DIP angle dependence on track formation sensitivity in antioxidant doped CR-39 plates

Recently, space radiation dosimetry measurements were made by passive and active detectors inside the Spacelab [STS-47 (FMPT): 300km, 57°, STS-65 (IML-2 mission): 300km, 28.5°]. The LET distributions obtained by antioxidant doped CR-39 inside the Spacelab were compared with those measured by the tissue equivalent proportional counter (TEPC) and the real time radiation monitoring device (RRMD) consisting of eight silicon detectors. While both distributions by CR-39 are in good agreement with those obtained by active detectors over the region of LET of several tens to 200 keV/μm, a significant difference in the LET region of smaller than several tens keV/μm is seen. It is considered to be caused by the dip angle dependence of track formation sensitivity in CR-39. The track formation sensitivity for different dip angle were measured for several high heavy energy ions. Using these results, the correction for the dip angle was made for the LET distribution. The corrected result is consistent with the results obtained by active detectors.     

Particularization of alpha contamination using CR-39 track detectors

Solid-state nuclear track detectors have found wide use in various domains of science and technology, e.g. in environmental experiments. The measurement of alpha activity on sources in an environment, such as air is not easy because of short penetration range of alpha particles. Furthermore, measurement of alpha activity by most gas ionization detectors suffers from high background induced by the accompanying gamma radiation. Solid state nuclear track detectors (SSNTDs) have been used successfully as detecting devices and as a passive system to detect alpha contamination on different surfaces. This work presents the response of CR-39 (for two types) to alpha particles from two sources, ²³⁸Pu with energy 5 MeV and ²⁴¹Am with energy 5.4 MeV. The methods of etching and counting are investigated, along with the achievable linearity, efficiency and reproducibility. The sensitivity to low activity and energy resolution are studied.      

Beam profile measurement with CR-39 track detector for low-energy ions

A CR-39 track detector was successfully used to measure the outline of thin low-energy ion beams. After the etching, the surface of the detector was examined with an observation system composed of a Normarski microscope, a CCD camera and a digital image processing computer. Beam images obtained with the system were in good agreement on the outline of the beam formed with a beam aperture. Also, the resolving power in the beam outline measurement was roughly explained from the consideration of the ion range and the etch-pit growth in the chemical etching for the CR-39 detector.     

Post-irradiation sensitization of CR-39 track detector in carbon dioxide atmosphere

The effect of post-irradiation treatment of CR-39 track detector in carbon dioxide atmosphere on the alpha particle registration sensitivity was investigated. Significant increase in etch rate ratio for 6.1 MeV ²⁵²Cf alpha particle was observed. The sensitization increasedboth as a function of trating time and as a function of carbon dioxide pressure in the treating vessel. Energy dependence of the sensitization was found to be small in the 2–9 MeV alpha particle energy interval. Fading of latent tracks after the sensitization process was slow in a one day period. Pre-irradiation treatment in carbon dioxide showed also some sensitization, though to a lesser extent than post-irradiation treatment. However, exposing CR-39 alpha particles in pure carbon dioxide atmosphere resulted in dramatic decrease in sensitivity. The role of dissolved oxygen and carbon dioxide in the primary latent track formation and in post-irradiation latent track transformation is discussed. Potential influence of the application of sensitization of CR-39 in radon, neutron and cosmic ray charged particle dosimetry is also discussed.     

Estimation of the latent track size of CR-39 using atomic force microscope

As a frame work of the study for the latent track size measurement using atomic force microscope, we have measured the minute etch pits and the extremely small amount of bulk etch of CR-39 at the beginning of chemical etching, and obtained its growth curves in nanometer dimensions. The pieces of CR-39 were exposed to 6 MeV/nC and Fe ions with normal incidence angle and were etched in 70°C 7 N NaOH solution for 0.5,1,2,3,5 min. The diameters of latent track were estimated to be 17 nm for Fe ions and 8 nm for C ions, respectively. These values are comparable to the experimental data on the average ‘track core diameters’ that have been obtained by various experimental techniques.     

