Total Stopping Research Articles

Effects of Time of Day and Sleep Deprivation on Motorcycle-Driving Performance

The aim of this study was to investigate whether motorcycle handling capabilities – measured by means of the efficiency of emergency manoeuvres – were dependent on prior sleep deprivation and time of day. Twelve male participants voluntarily took part in four test sessions, starting at 6 a.m., 10 a.m., 2 p.m., and 6 p.m., following a night either with or without sleep. Each test session comprised temperature and sleepiness measurements, before three different types of motorcycling tests were initiated: (1) stability in straight ahead riding at low speed (in “slow motion” mode and in “brakes and clutch” mode), (2) emergency braking and (3) crash avoidance tasks performed at 20 kph and 40 kph. The results indicate that motorcycle control at low speed depends on time of day, with an improvement in performance throughout the day. Emergency braking performance is affected at both speeds by time of day, with poorer performance (longer total stopping distance, reaction time and braking distance) in the morning, and also by sleep deprivation, from measurements obtained at 40 kph (incorrect initial speed). Except for a tendency observed after the sleepless night to deviate from the initial speed, it seems that crash avoidance capabilities are quite unaffected by the two disturbance factors. Consequently, some motorcycle handling capabilities (stability at low speed and emergency braking) change in the same way as the diurnal fluctuation observed in body temperature and sleepiness, whereas for others (crash avoidance) the participants were able to maintain their initial performance level despite the high levels of sleepiness recorded after a sleepless night. Motorcycle riders have to be aware that their handling capabilities are limited in the early morning and/or after sleep deprivation. Both these situations can increase the risk of falls and of being involved in a road accident.

Production of excitons in grazing collisions of protons with LiF surfaces: An onion model

In this work we evaluate the production of excitons of a lithium fluoride crystal induced by proton impact in the intermediate and high energy regime (from 100 keV to 1 MeV). A simple model is proposed to account for the influence of the Coulomb grid of the target by dressing crystal ions to transform them in what we call onions. The excited states of these onions can be interpreted as excitons. Within this model, total cross section and stopping power are calculated by using the first Born and the continuum distorted-wave (CDW) eikonal initial-state (EIS) approximations. We found that between 7 and 30 excitons per incident proton are produced in grazing collisions with LiF surfaces, becoming a relevant mechanism of inelastic transitions.

Radiological characterization and water equivalency of genipin gel for x-ray and electron beam dosimetry

The genipin radiochromic gel offers enormous potential as a three-dimensional dosimeter in advanced radiotherapy techniques. We have used several methods (including Monte Carlo simulation), to investigate the water equivalency of genipin gel by characterizing its radiological properties, including mass and electron densities, photon interaction cross sections, mass energy absorption coefficient, effective atomic number, collisional, radiative and total mass stopping powers and electron mass scattering power. Depth doses were also calculated for clinical kilovoltage and megavoltage x-ray beams as well as megavoltage electron beams. The mass density, electron density and effective atomic number of genipin were found to differ from water by less than 2%. For energies below 150 keV, photoelectric absorption cross sections are more than 3% higher than water due to the strong dependence on atomic number. Compton scattering and pair production interaction cross sections for genipin gel differ from water by less than 1%. The mass energy absorption coefficient is approximately 3% higher than water for energies <60 keV due to the dominance of photoelectric absorption in this energy range. The electron mass stopping power and mass scattering power differ from water by approximately 0.3%. X-ray depth dose curves for genipin gel agree to within 1% with those for water. Our results demonstrate that genipin gel can be considered water equivalent for kilovoltage and megavoltage x-ray beam dosimetry. For megavoltage electron beam dosimetry, however, our results suggest that a correction factor may be needed to convert measured dose in genipin gel to that of water, since differences in some radiological properties of up to 3% compared to water are observed. Our results indicate that genipin gel exhibits greater water equivalency than polymer gels and PRESAGE formulations.

