Secondary Photon Emission Research Articles

Optical nanotransceivers in photonics

The analogy used in nanophotonics with radiophysics, on the basis of which the notion of an optical nanoantenna was introduced and fruitfully used, is extended to the case of two-step processes with optical excitation of a quantum emitter (scatterer) and subsequent emission of secondary photons and the concept of an “optical nanotransceiver” (transceiver), i. e. a device receiving primary and generating secondary photons is introduced. The nanotransceiver efficiency parameter is introduced, which is defined by the product of the primary radiation intensity factor and the local density of photonic states at the secondary radiation frequency. This nanotransceiver parameter determines scattered radiation intensity enhancement and a maximum possible value of photoluminescence enhancement. The latter is achieved for emitters with low intrinsic quantum yield.

Abstract 1389: Bismuth gadolinium nanoparticles enhance radiation therapy in hepatocellular carcinoma

Abstract Introduction: Primary cancers of the liver is the fourth most common cause of cancer-related deaths and the second most lethal tumor, with a 5-year survival rate of only 18%. Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer. Although HCC is a radiosensitive tumor, radiotherapy (RT) has had a limited role in therapy due to the sensitivity of normal liver parenchyma, thus minimizing radiation exposure is optimal. High atomic number nanoparticles (NP) like bismuth (Bi) and gadolinium (Gd) have been shown to be effective radiosensitizers. Exposure of NP to ionizing radiation leads to the emission of secondary electrons and photons that can damage cells by free radical components, resulting in radiation dose-enhancement. Here we synthesized a multifunctional theranostic NP containing both Bi and Gd (BiGdNP) that can act both as a radiosensitizer and as a bimodal contrast agent for T1 MRI and CT imaging. Materials and Methods: BiGdNP were synthesized using one-pot thermal decomposition of Bi(III) acetate and Gd(III) acetate. Morphology of the NP was characterized by transmission electron microscopy (TEM, JEOL) while Bi and Gd were quantified by inductively coupled plasma-mass spectrometry (ICP-MS, Agilent). Dose-dependent cytotoxicity of BiGdNP was assessed by alamarBlueTM assay. HepG2 cells with BiGdNP were irradiated at 0, 2, and 4 Gy using a 137Cs irradiator. Irradiated cells were incubated at 300 cells/well for 2 weeks. Surviving colonies (1 colony ≥50 cells) were fixed with 10% formalin and stained with 0.5% crystal violet for counting. Magnetic resonance imaging at 4.7 Tesla (Bruker) and micro-computed tomography imaging (GE Medical Systems) were performed on BiGdNP-injected C57BL/6 mice to evaluate liver uptake. Results: Synthesized BiGdNP have good size and shape uniformity with average size of 118 ± 16 nm. No significant difference in cell viability was observed with non-treated and BiGdNP-treated cells at a maximum concentration of 50 μg/mL (p>0.05, t test). This concentration was then used to treat the cells prior to gamma irradiation. In the absence of RT, no adverse effects were observed with BiGdNP-treated cells. For both the 2 and 4 Gy doses, surviving fractions in the BiGdNP-treated groups were decreased than non-treated groups (p<0.05, t test). In addition to radiosensitization, increasing the BiGdNP concentration resulted in increased radiopacity in μ- CT and shorter T1 relaxation time in MRI in vitro and contrast enhancement of the liver in both μ-CT and MRI following intravenous administration in vivo. Conclusion: BiGdNP in combination with RT is more efficient in reducing reproductive viability of HCC than RT alone. The added MRI/CT imaging modality can potentially aid in the visualization of tumor delineation to facilitate localized radiation treatment. Citation Format: Avinash Kakulavar, Raniv D. Rojo, Jossana A. Damasco, Marites P. Melancon, Joy V. Perez. Bismuth gadolinium nanoparticles enhance radiation therapy in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1389.

