Energy Deposition In Water Research Articles

Optical properties of water relaxing after intense laser exposure

The dynamics of the optical properties of water bulk exposed to femtosecond radiation (Ti-sapphire laser, wavelength 800 nm, intensity ∼ 10 13 W / c m 2 ) was studied in the time window of ≈ 1.5 n s using a pump–probe technique. Both the refractive index and absorbance were measured by femtosecond interferometric microscopy, which allowed us to gather deconvoluting quantitative data about the induced processes: solvation of excess electrons, geminate recombination, and development of cavitation. We found that the number of electrons produced by a strong, near infrared (NIR) field in the cavitation regime ( < 10 19 c m − 3 ) is much lower than was previously thought. The obtained data clarify the mechanisms of laser energy deposition in water and are of crucial importance to understand intensive light action on aqueous-based systems.

Radioluminescence by synchrotron radiation with lower energy than the Cherenkov light threshold in water

Radioluminescence by protons and carbon ions of energy lower than the Cherenkov threshold (∼260 keV) in water has been observed. However, the origin of the luminescence has not been investigated well. In the present work, we imaged radioluminescence in water using synchrotron radiation that was of sufficiently lower energy (11 keV) than the Cherenkov threshold and we measured its spectrum using a high-sensitivity cooled CCD camera and optical longpass filters having 5 different thresholds. In addition, to determine effects of impurities in water, the water target was changed from ultrapure water to tap water. Monte Carlo simulation (Geant4) was also performed to compare its results with the experimentally obtained radioluminescence distribution. In the simulation, photons were generated in proportion to the energy deposition in water. As a result, the beam trajectory was clearly imaged by the radioluminescence in water. The spectrum was proportional to λ−3.4±0.4 under an assumption of no peaks. In the spectrum and distribution, no differences were observed between ultrapure water and tap water. TOC (total organic carbon) contents of ultrapure water and tap water as an impurity were measured and these were 0.26 mg l−1 and 2.3 mg l−1, respectively. The radioluminescence seemed to be attributable to water molecules not impurities. The radioluminescence distribution of the simulation was consistent with the experimental distribution and this suggested that radioluminescence was proportional to dose, which is expected to allow use for dose measurement.

SU‐E‐T‐46: A Monte Carlo Investigation of Radiation Interactions with Gold Nanoparticles in Water for 6 MV, 85 KeV and 40 KeV Photon Beams

Purpose:To determine the effect of gold‐nanoparticles (AuNPs) on energy deposition in water for different irradiation conditions.Methods:TOPAS version B12 Monte Carlo code was used to simulate energy deposition in water from monoenergetic 40 keV and 85 keV photon beams and a 6 MV Varian Clinac photon beam (IAEA phase space file, 10x10 cm2, SSD 100 cm). For the 40 and 85 keV beams, monoenergetic 2x2 mm2 parallel beams were used to irradiate a 30x30x10 µm 3 water mini‐phantom located at 1.5 cm depth in a 30x30x50 cm3 water phantom. 5000 AuNPs of 50 nm diameter were randomly distributed inside the mini‐phantom. Energy deposition was scored in the mini‐phantom with the AuNPs’ material set to gold and then water. For the 6 MV beam, we created another phase space (PHSP) file on the surface of a 2 mm diameter sphere located at 1.5 cm depth in the water phantom. The PHSP file consisted of all particles entering the sphere including backscattered particles. Simulations were then performed using the new PHSP as the source with the mini‐phantom centered in a 2 mm diameter water sphere in vacuum. The g4em‐livermore reference list was used with “EMRangeMin/EMRangeMax = 100 eV/7 MeV” and “SetProductionCutLowerEdge = 990 eV” to create the new PHSP, and “SetProductionCutLowerEdge = 100 eV” for the mini‐phantom simulations. All other parameters were set as defaults (“finalRange = 100 µm”).Results:The addition of AuNPs resulted in an increase in the mini‐phantom energy deposition of (7.5 ± 8.7)%, (1.6 ± 8.2)%, and (−0.6 ± 1.1)% for 40 keV, 85 keV and 6 MV beams respectively.Conclusion:Enhanced energy deposition was seen at low photon energies, but decreased with increasing energy. No enhancement was observed for the 6 MV beam. Future work is required to decrease the statistical uncertainties in the simulations.This research is partially supported from institutional funds from the Center for Radiation Oncology Research, The University of Texas MD Anderson Cancer Center.

