HRIBF Newsletter, Edition 16, No. 2, Aug. 2008

Feature Articles

1. HRIBF Update and Near-Term Schedule
2. Recent HRIBF Research - Direct Measurement of ¹⁷F(p,γ)¹⁸Ne at HRIBF
3. Recent HRIBF Research - Measurement of Nuclear Structure Properties
   Around N= 50
4. Update of the IRIS2 Project

Regular Articles

RA1.  RIB Development

RA2.  Accelerator Systems Status

RA3.  Experimental Equipment - New Dual MCP Fast Timing Detector

RA4.  Users Group News

RA5.  Suggestions Welcome for New Beam Development

RA6.  HRIBF Experiments, January-June, 2008

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

There is much to celebrate concerning recent accomplishments at HRIBF. Researchers have produced exciting new scientific results, and the facility has produced important beams at record intensity. There is also ample cause for concern. Once again we face funding uncertainty in fiscal 2009, and we face uncertainty associated with recovery from an "operational emergency" which was declared on the morning of July 28, 2008. While this event did not occur during the period normally covered by this newsletter (the six months from January 1 to June 30), it is so important to the near-term future of the facility that it is impossible to ignore it here. I will therefore include a brief summary of the event and what we know of its impact on operations at the end of this article.

We are coming off a record year in FY2007 in terms of hours of radioactive ion beam delivered to experiments. Furthermore, the facility achieved a major milestone as the astrophysics group completed a direct measurement of the ¹⁷F (p,γ) ¹⁸Ne capture reaction, using the DRS to detect the ¹⁸Ne. This achievement adds another important result to the study of reactions that create and destroy ¹⁸F in stellar explosions. The experiment was made possible by an improvement of a factor of 50 in the intensity of the ¹⁷F beam over our previous facility record. Another important milestone was achieved by the decay spectroscopy group who capped a truly remarkable year of scientific results with the completion and first use of the new Low Energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS). We have also made excellent progress toward the completion of the IRIS2 project, though delays in funding have resulted in postponement of the completion date (see IRIS2 article).

In the six month period ending June 30, HRIBF provided 1667 hours of beam on target for research, including 795 hours of ISOL RIB (including 131 hours of low-energy RIB), 180 hours of "in flight RIBs" (stable beam for experiments using the RMS to select and propagate beams of radioactive species for implantation decay studies at the focal plane of the RMS), and 294 hours of stable beam in direct support of RIB measurements (setup tests, calibrations, etc.). A total of 399 hours were devoted to stand-alone stable-beam experiments.

In the January Newsletter, I discussed the expected impact of the FY2008 continuing resolution (CR), which included up to two months budgetary shutdown of the facility. Such a shutdown was planned for August 4, 2008. The budget situation for FY2009 is again troubling. A likely scenario is a six month CR (i.e. operation at FY2008 budget levels), followed by six months at the levels of whatever FY2009 budget is enacted. We have also been instructed to develop plans for a twelve month CR. Either case would require substantial reductions in facility operations.

Now I turn to a discussion of the event that has introduced great uncertainty into our near term schedule. At approximately 8 AM on Monday, July 28, during operations with approximately 12 μA of 50-MeV protons on a uranium carbide target, delivering neutron-rich ⁸¹Zn beam to the new LeRIBSS facility, a radiological control technician (RCT) reported higher than normal radiation levels just outside the shield door to the IRIS1 vault (the room in which RIBs are produced at HRIBF). The measured dose rate equivalent was 4 mrem/hr. The presence of radiological contamination on the floor just outside the shield door was subsequently noted, as was the possible presence of airborne radioactivity. These observations were reported to facility management. Accelerators were shut down immediately and the building evacuated. The event was subsequently declared a laboratory operational emergency. Parts of the building were cleaned for reentry to collect belongings on Monday afternoon. The entire building was cleared for reoccupation on Tuesday morning after a detailed radiological survey found no contamination outside the shielded vaults. No decontamination was required.

