray Kozub and his student, Jonathan Wheeler, from Tennessee Tech. The 3He targets, to be irradiated with radioactive beams, will be used to study (3He,d) reaction cross sections that are important in the rp process of nucleosynthesis.

    During this period, we also completed another series of off-line tests with the HRIBF laser ion source in collaboration with Klaus Wendt and Tina Gottwald from Mainz University, along with Jens Lassen and Ruohong Li from TRIUMF. This year's campaign planned to investigate ionization schemes for three elements (Sb, Te, Sr) that had not previously been ionized at HRIBF and to make an efficiency measurement for Ga. Laser ionization of Sr was successful and several Rydberg states in Sr were observed. To the best of our knowledge, this is the first time resonant ionization schemes for Sr were demonstrated in a LIS with Ti:Sapphire lasers. On the other hand, we did not successfully produce laser-ionized beams of Sb and Te. We have several possible explanations (low laser power, misalignment, inaccurate ionization schemes), which will be investigated in the coming months. The measured efficiency for Ga was only 10%, which is quite low when compared to the 60% efficiency that was previously measured at Mainz and we are also investigating the cause for this discrepancy. These tests were carried out using the complete HRIBF laser system which includes a Nd:YAG pump laser and three tunable Ti:Sapphire lasers.


    RA2. Accelerator System Status

    ORIC Operations and Development (B. A. Tatum)

    During the reporting period, ORIC provided 85-MeV alpha and 50-MeV deuteron beams to IRIS1 for the production of Fluorine beams. However, this was a very difficult period of operation for ORIC that included a considerable amount of unscheduled maintenance related to failure of the coaxial magnetic extraction channel. This is a very high current device (up to 6000A dc) that developed water leaks which resulted in high tank pressure. We also experienced air and water leaks on the rf system shorting plane. All of these leaks were challenging to locate, and difficult and time-consuming to repair. We also experienced problems with the main field motor-generator set regulator and a few older power supplies. In addition, there was a scheduled shutdown period following Thanksgiving during which the new HRIBF cooling tower was brought on line and new substation circuit breakers installed.

    We are anticipating a resumption of routine operation in early 2010 with an extended neutron-rich campaign and final commissioning of IRIS2 with RIB.

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

    During the period from 1 July 2009 to 31 December 2009, the 25 MV Tandem Electrostatic Accelerator delivered beams of

  • 1 Mpps [10.76 MV 4+ terminal gas stripped] 54 MeV 50% 17F / 50% 17O to Beam Line 41, and
  • 1.1 Mpps [8.87 MV 4+ / 9+ terminal gas / post foil stripped] 44 MeV 17F to Beam Line 14.

    The 17F beams were produced via the 16O(d, n)17F reaction by bombarding a fibrous HfO2 target coupled to a Kinetic Ejection Negative Ion Source (KENIS) with 5 uA of 44 MeV 2H+ from the Oak Ridge Isochronous Cyclotron (ORIC).

    Also during this period, significant maintenance was performed on the high voltage platform in C111S. Five of the six turbopumps (excluding the one associated with the charge exchange cell) were replaced, as were all six of the turbopump controllers on the high voltage platform in C111N. The ORIC beam line (BL-9) acceleration tube was reconfigured to accommodate both a new diagnostics chamber with water-cooled, self-suppressed Faraday Cup and water-cooled insertable aperture and a rotating-wire beam position monitor, all identical to those used in C112 (IRIS2).

  • Tandem Operations and Development (M. Meigs)

    The Tandem Accelerator was operated for more than 1800 hours since the last report. The machine ran at terminal potentials of 1.34 to 23.38 MV. The KENIS ion source was used on IRIS1 to provide 289 hours of the radioactive beam, 17F. In addition, the SNICS was used to provide the stable beams 1H, 16,17O, 19F, 58Ni, and 124Sn. About 385 hours were spent conditioning, which was necessary to recover from a large SF6 leak in the low energy acceleration tube. Three tank openings were completed during this period; the first to allow the Discovery Channel to film inside the tank for a documentary, the second to remove the Faraday cup at the D4 position which had developed a large leak in its bellows, and the last to check for suspected leaks and to repair the gas stripper. Quite a few hours during this period were spent on SNICS development, leading to a greater understanding of the best methods to produce some difficult ion beams.


