We have measured the total cross sections for electron capture by bare Pb 821 ions and ionization of hydrogenlike Pb 811 ions at 33 TeV (160 GeV͞A, g 168) in solid targets of Be, C, Al, Cu, Sn, and Au. The total capture cross sections are dominated by electron capture from pair production and are compared with theoretical calculations. The 1s ionization cross sections obtained are significantly smaller than those predicted by Anholt and Becker [Phys. Rev. A 36, 4628 (1987)]. The Pb radiative lifetimes extended by g 168 have a strong effect on the survival probability of excited states against ionization in high-Z solid targets. [S0031-9007(97) PACS numbers: 34.50. Fa, 34.80.Lx Interactions involving high-Z ions in the ultrarelativistic regime ͑.10 GeV͞amu͒, where the relevant physics is best described in terms of the Lorentz factor g, are currently a frontier in high-energy atomic collision physics [1]. A theoretical description of electron capture and ionization processes has been challenging in this regime because the interaction of high-Z projectile and target species (where Za ϳ 0.5) is strong enough at small impact parameters and large g to potentially invalidate perturbation treatments. Numerous methods for treating these processes using quantum electrodynamics (QED) in the ultrarelativistic regime now exist [1][2][3][4][5][6][7][8][9][10].An ultrarelativistic ion can capture an electron via three mechanisms: (i) radiative electron capture (REC), (ii) nonradiative capture (NRC), and (iii) electron capture via e 1 e 2 pair production (ECPP), in which the e 1 e 2 pair is produced by the intense electromagnetic pulse that arises when the projectile ion passes near a target nucleus. Capture cross sections s REC , s NRC , and s ECPP scale roughly as ϳZ t ͞g, ϳZ 5 t ͞g, and ϳZ 2 t ln g, respectively, where Z t is the target atomic number [2]. Each process has approximately the same dependence on the projectile atomic number, i.e., Z 5 p . The REC and NRC mechanisms, which dominate below the ultrarelativistic regime [11][12][13], become insignificant compared to ECPP when g . 100 even for high Z t . We report the first highenergy measurements ͑g 168͒ where s ECPP dominates the capture cross sections of competing mechanisms. Ionization cross sections are several orders of magnitude larger than capture, and our measurements test theory at the highest energy reported to date [2,10].The development of new relativistic ion colliders such as the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory or the Large Hadron Collider at CERN [2,8,14] requires knowledge of the capture cross sections at high enough g so that beam lifetimes can be accurately predicted. The cross section for the ECPP process is of practical interest to collider designers because the lower charge-state projectiles produced are lost from the beam circulating in a ring. A significant loss rate of these ions by ECPP and also by nuclear loss processes decreases the ion storage time. These machines will operate at an effective g of 2.3 ...

Angular and momentum distributions have been measured for positrons from electron-positron pairs created in peripheral collisions of 6.4-TeV sulfur ions with fixed targets of Al, Pd, and Au. The data are compared with results of several theoretical treatments. Measured differential cross sections peak at low momentum (< 1 MeV/c), extend significantly to much higher momenta (> 17 MeV/c), and concentrate sharply in the forward direction, along the ion-beam axis. Positron yields scale as the square of the target nuclear charge as predicted by theory.

Radiation losses from the JET plasma are measured (temporally and spatially resolved) with three pin-hole cameras which observe one poloidal plasma cross section from underneath (one vertical camera with 14 bolometers) and from the side (two horizontal cameras with 10 bolometers each). In addition, eight collimated single bolometers monitor toroidal symmetry of plasma emissivity. An improved metal resistor bolometer capable of surviving at least 5000 D–T pulses in JET is composed of two identical foils (4-μm-thick gold absorber, 7.5-μm-thick Kapton substrate, and 0.1-μm-thick gold resistor), mounted one behind another in one housing. The rear foil serves as a reference bolometer in a bridge circuit. With an integration time constant of 20 ms a detection limit of 70 μW/cm2 was measured in JET. Examples of measuring results in JET are presented: strong poloidal asymmetries of the radiation density as precursor signals of a density limit disruption and the formation of a poloidally symmetric, cold plasma mantle before a disruption.

Experimental data and theoretical results on charge loss −27ഛ⌬Z ഛ −1, charge pickup ⌬Z = + 1, and total charge-changing cross sections for 158A GeV 82 208 Pb ions on CH 2 , C, Al, Cu, Sn, and Au targets are presented.Calculations based on the revisited abrasion-ablation model for hadronic interaction and the relativistic electromagnetic dissociation (RELDIS) model for electromagnetic interaction describe the data. The decay of excited nuclear systems created in both types of interaction is described by the statistical multifragmentation model (SMM), which includes evaporation, fission, and multifragmentation channels. We show that at very high projectile energy the excitation energy of residual nuclei may be described on average as ϳ40 MeV per removed nucleon, with some increase in this value compared to fragmentation of intermediate energy heavy ions at ϳ1A GeV. The importance of the electromagnetic interaction in production of 80 Hg, 81 Tl, and 83 Bi projectile fragments on heavy targets is shown. A strong increase of nuclear-charge pickup cross sections, forming 83 Bi, is observed in comparison to similar measurements at 10.6A GeV. This process is attributed to the electromagnetic production of a negative pion by an equivalent photon, which is quantitatively described by the RELDIS model.

2) Uncertainties in the nuclear wave functions. More recent Cabibbo-model predictions 9 of P y cc (1.08 MeV) are in qualitative agreement with, and somewhat larger than, the results of Ref. 8.(3) The "enhancement factor" to be expected from the neutral weak currents is difficult to calculate precisely; current estimates 10 for the Weinberg-Salam model point to a value of about 10. The 18 F system is one of the most favorable cases, both experimentally and theoretically, for studying AT= 1 PNC forces. With the Cabibbomodel prediction of Ref. 8, the present experiment yields an upper limit of 7.5 for the "enhancement factor" produced by neutral weak currents. 11