A "recovery team" was constituted by the laboratory consisting of HRIBF staff members supplemented by a few other ORNL staff members with relevant expertise. ORNL management also commissioned an investigative team who are charged with determining causes of the event and another team to develop corrective action. The function of the recovery team is to carry out a systematic collection of information under direction of the investigative team, and subsequently, to implement corrective actions and prepare for resumption of facility operations. The investigative team will report their findings in early October. Though the recovery team is convinced that the physical basis of the event is now understood, it would be inappropriate to discuss causes in any detail prior to the investigation team report. It is appropriate, however, to catalog a few facts about the event.

The first and most important fact is that no individual received any detectable radiological dose as a result of the event. Six individuals were sent for whole body counts on the morning of the event; all were negative. All seventy-one individuals who had been inside the HRIBF building (Building 6000) during the day of the evacuation and three days prior to it had their thermo luminescent dosimeters (TLDs) collected and read the morning of the event. Readings were all consistent with zero doses. All subsequent analysis is consistent with a release that consisted entirely of noble gasses (Xe and Kr isotopes). One of the several samples collected after the event contained some ¹³¹I (all others exhibited only Xe and Kr daughters). If we accept this single iodine sample, the suppression of iodine compared to its total inventory at the time of the event compared to that of Xe isotopes is on the order of a factor of 10⁷. Four high-volume charcoal filter air samples were taken soon after the event to search for ¹³¹I. The largest air concentration measured was on the order of 10^-12 μCi/ml (i.e., background). At this time, only the RIB production vault (C111S) remains classified as a contamination area (as it was before this event). The only measurable contamination present that is attributable to this event is low levels of ¹³⁷Cs (from ¹³⁷Xe) and ¹⁴⁰Ba and ¹⁴⁰La (from ¹⁴⁰Xe). As noted earlier, it is inappropriate to discuss causes in any detail at this point. We believe we have identified two unrelated failures, one associated with the HVAC system and the other with the roughing system exhaust which accounts for both the escape of noble gasses into the IRIS1 vault and their migration outside the vault.

It is very difficult to guess when we will be able to resume radioactive beam operation. The barriers to operation are not technical. The plan to begin operation on batch mode beams may help us start a little sooner, but we may well be down through November, or perhaps even longer. We have recently been given permission to resume operation of the HRIBF tandem for stable beams. When we are given permission to resume radioactive beam operations, we will begin with a two-month campaign of "batch mode" operations with beams of ¹⁰Be and ²⁶Al. This will be followed by an extended period of operation with neutron-rich radioactive beams that will probably fill the remainder of our FY2009 operating time.

2. Recent HRIBF Research - Direct Measurement of ¹⁷F(p,γ)¹⁸Ne at HRIBF
(M. S. Smith, Spokesperson)

The rate of the ¹⁷F(p,γ)¹⁸Ne reaction is of significant astrophysical importance in such explosive astrophysical events as novae and X-ray bursts. The decay of radioactive ¹⁷F is thought to help drive the expansion of the envelope ejected in the nova outburst, and the ¹⁷F(p, γ)¹⁸Ne reaction affects the production of ¹⁸F, a target of γ-ray astronomy, and influences the ¹⁷O/¹⁸O ratio produced in these explosions. It is also an important link in the alpha-p reaction chain during the ignition phase of X- ray bursts. The ¹⁷F(p,γ)¹⁸Ne reaction rate was thought to be dominated by the contribution from an unnatural parity 3+ state that was predicted to exist from analog nuclei but was missing in decades of spectroscopic studies of ¹⁸Ne. In 1999, this "missing" 3+ state was found at 599.8 keV in the center of mass via a measurement of the ¹⁷F(p,p)¹⁷F reaction at HRIBF, which was the first measurement with a reaccelerated beam in North America [1]. However, the strength of this resonance for (p,γ) was still unknown, resulting in more than an order of magnitude uncertainty in the capture reaction rate.