    RA3. Users Group News
    (C. J. Gross, HRIBF User Liaison)

    The Users Executive Committee met via telephone on January 21, 2010, and elected Jeff Winger to chair this year's committee. The meeting consisted of report on the facility and discussed the final report of the HRIBF Users Workshop: HRIBF, Upgrade for the FRIB Era held November 13-14, 2009, in support of a proposed 70-MeV cyclotron for HRIBF. The report has been posted on the website and is discussed in the workshop summary in this newsletter.


    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 grosscj@ornl.gov. In any case, a brief description of the physics to be addressed with the proposed beam should be included. Of course, any ideas on specific target material, production rates, and/or the chemistry involved are also welcome but not necessary. In many cases, we should have some idea of the scope of the problems involved.

    Beam suggestions should be within the relevant facility parameters/capabilities listed below.

    • The tandem accelerates negative ions only.
    • Positive ions may be charge-exchanged or used directly off the platform (E < 40 keV).
    • ORIC presently produces up to 52 MeV of 1H (12 uA); 49-MeV 2H (12 uA); 120-MeV 3He (not yet attempted, costly); 100-MeV 4He (3 uA). Higher currents may be possible.
    • Typical reactions required to produce more than 106 ions per second are n, 2n, pn, and alpha-n fusion-evaporation reaction channels and beam-induced fission products. More exotic reactions are possible if extremely low beam currents are all that is needed.
    • Species release is strongly related to the chemistry between the target material and the beam species. It is best when the properties are different and the target is refractory. Thin, robust targets (fibrous, liquid metals, a few grams per square centimeter) must be able to withstand 1500 degrees Celsius or more.
    • Minimum half-life is seconds unless chemistry is very favorable.
    • Very long-lived species (T1/2 > 1 h) are probably best done in batchmode, i.e., radioactive species are produced with ORIC beams and then transported to the ion source where beams are produced via sputtering. Sputter rates of the species and target substrates are important.
    • Isobaric separation is possible for light beams (fully stripped ions), while isobaric enhancement may be possible for heavy beams.
    • Beware of long-lived daughters or contaminant reaction channels.



    RA5. HRIBF Experiments, July through December 2009
    (M. R. Lay)



