A study on the etching properties of electron-irradiated plastic track detectors

The variations of the bulk etching rate of electron-bombarded CN, CA, CAB, PC and PET sheets were studied as a function of electron dose and etching temperature. A conclusion was made that in the plastics under study a radiation-damaged region produced, either by an electron beam or a heavily ionizing nuclear particle display, to a certain extent, analogous etching properties. It was shown that the ratio of the etching rates of an electron-bombarded and an unirradiated sheet increases with the increase of the etching temperature for PC and PET, and with the decrease of etching temperature for CN and CA. Similar temperature dependences were obtained for the ratio of track– and bulk-etching rates (i.e. for registration sensitivity) if the plastic sheets were irradiated with heavier nuclear particles. Our results seem to confirm the assumption that the delta electrons may play an important role in the formation of primary nuclear particle tracks in plastic track detectors.     

Fluid model of the positive column in argon‐oxygen direct current glow discharge

The positive column of argon‐oxygen direct current (DC) glow discharge was investigated using a fluid model at pressures of around 410 Pa and discharge currents from 10 to 40 mA. The model was used to study the influence of an oxygen admixture on the properties of argon discharge. The simulated intensity of the electric field strength was compared with measured values at 5% and 100% of oxygen concentration. The one‐dimensional model in a cylindrical tube is based on the drift‐diffusion approximation of particle flux and the mean‐electron‐energy approximation is used to describe the electron interaction. The model takes into account the radial profile of particle concentration, the neutral gas kinetic temperature profile, and interactions with the wall in the cylindrical glass discharge tube. It was shown that 2% of the oxygen admixture causes a significant increase in longitudinal electric field strength and gas heating.     

Study of current drain during electrochemical etching of polycarbonate detectors

Polycarbonate (PC) detector is one of the common detectors for neutron and radon gas detection. Using this detector it is possible to measure the dose in mSv, by counting tracks/cm² on an etched surface. In this paper, a special procedure has been suggested to determine the dose based on current drain during the etching process. In these experiments the effects of voltage, frequency, effective etched area, PC detector's thickness, etched area (one side or two sides), etching solution temperature and dose absorbed by the PC foil have been studied.The results obtained show the current drain variation for a voltage of 200–1600 V, a frequency of 2–10 kHz, effective area with a diameter of 2–12 cm, PC thickness of 125–250–375– and a temperature of etching solution of 25–.Lexan PC foils were exposed to doses of of neutrons. The unexposed foils were considered as the background (BG) foils. Most of the experiments were performed at a voltage of 800 V, a frequency of 2 and 8 kHz, foil thickness of , diameter of effective etched area of foils of 2, 6 and 12 cm, temperatures of 25 and and the etching process from 0 up to overload stage. Overload stage occurs when the foil becomes so thin due to growth of the tracks that it leads to sparking between phase and null that makes a hole in the foil.Current drain curves versus the function of the etching time are absolutely different for various doses from zero (BG) to 10 rad (BG up to ). This is true especially for the time interval from 3 h of etching up to overload stage. In this way, it is possible to obtain a calibration of PC detector net current drain based on its absorbed dose.In this experiment, the number and diameter of tracks and their relation with drain current and PC foil residual thickness at overload stage have been studied.The same experiment has been performed for various concentrations of radon gas (Bq/m3) as well.     

The statistical process of pore growth in multi pore foils

Using the electrolytical etching method the breakthrough-times (i.e. the time when the two etched cones from both sides of the detector contact) and the resulting track etching rates v_t of heavy ion tracks in 8 μm polycarbonate Makrofol KG have been measured. The samples were irradiated at the GSI, Darmstadt (Germany) with gold ions and different fluences at a specific energy of 11.6 MeV/u. All foils were etched in 6 n NaOH at room temperature. Fluctuations of breakthrough-times of single pore foils were analysed. Also the breakthrough-time of multi-pore-foils were measured. The dependence of the mean breakthrough-time on the ion fluence is dicussed. This dependence will be explained by the fluctuations of the breakthrough-time of the pores.     