Whole life cycle of femtosecond ultraviolet filaments in water

We present measurements fully characterizing the whole life cycle of femtosecond pulses undergoing filamentation in water at 400 nm. The complete pulse dynamics is monitored by means of a four-dimensional mapping technique for the intensity distribution I(x,y,z,t) during the nonlinear interaction. Measured events (focusing or defocusing cycles, pulse splitting and replenishment, supercontinuum generation, conical emission, nonlinear absorption peaks) are mutually connected.The filament evolution from laser energy deposition in water, which is of paramount importance for a wide range of technological and medical applications, is interpreted in light of simulation results.

Monte Carlo simulation on a gold nanoparticle irradiated by electron beams**This work was presented as part of the ‘International Workshop on Recent Advances in Monte Carlo Techniques for Radiation Therapy’.

This study investigated the secondary electron production from a gold nanoparticle (GNP) irradiated by monoenergetic electron beams using Monte Carlo (MC) simulation. Spherical GNPs with diameters of 2, 50 and 100 nm in water were irradiated by monoenergetic electron beams with energies equal to 50 keV, 250 keV, 1 MeV and 4 MeV. MC simulations were performed using the Geant4 toolkit to determine the energy of the secondary electrons emitted from the GNPs. The mean effective range and deflection angle of the secondary electrons were tracked. Energy depositions inside and outside the nanoparticles due to the secondary electrons were also calculated. For comparisons, simulations were repeated by replacing the GNPs with water. Our results show that the mean effective range of secondary electrons increased with an increase of the GNP size and electron beam energy. For the electron beam energy and GNP size used in this study, the mean effective range was 0.5–15 µm outside the nanoparticle, which is approximately within the dimension of a living cell. The mean deflection angles varied from 78 to 83 degrees as per our MC results. The proportion of energy deposition inside the GNP versus that outside increased with the GNP size. This is different from the results obtained from a previous study using photon beams. The secondary electron energy deposition ratio (energy deposition for GNP/energy deposition for water) was found to be highest for the smallest GNP of 2 nm diameter in this study. For the energy deposited by the secondary electron, we concluded that the addition of GNPs can increase the secondary electron energy deposition in water, though most of the energy was self-absorbed by the large nanoparticles (50 and 100 nm). In addition, an electron source in the presence of GNPs does not seem to be better than photons as the yield of secondary electrons per unit mass of gold is less than water.

Enhanced single strand breaks of supercoiled DNA in a matrix of gold nanotubes under X-ray irradiation

Single-strand-breaks (SSBs) of supercoiled DNA (scDNA) molecules were used to probe the enhancement of X-ray radiation effect on scDNA mixed with gold nanotubes (AuNTs) in water. The amounts of measured enhancements using SSBs were significantly lower than the expected increase in energy deposition in water by AuNTs under hard X-ray irradiation. Three factors were identified to negatively affect the enhancement: (1) Attenuation of kinetic energies carried by electrons escaped from AuNTs, (2) Scavenging of OH radicals (OH) by the surface of bare AuNTs, and (3) Steric effect due to soluble scDNA molecules away from the surface of AuNTs. Benefits and limits of using gold nanomaterials as radiation enhancers and contrast agents are discussed.

Geometry Enhancement of Nanoscale Energy Deposition by X-rays

A principle is established to show that nanoscale energy deposition in water by X-rays can be greatly enhanced via the geometry of nanostructures. The calculated results show that enhancement over background water can reach over 60 times for a single nanoshell made of gold. Other geometries and nanostructures are investigated, and it is found that a shell of gold nanoparticles can generate similar enhancement. The concepts of composition, matrix, and satellite effects are established and studied, all of which can further increase the enhancement of the effect of X-rays.

SU‐E‐T‐662: Further Development of a Power Approximation of Range‐Energy Relationship for Therapeutic Proton Beams

Purpose: The purpose of this work is to further develop a power approximation of energy‐range relationship for therapeutic proton beams based on range‐energy tables from Janniˈs Data, ICRU Data, and Monte Carlo simulated Data. Methods: The energy deposition in water was simulated with MCNPX. The energy tally in MCNPX physics cards included the total energy. The proton source was defined as a pencil beam with uniformly distributed in area. The proton energy in simulation ranged from 40 MeV to 250 MeV with increments of 5 MeV. A three dimensional dose matrix was simulated with voxel dimension of 1×1×1 mm̂3. A central‐axis‐slice for each individual simulation was used for range analysis. Results: The range difference between Janniˈs and ICRU data increased from sub‐millimeter to ∼4 mm as energy changed from 40 MeV to 250 MeV with average difference as 1.08%. The Monte Carlo simulation data lies between Janniˈs Data and ICRU data with average 0.57% below Janniˈs Data, and average 0.50% above ICRU Data. The range‐energy table from Janniˈs, ICRU and Monte Carlo Simulation are all in very good agreement with each other, with coefficients of correlation between 0.9999 to 1.000. The relationship between proton range and energy can be fitted by a power approximation. Generally the power relation can be expressed by R = a*Êp. With unit of R in mm and E in MeV, the factor a and the exponent p in proton energy‐range power approximation were determined to be 0.023, 1.763 from Janniˈs Data, 0.022, 1.770 from ICRU Data, and 0.0225, 1.766 from MC simulation. Conclusions: Monte Carlo simulation provided very close agreement to the two widely used proton range‐energy tables. The approximation of range‐energy power relationship based on Monte Carlo data provide slightly different factor a and exponent p from those based on Janniˈs and ICRU Data.

