Relativistic Heavy Ions Research Articles

One- and Two-Photon Physics with Relativistic Heavy Ions

The physics of peripheral collisions with relativistic heavy ions (PCRHI) is reviewed. One- and two-photon processes are discussed.

Ionization loss of relativistic structural heavy ions in collisions with atoms

A nonperturbative theory of energy loss in collisions between structural, highly charged heavy ions moving at relativistic velocities and atoms is developed. A simple formula for effective deceleration is derived. By structural ions are meant ions containing partially filled electron shells. It is such ions characterized, as a rule, by a significant charge (for example, partially “stripped” uranium ions) that are used in numerous experiments involving the use of modern heavy-ion accelerators.

Ionization of Hydrogen and Helium Atoms in Collisions with Relativistic Structural Heavy Ions

Based on the eikonal approximation, cross sections for single and double ionization of hydrogen and helium atoms in collisions with structural multiply charged heavy ions moving with relativistic velocities are calculated. In the present paper, the structural ions are taken to mean the ions with partially filled electronic shells. It is demonstrated that a consideration of the ion charge extension may noticeably change the corresponding cross sections compared to the cross sections for ionization by point ions having the same charges and energies.

The effective stopping of relativistic structural heavy ions colliding with atoms

A nonperturbative method is developed for calculating the energy losses upon collisions of relativistic structural large-Z ions with atoms. By structural ions are implied those containing partly occupied electron shells. Usually possessing a large charge, such projectiles (e.g., fully or partly stripped uranium ions) are frequently employed in the experiments on modern heavy-particle accelerators.

Gamma-ray spectroscopy with relativistic exotic heavy-ions

Feasibility of gamma-ray spectroscopy at relativistic energies with exotic heavy-ions and new generation of germanium detectors (segmented Clover) is discussed. An experiment with such detector array and radioactive is discussed.

Optically stimulated luminescence from Al2O3:C irradiated with relativistic heavy ions.

Optically stimulated luminescence (OSL) from Al2O3:C (ALOC) irradiated with selected heavy ions (4He, 12C, 40Ar, and 56Fe) was examined for discussion on the effectiveness of ALOC for space radiation protection dosimetry. The OSL efficiency on the absorbed dose basis was almost unity for He (LETinfinity x H2O: 2.2 keV x microm(-1)) and decreased with increasing LET for C (14 keV x microm(-1)), Ar (91 keV x microm(-1)), and Fe (198 keV x microm(-1)); a notable reduction greater than 60%, was observed for Fe ions. The linearity in dose response and the angular independence for the heavy ions were fairly good (+/- <15%) Although further experimental studies are clearly necessary, these results suggest that small ALOC chips can be a part of an integrating dosimetry system in future space missions.

Energy Losses in Collisions of Relativistic Structural Heavy Ions with Atoms

A nonperturbative theory of the energy losses in collisions of structural multiply charged heavy ions moving with relativistic velocities with atoms is worked out. Within the framework of this theory, by structural ions are meant ions containing partially filled electronic shells. It is such ions, having, as a rule, a considerable charge (for example, completely or partially stripped ions of uranium), that are used in many modern experiments on accelerators of heavy ions.

New formulae for the radiation intensity in the Tamm problem

The approximate analytic formula is obtained which describes theradiation intensity in the Tamm problem (charge motion on a finiteinterval) on finite distances. For the typical experimental situation, theangular spectrum of the Cherenkov radiation broadens enormously anddiffers essentially from that predicted by the Tamm formula. In addition,the approximate analytic formula is found which takes into account boththe deceleration of a charge due to the energy losses and a finitedistance of the observation point. Both these effects contribute to thebroadening of the angular spectrum. The approximate analytic formulae arein close agreement with the exact numerical calculations for the realexperimental situation. These formulae are applied to the description ofCherenkov radiation produced by relativistic heavy ions in the Darmstadtexperiments. An experiment is proposed to check the broadening of theCherenkov angular spectrum arising from its measurement on finitedistances.