Pion-induced fission in tin and bismuth observed with makrofol detectors

Pion is the field particle of nuclear force. Its interaction with the nucleons may lead to complete absorption resulting in the full deposition of the rest mass and kinetic energy within the nucleus. Consequently the nucleus can be excited to very high energies. This situation gives rise to binary decay even in those nuclei which are not normally prone to fission due to their high fission barriers. We have studied the occurrence of binary fission induced by pions of energies 500, 672, 1068 and 1665 MeV in the targets of Sn and Bi. The exposures have been made at the Brookhaven National Laboratory (USA). The experimental set-up was based on 2π-geometry with targets in the form of thin foils placed in front of Makrofol detectors. The fission events were counted manually with an optical microscope. The incident beam was monitored with the help of a scintillator and local fluences were determined in-situ. The fission cross-sections were calculated by using the known values of target thickness and local frequencies of fission counts.     

微空心阴极放电时空特性

为了揭示微空心阴极放电的放电机理,利用流体模型研究了矩形微空心阴极放电的时间和空间分布特性。在氩气环境下计算得到了压强为1.3×10~4Pa时电流、电势、电场、电子和离子密度等随时间的发展变化。结果表明,整个放电过程分为四个阶段,即预放电阶段、电场由轴向向径向转换阶段、电流缓慢增长向空心阴极效应过渡阶段和稳态放电阶段。稳态放电时出现明显的空心阴极效应,阴极位降区存在很高的径向电场和较高的电子平均能量,而负辉区径向电场很弱,电子平均能量较低,电子和离子密度峰值出现在负辉区,二者数值基本相等,而在阴极位降区离子密度远高于电子密度。     

Activation energy of etching for CR-39 as a function of linear energy transfer of the incident particles

In this work, we have studied the effect of the radiation damage caused by the incident particles on the activation energy of etching for CR-39 samples. The damage produced by the incident particle is expressed in terms of the linear energy transfer (LET). CR-39 samples from American Acrylic were irradiated to three different LET particles. These are N (LET₂₀₀ = 20 KeV/μm) as a light particle, Fe (LET₂₀₀ = 110 KeV/μm) as a medium particle and fission fragments (ff) from a ²⁵²Cf source as heavy particles. In general the bulk etch rate was calculated using the weight difference method and the track etch rate was determined using the track geometry at various temperatures (50–90 °C) and concentrations (4–9 N) of the NaOH etchant. The average activation energy F_b related to the bulk etch rate v_b was calculated from ln v_b vs. l/T. The average activation energy E_t related to the track etch rate v_t was estimated from ln v_t vs. l/T. It is shown that activation energy of etching is a constant value for CR-39 detector where E_t was found to be independent on the damage produced by the incident particle.     

AFM method for investigation of irradiated polymers

Tracks of swift heavy ions (Xe and Bi) at the surface of polymer (PET) were studied using AFM and surface defects—cavities (for Xe) and hillocks with cavities on its top (for Bi) were found. Thermal behavior of these Bi-irradiated samples (during annealing from 70°C to 180°C) was investigated. It was found that low-temperature annealing does not change the shape of surface defects, while high-temperature annealing leads to slow disappearance of these defects.

Irradiation of a stack of ultra-thin PET films by fission fragments was carried out and some sheets were then investigated separately. Two types of defects, corresponding to two main types of incident fragments (according to average energy distribution) were found. The deep structure of a track was studied and the ranges for two types of fragments were estimated. The increase of area of destruction was found at the depth 10–12 μm, which may be associated with changing of mechanism of interaction of passing particle with polymer and the dominant role of nuclear interaction. The obtained results are supported by a model calculation.     

Statistical properties of deexcitation of fragments originating from the spontaneous fission of 252Cf

A method of parametrizing radiative strength functions for electric dipole transitions is used to calculate the spectra of photons emitted by fragments originating from the spontaneous fission of ²⁵²Cf nuclei. The LDPL-98 library of parameters, which contains data for 2000 nuclei, is composed for performing relevant calculations. It is shown that the use of this method leads to regular agreement with experimental data—that the structure and the energy dependence of the spectra are reproduced without varying parameters suggests a statistical character of fission-fragment deexcitation.     

