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.     

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.     

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.     

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.     

Comparative analysis of CR-39 sensitivity for different sets of measurable track parameters

In the present paper the sensitivity V of plastic nuclear track detectors CR-39 to the space radiation, accelerated heavy ions in wide LET range and α-particles is studied. Different approaches for V evaluation are considered and compared. Main attention is given to the method that is appropriate for the measurement of short range heavy secondaries of space radiation. Finally, the experimental verification of the designed V function is carried out via simulation of the secondaries with low energy α-particles in the vicinity of the Bragg peak.     

Proton response of high sensitivity CR-39 copolymer

We studied the track response for the copolymer of CR-39 monomer with N-isopropylacrylamide (NIPAAm) as well as etching properties. It was found that copoly (CR-39/NIPAAm/Naugard 445) composed in wieght ratio of 99/1/0.01 is highly sensitive to low LET particles in the region below 10 keV/μm of LET and able to record normally incident particles of LET down to 1.5 keV/μm, recording protons up to the energy of 27 MeV. These results were compared with the responses for two types of CR-39 detectors containing a small quantity of antioxidant. The threshold energy proton registration is discussed.     

Development of copolymer of CR-39 with high sensitivity to low let particles

Several types of copolymers of CR-39 were prepared to find its usefulness as a nuclear track detector of high sensitivity. Track responses of these copolymers were investigated by irradiating energetic ions from proton through Ar. The copolymer of CR-39 monomer with N-isopropylacrylamide (NIPAAm) shows higher sensitivity than that of pure CR-39 for low LET particles such as protons. Preliminary results are reported for the track responses of copolymers (CR-39/NIPAAm) with various contents of NIPAAm as well as the etching properties.     

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     

Numerical study of the hydrodynamic drag force in atomic force microscopy measurements undertaken in fluids

When atomic force microscopy (AFM) is employed for in vivo study of immersed biological samples, the fluid medium presents additional complexities, not least of which is the hydrodynamic drag force due to viscous friction of the cantilever with the liquid. This force should be considered when interpreting experimental results and any calculated material properties. In this paper, a numerical model is presented to study the influence of the drag force on experimental data obtained from AFM measurements using computational fluid dynamics (CFD) simulation. The model provides quantification of the drag force in AFM measurements of soft specimens in fluids.The numerical predictions were compared with experimental data obtained using AFM with a V-shaped cantilever fitted with a pyramidal tip. Tip velocities ranging from 1.05 to 105 μm/s were employed in water, polyethylene glycol and glycerol with the platform approaching from a distance of 6000 nm. The model was also compared with an existing analytical model. Good agreement was observed between numerical results, experiments and analytical predictions. Accurate predictions were obtained without the need for extrapolation of experimental data. In addition, the model can be employed over the range of tip geometries and velocities typically utilized in AFM measurements.     

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.     

Registration temperature effect on sensitivity of CR-39(DOP) and SR-90 polymer track detectors

The samples of CR-39(DOP) and SR-90 polymer track detectors have been exposed to -particles from ²⁴¹Am source in an exposure unit. The temperature of the detectors during irradiation has been varied from −30°C to 70°C. These exposed samples have been etched in 6.25 N NaOH solution at 60°C for various etching times. The variation of sensitivity of these detectors as a function of registration temperature has been studied. It has been observed that at the fixed registration temperature, the sensitivity of SR-90 is more than CR-39(DOP) polymer track detector. However, the enhancement in sensitivity with the decrease in registration temperature is more pronounced in case of CR-39(DOP) than SR-90.     

The influence of solar radiations to the physical and structural properties of CR-39

Long chain polymers owe many of their properties to the structural arrangements of their molecules and are extensively used for many industrial and applied sciences. One of such application is their perspective use in the field of solid-state nuclear track detectors. However they are profoundly influenced by low LET radiations exposure and new structural arrangements may emerge. CR-39 is one of the most popular polymeric track detectors, however its aliphatic nature restricts its applications. Thus in the present investigations the damage densities produced by solar radiations to the polymer have been estimated by analyzing the structural, physical and etching properties of the polymer. The polymer is found to be highly sensitive towards solar radiations and great changes in physical and structural properties of polymer have been observed. The sensitivity of the polymer has been found to decrease by 83.40% during eight months.      

