Efficient alpha particle detection by CR-39 applying 50 Hz-HV electrochemical etching method

Alpha particles can be detected by CR-39 by applying either chemical etching (CE), electrochemical etching (ECE), or combined pre-etching and ECE usually through a multi-step HF-HV ECE process at temperatures much higher than room temperature. By applying pre-etching, characteristics responses of fast-neutron-induced recoil tracks in CR-39 by HF-HV ECE versus KOH normality (N) have shown two high-sensitivity peaks around 5–6 and 15–16 N and a large-diameter peak with a minimum sensitivity around 10–11 N at 25°C. On the other hand, 50 Hz-HV ECE method recently advanced in our laboratory detects alpha particles with high efficiency and broad registration energy range with small ECE tracks in polycarbonate (PC) detectors. By taking advantage of the CR-39 sensitivity to alpha particles, efficacy of 50 Hz-HV ECE method and CR-39 exotic responses under different KOH normalities, detection characteristics of 0.8 MeV alpha particle tracks were studied in 500 μm CR-39 for different fluences, ECE duration and KOH normality. Alpha registration efficiency increased as ECE duration increased to 90 ± 2% after 6–8 h beyond which plateaus are reached. Alpha track density versus fluence is linear up to 10⁶ tracks cm⁻². The efficiency and mean track diameter versus alpha fluence up to 10⁶ alphas cm⁻² decrease as the fluence increases. Background track density and minimum detection limit are linear functions of ECE duration and increase as normality increases. The CR-39 processed for the first time in this study by 50 Hz-HV ECE method proved to provide a simple, efficient and practical alpha detection method at room temperature.     

New developments on electrochemical etching processes at the atomic energy organization of Iran

Some highlights of new developments made in our laboratory at the Atomic Energy Organization of Iran on chemical and electrochemical etching (ECE) of polymer track detectors like polycarbonate (PC) are presented. They include introduction of new ECE chamber systems and methods for production of ECE signs and symbols, and a new versatile ECE chamber (VECE) system for multi-purpose, multi-size, and/or multi-shape detector processing; determination of photoneutron doses in and around high-energy X-ray beams of a 20 MV medical accelerator; verification of the Smythe and Mason equations for ECE of tracks in polymers; ECE of alpha and recoil tracks in PC using PMW, PEW and PEMW etchants; introduction of a novel method using ethylene diamine for treatment of PC detectors with its applications, for example in precision removal of surface layers of PC (e.g. bulk removal rates of about 0.04, 0.15, 0.36, 0.66, and 1.33 mm min⁻¹ for 60%, 65%, 70%, 75% and 80% ethylene diamine solution (v/v) in water respectively, with no effects on its transparency), and in significant reduction of background track density of PC detectors, in alpha energy discrimination and alpha spectrometry; and development of an image processing system for track counting and measurements; etc. Some main results are reviewed and discussed.     

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.     

A new method for detection of alpha particles in 1 mm thick polycarbonate detectors using 50 Hz – HV ECE method

Recent studies in our laboratory have proved that electrochemical etching (ECE) of polycarbonate track detectors (PCTD) under 50 Hz – high voltage (HV) field conditions has potentials for time-integrated heavy charged particle detection and dosimetry applications. The rationale in the study is the ECE process of alpha particle tracks in 1 mm thick PCTDs by a 50 Hz – HV generator at optimized ECE conditions. Tracks of 3.2 MeV alpha particles from a collimated beam of an ²⁴¹Am source degraded in air and background tracks were registered. The effects of HV and ECE duration on alpha track registration efficiency and track diameters were studied for 3 sets of 50 Hz – 4, 5 and 6 kV field conditions in a PEW solution (potassium hydroxide, ethanol and water) at 26 °C. The optimized ECE conditions obtained at this stage of development for 1 mm thick PCTDs are 50 Hz – 4 kV in PEW solution at 26 °C for 10 h. Alpha track registration efficiency at 3.2 MeV is about 30% with 37 ± 6 μm mean track diameter. The mean background track density at the above stated optimized conditions is about 571 ± 16 tracks.cm⁻² with a mean diameter of 65 ± 5 μm. All tracks are observable by the unaided eyes. The mean background track diameter is near two times larger than that of alpha particle tracks at the optimum conditions applied; they are easily distinguished against each other. This high background track density while at this stage of development seems a drawback for low dose and low fluence particle applications, it has minimal effects on high fluence ion detection applications. The simple 50 Hz – HV generator used proved to be convenient for efficient alpha track amplifications. Studies are underway for improvement of the method in particular for reducing background track density.     

