Tracks Of High-energy Electrons Research Articles

Mapping the material distribution of a complex structure in an electron beam

The simulation and analysis of High Energy Physics experiments require a realistic simulation of the detector material and its distribution. The challenge is to describe all active and passive parts of large scale detectors like ATLAS in terms of their size, position and material composition. The common method for estimating the radiation length by weighing individual components, adding up their contributions and averaging the resulting material distribution over extended structures provides a good general estimate, but can deviate significantly from the material actually present. A method has been developed to assess its material distribution with high spatial resolution using the reconstructed scattering angles and hit positions of high energy electron tracks traversing an object under investigation. The study presented here shows measurements for an extended structure with a highly inhomogeneous material distribution. The structure under investigation is an End-of-Substructure-card prototype designed for the ATLAS Inner Tracker strip tracker—a PCB populated with components of a large range of material budgets and sizes. The measurements presented here summarise requirements for data samples and reconstructed electron tracks for reliable image reconstruction of large scale, inhomogeneous samples, choices of pixel sizes compared to the size of features under investigation as well as a bremsstrahlung correction for high material densities and thicknesses.

Gaseous time projection chambers for rare event detection: results from the T-REX project. I. Double beta decay

As part of the T-REX project, a number of R&D and prototyping activities have been carried out during the last years to explore the applicability of gaseous Time Projection Chambers (TPCs) with Micromesh Gas Structures (Micromegas) in rare event searches like double beta decay, axion research and low-mass WIMP searches. In both this and its companion paper, we compile the main results of the project and give an outlook of application prospects for this detection technique. While in the companion paper we focus on axions and WIMPs, in this paper we focus on the results regarding the measurement of the double beta decay (DBD) of 136Xe in a high pressure Xe (HPXe) TPC. Micromegas of the microbulk type have been extensively studied in high pressure Xe and Xe mixtures. Particularly relevant are the results obtained in Xe + trimethylamine (TMA) mixtures, showing very promising results in terms of gain, stability of operation, and energy resolution at high pressures up to 10 bar. The addition of TMA at levels of ∼ 1% reduces electron diffusion by up to a factor of 10 with respect to pure Xe, improving the quality of the topological pattern, with a positive impact on the discrimination capability. Operation with a medium size prototype of 30 cm diameter and 38 cm of drift (holding about 1 kg of Xe at 10 bar in the fiducial volume, enough to contain high energy electron tracks in the detector volume) has allowed to test the detection concept in realistic experimental conditions. Microbulk Micromegas are able to image the DBD ionization signature with high quality while, at the same time, measuring its energy deposition with a resolution of at least a ∼ 3% FWHM @ Qββ. This value was experimentally demonstrated for high-energy extended tracks at 10 bar, and is probably improvable down to the ∼ 1% FWHM levels as extrapolated from low energy events. In addition, first results on the topological signature information (one straggling track ending in two blobs) show promising background discrimination capabilities out of reach of other experimental implementations. Moreover, microbulk Micromegas have very low levels of intrinsic radioactivity, and offer cost-effective scaling-up options. All these results demonstrate that Micromegas-read HPXe TPC remains a very competitive technique for the next generation DBD experiments.

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

A high-energy electron in condensed matter deposits energy by creation of electron-hole pairs whose density generally increases as the electron slows, reaching the order of ${10}^{20}$ eh/${\mathrm{cm}}^{3}$ near the end of its track. The subsequent interactions of the electrons and holes include nonlinear rate terms and transport as first hot and then thermalized carriers in the nanometer-scale radial dimension of the track. Charge separation and strong radial electric fields occur in a material such as CsI with contrasting diffusion rates of self-trapped holes and hot electrons. Eventual radiative recombination has a nonlinear relation to the primary electron energy because of these interactions. This so-called intrinsic nonproportionality of electron response limits the achievable energy resolution of a given scintillation radiation detector material. We use a system of coupled transport and rate equations to describe a pure host (three equations) and one dopant (four more equations per dopant). Applying it first to the experimentally well-characterized system of CsI and CsI:Tl in this work, we use results of picosecond absorption spectroscopy, interband $Z$-scan measurements of nonlinear rate constants, and other experiments and calculations to determine most of the more than 20 rate and transport coefficients required for modeling. The model is solved in a track environment approximated as cylindrical and is compared to the proportionality curve and total light yield of undoped CsI at temperatures of 295 and 100 K, as well as thallium dopant in CsI:Tl at 295 K. With this degree of validation, the space and time distributions of carriers and excitons, both untrapped and trapped, are examined within the model to gain an understanding of the main competitions controlling the nonproportionality of response.

On (3)H beta-particle and (60)Co gamma irradiation of aqueous systems.

