Cerenkov Emission Research Articles

Highly-efficient, octave spanning soliton self-frequency shift using a specialized photonic crystal fiber with low OH loss

We report the first demonstration of efficient, octave spanning soliton self-frequency shift. In order to achieve this we used a photonic crystal fiber with reduced OH absorption and widely spaced zero-dispersion wavelengths. To our knowledge, this is the largest reported frequency span for a tunable, fiber-based source. In addition, we observe the generation of light above 2 μm directly from a Ti:Sapphire laser in the form of Cerenkov emission by the soliton when the red-shift saturates at the edge of the anomalous dispersion region.

Fast-Specific Tomography Imaging via Cerenkov Emission

Development of more tumor-specific radiopharmaceuticals is not enough; to understand the disease, we must study data modeling. Although fluoro-18-deoxyglucose positron emission tomography can map a multi-peak distribution of trace radioisotopes, optical tomography should also be able to redirect the distribution. Multi-view image acquisition of small animals injected with 2-deoxy-2-[(18)F]fluoro-D: -glucose began with X-ray computed tomography scanning and Cerenkov luminescence imaging. After fusion processing, utilization of the geometric row scaling and L (1/2) regularization operator effectively generates in vivo Cerenkov luminescence tomography images with the SP(3) forward model. The identification is confirmed by the comparison between tumor-specific tomography from Cerenkov emission and the radioactivity measured in vitro. The proposed technique can quickly localize the mobility of radionuclides and uptake by organs, which provides an imaging methodology in oncology.

Cerenkov emission induced by external beam radiation stimulates molecular fluorescence

Cerenkov emission is induced when a charged particle moves faster than the speed of light in a given medium. Both x-ray photons and electrons produce optical Cerenkov photons in everyday radiation therapy of tissue; yet, this phenomenon has never been fully documented. This study quantifies the emissions and also demonstrates that the Cerenkov emission can excite a fluorophore, protoporphyrin IX (PpIX), embedded in biological phantoms. In this study, Cerenkov emission induced by radiation from a clinical linear accelerator is investigated. Biological mimicking phantoms were irradiated with x-ray photons, with energies of 6 or 18 MV, or electrons at energies 6, 9, 12, 15, or 18 MeV. The Cerenkov emission and the induced molecular fluorescence were detected by a camera or a spectrometer equipped with a fiber optic cable. It is shown that both x-ray photons and electrons, at MeV energies, produce optical Cerenkov photons in tissue mimicking media. Furthermore, we demonstrate that the Cerenkov emission can excite a fluorophore, protoporphyrin IX (PpIX), embedded in biological phantoms. The results here indicate that molecular fluorescence monitoring during external beam radiotherapy is possible.

Multispectral Cerenkov luminescence tomography for small animal optical imaging

Quite recently Cerenkov luminescence imaging (CLI) has been introduced as a novel pre-clinical imaging for the in vivo imaging of small animals such as mice. The CLI method is based on the detection of Cerenkov radiation (CR) generated by beta particles as they travel into the animal tissues with an energy such that Cerenkov emission condition is satisfied. This paper describes an image reconstruction method called multi spectral diffuse Cerenkov luminescence tomography (msCLT) in order to obtain 3D images from the detection of CR. The multispectral approach is based on a set of 2D planar images acquired using a number of narrow bandpass filters, and the distinctive information content at each wavelength is used in the 3D image reconstruction process. The proposed msCLT method was tested both in vitro and in vivo using 32P-ATP and all the images were acquired by using the IVIS 200 small animal optical imager (Caliper Life Sciences, Alameda USA). Source depth estimation and spatial resolution measurements were performed using a small capillary source placed between several slices of chicken breast. The theoretical Cerenkov emission spectrum and optical properties of chicken breast were used in the modelling of photon propagation. In vivo imaging was performed by injecting control nude mice with 10 MBq of 32P-ATP and the 3D tracer bio-distribution was reconstructed. Whole body MRI was acquired to provide an anatomical localization of the Cerenkov emission. The spatial resolution obtained from the msCLT reconstructed images of the capillary source showed that the FWHM is about 1.5 mm for a 6 mm depth. Co-registered MRI images showed that the Cerenkov emission regions matches fairly well with anatomical regions, such as the brain, heart and abdomen. Ex vivo imaging of the different organs such as intestine, brain, heart and ribs further confirms these findings. We conclude that in vivo 3D bio-distribution of a pure beta-minus emitting radiopharmaceutical such as 32P-ATP can be obtained using the msCLT reconstruction approach.

