HRIBF NEWS


Edition 8, No. 4 Fall Quarter 2000 Price: FREE

Feature Articles Regular Articles

Editors: C. J. Gross and W. Nazarewicz

Feature contributors: R. L. Auble, J. D. Fox, J. Gomez del Campo, J. F. Liang, D. C. Radford, M. Saltmarsh, D. Shapira
Regular contributors: M. R. Lay, M. J. Meigs, P. E. Mueller, D. W. Stracener, B. A. Tatum


1. Update of RIB Delivery Plans

Operation of the uranium carbide target for production of neutron-rich RIBs was continued until late October. The added time allowed us to complete the first neutron-rich RIB experiment and to investigate isobar-separation capability. The results of these studies are discussed elsewhere in this newsletter. At the present time, the RIB injector platform is being readied for installation of a batch-mode target/ion source which will be used to provide beams of 18F and 56Ni/56Co. At present, we plan to provide 18F beams through mid-December. At that time, it will be necessary to shut down for routine maintenance on the tandem electrostatic accelerator. Operation is expected to resume in late January 2001 with either additional 18F operation or beginning the 56Ni/56Co operation.

Studies of a negative-surface-ionization source (NSIS) for production of group VII elements are still in progress and are expected to be completed before the end of CY 2000. Implementation of the NSIS is expected to allow significantly higher beam intensities for neutron-rich bromine isotopes and other group VII elements than is possible using the EBP source/charge-exchange system.

Following the batch-mode source program, we will install either a KENIS source to produce 17F beams or a uranium carbide/EBP system to produce neutron-rich RIBs. The final selection will need to be made early in 2001 and will be guided by the interests of the researchers and readiness of the experimental apparatus. Operation with either 17F or neutron-rich beams is presently expected to begin in June or July 2001.

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2. PAC Meeting and Results

The Program Advisory Committee met on November 3-4, 2000 to discuss 38 proposals. In general, the quality of the proposals was very high, and a total of 115 RIB shifts and 93 SIB shifts were allocated out of a total request of 544 RIB and 306 SIB shifts. The approved RIB experiments utilize beams of 17,18F, 92Sr, 126,128,130Sn, and 132,133Te. A complete list of experiments is available.

The electronic proposal process went extremely well with very few conversion problems. We will continue to require electronic submissions. The PAC recommended that a mechanism be setup to solicit beam development suggestions and quick proposal approval for recently developed RIBs. Starting with this issue, every newsletter will have a reminder that we welcome suggestions for new beams from our community. In addition, whenever a RIB is to be tested for the first time, a newsletter will be issued soliciting proposals which can be run under uncertain initial conditions and according to the expected experimental endstation configuration. The proposals will undergo expedited PAC review, and it is anticipated that only one or two experiments would be accepted.

The next Call for Proposals is expected to be issued in April of next year with the PAC meeting June 15-16, 2001.

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3. Recent HRIBF Research - Coulex and Fusion-Evaporation Reactions with Neutron-rich Radioactive Ion Beams*

A team of researchers from HRIBF and the University of Tennessee have performed an experiment using neutron-rich radioactive ion beams from the HRIBF facility, together with the CLARION Ge detector array and the HyBall CsI charged-particle detector array. A foil-plus-multichannel-plate detector was also placed at the achromatic focus of the Recoil Mass Spectrometer and used to detect recoiling fusion-evaporation reaction products.

A beam of 118Ag (T1/2 ~2 s for 118mAg, T1/2 ~4 s for 118gAg) was produced by proton-induced fission of 238U, and accelerated to energies of 455 and 500 MeV in the tandem accelerator. These energies required the use of the second stripping foil in the high-energy beam tube, but beam intensities on target of at least 1,000,000 118Ag ions per second were obtained. The data collected consisted of gamma-HyBall coincidences, together with gamma-gamma-recoil coincidences where the recoiling nucleus was detected in the multichannel-plate detector. The overall efficiency for detecting such products was about 40%.