Method of spatial size measurement of relativistic electrons beams with small bunch length

We investigate the practical implementation of a previously proposed method for determining the transverse dimensions of an electron beam on a target by measuring the two-dimensional angular distributions of diffracted transition radiation of relativistic electrons for two distances between the crystal where the radiation is generated and the coordinate detector for femtosecond bunches. We show that determining electron microbunches with small longitudinal sizes requires an increased photon energy, achieved by decreasing the observation angle. The sensitivity limits of the method and the influence of the emission of secondary electrons and photons from the detector pixels are discussed.

Radioembolization for the Treatment of Primary and Metastatic Liver Cancers.

Radioembolization using 90Y microspheres (glass or resin) has been introduced as an effective intraarterial therapy for unresectable primary and metastatic liver cancers. Although the basic therapeutic effect of chemoembolization results from ischemia, the therapeutic efficacy of radioembolization comes from radiation. Furthermore, compared with surgical resection and local ablation therapy, radioembolization is available with less limitation on the sites or number of liver cancers. The radioisotope 90Y is a β-radiation emitter without γ-radiation, with the emission of secondary bremsstrahlung photons and small numbers of positrons. Administration of 90Y microspheres into the hepatic artery can deliver a high dose of radiation selectively to the target tumor with limited radiation exposure to the surrounding normal parenchyma, and has low systemic toxicity. In general, radioembolization has been considered for patients with unresectable primary or metastatic liver-only or liver-dominant cancers with no ascites or other clinical signs of liver failure, life expectancy of > 12weeks, and good performance status. Here, we review the current radioactive compounds, pretreatment assessment, and indications for radioembolization in patients with hepatocellular carcinoma, intrahepatic cholangiocarcinoma, and liver metastases from colorectal cancer.

Eavesdropping and countermeasures for backflash side channel in fiber polarization-coded quantum key distribution

Nowadays, the practical security of quantum key distribution (QKD) is the biggest challenge. In practical implementation, the security of a practical system strongly depends on its device implementation, and device defects will create security holes. The information leakage from a receiving unit due to secondary photon emission (backflash) is caused by a single-photon detector in the avalanche process. Now studies have shown that the backflash will leak the information about time and polarization and the eavesdropping behavior will not generate additional error rate in the communication process. An eavesdropping scheme obtaining time information by using backflash is proposed. Targeting this security hole for backflash leaking polarization information, an eavesdropping scheme for obtaining polarization information by using backflash is proposed in free-space QKD; however, it has not been reported in fiber QKD. In this study, the eavesdropping scheme and countermeasures for obtaining information by using backflash in fiber polarization-coded QKD is proposed. Since the polarization state of the fiber polarization-coded QKD system is easy to change, the scheme is proposed based on the time-division multiplexing polarization compensation fiber polarization-coded QKD system. In theory, the eavesdropper in this scheme obtaining the key information by using the backflash is theoretically deduced, and corrects the polarization change of the backflash by time-division multiplexing polarization compensation method, thus obtaining the accurate polarization information. The probability of backflash in the fiber polarization-coded QKD is measured to be 0.05, and the information leakage in the proposed eavesdropping scheme is quantified. The lower limit of the information obtained by the eavesdropper is 2.5 × 10<sup>–4</sup>. Due to the fact that the polarization compensation process increases invalid information in actual operation, the information obtained by the eavesdropper will be further reduced, thus obtaining the lower limit of information leakage. The results show that the backflash leaks a small amount of key information in a time-multiplexed polarization-compensated fiber polarization-coded QKD system. The wavelength characteristics of the backflash can be utilized to take corresponding defense methods. Backflash has a wide spectral range, and the count of backflash has a peak wavelength. So, tunable filters and isolators can be used to reduce backflash leakage, thereby reducing the information leakage.