Neutron production from ultrashort pulse lasers using linear and circular polarization

An implicit 2D3V particle-in-cell code is used to study proton and deuteron acceleration from an ultrathin CD foil with thickness between 20 and 200 nm using linear and circular polarization. The proton and deuteron beams drive nuclear fusion reactions from converter foils in a pitcher-catcher set-up. The neutron yield for three representative reactions d − d, d − Li, and p − Li has been calculated analytically using the total neutron production cross section and ion stopping power. For linear polarization, maximum normalized neutron yield of Y−d-d=3.4×106, Y−d-Li=3.2×107, and Y−p-Li=6.8×106 neutrons/J laser energy has been calculated at the optimum foil thickness of 50 nm. For circular polarization, the optimum foil thickness is 20 nm, for which the corresponding neutron yields are Y−d-d=1.9×106, Y−d-Li=2.0×107, and Y−p-Li=2.7×106, respectively. The laser polarization strongly affects the neutron production; for our regime, i.e., intensity I=1×1021 W/cm2, pulse duration τFWHM=30 fs, and laser energy ɛlaser=3.8 J, both the conversion efficiency of laser energy into ion kinetic energy and neutron yield are higher for linear polarization. Only for ultrathin (∼20 nm) foils in the radiation pressure acceleration regime, circular and linear polarizations yield comparable results.

A study on the calculation of stopping power and CSDA Range for incident positrons

In this work, we have given a new method to calculate stopping power for incident positrons in a number of different targets. Our method are based on the Gümüş’s method for incident electrons. We have calculated the collisional and radiative stopping power and then found the total stopping power of targets. For collisional stopping power, we used Gümüş’s method for electrons but adapted it to the positrons. Tsai’s method has been used to calculate the radiative stopping power and after the founding the total stopping power with these two values, we used the Continuous Slowing Down Approximation to obtain the range values. Calculation was done for Al, Si, Ag, LiF, CaF 2 and H 2O targets and results were compared with the ICRU 37 report and Penelope 2005 code and found that agreement is less than 10%.

Stopping Power of Electrons and Positrons for C, Al, Cu, Ag, Au, Pb, Fe, U, Ge, Si and Mo

In this paper we present an empirical relation for total stopping power keV in terms of total energy (kineticenergy + rest mass energy) for electrons and positrons from 20 keV to 50000 and have been fitted by a twoparameter approximation. These parameters depend upon the atomic number (Z) of the absorber and areapplicable in absorbers of atomic number from Z=1 to 92. A fairly good agreement has been found between oursimplified values for total stopping power of electrons and positrons for Carbon, Aluminum, Copper, Silver,Gold, Lead, Iron, Uranium, Germanium, Silicon and Molybdenum and that of Berger and Seltzer calculatedvalues.

Microstructure evolution of irradiated tungsten: Crystal effects in He and H implantation as modelled in the Binary Collision Approximation

It is important to develop an understanding of the evolution of W microstructure the conditions the International Thermonuclear Experimental Reactor (ITER) as well as the DEMOnstration Power Plan (DEMO), and modelling techniques can be very helpful. In this paper, the Binary Collision Approximation of Molecular Dynamics as implemented in the Marlowe code is used to model the slowing down of atomic helium and hydrogen on tungsten in the 1–100 keV range. The computed helium and Frenkel Pairs (FP) distributions are then used as input for the simulation of isochronal annealing experiments with an Object Kinetic Monte Carlo (OKMC) model. Parameterisation is discussed in a companion paper to this one. To model inelastic energy losses beyond the Lindhard regime, a new module has been implemented in the Marlowe code which is presented here, along with a discussion on various parameters of the model important in the modelling of channelled trajectories. For a given total inelastic stopping cross section, large differences in low energy channelling ranges are identified depending on whether inelastic energy loss is considered to be purely continuous or to also occur during the atomic collisions. In polycrystals, the channelling probability is shown to be significant over the whole range of slowing down energies considered. Channelling together with short replacement sequences has the effect of reducing the FP production efficiency by more than a factor two in polycrystalline as compared with an hypothetical structureless tungsten. This has a crucial effect on the helium isochronal desorption spectra predicted by the OKMC simulations. Those predicted with structureless tungsten are at variance with experiment, due to the overestimation of He trapping on the radiation induced defects.

SU‐GG‐T‐383: Investigation of Water Equivalency of PRESAGE Dosimeters for Electron Beam Radiotherapy

