Investigation of neutron emission from relativistic heavy ion interactions by nuclear tracks

Fast neutrons produced in 44 and 22 GeV ¹²C+Cu interactions have been recorded and analysed with a CR-39 detector stack. The irradiation of the CR-39 stack to fast neutrons was carried out at the accelerator Synchrophasotron, Joint Institute for Nuclear Research, Dubna, Russia. Areal and volume densities of tracks induced by fast neutrons in the CR-39 at different positions and for different etching time have been measured. The neutron production ratio of 44 GeV to 22 GeV ¹²C+Cu interactions has been obtained, which is 2.17 ± 0.30 by areal track density, or 2. 12±0.33 by step etch technique, or 2.03±0.34 by volume track density measurement. These results confirm that the production rate at 44 GeV ¹²C+Cu interactions is more than theoretical estimation.     

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

Summary 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 chargeZ _F≥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). The authors of this paper have agreed not to receive the proofs for correction.     

Optimization of CR-39 for fast neutron dosimetry applications

We present the results of an experimental work aimed at improving the performances of the CR-39^® (Registered Trademark of PPG Industries Inc.) nuclear track detector for neutron dosimetry applications. The work was done in collaboration with the Intercast Europe S.p.A., producer of CR-39 for commercial and scientific applications. We compare the CR-39 made with different additives concentrations and different polymerization processes. We evaluate the response of the CR-39 to fast neutrons from three sources: ²⁴¹Am---Be, ²⁵²Cf and ²³⁸Pu---Li. Particular attention was paid to background fluctuations that limit the lower detectable dose.     

Measurements of neutron yields and spatial distributions in U/Pb, Pb and Hg thick targets bombarded by 0.5 and 1.0 GeV protons

Measurements have been carried out on neutron yields and spatial distributions in U/Pb, Pb and Hg thick targets and the surrounding paraffin moderators bombarded by 0.533 and 1.0 GeV protons. CR-39 detectors were deployed on the surfaces of targets and moderators to record the neutrons produced in the targets. The measurements show that:

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Studies on elemental charge-changing cross-section for relativistic U+Al collisions using CR-39 (DOP) detector

Summary A search has been made on the charge-changing partial cross-sections by using 0.927 GeV/n²³⁸U ion from LBL BEVALAC projected at an angle 30° on²⁷Al target and CR-39 (DOP) was used as analyser. The irradiated plastic sheets were duly etched for one hour in 6.25N NaOH solution and about 1680 cone lengths at both the surfaces of the CR-39 (DOP) sheets were optically measured. The cone length distribution exhibits the existence of U fragments in the charge range 84≤Z≤91 and the estimated partial cross-sections range from 60 to 400 mb. The present data are in accord with the fit to the extrapolated data of Binnset al.     

中高能重离子弹核碎裂反应研究

通过CR-39 核径迹探测器对471 AMeV 56Fe 和400 AMeV 20Ne 诱发Al,C 和CH₂ 靶反应的弹核碎裂反应截面及出射角度进行了测量,并利用改进的量子分子动力学(ImQMD) 模型和描述统计衰变的GEMINI 模型对实验结果进行了分析和讨论。实验结果表明,总反应截面与弹核的能量无关,但随着靶核质量的增加而增加。这与其他的实验结果以及Bradt-Peters 的半经验理论公式所得结果一致。理论计算和实验测量结果中,分截面出现了明显的奇偶效应。理论计算结果表明,奇偶效应主要产生于受激碎块的衰变过程,其中对效应起着重要作用,而且,主要形成于擦边碰撞的反应中且多来自于同位旋为T_Z = 0; ±0:5 的弹核碎块的贡献。产生碎块的同位素分布与弹核的种类有关,与入射能量和靶核的种类没有太大依赖性,其较小的偏转角大部分来自于擦边碰撞产生的较重的类弹碎块的贡献。We have measured the fragmentation cross sections and the emission angles for 471 AMeV 56Fe and 400AMeV 20Ne on Al, C and CH₂ targets using CR-39 plastic nuclear track detector. The total charge changing cross sections agree well with other previous experimental results at different energies and the theoretical prediction of Bradt-Peters semiempirical formula, which are pproximately independent of the beam energy but increase with the increase of the target mass. The experimental results are compared with the prediction of the improved quantum molecular dynamical model (ImQMD) together with the GEMINI model. The odd-even effect of the partial cross sections observed in experiments is well produced. It is found that such effect is mainly formed in the grazing collisions and comes from the fragments with T_Z = 0; ±0:5. The shape of the isotopic distribution is independent on the target mass and the incident energy but the projectile mass and charge, and the small angular distribution of all fragments comes from the heavier projectile-like fragments which produced in the peripheral collision.     