Quantifying backflash radiation to prevent zero-error attacks in quantum key distribution

Single-photon avalanche diodes (SPADs) are the most widespread commercial solution for single-photon counting in quantum key distribution applications. However, the secondary photon emission that arises from the avalanche of charge carriers that occurs during the detection of a photon may be exploited by an eavesdropper to gain information without inducing errors in the transmission key. In this paper, we characterize such backflash light in gated InGaAs/InP SPADs and discuss its spectral and temporal characterization for different detector models and different operating parameters. We qualitatively bound the maximum information leakage due to backflash light and propose solutions for preventing such leakage.

Improving the neutron-to-photon discrimination capability of detectors used for neutron dosimetry in high energy photon beam radiotherapy

The increasing interest of the medical community to radioinduced second malignancies due to photoneutrons in patients undergoing high-energy radiotherapy, has stimulated in recent years the study of peripheral doses, including the development of some dedicated active detectors. Although these devices are designed to respond to neutrons only, their parasitic photon response is usually not identically zero and anisotropic. The impact of these facts on measurement accuracy can be important, especially in points close to the photon field-edge.A simple method to estimate the photon contribution to detector readings is to cover it with a thermal neutron absorber with reduced secondary photon emission, such as a borated rubber. This technique was applied to the TNRD (Thermal Neutron Rate Detector), recently validated for thermal neutron measurements in high-energy photon radiotherapy. The positive results, together with the accessibility of the method, encourage its application to other detectors and different clinical scenarios.

Shielding implications for secondary neutrons and photons produced within the patient during IMPT

Intensity modulated proton therapy (IMPT) uses a combination of computer controlled spot scanning and spot-weight optimized planning to irradiate the tumor volume uniformly. In contrast to passive scattering systems, secondary neutrons and photons produced from inelastic proton interactions within the patient represent the major source of emitted radiation during IMPT delivery. Various published studies evaluated the shielding considerations for passive scattering systems but did not directly address secondary neutron production from IMPT and the ambient dose equivalent on surrounding occupational and nonoccupational work areas. Thus, the purpose of this study was to utilize Monte Carlo simulations to evaluate the energy and angular distributions of secondary neutrons and photons following inelastic proton interactions within a tissue-equivalent phantom for incident proton spot energies between 70 and 250 MeV. Monte Carlo simulation methods were used to calculate the ambient dose equivalent of secondary neutrons and photons produced from inelastic proton interactions in a tissue-equivalent phantom. The angular distribution of emitted neutrons and photons were scored as a function of incident proton energy throughout a spherical annulus at 1, 2, 3, 4, and 5 m from the phantom center. Appropriate dose equivalent conversion factors were applied to estimate the total ambient dose equivalent from secondary neutrons and photons. A reference distance of 1 m from the center of the patient was used to evaluate the mean energy distribution of secondary neutrons and photons and the resulting ambient dose equivalent. For an incident proton spot energy of 250 MeV, the total ambient dose equivalent (3.6 × 10(-3) mSv per proton Gy) was greatest along the direction of the incident proton spot (0°-10°) with a mean secondary neutron energy of 71.3 MeV. The dose equivalent decreased by a factor of 5 in the backward direction (170°-180°) with a mean energy of 4.4 MeV. An 8 × 8 × 8 cm(3) volumetric spot distribution (5 mm FWHM spot size, 4 mm spot spacing) optimized to produce a uniform dose distribution results in an ambient dose equivalent of 4.5 × 10(-2) mSv per proton Gy in the forward direction. This work evaluated the secondary neutron and photon emission due to monoenergetic proton spots between 70 and 250 MeV, incident on a tissue equivalent phantom. Example calculations were performed to estimate concrete shield thickness based upon appropriate workload and shielding design assumptions. Although lower than traditional passive scattered proton therapy systems, the ambient dose equivalent from secondary neutrons produced by the patient during IMPT can be significant relative to occupational and nonoccupational workers in the vicinity of the treatment vault. This work demonstrates that Monte Carlo simulations are useful as an initial planning tool for studying the impact of the treatment room and maze design on surrounding occupational and nonoccupational work areas.

