Etchability of Latent Fission Fragment Tracks in CR-39

We report the chemical etching behaviour of the CR-39 polymer detector exposed to fission fragments of 252Cf describing etchability of latent tracks, which are like nanocylinders. The fission fragment exposed detectors were etched in 1-7 N NaOH water solutions at temperatures 50-80℃ for 45 min in the case of track length and 180 min in the case of track diameter measurements. The reduced etch rate S （called here etchability） is determined using experimental results for all etching conditions and the etching conditions with the highest reduced etch are obtained. Physics and energetics of bulk and track etching are discussed. Possible effects causing spurious changes in determination of activation energy of etching are investigated.     

Cross Section of Heavy Ion Reaction （14.5 MeV/u） ^132Xe ＋ Bi

We investigate the cross section of the heavy ion reaction （14.5 MeV/u） ^132Xe ＋ Bi by using a CR-39 plastic track detector. The target-detector assembly is exposed at UNILAC beam facility of GSI, Germany. After etching under appropriate etching conditions, the detector is scanned for multipronged events produced as a result of interactions of projectile ions with target atoms. The elastic events are separated from binary events and used for the determination of the quarter-point angle. The quarter-point angle obtained is used to determine the total reaction cross section. The total experimental reaction cross section is determined by using statistics of inelastic events of two-pronged and higher multiplicity events. The experimental reaction cross sections determined by using elastic and inelastic data observed in the reaction under study are found to be in good agreement with the theoretically calculated value of reaction cross section using a sharp cutoff model.     

Excitation Function Measurement in Reaction of ^19F＋^27Al

The measurement of excitation functions for the strongly dissipative collision with the reaction system of ^19F ^27Al has been carried out at the China Institute of Atoraic Energy, Beijing. The ^19F^8 beam was extracted from the HI-13 tandem accelerator. The beam incident energies were varied from 110 to 118.75 MeV in steps of 250 keV. The self-supporting ^27A1 target foil with the thickness of 60μg/cm^2 was used. The detector arrangement is shown in Fig.1.     

Varying Track Etch Rates along the Fission Fragments＇ Trajectories in CR-39 Detectors

We determine the behavior of track etch rate VT along the tracks in CR-39 detectors exposed to fission fragments from ^252Cf source. CR-39 detectors are etched at 70℃ in different concentrations of Na2COa-mixed 6M NaOH solutions for different etching time intervals of 5-10min starting from 15 min up to 210min. Two values of track etch rate are determined along the fission fragment trajectories. The variation in VT is correlated with the energy loss rate of the fission fragment in the detector material.     

Annihilation of Antiprotons in Light Nuclei

CR-39 detectors have been exposed to a 5.9-MeV antiproton beam using the low energy antiproton ring （LEAR） facility at CERN. At this energy, tracks of antiprotons appear in a CR-39 detector after 135 rain of etching in 6M NaOH at 70℃. Fluence of the antiproton beam has been determined using track density. We have also found tracks in the etched CR-39 detector at different depths （250-500μm）. These tracks have resulted from the annihilation of antiprotons with the constituents （H, C and O） of the CR-39 detector. The goal of the experiment is to develop a simple and low-cost method to study properties of antiparticles and those formed after annihilation of these particles with the target matter.     

Calibration Experiments for Identification of Space Heavy Ions by CR-39

A subject “Study of mechanism and application of space radiation induced mutation breeding on rice“ has been established in NSFC, China. In order to verify space heavy particles being main cause (in addition, microgravity, vacuum, magnetic field etc.) of induced biological effects in space and in order to study correlation of various mutation and its serious degree with different particle parameters, measurement and identification of the particles are necessary. CR-39 sheets are a part of a sandwich detecting system. The system consists of rice seeds and CR-39 solid state nuclear track detectors. The seeds hit by space particles could be determined withetched tracks in CR-39. Furthermore, the space heavy particles could be identified with measured parameters of the tracks such as residual range and etch rate.     

Total Fragmentation Cross Section of 158A GeV Lead Projectiles in Cu Target

Total fragmentation cross section for the reaction 158A Pb ions ＋ Cu target is measured using the most sensitive track detector CR-39. Measured values are compared with calculations. Exposures of target-detector stack with 158A P5 projectiles are made at CERN-SPS beam facility. Results of calibration of CR-39 detector in a charge region （63 ≤ Z ≤ 83） are also reported, which can be used for high energy particle identification using CR-39 and in determination of partial charge changing cross sections. The charge resolution δz achieved by this technique is about 0.2e. A systematic dependence of total fragmentation cross section on target properties is revealed and the corresponding results are presented.     