Study of mass spectra of light-actinide fission isotopes Kr and Xe in the framework of a new statistical approach

Results on light-actinide fission fragments Kr and Xe yields calculated within the framework of a new statistical approach are presented. The proposed statistical method is derived from the equilibrium condition of the ensemble of all possible fission fragments. Using ²³⁷Np isotope as an example, we investigate the influence of excitation energy (nuclear temperature) and nuclear particle emission on the formation of mass fission channels. The results obtained are compared with the experimental data on Kr and Xe isotope yields at the fission of Th, U, Np, and Pu.     

Townsend coefficient,escape curve,and fraction of runaway electrons in copper vapor

Ionization and drift characteristics of electrons in copper vapor in the presence of an external electric field are analyzed. In contrast to normal gases, in copper vapor, the excitation energy of lower states is significantly lower than the ionization potential and the excitation cross section is several times greater than the ionization cross section at the incident-electron energy on the order of the ionization energy. This can affect the characteristics of electron bunching in gas. It is demonstrated that, as in previously studied gases, the notion of the Townsend coefficient remains meaningful even in the presence of strong fields at which the electric force exceeds the electron drag force acting in gas. The dependences of the main ionization and drift characteristics on the reduced field strength, the escape curve (which separates the region of effective electron multiplication and the region where electrons leave the discharge gap without multiplication), and the curves of equal efficiency for the formation of runaway electrons are obtained. It is demonstrated that a relatively high excitation cross section of copper levels leads to a sharper peak on the dependence of the Townsend coefficient on the field strength and a narrower region of the effective electron multiplication in comparison with previously studied gases.     

Angular momentum and energy dependence of fission andn,p,4He emission from194Hg compound nucleus

Spin and temperature dependence of the fission and particle emission is studied for¹⁹⁴Hg. The compound nucleus is described using the Strutinsky shell correction approach extended for finite angular momenta and temperature. The shell corrections to the potential energy, free energy and the angular momentum are calculated using the Woods-Saxon average field. Results are compared with the experimental data and show a good qualitative agreement. It is found that the inclusion of the shell effects is necessary to understand the decay properties of¹⁹⁴Hg even for temperatures as high as 1.5–2.0 MeV.     

先进磁镜装置中径向电场对高能粒子的约束性能研究

本文运用Boris算法对紧凑型聚变反应装置(compact fusion reactor, CFR)中高能a粒子的运动轨道进行了数值模拟,分析了高能a粒子在不同径向电场作用下运动轨道的差异性;探究了不同径向电场对CFR装置中不同位置处a粒子约束性能的影响.研究结果表明,当正、负径向电场强度达到一定临界值时,都能够使高能a粒子很好地约束在CFR装置内部,但不同位置处径向电场强度临界值与a粒子初始条件有关.     

双外场对费米气体Joule-Thomson效应的调控

研究匀强电场和谐振场构成的双外场对带电费米粒子系统化学势和Joule-Thomson系数的调控作用．在满足Thomas-Fermi近似的条件下,给出有限温度范围内匀强电场和谐振场中带电费米粒子系统的化学势和内能随温度变化的显式函数关系,分析双外场对带电费米粒子系统焦耳-汤姆逊系数的调控作用.研究结果表明：随着温度的升高,带电费米粒子系统的焦汤系数值逐渐由负变正,且临界温度Tc随外电场增强而降低;在适当温度下,外势场的存在会使带电费米粒子系统产生焦耳-汤姆逊正效应.     

Effective ionization of air in a near-critical electric field at high temperatures

The effective ionization at the early stages of the development of an electric discharge in air at moderate and high temperatures and pressures was analyzed. Ionization in an external electric field were studied with consideration given to background electrons, the attachment and detachment of electrons from atoms and molecules, and recharging and conversion of anions. The rates of ion-molecular reactions, in particular, detachment, depend not only on the external field strength but also on the temperature. The ionization thresholds were demonstrated to decrease with increasing temperature.     