Kinetics of pulse-induced photoluminescence from a semiconductor quantum dot

Optical methods, which allow the determination of the dominant channels of energy and phase relaxation, are the most universal techniques for the investigation of semiconductor quantum dots. In this paper, we employ the kinetic Pauli equation to develop the first generalized model of the pulse-induced photoluminescence from the lowest-energy eigenstates of a semiconductor quantum dot. Without specifying the shape of the excitation pulse and by assuming that the energy and phase relaxation in the quantum dot may be characterized by a set of phenomenological rates, we derive an expression for the observable photoluminescence cross section, valid for an arbitrary number of the quantum dot's states decaying with the emission of secondary photons. Our treatment allows for thermal transitions occurring with both decrease and increase in energy between all the relevant eigenstates at room or higher temperature. We show that in the general case of N states coupled to each other through a bath, the photoluminescence kinetics from any of them is determined by the sum of N exponential functions, whose exponents are proportional to the respective decay rates. We illustrate the application of the developed model by considering the processes of resonant luminescence and thermalized luminescence from the quantum dot with two radiating eigenstates, and by assuming that the secondary emission is excited with either a Gaussian or exponential pulse. Analytic expressions describing the signals of secondary emission are analyzed, in order to elucidate experimental situations in which the relaxation constants may be reliably extracted from the photoluminescence spectra.

Resonant X-ray Enhancement of the Auger Effect in High-Z Atoms, Molecules, and Nanoparticles: Potential Biomedical Applications

It is shown that X-ray absorption can be considerably enhanced at resonant energies corresponding to K-shell excitation into higher shells with electron vacancies following Auger emissions in high-Z elements and compounds employed in biomedical applications. We calculate Auger resonant probabilities and cross sections to obtain total mass attenuation coefficients with resonant cross sections and detailed resonance structures corresponding to Kalpha, Kbeta, Kgamma, Kdelta, and Keta complexes lying between 6.4-7.1 keV in iron and 67-80 keV in gold. The basic parameters were computed using the relativistic atomic structure codes and the R-matrix codes. It is found that the average enhancement at resonant energies is up to a factor of 1000 or more for associated K --> L, M, N, O, P transitions. The resonant energies in high-Z elements such as gold are sufficiently high to ensure significant penetration in body tissue, and hence the possibility of achieving X-radiation dose reduction commensurate with resonant enhancements for cancer theranostics using high-Z nanoparticles and molecular radiosensitizing agents embedded in malignant tumors. The in situ deposition of X-ray energy, followed by secondary photon and electron emission, will be localized at the tumor site. We also note the relevance of this work to the development of novel monochromatic or narrow-band X-ray emission sources for medical diagnostics and therapeutics.

The science and technology of low-energy ion-surface interactions

Low-energy ion-surface interactions have played a significant role in both the analysis and modification of the near-surface layers of solid materials. From ion scattering spectrometry to eV implantation, the technology of the ion beam or plasma system has played a key role in determining the effectiveness of the processes involved. The development and understanding of the technology required for low-energy ion implantation, ion-beam deposition, ion plating and reactive ion etching has relied heavily on the availability of analytical systems capable of characterising the nature of both the ion beams or plasmas and the surface region of the solid being treated. The present review follows the development of ion beam systems from the low-current analytical beams used for low and medium ion scattering and secondary ion and photon emission through to the high-current machines used for ion implantation and ion beam deposition. The transport concepts used in the latter machines formed the basis of high current, low-energy systems used commercially to produce the ultra-shallow junctions required for the current generation of MOS devices. These developments will be described in the context of the growth in understanding of the beam and plasma physics and the atomic collision processes involved. All the technological developments at Salford were carried out in the course of detailed studies of the atomic collision processes associated with ion trapping and release, ion scattering and sputtering. The results of some of these studies and the ways in which they have contributed to our current understanding of the physics of ion-surface interactions will also be reviewed.

