Tracks Of Ionizing Particles Research Articles

A Critical Review of Radiolysis Issues in Water-Cooled Fission and Fusion Reactors: Part I, Assessment of Radiolysis Models

A critical review is presented on modeling of the radiolysis of the coolant water in nuclear power reactors with emphasis on ITER. The review is presented in two parts: In Part I, we assess previous work in terms of compliance with important chemical principles and conclude that no model proposed to date is completely satisfactory, in this regard. Thus, some reactions that have been proposed in various radiolysis models are not elementary in nature and can be decomposed into two or more elementary reactions, some of which are already included in the models. These reactions must be removed in formulating a viable model. Furthermore, elementary reactions between species of like charge are also commonly included, but they can be discounted upon the basis of Coulombic repulsion under the prevailing conditions (T < 350 °C) and must also be removed. Likewise, it is concluded that the current state of knowledge with respect to radiolytic yields (i.e., G-values) is also unsatisfactory. More work is required to ensure that the yields used in radiolysis models are truly “primary” yields corresponding to a time scale of nanoseconds or less. This is necessary to ensure that the impact of the reactions that occur outside of the spurs (ionizing particle tracks in the medium) are not counted twice. In Part II, the authors review the use of the radiolysis models coupled with electrochemical models to predict the water chemistry, corrosion potential, crack growth rate in Type 304 SS, and accumulated damage in the coolant circuits of boiling water reactors, pressurized water reactors, and the test fusion reactor, ITER. Based on experience with fission reactors, the emphasis should be placed on the control of the electrochemical corrosion potential because it is the parameter that best describes the state of corrosion in coolant circuits.

Luminescent properties of LiF crystals for fluorescent imaging of nuclear particles tracks

Fluorescent nuclear track detectors (FNTD) based on LiF crystals were used for imaging ionizing particle tracks (including high-energy iron ions), by exploiting photoluminescence of radiation induced F2 and F3+ color centers. The relation between photoluminescence emission spectrum of LiF and quality of FNTD images was investigated. It was found that in the applied experimental conditions, the emission within the green band (530 nm, F3+) is very weak compared to the red band (670 nm, F2). The optimum signal to noise ratio was achieved with setting the measuring window at wavelengths longer than 570 nm. Good quality track images in the green spectral range were obtained only for the highest ionization density: for stopping iron ions.Investigations of the bleaching phenomenon revealed a strong decrease of the PL intensity after long excitation times, in the range of several minutes. The amount of this decrease depends on the used excitation power. In the conditions which were typically applied during FNTD measurements the intensity loss was negligible.

Fluctuations of ionizing particle track structure and energy resolution of scintillators

Fluctuations of ionizing particle track structure and energy resolution of scintillators

Is Ionizing Radiation Harmful at any Exposure? An Echo That Continues to Vibrate.

The health risks to humans and non-human biota exposed to low dose ionizing radiation remain ambiguous and are the subject of intense debate. The need to establish risk assessment standards based on the mechanisms underlying low-level radiation exposure has been recognized by regulatory agencies as critical to adequately protect people and to make the most effective use of national resources. Here, the authors briefly review evidence showing that the molecular and biochemical changes induced by low doses of radiation differ from those induced by high doses. In particular, an array of redundant and inter-related mechanisms act in both prokaryotes and eukaryotes to restore DNA integrity following exposures to relatively low doses of sparsely ionizing radiation. Furthermore, the radiation-induced protective mechanisms often overcompensate and minimize the mutagenic potential of the byproducts of normal oxidative metabolism. In contrast to adaptive protection observed at low doses of sparsely ionizing radiation, there is evidence that even a single nuclear traversal by a densely ionizing particle track can trigger harmful effects that spread beyond the traversed cell and induce damaging effects in the nearby bystander cells. In vivo studies examining whether exposure to low dose radiation at younger age modulates the latency of expression of age-related diseases such as cancer, together with studies on the role of genetic susceptibility, will further illuminate the magnitude of risk of exposure to low dose radiation.

Effect of Polarization on Recombination of Charge States in an Ionizing Particle Track in Organic Molecular Crystals

The effect of polarization on the energy exchange of charge states in molecular media is studied for the case when no external electric field exists. Measurements of the light yield of organic molecular crystals excited by ionizing radiations are used to verify theoretical hypotheses. This allows us to carry out experiments for a wide range of the initial density of charge states. The polarization process initiates the primary recombination of hot carriers those are generated in the particle track. This reduces the radioluminescence (RL) energy yield of organic molecular crystals with increasing the specific energy loss of an ionizing particle.