用20—1020 keV单能质子刻度CR-39固体核径迹探测器

用北京师范大学2×1.7MV串列加速器和400 kV高压倍加器产生的20—1020 keV单能质子束对CR-39固体核径迹探测器进行了刻度.为了保证质子的单能性和固体核径迹探测器上径迹密度不能超过10⁶/cm²的要求,对两台加速器分别采用了不同方法控制质子辐照数量.在串列加速器上采用了狭缝加转盘的方法,在高压倍加器上采用了100 ns单次高压脉冲扫描束流的方法,既保持了质子的单色性,又达到了质子注量小于10⁶/cm²的 关键词： 单能质子 固体核径迹探测器 CR-39     

Angular response of CR-39 to relativistic heavy ions and high-energy protons

Track etch detectors CR-39 irradiated with relativistic heavy ions (C, Ne, Si and Fe, ) and high-energy protons (35–230 MeV) were etched both chemically and electrochemically. To determine an angular dependence of response in detail (step 1), an arrangement of a single detector bent into a semi-cylindrical form was used. Experimental data were fitted by polynomic functions and the detection efficiencies for isotropic irradiation were calculated. Critical angles of registration were also determined for heavy ions. The possible influence of additional absorbers and radiators was also estimated.     

Calibration study on the triton response of CR-39 track detector

Triton response of the CR-39 track detector has been studied at energy ranges below 2.7 MeV. Triton irradiation was made both on the top and the well polished side surface of the CR-39 sample sheets, using ⁶Li(n,t)⁴He reaction in a thermal neutron field. At large residual ranges more than 10 μm, fine results of etch rate ratio were obtained by analysing the growth curves of etch-pit radius on the top surface. But the response at near the track end-point could not be obtained well in this method, as a result of the missing track effect. Clearly resolved response at short residual ranges was attained by means of the shape analysis of the etch-pit profile observed on the side surface.     

CR-39 sensitivity analysis on heavy ion beam with atomic force microscope

Preliminary results of feasibility study to apply atomic force microscope (AFM) to the quantitative analysis for minute etch pits on CR-39 are reported comparing with the optical microscope observation. The growth curves of the Si track diameter and length obtained by both technqiues were discussed in relation to the track sensitivity and the etch induction time.     

Study on response of CR-39 detector to light ions

The response of CR-39 detector has been obtained precisely for protons, deuterons, tritons, alpha-particles and lithiumions with energies of a few MeV/nucleon. The track etch rates were determined from the growth curves of pit radius and summarized as the response functions. The accuracy of this method is high enough to discriminate among hydrogen isotopes under a certain condition. The correlation between the response and LET with various cut-off energies has also been examined. It was found that LET is not an unique parameter describing the response function adequately for different ions by the same expression.     

On the effect of cure cycle parameters and dopants on pre and post irradiation annealing response of CR-39 track detectors

The effect of additives and cure cyle parameters on pre and post irradiation annealing characteristics of CR-39 detectors has been investigated. Effect of pre and post irradiation annealing on bulk etch rate, sensitivity, track diameter and etching behaviour of various CR-39 detectors has been investigated.     

Range and energy-loss measurement of238U in Makrofol-N using CR-39 track detector

A simple experimental technique has been described for measuring range and energy-loss of any heavy ion in any complex medium with the help of a sensitive solid state nuclear track detectors (SSNTDs). In this paper we present the results obtained from our measurements of ranges and energy-loss of 16.34 MeV/u²³⁸U in Makrofol-N using CR-39 track detector. Experimental ranges are compared with the corresponding theoretical values. The significance and scope of the present work are discussed.     

The fission systematics of (15.9 MeV/u) Au ions in polymer CR-39

It has been demonstrated that high-energy heavy ions undergo fission while propagating in dielectric solids. Since these materials act as particle detectors because of their ability to retain primary ionization damage that can be fixed and enlarged with chemical etching, therefore, in principle, a complete kinematical analysis of fission events is possible. The crucial point in this regard is the availability of a well-calibrated range-energy relation, which is necessary for mass identification. We have developed an analytical method to convert the geometrical parameters of fission fragment tracks into physical parameters using an equation that expresses velocity as a polynomial of mass and range. A set of nine different polynomials was used to represent small regions of mass and range in order to improve accuracy. In the case of (15.9 MeV/u) Au ions incident normally on CR-39, we have found about 200 events which could be categorized as in-flight fission of Au ions inside the body of the detector. Mass distributions and cross sections of fission events have been calculated.     