Spatial pileup considerations for pixellated gamma-ray detectors

High-spatial-resolution solid-state detectors being developed for gamma-ray applications benefit from having pixel dimensions substantially smaller than detector slab thickness. This leads to an enhanced possibility of charge partially spreading to neighboring pixels as a result of diffusion (and secondary photon emission) transverse to the drift direction. An undesirable consequence is the effective magnification of the event "size" and the spatial overlap issues which result when two photons are absorbed in close proximity within the integration time of the detector/readout system. In this work, we develop the general statistics of spatial pileup in imaging systems and apply the results to detectors we are developing based on pixellated cadmium zinc telluride (CdZnTe) and a multiplexing application-specific integrated circuit (ASIC) readout. We consider the limitations imposed on total count rate capacity and explore in detail the consequences for the LISTMODE data-acquisition strategy. Algorithms are proposed for identifying and, where possible, resolving overlapping events by maximum-likelihood estimation. The efficacy and noise tolerance of these algorithms will be tested with a combination of simulated and experimental data in future work.

Towards two-dimensional brachytherapy dosimetry using plastic scintillator: localization of the scintillation process

Detecting the scintillation light coming from a thin sheet of plastic scintillator (PS) provides a promising fast and precise tissue equivalent method for radiation dose measurements in two dimensions. The successful implementation of such technique requires high efficiency, dosimetric tissue equivalence and high localization of the scintillation process. The last is needed to assure that the light photons originating from a pixel of the scintillator sheet correspond to energy deposited in the same pixel. Since no such information is available for PS material with standard or modified chemical composition we have developed two experimental methods for assessing the scintillation locality by measuring the optical spectra and the scintillation light profile (SLP) of PS samples with different thickness. The results of the two types of measurements are consistent with each other and with a simple theoretical model of the energy conversion process. We have demonstrated that comparing the relative intensities of the primary and secondary photon peaks in the optical spectra of the scintillator is a sensitive approach to determine the delocalization of the secondary photon emission. The ratio of the number of primary to secondary photons shows strong dependence on PS dye composition. Two types of plastic scintillator materials were tested and the advantages of one of them for radiation dosimetry are demonstrated.

Spatially resolved optical emission study of sputtering in reactive plasmas

The study of material sputtering under low-pressure reactive ion etching conditions in various gases (Cl2, SiCl4, O2) was performed using optical emission spectroscopy with high spatial resolution. Sputtering-induced secondary photon emission (atomic and molecular) from the processed materials (Si, Al2O3, GaAs) was found to be strongly localized near the target surface. A spatial distribution of atomic line emission intensity was shown to be essentially nonmonotonical with distance from the surface. This effect was explained by a cascade feeding from the upper lying atomic levels, which is enhanced in plasma (collisional) environment. A simplified model accounting for the cascading has been developed, and velocities of sputtered excited atoms (in the range of 2–7×106 cm/s) and molecules (about 2–5×105 cm/s) have been evaluated from the emission spatial decay parameters. The excited sputtered atoms and molecules are produced in different types of collisions. Fast excited atoms can be produced only in the first few collisions of the incident ion in the surface top layers, whereas excited molecules are knocked off by secondary (slow) atoms originated from a collision cascade inside the solid. Based on this concept of the process, simple expressions for atomic and molecular excitation yields as functions of the incident ion flux and surface coverage were deduced. The technique can be used for in situ surface probing during plasma processing.

Study of Ion-Induced Secondary Photon Emission in Reactive Ion Etching Experiment

Optical emission spectroscopy with high spatial resolution was employed for the study of surface sputtering under reactive ion etching conditions in chlorine-containing gas mixtures. Secondary photon emission (both atomic and molecular) from the processed material was found to be strongly localized near the surface. A simple model, considering the observed features of the secondary photon emission as induced by ion sputtering of the processed surface, has been presented. This technique can give new opportunities for in-situ diagnostics and modeling of plasma-surface interaction in various plasma technologies.

