Dosimetry of Ionizing Radiation Based on Photoelectron Emission from PbS Nanoparticles

Lead sulfide nanoparticles with a diameter of 2.5 nm embedded in a 100 nm thick matrix of zirconium oxide by sol-gel technology (ZrOz:PbS nanofilms) were studied for application in dosimetry of ionizing radiation

Influence of Ultraviolet and Electron Radiation on Photoelectron Emission Spectra of Lead Sulfide Nanoparticles Embedded in a Matrix of Zirconium Oxide

Lead sulfide (PbS) nanoparticles embedded in a thin-film matrix of zirconium oxide (ZrO2), ZrO2:PbS nanofilms, were studied for application in nanodosimetry of ionizing radiation. Readout of the delivered dose was carried out by measurements of photoelectron emission (PE) current from ZrO2:PbS nanofilms. PE emission was excited by UV photons having energy of 4.6–6.2 eV. First, the nanofilms were irradiated with non-ionizing UV radiation used as a model of ionizing radiation in order to extract exposure-dependent signal from PE spectra of ZrO2:PbS nanofilms. It was found that exposure-dependent signal is provided by PbS nanoparticles and it is the decrease of the increment of PE current calculated in energy range of 4.9–5.5 eV. The extracted signal was further analyzed by irradiating ZrO2:PbS nanofilms with 9 MeV electron radiation. Second degree polynomial relationship was observed between the decrease of the increment of PE spectra calculated in the energy range of 4.9–5.5 eV and dose of electron radiation in the range of 0–10 Gy. Error of dose measurement was calculated for each delivered dose. Error of dose measurement decreases from 65% to 11% when the delivered dose increases from 2 Gy to 5 Gy and doesn’t exceed 11% in the dose range of 5–10 Gy. Changes in PE spectra of ZrO2:PbS nanofilms under influence of electron radiation suggest that the nanofilms have potential to be used in nanodosimetry of ionizing radiation; however, further adjustment of the method is required to reduce dose measurement error

Photoelectron Emission from PbS Nanodots for Dosimetry of Electron Radiation Used in Radiation Therapy

New advances in modern radiation therapy are associated with use of high dose gradient fields. For instance, difference in surviving factor of healthy tissue and cancer tissue depends on dose gradient (C. Trainor, 2012). To achieve accurate dose delivery to the tumor, high precision of dose measurement is very important. In addition, distribution of radiation induced damage to the human DNA is of a great interest for radiobiology. Therefore, it is important to reduce size of a dosimeter which is capable to measure doses in micro and nano volumes. Moreover, the dosimeter must not be influenced by measurement process. Therefore, contactless technologies are preferable. We studied application of PbS nanodots (NDs) embedded in ZrO2 thin-film for stabilization as a dosimeter of 9 MeV electron radiation supplied by medical linear accelerator. Electron radiation was absorbed by the NDs and the non-contact readout was provided by measurement of the low energy (~0.1-1eV) photoelectron emission (PE) current from the NDs. PE was stimulated by UV photons with energy hv=4.7-6 eV. It was found that electron radiation decreased PE current I(hv) from the PbS:ZrO2 films. To investigate dose-dependent features of the PE spectra, derivatives of the PE current were calculated. Derivative maximums at UV photon energies 5.65 eV and 5.75 eV (±0.03 eV) were observed. Radiation decreased amplitudes of the maximums and this decrease correlated linearly with the dose of electron radiation. Explanation was proposed that this decrease resulted due to the loss of emission active centers in PbS NDs under influence of the electron radiation. The results of the research suggest that PbS NDs are sensitive to dose of 9 MeV medical electron radiation and have potential to provide non-contact readout of the dose by recording PE current from the NDs

ZrO2 Glass Films Influenced by Ultraviolet Radiation

PbS nano punktu īpašības, apstarojot ar gaism

PbS Nanodots in ZrO2 Thin-Film Matrix as a Possible Material for Microdosimetry of Ionizing Radiation