The Study of Neutrino Oscillations with Emulsion Detectors

Particle detectors based on nuclear emulsions contributed to the history of physics with fundamental discoveries. The experiments benefited from the unsurpassed spatial and angular resolution of the devices in the measurement of ionizing particle tracks and in their identification. Despite the decline of the technique around the 1970’s caused by the development of the modern electronic particle detectors, emulsions are still alive today thanks to the vigorous rebirth of the technique that took place around the beginning of the 1990’s, in particular due to the needs of neutrino experiments. This progress involved both the emulsion detectors themselves and the automatic microscopes needed for their optical scanning. Nuclear emulsions have marked the study of neutrino physics, notably in relation to neutrino oscillation experiments and to the related first detection of tau-neutrinos. Relevant applications in this field are reviewed here with a focus on the main projects. An outlook is also given trying to address the main directions of the R&D effort currently in progress and the challenging applications to various fields.

Description of current pulses induced by heavy ions in silicon detectors (II)

Current pulses induced in a silicon detector by 10 different heavy ion species at known energies around 10 A MeV have been sampled in time at high frequency. Their individual average shapes are quite well reproduced by a fit procedure based on our recent charge carrier collection treatment which considers the progressive extraction of the electrons and holes from the high carrier density zone along the ionizing particle track. This region is assumed to present a supplementary dielectric polarization and consequently a disturbed electric field. The influence of the nature of the heavy ion on the values of the three fit parameters is analyzed.

Resemblance of intratrack processes as a common starting point of radiation chemistry and positron, muon, and Mössbauer spectroscopies

A comparison of the yields of final products (57Fe2+, 119Sn2+) of the transformation of Mossbauer nuclei (57Co, 119Sn) in frozen aqueous and alcoholic glassy solutions with the Ps, Ms, and radiolytic-hydrogen formation probabilities in the same liquid media subjected to irradiation with positrons, muons, and fast electrons, respectively shows that the yields of 57Fe2+, 119Sn2+, Ps, Mu, and H2 vary in similar manners with a change in the concentration of electron scavengers or the temperature of the medium. These correlations are a manifestation of a profound similarity between the primary processes occurring in ionizing-particle tracks. Obviously, the recombination of ion-electron pairs inside large swarms (blobs) involving H2O+, e+, μ+, Fe3+, and 119Sn3+, respectively, is the most important process for understanding the formation of H2, Ps, Mu, 57Fe2+, and 119Sn2+.

Sci‐Sat AM (1) General‐08: Study of Characteristics of a New Liquid Ionization Chamber

Liquid ionization chambers (LICs) have characteristics that can remedy some of the drawbacks of air‐filled ionization chamber dosimetry: large sensitive volumes, fluence perturbations, and energy dependence over the clinical range of beam qualities. However, there are significant problems in liquid chambers. High ionization density and low ion mobility leads to high ion recombination rates. In this work, extensive experimental work has been performed to investigate properties of a new liquid chamber, including chamber stability over time, chamber reproducibility, and establishing recombination corrections. The new chamber is called the GLIC‐03 (Guarded Liquid Ionization Chamber), and is filled with isooctane. The sensitive volume is 0.7 mm3. We used the 18 MV beam of a Varian Clinac 21EX linear accelerator. The lowest pulse rate setting was used in order to minimize ion recombination. Measurements were taken in solid water at 15 cm depth, with various field sizes and SSDs. Boag's theory for general collection efficiency for parallel‐plate gas ionization chambers, applied to isooctane in pulsed radiation, was used for recombination corrections. The GLIC‐03 response varied by less than 1% over 10 hours, and was reproducible within 1.5% of the mean over different liquid fills. The collection efficiency decreased with increasing dose per pulse due to general recombination of ions from a larger number of ionizing particle tracks. Recombination corrections were within 1% for low dose rates and high electric field strengths. The establishment of these characteristics in the present work allows us to perform accurate measurements in high gradient non‐equilibrium fields.

