Increasing Beam Energy Research Articles

Inference on fission timescale from neutron multiplicity measurement in 18O + 184W

The pre-scission and post-scission neutron multiplicities are measured for the 18O + 184W reaction in the excitation energy range of 67.23–76.37 MeV. Langevin dynamical calculations are performed to infer the energy dependence of fission decay time in compliance with the measured neutron multiplicities. Different models for nuclear dissipation are employed for this purpose. Fission process is usually expected to be faster at a higher beam energy. However, we found an enhancement in the average fission time as the incident beam energy increases. It happens because a higher excitation energy helps more neutrons to evaporate that eventually stabilizes the system against fission. The competition between fission and neutron evaporation delicately depends on the available excitation energy and it is explained here with the help of the partial fission yields contributed by the different isotopes of the primary compound nucleus.

Fusion studies in O16+Nd142,150 reactions at energies near the Coulomb barrier

Background: Enhancement in fusion cross sections over one-dimensional barrier penetration model (1D-BPM) predictions has been observed at sub-barrier energies owing to the coupling of various internal degrees of freedom to the relative motion. On the other hand, hindrance in fusion is noticed at energies well above the barrier in a few cases.Purpose: The purpose is to probe the dynamics of heavy ion fusion at energies below and well above the Coulomb barrier.Methods: Fusion excitation functions for the $^{16}\mathrm{O}+^{142,150}\mathrm{Nd}$ reactions are measured using the Heavy Ion Reaction Analyzer (HIRA) at IUAC, New Delhi. Measurements have been performed in the range $12%$ below to $50%$ above the Coulomb barrier for both systems. The measured fusion cross sections are compared with coupled channels calculations using ccfull code. The cross sections are also compared with reactions using $^{16}\mathrm{O}$ beams with other isotopes of Nd to explore the systematic behavior of fusion.Results: Compared with 1D-BPM predictions, fusion enhancement is observed in both $^{16}\mathrm{O}+^{142}\mathrm{Nd}$ and $^{16}\mathrm{O}+^{150}\mathrm{Nd}$ reactions at below-barrier energies, with the latter reaction showing a higher enhancement. Coupled channels calculations incorporating the collective excitations of the target nuclei reproduce the fusion cross sections in both reactions. The collective excitations of the projectile nucleus do not seem to contribute to the observed fusion enhancement. Calculations using Aky\"uz-Winther potential parameters fail to reproduce the fusion cross sections at energies well above the barrier.Conclusions: Fusion enhancement is observed in both reactions studied. Degree of enhancement of sub-barrier fusion cross section is larger for the reaction using $^{150}\mathrm{Nd}$ target. Fusion hindrance is observed in both reactions at very high energies. The hindrance seems to increase with increasing beam energy. Larger value of diffuseness parameter compared with the value consistent with elastic-scattering measurements is required to reproduce the fusion excitation function at energies well above the barrier. This could be a strong indication of dynamical effects in fusion at very high energies.

Electrostatic Ion-cyclotron Wave Excitation by a Gyrating Ion Beam in a Magnetized Plasma Containing Heavy Positive Ions

In the present paper, we have developed a theoretical model of cylindrical magnetized plasma column consisting of electrons, ions & heavy positive ion species. A gyrating ion beam of potassium having radius ~1.5 cm and energy 10eV is launched through one end of the cylinder parallel to the static magnetic field and the electrostatic ion cyclotron wave is assumed to propagate nearly perpendicular to the magnetic field. The presence of heavy positive ions in the collisionless magnetized plasma decreases the critical drift for the excitation of EIC waves and hence the injected beam drives the electrostatic ion cyclotron (EIC) waves to instability through Cerenkov interaction. Therefore, the plasma is observed to contains two excited EIC wave modes; a (light positive) ion mode and a (heavy positive) ion mode. The frequencies and growth rates for both the positive unstable modes are worked out using fluid theory for the typical existing experimental parameters which are found to increase with the increase in ion beam energy and beam density. It is also observed that the unstable wave frequency and growth rate for both the modes increases with the increase in relative ion concentration of and heavy positive ions respectively. Magnetic field is also one of the important factors which influence the plasma instabilities appreciably. As the magnetic field increases, the frequency of both the ion modes increases linearly.