To address this, the ¹⁷F(p,γ)¹⁸Ne reaction has now been measured directly, to roughly 40% statistics. The HRIBF measurement used a mixed beam of 35 - 70% radioactive ¹⁷F and the remainder stable ¹⁷O at beam intensities of typically more than 5X10⁶ pps of ¹⁷F ions. This was a factor of ~50 increase in low-energy ¹⁷F beam from previous measurements. The radioactive beam bombarded a differentially-pumped windowless hydrogen-gas target, and the Daresbury Recoil Separator was used to separate ¹⁸Ne recoils from unreacted primary beam. The spectra below show the excellent separation of recoils in the gas-filled ionization chamber at the focal plane. Resonant proton capture cross sections, gamma widths, and strengths for two resonances at 1178 keV and 599 keV in the center of mass have been determined, as well as an upper limit on the direct capture cross section at 800 keV in the center of mass. The strength of the 599-keV level was found to be more than a factor of two larger than a recent estimate based on shell model calculations of the gamma width of the analog level in ¹⁸O [2], resulting in an increase in the total ¹⁷F(p,γ)¹⁸Ne reaction rate. A set of nova simulations have been run with this new rate, and preliminary results indicate that over 400 times more ¹⁸F and ¹⁷O can be made in the hot, inner zones of one nova model when compared to simulations run with the most widely used ¹⁷F(p,γ)¹⁸Ne reaction rate. This work was the Ph.D. thesis for Kelly Chipps from the Colorado School of Mines. Future work may include a measurement of the direct capture cross section to three states just below the proton threshold in ¹⁸Ne.

[1] D.W. Bardayan et al., Phys. Rev. Lett. 83 (1999) 45.
[2] A. Garcia et al., Phys. Rev. C. 43 (1991) 2012.

Figure 2-1: Ionization-counter spectrum from direct measurement of ¹⁷F(p, γ)¹⁸Ne at HRIBF showing identification of ¹⁸Ne recoils and scattered ¹⁷F and ¹⁷O beam particles at the focal plane of the Daresbury Recoil Separator (DRS). This yield is at the dominant resonance at an energy of 599 keV in the center of mass.

3. Recent HRIBF Research - Measurement of Nuclear Structure Properties
Around N=50
( E. Padilla-Rodal & A. Galindo-Uribarri, Spokespersons)

As part of a research program devoted to the measurement of nuclear structure properties of neutron-rich nuclei around the mass A~80 region, during the months of September and October 2007 our collaboration performed three experiments using Radioactive Ion Beams (RIBs) produced at the Holifield Radioactive Ion Beam Facility (HRIBF):

RIB-144 Coulomb excitation of n-rich nuclei.

RIB-135 Static quadrupole moment of the first 2⁺ in ⁷⁸Ge.

RIB-151 g-factor measurements of n-rich isotopes near N=50.

Our aim has been to obtain a comprehensive picture of the shell structure in this region through the study of a series of properties: E (2⁺), B (E2), g-factors and electric quadrupole moment Q. The beams, instrumentation and techniques developed at HRIBF specifically for this purpose have allowed us to systematically study the behavior of these observables along isotopic and isotonic chains using both stable and radioactive nuclei under almost identical experimental conditions.

We have done pioneering studies of the evolution of collectivity in the neutron-rich radioactive isotopes ^78,80,82Ge using the B(E2) as an indicator of the nuclear structure [1]. For this work we also did a systematic measurement of the stable germanium and selenium isotopes. Recently a collaboration using REX-ISOLDE at CERN reported on the first observation of the 2⁺ state in ⁸⁰Zn by Coulomb excitation [2]. This together with our measurements on other N=50 nuclei gives a more complete picture of the nuclear structure for this isotones.

High quality radioactive ion beams were delivered to the RMS experimental station for the three new experiments. In Fig. 3-1 we show a scheme of the experimental setup. Around the target position we used the combination of the CLARION array, consisting of 11 HP-Ge clover detectors formed by four crystals, each segmented longitudinally in half, and the new particle array BAREBALL, with 54 CsI(Tl) detectors with minimum absorbers arranged in five rings. The de-excitation gamma-rays emitted by the Coulomb-excited projectile were detected in coincidence with the light target recoil nuclei. The beam composition was continuously monitored using a Bragg curve detector placed at zero degrees with respect to the incoming beam.

Figure 3-1: Experimental setup for the three RIB experiments performed in the mass A~ 80 region.

