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

Light MeV-ions etching studies in a plastic track detector

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

SummaryThe « knock-on electron » technique has been employed to determine the energy spectrum of nuclei with chargeZ⩾6 in the primary cosmic radiation. In this technique the energy per nucleon of a heavy primary cosmic ray nucleus is determined by measuring the angles of emission and the energies of electrons which the nucleus « knocks on » in elastic collisions along its path in traversing nuclear emulsion. Since the energies of the knock-on electrons are relatively small (<100 MeV in this experiment), they can be measured with precision by the method of multiple Coulomb scattering. The conditions for reliable estimation of primary energy have been determined and the reliability of the method verified by comparison with results obtained by other methods. The charges and energies of the particles have been determined in the following two ways: (i) for particles which are arrested in the emulsion, from measurements of range andδ-ray density; (ii) for particles which do not stop, from measurements ofδ-ray density and of the energies and the angles of emission of the fast knock-on electrons; in the few cases where the particle slowed down in traversing the stack, the variation ofδ-ray density along the track was determined. Measurements were made on 291 tracks obtained in a stack flown from Iowa, (λ=53° N), at 113 000ft. for four hours on March 13, 1956. 206 of these tracks were due to particles with chargeZ⩾6. The exponent of the integral energy spectrum of the medium (6⩽Z⩽9) group of nuclei has been obtained as 1.65±0.27 in the energy range 0.23 to 9 GeV/nucleon and that of the heavy (Z⩾10) group of nuclei as 1.82±0.59 in the energy interval 0.41 to 9 GeV/nucleon. The exponent for the S-group of nuclei (Z⩾6) is then 1.78±0.24. The geomagnetic cut-off energy atλ=54.5° N has been estimated to be 230 MeV/nucleon. The values of the flux of M and H-nuclei were found to be 10.7±1.0 and 5.3±0.7 particles/m2s sr, respectively (on March 13, 1956). A comparison of these values with those obtained in other experiments shows that a Forbush type of decrease had taken place in the intensity of the heavy nuclei, similar to that observed by McDonald in the α-particle flux on the same flight; neutron monitors on ground had also recorded a Forbush decrease at the same time.RiassuntoLa tecnica degli « elettroni d’urto » è stata impiegata per determinare lo spettro dell’energia dei nuclei con caricaZ⩾6 nella radiazione cosmica primaria. In questa tecnica l’energia per nucleone di un nucleo pesante di raggi cosmici primari si determina misurando gli angoli di emissione e le energie degli elettroni che il nucleo « colpisce » nelle collisioni elastiche lungo il suo cammino attraverso l’emulsione nucleare. Poichè le energie degli elettroni d’urto sono relativamente piccole (<100 MeV in questo esperimento), possono essere misurate con precisione col metodo dello scattering multiplo di Coulomb. Si sono determinate le condizioni per una attendibile valutazione dell’energia primaria e si è verificata l’attendibilità del metodo per confronto con i risultati ottenuti con altri metodi. Le cariche e le energie delle particelle sono state determinate in due modi: 1) per le particelle che si arrestano nell’emulsione con misure del percorso e della densità dei raggiδ; 2) per le particelle che non vi si fermano, misurando la densità dei raggiδ e le energie e gli angoli di emissione degli elettroni d’urto veloci; nei pochi casi in cui le particelle rallentavano nell’attraversare lo stack, si è determinata la variazione della densità dei raggiδ lungo la traiettoria. Si fecero misurazioni su 291 tracce ottenute in uno stack di emulsioni lanciato dallo Iowa, (λ=53° N) a 113 000 ft. per quattro ore il 13 Marzo 1956. 206 di queste tracce erano dovute a particelle con caricaZ⩾6. L’esponente dello spettro integrale dell’energia del gruppo medio (6⩽Z⩽9) di nuclei si è determinato in 1.65±0.27 nel campo di energie fra 0.23 e 9 GeV/nucleone e quello del gruppo pesante (Z⩾10) di nuclei in 1.82±0.59 nell’intervallo di energie fra 0.41 e 9 GeV/nucleone. L’esponente del gruppo S (Z⩾6) di nuclei è quindi 1.78±0.24. L’energia di cut-off geomagnetico aλ=54.5° N si è stimata in 230 MeV/nucleone. Si è trovato che i valori del flusso di nuclei M ed H sono (10.7±1.0) e (5.3±0.7) particelle/m2 s sr, rispettivamente (13 Marzo 1956). Un confronto di questi valori con quelli ottenuti in altre prove mostra che ha avuto luogo un decremento di tipo Forbush nell’intensità dei nuclei pesanti, analogo a quello osservato daMcDonald nel flusso di particelleα nello stesso volo; nella stessa epoca, rivelatori di neutroni a terra hanno pure registrato un decremento di Forbush.