Ring puckering progressions in the infrared CH2 scissoring region of several deuterated analogs of trimethylene sulfide

Band progressions were observed in the CH₂ scissoring region of the infrared spectra of trimethylene sulfide (TMS) and three of its deuterated analogs (viz., α - d₂, β - d₂, and α, α′ - d₄). These absorptions are assigned to combination tones of CH₂ scissoring fundamentals with the ring puckering mode and its overtones. The scissoring vibrations of the α- and β-methylene groups were identified. Some comments are made regarding the potential governing the puckering mode in the excited states of other vibrations.     

Preparation of SiC nanowires with fins by chemical vapor deposition

SiC nanowires with fins have been prepared by chemical vapor deposition in a vertical vacuum furnace by using a powder mixture of milled Si and SiO₂ and gaseous CH₄ as the raw materials. The products were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). These investigations confirm that the nanowires with fins are cubic β-SiC. The diameter of the fins is about 100–120 nm and the diameter of the inner core stems is about 60–70 nm. The formation process of the β-SiC nanowires with fins is analyzed and discussed briefly.     

Density, viscosity, and excess properties of the binary mixture of diethylene glycol monomethyl ether + water at T = (293.15, 303.15, 313.15, 323.15, 333.15) K under atmospheric pressure

Densities and viscosities have been measured as a function of composition for the binary liquid mixture of diethylene glycol monomethyl ether CH₃O(CH₂)₂O(CH₂)₂OH + water at T = (293.15, 303.15, 313.15, 323.15, 333.15) K under atmospheric pressure. Densities were determined using a capillary pycnometer. Viscosities were measured with Ubbelohde capillary viscometer. From the experimental data, the excess molar volumes V^E, and viscosity deviations δη, and the excess energies of activation for viscous flow ΔG^*E were calculated. These data have been correlated by the Redlich–Kister type equations to obtain their coefficients and standard deviations. The results suggest that molecular interaction between diethylene glycol monomethyl ether and water is strong.     

Dry etching of ITO by magnetic pole enhanced inductively coupled plasma for display and biosensing devices

The dry etching of indium tin oxide (ITO) layers deposited on glass substrates was investigated in a high density inductively coupled plasma (ICP) source. This innovative low pressure plasma source uses a magnetic core in order to concentrate the electromagnetic energy on the plasma and thus provides for higher plasma density and better uniformity. Different gas mixtures were tested containing mainly hydrogen, argon and methane. In Ar/H₂ mixtures and at constant bias voltage (−100 V), the etch rate shows a linear dependence with input power varying the same way as the ion density, which confirms the hypothesis that the etching process is mainly physical. In CH₄/H₂ mixtures, the etch rate goes through a maximum for 10% CH₄ indicating a participation of the radicals to the etching process. However, the etch rate remains quite low with this type of gas mixture (around 10 nm/min) because the etching mechanism appears to be competing with a deposition process. With CH₄/Ar mixtures, a similar feature appeared but the etch rate was much higher, reaching 130 nm/min at 10% of CH₄ in Ar. The increase in etch rate with the addition of a small quantity of methane indicates that the physical etching process is enhanced by a chemical mechanism. The etching process was monitored by optical emission spectroscopy that appeared to be a valuable tool for endpoint detection.     