Purpose: To evaluate water equivalency of PRESAGE dosimeters for electron beam radiotherapy. Method and Materials: In this work, three different PRESAGE polymer dosimeters were evaluated: the currently available PRESAGE as well as two with a new chemical formulation. Total mass stopping powers were calculated over the energy range 10keV‐20MeV using the NIST ESTAR database for the three PRESAGE dosimeters and water. Monte Carlo modeling was used to determine the differences in depth doses between the PRESAGE dosimeters and water for a clinical 12MeV electron beam with a 10×10 cm2 field size. The Monte Carlo calculations were performed using the EGSnrc/BEAMnrc package. The BEAMnrc user code was used to calculate the phase space file for the electron beam. The phase space file generated by BEAMnrc were then used to calculate depth dose curves for each of the three PRESAGE dosimeters and water using the DOSXYZnrc user code. Results: Above 10MeV, total mass stopping power of the existing PRESAGE dosimeter has the highest differences with the value of water due to having the highest effective atomic number. For the calculated relative dose versus water equivalent depth, new PRESAGE dosimeters were in better agreement with the depth doses in water. For depths of less than 2cm water equivalent, the relative dose in water is up to 2% higher than the new PRESAGE dosimeters and 3% higher than the existing PRESAGE dosimeter. This can be attributed to higher collisional stopping power of water than the PRESAGE dosimeters due to its lower effective atomic number than the PRESAGE dosimeters. The maximum energy deposition in the three PRESAGE dosimeters is approximately in the same depth as water (2.7cm depth). Conclusion: The PRESAGE dosimeters with the new chemical formulations are more water equivalent than the existing PRESAGE dosimeter and are suitable for dosimetry of electron beams.

MO‐FF‐A3‐04: Biological Effects of Variable RBE in Different Proton Therapy Delivery Modalities

Purpose: To evaluate and compare dosimetric effects of variable Relative Biological Effectiveness (RBE) in scanning and passive scattering proton therapy treatments. Method and Materials: Three prostate treatment plans for an actual patient treated in our clinic were simulated using a Monte Carlo code MCNPX. Two Intensity Modulated Proton Therapy (IMPT) and one passive scattering (PSPT) treatment plan in a typical, two‐field, lateral, parallel‐opposed configuration were created using a computed tomography (CT) scan of the patient and a commercial treatment planning system (Varian Eclipse). The plans were simulated using the Monte Carlo code MCNPX scoring the total energy deposition and the fluence inside the patient volume using a three‐dimensional mesh tally. The energy deposition and the fluence were used to compute the total unrestricted stopping power, or LET. A space‐variable RBE as a function of LET, dose, and tissue type was calculated using a phenomenological model developed by Wilkens and Oelfke. Results: The RBE‐weighted dose was compared for three treatment plans for constant and variable RBE and significant differences were observed inside the treatment volume. While the three‐dimensional LET distribution in PSPT is relatively easy to predict with simple models, the LET distribution in IMPT can be much more complex and may require a detailed MC simulation in order to be estimated accurately. Conclusion: This example illustrates how very similar physical doses may have significantly different biological effects depending on the modality and the beam configuration of the treatment plan. This approach can be used for biologically based treatment planning and to explain some unexpected treatment toxicities in proton therapy patients.

Deposition Yield and Physical Properties of Carbon Films Deposited by Focused-Ion-Beam Chemical Vapor Deposition

The deposition yield and physical properties of carbon films fabricated by focused-ion-beam (FIB) chemical vapor deposition were examined using several ion beam species of hydrogen, helium, xenon, and gallium. A gas-FIB was generated using an inductively coupled plasma ion source. It was found that the deposition yield is proportional to the total stopping power of the beam that penetrates into the carbon film. The physical properties of the carbon films deposited using gas-FIB are similar to those of films deposited using Ga-FIB, except for the Young's modulus.

Semi-empirical calculation of quenching factors for ions in scintillators

Semi-empirical method of calculation of quenching factors for scintillators is described. It is based on classical Birks formula with the total stopping powers for electrons and ions which are calculated with the ESTAR and SRIM codes, respectively. Method has only one fitting parameter (the Birks factor kB) which can have different values for the same material in different conditions of measurements and data treatment. A hypothesis is used that, once the kB value is obtained by fitting data for particles of one kind and in some energy region (e.g. for a few MeV α particles from internal contamination of a detector), it can be applied to calculate quenching factors for particles of another kind and for another energies (e.g. for low energy nuclear recoils) if all data are measured in the same experimental conditions and are treated in the same way. Applicability of the method is demonstrated on many examples including materials with different mechanisms of scintillation: organic scintillators (solid C 8 H 8 , and liquid C 16 H 18 , C 9 H 12 ); crystal scintillators (pure CdWO 4 , PbWO 4 , ZnWO 4 , CaWO 4 , CeF 3 , and doped CaF 2 (Eu), CsI(Tl), CsI(Na), NaI(Tl)); liquid noble gases (LXe). Estimations of quenching factors for nuclear recoils are also given for some scintillators where experimental data are absent ( CdWO 4 , PbWO 4 , CeF 3 , Bi 4 Ge 3 O 12 , LiF, ZnSe).