X-Rays through the Looking Glass: Mobile Imaging Dosimetry and Image Quality of Suspected COVID-19 Patients

Background: This paper aims to evaluate the clinical utility and radiation dosimetry, for the mobile X-ray imaging of patients with known or suspected infectious diseases, through the window of an isolation room. The suitability of this technique for imaging coronavirus disease 2019 (COVID-19) patients is of particular focus here, although it is expected to have equal relevance to many infectious respiratory disease outbreaks.Materials and Methods: Two exposure levels were examined, a “typical” mobile exposure of 100 kVp/1.6 mAs and a “high” exposure of 120 kVp/5 mAs. Exposures of an anthropomorphic phantom were made, with and without a glass window present in the beam. The resultant phantom images were provided to experienced radiographers for image quality evaluation, using a Likert scale to rate the anatomical structure visibility.Results and Discussion: The incident air kerma doubled using the high exposure technique, from 29.47 μGy to 67.82 μGy and scattered radiation inside and outside the room increased. Despite an increase in beam energy, high exposure technique images received higher image quality scores than images acquired using lower exposure settings.Conclusion: Increased scattered radiation was very low and can be further mitigated by ensuring surrounding staff are appropriately distanced from both the patient and X-ray tube. Although an increase in incident air kerma was observed, practical advantages in infection control and personal protective equipment conservation were identified. Sites are encouraged to consider the use of this technique where appropriate, following the completion of standard justification practices.

Simulations of the radial electric field induced by neutral beam injection in a tokamak

A model based on Poisson’s equation has been proposed to study the radial electric field induced by neutral beam injection (NBI). The radial electric field is produced by charge separation of beam induced electrons and beam ions. The charge separation is produced by redistribution and loss of NBI ions, which is due to the magnetic drift and collision effects. The birth and steady-state distributions of NBI fast ions related to charge separation were numerically computed by the orbit code GYCAVA and the NBI code TGCO. According to our model, the neoclassical polarization density of bulk ions has a great shielding effect on the radial electric field due to charge separation. The simulation results show that NBI ions can produce a significant radial electric field (∼10 kV m−1) in the core region. The counter-current NBI (injection anti-parallel to the plasma current) can produce a negative radial electric field, which is due to the magnetic drift and collision effects of NBI ions. While the co-current injection (injection parallel to the plasma current) produces a positive radial electric field in the core region, which is mainly related to the magnetic drift of NBI ions. The dependence of the radial electric field on the injection direction and the beam energy of NBI has been investigated. As the beam energy increases, the magnitudes of the electric field for counter-injections increase and the magnitude of the electric field for co-current perpendicular injection decrease.

Dose-area product ratio in external small-beam radiotherapy: beam shape, size and energy dependencies in clinical photon beams

In small-field radiotherapy (RT), a significant challenge is to define the amount of radiation dose absorbed in the patient where the quality of the beam has to be measured with high accuracy. The properties of a proposed new beam quality specifier, namely the dose-area-product ratio at 20 and 10 cm depths in water or DAPR20,10, were studied to yield more information on its feasibility over the conventional quality specifier tissue-phantom ratio or TPR20,10. The DAPR20,10 may be measured with a large-area ionization chamber (LAC) instead of small volume chambers or semi-conductors where detector, beam and water phantom positioning and beam perturbations introduce uncertainties. The effects of beam shape, size and energy on the DAPR20,10 were studied and it was shown that the DAPR20,10 increases with increasing beam energy similarly to TPR20,10 but in contrast exhibits a small beam size and shape dependence. The beam profile outside the beam limiting devices has been shown to have a large contribution to the DAPR20,10. There is potential in large area chambers to be used in DAPR measurement and its use in dosimetry of small-beam RT for beam quality measurements.