The Energy Spectrum of Nuclei with Charge Z 13 in the Primary Cosmic Radiation

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

A stack consisting of CR-39 (HCB 0.5%), nuclear emulsions and X-ray films was exposed to primary cosmic rays by a balloon lauched from Alice Springs in 1983 and was flown for 32 hours at an atmospheric depth 9.8 g cm−2 air. The recovered plastic plates were etched in 7.5 N NaOH solution at 80°C for 96 hours. The major and minor axes of the elliptic etch pits were analysed. About 1112 elliptic etch pits were scanned. The measured integral flux of very heavy (VH) and Fe nuclei above 3.5 GeV/n are in approximate aggreement with the earlier survey of Dokeet al., but yield a flatter energy spectrum when compared to the recent high-energy extrapolated spectrum of Zatsepinet al. The charges of the detected heavy nuclei were also confirmed from delta-ray counting of heavily ionized tracks in nuclear emulsions. The energy of the incident heavy nuclei has been measured from the distribution of opening angles of alpha fragments initiated by heavy nuclei in nuclear emulsions.

Estimation of chemical abundance of primary cosmic-ray nuclei over Alice Springs using balloon-borne passive detectors

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)

Final results of the experiment for the estimation of charge abundances using plastic emulsion chamber consisting of CR-39 (HCB) and Fuji ET-7B nuclear-emulsion sheet, launched from Alice Springs for 32 hours at an atmospheric depth of 9.8 g cm−2 is presented. The latest long hour etching technique was used for track detection in plastics. The estimated reduced etch rate distribution presented was based on 2968 measured track diameter data in CR-39 (HCB) stacks. The observed charge spectrum from the reduced etch rate distribution was duly corrected for the top of the atmosphere by adopting the conventional formulation for cosmic-ray propagation along with the latest modified partial cross-sections for A-A collisions after Tsaoet al. The average value of the observed energy of the 77 very heavy primaries was estimated from the opening angle measurements of alpha fragments in Fuji ET-7B nuclear emulsion and was found to be 5.01 GeV/n which comes out to be 8.2 GeV/n, when corrected for the top of the atmosphere due to propagation in the residual atmospheric depth. The measured integral fluxes for NeMgSi and Fe groups above 4 GeV/n have been compared with the global data surveyed by Ichimuraet al. Our results on element/Si and element/Fe have been compared with the HEAO-3-C2 data after Englemannet al. Using SSLB model, the source abundance is derived from the observed result and that was compared with the results of Juliusson,et al., Lezniak and Webber and Garcia-Munozet al.

Estimation of elemental abundances of heavy cosmic-ray primaries at the top of the atmosphere using plastic emulsion chamber and the derived source spectrum from the steady-state leaky box model

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).

B. Basu

Papers

Fragmentation of56Fe in Al at 1.88A GeV

Estimation of chemical abundance of primary cosmic-ray nuclei over Alice Springs using balloon-borne passive detectors

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

Estimation of elemental abundances of heavy cosmic-ray primaries at the top of the atmosphere using plastic emulsion chamber and the derived source spectrum from the steady-state leaky box model

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