A computer program for relativistic multiple Coulomb and nuclear excitation

A computer program is presented by which one may calculate the multiple electric dipole, electric quadrupole and magnetic dipole Coulomb excitation with relativistic heavy ions. The program applies to an arbitrary nucleus, specified by the spins and energies of the levels and by all El, E2 and M1 matrix elements. Nuclear excitation is calculated optionally for monopole, dipole and quadrupole excitations and needs inputs of optical potentials. For given bombarding conditions, the differential cross sections and statistical tensors (useful to calculate γ-ray angular distribution functions) are computed.

Ground State Hyperfine Splitting of Hydrogenlike207Pb81+by Laser Excitation of a Bunched Ion Beam in the GSI Experimental Storage Ring

Using a new bunched-beam technique in the GSI heavy-ion experimental storage ring (ESR), we performed precision laser spectroscopy on relativistic heavy ions in the hitherto inaccessible infrared optical region. We determined the wavelength of the $M1$ transition between the $F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ $(\ensuremath{\tau}\ensuremath{\approx}50\mathrm{ms})$ and $F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ hyperfine states of the $1s$ ground state of hydrogenlike ${}^{207}{\mathrm{Pb}}^{81+}$. Comparing the result of 1019.7(2) nm with very recent theoretical predictions concerning QED and nuclear size contributions, a disagreement of 4.5 nm is found. Since the nucleus of ${}^{207}{\mathrm{Pb}}^{81+}$ is well described by the single-particle shell model, uncertainties in nuclear corrections are expected to be small.

A beam vertex detector using scintillating fibers

A beam vertex detector system based on 200 μm square scintillating fibers has been built and utilized in an experiment with 6,8, and 10.8 GeV /u 197 Au beams with intensities of up to 3×10 5 particles per 1.6 s spill at the AGS at Brookhaven National Laboratory. The position of each beam particle traversing the target which subsequently caused a trigger was determined with a precision of σ≃150 μ m, independent of beam intensity. The detection efficiency exceeded 99% per detector layer. Information on radiation damage with relativistic heavy ions was obtained.

Low temperature bolometers for experiments with cooled heavy ion beams from storage rings

The development of calorimetric low temperature detectors for the energy sensitive detection of heavy ions is discussed. Due to its high intrinsic energy resolution this detector type promises to be a useful tool for nuclear physics experiments with cooled heavy ion beams from storage rings. Detector tests performed with relativistic heavy ions from the SIS synchrotron at GSI yielded relative energy resolutions of 2 – 4 · 10 −3 for 20Ne and for 209Bi ions, limited in this case by the energy spread of the beam. In a first application of such detectors the excitation of the giant resonance in lead nuclei via the reaction natPb ( 20Ne, 20Ne′) natPb ∗ was investigated by separating inelastically from elastically scattered 20Ne ions in the energy spectrum. At a scattering angle of Θ Lab=3° the excitation energy and the strength of the giant resonance were found to be in good agreement with theoretical predictions. In a recent experiment calorimetric detectors were bombarded with cooled 238U ions at E = 360 MeV/u, extracted from the storage ring ESR. An energy resolution of ΔE = 97 MeV, corresponding to a relative resolution of Δ E E = 1.1 · 10 −3 , was obtained.

Radiative electron capture by relativistic heavy ions

We present a direct method for calculation of radiative electron capture (REC) X-ray emission in relativistic ion-atom collisions. Results obtained within the distorted-wave impulse approximation (DWIA) are compared with recent experimental data for the collisions of heavy ions with light atoms. Simple closed analytic formulae are derived for small αZ describing the polarization and the angular distribution of radiation. Good agreement with recent experiments is found for photoemission rates and angular distributions. Our results for helium and beryllium targets indicate that the photon spectrum is rather insensitive to target structure, but strongly dependent on multiple-scattering corrections, and this contradicts other recent theoretical predictions. In asymmetric collisions our results are in broad agreement with experiment and relativistic impulse approximation (RIA) calculations. Through detailed analysis of magnetic transitions in terms of the electron and photon polarization correlation parameters, important new features are introduced and discussed.