Extension of alpha particles in CR-39-etched track depth model to heavier ions

In this paper, the previous modeling of protons and alpha particles tracks depth in CR-39 nuclear track detectors was extensively extended to describe tracks of heavier ions. These ions include deuteron, lithium, boron, carbon, nitrogen and oxygen. Based on a compilation of published experimental results related to these ions, a set of empirical fitted model parameters is obtained for each type of ion. The A dependence of these model parameters is obtained.     

Studies on the variation of the track etch rate along alpha particle trajectories in CR-39

At the beginning of the etching process a constant track etch rate can be assumed. In deeper detector layers, however, the etch rate varies drastically along the particle trajectories. Consequently, the indirect determination of the track etch rate by measuring the etch pit diameters on the detector surface does not yield correct results. Therefore, a method for the direct measurement of the track etch rate as a function of the depth within the detector was developed. Applying this method, the relationship between the track etch rate and the energy loss in CR-39/PATRAS could be derived.     

Empirical parameterization of CR-39 longitudinal track depth

In this work, new empirical equation describing the charged particles radiation track development against etching time and track longitudinal depth are presented. The equation involves four free fitting parameters. It is shown that this equation can reproduce tracks depth formed on the CR-39 by alpha particles at different energies and etching times. Parameters values obtained from experimental data can be used to predict etched track lengths at different energies and etching times. The empirical equation suggested is self consistent as far as reproducing all features of track depth development as a function of etching time and energy are concerned.     

Studies on the nuclear tracks in CR-39 plastics

A review was given for our recent studies on the latent tracks in CR-39 nuclear track detector. The radial size of track core has been determined through UV spectral measurements combined to the model of track overlapping and by AFM observations of slightly etched detectors. The track core radius was found to be about a few nano-meters and almost proportional to the cubic root of stopping power. As a control study, the etching properties of CR-39, irradiated by low-LET radiation, has been examined. The observed depth dependence and dose-rate dependence of the bulk etch rate of the irradiated CR-39 were explained that the damage formation process was governed by the reaction between the radiation induced radicals and the oxygen supplied from the air. This indicated that latent tracks in CR-39 are produced through local radiation induced oxidation process along the ion paths. Studies on vibration spectra, near-IR, FT-IR and Raman spectra, of CR-39 have also been carried out to estimate the chemical structure of the latent tracks. The creation of OH group in irradiated CR-39 has been confirmed.     

Neutron response calculation on the basis of variable track etch rates along the secondary particle trajectories in CR-39

The calculation of the response of CR-39 detectors exposed to neutrons is of high importance for their dosimetric application. A computer code system has been developed for this purpose. Whereas the generation of secondary charged particles is carried out using non-analogue Monte-Carlo techniques with variance reduction the simulation of the track formation process is treated without any free parameter starting from the etch rate ratio V(REL) only. Results are given for the contribution of recoil protons to the response as a function of the neutron energy and angle of incidence. Furthermore, the influence of an external radiator has been studied. The comparison of the calculated values with experimental data confirm the reliability of the track etch model applied.     

Investigation of response of CR-39, PM-355 and PM-500 types of nuclear track detectors to energetic carbon ions

Samples of CR-39, PM-355, and PM-500 plastic detectors were irradiated with carbon ions of energy ranging from 0.9 MeV to 14.7 MeV. After the irradiation the detector samples were etched for a period from 2 hrs to 10 hrs. Dependence of track diameters on the ion energy values for different etching times, and dependence of V_T/V_B as a function of incident carbon-ion energy, are presented.     

Supervised nuclear track detection of CR-39 detectors by cellular automata

In this paper, cellular automata are used to detect the nuclear tracks in the track images captured from the surface of CR-39 detectors. Parameters of the automaton as the states, neighborhood, rules and quality parameters are defined optimally for the track image data set under analysis. The presented method is a supervised computational algorithm which comprises a rule definition phase as the learning procedure. Parameter optimization is also performed to adapt the algorithm to the data set used.