Track recording properties of soda glass detector for accelerated heavy ions

The etch pit diameters of soda glass detector samples exposed to ₅₄ ¹³² Xe-ions of different energies are measured for different etching times after etching the detector in a ‘new etchant’ free of the adverse effect of the etch product layer. The dependence of track diameter on the energy and on the energy loss, dE/dx of ₅₄ ¹³² Xe-ion in soda glass has been presented. The energy resolution of soda glass and the critical angle for etching of fission fragment tracks in glass detectors have also been determined. The maximum etched track length of ₅₄ ¹³² Xe-ion in soda glass has been compared with the theoretical range. The effects of different annealing conditions on bulk etch rate of glass detector and on diameters of ₅₄ ¹³² Xe-ion tracks have been presented. Experimental results show that there is a decrease in track etch rate, etching efficiency and etchable range of ₅₄ ¹³² Xe-ions with annealing. The annealing of oblique tracks shows that the vertical tracks are more stable than the oblique tracks.     

Reactive ion etching of FePt using inductively coupled plasma

We propose a reactive ion etching (RIE) process of an L1₀-FePt film which is expected as one of the promising materials for the perpendicular magnetic recording media. The etching was carried out using an inductively coupled plasma (ICP) RIE system and an etching gas combination of CH₄/O₂/NH₃ was employed. The L1₀-FePt films were deposited on (1 0 0)-oriented MgO substrates using a magnetron sputtering system. The etching masks of Ti were patterned on the FePt films lithographically. The etch rates of ∼16 and ∼0 nm/min were obtained for the FePt film and the Ti mask, respectively. The atomic force microscopy (AFM) analyses provided the average roughness (R_a) value of 0.95 nm for the etched FePt surface, that is, a very flat etched surface was obtained. Those results show that the highly selective RIE process of L1₀-FePt was successfully realized in the present study.     

Experimental determination of CR-39 counting efficiency to α particles to design the holder of a new radon gas dosemeter

To design a new radon gas dosemeter, the knowledge of the SSNTD α counting efficiency is essential. It depends primarily on the energy and incidence angle into the detector, then on the etching conditions and finally on the track counting procedure. Therefore the elicited efficiency function represents all these factors. The detectors were exposed to α particles at different angles of incidence and energies, by using a ²⁴⁴Cm source; two alternative NaOH solution etching conditions were tested, 6.25 N 70°C at 6 and 12 h, respectively. The counting was performed with a light microscope, 267×, and with an automatic track analysis procedure. The critical incidence angle dependance on energy, in our standard condition (6 h), resulted θ_C(E)=380.0e^{(−0.286•(E−0.050))}(1−e^{(−0.186•(E−0.050))}), and it was used to design our new radon gas holder.     

Electron heating in a submicron-size n GaAs wire

We have studied electron heating in a submicron-size GaAs wire from 4.2 K to 50 K. We find that the energy relaxation rate for the electrons is of the form τ_E⁻¹ = α + βT_eⁿ where α, β are constants and T_e is the electron temperature. We associate the temperature-independent term with a quasi-elastic surface scattering process in which an electron losses 1% of its energy at each collision. The temperature dependent term may be due to electron-phonon scattering. It is possible to fit the data to 2 < n < 3.     

Speeds of sound and isentropic compressibilities of (2-ethoxyethanol + ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol) binary mixtures at 298.15 K

The speed of sound (u) has been obtained at a frequency of 8.3 MHz in {CH₃CH₂OCH₂CH₂OH + HOCH₂CH₂(OCH₂CH₂)_nOH}for n = 0, 1, 2, and 3 over the whole composition range of studied binary liquid mixtures, at T = 298.15 K. The speed of sound values were combined with those of our previous results for densities and viscosities to obtain isentropic compressibility (κ_s), free volume (V_f), and intermolecular free length (L_f). From all these data excess isentropic compressibility (κ_s^E), excess free volume (V_f^E) and excess intermolecular free length (L_f^E) as well as the deviations of the speed of sound (Δu) were obtained. The results are interpreted in terms of molecular interactions occurring in the solutions.     