Anomalous scaling in surface roughness evaluation of electrodeposited nanocrystalline Pt thin films

Atomic force microscopy (AFM) is used to measure the surface roughness of crystalline Pt thin films as a function of film thickness and growth rate. Our films were electrodeposited on Au/Cr/glass substrates, under galvanostatic control (constant current density), from a single electrolyte containing Pt⁴⁺ ions. Crystalline structure of the films was confirmed by X-ray diffraction (XRD) technique. The effect of growth rate (deposition current density) and film thickness (deposition time) on the kinetic roughening of the films were studied using AFM and roughness calculation. The data is consistent with a rather complex behaviour known as “anomalous scaling” where both local and large scale roughnesses show power law dependence on the film thickness.     

Studies on the track formation mechanism of the heavy ions in CR-39

The bulk etch rate for two types of CR-39 detector was measured as a function of temperature and the activation energies of bulk etching was determined. Experimental values of track etch rate were derived directly from the function of the succesive measured track length vrs. etching time for ²⁰⁹Bi, ¹²⁹Xe and ²⁰Ne ions.

The maximum etchable length of 13 MeV/u ²⁰⁹Bi and 13.04 MeV/u ¹²⁹Xe ions have been measured at and below these energies. A comparison of the measured and calculated track length data is presented.     

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.      

Ion beam modification of surface properties of CR-39

The effects of ion-beam bombardment on the physical and chemical properties of poly(allyl diglycol carbonate) (CR-39) polymer have been investigated. CR-39 samples were bombarded with 320 keV Ar and 130 keV He ions at fluences ranging from 1 × 10¹³ to 2 × 10¹⁶ ions/cm². The nature and extent of radiation damage induced were studied by UV–VIS spectrometry, Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, as well as Vickers' hardness measurements. In addition, the effect of ion fluence on the wetting properties of ion-beam bombarded CR-39 polymer was determined by measuring the contact angle for distilled water. UV–VIS spectra of bombarded samples reveal that the optical band gap decreases with increasing ion fluence for both Ar and He ions. In the FTIR spectra, changes in the intensity of the bands on irradiation relative to pristine samples occurred with the appearance of new bands. XRD analyses showed that the degree of ordering of the CR-39 polymer is dependent on the ion fluence. Changes of surface layer composition and an increase in the number of carbonaceous clusters produced important change in the energy gap and the surface wettability. The surface hardness increased from 10.54 MPa for pristine samples to 28.98 and 23.35 MPa for samples bombarded with Ar and He ions at the highest fluence, respectively.     

Fractal analysis and atomic force microscopy measurements of surface roughness for Hastelloy C276 substrates and amorphous alumina buffer layers in coated conductors

In coated conductors, surface roughness of metallic substrates and buffer layers could significantly affect the texture of subsequently deposited buffer layers and the critical current density of superconductor layer. Atomic force microscopy (AFM) is usually utilized to measure surface roughness. However, the roughness values are actually relevant to scan scale. Fractal geometry could be exerted to analyze the scaling performance of surface roughness. In this study, four samples were prepared, which were electro polished Hastelloy C276 substrate, mechanically polished Hastelloy C276 substrate and the amorphous alumina buffer layers deposited on both the substrates by ion beam deposition. The surface roughness, described by root mean squared (RMS) and arithmetic average (R_a) values, was analyzed considering the scan scale of AFM measurements. The surfaces of amorphous alumina layers were found to be fractal in nature because of the scaling performance of roughness, while the surfaces of Hastelloy substrates were not. The flatten modification of AFM images was discussed. And the calculation of surface roughness in smaller parts divided from the whole AFM images was studied, compared with the results of actual AFM measurements of the same scan scales.     

Measurement of bulk etch rate of LR115 detector with atomic force microscopy

Equations for calculating track parameters have been proposed, which invariably involve the track etch rate V_t and the bulk etch rate V_b. The present study measured V_b for the LR115 solid-state nuclear track detector using atomic force microscopy (AFM). The detectors were partially masked using rubber cement and then etched in 2.5 N NaOH solution at 60°C for time periods ranging from 5 to 40 min. The rubber cement was then peeled off and cross-sectional images of the LR115 detectors were obtained by AFM. V_b has been found to have different values below and beyond the etching time of about 13.5 min, with the values of 0.0555 and 0.0875 μm min⁻¹, respectively. The increase in V_b with the etching time can be explained by a diffusion-etch model, in which the additional damage of the detector material is due to those etchant ions diffused into the detector over time. Now that V_b has been determined, this can be combined with the track etch rate V_t to calculate track parameters.     

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.     

固体核径迹探测器的刻度

为了测量在神舟飞船返回舱内由空间重电离粒子引起的辐射剂量，采用了固体核径迹探测器CR-39来测量飞船飞行期间，返回舱内由重电离粒子引起的能量沉积. 本文介绍了CR-39探测器对能量沉积的响应的刻度.