Two different reactions were used. Firstly, a target of 0.6 mg/cm2 12C was bombarded at a beam energy of 500 MeV. Fusion-evaporation reactions leading to the known nuclides 125,126I [1] (5n and 4n evaporation) and 126Te (p3n) were observed, together with alpha-3n evaporation to previously unobserved states in 123Sb. Also observed were ineleastic scattering events, where a scattered 12C from the target was detected with HyBall in coincidence with a gamma ray detected in CLARION. A particle-identification spectrum for one of the HyBall detectors is shown in Fig. 3-1, together with gamma spectra gated by the different charged particles. Inelastic excitation of the first 2+ state of 118Sn, from a weak (less than 5%) isobaric contamination of the beam can be clearly identified in the carbon-gated spectrum, suggesting an excellent means of performing Coulomb-excitation measurements of RIBs in future experiments. In the gamma-gamma-recoil events, levels up to the known [1] 31/2- state of 125I were observed.

Fig. 3-1 - Particle identification data from pulse shape analysis of HyBall (top) and particle-gated gamma-ray spectra taken with a 118Ag beam.
Secondly, a target of 1.25 mg/cm2 9Be was bombarded at a beam energy of 455 MeV in an attempt to observe new levels in the 4n-evaporation product, 123Sb. The gamma-gamma spectrum observed in coincidence with recoils was virtually identical to the alpha-gated gamma-ray spectrum from the C target, confirming the assignment of the peaks to 123Sb. With the Be target, a large number of alpha particles from incomplete fusion were also observed in the HyBall array. Analysis of the gamma-gamma coincidence data is ongoing.

References

*Participants include D. C. Radford, C. Baktash, A. Galindo-Uribarri, C. J. Gross, D. J. Hartley, T. A. Lewis, P. E. Mueller, L. L. Riedinger, D. Shapira, D. W. Stracener, C.-H. Yu.
[1] D. Hartley et al., private communication.

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4. Recent HRIBF Research - Isobaric Separation and Beam Purity*

Most reactions used to produce radioactive atoms also produce other isotopes at rates similar to the production rate of the isotope of interest. Separation of the ion of interest from other nuclides with mass difference of at least 1 amu is easily done using a dipole magnet on the RIB Injector Platform that has a resolving power (M/dM) of 1000. Separation of isobars where the mass difference is often less than a part in 10000 is much more difficult. The design and operation of the target and ion source are important factors in using chemical selectivity to reduce the level of isobaric contamination before the ions are formed and accelerated. Once the negative ions are accelerated off the RIB Injector Platform, isobars can be separated using a high-resolution, two-sector dipole magnet. The design goal for the resolving power of this magnet (M/dM ~ 20000) assumes a beam with a 0.25-mm diameter. In practice, the beams are somewhat larger and the resolving power of the isobar separator is about a part in 10000. Another technique that has been used with low-Z elements involves passing the high-energy beam through a foil immediately after the tandem and then separating the fully stripped ions in a low-resolution dipole magnet (e.g. removing the 17O8+ ions from the 17F9+ beam).

We recently used a radioactive ion beam (A=132) to measure the capability of the isobar separator. The beam was composed of negative ions of Te, Sb, and Sn, and the yield of each element was measured using a moving-tape system and a high-purity Ge detector situated just after the image slits of the isobar separator. The mass differences in terms of M/dM are 14300 for 132Te and 132Sn, 22400 for 132Te and 132Sb, and 39400 for 132Sb and 132Sn. Shown in Fig. 4-1 are the yields and ratios of yields as a function of the magnetic field in the isobar separator. The ratio of Te:Sb:Sn was 75:15:1 when the beam was tuned through narrow object slits (0.1 mm) and the beam intensity was maximized on the Faraday cup immediately after the image slits of the isobar separator. The beam was scanned across an edge of one of the image slits and the ratio changed as the lighter mass, Te, was blocked by the slit. The ratio Te:Sb:Sn improved to 0.8:3.5:1, while the Sn beam intensity decreased by a factor of six.

Fig. 4-1 - Yields and relative yields for A=132 isobars after the isobaric separator.