The aim of the first experiment was to measure the B(E2) values of the N=50 ⁸⁴Se. The conditions were very favorable in terms of beam purity and intensity. We bombarded a natural Al target [~1.5 mg/cm2 ] with an A=84 RIB at a beam energy of 193.2 MeV (2.3A MeV). The measured average beam intensity was 4X10⁴pps, and the beam composition was 45% ⁸⁴Se, 54% ⁸⁴Br, and 1% ⁸⁴Rb.

Figure 3-2: Left panel shows a typical two dimensional spectrum from the Bragg Curve Detector placed at zero degrees for an A=84 RIB. In the right panel one can see the projection of the charge distribution along a tilted axis, showing the two main components of the beam.

⁸⁴Se is the N=50 isotone that lies right in the middle between Z= 28 and Z= 40 and therefore is expected to have maximum sensitivity to constrain the shell model effective interaction. In Fig. 3-3 we show a particle-gamma coincidence spectrum Doppler corrected event-by-event using both the clover segmentation and the recoil information obtained with BAREBALL. New transitions in the odd-odd ⁸⁴Br isobar and a very clean peak for the 2⁺₁ to 0⁺_g transition in ⁸⁴Se are observed.

Figure 3-3: Gamma-ray energy spectrum for an A=84 RIB.

The aim of the second experiment was to measure the electrical quadrupole moment of ⁷⁸Ge. Using a sulfur purification technique [3], a pure beam of ⁷⁸Ge was produced with typical intensity of 2X10⁶ pps. We bombarded two targets of ¹²C and ²⁴Mg alternately to minimize systematic effects such as beam intensity, beam composition and target thickness variations.

In the last experiment we intended to measure the gyromagnetic ratio in the mass A~80 region (⁷⁸Ge and ⁸⁰Ge) using the recoil-in-vacuum technique. Fig. 3-4 shows the angular correlation for ⁷⁸Ge and ⁷⁶Ge. The beam conditions for the data of ⁸⁰Ge were less favorable as the overall source intensity had started to decline. The analysis of these data is in progress to determine if more data will be required for ⁸⁰Ge.

Figure 3-4: Angular correlation for the Stable Ion Beam (SIB) ⁷⁶Ge and the RIB ⁷⁸Ge.

Data sets using stable beams under nearly equal conditions to the RIB experiments were obtained for reference, normalization or calibration. Tests have been performed with the Bragg Detector to measure target thickness homogeneity and energy loss variations due to intense beam bombardment.

[1] E. Padilla-Rodal et al. Phys. Rev. Lett. 94 (2005) 122501.
[2] J. Van de Walle et al., Phys. Rev. Lett. 99 (2007) 142501.
[3] D.W. Stracener, HRIBF NewsLetter Supplement, Edition 9, No.3, Spring Quarter 2001.

4. Update of the IRIS2 Project
(B. A. Tatum, Spokesperson)

The Annual Progress Review for the IRIS2 project was held in April. All technical and management aspects of the project were favorably reviewed with only one recommendation: to submit change requests discussed at the review. Funding delays in two consecutive years have necessitated the request for changes to the funding profile, and delay of major project milestones including the project completion date. In the original project baseline, all project funds ($4,735K) were to have been received early in fiscal year 2008. Presently, $635K of project funds are now delayed until FY 2009 and thus the completion date has been moved from February 28, 2009 to September 30, 2009.

Technical progress on the IRIS2 Project has been good during the reporting period. All of the major beamline components for both the injector and transport beamlines have been received with the exception of the vacuum pumps which are due to arrive in late July. Assembly of injector beamline vacuum components is approximately 70% complete. Preparations have been made for tying in the transport beamline to existing beamline 12 (beamline from IRIS1 through the isobar separator). These activities have included relocation of piping, electrical circuits, and cable trays. Electrodes and vacuum chambers for both of the transport beamline spherical electrostatic deflectors have been received. The 35-degree deflector has been assembled, aligned, and tested and is now ready for installation. Assembly of the 90-degree deflector has begun. Installation activities will continue to be the primary focus during the remainder of the calendar, with beamline commissioning expected to begin early in calendar year 2009.

RA1. RIB Development
(D. W. Stracener)

Significant progress has been made in the last few months on a number of ion source and target development projects. The efforts of the ISOL development group are devoted to developing techniques to improve the quality of radioactive ion beams at the HRIBF. The following is a summary of capabilities and recent activities at the facilities that are available at the HRIBF for testing RIB production targets and ion sources.

