Air Fluorescence Research Articles

PET nano-woven luminescent fibers for efficient air filtration and fluorescence indication of particulate matter

Inhalable particulate matter poses significant health risks, and current air filtration materials often struggle with efficiently capturing particles smaller than 300 nm and providing real-time feedback on filtration performance. We present the synthesis and characterization of polyethylene terephthalate (PET) nano-woven luminescent fibers (PNWLFs), created through a positive and negative dual high-voltage electrospinning method. The PNWLFs feature a unique nano-woven structure composed of backbone fibers (200–1000 nm) and nanofibers (20–160 nm), which endow them with remarkable mechanical strength, maintaining a breaking force of 117.5 cN and structural integrity under a 138 mm water column. The fibers exhibit excellent breathability and waterproof performance, with a water vapor transmission rate of 4.69 kg/m2/day. More importantly, the PNWLFs demonstrate exceptional air filtration capabilities, achieving filtration efficiencies of 99.77 % for PM5.0, 99.76 % for PM2.5, 99.72 % for PM1.0, 99.53 % for PM0.5, and 99.40 % for PM0.3, with minimal pressure drop of 106 Pa. Additionally, these fibers possess a unique fluorescence-indicating function: the fluorescence intensity decreases in response to increasing particulate matter concentration and the number of filtration cycles, allowing for intuitive visual monitoring of filter performance and particulate levels. These attributes underscore the significant potential of PNWLFs synthesized by this work for advanced air filtration applications and effective air quality monitoring.

Informing solar blind radioluminescence imaging through a calibrated spectrum

While direct radiation detection methods offer great insight into the origin of ionizing particles and photons, their use to locate contaminated areas or concealed radioactive sources can lead to undue exposure of personnel and equipment to ionizing radiation or the potential for contamination. These same sources induce ultraviolet (UV) optical photon fluorescence in air – a process referred to as radioluminescence – that may be imaged from low dose regions over larger attenuation lengths than ionizing radiation. However, most optical detection methods are limited to low lighting conditions to image the more abundant ultraviolet-A (UV-A) photons. To extend this capability to room light or daytime conditions, the solar blind region (Ultraviolet-C (UV–C), <280 nm) can be tapped. Though the emission yield of UV-C photons is roughly two orders of magnitude lower than that in the UV-A regime, the UV-C offers dramatic improvements in signal-to-noise ratios under bright lighting conditions due to decreased background interferences. The yield of specific UV-C lines, if present in the literature at all, varies widely, which has a large impact in modeling and analyzing standoff UV-C measurement scenarios. Thus, we have captured improved radioluminescence spectra over 250–400 nm and identified observed emission peaks in ambient air. Many of the UV-C photons produced by ionizing radiation excitation result from high-energy, molecular nitrogen Gaydon-Herman transitions which have had limited study to date for this application. Relating these findings to published UV-A yields, we estimate emissions between 0.15 and 0.19 photons/MeV over 250–280 nm. We also use a commercial corona-discharge imaging camera to demonstrate outdoor UV-C radiation mapping of alpha and gamma emitters from 50 to 75 m standoffs, respectively. The imaged “counts” are compared to optically modeled values and show the same trend over distance.

Remote measurement and calibration of alpha-emitting radionuclides through the utilization of characteristic ultraviolet fluorescence

During the decommissioning of nuclear facilities and spent fuel reprocessing, conventional alpha particle detectors are insufficient for accurately measuring the emissivity of alpha particles due to their high radiation intensity and complex nuclide types. The air fluorescence method is developed to detect the α particle emissivity through measuring the intensity of ultraviolet fluorescence generated by the interaction between α particles and nitrogen or other inert gas mediums. This method offers advantages such as long detection range and immunity to γ radiation interference. The measurement results are primarily influenced by factors including α particle energy, detection distance, and gas medium composition, with photon noise and detection distance determining the detection limit. The obtained results indicate that: In the condition of measured in darkness, measurement time for 1000s, and distance for 1 m, The minimum detection limit for α sources is 7.6 kBq with a relative standard uncertainty of 10%.