SU‐E‐T‐211: Optical Fluorescence Monitoring during External Beam Radiation Therapy Using Cerenkov Emission as Excitation Source

Purpose: Cerenkov emission is induced when a charged particle travels faster than the speed of light in a given medium. The Cerenkov effect occurs in everyday radiation therapy of tissue, yet this phenomenon has never been quantitatively characterized. In this study, an investigation of high‐energy radiation from a linear accelerator was carried out, to quantify the induced Cerenkov emission in biological media. Furthermore, we demonstrate that the Cerenkov emission can excite a molecularly produced fluorophore, protoporphyrin IX (PpIX), embedded in biological phantoms. Methods: Electrons at 6–18 MeV energies and photons at 6 or 18 MV energies, from a linear accelerator, were used to induce Cerenkov emission in aqueous phantoms. First, a CMOS camera imaged a water tank in order to investigate the dose distribution of external beam radiation. Secondly, the fluorescent photosensitizer PpIX was mixed into the phantom. An optical fiber bundle, positioned at the phantom surface, collected the Cerenkov emission and the Cerenkov‐induced optical fluorescence. Results: Images acquired in a water tank clearly shows the cross section of the electron (or photon) beam at all energies using a dose rate of approximately 4Gy/min. As expected from the Cerenkov theory the intensity increases as the energy of the radiation increases. Spectra acquired, either with photons or electrons, reveal that the Cerenkov emission excites the PpIX molecule, leading to optical fluorescence in the red spectral region. Conclusions: The results here indicate that molecular fluorescence monitoring during external beam radiotherapy is possible. This could potentially be used as a tool for treatment assessment through the evaluation PpIX production from e.g. high‐grade glioma.This work has been funded by NIH grants RO1CA120368 and PO1CA084203.

Bi-galileon theory II: phenomenology

We continue to introduce bi-galileon theory, the generalisation of the single galileon model introduced by Nicolis et al. The theory contains two coupled scalar fields and is described by a Lagrangian that is invariant under Galilean shifts in those fields. This paper is the second of two, and focuses on the phenomenology of the theory. We are particularly interesting in models that admit solutions that are asymptotically self accelerating or asymptotically self tuning. In contrast to the single galileon theories, we find examples of self accelerating models that are simultaneously free from ghosts, tachyons and tadpoles, able to pass solar system constraints through Vainshtein screening, and do not suffer from problems with superluminality, Cerenkov emission or strong coupling. We also find self tuning models and discuss how Weinberg's no go theorem is evaded by breaking Poincar\'e invariance in the scalar sector. Whereas the galileon description is valid all the way down to solar system scales for the self-accelerating models, unfortunately the same cannot be said for self tuning models owing to the scalars backreacting strongly on to the geometry.

Factors Influencing Time Resolution of Scintillators and Ways to Improve Them

The renewal of interest in Time of Flight Positron Emission Tomography (TOF-PET), as well as the necessity to precisely tag events in high energy physics (HEP) experiments at future colliders are pushing for an optimization of all factors affecting the time resolution of the whole acquisition chain comprising the crystal, the photo detector, and the electronics. The time resolution of a scintillator-based detection system is determined by the rate of photo electrons at the detection threshold, which depends on the time distribution of photons being converted in the photo detector. The possibility to achieve time resolution of about 100 ps Full Width at Half Maximum (FWHM) requires an optimization of the light production in the scintillator, the light transport and its transfer from the scintillator to the photo detector. In order to maximize the light yield, and in particular the density of photons in the first nanosecond, while minimizing the rise time and decay time, particular attention must be paid to the energy transfer mechanisms to the activator as well as to the energy transition type at the activator ion. Alternatively other light emission mechanisms can be considered. We show that particularly Cerenkov emission can be used for this purpose. Special emphasis was put on the light transport within the crystal and at its interface with the photo detector. Since light is produced isotropically in the scintillator the detector geometry must be optimized to decrease the optical path-length to the photo detector. Moreover light bouncing within the scintillator, affecting about 70% of the photons generated in currently used crystals, must be reduced as much as possible. We also investigate photonics crystals that are specifically designed to favor specific light propagation modes at the limit of total reflection inside and outside of the crystal and how they might increase the light transfer efficiency to the photo detector and hence improve time resolution. Examples for the production and deposition of photonics crystals as layers on Lutetium Yttrium Ortho-Silicate (LYSO) and Lutetium Yttrium Aluminum Perovskite (LuYAP) crystals are shown here, as well as first results on an improved light extraction resulting from this method.

Terahertz radiation from Josephson sandwiches

Basic results are presented from a study of the Cerenkov emission of electromagnetic waves by solitary vortices and Swihart waves moving in a long Josephson sandwich embedded in a dielectric. The energy fluxes of the electromagnetic field along a long sandwich are examined. The magnitudes of the fluxes are compared over a wide range of frequencies and wave numbers of surface waves in the sandwich.

