Alpha Particle Tracks Research Articles

Radionuclide-induced evolution of DNA and the origin of life.

Artesian groundwaters of high radionuclide concentration are ubiquitous and may have provided the large, sustained energy sources that were required to drive the multistage process of DNA and primordial cell evolution. The rapid, early development of the genetic code as well as its degeneracy can be attributed to exceptionally high radiation-induced mutation rates in this unique environment. The ability of double-strand DNA to direct enzymatic repair of radiation damage to single strands contributed importantly to its selective evolution. It is postulated that the polymerization of nucleotides took place at elevated temperatures within alpha-particle tracks of high ion and free-radical density, followed by rapid quenching to ambient conditions. It also is evident that radiation resistance and ploidy were important selection factors in cellular evolution.

Charge Carrier Dynamics in Alpha Particle Tracks

An alpha particle event in a semiconductor device is modeled as the instantaneous generation of holes and electrons. The resulting axisymmetric potential of charge carriers is shown to be represented by a similarity solution of the drift-diffusion equations. The ordinary differential equations (ODEs) that arise are integrated numerically, after two quadratures. The results help to clarify the field funneling mechanism in dynamic random access memory (DRAM) storage devices.

The “instantaneous” radial distribution of electric charge, field strength and potential in proton and alpha-particle tracks in dielectrics

Abstract The radial distribution of electric charge, field strength and potential in proton and alpha-particle tracks in dielectrics has been calculated for the first time, NaCl being used as an example.

Unique characteristics of thin film electrochemical etching

The spark counter makes it possible to scan large detector areas and to measure neutron fluences and radon exposures with unique sensitivity. For neutron-induced recoils and for short-etchable tracks (such as alpha-particle tracks in polycarbonate) the spark counter is no more useful. In this case the electrochemical etching process is very often used to facilitate the track counting, in spite of its limitations of high-voltage requirements. In this paper, it will be illustrated how simple is to overcome these shortcomings by thin-film electrochemical etching.

Contribution of Radon Daughters Plated-Out in a Cylindrical Device by Track-Technique

CR-39 plastic nuclear track detector is used to measure the fraction of alpha-particle tracks due to radon daughters activities plated-out on the internal walls of a cylindrical-shaped plastic can. Radium chloride solution is used as a radon source, the exposure time is ranged from 4 hours to 3 days. To assess the percentage of plate-out effect on CR-39 nuclear track detector, two different methods were used. In one experiment, a few circular parallel pairs of CR-39 sheets were hanged in the can device. In the other experiment, the estimation of the plate-out effect has been performed, after exposure to the radon source, by detecting tracks with a second unexposed sheet placed in close contact to the exposed wall and detectors. In the two methods, it was found that the chemically etched tracks related to plated-out activities contribute about 50% of the measured alpha-particles tracks. Der CR-39 Plast-Kernspurdetektor wurde zur Messung des Anteils an Spuren von Alphateilchen verwendet, die sich von den Ra...

Current flow between neighbouring trench cells triggered by alpha particle strikes

The track of an alpha particle that traverses two adjacent trench-type memory cells acts as a conductive channel because of the high concentration of generated carriers so that, where the hit cells have different potential levels, a current flow is triggered which leads to an additional charge collection. The process of charge transfer between the cells owing to alpha particle striking is described by an equivalent circuit, which allows rapid calculation of the current through the parasitic channel, taking into account the total angle and energy spectrum of alpha particle radiation. It is found that the collected charge is appreciably increased only when the trench distance is comparable to the width of the p-n spacecharge region of the cell at high-level potential and when the alpha particle tracks run approximately parallel to the semiconductor surface.

Attenuation of alpha particle track dose for spherical grains

For both TL and ESR dating, it is now well established that the signal induced by alpha particles is not proportional to the energy deposited in a sample, but rather is approximately proportional to the total track length deposited. We present here the expected attenuation of the signal to a spherical grain due to alpha sources both external and internal to the grain. The effect of etching grains is also considered. For an unetched grain, the absorbed track dose due to a single alpha particle energy can be expressed in simple analytical form. These results update and extend the data presented in Bell [ Ancient TL 12 , 4–8 (1980)], which considered deposited energy rather than deposited track length. Because the density of deposition of alpha particle energy increases towards the end of the track, attenuation effects for a given size grain are greater than those presented by Bell.