Dosimetry of 40 and 70 MeV/n O beams

Using CR-39 plastic track detectors the range values of ¹⁶O ions at two different energies (initially in the beam line, 39.97 MeV/n and 69.98 MeV/n) were measured after escaping the beam pipe and found to be (3050 ± 40) μm and (8210 ± 90) μm, respectively. The longitudinal and projected angular spread of oxygen ions of an initial energy of 69.98 MeV/n in the region of the Bragg peak was derived from the measured geometrical parameters of tracks. Based on a calibration curve (etch rate ratio vs total linear energy transfer in CR-39) and the measured track length distribution at the range end of oxygen ions, the complete depth dose profile of a 67.7 MeV/n ¹⁶O beam in CR-39 (plateau, extended Bragg peak and residual ionization caused by projectile like fragments) was obtained.     

New results from exposures of CR-39 nuclear track detectors

Six stacks of nuclear track detectors were exposed in December 1994 to ²⁰⁷Pb⁸²⁺ ions of 158 A GeV at the CERN-SPS. Each stack was made of CR39 sheets placed after a target. The CR39 was manufactured by the Intercast Europe Co. of Parma (Italy). The exposures were carried out at normal incidence to an average density of 400 ions/cm². The main purpose of the exposures was the calibration of the CR39 nuclear track detector used in a large area detector to search for magnetic monopoles (experiment MACRO at the Gran Sasso Laboratory). We compare the response of CR39 of different production batches in different etching conditions. The results indicate no relevant aging effect for the CR39 made more than 5 years ago. The first result of a “long period” investigation of possible fading effects for the CR39 is also presented.     

Measurement of the production of charged pions by protons on a tantalum target

A measurement of the double-differential cross-section for the production of charged pions in proton–tantalum collisions emitted at large angles from the incoming beam direction is presented. The data were taken in 2002 with the HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 GeV/c to 12 GeV/c hitting a tantalum target with a thickness of 5% of a nuclear interaction length. The angular and momentum range covered by the experiment (100 MeV/c ≤p< 800 MeV/c and 0.35 rad ≤θ< 2.15 rad) is of particular importance for the design of a neutrino factory. The produced particles were detected using a small-radius cylindrical time projection chamber (TPC) placed in a solenoidal magnet. Track recognition, momentum determination and particle identification were all performed based on the measurements made with the TPC. An elaborate system of detectors in the beam line ensured the identification of the incident particles. Results are shown for the double-differential cross-sections d²σ/dpdθ at four incident proton beam momenta (3 GeV/c, 5 GeV/c, 8 GeV/c and 12 GeV/c). In addition, the pion yields within the acceptance of typical neutrino factory designs are shown as a function of beam momentum. The measurement of these yields within a single experiment eliminates most systematic errors in the comparison between rates at different beam momenta and between positive and negative pion production. PACS 13.75.Cs; 13.85.Ni     

A systematical study of the chiral magnetic effects at the RHIC and LHC energies

Considering the magnetic field response of the QGP medium,we perform a systematical study of the chiral magnetic effect(CME),and make a comparison with the experimental results for the background-subtracted correlator H at the energies of the RHIC Beam Energy Scan(BES)and the LHC energy.The CME signals from our computations show a centrality trend and beam energy dependence that are qualitatively consistent with the experimental measurements of the charge dependent correlations.The time evolution of the chiral electromagnetic current at the RHIC and LHC energies is systematically studied.The dependence of the time-integrated current signal on the beam energy√s with different centralities is investigated.Our phenomenological analysis shows that the time-integrated electromagnetic current is maximal near the collision energy√s≈39 GeV.The qualitative trend of the induced electromagnetic current is in agreement with the CME experimental results at the RHIC and LHC energies.     

The spatial distribution of thermal and epithermal neutrons in a graphite moderated spallation neutron field

The Gamma-3 assembly is located at the Joint Institute for Nuclear Research, Dubna, Russia. It consists of a cylindrical lead target (ø = 8 cm, L = 58.8 cm) surrounded by reactor grade graphite (110 × 110 × 60 cm). The target was irradiated with a beam of 1.6 GeV deuterons from the Nuclotron accelerator and CR-39 track detectors coupled to LR-115 2B film were used to measure the slow neutron distribution on the surface of the graphite. The detection efficiency of the CR-39 in the CR-39/LR-115 2B system was measured using a custom made calibration setup and found to be (1.12 ± 0.05) × 10⁻³ and (6.1 ± 1.2) × 10⁻⁴ tracks per neutron, for thermal and epithermal neutrons respectively, under the etching and counting procedures described in this work. The irradiation of the Gamma-3 was also simulated using MCNPX 2.7 Monte Carlo code and good agreement between the experimental and calculated track densities was found. This serves as a good validation for the computational models used to simulate spallation neutron production, transport and moderation.     

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

Summary 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.     