In most cases, the experiments need a pure beam or the capability to identify the beam particles on an event-by-event basis. To this end, recent tests have been performed using two micro-channel-plate (MCP) transmission detectors (see article RA3) to measure the time-of-flight of each beam particle. The beam passes through a thick gas target that degrades the energy, and the time-of-flight is measured between two MCP detectors that are about 10 meters apart. This detector system was tested with the A=132 beam from the RIB Injector that was subsequently accelerated to 450 MeV in the tandem. Using a gas cell to degrade the energy of the beam (Eloss~245 MeV), the time-of-flight spectra were collected for various settings of the isobar separator magnet and the object slits. The results are shown in Fig. 4-2. The first panel shows the change in the relative intensity of the components in the beam as a function of the magnet setting. This data was taken with a 2-mm opening in the object slits, which is larger than the beam. The second panel shows the effect of decreasing the beam size for a given magnet setting. The slits were reduced to a 1-mm opening, and the magnet setting was chosen to enhance the concentration of 132Sb in the beam. The ratios of the various components in the beam agree with the gamma-ray measurements. This technique should work well for low-to-intermediate-mass beams; however, for beams with mass greater than 100 amu, the energy loss required for identification is too large. The beam energy will be less than the energy required to overcome the Coulomb barrier for most reactions. So while this technique may be not be useful for the A=132 beam, it should work quite well for the 56Ni/56Co beam.

Fig. 4-2 - Isobar identification spectra for A=132 using energy loss and time-of-flight techniques.

References

*Participants include D. W. Stracener, R. L. Auble, T. A. Lewis, P. E. Mueller, and D. Shapira.

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5. Recent HRIBF Research - A Negative-ion Beam Cooler for the HRIBF*

Radioactive beams produced by the ISOL technique are often accompanied with neighboring isotopes and isobars. Since many experiments require high purity beams, a high-resolving power (M/dM~20,000) isobar separator is installed at the HRIBF to remove beam contaminants. In order to achieve the high resolving power of the isobar separator, it is necessary to have a beam of very small emittance. Moreover, the 25-MV tandem postaccelerator requires the input of negative ions. Negatively charged radioactive beams can be produced using a sputter-type negative ion source or by means of charge exchange from positive ions. In either case, the negative ions have a large emittance due to the large energy spread associated with the energetic-sputtering process or charge exchange process. The performance of the isobar separator is therefore limited by less than than optimal beam qualities.

We have explored the feasibility of using a collisional ion guide as an ion cooler to improve the emittance and reduce the energy spread of negative-ion beams. The negative-ion cooler consists of a deceleration stage, a gas-filled RF quadrupole, and a reacceleration stage. Since the negative ions are very fragile because electron detachment can take place during collision, they have to be decelerated to sufficiently low energies to prevent the loss of ions. The quadrupole has 4 cylindrical rods of 8 mm in diameter and 40 cm in length. The inscribing diameter of the quadrupole is 7 mm. In the RF quadrupole, the ions lose their kinetic energies in both longitudinal and transverse directions through collisions with the buffer gas. Eventually, the ions can be confined near the optical axis of the quadrupole with energy equal to the thermal energy of the buffer gas. A longitudinal DC field is applied to drag the cooled ions out of the quadrupole. The ions are subsequently reaccelerated to an energy which matches that of the ion source.

The ion cooler was tested at the Ion Source Test Facility in the HRIBF. An electrostatic energy analyzer located downstream of the cooler was used to measure the energy spread of ion beams. Because the electrostatic-energy analyzer was designed for low-energy beams, the tests were performed for ions of 5 keV. The transmission efficiency was determined by comparing the beam intensity measured in Faraday cups before and after the device. Negatively charged Cl and F ions were used with N2 and He as the buffer gas, respectively. The negative F ions were generated by the kinetic-ejection ion source with an energy spread of 4 eV FWHM and a high-energy tail extending to 10 eV. With a He pressure of 4.5 mTorr in the quadrupole, a cooled F beam with an energy spread of ~2 eV FWHM after reacceleration was obtained. The shape of the energy distribution was similar to Gaussian as can be seen in Fig. 5-1.

Fig. 5-1 - Energy distributions of negative F beam generated by the kinetic ejection ion source (red curve) and negative F beam cooled with a 4.5 milliTorr He buffer gas (blue dots).

The transmission efficiency of F ions increased as the gas pressure increased in the quadrupole until it reached ~10%. However, the width of the energy spread reached 2 eV FWHM before the transmission reached 10% and remained constant as the transmission increased. This suggests that scattering with the buffer gas at the exit of the quadrupole contributed to the observed energy spread. We should be able to further reduce the energy spread of the reaccelerated beam by improving the reacceleration scheme. Due to a limitation of the RF amplifier, the quadrupole was operated at 2.7 MHz which was not sufficient to confine ions with large transverse energies. Simulations show that at higher frequencies, the transmission efficiency will increase. Additionally, the deceleration and reacceleration electrodes can be further optimized to improve the transmission.