Evolution of alpha particle tracks in silicon strip detectors

The evolution of the plasma tracks is studied for charged particles incident between strips of a silicon strip detector. The registration of the charges collected by adjacent strips at different times allows to obtain information about behavior of the plasma track. Possibility of the alpha particle coordinate determination with accuracy better then 1 μm for the strip detector with the interstrip distance of 50 μm and the strip width of 200 μm fabricated from silicon with resistivity of 1kOhm·cm is shown. Experimental data show that drift in the nonuniform electric field is essential for the track evolution of excess carriers.

Relative Thermoluminescent Efficiency of LiF:Cu,Mg,P to Alpha Particles: Theory and Experiment

Abstract The relative thermoluminescent response of LiF:Cu,Mg,P to 4 MeV alpha particles has been calculated theoretically using the convolution of the radial dose around the alpha particle track with the gamma generated TL dose response function, with the result ?a? = 0.04 ± 0.01. Experimentally, the alpha particle generated TL signal was measured with the irradiated side both facing and away from the photomultiplier in order to measure TL light self-absorption with the result µd = 1.32 ± 0.03 (1 SD), and ?a? = 0.065 ± 0.01 in reasonable agreement with theory and previous measurements of the fast neutron relative TL response. The very low sensitivity of LiF:Cu,Mg,P to high LET particles is a microdosimetric effect arising from the very rapid saturation of the TL signal at high ionisation density.

Comparison of Particle Tracks Calculated by Monte Carlo Computer Codes with Experimental Tracks Observed with the Harwell Low Pressure Cloud Chamber

Abstract Photographs of the droplets associated with the ionisations caused by charged particle tracks in the Harwell low pressure cloud chamber have been analysed. The radiation types these represent are alpha particles, protons and low energy X rays (carbon and aluminium) in either tissue-equivalent gas or water vapour. The tracks were used to test the validity of two Monte Carlo codes developed by Wilson and Paretzke, namely MOCA14 for the generation of proton and alpha particle tracks, and MOCA8 for the generation of electron tracks. The comparisons showed that the code MOCA14 would appear to be valid for protons with energies greater than about 390 keV, and for alpha particles with energies greater than 1.6 MeV. No disagreement was found between the low energy X ray tracks from the cloud chamber and the tracks calculated from MOCA8, although this comparison was severely limited by droplet diffusion.

Comparison of chemical etching with the alkali-alcohol mixture and the ultrasonic etchings of fission fragment and alpha particle tracks in lexan polycarbonates

Abstract Tracks of the fission fragments from the thermal neutron fission of 235U and of the alpha particles from the (n, alpha) reaction of 6Li registered in Lexan samples respectively and etched by the mixed solution of alcohol and KOH, a short name PEW,4 the ultrasonic and the normal chemical etching processes at 40°C for 40 min and 50 min respectively were compared. The differences of the tracks revealed by these methods have been shown in photomicrographs. To compare the bulk etching rates, the rates of decrease in thickness of the Lexan samples were obtained for the PEW, ultrasonic, and the chemical etchings to be 12, 1.2, and 0.73μm/h respectively for the samples without the neutron irradiations, and 18.8,1.6, and 0.85 μm/h respectively for the samples irradiated by the neutrons fluence of 3 × 1014 neutrons/cm2.

Energy deposition by protons and alpha particles in spherical sites of nanometer to micrometer diameter

Monte Carlo stimulated proton- and alpha-particle tracks in water vapor were used to develop an analytical function for calculating number distributions of ionizations induced in spherical sites. For charged particles crossing the site, Fermi-like functions were used to approximate the ionization distributions. Ionization event distributions due to particles passing outside the site were approximated with an exponentially decreasing function. The function parameters were calculated for protons and alpha particles in the energy range 0.3-5.0 MeV/amu and for site diameters of 1 to 1000 nm. The quality of fit obtained is very good for the particles, energy range and site diameters considered.

