Holifield Heavy Ion Research Facility Research Articles

A recoil mass spectrometer for HHIRF

A recoil mass spectrometer (RMS) is to be built that will carry out a broad research program in heavy-ion science at the Holifield Heavy Ion Research Facility at Oak Ridge, Tennessee. The RMS will make possible the study of otherwise inaccessible exotic nuclei. Careful attention has been given to match the RMS to all the beams available from the HHIRF accelerators, including those beams with the highest energy as well as massive particles for use in inverse reactions. The RMS is to be a momentum achromat followed by a split electric dipole mass spectrometer of the type operating at NSRL at the University of Rochester. The RMS is essential for many of the proposed experiments on short lived and/or low cross section products. The spectrometer design will be discussed, with attention paid to the aberrations present and their corrections.

New approaches to studies of exotic nuclei

New generations of 4π gamma-ray detectors, recoil mass spectrometers (RMS), and radioactive beam accelerators will open up many new areas of research, including presently inaccessible in-beam and radioactive decay studies of exotic nuclei still farther off stability. The new generation RMS and radioactive beam developments at the Holifield Heavy Ion Research Facility are presented. Current research and future prospects to probe the N = Z line up to 100Sn are described. Superdeformation in A = 70 to 190 nuclei is described in terms of its underlying physics of reinforcing proton and neutron shell gaps which lead to new superdeformed, doubly-magic nuclei. Recent results provide new insights into the coexistence of multiple nuclear shapes near the ground states.

LEVELS IN ${}_{38}^{80}{\rm Sr}$, ${}_{39}^{83}{\rm Y}$ AND ${}_{40}^{83}{\rm Zr}$ AND THE NEW REGION OF STRONG DEFORMATION AROUND N=Z≈38

The energy levels in [Formula: see text] and [Formula: see text] were identified and investigated along with 80 Sr via in-beam γ-ray spectroscopy to explore the new region of strong deformation centered around N=Z=38. The reaction 51 V (32 S , p2n)80 Sr was studied at the Holifield Heavy Ion Research Facility and reactions 54 Fe (32 S , α2p)80 Sr ; 54 Fe (32 S , 3p)83 Y and 54 Fe (32 S , 2pn)83 Zr at the Max Planck Tandem. The deformation in the ground state band in 80 Sr observed to 12+ shows a significant increase as N decreases toward 38. A 9/2+ ground state band in [Formula: see text] observed to (29/2+) exhibits larger deformation than an excited (9/2+) band in [Formula: see text] as expected as Z moves away from 38. These nuclei support the proposal that the large deformation observed in this region arises from the reinforcing of the proton and neutron shape driving force as both N and Z approach shell gaps at large deformation for N and Z of 38.

Determination of the spin alignment in heavy-ion reactions with the spin spectrometer

A detailed procedure is outlined that permits one to deduce the spin direction in heavy-ion fusion reactions on an event-by-event basis using data from the spin spectrometer at the Holifield Heavy Ion Research Facility of Oak Ridge National Laboratory. The parameters that govern the ability of the spin spectrometer in determining the spin direction, namely the γ-ray multiplicity, the multipolarity, the crystal-to-crystal scattering, and coincidence summing, are examined in detail. Removal of detectors from the complete spectrometer causes large misalignment in the deduced spin distributions. A procedure to correct for this induced misalignment based on local density distributions is presented. Some results from measurement of angular distributions of α-particles using the spin alignment method are also discussed.

Ion-induced X-ray studies with a high luminosity von Hamos crystal spectrometer

A high-resolution, high-efficiency, von Hamos geometry, Bragg crystal X-ray spectrometer has been developed and mounted on a beamline at the Holifield Heavy Ion Research Facility at the Oak Ridge National Laboratory. Measurements have been made of K and L X-rays emitted from a variety of targets and projectiles. Instrument performance characteristics are reported here along with spectra from fast projectile ions and very low intensity target emission — areas of measurement for which this spectrometer is especially suitable.

The histrap proposal: Heavy-ion storage ring for atomic physics

HISTRAP, Heavy-Ion Storage Ring for Atomic Physics, is a proposed 46.8-m-circumference synchrotron-cooling-storage ring optimized to accelerate, decelerate, and store beams of highly charged very-heavy ions at energies appropriate for advanced atomic physics research. The ring is designed to allow studies of electron-ion, photon-ion, ion-atom, and ion-ion interactions. An electron cooling system will provide ion beams with small angular divergence and energy spread for precision spectroscopic studies and also is necessary to allow the deceleration of heavy ions to low energies. HISTRAP will have a maximum bending power of 2.0 T m and will be injected with ions from either the existing Holifield Heavy Ion Research Facility 25-MV tandem accelerator or from a dedicated ECR source and 250 keV/nucleon RFQ linac.