    Date Exp No. Spokesperson Title of Experiment
    7/2-5 Shutdown
    7/6-10RIB-035Stracener/ORNLTarget ion source development
    7/11-12Shutdown
    7/13-16RIB-152Krolas/Institute of Nuclear Physics, Krakow Structure of neutron-rich Cu and Zn isotopes produced in deep-inelastic transfer reactions with radioactive ion beams
    7/16-17RIB-035Stracener/ORNLTarget ion source development
    7/18-19Shutdown
    7/20-21RIB-152Krolas/Institute of Nuclear Physics, Krakow Structure of neutron-rich Cu and Zn isotopes produced in deep-inelastic transfer reactions with radioactive ion beams
    7/21-22RIB-037Meigs,Juras/ORNLTandem development
    7/22-24RIB-035Stracener/ORNLTarget ion source development
    7/25-26Shutdown
    7/27-28RIB-037Meigs,Juras/ORNLTandem development
    7/29-8/2RIB-205Bardayan/ORNL The Astrophysical 14O(α,p)17F Reaction Rate
    8/2-8 RIB-035Stracener/ORNLTarget ion source development
    8/8-10Shutdown
    8/10-13RIB-037Meigs,Juras/ORNLTandem development
    8/13-16Shutdown
    8/17-20RIB-035Stracener/ORNLTarget ion source development
    8/20-25RIB-205Bardayan/ORNL The Astrophysical 14O(α,p)17F Reaction Rate
    8/25-26RIB-152Krolas/Institute of Nuclear Physics, Krakow Structure of neutron-rich Cu and Zn isotopes produced in deep-inelastic transfer reactions with radioactive ion beams
    8/27-30Shutdown
    8/31-9/4RIB-205Bardayan/ORNL The Astrophysical 14O(α,p)17F Reaction Rate
    9/5-7 Shutdown
    9/8-16RIB-061Galindo-Uribarri/ORNL Decay mechanisms in the emission of two protons from a resonance in 18Ne
    9/16-18RIB-205Bardayan/ORNL The Astrophysical 14O(α,p)17F Reaction Rate
    9/18 RIB-082Gross/ORNL A time-of-flight system for measuring fusion-evaporation cross-sections using radioactive ion beams
    9/19-20Shutdown
    9/21 RIB-082Gross/ORNL A time-of-flight system for measuring fusion-evaporation cross-sections using radioactive ion beams
    9/22-30Shutdown
    10/2-5 Shutdown
    10/5-7 RIB-037 Meigs,Juras/ORNLTandem development
    10/8-9 RIB-082 Gross/ORNL A time-of-flight system for measuring fusion-evaporation cross-sections using radioactive ion beams
    10/9 RIB-037 Meigs,Juras/ORNL Tandem development
    10/10-11 Shutdown
    10/12 RIB-037 Meigs,Juras/ORNL Tandem development
    10/13 RIB-082 Gross/ORNL A time-of-flight system for measuring fusion-evaporation cross-sections using radioactive ion beams
    10/14-16RIB-037 Meigs,Juras/ORNLTandem development
    10/17-18Shutdown
    10/19 RIB-082 Gross/ORNL A time-of-flight system for measuring fusion-evaporation cross-sections using radioactive ion beams
    10/20-22RIB-035 Stracener/ORNLTarget ion source development
    10/23 RIB-082 Gross/ORNL A time-of-flight system for measuring fusion-evaporation cross-sections using radioactive ion beams
    10/24-11/5Shutdown
    11/6 RIB-037 Meigs,Juras/ORNL Tandem development
    11/7-8 Shutdown
    11/9-13 RIB-037 Meigs,Juras/ORNLTandem development
    11/14-15Shutdown
    11/16 RIB-037 Meigs,Juras/ORNLTandem development
    11/16-17 RIB-152 Krolas/Institute of Nuclear Physics, Krakow Structure of neutron-rich Cu and Zn isotopes produced in deep-inelastic transfer reactions with radioactive ion beams
    11/17-18 RIB-035 Stracener/ORNLTarget ion source development
    11/18 RIB-037 Meigs,Juras/ORNLTandem development
    11/18-20 RIB-082 Gross/ORNL A time-of-flight system for measuring fusion-evaporation cross-sections using radioactive ion beams
    11/20 RIB-037 Meigs,Juras/ORNLTandem development
    11/21-22 Shutdown
    11/23-24 RIB-035 Stracener/ORNL Target ion source development
    11/24 RIB-188 Bardayan/ORNL Astrophysics Stable Beam Experiments
    11/25 RIB-035 Stracener/ORNLTarget ion source development
    11/26-12/7Shutdown
    12/7-9 RIB-035 Stracener/ORNL Target ion source development
    12/9-18RIB-143 Amro,Kolata/University of Notre Dame Fusion of 132,124Sn with 48,40Ca
    12/19 RIB-037 Meigs,Juras/ORNLTandem development
    12/19-20Shutdown
    12/21-22RIB-037 Meigs,Juras/ORNLTandem development
    12/22 Shutdown
    12/22-23 RIB-169 Rykaczewski/ORNL LeRIBSS Development
    12/23-31 Shutdown