A new MRPC prototype with diamond-like-carbon coated glass electrodes

The Multi-gap Resistive Plate Chamber (MRPC) has been used in many high energy physics and nuclear experiments in the last decade, such as ALICE [1] and STAR [2]. Normally, the MRPC is built with commercial floating glass (bulk resistivity ρ≈ 1012Ω· cm), which limits the rate capability to less than 1 kHz/cm2. In modern high energy physics, with the increase of colliders beam energy and luminosity, the rate capability of MRPC has to be enhanced accordingly. One normal way is to decrease the bulk resistivity ρ of the resistive plate, as the low resistive glass developed by Tsinghua University for the CBM experiment [3]. Alternatively, the surface of the electrode is also a possible path for the neutralization of the avalanche charges. Recently, we managed to carry this method out by coating a Diamond-Like-Carbon (DLC) layer on the surface of the floating glass. The DLC layer, realized by the magnetron sputtering method, has very good physical and chemical stability. The demanded surface resistivity can be achieved easily. A series of DLC-coated glasses with different resistivity has been tested in our lab. We have also made some MRPC prototypes and tested them with cosmic rays. Some preliminar results, including the operating current, the efficiency and the time resolution, have been achieved. More research is ongoing to improve the design and performance of this new method of increasing the rate capability of MRPC.

The effect of underlying bone on the beam angular correction in calculating the skin dose of the head in neuro-interventional imaging.

Skin dose depends on the surface shape, underlying tissue, beam energy, field size, and incident beam angle. These dependencies were determined in order to apply corrections in the skin-dose-tracking system (DTS) for accurate estimation of the risk of deterministic skin effects during fluoroscopically-guided neuro-interventional procedures. The primary-plus-scatter dose was calculated averaged over the skin thickness with underlying subcutaneous fat, and various thicknesses of skull bone on the surface of a cylindrical water phantom to simulate the head. The skin dose was calculated using EGSnrc Monte-Carlo (MC) software with 2×1010 incident photons and was normalized to the incident primary dose. Simulations were done for beam incident angles from 90 to 10 degrees with the skin surface, field sizes from 5 to 15 cm, bone thicknesses of 0, 1, 5, and 9 mm, and beam energies from 60 to 120 kVp. The results show the scatter-plus-primary to incident-primary dose ratio decreases with decreasing incident angle to the skin and with increasing thickness of underlying bone, while it increases with increasing field size and with increasing beam energy. The correction factor reduces the skin dose for angled rays and the reduction can be substantial for small angles of incidence, especially for angles below 50 degrees. For neuro-interventional procedures, the skin dose-area product (SDAP) with angular and bone correction is shown to be less than that without correction. The results of this study can be used to increase the accuracy of patient-skin-dose estimation for the head during fluoroscopic procedures.

Study on attenuation of 3D printing commercial filaments on standard X-ray beams for dosimetry and tissue equivalence

3D printing techniques and materials have become widely available in the last couple of decades and remains an important topic of research as the equipments and supplements gets chipper. This study aims to evaluate the attenuation behaviour of several commercially available 3D printing filaments (ABS and PLA-based filaments and other polymers blends) over standard X-ray beams ranging from ~30 keV - to ~50 keV and comparing the experimental results with theoretical data of Cortical Bone, Soft Tissue and PMMA. It was used the transmission method to obtain experimental attenuation coefficients to all materials. HVL for the materials were also calculated. Results show that PLA-based printing filaments mixed with metals (Al, BRASS and Cu) has higher attenuation than pure PLA. Comparing the experimental data with theoretical cross section of Soft Tissue, Cortical Bone and PMMA, it was possible to observe that with the increase of beam energy, ABS-based and other blends’ attenuation behaviour agree with PMMA/Soft tissue. None of the studied materials showed agreement of attenuation with Cortical Bone. Some variations of PLA (SILK, Black and Bone) and some of the other blends of PETG and TPU showed good agreement with Soft Tissue/PMMA since about 30 keV and it can be concluded that these filaments can be used as substitute of PMMA for mimetizing soft tissue in 3D printed phantoms.