TU‐C‐224C‐01: Investigation of Properties of a New Liquid Ionization Chamber

Purpose: Liquid ionization chambers (LICs) have characteristics that can remedy some of the drawbacks of air‐filled ionization chamber dosimetry: large sensitive volumes (i.e. low spatial resolution), fluence perturbations, and energy dependence over the clinical range of beam qualities. However, there are significant problems in liquid chambers. High ionization density and low ion mobility lead to high ion recombination rates. In this work, extensive experimental work has been performed to investigate properties of a new liquid chamber. This includes chamber stability over time, chamber reproducibility, and establishing recombination corrections. Methods and Materials: The new chamber is called the GLIC‐03 (Guarded Liquid Ionization Chamber). The diameter of the collecting electrode is 1.5 mm and the plate separation is 0.4 mm, giving a sensitive volume of 0.7 mm3. The dielectric liquid used is isooctane. We used the 18 MV beam of a Varian Clinac 21EX linear accelerator. The lowest pulse rate setting, 100 MU/min, was used in order to avoid incomplete collection of charge from one pulse before the arrival of the next. Measurements were taken in solid water at 15 cm depth, with various field sizes and SSDs. Boag's theory for general collection efficiency for parallel‐plate gas ionization chambers, applied to isooctane in pulsed radiation, was used for recombination corrections. Results: The GLIC‐03 response varied by less than 1% over 10 hours, and was reproducible within 1.5% of the mean over different liquid fills. The collection efficiency decreased with increasing dose per pulse due to general recombination of ions from a larger number of ionizing particle tracks. Recombination corrections were within 1% for low dose rates and high electric field strengths. Conclusion: The establishment of these characteristics in the present work allows us to perform accurate relative measurements in high gradient non‐equilibrium fields as well as energy dependence investigations.

Determination of through-going tracks’ direction by means of δ-rays in the ICARUS liquid argon time projection chamber

We exploited the crossing muon data, collected in the 50 l liquid argon TPC exposed at the CERN neutrino beam in 1997, to investigate the possibility of identitying the direction of minimum ionizing particle tracks relying only on δ-rays orientation. In this note we show that simple selection criteria allow using δ-rays down to very low energy (few MeV) with high efficiency and no misidentification of their direction. The Monte Carlo prediction – two recognized δ-rays per meter of track – is very well matched by the result of the scanning of the experimental data.

Influence of Radiation Quality on the Yield of DNA Strand Breaks in SV40 DNA Irradiated in Solution

Using highly energetic particles to irradiate plasmid DNA in aerobic aqueous solution, we have compiled an extensive database on how yields of DNA single- and double-strand breaks (SSBs and DSBs) vary with radiation quality. This study was performed in a low-scavenging buffer system and covers a wide range of ion species (helium to uranium) and LETs (5 to 16,000 keV/microm). For LETs up to around 40 keV/microm for SSBs and 400 keV/microm for DSBs, the total energy deposition determines cross section. At higher LET, cross sections level off and individual plateaus for particles of different atomic numbers are observed. For each ion species this is more pronounced and occurs at lower LET for SSBs than for DSBs, leading to an increase in the DSB:SSB ratio from 1:70 for X rays to 1:6 at 500 keV/microm. At this LET, the influence of track structure becomes evident, with high local concentrations of ionization events favoring the formation of DSBs and also intratrack recombination reactions. For lower-energy ions, a saturation in production of measurable DSBs is apparent, due to correlated lesion induction within densely ionizing particle tracks. For very heavy low-energy ions, both SSB and DSB cross sections decrease with particle velocity at nearly constant LET, forming individual hooked curves when plotted as a function of LET.

Tracking with capillaries and liquid scintillator

The technique of glass capillaries filled with liquid scintillator allows the reconstruction of ionizing particle tracks with high spatial resolution. Detectors based on this technique consist of coherent arrays of capillaries having diameters of the order of 20 μ m. Light signals are amplified by an optoelectronic chain composed of a series of image intensifiers: the readout is performed through a CCD. The ongoing research in the field of liquid scintillators has led to excellent results in terms of information density (≥ 5 hits/mm) and radiation resistance (order of 1 MGy). In this paper new results about the effect of ageing and purification of liquid scintillators will be presented. The RD46 collaboration has developed a completely new detector having a readout chain composed of only one image intensifier followed by a new device: a Megapixel Electron Bombarded CCD. First images of neutrino interactions will be shown, together with preliminary measurements of the resolution of the detector.

A new vertex detector made of glass capillaries

We have developed a new detector technique that allows high quality imaging of ionizing particle tracks with very high spatial and time resolution. Central to this technique are liquid-core fibres of about 20 μm diameter read out by an optoelectronic system including a CCD. The fibres act simultaneously as target, detector and light guides. A large-volume prototype, consisting of 5 × 10 5 capillaries of 20 μm diameter and 180 cm length, has been tested in the CERN wide-band neutrino beam. A sample of high-multiplicity neutrino interactions was recorded, demonstrating the imaging quality of this detector. First results from the reconstruction of these events are reported. A track residual of 28 μm and a vertex resolution of 30 μm has been achieved. Future applications of capillary detectors for neutrino and beauty physics are being investigated within the framework of the RD46 collaboration.