Secondary photon emission in plasma processing

Optical emission spectroscopy with high spatial resolution was applied for the study of plasma–material interaction in low-pressure reactive ion etching. Atomic and molecular emission by sputtered material has been found to be strongly localized near the surface. Excited particles are produced during sputtering by energetic ions, with the mechanisms being different for atoms and molecules. In atomic secondary photon emission, a cascade from highly excited levels is shown to be important. This method can be used as a probe during plasma processing.

Investigations of the interactions of highest charge state ions with surfaces

Experimental results from a series of investigations, the aim of which is to provide an exploratory overview of the wide range of phenomenon associated with the interaction of slow very highly charged ions with solids and solid surfaces, are reported. Incident charge state dependencies of secondary electron, x-ray and secondary ion emission are measured. In addition, microscopic studies are performed using an "Atomic Force Microscope" to investigate highly charged ion induced surface defects. The ions, used for these studies, range from O7+ to Th80+ and U82+ with low incident kinetic energies (~2 eV/amu to 3 keV/amu). As an overall result, enhancements for the low energy secondary electron, sputter ion and photon emission are observed with increasing charge states. X-ray emission spectra are found to be consistent with the formation of so called "hollow" atoms above and at the surface as part of the neutralization processes. Small angle scattering behaviour, under specular reflection conditions, indicate very fast decay processes for the hollow atom, outside the solid surface. The microscopic studies reveal interesting nano-size surface defects caused by single highly charged ion incidence.

Bombardment-induced light emission spectroscopy of GaAs

Gal spectral lines originating from the sputtering of GaAs under 6–10 keV Ar + ion bombardment have been studied. Results of the measurements on the target position, beam current and projectile energy dependences of 4172, 4033 and 2944 Å lines are presented. It is found that the secondary photon emission yields can be well described by the model proposed by Wright and Gruen.

Simultaneous detection of secondary ions and photons produced by the impact of keV polyatomic ions

(CsI) n I −( n=0−3), low mass organic negative clusters, and H −, in the 20–46 keV energy range, have been used in time-of-flight secondary ion mass spectrometry (TOF-SIMS) experiments to study the relationships between secondary ion and photon emission from a surface. We report on the simultaneous detection of secondary ions and photons produced by the impact of keV polyatomic ions. Our results indicate that, for a CsI target, secondary ions and photons are produced independently of each other through different mechanisms. Secondary ion emission is strongly dependent upon the complexity of the primary ion, i.e. monoatomic or polyatomic. However, photon emission appears to be independent of the primary ion's complexity and depends primarily upon the velocity of the primary ion. Unlike the secondary ion yields, no yield enhancements for the photons were observed due to polyatomic primary ions. Only broad band light emission from the bulk of the target was observed; no line emissions from sputtered species were detected. We compare the yields of both secondary ions and photons that were collected simultaneously, and present a simple model that describes the observed photon yields as a function of both the electronic and nuclear stopping powers of the primary ion.

Ion/surface interaction studies with 1-3 keV/amu ions up to Th80+

Abstract First results from a series of experiments aimed at the study of the interaction of slow very highly charged ions with conductor and insulator surfaces are reported. Charge state dependences of secondary electron, x-ray and secondary ion emission are measured. In addition, microscopic studies are performed using an ‘Atomic Force Microscope’ to investigate surface defects, produced through the stored electrostatic potential of the incident ion. The ions that have been used for these studies range from O7+ to Th80+, with low kinetic energies (generally 1–3 keV/amu). Overall, enhancement of the low energy secondary electron, sputter ion and photon emission are observed with increasing charge states. Saturation in the electron emission yield at very low velocities confirm present models for image charge acceleration effects. X-ray emission spectra are found to be consistent with the formation of so called ‘hollow’ atoms near the surface during the neutralization processes. The microscopic studies rev...