Calibration of the HHIRF tandem accelerator energy-analyzing magnet

A description is given of the calibration of the Holifield Heavy Ion Research Facility tandem accelerator energy-analyzing magnet. Two methods were used to measure beam energies: a novel time-of-flight technique using a variable frequency buncher; and an alpha-particle reaction-energy technique. Calibrations, accurate to better than 0.04%, were obtained for 11 different magnet excitations corresponding to mass-energy products between 28 and 298.

The ORNL 25 MV tandem accelerator control system

The CAMAC-based control system for the 25 MV tandem electrostatic accelerator of the Holifield Heavy Ion Research Facility at Oak Ridge National Laboratory (ORNL) was specified by ORNL and built by the National Electrostatics Corporation. Two Perkin-Elmer 32-bit minicomputers are used in the system: a message switching computer and a supervisory computer. The message switching computer transmits and receives control information on six serial highways. This computer shares memory with the supervisory computer. Operator consoles are located on a serial highway; control is by means of a console CRT, trackball, and assignable shaft encoders and meters. Two identical consoles operate simultaneously: one is located in the tandem control room; the other is located in the cyclotron control room to facilitate operation during injection of tandem beams into the cyclotron or when beam lines under control of the cyclotron control system are used. The supervisory computer is used for accelerator parameter setup calculations, actual accelerator setup for new beams based on scaled, recorded parameters from previously run beams, and various other functions. The experience of nearly seven years of control system operation and improvements is discussed.

The holifield heavy ion research facility

The Holifield Heavy Ion Research Facility has been in routine operation since July 1982. Beams have been provided using both the tandem accelerator alone and a coupled mode in which the Oak Ridge Isochronous Cyclotron is used as an energy booster for tandem beams. The coupled mode has proved to be especially effective and has allowed us to provide a wide range of energetic beams for scheduled experiments. In this report we discuss our operational experience and recent development activities.

An axial geometry cesium sputter negative ion source with continuous tungsten surface ionizer

A high brightness axial geometry negative ion source has been designed, developed, and used as an “on-line” source for routine operation of the Holifield Heavy Ion Research Facility tandem accelerator. The present source utilizes a continuous surface, solid tungsten ionizer to effect ionization of cesium vapor which, in turn, is used to sputter a negatively biased probe containing the material of interest. Operational experience with the source indicates that the source is reliable, long lived, stably operating and a prolific producer of a wide spectrum of negative ions. To date the source has been used to produce more than eighteen negative ion species including Ag −, Au −, B −, CaH 3 −, Cl −, CrH 2 −, Cu −, Lu −, MgH 3 −, Mo −, Ni −, O −, S −, Si −, Sn −, TiH 3 −, Tm −, and Yb −. Details of the mechanical design features and computational techniques utilized in arriving at the final electrode configuration are presented in the text. Data pertinent to source operation, the dependence of negative ion yields on certain source operational parameters, and examples of intensities typical of particular negative ion species are also given.

Charge-state distributions of 100, 175, 275 and 352 MeV gold ions emerging from thin carbon foils

Ion charge-state distributions were measured for 100, 175, 275 and 352 MeV gold ions emerging from thin carbon foils. The 90° double-focusing energy analyzing magnet of the Holifield Heavy Ion Research Facility 25 MV tandem accelerator was used to separate the charge-states. Carbon foil thicknesses of 10, 20, 40 and 80 μg/cm 2 were used depending on the beam energy. At least two different foil thicknesses were used at each energy to insure that equilibrium distributions were measured. The measured mean charge was compared with the predictions of the Sayer, Nikolaev-Dmitriev, and Shima et al. semi-empirical charge-distribution formulas. The measurements are in general agreement with the semi-empirical predictions at 100 MeV but were systematically lower at the higher energies. The largest discrepancy was −4.9 charge-states at 352 MeV. These results are especially significant for the design of booster accelerators for large tandem accelerators and for the design of coupled cyclotron systems.

A radial geometry cesium plasma source with improved mechanical features

An improved version of the radial geometry cesium plasma negative ion source, described by Alton and Blazey, has been designed, evaluated and employed for use during routine operation of the Holifield Heavy Ion Research Facility (HHIRF) tandem accelerator. The mechanical features of the source have been improved to facilitate rapid change of degradable parts such as the sputter probe insulator and cathodes and to provide better thermal isolation of the externally mounted oven from the discharge chamber. The source has demonstrated improved operational stability, higher intensities and increased reliability over its predecessor. Negative ion beams from more than 25 elements have been provided for the HHIRF experimental program including several molecular hydride beams from difficult elements such as Be, Mg, Ti, Sc, Nd and Zr. A detailed description of the mechanical features of the source as well as the negative ion yield dependence on certain operational parameters are presented.