References

* Participants include J. F. Liang, Y. Liu, G. D. Alton, J. R. Beene, H. Wollnik, and Z. H. Zhou.

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6. Production and Helium-Jet Transport of Fission-Product Radioisotopes: Considerations on Using ORELA for RIB Production*

We are exploring the possibility of using the 60-kW, 150-MeV Oak Ridge Electron Linear Accelerator (ORELA) for the production of radioactive species from the fission of actinide targets. As reported previously, calculations indicate that we can produce fission fragments using the ORELA electron beam at a rate of one or two orders of magnitude larger than that at the current HRIBF.

We have investigated the production of fission fragments from a uranium target irradiated by bremsstrahlung X-rays and transported to the "Electron Room" target area by means of a helium jet. While it became clear that the system was able to function as designed, the ambient gamma-ray background in the counting area prohibited a determination of the radioactive species being detected or any quantitative measurement of the efficiency for capture and transport of fission products.

In order to improve the background situation and reduce the uncertainties in fission product production, the experiment was relocated to the RMS area of the HRIBF. A 2-mCi 252Cf source, which has a 3% spontaneous fission branch, was installed in the target holder in place of the uranium target foils and was located in a shielded enclosure within 30 meters of the CLARION array. The detection apparatus was reconfigured and installed in a framework designed by Louisiana State to hold the CLARION Clover Ge detectors and is shown in Fig. 6-1.

While the target holder geometry was not ideal for use with the fission source, we detected and identified many fission fragment species, many of which with halflives less than 1 minute. Among the fragments detected and analyzed were 93Sr (7.4m), 104Tc (18m), 108Rh (4.55m), 116Ag (2.7m), 130Sn (3.7m), 132Sn (39.7s), 132Sb (4.1m), 134Sb (10.2s), 140Cs (63.7s), 142La (91.1m), and 144La (41s).

A much simpler "beer can" target assembly was built and tested with ORELA beams using a single uranium foil with larger area. Activity yield with the new design was improved by more than an order-of-magnitude over the earlier design when operated under similar beam conditions. This simpler design has been incorporated into an enclosure for the 252Cf source; a test using the CLARION detectors will begin soon.

Fig. 6-1 - The apparatus used for collection and detection of fission products in the He jet experiment. The 1.5-mm (ID) teflon tube entering from the right-hand side directs the aerosol-loaded Helium jet onto a tape of 35-mm film, which can be moved to place the collected activity between two large Clover Ge detectors from the CLARION array.
Whether helium jet transport should be considered as the means to bring useful ORELA RIBS to the HRIBF remains to be seen. The distance between the two facilities is over 200 meters and the transit time would be of order 20 seconds. Although the system is inexpensive to construct and the transport efficiencies are around 30%, the final yields may not be competitive. The high-energy electron beam is difficult to use efficiently since the ranges of fission fragments in the targets restrict the effective target thickness to about 100 microns. Other means of fission product transport are being considered, but they entail considerably higher cost than the helium jet method.

References

*Participants include J. D. Fox, M. Saltmarsh, W. T. Diamond, J. R. Beene, A. Galindo-Uribarri, N. L. Jones, and D. C. Radford, D. W. Stracener.

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7. Abstracts for ISOL'01 Due December 15

Receipt of electronic abstracts is due December 15 for the International Conference on Physics with Radioactive Ion Beams (ISOL'01), which will be held in Oak Ridge, March 11-14, 2001. Registration and instructions for abstract submission may be found on the conference website. The meeting is a celebration of the past 20 years of science at the Holifield Facility and will address the important technical and science issues of physics research with radioactive ion beams.