The chemistry of water and aqueous solutions is very different after irradiation with (3)H beta particles and high-energy electrons or (60)Co gamma rays. The greater the linear energy transfer (LET) of the medium for (3)H beta particles compared to high-energy electrons or (60)Co gamma rays leads to an increased local concentration of reactants. There is an increased amount of intratrack chemistry, which reduces the escape yield of and OH by about 50%, but increases the yield of H(2) by about 50% and of H(2)O(2) by about 35%. Analysis of stochastic-diffusion kinetic calculations employing simulated track structures reveals that the yield of H(2) produced by diffusion-kinetic processes increases significantly for (3)H beta particles compared to (60)Co gamma radiation, while production of H(2) by sub-picosecond processes is essentially the same. In both (3)H beta-particle and (60)Co gamma radiolysis, the reactions + and are equally important in the production of H(2). In the former case, each reaction has a yield of approximately 0.18, and in the latter a yield of approximately 0.08. In neutral water, the reaction (H + H) is negligible. The yield of Fe(III) in (3)H beta-particle radiolysis of the Fricke dosimeter is much smaller than in radiolysis with more energetic electrons. Simulations show that this change is primarily due to the reduced escape yield of H, formed from the scavenging of by the bulk H(3)O(+) of the acid. The chemical differences observed in experiments, and in calculations, reflect the underlying structure of the electron tracks: Examination of the track structure simulations demonstrates that primary events are considerably more well-separated in high-energy electron tracks compared to (3)H beta-particle tracks.

Computer simulation of charge recombination in model tracks of high-energy electrons in nonpolar liquids; kinetics and escape

The evolution in time of the recombination of ions in model tracks and spurs produced by high-energy electrons was calculated by computer simulation of the diffusion and drift of the ions in each other's Coulomb field. Tracks of high-energy electrons are subdivided into tracks of secondary electrons that can be considered as independent one from another. Energy losses smaller than 50 or 100 keV are assumed to give rise to correlated groups of charges. The diffusion and recombination in the groups is directly simulated. For electrons with an initial energy in excess of 50 or 100 keV calculations are performed by summing the contributions of energy losses below this value. The nonhomogeneous kinetics of the charge recombination has been studied for both the short-time and long-time domains. The survival probability as a function of time, W( t), has been calculated for the charged species in electron tracks with different initial energy of the electron, for gaussian and exponential distributions of the initial distance between the positive and the negative species. The behaviour of W( t) and comparisons with the available short-time experimental data do not provide any clear distinction between the two distributions. The behaviour of W( t) at long times was also investigated in detail. The region of applicability of the theoretical limiting behaviour t −0.5 was checked and found to be very small. The experimentally observed behaviour t −0.6 was critically examined. Results are obtained for the probability of ion escape from recombination in the track as a function of the initial energy of the electron. The experimentally observed decrease of the yield of escape with decreasing energy of the electron for two liquids is adequately explained.

Computer Simulation of the Ion Escape from High-Energy Electron Tracks in Nonpolar Liquids

The number of ions escaping from recombination in high-energy electron tracks in saturated hydrocarbon liquids is calculated and compared with experimental results from the literature. The initial ...

Kinetics of charge recombination in high-energy electron tracks in nonpolar liqiuds, calculated by computer simulation. The survival of the charged species at long times

The nonhomogeneous kinetics of the charge recombination in tracks of high-energy electrons in nonpolar liquids has been studied by computer simulation. The survival probability as a function of time, W( t), has been calculated for the charged species in a 1 MeV electron track for Gaussian and exponential distributions of the initial distance between the positive and the negative species. The contributions of groups and tracks resulting from different energy losses in the track of the 1 MeV electron have been considered also. The behaviour of W( t) at long times is investigated in detail. The region of applicability of the theoretical limiting behaviour t -0.5 is checked and found to be very small. The experimentally observed behaviour t -0.6 is critically examined, and the relation with the spatial distribution of the charged species in the track is discussed.