Track segment finding with CGEM-IT and matching to outer drift chamber tracks in the BESIII detector

The relative differences in coordinates of Cylindrical Gas Electron Multiplier Detector-based Inner Tracker(CGEM-IT) clusters are studied to search for track segments in CGEM-IT for the BESIII experiment.With the full simulation of single muon track samples, clear patterns are found and parameterized for the correct cluster combinations. The cluster combinations satisfying the patterns are selected as track segment candidates in CGEM-IT with an efficiency higher than 99%. The parameters of the track segments are obtained by a helix fitting.Some χ~2 quantities, evaluating the differences in track parameters between the track segments in CGEM-IT and the tracks found in the outer drift chamber, are calculated and used to match them. Proper χ~2 requirements are determined as a function of transverse momentum and the matching efficiency is found to be reasonable.     

A New Numerical Approach to Evaluate Variation of Electric Field Strength at the End of Particle Trajectory in Nuclear Track Detectors

A geometrical model for an electrochemical etching （ECE） track in a dielectric detector is defined and a primaxy programme is written to generate the track. The generated track is transformed to an M× N matrix of primary voltages. Using a numerical method, the matrix of final voltages is computed, and using another numerical approach, the electric field strengths in the elements of detector volume are computed. The final field strength at the end of particle trajectory is obtained. The results of our numerical computation show that there are exact correlations between the field strength at the end of particle trajectory and the parameters of track under ECE. It is found that although two traditional models of Mason and Smythe in dielectrics can be partly applied for short and long tracks, none of them are able to explain the behaviour of field strength in a ‘general case＇. Furthermore, we find that there is an expressive relationship between the field strength and the incidence angle of impacted particle, while the mentioned traditional models are not able to explain this effect.     

Charge-Changing Cross Sections of 736 A MeV ~(28)Si on Carbon Targets

The total and partial charge-changing cross sections of ~(28) Si on carbon targets at 736 and 723 AMeV are studied by CR-39 plastic nuclear track detectors using the HSP-1000 microscope system and the PitFit track measurement software. The values of the total charge-changing cross section are σ_((tot)) =(1179±50) mb and σ_((tot))t =(1186 ±42) inb at 736 and 723 A MeV, respectively. The result is compared with the ones obtained by other experimental and theoretical results. The odd-even effect of the partial charge-changing cross section is observed.     

The fragmentation of 20Ne at 400 A MeV

The total charge-changing cross sections and partial cross sections for the production of projectile fragments are measured in the interactions of 400 A MeV ²⁰Ne with aluminum, carbon and polyethylene targets sandwiched with CR-39 plastic nuclear track detectors. The measured total charge-changing cross sections are compared with the predictions using the Bradt-Peters semi-empirical formula, and the NUCFRAG2 and PHITS models. It is shown that the measured experimental results are in good agreement with the theoretical model prediction and other experimental results, and it can be clearly seen that the partial cross sections for fragment production show obvious odd-even effects.     

Adaptive multitrack reconstruction for particle trajectories based on fuzzy c-regression models

In this paper, an approach to straight and circle track reconstruction is presented, which is suitable for particle trajectories in an homogenous magnetic field (or 0 T) or Cherenkov rings. The method is based on fuzzy c-regression models, where the number of the models stands for the track number. The approximate number of tracks and a rough evaluation of the track parameters given by Hough transform are used to initiate the fuzzy c-regression models. The technique effectively represents a merger between track candidates finding and parameters fitting. The performance of this approach is tested by some simulated data under various scenarios. Results show that this technique is robust and could provide very accurate results efficiently.     

Electronic Transport in Molecular Junction Based on C20 Cages

Choosing closed-ended armchair （5, 5） single-wall carbon nanotubes （CCNTs） as electrodes, we investigate the electron transport properties across an all-carbon molecular junction consisting of C20 molecules suspended between two semi-infinite carbon nanotubes. It is shown that the conductances are quite sensitive to the number of C20 molecules between electrodes for both configuration CF1 and double-bonded models： the conductances of C20 dimers are markedly smaller than those of monomers. The physics is that incident electrons easily pass the C20 molecules and are predominantly scattered at the C20-C20 junctions. Moreover, we study the doping effect of such molecular junction by doping nitrogen atoms substitutionally. The bonding property of the molecular junction with configuration CF1 has been analysed by calculating the Mulliken atomic charges. Our results have revealed that the C atoms in N-doped junctions are more ionic than those in pure-carbon ones, leading to the fact that N-doped junctions have relatively large conductance.     

Femtosecond laser-inscribed waveguides in Nd3^＋：y3^＋：SrF2 crystals

Optical waveguides are fabricated in Nd3^＋：y3^＋：SrF2 crystals by a 1-kHz femtosecond laser using the double-line approach. Waveguides with different separations （10, 15, and 20 μm） between two consecutive optical breakdown tracks are produced, and their optical performances are explored by end-fire coupling to 780-and 532-nm lasers. Propagation loss of the waveguide with 20-pro separation is estimated. The micro- photohmlinescence and micro-Raman spectra indicate that the original fluorescence and lattice structure of the Nd3^＋：y3^＋：SrF2 crystals are well preserved in the waveguide. Therefore, the obtained waveguide structures are promising candidate for application in integrated waveguidc lasers.     