Eley–Rideal reaction dynamics between O atoms on β-cristobalite (1 0 0) surface: A new interpolated potential energy surface and classical trajectory study

We present a theoretical study of the collisions of atomic oxygen with O-precovered β-cristobalite (1 0 0) surface. We have constructed a multidimensional potential energy surface for the O₂/β-cristobalite (1 0 0) system based mainly on a dense grid of density functional theory points by using the interpolation corrugation-reducing procedure. Classical trajectories have been computed for quasithermal (100–1500 K) and state-specific (e.g., collision energies between 0.01 and 4 eV) conditions of reactants for different O incident angles (θ_v). Atomic sticking and O_2(adsorbed) formation are the main processes, although atomic reflection and Eley–Rideal (ER) reaction (i.e., O₂ gas) are also significant, depending their reaction probabilities on the O incident angle. ER reaction is enhanced by temperature increase, with an activation energy derived from the atomic recombination coefficient (γ_O(θ_v = 0°, T)) equal to 0.24 ± 0.02 eV within the 500–1500 K range, in close agreement with experimental data. Calculated γ_O(θ_v = 0°, T) values compare quite well with available experimental γ_O(T) although a more accurate calculation is proposed. Chemical energy accommodation coefficient β_O(T) is also discussed as a function of ER and other competitive contributions.     

A novel method for observation by unaided eyes of nitrogen ion tracks and angular distribution in a plasma focus device using 50 Hz–HV electrochemically-etched polycarbonate detectors

A novel ion detection method has been developed and studied in this paper for the first time to detect and observe tracks of nitrogen ions and their angular distribution by unaided eyes in the Amirkabir 4 kJ plasma focus device (PFD). The method is based on electrochemical etching (ECE) of nitrogen ion tracks in 1 mm thick large area polycarbonate (PC) detectors. The ECE method employed a specially designed and constructed large area ECE chamber by applying a 50 Hz–high voltage (HV) generator under optimized ECE conditions. The nitrogen ion tracks and angular distribution were efficiently (constructed for this study) amplified to a point observable by the unaided eyes. The beam profile and angular distribution of nitrogen ion tracks in the central axes of the beam and two- and three-dimensional iso-ion track density distributions showing micro-beam spots were determined. The distribution of ion track density along the central axes versus angular position shows double humps around a dip at the 0° angular positions. The method introduced in this paper proved to be quite efficient for ion beam profile and characteristic studies in PFDs with potential for ion detection studies and other relevant dosimetry applications.     

The microwave spectrum of 1-phosphabut-3-ene-1-yne, CH2=CHCP

The new molecule 1-phosphabut-3-ene-1-yne, CH₂=CHCP, produced by pyrolyzing prop-1-ene-3-phosphorus dichloride, CH₂=CHCH₂PCl₂, was detected by microwave spectroscopy. The analysis of the rotational transitions indicates that the molecule is planar with constants: A₀ = 46 694(24), B₀ = 2807.7100(21), and C₀ = 2645.8356(21) MHz. These rotational constants indicate that the structure of the vinyl group is essentially the same as that in CH₂=CHCN and CH₂=CHCCH; r(C---C) = 1.432 Å and (C=C---C) = 123.9°. The dipole moment parameters are μ_A = 1.181(2), μ_B = 0.074(1), and μ = 1.183(2) D. The vibrational satellite spectra for the C---CP bending modes indicate that ν₁₁(a′) = 184 ± 30 cm⁻¹ and ν₁₅(a″) = 263 ± 30 cm⁻¹.     

Theoretical study on the mechanism and kinetics of atmospheric reactions NH2OH + OOH and NH2CH3 + OOH

Mechanism and kinetics of NH₂OH + OOH and NH₂CH₃ + OOH reactions were studied at the B3LYP and M062X levels of theory using the 6-311++G(3df, 3pd) basis set. The NH₂OH + OOH and NH₂CH₃ + OOH reactions proceed through different paths which lead to different products. Transition state structure and activation energy of each path were calculated. The calculated activation energies of hydrogen abstraction reactions were smaller than 25 kcal/mol and of substitution reactions are in the range of 50–70 kcal/mol. The rate constants were calculated using transition state theory (TST) modified for tunneling effect at 273–2000 K.     