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8. Dan Bardayan Receives Dissertation Award from APS

Dan Bardayan has been awarded the 2001 Dissertation Award in Nuclear Physics by the American Physical Society for his Ph.D. thesis "Explosive 17F(p,gamma)18Ne Burning Through the 3+ State in 18Ne", Yale University, June 1999. This award from the American Physical Society is for the best dissertation by a student earning a Ph.D. degree in experimental or theoretical nuclear physics from a North American university within the two-year period preceding 1 September 2000. Dan's work resulted in the first scientific publication reporting a measurement with a beam of radioactive ions from HRIBF. The award consists of $1000 and an allowance for travel to the annual Spring Meeting of the Division of Nuclear Physics of the American Physical Society at which the award will be presented.

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RA1 - RIB Development

Neutron-rich RIB Development

We have completed two on-line experiments to measure yields of radioactive neutron-rich isotopes from a uranium carbide target. The target consists of a thin layer (~10 um) of UC deposited on a low-density graphite matrix that has a high thermal conductivity. The material was described in the last HRIBF Newsletter. The main differences between this UC target and the previous UC target are the thermal conductivity and the density of the support matrix. This graphite foam material is less open and the average ligament thickness is about twice that of the reticulated vitreous carbon (RVC) matrix, but the thickness of the UC layer was about the same in both targets.

In the initial test, this target was coupled to an Electron Beam Plasma Ion Source (EBPIS), and the measured yields were compared to those measured previously. The RIB yields were measured using low-intensity proton beams (33 MeV, 17 nA) at the UNISOR facility, and we found that, on average, the yields were the same from both targets. It does seem that the UC/C foam target is slightly better for short-lived, lighter isotopes (A<100 amu), while the UC/RVC target is better for the heavier isotopes, but the differences are less than a factor of two in most cases. Given the higher thermal conductivity of the UC/C foam target, the real advantages may be realized when high-intensity proton beams are used on the RIB Injector Platform.

The purpose of the second on-line experiment was to compare the neutron-rich RIB yields from a UC target coupled to an EBPIS (positive ion source) to the yields measured when this target was coupled to a Negative Surface Ionization Source (NSIS) that produces negative ions directly. The NSIS uses a LaB6 surface, which has a relatively low work function, to generate negative ions of electronegative elements (e.g., F, Cl, Br, I). A survey of many masses showed that with this target only isotopes of bromine and iodine can be extracted from this ion source. The good news is that the measured yields of these elements are at least an order of magnitude higher than the yields measured from the EBPIS followed by a Cs-vapor charge exchange cell. The yields of Br isotopes are 30 times higher, while the yields for I isotopes are 10 times higher. Also, the emittance of the beam from this source is quite good (even better than from the EBPIS), which should result in good transmission to the experiment. Poisoning of the LaB6 surface is a problem that has been reported in the literature, so another low-intensity test of this target/ion source is planned to determine the durability of this system over several days before it is moved to the RIB Injector.

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RA2 - Accelerator Systems Status

ORIC Operations and Development
ORIC operated extremely well during the reporting period. Up to 12 microamps of 42-MeV protons were provided to the UC2 target/ion source on the RIB injector platform for the very successful production of neutron-rich beams. ORIC central region studies were also performed on proton beam production using a newly designed experimental ion source chimney and rf puller electrode. The design permits the source exit aperture and the puller electrode to operate in closer proximity to one another, thus more clearly defining and separating individual turns. Separated turns yield a higher efficiency in extracting the beam. Initial tests indeed showed improved turn separation compared to the existing central region geometry, and proton efficiencies were increased to ~65% at microampere intensity levels. Future studies with this geometry will focus on enlarging the source aperture, evaluating the effect at higher intensities, and experimenting with deuteron and alpha beams.

Tandem Operations and Development
The tandem accelerator has provided more than 1300 hours of beam on target since the last report. The machine ran at terminal potentials of 16.35 to 23.0 MV, and 58Ni, 82Se, 35Cl, 36Cl, 40Ca, 117Ag, 118Ag, 126Sn, 132Sn, 134Te, and 1H were provided. Double stripping (using both the terminal and the high-energy, upper-dead-section foil strippers) was employed to provide higher energies for the heaviest ions. Double stripping has not been used for many years, but the operators quickly became efficient in its use. The tank was opened twice during this period, once for repairing spark-damaged electronics and once for a short scheduled opening, primarily to allow conditioning and diagnosis of problems with previously recalcitrant tube sections. Since there may be a need to go to higher terminal voltages, the tank opening was scheduled to remove a shorting strap that has been in place on three tube sections for more than a year. Magnets were placed on the spool piece just underneath these sections to try to alleviate any electron leakage from the dead section. This is a light time in the schedule, and some time will be used to try to determine if these tube sections will act properly or if we must do more extensive work in the next long scheduled tank opening.

