Microdosimetry of electrons in liquid water using the low-energy models of Geant4

The biological effects of ionizing radiation at the cellular level are frequently studied using the well-known formalism of microdosimetry, which provides a quantitative description of the stochastic aspects of energy deposition in irradiated media. Energy deposition can be simulated using Monte Carlo codes, some adopting a computationally efficient condensed-history approach, while others follow a more detailed track-structure approach. In this work, we present the simulation of microdosimetry spectra and related quantities (frequency-mean and dose-mean lineal energies) for incident monoenergetic electrons (50 eV-10 keV) in spheres of liquid water with dimensions comparable to the size of biological targets: base pairs (2 nm diameter), nucleosomes (10 nm), chromatin fibres (30 nm) and chromosomes (300 nm). Simulations are performed using the condensed-history low-energy physics models ( Livermore and Penelope ) and the track-structure Geant4-DNA physics models, available in the Geant4 Monte Carlo simulation toolkit. The spectra are compared and the influence of simulation parameters and different physics models, with emphasis on recent developments, is discussed, underlining the suitability of Geant4-DNA models for microdosimetry simulations. It is further shown that with an appropriate choice of simulation parameters, condensed-history transport may yield reasonable results for sphere sizes as small as a few tens of a nanometer

Electrocaloric Response of the Dense Ferroelectric Nanocomposites

Using the Landau-Ginzburg-Devonshire approach and effective media models, we calculated the spontaneous polarization, dielectric, pyroelectric, and electrocaloric properties of BaTiO$_3$ core-shell nanoparticles. We predict that the synergy of size effects and Vegard stresses can significantly improve the electrocaloric cooling (2- 7 times) of the BaTiO$_3$ nanoparticles with diameters (10-100) nm stretched by (1-3)% in comparison with a bulk BaTiO$_3$. To compare with the proposed and other known models, we measured the capacitance-voltage and current-voltage characteristics of the dense nanocomposites consisting of (28 -35) vol.% of the BaTiO$_3$ nanoparticles incorporated in the poly-vinyl-butyral and ethyl-cellulose polymers covered by Ag electrodes. We determined experimentally the effective dielectric permittivity and losses of the dense composites at room temperature. According to our analysis, to reach the maximal electrocaloric response of the core-shell ferroelectric nanoparticles incorporated in different polymers, the dense composites should be prepared with the nanoparticles volume ratio of more than 25 % and fillers with low heat mass and conductance, such as Ag nanoparticles, which facilitate the heat transfer from the ferroelectric nanoparticles to the polymer matrix. In general, the core-shell ferroelectric nanoparticles spontaneously stressed by elastic defects, such as oxygen vacancies or any other elastic dipoles, which create a strong chemical pressure, are relevant fillers for electrocaloric nanocomposites suitable for advanced applications as nano-coolers.Comment: 38 pages, including 10 figures and 2 appendixe

A Roadmap for HEP Software and Computing R&D for the 2020s

Particle physics has an ambitious and broad experimental programme for the coming decades. This programme requires large investments in detector hardware, either to build new facilities and experiments, or to upgrade existing ones. Similarly, it requires commensurate investment in the R&D of software to acquire, manage, process, and analyse the shear amounts of data to be recorded. In planning for the HL-LHC in particular, it is critical that all of the collaborating stakeholders agree on the software goals and priorities, and that the efforts complement each other. In this spirit, this white paper describes the R&D activities required to prepare for this software upgrade.Peer reviewe

Hard color-singlet exchange in dijet events in proton-proton collisions at root s=13 TeV

Events where the two leading jets are separated by a pseudorapidity interval devoid of particle activity, known as jet-gap-jet events, are studied in proton-proton collisions at root s = 13 TeV. The signature is expected from hard color-singlet exchange. Each of the highest transverse momentum (p(T)) jets must have p(T)(jet) > 40 GeV and pseudorapidity 1.4 0.2 GeV in the interval vertical bar eta vertical bar < 1 between the jets are observed in excess of calculations that assume only color-exchange. The fraction of events produced via color-singlet exchange, f(CSE), is measured as a function of p(T)(jet2), the pseudorapidity difference between the two leading jets, and the azimuthal angular separation between the two leading jets. The fraction f(CSE) has values of 0.4-1.0%. The results are compared with previous measurements and with predictions from perturbative quantum chromodynamics. In addition, the first study of jet-gap-jet events detected in association with an intact proton using a subsample of events with an integrated luminosity of 0.40 pb(-1) is presented. The intact protons are detected with the Roman pot detectors of the TOTEM experiment. The f(CSE) in this sample is 2.91 +/- 0.70(stat)(-1.01)(+1.08)(syst) times larger than that for inclusive dijet production in dijets with similar kinematics.Peer reviewe

Latest Geant4 developments for PIXE applications

We describe the recent inclusion in Geant4 of state-of-the-art proton and alpha particle shell ionisation cross sections based on the ECPSSR approach as calculated by Cohen et al., called here ANSTO ECPSSR. The new ionisation cross sections have been integrated into Geant4. We present a comparison of the fluorescence X-ray spectra generated by the ANSTO ECPSSR set of cross sections and, alternatively, the currently available sets of Geant4 PIXE cross sections. The comparisons are performed for a large set of sample materials spanning a broad range of atomic numbers. The two alternative PIXE cross sections approaches (Geant4 and ANSTO) have been compared to existing experimental measurements performed at ANSTO with gold, tantalum and cerium targets of interest for nanomedicine applications. The results show that, while the alternative approaches produce equivalent results for vacancies generated in the K and L shell, differences are evident in the case of M shell vacancies. This work represents the next step in the effort to improve the Geant4 modelling of the atomic relaxation and provide recommended approaches to the Geant4 user community. This new Geant4 development is of interest for applications spanning from life and space to environmental science