Lead sulfide (PbS) nanodots embedded in a thin layer of zirconia (ZrO2) (ZrO2:PbS thin films) can be a promising material for radiation dosimetry purposes [1]. Application of the ZrO2:PbS thin films for microdosimetry of ionizing electron radiation was studied in this research. Spatial resolution of the radiation dosimeter is important in microdosimetry. This means it is important to define the smallest sensitive area of the dosimeter that can respond to radiation. To estimate the detection resolution of the ZrO2:PbS films, the samples were irradiated with 6 MeV electron beam using medical linear accelerator. One half of each sample was covered with radiation attenuating material (2.3 mm thick aluminium plate). This resulted in scattering of the electrons on the border between the irradiated and covered parts of the samples. It was hypothesized that electron scattering distance limited the resolution of the potential dosimeter. Electron scattering distance was estimated by scanning surface electrical potential of the films in the direction from the covered to the irradiated part perpendicularly to the border line. Measurements were done using Kelvin mode of atomic force microscopy. The film surface right and left to the border line had an increased value of the electrical potential in comparison with the other parts of the films. It was found that the electron scattering distance depended on the concentration of the PbS nanodots in the ZrO2 matrix. The estimated electron scattering distance was: in the ZrO2:20%PbS films ~ 1.5 mm; in the ZrO2:10%PbS films ~ 0.6 mm; in the ZrO2 matrix ~ 0.4 mm. It was supposed that increase in the concentration of the PbS nanodots might have resulted in possible deterioration of the ZrO2:PbS dosimeter spatial resolution. Perhaps this was due to the electron scattering on PbS nanodots

Application of Lead Sulphide Nanoparticles for Dosimetry of Ionizing Radiation

The aim of the research is to design a dosimeter that provides measurements of doses of ionizing radiation absorbed in nano-sized objects. Such dosimeters can be useful for radiobiology in order to study effects of radiation on nanosized biological structures such as DNA molecule. We offer to use radiation-sensitive semiconductor nanoparticles as nanosized active elements of the dosimeter. Nanoparticles have to be embedded into a dielectric matrix that provides physical and chemical stability of the nanoparticles. Ionizing radiation can change concentration of electrons on localized levels of dosimeter material. Therefore, readout of the absorbed dose can be provided by measurements of photoelectron emission (PE) from the dosimeter. Lead sulphide (PbS) nanoparticles having diameters of 2.5–4.5 nm embedded in a matrix of zirconium oxide (ZrO2) by sol-gel technology [1] were studied (ZrO2:PbS films). The films were irradiated with 0–10 Gy of 9 MeV electron radiation generated by a medical linear accelerator. It was found that PbS nanoparticles create active PE centres in ZrO2:PbS film. Concentration of the active PE centres decreases under influence of ionizing radiation

Electron Emission for Nanodosimetry of Ionizing Radiation and Gas Sensing

Photoelectron (PE) and thermostimulated exoelectron (TE) emission spectroscopies were explored for nanodosimetry of electron radiation and gas sensing. Lead sulphide (PbS) nanocrystals embedded in zirconia (ZrO2) thin-films were employed to absorb electron radiation and changes in PE properties of the films in dependence on absorbed dose were studied. Gases benzene and isopentane were adsorbed onto silicon substrates and changes in PE and TE emission properties of the substrates were explored. The research demonstrated that both PE and TE are promising approaches to use in sensing applications

Chapter 14. Electron Emission Standed Nanodosimetry and Gas Detection

Photoelectron (PE) and thermostimulated exoelectron (TE) emission spectroscopies were explored for gas sensing and electron radiation nanodosimetry. Silicon substrates were in use as the working matter for benzene and isopentane sensing. PbS nanocrystals embedded in ZrO2 thin-films were employed to absorb electron radiation. Both PE and TE influenced by gas absorption and radiation deliver promising approaches for gas sensing and nanodosimetry

PbS Nanodots Embedded in ZrO2 Thin Films for Ultraviolet Radiation Dosimetry

PbS nanodots embedded in ZrO2 thin film matrix (ZrO2:PbS films) were investigated for UV radiation dosimetry purposes. ZrO2:PbS films were UV irradiated using wavelengths 250 – 400 nm. Photoelectron emission spectra of ZrO2:PbS films were recorded and band structure of the films was calculated. It was found that density of localized states increased with increase in concentration of PbS nanodots which allowed to suggest that PbS nanodots are responsible for creation of localized states. Number of localized states decreased after UV irradiation. The linear correlation between number of localized states and time of UV exposure was observed. Observed changes in band structure of ZrO2:PbS films under the influence of UV irradiation suggest that the films may be considered as an effective material for UV radiation dosimetry, PbS nanodots being the UV sensitive substance of the films