The tandem accelerator was used to examine the possibility that it could be used for Accelerator Mass Spectrometry (AMS) studies. The test, using 36Cl, beams gave some very promising results and will be followed by more work to determine just what the machine can do to provide AMS measurements that cannot be done elsewhere.

RIB Injector Operations and Development
After our initial success with 117Ag we delivered 1.5 million particles per second of double stripped 455 MeV 118Ag to the CLARION Array and the Recoil Mass Spectrometer. Additional contaminants (118In and 118Sn, Cd does not charge exchange) were present at the 10% level. The 118Ag was produced by bombarding a target of nine 2-mm-thick by 15-mm-diameter discs of depleted uranium carbide on a reticulated vitreous carbon matrix with 11 microamperes of 42-MeV protons. The target was coupled to our standard electron beam plasma positive ion source. The positive ions passed through our new cesium vapor charge exchange cell, and the resulting negative ions were injected into the 25-MV tandem electrostatic accelerator. The short halflives of 118Ag made it easy to see the effect of unsuppressible beta decay electrons on Faraday cup measurements.

After the 118Ag experiment, we studied the isobar separation properties of the second stage mass separator. The measurements made on 132Sn, 132Sb, and 132Te are reported elsewhere in this newsletter. This was the first use of our new tape system which was fabricated at Louisiana State University. It worked flawlessly. This was also the first real test of our new remotely controllable image slits. We easily closed the horizontal slits to +/- 0.1 mm. We used a portable germanium detector with a stand-alone data acquisition system for these initial tests. A dedicated germanium detector system including automatic liquid nitrogen fill capabilities is being designed.

After studies with the second-stage mass separator, we delivered beam to beam line 23 for studies of isobar separation by the time-of-flight technique. Finally, we did a quick test to see if introducing CF4 into the target/ion source would increase the mass 132 beam. It did not.

During this reporting period, we also installed a new DANFYSIK power supply for the vertical bending magnet at the end of the radioactive ion beam injector and made significant improvements to the remote handling system programming for storage pig and piglet operations in C110. As of this writing, we have mounted the batch-mode target ion source in C111S with four targets of CaF2(Cu) and four targets of natural Ni in preparation for 18F and 56Ni production.

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RA3 - Experimental Equipment - Development of Electronic Phosphor for Low Intensity Beams*

A significant hurdle to clear before routine operations with RIBs of varying intensity can be achieved is the proper transport of the beam to the target with high transmission and suitable dimensions. Although chromium-doped alumina and CCD cameras are able to produce a beam image with 105 ions per second that are roughly in focus, the process of finding the beam and operations with lower intensities requires other methods. Intensity and position-sensitive detectors based on microchannel plates and foils together with a data acquisition system and a continuously refreshed display of the data (position and intensity) have been developed. The tandem operators are now able to tune the beam in the same manner as they do with more intense stable beams.

Position information and intensities are processed through a data acquisition system. The system sends the data to a display in the control room which is constantly refreshed, providing a near instantaneous profile of the beam. This system can be used for beam focussing and steering at counting rates starting at a few hundred particles per second. This "electronic phosphor" provides reliable profiles at count rates reaching 106 particles per second - a rate at which our standard alumina and CCD camera combination can operate.

A brief description of the process is provided below (for details see [1]).

A fast signal from the anode is used for timing (gating the data acquisition system) and is fed into a scaler to provide intensity. The three bar graphs at the bottom of Fig. RA3-1 provide a logarithmic display of continuously updating scalers. They provide instantaneous rate data up to 1 MHz each bar corresponding to two decades. The position signals from this detector are processed by software tailored to simulate a phosphor effect [2] and are also shown in Fig. RA3-1. The display sequence is described below:

  1. Accumulate up to 10000 entries of X-Y hits in a circular buffer.
  2. Up to 2000 X-Y entries are removed from the buffer and are replaced with a newly accumulated sample at fixed time intervals.
  3. The previous display is erased and all the X-Y entries in the circular buffer are displayed.
  4. The display can be refreshed at rates of 100 Hz (default = 10 Hz).
  5. The response time (simulated phosphor decay time) is related to the number of deleted entries and the rate at which new data are added.