Some properties of etched alpha particle tracks in CR-39

Some properties of etched alpha particle tracks in CR-39

Automatic measurement of alpha-particle track density by the spark count method

Automatic measurement of alpha-particle track density by the spark count method

The enhancement of the alpha track revelation in Lexan and LR-115 by ultrasonic etching

The revelation of alpha particle tracks in Lexan polycarbonate and in LR-115 cellulose nitrate has been enhanced by the ultrasonic etching process. Alpha particles from 244Cm and 147Sm radioactive sources were used to irradiate the samples. The energies of the alpha particles were obtained by selecting the source to detector distances to give the required energy attenuations of the alpha particles by the air absorber. Alpha particles of energies from approximate 0.1 MeV to 5.8 MeV have been registered in Lexan and LR-115 and the ultrasonic etching process was used to reveal the tracks. Comparisons of the ultrasonic etching with the standard chemical etching of the samples at the same etching conditions have been made, and the mechanism of the enhancement of track revelation by ultrasonic wave has also been discussed.

A heat deposition model of Josephson junction soft upset rates from alpha-particle irradiation

Experimental “soft” upset rates of Josephson junctions induced by alpha-particle irradiation are analyzed using a heat-deposition model. This model takes into account the full diversion (for T> T c ) or partial diversion (for T< T c ) of current f about the alpha particle track as the alpha particle gives up energy to the superconductor as it traverses the junction. An approximate solution of the heat conduction equation is discussed for such a situation under various boundary conditions describing the heat exchange at interfaces and the low temperature “bath”. The calculations carried out for junctions of 4–110 μm 2 indicate that the heat deposition model generally accounts for the magnitude and shape of the observed upset rate versus bias current, but it is important to take into account heat exchange with the heat bath. The relation of upset rates with heat exchange renders thinner junctions less sensitive to upsets, but similar devices used as particle detectors should be thicker. At bias currents less than or near the threshold bias current predicted by the heating model, this model severely underestimates the number of upsets. Thus the heat-deposition model accounts for the great majority of observed upsets, but some other mechanism initiates such upsets when the bias current is low.

Digital characterization of recoil charged-particle tracks for neutron measurements

We are developing a new optical ionization detector for imaging the track of a charged neutron-recoil particle in a gas. Electrons produced in the path of the recoil particle are excited by an external, high-voltage, rf, electric field of short duration. Their oscillatory motion causes ionization and excitation of nearby gas molecules, which then emit light in subsequent de-excitation. Two digital cameras image the optical radiation across two perpendicular planes and analyze it for the numbers of electrons in various volume elements along the track. These numbers constitute the digital characterization of the track. This information can then be used to infer the energy deposited in the track and the track LET in the gas. We have now observed alpha-particle tracks in a chamber utilizing these principles. The application of such a device for neutron dosimetry and neuron spectrometry will be described.

Glass Track Detectors

A Chemically machinable photosensitive glass was shown to have a high potentiality as a material for new type particle track detectors. Micro crystals grow only along the alpha particle track in the glass through two steps of heat treatment, 500°C for 1h and 600°C for 5min, and the micro crystals grown in the glass are selectively etched in HF 3% solution. The etchpits are observed and counted using either scanning electron micrographs or an optical microscope with TV monitor. The proportionality of the number of etchpits to the alpha particle fluence is fairly good after the correction for the etchpits overlapping.

Electrochemical etching of CR-39 detectors irradiated with alpha particles

Abstract The diameters of electrochemically etched alpha particle tracks of different energies were investigated as a function of etching and pre-etching time and angle of incidence. The measurements were carried out with Pershore Mouldings and MA-ND CR-39 nuclear track detectors. The mean track etching rate, at different particle energies, was determined as a function of pre-etching time. From the measurements of track diameters it is shown that electrochemical etching combined with chemical pre-etching is suitable for determining the energy and/or the incidence angle of alpha particles.

Breakage of Human Interphase Chromosomes by Alpha Particles and X-rays

The technique of premature chromosome condensation (PCC) was used to compare the early formation of chromosome breaks in non-cycling HF19 human diploid fibroblasts when irradiated with slow alpha particles (3.2 MeV, 128 keV micron-1) or 250 kVP X-rays. For both radiations the production of PCC breaks increased approximately linearly with dose. The production coefficient for alpha particles was 12.5 +/- 0.6 per cent per Gy and for X-rays it was 5.8 +/- 0.2 per cell per Gy. Hence, the relative biological effectiveness (RBE) of the alpha particles was 2.16 +/- 0.13. This is smaller than reported values of the RBE for the production of chromosome-type exchange aberrations by slow alpha particles. This implies that there is a difference, spatial or qualitative, in the initial breaks produced by the densely ionizing alpha particle tracks and the more sparsely ionizing electron tracks from the X-rays.