Measurement of the spin asymmetry in the photoproduction of pairs of high- p(T) hadrons at HERMES

We present a measurement of the longitudinal spin asymmetry A(||) in photoproduction of pairs of hadrons with high transverse momentum p(T). Data were accumulated by the HERMES experiment using a 27.5 GeV polarized positron beam and a polarized hydrogen target internal to the HERA storage ring. For h(+)h(-) pairs with p(h(1))(T)>1.5 GeV/c and p(h(2))(T)>1.0 GeV/c, the measured asymmetry is A(||) = -0. 28+/-0.12(stat)+/-0.02(syst). This negative value is in contrast to the positive asymmetries typically measured in deep inelastic scattering from protons, and is interpreted to arise from a positive gluon polarization.     

Depth-dependence of the bulk etch rate of gamma-ray irradiated CR-39 track detector

The depth-dependent bulk etch rate has been examined for the gamma-irradiated CR-39 at doses ranging from 20 to 100 kGy. The thickness of the damaged region in gamma-irradiated CR-39 plastics, in which the bulk etch rate was significantly enhanced, was found to be limited in the thin layer near the surface and decreases with increasing the dose-rate, while it barely depend on the total dose. This indicates that it is possible to apply CR-39 plastics as high dose gamma-dosimeter by assessing both the bulk etch rate in the damaged region and its thickness in principle.     

Observation of the reaction products formed in the interaction of 3.65 A GeV O ions with thick copper target at wide angles

Experiments have been carried out to study the ‘heavy fragments’ emitted at wide angles in the interaction of 3.65 A GeV ¹⁶O ions with a thick Cu target, using a stack of CR-39 track detectors. Diametric distribution in a stack registering ¹⁶O-beam halo are compared with diameters observed in a stack placed downstream at an angle of 25°. There is a strong indication that the heavy fragments are scattered at large angles.     

The investigation of fragments produced in the interaction of relativistic F-ions and copper and emitted at large angles

Within the framework of the study of the behaviour of relativistic particles formed in the interaction of 65 GeV ¹⁹F-ions and a 1 cm thick Cu target, the wide angle emission of heavy fragments has been studied using CR-39 (INTERCAST) as a detector.     

Investigation of the very heavy cosmic abundances at source estimated from balloon-borne passive-detector results over alice springs

Summary A detailed study on the relative abundances of very heavy elements of cosmic rays with charges 10≤Z≤28 in the interstellar medium has been estimated from the results obtained from the balloon-borne passive-detector experiments flown for 32 hours from Alice Springs. The recovered CR-39 (HCB) detectors were etched for 96 hours in 7.5N NaOH solution at 80°C. About 2126 elliptic etch pit cones were scanned from the 250 cm² area of the track detector and the chemical abundances of elements with charges 10≤Z≤28 above 2 GeV/n have been estimated. We have adopted the charge-changing cross-sections calculated from the abrasion/ablation model after Norbury and duly fitted in the slab model to account for the loss of intensity due to nuclear fragmentation in the upper atmosphere. The predicted source composition is comparable with the derived result of Lezniak and Webber. Our result on (Sc−Cr)/Fe flux ratio at 6.52 GeV/n energy is in accord with the results derived from the leaky-box model.     

Determination of the range of alpha particles in SSNTD by optical density method

A technique based on the optical density (D) measurement of the etched track is useful for charged particles spectroscopy using SSNTD. It was shown that the stopping power of alpha particles in CR-39 is proportional to D. We measured the optical density and derived an expression to estimate the range of alpha particles in CR-39 detector as a function of the bulk etching rate and etching time. The relation between the etching time, track parameters (depth, radius) and D for different alpha particles energy and etching conditions were studied. A relation describing D as a function of track size is proposed.     

Total charge-changing and partial cross-section measurements in the reaction of 110 MeV/u C with paraffin

We have measured the total and partial charge-changing cross-sections (Z=5) after the passage of a 110 MeV/u ¹²C beam through an assembly consisting of CR-39 thin detectors and paraffin targets. These experimental cross-sections were compared to the predictions of known models. It was found that the measured total cross-sections agree with the model calculations to within about 8% or even less, while, depending on a model, discrepancies of up to a factor 1.2 higher and up to a factor 2.7 lower values of cross-sections for the production of fragment with Z=5 were observed.     

Interferometric investigation of the effect of gamma radiation on the refractive index of CR-39 polymer

A non-contact and simple interferometric technique has been used to measure the refractive index variation of gamma irradiated CR-39 polymer samples. Six samples of thickness (750 μm) and dimensions of 1.5 × 3 cm², have been irradiated with gamma radiation doses in the range from zero to 600 kGy. It is observed that the refractive index increases by increasing the dose and reaches its maximum value at 40 kGy dose, and then starts to decrease again. This means that the gamma radiation deformation in the CR-39 polymer is a chain scission effect. This interferometric technique could make a contribution to recombination and degradation mechanisms on CR-39 polymer.