Study on nonlinear optical absorption properties of [(CH3)4N]2[Cu(dmit)2] by Z-scan technique

The third-order optical nonlinearities of an organo-metallic compound, [(CH₃)₄N]₂[Cu(dmit)₂] (dmit²⁻=4,5-dithiolate-1,3-dithiole-2-thione), abbreviated as MeCu, dissolved in acetone are characterized by Z-scan technique with picosecond and nanosecond laser pulses in the near-infrared region. Two-photon absorption has been found when the sample solution is irradiated by 40 ps pulse width at 1064 nm and the two-photon absorption (TPA) coefficient β_TPA is 4×10⁻¹³ m/W. While excited by 15 ns laser pulses at 1053 nm, the Z-scan spectra reveal strong reverse saturable absorption (RSA) and the nonlinear absorption coefficient β_RSA is estimated to be as high as 7.07×10⁻¹¹ m/W which is much larger than β_TPA. An explanation for this enhancement is given. All the results suggest that MeCu may be a promising candidate for the application to optical limiting in the near-infrared region.     

The microwave spectrum of phosphabutadiyne, H---CC---CP

A detailed rotational analysis of the microwave spectrum between 26.5 and 40 GHz of phosphaethene, CH₂=PH, has been carried out. This molecule is the simplest member of a new class of unstable molecules—the phosphaalkenes. The species can be produced by pyrolysis of (CH₃)₂PH, CH₃PH₂ and also somewhat more efficiently from Si(CH₃)₃CH₂PH₂. Full first-order centrifugal distortion analyses have been carried out for both ¹²CH₂³¹PH and ¹²CH₂³¹PD yielding: A₀ = 138 503.20(21), B₀ = 16 418.105(26), and C₀ = 14 649.084(28) MHz for ¹²CH₂³¹PH. The 1₀₁-0₀₀ μ_A lines have also been detected for ¹³CH₂PH, cis-CDHPH and trans-CHDPH. These data have enabled an accurate structure determination to be carried out which indicates: r(H_cC) = 1.09 ± 0.015 Å, (H_cCP) = 124.4 ± 0.8°; r(H_tC) = 1.09 ± 0.015 Å, (H_tCP) = 118.4 ± 1.2°; r(CP) = 1.673 ± 0.002 Å, (HCH) = 117.2 ± 1.2°; r(PH) = 1.420 ± 0.006 Å, (CPH) = 97.4 ± 0.4°. The dipole moment components have been determined as μ_A = 0.731 (2), μ_B = 0.470 (3), μ = 0.869 (3) D for CH₂PH; μ_A = 0.710 (2), μ_B = 0.509 (10), μ = 0.874 (7) D for CH₂PD.     

Substituent effects in cooperativity of chalcogen bonds

In the present work, substituent effects on cooperativity of S···N chalcogen bonds are studied in XHS···NCHS···4-Z–Py (X = F, Cl; Z = H, F, OH, CH₃, NH₂, NO₂, and CN; and Py = pyridine) complexes using ab initio calculations. An increased attraction or a positive cooperativity is observed on introduction of a third molecule to the XHS···NCHS and NCHS···4-Z–Py binary systems. The shortening of each chalcogen bond distance in the ternary systems is dependent on the substituent Z and is increased in the order Z = NH₂ > OH > CH₃ > H > F > CN > NO₂. The electronic aspects of the complexes are analysed using molecular electrostatic potential, and the parameters derived from the atoms in molecules and natural bond orbital methodologies. According to interaction energy decomposition analysis, the electrostatic energies are important in the interaction energy of S···N bonds and may be regarded as being responsible for the stability of these complexes.