Ion Source Test Facility I (ISTF-1)

There are two facilities at the HRIBF where ion sources are developed. Operation of production ion sources on the RIB production platform has benefited greatly from the operational experiences gained at these facilities. Researchers at the ISTF-1 (including two summer students) have recently designed, installed, and tested an improved RFQ negative-ion beam cooler, which will be implemented at the new IRIS-2 production facility when it becomes available. This cooler is used in a beam purification technique where a laser interacts with a slow-moving ion beam and in specific cases where the electron affinities are favorable, unwanted negative ions are removed from the beam via photodetachment (see the August 2006 HRIBF Newsletter). This change in design will improve transmission through the cooler and allow it to be used with beams having energies that are typical of those from the ion source.

Ion Source Test Facility II (ISTF-2)

Development of an ion source based on resonant laser ionization using Ti:Sapphire lasers has been the primary focus of efforts at the ISTF-2 for the last few years. This project has been quite successful and the HRIBF laser ion source will be ready for utilization at the new IRIS-2 production platform. The laser system uses a Nd:YAG laser to pump three tunable Ti:Sapphire lasers, which provide the laser beams tuned to the frequencies needed to selectively ionize the atoms of interest. The last two Ti:Sapphire lasers have been ordered from Photonics and they should be delivered by October of this year. We are preparing to test the complete system with all HRIBF-owned lasers later this year.

On-Line Test Facility (OLTF)

At the OLTF, low intensity beams (up to 50 nA of 40-MeV protons) are available from the Tandem to irradiate RIB production targets. The separator at the OLTF was formerly known as the University Isotope Separator at Oak Ridge (UNISOR) where experiments with low-energy radioactive beams have been conducted since 1971. Recent efforts have focused on off-line testing of a novel ion source, which may result in purified beams of radioactive strontium isotopes. This source uses a quartz tube in the transfer line between the production target and the ion source to selectively slow down some elements such as rubidium and cesium. On-line characterization of this ion source was started in July and the analysis of the yield data has begun. Another recent on-line test measured the yields from a medium-density (6 g/cm³) uranium carbide target. The results are preliminary, but it appears that the beam intensities are lower than are extracted from the standard HRIBF uranium carbide targets, which have densities in the range of 1-2 g/cm³.

High Power Target Laboratory (HPTL)

High intensity production beams from ORIC are available at the HPTL to irradiate RIB production targets. This is the newest of the ISOL test facilities and will be co-located with the second RIB production platform (IRIS2). At the HPTL, we have begun off-line testing of a niobium silicide target coupled to a hot plasma ion source. In an upcoming on-line test, the yields of Al-25 and the short-lived isomer of Al-26 will be measured as a function of target temperature and production beam intensity. The yields of these radioactive aluminum isotopes will be compared to the measured yields extracted from previously-tested silicon carbide targets. These on-line tests have been delayed due to the installation of the high-voltage platforms and conduits for the IRIS2 project but we are now poised to take full advantage of the unique capabilities of the HPTL.

RA2. Accelerator System Status

ORIC Operations and Development (B. A. Tatum)

ORIC operated for much of the reporting period, providing proton, deuteron, and alpha beams for the production of 664 hours of RIB on target for the experimental program. The only major problem encountered during the period that required significant downtime was a small water leak on the coaxial magnetic extraction channel. This leak was temporarily repaired by an internal sealant, but ultimately the channel had to be removed from the machine for replacement of the insert coil. Removal and repair of any extraction channel requires 3-6 weeks of downtime due to the complexity of the work and radiological conditions.

New harmonic coil power supplies have been purchased to replace aging supplies that have been a chronic source of instabilities in recent months. ORIC contains four sets of harmonic coils, but only the #1 and #4 (or valley) coils are required for beams that we presently accelerate. The new #4 power supplies are now in service and the #1 power supplies will be received and installed in the coming quarter. To help maintain good vacuum in ORIC, a new 20" cryopump has been procured and will be installed in the near future. This pump replaces a failed unit located on the south end of the resonator which provides supplemental pumping to the three diffusion pumps. We have also ordered a new 4648 rf power amplifier tube from Burle Industries to ensure many more years of operation.