The process of recovery of cell membrane damage produced by the lowlevel microwave radiation

The process of cell membrane recovery after the influence of microwave radiation (f = 36.64 GHz, E = 10, 100, 400 μW/cm2, irradiation time 10 s) on human buccal epithelium cells was investigated. The stainability of cells with indigo carmine (5 mM) or trypan blue (0.5%) after 5 min of staining was investigated. It was shown irradiation to be induced decrease of percentage of unstained cells. Recovery of cell membrane permeability after microwave irradiation was shown. Cell recovery after microwave irradiation of low intensity (10 μW/cm2) was shown after 1 h. Microwave irradiation of higher intensity (100, 400 μW/cm2) induced more strongly effects of cell membrane permeability. Cell recovery after microwave irradiation of higher intensity was shown after 3 h. For the first time recovery of cell membrane after microwave irradiation of low intensity was shown

Influence of track structure and condensed history physics models of Geant4 to nanoscale electron transport in liquid water

The Geant4 toolkit offers a range of electromagnetic (EM) models for simulating the transport of charged particles down to sub-keV energies. They can be divided to condensed-history (CH) models (like the Livermore and Penelope models) and the track-structure (TS) models included in the Geant4-DNA low-energy extension of Geant4. Although TS models are considered the state-of-the-art for nanoscale electron transport, they are difficult to develop, computationally intensive, and commonly tailored to a single medium (e.g., water) which prohibits their use in a wide range of applications. Thus, the use of CH models down to sub-keV energies is particularly intriguing in the context of general-purpose Monte Carlo codes. The aim of the present work is to compare the performance of the CH models of Geant4 against the recently implemented TS models of Geant4-DNA for nanoscale electron transport. Calculations are presented for two fundamental quantities, the dose-point-kernel and the microdosimetric lineal energy. The influence of user-defined simulation parameters (tracking and production cuts, and maximum step size) on the above calculations is also examined. It is shown that Livermore offers the best performance among the CH models of Geant4 for nanoscale electron transport. However, even under optimally-chosen simulation parameters, the differences between the CH and TS models examined may be sizeable for low energy electrons (\u3c1 keV) and/or nanometer size targets (\u3c100 nm)

Investigation of track structure and condensed history physics models for applications in radiation dosimetry on a micro and nano scale in Geant4

Monte Carlo methods apply various physical models, either condensed history (CH) or track structure (TS), to simulate the passage of radiation through matter. Both CH and TS models continue to be applied to radiation dosimetry investigations on a micro and nano scale. However, as there has been no systematic comparison of the use of these models for such applications there can be no quantification of the uncertainty that is being introduced by the choice of physics model. A comparison of CH and TS models available in Geant4, along with a quantification of the differences in calculated quantities on a micro and nano scale, has been undertaken in this study. A sphere of liquid water was simulated, with an incident beam of monoenergetic electrons with kinetic energy between 50 eV and 10 keV. The energy deposition (typical of microdosimetry) and number of ionisations (typical of nanodosimetry), per incident particle, were recorded in a water sphere with diameter varying between 1 nm and 1 m. The simulations were repeated using the following physics packages: Livermore (CH), Penelope (CH) and Geant4-DNA (TS). Results indicated that substantial differences were present between calculated physical quantities, depending on the physics model, target diameter and ratio of the target diameter and mean track length of the incident electron. In the case of the smallest targets, the calculated energy deposition was higher when using the CH models, while the number of ionisations was typically underestimated. In larger targets the energy deposition was in good agreement for all physics models, however the number of ionisations was significantly underestimated by the CH approach, in some cases by almost two orders of magnitude. Regarding CH models, the parameter that had the greatest impact on the results was found to be the threshold of production of secondary particles; when this was minimised the CH and TS results showed the best agreement

Simulation of microwave exposure of human cells by electromagnetic field of EMF band

To implement a novel method of investigation of electromagnetic field action on state of cell nucleus the simulation of irradiation of the cells of human buccal epithelium by electromagnetic field of EMF band is carried out. The cells were exposed to radiation of frequency f = 36.64 GHz, with power densities W = 10–1, 1 and 4 W/m2during 10 seconds. To answer on the question of existence of nonthermal biological effect of electromagnetic field onto living cells the specific absorption rate (SAR) of a solution that contained cells is calculated. The numerical simulation based on FDTD method permitted to take into account different parts of experimental setup to obtain real distribution of electromagnetic field inside irradiated solution

Drosophila melanogaster viability and mutability under the influence of low energy microwave monochromatic and ultra wideband impulse field

The influence of microwave radiation (int = 35 GHz, intensity P = 30, 70, 180, 265 mW /cm2) and ultra wideband irradiation at irradiation intensity of 10-5, 10-4, 10-3, and 10-2 W/cm2 on stocks of Drosophila melanogaster was investigated. Irradiation was performed on the stage of egg &lt; exposure time was 10 sec... Irradiation by monochromatic radiation (35 GHz) of intensity 70, 180 and 265 mW/cm2 negatively influences upon the viability of Drosophila. No viability decrease registered after ultra wideband irradiation. Monochromatic microwave radiation induced dominant lethal mutations (DLM). The effect of radiation depends on state of polarizations of radiation. Linear polarized radiation and right circular polarized radiation induce more DLM than left circular polarized radiation. Ultra wideband .impulse radiation induced no significant decrease of Drosophila viability. Incidence of DLM increased after ultra wideband impulse irradiation at the intensity 10-4 and 10-2 W/cm2