Energy deposition model for I-125 photon radiation in water

In this study, an electron-tracking Monte Carlo algorithm developed by us is combined with established photon transport models in order to simulate all primary and secondary particle interactions in water for incident photon radiation. As input parameters for secondary electron interactions, electron scattering cross sections by water molecules and experimental energy loss spectra are used. With this simulation, the resulting energy deposition can be modelled at the molecular level, yielding detailed information about localization and type of single collision events. The experimental emission spectrum of I-125 seeds, as used for radiotherapy of different tumours, was used for studying the energy deposition in water when irradiating with this radionuclide.

Beam-forming and matched filter techniques for the underwater acoustic detection of UHE neutrino

The search for UHE neutrinos is one of the most promising fields in astroparticle physics. The experimental techniques proposed to identify cosmic neutrino signatures are mainly three: the detection of Cherenkov blue light originated by charged leptons (electrons, positrons, muons and tauons) from neutrino interaction in water or ice; the detection of acoustic waves produced by neutrino energy deposition in water, ice or salt; the detection of radio pulses following neutrino interaction in ice or salt. Due to the expected neutrino fluxes (≈10 −8 E 2 Gev/cm 2 s sr) and due to their extremely low interaction cross-section (≈10 −32 cm 2 at 10 20 eV), huge target volumes (≈km 3) are required to detect them. Acoustic detection of neutrino is a very suitable technique since the sound attenuation length, at the frequency of interest, is of the order of km. Due to the small amplitude of the expected neutrino bipolar signal (≈10 mPa), it is mandatory to develop an effective algorithm that increases the signal to noise ratio (SNR). In the present work a combination of matched filter, applied to each single hydrophone, and a beam-forming technique applied to a small array of hydrophones is proposed. The matched filter is a well-known technique of signal processing that maximizes the SNR in the presence of white noise. Beam forming is a signal-processing technique used in sensor arrays for directional analysis; the signals from different sensors are combined in such a way that pressure waves arriving from a specific direction are coherently summed. Preliminary results on simulated data will be shown.

Utilization of gamma-ray irradiation for hydrogen production from water

A technique has been proposed to promote hydrogen production from water by increasing the energy deposition in water through the conversion of γ-ray to low-energy electrons, which is achieved by putting solid materials into water. Simulation studies by the MCNP code indicate that the average deposited energy in water can be increased by optimizing geometry of the materials. In the present experiments using Al2O3 particles of various average diameters, the maximum amount of hydrogen produced is 3.48 μmol/cm3 for the water containing Al2O3 particles of 3 μm diameter, which is more than two order of magnitude larger of the H2 produced in water-only configuration.

Monte Carlo validation in the diagnostic radiology range

The present paper aimed to the validation of Monte Carlo simulation codes already developed by the reporting team, for the study of photon transport and absorption in scintillator materials. Comparisons are reported between the developed codes, MCNP developed codes and other published data. First, the mean number of interactions for each incident photon was determined and compared to the published data. Agreement to within ±1.5% was achieved. Second, the depth of energy deposition in water was assessed for three monoenergetic X-ray beams (15, 20, 30 keV). The energy deposited in slabs of water phantoms of varying depths was tallied. Excellent agreement within ±2% was achieved, except that for 15 keV were a more rapid drop with increasing depth was found. Second, spatial distribution of the energy absorption due to scatter radiation was assessed. Good agreement (below ±5%) with published data was achieved. Third, a water slab with thickness 5, 10, 15, 20 cm was modeled, irradiated by a monoenergetic narrow beam of photons of various energies. Last, the lateral spread of energy deposition was assessed in a 1 cm thick slab in the center of an 8 cm thick water phantom, irradiated by a 50 keV narrow beam. Again, good agreement (below ±2%) was achieved.

