Fragmentation studies of 158 A GeV Pb ions using CR39 nuclear track detectors

The first results of the observation of superradiance from a single, subnanosecond, high current, electron bunch passing through a wiggler immersed in a guide magnetic field are presented. The 300–500 ps microwave pulses were generated in the high gain regime for both the conventional and reverse directions of the guide magnetic field. The dependence of the radiation power on the interaction length as well as the absolute value of the power, 100–200 kW, were related with the development of self-bunching and consequently with coherent emission.

Experimental observation of wiggler superradiance under group synchronism condition

Three stacks of plastic CR-39 Nuclear Track Detectors (NTD) were exposed to 158 A GeV 207 Pb ions at the CERN-SPS beam facility. The main purpose of this experiment was the calibration of the CR-39 for the search of atmospheric magnetic monopoles. Different targets (Al, Cu and Pb) were used to produce a large spectrum of charge ions for the purpose of calibration as well as the study of ultrarelativistic lead ion fragmentation. The exposure of each stack was performed at normal incidence with a fluence of about 1500 ion/cm 2 . The total number of lead ions in each spill was about 7.8×10 4 and there were eight spills incident on each stack. For the stack with the Cu target, the lengths of etched cones on one face of the CR-39 were measured. From this measurement procedure, a new calibration curve has been generated for the extended charge region 63⩽ Z ⩽83. The charge resolution ( σ Z ) achieved by this technique is ∼0.18 e –0.21 e .

Charge identification in CR-39 nuclear track detector using relativistic lead ion fragmentation

Total and partial charge-changing cross-sections of 600 A MeV Si14+ ions in a thick polyethylene target were measured by CR39 track etch detectors using an optical microscope DM 6000 M system installed with Leica QWin Plus software. The CR39 nuclear track detectors were used to identify the incident charged particles and their fragments using the cone-height distribution method. The charge resolution of CR39 detectors was achieved to be 0.17e in the present condition. The value of the total charge-changing cross-section was calculated to be σ
 tot
 = (766±17) mb. To calculate the partial charge-changing cross-sections for ΔZ = −11, −10, ..., −1, , number of events corresponding to each fragment were determined from multiple Gaussian fitting of cone-height distributions within 95.5% confidence level and the number of incident and survived beam ions were counted within 99.7% confidence level. Possible odd-even pattern in the values of the partial charge-changing cross-section is also presented. The measured charge pick-up cross-section for ΔZ = +1 is (7.2 ±1.7) mb.

Fragmentation cross-section of 600 A MeV Si14+ ions in thick polyethylene target

Solid state nuclear track detectors in hadrontherapy and radiation protection in space

The production of fragmented nuclei from relativistic56Fe beam available from LBL Bevalac at 1.88A GeV has been studied using CR-39 (DOP) passive detector placed at an angle of 60° with respect to the beam. The histogram showing the experimental frequency distribution of minor axes of the elliptic etch pit shows the presence of the fragmented nuclei produced with charge numberZ from 25 up to 21. The histogram further reveals the presence of nuclei withZ=27 and 28. The production of nuclei heavier than56Fe is possibly due to the charge exchange or pick-up phenomena.

Fragmentation of56Fe in Al at 1.88A GeV

Hungarian brand CR-39(MA-ND) stack was irradiated at a zenith angle 30° by 36 84 Kr ions of energy 0.45 GeV/ n using Lawrence Berkeley Laboratory BEVALAC beam. The exposed plate was etched in 6N NaOH aqueous solution at 70°C for 20 h. About 636 etch pit diameters were optically measured. The response to Kr ions and the projectile fragment tracks produced in CR-39(MA-ND) target were determined for gb = 0.737. The charge resolution of the CR-39 plastic at the Kr peak was found to be 0.26 e obtained from the average of double cone etch pit data. An increase of the measured partial inelastic cross sections with nuclei charge number in the range 25 ⩽ Z ⩽ 35 has been found. Indication of ΔZ = + 1 events has been observed whose cross section is in accord with the survey presented by Ren Guoxiao et al. The experimental fragmentation cross sections have been compared with the expected results from the semi-empirical nuclear fragmentation model of Wilson et al.

Interactions of 0.45 GeVn 3684Kr ions on CR-39(MA-ND)

A stack consisting of CR-39(DOP) detector with 2.6 cm Al target was exposed to a238U beam of energy 0.927 GeV/n from LBL BEVALAC to study the large-fragmentation phenomena during U+Al interaction. The diameter distribution of the etch pits formed in the plastic detectors for the first three projectile fragments of chargeZF≥89 yields the partial cross-section data which is comparable to the data obtained from the cone length distribution. The present result on the partial cross-section is significantly higher than those expected from the abrasion-ablation model of Wilson, Townsed and Badavi (1987).

Study of large fragments of uranium projectiles of energy 0.927 GeV/n in Al target

1.88A GeV56Fe beam of Lawrence Berkeley Laboratory BEVALAC irradiated at an angle 30° to the stack, composed of Al target and CR-39 (DOP) solid-state nuclear-track detector. These polymer sheets were etched in 6.25N NaOH solution at 70°C for 48 hours. The minor axes of the elliptic etch pits were measured by a Leitz Ortholux microscope. The measured projectile fragmentation cross-section for nuclei of chargeZ ranging from 21 to 25 is in approximate agreement with the calculated result from the semi-empirical nuclear fragmentation model after Wilson, Townsend and Badavi. The existence of trans Fe nuclei was noticed. The measured double-cone charge resolution was found to be 0.20e.

Study of fragmentation in56Fe+27Al interactions at 1.88A GeV using CR-39 (DOP) solid-state nuclear-track detector

Pershore made CR-39(DOP) stack was exposed at a zenith angle of 30° by 197Au-ions of energy 1.015 GeV/n using LBL BEVALAC beam. The top of the irradiated plate of the stack has been etched in 6.25N NaOH solution at 70°C for one hour. About 1202 cone lengths were optically measured. The estimated etch rate ratio of the incident 197Au projectile beam in CR-39 has been found to be 27 ± 2. The result has been compared with earlier observations. The charge resolution of the detector has been estimated from the average of double cone lengths and has been found to have a value of (0.58 ± 0.03)e for 197Au-ions.

R. Rakshit

Papers

Fragmentation of56Fe in Al at 1.88A GeV

Interactions of 0.45 GeVn 3684Kr ions on CR-39(MA-ND)

Study of large fragments of uranium projectiles of energy 0.927 GeV/n in Al target

Study of fragmentation in56Fe+27Al interactions at 1.88A GeV using CR-39 (DOP) solid-state nuclear-track detector

Pershore made CR-39(DOP) as a 1.015 GeV/n197Au-ion detector