Self-consistent charging of PMMA thin film induced by a penetrating electron beam in electron microscopy.

The charging of the polymer thin film irradiated by penetrating electron beam (e-beam) is investigated, in parallel with the numerical simulation and experiment. The simulation is performed by combining scattering, drift, diffusion, trapping and recombination. Results show that, due to the electron emission the net charge near the surface is distribution positively, but negatively inside the film because of low electron mobility. The surface potential is positive near surface and accordingly forces some of secondary electrons to return surface. As irradiation proceeds, currents flowing into and out of the film can tend to equilibrium. In the equilibrium state, with increasing beam energy, the surface potential and the efficient emission current decrease, and the electron beam-induced current and the transmission current tend to zero and the beam current valuable, respectively. E-beams of 10-30keV cause positive charging on PMMA film of 2 µm, which means the high-energy e-beam can effectively discharge a thin film that has been charged negatively by irradiation with low-energy e-beam. With the increase of the film thickness from 1 to 3 µm, the positive surface potential and the emission current decreases and increases, respectively, and the transmission current tends to zero.

Simulation study of electron beam irradiation damage to ZnO and TiO<sub>2</sub>

Wurtzite ZnO and rutile TiO<sub>2</sub> have important application value in solar cells, photocatalysts, self-cleaning coatings, etc. In addition, ZnO and TiO<sub>2</sub> are crucial basic materials for the development of semiconductor spintronics devices due to room temperature ferromagnetism in the state of defects or doped specific elements. Many studies indicate that the magnetic, optical, and electrical properties of ZnO and TiO<sub>2</sub> are affected by intrinsic defects (such as vacancies, interstitial atoms, etc.). Electron irradiation has the incomparable advantages over other particle beam irradiation, the defects produced by electron beam irradiation are mainly independent vacancy-interstitial atom pairs (Frenkel pairs), and there are no new doping elements introduced into the material during the irradiation by electron beam with energy of several MeV, that is, electron irradiation is a relatively “pure” particle irradiation method. On the one hand, since the displacement threshold energy values of different atoms are different from each other, the type of defect during electron irradiation can be controlled by the energy of the electron beam. On the other hand, the electron fluence can determine the concentration of defects. Therefore, various defects of different concentrations can be generated by electron irradiation, thereby studying the influences of related defects on the magnetic, optical, and electrical properties of ZnO and TiO<sub>2</sub>. However, simulation calculations related to electron beam irradiation damage are relatively scarce. Therefore, in this work, the electron beam irradiation damage is taken as a research topic and the related theoretical simulation calculations are carried out, which lays a theoretical foundation for subsequent experimental researches. The size and the distribution of radiation damage (dpa) caused by point source electrons and that by plane source electrons with different energy values in ZnO and TiO<sub>2</sub> are simulated and calculated through the MCNP5 program combined with the MCCM algorithm. The calculation results show that O atoms and Zn atoms can be dislocated when the electron energy values are greater than 0.31 MeV and 0.87 MeV in ZnO, respectively; while in TiO<sub>2</sub>, O atoms and Ti atoms can be dislocated when the electron beam energy values are greater than 0.12 MeV and 0.84 MeV, respectively. The dpa caused by point source electrons is mainly distributed in the longitudinal direction, and attenuates quickly in the lateral direction; on the contrary, the dpa caused by plane source electrons first increases and then decreases with the augment of the electron incidence depth, and the unevenness of the dpa distribution becomes more serious with the increase of the electron energy. Therefore, for each of ZnO and TiO<sub>2</sub>, the dpa will be relatively even distribution when the thickness of the sample is about 0.25 mm. Furthermore, the calculation results of the electron energy deposition show that the size of the energy deposition area is closely related to the electron beam energy. At the same time, with the increase of the electron beam energy, the position where the maximum energy deposition appears gradually moves to the inside of the sample, and the entire energy deposition area has a tendency to lean forward.