Fig. RA3-1 - Snapshots of the continuous XY display generated by the beam hitting the "electronic phosphor". Intensity information is displayed at the bottom in the form of a bar graph.

The data are available on the local area network and can be displayed at the accelerator operator's console at will. The operators have adjusted to this "electronic phosphor" quite readily.

*Participants include D. Shapira, T. A. Lewis, and W. T. Milner.
[1] D. Shapira, T. A. Lewis, and L. D. Hulett, Nucl. Instrum. & Methods A454, 409 (2000).
[2] W. T. Milner, D. Shapira, and T. A. Lewis, BAPS 45, No.5, KB11 (2000); see also computer code DDMAN manual, HRIBF computer user guide.

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RA4 - User Group News

The annual HRIBF Users Group meeting was held at the DNP meeting in Williamsburg, Virginia, on Thursday, October 5. In a joint session with the users group of ATLAS, the 88-Inch, and GAMMASPHERE, our users were informed of our recent results on neutron-rich beam development including a report on fusion-evaporation and Coulex reactions of a 500 MeV 118Ag beam on a 12C target.

The ballots for the annual election of the Users Executive Committee have been counted. We welcome Ani Aprahamian and Demetrios Sarantites to the committee. Their terms will begin in January and will last three years. We would like to thank Brad Sherrill and Michael Wiescher for their service on the committee.

HRIBF Users Group Executive Committee for 2001
Ani Aprahamian Notre Dame University
I-Yang Lee Lawrence Berkeley National Laboratory
Peter Parker Yale University
Kris Rykaczewski (chair) Oak Ridge National Laboratory
Demetrios Sarantites Washington University
Bill Walters University of Maryland

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

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

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RA6 - HRIBF Experiments, August-October 2000

Experiment Title Spokesperson/Institution Dates
RIB-000 Commissioning of the RMS Gross,Galindo-Uribarri/ORNL
Radford/ORNL
Gross,Galindo-Uribarri/ORNL
Gross/ORNL
7/31-8/1/00
8/21/00
9/6/00
9/8/00
RIB-012 Enge development Liang/ORNL 8/3/00
9/7/00
RIB-013 Commissioning of the DRS Blackmon/ORNL 9/5/00
RIB-016 In-beam gamma studies of self-conjugate even-even nuclei near A=80 Hamilton/Vanderbilt Univ 10/11-15/00
RIB-024 Decay studies at the proton drip line in the 100Sn region with a 56Ni radioactive beam Rykaczewski/ORNL 10/27/00
10/30-11/3/00
RIB-030 Study of the N=Z nucleus 88Ru Gelletly/Univ Surrey 9/18-22/00
RIB-035 Neutron-rich RIB development Stracener/ORNL
Stracener/ORNL
Radford/ORNL
Radford/ORNL
Stracener/ORNL
Stracener/ORNL
8/2/00
8/18/00
8/23-25/00
8/29-9/1/00
10/9-10/00
10/26/00
RIB-040 Beam diagnostics development Shapira/ORNL 8/11/00
8/17/00
8/22/00
RIB-048 Study of the 71Kr/71Br mirror pair Rubio/Univ Valencia 9/11-15/00
RIB-057 Gamma spectroscopy using neutron-rich RIBs Radford/ORNL 9/26-30/00
10/1-6/00
RIB-058 Search for fine structure in 145Tm Karny,Rykaczewski/ORNL 8/7/00
8/8-10/00
RIB-059 Nuclear structure at (near) the drip line: first identification of 129,130Pm Galindo-Uribarri/ORNL 10/16/00
10/17-20/00
10/23-25/00
Scheduled Maintenance, controls upgrade 10/16/00
Shutdown, water outage 8/4/00
Unscheduled Maintenance 8/14-16/00
8/28-29/00
9/25-26/00
10/17/00

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You may contact us at the addresses below.

Witek Nazarewicz Carl J. Gross
Deputy Director for Science Scientific Liaison
Mail Stop 6368 Mail Stop 6371
witek@mail.phy.ornl.gov cgross@mail.phy.ornl.gov
+1-865-574-4580 +1-865-576-7698

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