Research of cornea section''''s shape ablated by 193-nm ArF laser spots

The ablation theory of cornea and biology effect by 193-nm ArF excimer laser are introduced. The ablation tracks model is put forward to make laser spots scan around cornea by many steps and many areas to change cornea curvature. The corneal average ablation curve is calculated by software so as to explain the feasibility of the ablation tracks model. By analyzing the actual ablation shapes of many arbitrary cornea sections, the optimal ablation method for deciding the random position of every laser spot in every ablation track is obtained. Experiments combining the ablation model with the device testify the energy stability of laser spots and the accuracy of rectifying anisometropia.     

Fission studies of gold induced by (1665 MeV) π- using a CR-39 detector

The fission cross section and fission probability of ¹⁹⁷Au, induced by (1665 MeV) π^-, have been studied using CR-39 track detectors. A 4π-geometry was used to count track statistics. A beam of negative pions of 1665 MeV was produced at AGS of Brookhaven National Laboratory, USA, and allowed to fall normally on the stack. Two detectors from the stack were scanned for fission fragment tracks after etching in 6N NaOH at 70℃. The statistics of fission fragment tracks in both detectors were obtained. It was found that there was a marked asymmetry of registered tracks with respect to the forward and backward hemispheres. This asymmetry could be partly accounted for on the basis of momentum transfer to the struck nucleus. On the basis of counting statistics fission cross section was measured, and fission probability was determined by dividing the fission cross section with the reaction cross section. The fission cross-section and fission probability were compared with the computed values using the cascade-exciton model code CEM95.     

Generation of fast protons in moderate-intensity laser－plasma interaction from rear sheath

Forward fast protons are generated by the moderate-intensity laser--foil interaction. Protons with maximum energy 190~keV are measured by using magnetic spectrometer and CR-39 solid state track detectors along the direction normal to the rear surface. The experimental results are also modeled by the particle-in-cell method, investigating the time-varying electron temperature and the rear sheath field. The temporal and spatial structure of the sheath electrical field, revealed in the simulation, suggests that these protons are accelerated by target normal sheath acceleration (TNSA) mechanism.     

Simulation of induced radioactivity for a heavy ion medical machine

The radioactivity induced by carbon ions of the Heavy Ion Medical Machine (HIMM) was studied to asses its radiation protection and environmental impact. Radionuclides in the accelerator component, and in the cooling water and air at the target area, which are induced from primary beam and secondary particles, are simulated by FLUKA Monte Carlo code. It is found that radioactivity in the cooling water and air is not very important at the required beam intensity and energy that is needed for treatment, while radionuclides in the accelerator component may cause some problems for maintenance work and, therefore, a suitable cooling time is needed after the machine is shut down.     

Track reconstruction in the BESⅢ muon counter

The reconstruction algorithm for BESⅢ Muon Counter, MucRecAlg, is developed with the objectoriented language C＋＋ in BESⅢ offine software environment. MucRecAlg consists of the following functions：to find track seeds either from extrapolation of tracks in the main drift chamber or from the fired strips in muon counter, to select fired strips associated to the candidate tracks, to fit the candidate tracks with a linear or quadratic function and to calculate other parameters of the tracks for muon identification. Monte Carlo samples are generated to check the performance of the reconstruction package, such as reconstruction effciency, muon remaining rate and pion rejection rate, etc. The preliminary results show that the pion rejection rate is around 3%—4% while the muon remaining rate is better than 90% in 0.4—1.6 GeV/c momentum region, which meets the requirement as shown in the design report.     

Secondary Beam Fragments Produced by 200 and 400 MeV/u ^12C^6＋ Ions in Water

Based on the GEANT4 toolkit, we study the transportation of nucleons and nuclei in tissue-like media. The fragmentation of projectile nuclei and secondary interactions of produced nuclear fragments are considered. Livermore data is used to calculate electromagnetic interaction of primary and secondary charged particles. We validate the models using experimental data of 200 MeV/u and 400 MeV/u carbon ions, interacting with tissue equivalent materials of water. The model can well describe the depth-dose distributions in water and the doses measured for secondary fragments of certain charge and certain mass number. The secondary beam fragments produced by 200 MeV/u and 400 MeV/u ^12C^6＋ ions in water are investigated using the model. When the primary nuclei are in water, several neutron production mechanisms are involved. The light charged particles （p, d, t, ^3He and ^4He） and fast neutrons contribute to the dose tail behind the Bragg peak. The ^11C fragments which may be the most suitable nuclei for monitoring the energy deposition in carbon-ion therapy are also discussed.