Determination of effective source to surface distance and cutout factor in small fields in electron beam radiotherapy: A comparison of different dosimeters

Abstract Objective: The main purpose of this study is to calculate the effective source to surface distance (SSDeff) of small and large electron fields in 10, 15, and 18 MeV energies, and to investigate the effect of SSD on the cutout factor for electron beams a linear accelerator. The accuracy of different dosimeters is also evaluated. Materials and methods: In the current study, Elekta Precise linear accelerator was used in electron beam energies of 10, 15, and 18 MeV. The measurements were performed in a PTW water phantom (model MP3-M). A Semiflex and Advanced Markus ionization chambers and a Diode E detector were used for dosimetry. SSDeff in 100, 105, 110, 115, and 120 cm SSDs for 1.5 × 1.5 cm2 to 5 × 5 cm2 (small fields) and 6 × 6 cm2 to 20 × 20 cm2 (large fields) field sizes were obtained. The cutout factor was measured for the small fields. Results: SSDeff in small fields is highly dependent on energy and field size and increases with increasing electron beam energy and field size. For large electron fields, with some exceptions for the 20 × 20 cm2 field, this quantity also increases with energy. The SSDeff was increased with increasing beam energy and field size for all three detectors. Conclusion: The SSDeff varies significantly for different field sizes or cutouts. It is recommended that SSDeff be determined for each electron beam size or cutout. Selecting an appropriate dosimetry system can have an effect in determining cutout factor.

Spatially dependent modeling and simulation of runaway electron mitigation in DIII-D

New simulations with the Kinetic Orbit Runaway electron (RE) Code KORC show RE deconfinement losses to the wall during plasma scrape off are the primary current dissipation mechanism in DIII-D experiments with high-Z impurity injection, and not collisional slowing down. The majority of simulations also exhibit an increase in the RE beam energy due to acceleration by the induced toroidal electric field, even while the RE beam current is decreasing. In this study, KORC integrates RE orbits using the relativistic guiding center equations of motion, and incorporates time-sequenced, experimental reconstructions of the magnetic and electric fields and line integrated electron density to construct spatiotemporal models of electron and partially-ionized impurity transport in the companion plasma. Comparisons of experimental current evolution and KORC results demonstrate the importance of including Coulomb collisions with partially-ionized impurity physics, initial RE energy, pitch angle, and spatial distributions, and spatiotemporal electron and partially-ionized impurity transport. This research provides an initial quantification of the efficacy of RE mitigation via injected impurities, and identification of the critical role played by loss of confinement due to plasma scrape off on the inner wall as compared to the relatively slow collisional damping.

Particle production via strings and baryon stopping within a hadronic transport approach

The stopping of baryons in heavy ion collisions at beam momenta of plab = 20–160A GeV is lacking a quantitative description within theoretical calculations. Heavy ion reactions at these energies are experimentally explored at the Super Proton Synchrotron (SPS) and the Relativistic Heavy Ion Collider (RHIC) and will be studied at future facilities such as FAIR and NICA. Since the net baryon density is determined by the amount of stopping, this is the pre-requisite for any investigation of other observables related to structures in the QCD phase diagram such as a first-order phase transition or a critical endpoint. In this work we employ a string model for treating hadron–hadron interactions within a hadronic transport approach (SMASH, Simulating Many Accelerated Strongly-interacting Hadrons). Free parameters of the string excitation and decay are tuned to match experimental measurements in elementary proton–proton collisions, where some mismatch in the xF distribution of protons is still present. Afterwards, the model is applied to heavy ion collisions, where the experimentally observed change of the shape of the proton rapidity spectrum from a single peak structure to a double peak structure with increasing beam energy is reproduced. Heavy ion collisions provide the opportunity to study the formation process of string fragments in terms of formation times and reduced interaction cross-sections for pre-formed hadrons. A good agreement with the measured rapidity spectra of protons and pions is achieved while insights on the fragmentation process are obtained. In the future, the presented approach can be used to create event-by-event initial conditions for hybrid calculations.