Stopping cross sections of 50- to 230-keV nitrogen ions in silicon measured by ion backscattering spectroscopy

The energy dependence of the total stopping cross section of 50- to 230-keV nitrogen ions in silicon (σS(E)) is measured in order to develop the diagnostics of heavy impurities in films of a nanometer thickness by heavy ion backscattering (HIBS) spectroscopy. At ion energies lower than 150 keV, this σS(E) dependence occupies an intermediate position between the dependences given in the SRIM and MSTAR data-bases; at higher energies, our dependence is closer to the former dependence. The estimation of the effect of inelastic processes on the stopping cross section demonstrates that the effect of these processes for nitrogen ions can be neglected when heavy impurities in such films are studied by HIBS.

Rapid gait termination: Effects of age, walking surfaces and footwear characteristics

The aim of this study was to systematically investigate the influence of various walking surfaces and footwear characteristics on the ability to terminate gait rapidly in 10 young and 26 older people. Subjects walked at a self-selected speed in eight randomized shoe conditions (standard versus elevated heel, soft sole, hard sole, high-collar, flared sole, bevelled heel and tread sole) on three surfaces: control, irregular and wet. In response to an audible cue, subjects were required to stop as quickly as possible in three out of eight walking trials in each condition. Time to last foot contact, total stopping time, stopping distance, number of steps to stop, step length and step width post-cue and base of support length at total stop were calculated from kinematic data collected using two CODA scanner units. The older subjects took more time and a longer distance to last foot contact and were more frequently classified as using a three or more-steps stopping strategy compared to the young subjects. The wet surface impeded gait termination, as indicated by greater total stopping time and stopping distance. Subjects required more time to terminate gait in the soft sole shoes compared to the standard shoes. In contrast, the high-collar shoes reduced total stopping time on the wet surface. These findings suggest that older adults have more difficulty terminating gait rapidly than their younger counterparts and that footwear is likely to influence whole-body stability during challenging postural tasks on wet surfaces.

Simplified Analytical Model of Extended Second-Order Lindhard–Scharff–Schiott Theory

The derivation of second-order extended Lindhard–Scharff–Schiott theory (E2LSS) has shown that it is possible to predict accurate ion implantation moment parameters for a projected range of Rp, a straggling parameter ΔRp, and a lateral straggling parameter ΔRpt. Starting from E2LSS theory, we divided the energy region and introduced the ratio rs of the nuclear stopping power Sn to the total stopping power in each energy region, related Sn to energy straggling, and succeeded in obtaining a simplified analytical model. We showed that the range and the ratio rs have a universal dependence on the energy, normalized with respect to the reference energy E1 where Sn equals the electron stopping power at that energy. The simplified model can be applied to any combination of ion and substrate atoms, similarly to E2LSS. The simplified model reproduces E2LSS over a wide range of ion implantation conditions and can be used to generate Gaussian profiles easily and obtain physical intuition for ion implantation profiles.

Calculation of low-Z impurity pellet induced fluxes of charge exchange neutral particles escaping from magnetically confined toroidal plasmas

Measurements of energy- and time-resolved neutral hydrogen and helium fluxes from an impurity pellet ablation cloud, referred to as pellet charge exchange or PCX experiments, can be used to study local fast ion energy distributions in fusion plasmas. The estimation of the local distribution function f(i)(E) of fast ions entering the cloud requires knowledge of both the fraction F(0)(E) of incident ions exiting the cloud as neutral atoms and the attenuation factor A(E,rho) describing the loss of fast atoms in the plasma. Determination of A(E,rho), in turn, requires the total stopping cross section sigma(loss) of neutral atoms in the plasma and the Jacobian reflecting the measurement geometry and the magnetic surface shape. The obtained functions F(0)(E) and A(E,rho) enter multiplicatively into the probability density for escaping neutral particle kinetic energy. A general calculation scheme has been developed and realized as a FORTRAN code, which is to be applied for the calculation of f(i)(E) from PCX experimental results obtained with low-Z impurity pellets.