Energy dependence of fission probabilities induced by negative pions in Sn,Au and Bi

Fission probabilities induced by negative pions in Sn, Au and Bi at different energies using variety of nuclear track detectors have been studied. The target-detector assemblies in 4π-geometric configuration were irradiated at the AGS facility of Brookhaven National Laboratory, USA. After etching the exposed detectors at appropriate etching conditions the detectors have been scanned for the tracks of fission fragments produced as a result of interaction of pions with the target nuclei. Based on the track counts, the values of fission cross sections have been measured and fission probabilities have been calculated using the reaction cross-section calculated with the help of the cascade-exciton model code CEM95. The values of fission probability based on experimental fission cross-sections have been compared with the theoretically calculated values of fission probabilities obtained using the CEM95 code. Theoretical values of fission probability have been computed for incident pion energy up to 2500 MeV in Sn, Au and Bi for comparison to fission data for high energy negative pions at 500, 672, 1068, 1665 MeV and 2300 MeV energies for the same targets. The values of fission probability based on the experimental fission cross section and theoretically calculated values of fission probability have been compared. Reasonable agreement has been observed among the experimentally measured and theoretically computed values of fission probabilities. A saturation of probabilities has been observed for Au and Bi at higher energies, but for Sn an increase of probability with the increase of pion beam momentum up to 1665 MeV has been observed.     

46．7MeV／A~（12）C轰击~（159）Tb、~（197）Au和~（209

用４６．７ＭｅＶ／Ａ１２Ｃ轰击１５９Ｔｂ、１９７Ａｕ和２０９Ｂｉ，测量关联裂片的速度和角度．研究了线动量转移、质量和出平面角分布，提取了核温度．应用级联两体统计衰变理论进行了拟合与解释，结果表明：在入射能约为５０ＭｅＶ／Ａ的中能重离子碰撞中，以非完全熔合方式形成了核温度高达４－５ＭｅＶ的类复合核，其后通过裂变、蒸发级联统计两体衰变而退激．     

双外场对费米气体Joule-Thomson效应的调控简

研究匀强电场和谐振场构成的双外场对带电费米粒子系统化学势和Joule-Thomson系数的调控作用.在满足Thomas-Fermi近似的条件下,给出有限温度范围内匀强电场和谐振场中带电费米粒子系统的化学势和内能随温度变化的显式函数关系,分析双外场对带电费米粒子系统焦耳-汤姆逊系数的调控作用.研究结果表明,随着温度的升高,带电费米粒子系统的焦汤系数值逐渐由负变正,且临界温度Tc随外电场增强而降低.在适当温度下,外势场的存在会使带电费米粒子系统产生焦耳-汤姆逊正效应.     

The effect of discharge power density on polyethylene terephthalate film surface modification by dielectric barrier discharge in atmospheric air

Polyethylene terephthalate (PET) films are modified using non-equilibrium plasma generated by DBD in atmospheric air, and the effects of discharge power density on the surface modification are studied. It is found that increasing discharge power density can induce more effective treatment of PET films, because this leads to a faster decrease in water contact angle and a faster increase in surface energy due to more creation of polar groups and more obvious etching occurring on the PET surface. So the treatment time needed to achieve the same level of surface treatment can be reduced by increasing the discharge power density.     

Chemical etching op fission tracks in ethylene-tetrafluoroethylene copolymer

The chemical etching of fission tracks in ethylene-tetrafluoro-ethylene copolymer was studied. Etched holes 3000–4000 Å in diameter was recognized by electron microscopy for a film bombarded by fission fragments in oxygen and etched in a 12N sodium hydroxide solution at 125°C. The radial etching rate at 125°C was 6–8 Å/hr, which is less than 17 Å/hr for polyvinylidene fluoride in the same sodium hydroxide concentration at 85°C. The smaller rate is a reflection of the larger chemical resistivity of ethylene-tetrafluoro-ethylene copolymer than polyvinylidene fluoride.