ORNL is in the process of replacing our almost 50-year-old substation circuit breakers. The modern breakers, which are expected to be received and installed prior to the end of the fiscal year, should improve facility reliability and personnel safety.

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

During the period from 1 January 2008 to 30 June 2008, the 25 MV Tandem Electrostatic Accelerator delivered beams of

13 Mpps [5.31 MV 3+ terminal gas stripped] 21.2-MeV ¹⁷F,

8 Mpps [3.54 MV 2+ terminal gas stripped] 10.8-MeV ¹⁷F, and

13 Mpps [4.73 MV 2+ terminal gas stripped] 14.3-MeV ¹⁷F to the H₂ gas target in front of the Daresbury Recoil Separator and

40 Mpps [21.35 MV 7+ / 9+ terminal foil / post foil stripped] 171-MeV pure ¹⁷F to Beam Line 21.

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 3-5 uA of 44-MeV ²H from the Oak Ridge Isochronous Cyclotron (ORIC).

Tandem Operations and Development (M. Meigs)

The Tandem Accelerator was operated for more than 2700 hours since the last report. The machine ran at terminal potentials of 2.02 to 22.87 MV and the stable beams ¹H, ¹²C, ^16,17,18O, ¹⁹F, ³¹P, ³⁵Cl, ⁵⁶Fe, ⁵⁸Ni, ¹⁰⁷Ag, and ^118,120Sn were provided. Radioactive beams of ^17,18F accounted for more than 660 hours of beam on target. Conditioning was done for about 24 hours to return the machine to operation at 23.5 MV after having the tank open for maintenance. Two tank openings were required during this period; the first for scheduled maintenance and the second to repair a shorting rod contact that had been incorrectly installed in the first tank opening.

RA3. Experimental Equipment - New Dual MCP Fast Timing Detector
(K. Schmitt, Spokesperson)

A variation of the foil+MCP base timing detector has been developed to address the lower efficiencies for detecting ions with low specific energy loss (DE/DX) . The system features two micro-channel plate (MCP) detectors viewing the opposing surfaces of a single foil. This allows for monitoring the detection efficiency in-beam as well as extracting a fast timing signal with significantly increased efficiency.

In this detector secondary electrons are ejected as ions pass through a thin carbon or aluminized Mylar foil. Electric fields guide the electrons emitted from the foils toward the surface of a micro-channel plate detector assembly where fast multiplication of the electron current takes place. The amplified electron current is collected at a metal anode and used to provide a fast timing signal.

Efficiency is measured using the count rates from the individual anodes and the count rate of signals that are coincident in time. Since the probability that signals coincide is the product of the efficiencies of the individual detectors, the efficiency of one detector is the coincident count rate divided by the count rate of the other detector.

The first experiment to take advantage of this detector will be ¹⁰Be(d,p) as part of a long-lived RIB campaign scheduled for this fall at HRIBF. A position-sensitive Dual MCP will be constructed in the coming months.

RA4. User Group News

It is time to hold the biennial election for the Users Executive Committee. The nomination committee (Walt Loveland, Robert Grzywacz, and Witek Nazarewicz) has selected the slate of candidates below.

Additional nominations may be submitted from the users group at-large by collecting the support of 10 members and forwarding the name of the nominee to Carl Gross at grosscj@ornl.gov. Deadline for at-large nominations is October 10. More information may be found in the Users Group Charter or by contacting Carl Gross. The candidate receiving the most votes for a given seat will take office January 1 and serve for 4 years.

The HRIBF will hold its annual Users Group Meeting at this year's DNP meeting in Oakland, CA, on Friday evening, October 24. As in the past, this meeting will be held jointly with the ATLAS, NSCL, GAMMASPHERE/GRETINA, and RIA Users groups. The meeting is scheduled to start at 7 pm with HRIBF going first. Each group will have 20 minutes. We hope you will be able to join us in Oakland.

RA5. 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 (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.

RA6. HRIBF Experiments, January through July 2008
(M. R. Lay)