Cross sections forH+and H atoms colliding with Li in the low-keV-energy region

State-to-state, summed charge transfer and stopping cross sections in collisions of protons and neutral hydrogen atoms with lithium atoms have been studied at collision energies ranging from $10\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}25\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. Cross sections were calculated using electron-nuclear dynamics (END), which is a nonadiabatic, time-dependent, direct approach for the study of ion-atom-molecule interaction processes. Our results show good agreement when compared to available theoretical and experimental data. We find that the charge transfer cross section for protons shows a bump and a maximum as a function of the projectile energy, both of them as a result of the large probability for capture into the projectile $2p$ orbital. The bump corresponds to a projectile energy of approximately ${E}_{p}\ensuremath{\sim}0.7\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$, and results from the electron capture probability in the low impact parameter region of approximately $b\ensuremath{\sim}2.0\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ The maximum occurs at ${E}_{p}\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ as a result of the larger capture probability in the intermediate impact parameter region near $b\ensuremath{\sim}8\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ A similar behavior is found for the electron loss cross section for hydrogen projectiles. We find that the beam charge fraction, for all the energies considered, is nearly neutral. We also find that the largest contribution to the stopping cross section is for impact parameters around $b\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ Finally, we report the total, electronic, and nuclear stopping cross sections to be within a factor of 2 of the reported values in the SRIM 06 code (SRIM stands for stopping and range of ions in matter) and other available experimental data. The largest discrepancy is due to the charge transfer process as well as to a transient $\mathrm{Li}{\mathrm{H}}^{+}$ molecular ion formed in the low projectile energy region.

Dynamics of the generalized 3 x + 1 function determined by its fractal images

Two different complex maps were obtained by generalizing 3 x + 1 function to the complex plane, and fractal images for these two complex maps were constructed by using escape time, stopping time and total stopping time arithmetic. The dynamics of the generalized 3 x + 1 function based on the structural characteristics of the fractal images was studied. We found that: (1) the size and structure of the stable regions, stopping regions, total stopping regions, and divergent regions for the three types of fractal images depend on convergence rate of the map on the x and y axes. (2) The black stable regions constructed, respectively, by escape time and total stopping time are almost overlapped, demonstrating that 3 x + 1 function converged steadily. (3) All of the three fractal images are symmetric to the real axis. The structures on the neighborhood of positive integer number are symmetric to a perpendicular line, which is corresponding to the point or its nearby points on the x axis. And the structures have complicated fractal structure characteristics. These findings indicate that the generalized 3 x + 1 function on integer number and its neighborhood contains plentiful information in the complex plane.

Measurement of the energy deposition profile for 238U ions with specific energy 500 and 950 MeV/u in stainless steel and copper targets

The paper presents the results of precision measurements of the total stopping range and energy deposition function of 238U ions with specific energies E = 500 and 950 MeV/u in stainless steel and copper targets. The experiment was performed at the SIS-18 facility (GSI Darmstadt) in the experimental area Cave A in September 2004–May 2005. The measured energy deposition profiles are compared with calculations using the codes ATIMA, PHITS, SHIELD and SRIM.

Total electron yields and stopping power of protons colliding with NaCl-type insulator surfaces

In this paper we report electron yields and stopping power of protons colliding with surfaces of NaCl-type insulators formed with the alkali-metal ions ${\mathrm{Li}}^{+}$, ${\mathrm{Na}}^{+}$, ${\mathrm{K}}^{+}$, and ${\mathrm{Rb}}^{+}$ and the halides ${\mathrm{F}}^{\ensuremath{-}}$, ${\mathrm{Cl}}^{\ensuremath{-}}$, ${\mathrm{Br}}^{\ensuremath{-}}$, and ${\mathrm{I}}^{\ensuremath{-}}$. We also report fitted models for the static and dynamic polarization potentials of the eight ions of interest. The calculations are carried out within the shellwise local plasma approximation using the Levine-Louie response function, instead of the usual Lindhard one, to account for the ionization energy.

Water equivalence of polymer gel dosimeters

To evaluate the water equivalence and radiation transport properties of polymer gel dosimeters over the wide range of photon and electron energies 14 different types of polymer gels were considered. Their water equivalence was evaluated in terms of effective atomic number ( Z eff ), electron density ( ρ e ), photon mass attenuation coefficient ( μ / ρ ), photon mass energy absorption coefficient ( μ en / ρ ) and total stopping power ( S / ρ ) tot of electrons using the XCOM and the ESTAR database. The study showed that the effective atomic number of polymer gels were very close ( < 1 % ) to that of water except PAGAT, MAGAT and NIPAM which had the variation of 3%, 2% and 3%, respectively. The value of μ / ρ and μ en / ρ for all polymer gels were in close agreement ( < 1 % ) with that of water beyond 80 keV. The value of ( S / ρ ) tot of electrons in polymer gel dosimeters were within 1% agreement with that of water. From the study we conclude that at lower energy ( < 80 keV ) the polymer gel dosimeters cannot be considered water equivalent and study has to be carried out before using the polymer gel for clinical application.