Pulsed mode evaluation of an axial geometry cesium sputter negative ion source

An axial geometry negative ion source has been evaluated as a source of pulsed negative ion beams for possible future use of the Holifield Heavy Ion Research Facility (HHIRF) tandem accelerator as a synchrotron injector. During test stand operation and HHIRF tandem accelerator testing, high-intensity, square wave-form, 100 μs wide, pulsed beams of Ag −, Au −, Cu −1, Ni − and O −1 were produced at peak intensity levels ranging between 100 and 350 μA. The beam intensities were observed to increase approximately linearly with pulsed voltage amplitude over a range of voltages between 400 and 2400 V. In most cases, the pulsed and dc beam components were found to be essentially independent of each other, i.e., the dc component could be adjusted without significantly affecting the pulsed component. Pulsed 16O − beams at peak intensities of 100μA were injected into the HHIRF tandem accelerator without observable effects on the operational stability of the accelerator.

Negative Ion Sources Equipped with Continuous Annular and Spherical Geometry Surface Ionizers

Axial geometry negative ion sources have been designed, developed, and evaluated for use in conjunction with tandem accelerator applications. These sources utilize continuous surface solid tungsten ionizers in either annular or spherical geometries to effect ionization of cesium vapor, which in turn is used to sputter a negatively biased probe containing the material of interest. The annular ionizer geometry source been incorporated as an on-line source for routine operation of the Holifield Heavy Ion Research Facility (HHIRF) tandem accelerator. Both test stand and tandem accelerator operational experience indicate that such sources are reliable, long lived, stably operating and prolific producers of a wide spectrum of negative ions. To date these sources have been used to produce more than 18 negative ion species including Ag-, Au-, B-, CaH3-, Cl-, CrH2-, Cu-, Lu-, MgH3-, Mo-, Ni-, O-, S-, Si-, Sn-, TiH3-, Tm-, and Yb-. Details of the mechanical design features and computational techniques utilized in arriving at the final electrode configuration are presented in the text. Examples of data pertinent to source operation, the dependence of negative ion yields on certain source operational parameters and of intensities typical of a particular negative ion source are also given.

CHIL - A Comprehensive Histogramming Language

A high level language, CHIL, has been developed for use in processing event-by-event experimental data at the Holifield Heavy Ion Research Facility (HHIRF) using PERKIN-ELMER 3230 computers. CHIL has been fully integrated into all software which supports on-line and off-line histogramming and off-line preprocessing. CHIL supports simple gates, free-form-gates (2-D regions of arbitrary shape), condition test and branch statements, bit-tests, loops, calls to up to three user supplied subroutines and histogram generating statements. Any combination of 1, 2, 3 or 4-D histograms (32 megachannels max) may be recorded at 16 or 32 bits/channel. User routines may intercept the data being processed and modify it as desired. The CPU-intensive part of the processing utilizes microcoded routines which enhance performance by about a factor of two.

Status report on the holifield heavy ion research facility

The Holifield Heavy Ion Research Facility has been in routine operation since July, 1982. Beams have been provided using both the tandem accelerator alone and a coupled mode in which the Oak Ridge Isochronous Cyclotron is used as an energy booster for tandem beams. The coupled mode has proved to be especially effective and has allowed us to provide a wide range of energetic beams for scheduled experiments. In this report we will discuss the status of the tandem accelerator and some aspects of our experience with coupled operation.

Coupled Operation Experience at the Holifield Heavy Ion Research Facility

The 25URC Pelletron tandem electrostatic accelerator and the Oak Ridge Isochronous Cyclotron (ORIC) comprise the accelerators of the Holifield Heavy-Ion Research Facility (HHIRF). The two machines may be operated individually or coupled, with ORIC serving as an energy booster for the tandem. In the coupled dode, the ion beam enters the cyclotron through the dee stem and is directed by the inflection magnet so that it is tangent to an orbit suitable for acceleration at a higher charge state. A thin carbon foil, placed at the point of tangency, strips the ions so that a substantial fraction are in the desired higher charge state. This fraction of the beam is then accelerated and extracted in the normal fashion. Full energy performance (25 MeV/A oxygen) was demonstrated during first coupled operation in January 1981. Routine coupled operation for experiments commenced in July 1982.

Research highlights from the holifield heavy ion research facility

Research highlights from the holifield heavy ion research facility

RIP - General Purpose Interactive Display at HHIRF

RIP is a general purpose interactive code for display and analysis of data acquired with the Holifield Heavy Ion Research Facility (HHIRF) accelerators at Oak Ridge National Laboratory. The HHIRF data acquisition system includes a version of RIP for on-line display of one-and two-dimensional histograms on color graphic terminals and hard copy on color printer/plotters. General features of the program and interactive techniques will be described.

Data Acquisition Software for the Holifield Heavy Ion Research Facility

A new computer system to perform data acquisition and analysis for the Holifield Heavy Ion Reseach Facility's Oak Ridge Isochronous Cyclotron (ORIC) and the newer 25 MV tandem accelerator has been under development. This paper presents the current implementation and discusses the design of the data acquisition/analysis software.