TH‐C‐204B‐04: Assessing the Potential of Cerenkov Radiation for in Vivo Imaging of Tumor Hypoxia

Purpose: To assess whether in vivo optical imaging using Cerenkov radiation can (a) produce results that are comparable to those from microPET tumor imaging and (b) provide information that facilitates future dual‐tracer imaging experiments. Method and Materials: (a) Subcutaneous tumors were established by injecting HT‐29 human colon adenocarcinoma cells into the shoulders of 4 nude mice and were grown until they reached a volume of 1cm3. 200microCi of 18F‐EF5 was injected via intraperitoneal injection and 3 mice were imaged using microPET whilst the other was imaged in an IVIS Spectrum. Images were acquired immediately and 1 hour following injection on both machines using acquisition times of 10mins (PET) and 2mins (IVIS). (b) A mathematical model of the Cerenkov emission spectrum was developed and used to predict the ability of Cerenkov imaging to resolve signals from different tracers. Results: (a) In the initial PET and IVIS images the tracer signal was confined to the region of the gastrointestinal region and there was no accumulation in the tumor. After 1 hour both sets of images showed similar biodistribution throughout the body along with uptake in the tumor. (b) The model predicted that different radionuclides can be distinguished through an energy‐dependent red‐shift in their emission spectra leading to higher intensity signals in the optical spectrum. Conclusion: We have shown that 18F‐EF5 Cerenkov imaging of subcutaneous tumors can be performed optically. More specifically our results show that the biodistribution and tumor uptake observed using this technique is in agreement with the microPET data. Our modeling suggests that the spectral differences between radionuclides coupled with the differences in decay rates between tracers labeled with different radioisotopes could be used to develop techniques for separating signals from two tracers for surface‐level tumors thus potentially allowing multiple aspects of tumor biology to be imaged simultaneously.

Cerenkov emission as a positive tag of double beta decays in bolometric experiments

Active background reduction in high resolution calorimeters is a promising approach to achieve ultimate sensitivity in neutrinoless double beta decay experiments. We propose Cerenkov emission from beta rays in bolometric crystals as a viable alternative to scintillation. This novel approach could broaden the range of materials of interest for calorimetric searches of the double beta decay. We discuss the optical properties of TeO2 crystals, as a show case.

Ultraviolet-visible conical emission by multiple laser filaments

We characterized the angular distribution of the supercontinuum emission from multiple infrared laser filaments propagating in air over long distances, from the infrared (1080 nm) to ultraviolet (225 nm). These experimental data suggest that the X-Waves modeling or Cerenkov emission, rather than phase matching of four-wave mixing, could explain the conical emission. We also estimate the total light conversion efficiency from the original laser wavelength into the white-light continuum.

Feasibility of Fibered Monitoring System for Pulsed Dose-Rate Facilities Based on Radioluminescence of SrS:Ce,Sm Phosphor

The possibility to monitor pulsed dose-rate facilities by means of real-time fibered dosimetry is investigated. A system based on the luminescence of the SrS:Ce,Sm is used to monitor pulses from a medical accelerator with four different dose-rates. The RL signal is characterized using a dedicated acquisition system. The RL recorded is linear with dose-rate and dose. The stem effect due to both Cerenkov emission and photoluminescence in the fiber was also investigated with 18 MV photons and 12 MeV electrons.

On electromagnetic waves by an accelerated charged particle in medium

We have investigated the effects of acceleration of a charged particle on its Cerenkov emission and ionization-losses. We have considered the accelerated motion of a charged particle in an infinite medium with the acceleration parallel to the direction of its motion. We have used the method of Fourier transforms to solve the Maxwell's equations with appropriate current and charge-densities to find electromagnetic fields and hence the force experienced by the incident charge due to its interaction with the medium (dielectric or plasma). The results obtained are general and applicable to any acceleration. In the approximations of ‘small acceleration’ and ‘small interaction time’, we have solved the wave equations and determined electromagnetic potentials. It is found that the acceleration of the charged particle strongly changes both its ionization-loss and Cerenkov emission.

METHODS FOR JET STUDIES WITH THREE-PARTICLE CORRELATIONS

We present a method based on three-particle azimuthal correlation cumulants for the study of the interaction of jets with the medium produced in heavy ion collisions at RHIC and LHC where jets cannot be reconstructed on an event-by-event basis with conventional jet finding algorithms. The method is specifically designed to distinguish a range of jet interaction mechanisms such as Mach cone emission, gluon Cerenkov emission, jet scattering, and jet broadening. We discuss how anisotropic flow background conti-butions of second order (e.g. [Formula: see text]) are suppressed in three-particle azimuthal correlation cumulants, and discussed specific model representations of di-jets, away-side scattering, and Mach cone emission.