Beam energy dependence of cumulants of the net-baryon, net-charge, and deuteron multiplicity distributions in Au + Au collisions at sNN=3.0–5.0 GeV

Within the ultra-relativistic quantum molecular dynamics (UrQMD) model, in which the Lorentz-covariant treatment of nuclear mean-field potential is considered, the fluctuations of net-baryon, net-charge and deuterons multiplicity distributions in Au+Au head-on collisions at $\sqrt{s_{NN}}=3.0-5.0$ GeV are calculated. The results show that the nuclear mean-field potential can significantly enhance the magnitude of baryon number fluctuations in narrow rapidity windows, and this enhancement rapidly weakens with increasing beam energy. However, for proton and net-charge number fluctuations, the mean-field effects are less noticeable than that for baryon number. In addition, for net-charge number fluctuations, the negative binomial distribution agrees well with the calculated results at mid-pseudorapidity window. Finally, the event-by-event fluctuations of deuteron number in the coalescence production picture are calculated as well, it is found that its cumulant ratios decrease linearly with increasing the average multiplicity of deuterons per event, i.e., increase with increasing beam energy.

A technique for spatial resolution improvement in helium-beam radiography.

Ion-beam radiography exhibits a significantly lower spatial resolution (SR) compared to x-ray radiography. This is mostly due the multiple Coulomb scattering (MCS) that the ions undergo in the imaged object. In this work, a novel technique to improve the spatial resolution in helium-beam radiography was developed. Increasing helium-beam energies were exploited in order to decrease the MCS, and therefore increase the SR. The experimental investigation was carried out with a dedicated ion-tracking imaging system fully composed of thin, pixelated silicon detectors (Timepix). Four helium beams with increasing energies (from 168.8 to 220.5MeV/u) were used to image a homogeneous 160mm PMMA phantom with a 2mm air gap at middle depth. An energy degrader (ED) was placed between the rear tracking system and the energy-deposition detector to compensate for the longer range associated with more energetic ions. The SR was measured for each beam energy. To take into account the overall impact on the image quality, the contrast-to-noise ratio (CNR), the single-ion water equivalent thickness (WET) precision and the absorbed dose in the phantom were also evaluated as a function of the initial beam energy. FLUKA Monte Carlo simulations were used to support the conceptual design of the experimental setup and for dose estimation. In the investigated energy interval, a total SR increase by around 30% was measured with increasing beam energy, reaching a maximum value of 0.69lp/mm. For radiographs generated with 350μGy of absorbed dose and 220μm pixel size, a CNR decrease of 32% was found as the beam energy increases. For 1mm pixel size, the CNR decreases only by 22%. The CNR of the images was always above 6. The single-ion WET precision was found to be in a range between 1.2% and 1.5%. We have experimentally shown and quantified the possibility of improving SR in helium-beam radiography by using increasing beam energies in combination with an ED. A significant SR increase was measured with an acceptable decrease of CNR. Furthermore, we have shown that an ED can be a valuable tool to exploit increasing beam energies to generate energy-deposition radiographs.

Effects of impact parameter filters on observables in heavy-ion collisions at INDRA energies

The collision centrality (or the impact parameter b) in heavy-ion experiments is inferred from final state observables, however, usually b is an input to theoretical calculations. The effects of different methods used for the centrality selection (i.e. total charged multiplicity Mch, total transverse kinetic energy of light charged particles , and the ratio of transverse-to-longitudinal kinetic energy ERAT) on the nuclear stopping and the collective flow are studied in Xe+Sn collisions at INDRA energies (/nucleon). The study is conducted within the framework of the ultra-relativistic quantum molecular dynamics (UrQMD) model. It is found that the nuclear stopping power RE obtained from events binning with ERAT is larger than the experimental data as well as the results obtained using Mch and . At Ebeam = 50 MeV/nucleon, the elliptic flow from events selected with different methods spreads widely, especially for more central collisions. The elliptic flow from events sorted by ERAT is weakly dependent on the collision centrality. The difference in elliptic flow at mid-rapidity among different centrality filters steadily decreases with increasing beam energy and impact parameter. At 150 MeV/nucleon, the differences in directed and elliptic flows arising from different centrality filters vanish.