Radial energy distribution around ionizing-particle tracks in SiO2

The radial energy distribution around ionizing particle tracks has been found to be important in several phenomena ranging from scintillation efficiency to radiobiological effects. The relevant phenomenological aspects of these experiments, together with the models proposed to explain them, have been reviewed and the dynamics of energy deposition discussed in detail. New data on low-energy electrons stopping power in SiO2 allow us to propose a calculation method of radial energy distribution that compares favourably with the former ones, due to the rejection of a restrictive hypothesis, as the orthogonal emission of δ-rays. Furthermore, our method is consistent with the experimental data on the stopping power of the incident particle.

Hydrogen streamer chamber with localizing admixtures

By introducing hydrocarbon admixtures and small amounts of water vapour to the hydrogen at 1 atm in the self-shunted streamer chambers it is possible to achieve significant improvement in the brightness and localization of the ionizing particle tracks.

The appearance of inclined discharge channels along an ionizing particle track

The formation of discharge channels inclined to the field was investigated in a 2-gap spark chamber with various amplitudes of the high-voltage pulse and with different gas fillings of the chamber. It was shown that the limiting angle for the formation of a spark channel along the chain of electrons produced by ionizing particles increases with the increase of the high-voltage pulse amplitude. The largest iimiting angle for the formation of an inclined streamer channel was observed when the chamber was filled with pure Ne and with Ne--0.5% Ar. When a particle traversed the chamber at an angle larger than 30 un. Concent 85% , distortions of the spark appeared at the electrodes. The cause of the distortions is considered. In a search for a gaseous mixture that couid reduce the memory time, positive experimental data were obtained with the chamber filled with a mixture of 90.5% Ne, 0.4% Ar and 0.1% CH/sub 4/. (A.G.W.)

On the thermochemical action of ionizing radiation

Abstract General characteristics of the thermochemical action of ionizing radiation are considered, namely the initiation of endothermic reactions by local heating up of microvolumes along nuclear particle tracks, and also by the overall heating up of the system irradiated. The following problems are treated: (1) determination of the maximum (quasi-equilibrium) thermochemical action of radiation; (2) determination of the amount of heat spent in an endothermic reaction within a microvolume along the ionizing particle track; (3) determination of the total efficiency for a quasi-stationary case of averaged heating up of a mixture; (4) determination of the energy imparted to the reaction by a narrow beam of charged particles coaxial to a cylindrical volume. The results obtained (especially in Part 2) may also be of some interest for discussing the problems of annealing and retention effects upon nuclear transformations in solids.

Present Status of Image Intensifier Systems

In its application to high-energy physics the luminescent chamber image intensifier system holds forth the promise of combining the advantage of visual measuring techniques with the advantage of the high time resolution of electronic counters. To realize this potential it is necessary that a system satisfy three basic requirements: 1) it should be a competent image-producing device capable of yielding pictures of minimum ionizing particle tracks with small distortion and with sufficient spatial resolution to permit adequate measurements to be made; 2) it should be a gated system with a time resolution of about one microsecond or less; and 3) it should utilize luminescent chambers large enough to allow useful experiments to be done, which demands high efficiency of the image preserving optical coupling between chamber and intensifier. This paper will describe the extent to which presently existing systems meet these requirements and indicate the improvements likely to be forthcoming from developmental efforts now in progress.

The nature, significance, and evaluation of the Schwarzschild-Villiger (SV) effect in photometric procedures.

The Schwarzschild-Villiger effect has been experimentally demonstrated with the optical system used in this laboratory. Using a photographic mosaic specimen as a model, it has been shown that the conclusions of Naora are substantiated and that the SV effect, in large or small magnitude, is always present in optical systems. The theoretical transmission error arising from the presence of the SV effect has been derived for various optical conditions of measurement. The results have been experimentally confirmed. The SV contribution of the substage optics of microspectrophotometers has also been considered. A simple method of evaluating a flare function f(A) is advanced which provides a measure of the SV error present in a system. It is demonstrated that measurements of specimens of optical density less than unity can be made with less than 1 per cent error, when using illuminating beam diameter/specimen diameter ratios of unity and uncoated optical surfaces. For denser specimens it is shown that care must be taken to reduce the illuminating beam/specimen diameter ratio to a value dictated by the magnitude of a flare function f(A), evaluated for a particular optical system, in order to avoid excessive transmission error. It is emphasized that observed densities (transmissions) are not necessarily true densities (transmissions) because of the possibility of SV error. The ambiguity associated with an estimation of stray-light error by means of an opaque object has also been demonstrated. The errors illustrated are not necessarily restricted to microspectrophotometry but may possibly be found in such fields as spectral analysis, the interpretation of x-ray diffraction patterns, the determination of ionizing particle tracks and particle densities in photographic emulsions, and in many other types of photometric analysis.