The track imaging Cerenkov experiment

The Track Imaging Cerenkov Experiment (TrICE) aims for a ground-based measurement of high energy cosmic-ray composition using a novel technique. By separating the Cerenkov emission from the primary and secondary particles, nearly elemental charge resolution can be established. Here the status of the TrICE experiment is discussed.

Methods for jet studies with three-particle correlations

We present a method based on three-particle azimuthal correlation cumulants for studying jet interactions with the medium produced in heavy ion collisions (at RHIC) where jets cannot be reconstructed on an event-by-event basis with conventional jet-finding algorithms. The method is specifically designed to distinguish a range of jet interaction mechanisms such as Mach cone emission, gluon Cerenkov emission, jet scattering, and jet broadening. We describe how anisotropic flow contributions of second order (e.g., ${v}_{2}^{2})$ are suppressed in three-particle azimuthal correlation cumulants, and discuss specific model representations of dijets, away-side scattering, and Mach cone emission.

Plastic scintillation dosimetry and its application to radiotherapy

We present a review of the dosimetric characteristics and properties of plastic scintillation detectors when exposed to high-energy photon and electron beams. The detectors show many desirable qualities, including water equivalence, energy independence, reproducibility, dose linearity, resistance to radiation damage, and near temperature independence. Therefore, these detectors do not require the usual conversion and/or correction factors used for other commonly used detectors to convert the dosimeter reading to absorbed dose. Furthermore, due to their small detecting volume, plastic scintillation detectors exhibit excellent spatial resolution. One issue concerning detector performance is the radiation-induced light arising in the optical fibers that carry the scintillator output to a photomultiplier tube or photodiode. The radiation-induced light produced in optical fibers could be a combination of Cerenkov emission, fluorescence or luminescence depending on the type of material of the fibers utilized. For pure fused silica optical fibers, this spurious light emission is predominantly due to Cerenkov. This is most easily resolved by subtracting the signals from two sets of optical fibers, one carrying the entire signal and the other carrying just the Cerenkov background. Finally, we present two applications for plastic scintillation detectors in clinical radiotherapy: stereotactic radiosurgery dosimetry and the quality assurance of Co 60 and high-energy therapy beams.

AIRFLY: Measurement of the uorescence yield in atmospheric gases

The goal of the AIRFLY (AIR FLuorescence Yield) experiment is to measure the fluorescence yield (FLY) induced by electrons in air to better than 10% precision. A detailed knowledge of the fluorescence emission characteristics is crucial for UHECR (Ultra High Energy Cosmic Ray) air shower energy reconstruction using the fluorescence technique. AIRFLY has been taking data at the Beam Test Facility (BTF) of the INFN Laboratori Nazionali di Frascati, Italy. The dependence of FLY on the atmospheric gas pressure and temperature has been studied. The dependence on electron energy has been measured in the range 50–420 MeV. A new method of absolute calibration by comparison with Cerenkov emission has been investigated. The status of the experiment and the results achieved so far are presented.

An algorithm for real-time dosimetry in intensity-modulated radiation therapy using the radioluminescence signal from Al2O3:C

Although the radioluminescence (RL) signal from optical fibre Al(2)O(3):C dosemeters used in medical applications is essentially proportional to dose rate, the crystals used so far are imperfect in the sense that their RL sensitivity changes with accumulated dose. A computational algorithm has been developed that corrects for these sensitivity changes. We further report on a new system that effectively separates the RL signal generated in the crystal from fluorescence and Cerenkov emission generated in the optical fibre cable using a gating technique in connection with pulsed linear accelerator radiation beams. The dosimetry system has been used for dose measurements in a phantom during an intensity-modulated radiation therapy (IMRT) treatment with 6 MV photons. The RL measurement results are in excellent agreement (i.e. within 1%) with both the OSL results and the dose delivered according to the treatment planning system. RL signals from Al(2)O(3):C can be used for real-time dose rate measurements with a time resolution of approximately 0.1 s and a spatial resolution only limited by the size of the detector (<0.5 mm).

Acoustic wave amplification in one-dimensional quantum well wires

We analyze the Cerenkov emission of acoustic phonons by drifting electrons in a one-dimensional quantum well wire. We find that the electron drift can cause generation of strong acoustic phonons. A general formula for the attenuation coefficient α is obtained as a function of acoustic phonon frequency and drift velocity. Enhancement of amplification is found by considering lower dimensional structures. The attenuation coefficient increases sharply to maximum by increasing drift velocity of electrons in the short wave region. In GaAs Quantum well wire, it is shown that amplification coefficients can be achieved in the terahertz frequency range.