Track Structure, Target Structure and Radiation Effectiveness

Abstract A track structure model based on energy deposition in water is used to investigate the dependence of the response of a typical 'single hit' detector and a biological effect, the induction of double strand breaks, on the type and energy of the radiation. In making the calculations for a single hit detector, it is assumed that an energy deposition event within a small sphere around the target causes the effect. For the induction of DNA double strand breaks it is assumed that two energy deposition events along the same track are necessary, one occurring in each of two small spheres at a distance of 1.2 nm from each other to simulate the two strands of the DNA helix. The calculations show that for a series of different particles, a series of differing curves of effectiveness relative to stopping power are found. These differing curves offer an explanation for the differences in effectiveness of two different particles having the same stopping power.

Comparison between cobalt-60 gamma and tritium beta in the degradation spectrum of electrons and heterogeneous energy deposition in water

The degradation spectra of electrons in water irradiated with cobalt-60γ and tritium β were calculated. From these spectra, spur size distributions were estimated. Their implication to the radiation effects were also discussed.

Radiation Energy Deposition in Water: Calculation of DNA Damage and its Association with RBE

A track structure model is presented which describes the energy deposition of ions, electrons, gamma rays and X rays in liquid water. The model starts from first physical principles, includes the single excitation spectrum of liquid water and takes into account all particles involved in the energy deposition process. This model is used to calculate DNA single strand breaks and double strand breaks and a good fit has been found for X rays and various ions. The model is also used to calculate the linear coefficient of the dose survival curve for two cell types, assuming that DNA double strand breaks are the crucial lesions. In this case a good description of the behaviour of the linear dose term was found for various ions, gamma rays and X rays of 300 keV, 1.5 keV and 0.3 keV, assuming one type of interaction of the water radicals with DNA to produce DNA double strand breaks. The results support the hypothesis that one type of lesion is responsible for the low dose component of cell lethality.

Monte Carlo calculations of the energy response of lithium dosemeters to high energy electrons (

Calculations for LiF dosemeters have been carried out to help resolve the discrepancy between the measurements of Holt et al. (see ibid., vol.20, p.559, (1975)) and those of Paliwal and Almond (see ibid., vol.20, p.547 (1975)) and others. It is concluded that the assumptions used by Holt et al. are largely responsible. They assume, in converting energy deposition in an air-filled ionization chamber to energy deposition in water, that as electrons penetrate a medium they are monoenergetic and the energy is given by Harder's expression (ICRU Report 21, 1972). The assumption gives poor results as the stopping power for electrons in air is strongly energy dependent, and the energy spectrum has been significantly broadened. The Monte Carlo calculations are also used to criticize some electron cavity theories and to suggest as an alternative a slightly modified version of the Bragg-Gray theorem.

Tabulation and Empirical Representation of Infinite-Medium Gamma-Ray Buildup Factors for Monoenergetic, Point Isotropic Sources in Water, Aluminum, and Concrete

Buildup factors for energy deposition in water and aluminum and for exposure in concrete are presented for monoenergetic, point isotropic gamma-ray sources. The buildup fac. tors were evaluated usi...

The use of a holographic interferometer to measure absorbed energy distributions in water from pulsed electron beams

An optical holographic interferometer was used to measure the energy deposition as a function of depth in water, as well as the total energy deposited in the water from various intensities of pulsed, monoenergetic electron beams. The energy of the electron beams varied from 1.00 MeV to 2.50 MeV in increments of 0.25 MeV. Data for 1.00, 1.75 and 2.50 MeV are presented. The interferometer and the analytical technique used to reduce the data are described. The measured results are compared to those predicted by ETRAN-15, a Monte Carlo radiation transport code. Reasonable agreement was found between the measured and the computed energy deposition in water as a function of depth of penetration of the electrons. Measured values for the total energy deposited agreed well with those predicted by ETRAN-15 and showed good correlation with the changes in the electron-flux densities. In view of the results of this study, there is no apparent reason why this technique could not be extended to measure the energy deposition of intense pulsed beams of other types of charged particles.

Analysis of energy deposition in water around the site of capture of a negative pion by an oxygen or carbon nucleus

A study was made of the energy deposited in water spheres and cylinders of increasing size around the site at which an oxygen or carbon nucleus captures a stopped negative pion. No great differences were found either between results for O and C or between results for spheres and cylinders. As known from the literature, approximately 100 MeV is released as kinetic energy of secondary products after capture, about 60 MeV to neutrons and 40 MeV to charged particles. Most of the neutron energy is transported away from the immediate capture site. Calculations here show that 50% of the charged-particle energy is deposited within a distance of 0.1 cm from the site and 90% within 2 cm. Practically all charged particles with an LET ⩾ 170 MeV cm-1 in water lose their energy within ~0.2 cm. The calculations also show that, on the average, 30 NeV of energy is deposited inside a sphere of 1 cm radius per π- capture by oxygen and 35 XeV per capture by carbon.