Singlet and triplet excited-state formation in high-energy electron tracks in liquid cis- and trans-decalin as studied by product formation in radiolysis and photolysis

The yields of products formed as a result of irradiation of liquid cis- and trans-decalin with γ-rays and 3 MeV electrons as well as with 7.6 eV photons have been determined by means of gas–liquid chromatography (GLC). The major products for both cis- and trans-decalin are hydrogen, unsaturated C10 products and dimers; in the case of cis-decalin, cis–trans isomerization takes place via a chain reaction. Singlet and triplet excited states are formed by direct excitation and by charge recombination in the tracks of high-energy electrons. The product formation resulting from the singlets is determined by the photolysis. From a knowledge of the total yield of singlets from the radiolysis, the contribution of the singlet excited states to product formation during radiolysis is calculated and the remaining products are assigned to the triplets.For the sum of the yields of singlets and triplets a value of 6.4 (100 eV)–1(= 6.6 × 10–7 mol J–1) is found for cis-decalin and 6.0 (100 eV)–1(= 6.2 × 10–7 mol J–1) for trans-decalin and for the singlet fractions 0.53 and 0.47 in cis- and trans-decalin, respectively. The probability of C—H bond breakage in the singlet and triplet states is 0.42 and 0.82, respectively, for cis-decalin and 0.50 and 0.94, respectively, for trans-decalin.

Formation of singlet and triplet excited states on charge recombination in tracks of high-energy electrons in nonpolar liquids. A computer simulation study

The diffusion and drift in each other's field of the ions and electrons in the tracks of high-energy electrons in nonpolar liquids is simulated by computer and the formations of singlet and triplet excited states on charge recombination is studied. Tracks of high-energy electrons are subdivided into tracks of secondary electrons that can be considered as independent from one another. Energy losses smaller than 50 or 100 keV are assumed to give rise to correlated groups of charges. The formation of singlets, resulting from the recombination of charges in these groups, is calculated as a function of the size of the energy loss. For electrons with an initial energy in excess of 50 or 100 keV the probability of singlet formation is calculated by summing the contributions of the energy losses below this value. The probability of singlet formation shows a pronounced energy dependence. Also the time evolution of the singlet formation is considered.

Computer simulation study of spatial distribution of the ions and electrons in tracks of high-energy electrons and the effect on the charge recombination

The diffusion and drift in each other's field of the ions and electrons in the tracks of high-energy electrons in nonpolar liquids are computer simulated, and the nonhomogeneous kinetics of the recombination of the charged species is calculated. Results are presented for the probability of escape from recombination in the track as a function of the initial energy of the electron. The experimentally observed decrease of the yield of escape with decreasing energy of the electron for two liquids is adequately explained

Formation of singlet and triplet excited states by recombination of ions in tracks of high-energy electrons in nonpolar liquids. A computer simulation study

The evolution in time of the recombination of ions in tracks produced by high-energy electrons was calculated by computer simulation of the diffusion and drift of the ions in each other's Coulumb field. The formation of singlet and triplet excited states on ion recombination was taken into account in the simulation codes. The time dependent probability f( t) of the singlet production on ion recombination was calculated for different groups of ion pairs. It was found that the initial geometry of the ionic cluster is of primary importance for the time evolution and asymptotic value of the probability f( t). Calculations have been carried out for ion groups of different sizes corresponding to different energy losses, using a simplified model for the initial configuration. The contributions of the ions in different clusters to the over-all kinetics of the singlet and triplet production in a 200 keV electron track were analyzed and the weighted averages for f( t) were obtained.

Computer simulation of the recombination of the ions in tracks of high-energy electrons in nonpolar liquids

The evolution in time of the recombination of the ions in tracks of high-energy electrons in nonpolar liquids is calculated by computer simulation of the diffusion and drift of the ions in each other's Coulomb field. The track of the fast electron is subdivided into groups of ion pairs that may be considered independent of one another. Calculations have been carried out for groups of various sizes corresponding to different energy losses, using a simplified model for the initial configuration. The contribution of the ions in various cluster sizes to the over-all kinetics and escape of the ions in a fast electron track is analyzed.

Triplet formation in the ion recombination in irradiated liquids

The formation of singlet and triplet excited stages in the ion recombination in groups of oppositely charged ions (or positive ions and electrons) in nonpolar liquids, as occurs in the tracks of high energy electrons, is considered. Theoretical studies on triplet formation in groups of ion pairs have thus far concentrated on the case where recombination of the negative ions with any of the positive ions in the group is equally probable (random recombination). In this paper the probability for geminate recombination (electron and parent positive ion) vs cross-recombination (an electron with a positive ion other than its parent ion) in multiple ion pair groups is calculated by computer simulation and the effect of the initial spatial configuration of the charged species is investigated. It is also shown explicitly that the probability for singlet formation as a result of cross recombination is equal to 1 4 , when spin relaxation by magnetic interaction with the medium and by exchange interaction can be neglected. The effect of the preferential recombination on the singlet formation probability is illustrated and recent experimental results on singlet to triplet ratios are discussed.

Investigation of electron runaway in lightning

Electron-sensitive photographic emulsions were placed at points where lightning strokes occurred to a 300-m tower. No tracks of high-energy electrons, which might be associated with lightning, were observed. A search for radioactivity also showed no effects of lightning. (auth)