Beam-energy dependence of identified two-particle angular correlations in sNN=7.7–200 GeV Au+Au collisions

The two-particle angular correlation functions, $R_2$, of pions, kaons, and protons in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV were measured by the STAR experiment at RHIC. These correlations were measured for both like-sign and unlike-sign charge combinations and versus the centrality. The correlations of pions and kaons show the expected near-side ({\it i.e.}, at small relative angles) peak resulting from short-range mechanisms. The amplitudes of these short-range correlations decrease with increasing beam energy. However, the proton correlation functions exhibit strong anticorrelations in the near-side region. This behavior is observed for the first time in an A+A collision system. The observed anticorrelation is $p_{T}$-independent and decreases with increasing beam energy and centrality. The experimental results are also compared to the Monte Carlo models UrQMD, Hijing, and AMPT.

Jet overlap in heavy ion collisions at energies available at the CERN Large Hadron Collider and its consequences for the jet shape

Central lead-lead collisions at the LHC energies may pose a particular challenge for jet identification as multiple jets are produced per each collision event. We simulate the jet evolution in central Pb-Pb events at $\sqrt{s_{\rm NN}} = 2.76$ GeV collision energy with EPOS3 initial state, which typically contains multiple hard scatterings in each event. Therefore the partons from different jets have a significant chance to overlap in momentum space. We find that 30% of the jets with $p_\perp > 50$ GeV, identified by the standard anti-$k_\perp$ jet finding algorithm with jet cone size R=0.3, contain `intruder' particles from overlapping generator-level jets. This fraction increases with increasing beam energy and increasing R. The reconstructed momentum of the jet differs from that of the modelled jet by the loss due to jet partons which are outside of the jet cone and by the gain due to intruder partons. The sum of both may be positive or negative. These intruder partons particularly affect the radial jet momentum distribution because they contribute mostly at large angles $\Delta r$ with respect to the jet centre. The study stresses the importance of the jet overlap effect emerging in central lead-lead collisions at the LHC energies, while being negligible in peripheral PbPb or $p$Pb/$pp$ collisions.

Bragg peak characteristics of proton beams within therapeutic energy range and the comparison of stopping power using the GATE Monte Carlo simulation and the NIST data

AbstractPurpose:To examine detail depth dose characteristics of ideal proton beams using the GATE Monte Carlo technique.Methods:In this study, in order to improve simulation efficiency, we used pencil beam geometry instead of parallel broad-field geometry. Depth dose distributions for beam energies from 5 to 250 MeV in a water phantom were obtained. This study used parameters namedRpeak,R90,R80,R73,R50, full width at half maximum (FWHM), width of 80–20% distal fall-off (W(80–20)) and peak-to-entrance ratio to represent Bragg peak characteristics. The obtained energy–range relationships were fitted into third-order polynomial formulae. The present study also used the GATE Monte Carlo code to calculate the stopping power of proton pencil beams in a water cubic phantom and compared results with the National Institute of Standards and Technology (NIST) standard reference database.Results:The study results revealed deeper penetration, broader FWHM and distal fall-off and decreased peak-to-entrance dose ratio with increasing beam energy. Study results for monoenergetic proton beams showed thatR73can be a good indicator to characterise a range of incident beams. These also suggest FWHM is more sensitive thanW(80–20)distal fall-off in finding initial energy spread. Furthermore, the difference between the obtained stopping power from simulation and NIST data almost in all energies was lower than 1%.Conclusion:Detail depth dose characteristics for monoenergetic proton beams within therapeutic energy ranges were reported. These results can serve as a good reference for clinical practitioners in their daily practice.