SSNTD and radiochemical studies on the transmutation of nuclei using relativistic ions

Extended targets were irradiated for transmutation studies with relativistic heavy ions. For this, a metal core was surrounded by a paraffin moderator. The metal is either copper or lead and it was irradiated with deuterium, alpha, or carbon beams of 1.5 or 3.7 GeV/u at the SYNCHROPHASOTRON, LHE, JINR, Dubna, Russia. During this irradiation copious amounts of secondary neutrons are produced and studied with SSNTD detectors and radiochemical sensors, for example 139La (n, γ) 140La→β − . The yield of reaction products allows an estimation of secondary neutron fluxes. The yields of all kinds of reactions produced with deuterium and alpha beams obey to some extent the law of “limiting fragmentation”, i.e. they show little influence on the energy and the kind of incoming particles. However, one observes with 44 GeV 12C ions always enhanced nuclear cross-sections induced by secondary particles. This behavior could not be confirmed with theoretical estimations based on the Dubna Cascade Model in its Cascade Evaporation Model version (DCM-CEM). Finally, some results for transmutation studies on 127I and Cu will be presented.

Channeling with 290 MeV/u C6+ ions in a Si crystal

We have developed a parallel beam suitable for channeling experiments with relativistic heavy ions at HIMAC (Heavy Ion Medical Accelerator in Chiba). To observe channeling phenomena, we used a silicon surface barrier detector (SSD) as a sample crystal and as a detector for the energy loss in itself. Further, we measured the angular spread of the beam transmitted through the SSD by a position sensitive detector (PSD) placed downstream of the SSD. Under <110> axial and (111), (220) and (004) planar channeling conditions, we observed that the energy loss of the channeled ions in the SSD became almost a half and their angular spread was also reduced.

A New Silicon Detector Telescope for Measuring the Linear Energy Transfer Distribution over the Range from 0.2 to 400 keV/µm in Space

A new telescope consisting of three two-dimensional position-sensitive silicon detectors which can measure the linear energy transfer (LET) distribution over the range from 0.2 to 400 keV/µ m has been developed as a real-time radiation monitor in manned spacecraft. First, the principle of LET measurement and its design method are described. Second, suitable electronic parameters for the LET measurement are experimentally determined. Finally, the telescope performance is investigated by using relativistic heavy ions. The first in-flight test of this type of telescope on the US Space Shuttle (STS-84) is scheduled for May, 1997.

Energy-Loss-Straggling Experiments with Relativistic Heavy Ions in Solids.

Energy-loss straggling measurements performed at the high-momentum-resolution magnetic spectrometer fragment separator with bare and highly charged {sub 8}O, {sub 54}Xe, {sub 79}Au, and {sub 92}U ions with specific kinetic energies (700{endash}1000)MeV/u are reported. The results are in good agreement with rigorous calculations recently reported by Lindhard and So/rensen and reveal systematic deviations from the well-known relativistic Bohr formula, which was obtained within the framework of the first-order Born approximation. {copyright} {ital 1996 The American Physical Society.}

Calculation of ionization of helium by relativistic heavy ions with a relativistic CTMC-method

We have used a relativistic classical trajectory Monte Carlo (CTMC)-method to calculate cross sections for single and double ionization of helium by relativistic heavy ions. We compare our results with experimentally obtained cross sections. We comment on the limits of the validity of relativistic classical calculations.

Ionization of atomic vapors and helium by collision with relativistic heavy ions

We have studied collisions of atomic vapors and helium with relativistic, highly charged ions having Z ∼ v ∼ c. Formulas for the cross-sections of ionization and excitation of discrete levels of the atomic vapor and the cross-section of single and double ionization of helium atoms have been obtained. Comparisons with experimental data of the single and double ionization of helium are presented.

Energy deposition by relativistic heavy ions in thin argon absorbers

Experimental data on energy deposition for argon, krypton and xenon ions in the energy range from 100 to 950 MeV/u passing through an ionization chamber filled with an Ar (90%) + CH 4 (10%) gas mixture of thickness equivalent to 60 mg/cm 2 of argon are reported. Measured values are compared with the proposed model of energy deposition and with the model of Badhwar and Adams et al. The observed data support the picture of the escape of high energy δ rays from the active detector volume.