Physicochemical characterization of urban dust in Southern Tamaulipas using X-ray fluorescence

Urban dust is composed mostly of particles emitted by anthropogenic processes such as industry, vehicular, and maritime transport, so it may contain heavy metals and PM10 and PM2.5 particles, which affect human health, so its characterization should be taken into account in an environmental monitoring plan. Regarding UD, there are studies about heavy metal contamination conducted in Mexico City (CdMx) and the suburbs of the State of Mexico, but to date, there are none for the Tampico, Ciudad Madero, and Altamira. The manuscript describe the elemental distribution found in urban dust and the possible relationship of the detected elements with emission sources according to the meteorological parameters of the area. The study presents the elemental composition of dust particles from 17 samples collected in the January-April 2023 period, at determined points in the Tampico-Madero-Altamira metropolitan area (TMA). The samples were collected in polyethylene bags and analyzed by X-ray fluorescence in air at an energy of 50 kV. There were 21 elements identified in the TMA. Through the Mexican regulation Pollutant Release and Transfer Register (RETC), it was possible to identify and relate some of the detected elements to some elements reported by local companies such as nickel, lead, and chromium. The most frequently detected metals were Ca, Mn, Zr, Sr, Pb, and V. These results indicate that more extensive work is needed to quantify elements such as Ni, Cr, Pb, and V due to the health problems they may cause. Funded by CONAHCYT 2022-321595.

Test beam results of a fluorescence-based monitor for ultra-high dose rates

In recent years, there has been a significant focus on improving the effectiveness of radiotherapy (RT) and particle therapy in treating tumors while minimizing damage to healthy tissue. A promising development is offered by the observation of the so-called FLASH effect, where ultra-high dose rates delivered in a short time have shown to protect healthy tissues while maintaining anti-tumor efficacy. However, conventional detectors face challenges in monitoring charged beams at these ultra-high dose rates due to non-linear effects. To address this challenge, the FlashDC (Flash Detector beam Counter) has been developed. It uses air fluorescence to monitor beam fluence and spatial distribution in real-time with high accuracy and minimal impact on treatment delivery. This innovative detector offers a linear response for various charged beams, dose rates, and energies, making it a cost-effective solution. Multiple prototypes have been developed and optimized using Monte Carlo simulations. The analysis of data from recent test beam campaigns with electrons delivered at FLASH intensities has demonstrated a linear correlation between the detector signal and the delivered dose per pulse, confirming that fluorescence can be used for beam monitoring in FLASH-RT studies. This contribution introduces the FlashDC monitor, discusses its expected performance, and presents preliminary test beam results obtained with electron beams in FLASH mode.

Thermally activated delayed fluorescence of a Ir(III) complex: absorption and emission properties, nonradiative rates, and mechanism.

One recent experimental study reported a Ir(III) complex with thermally activated delayed fluorescence (TADF) phenomenon in solution, but its luminescent mechanism is elusive. In this work, we combined density functional theory (DFT), time-dependent DFT (TDDFT) and multi-state complete active space second-order perturbation theory (MS-CASPT2) methods to investigate excited-state properties, photophysics, and emission mechanism of this Ir(III) complex. Two main absorption bands observed in experiments can be attributed to the electronic transition from the S0 state to the S1 and S2 states; while, the fluorescence and phosphorescence are generated from the S1 and T1 states, respectively. Both the S1 and T1 states have clear metal-to-ligand charge transfer (MLCT) character. The present computational results reveal a three-state model including the S0, S1 and T1 states to rationalize the TADF behavior. The small energy gap between the S1 and T1 states benefits the forward and reverse intersystem crossing (ISC and rISC) processes. At 300 K, the rISC rate is five orders of magnitude larger than the phosphorescence rate therefore enabling TADF. At 77 K, the rISC rate is sharply decreased but remains close to the phosphorescence rate; therefore, in addition to the phosphorescence, the delayed fluorescence could also contribute to the experimental emission. The estimated TADF lifetime agrees well with experiments, 9.80 vs. 6.67 μs, which further verifies this three-state model.

Progress and future prospect of the CRAFFT project for the next generation UHECR observatory

The next generation of ultra-high energy cosmic ray observations will require large detector arrays to achieve large statistics. In order to realize next-generation large-scale detector arrays, the Cosmic Ray Air Fluorescence Fresnel lens Telescope (CRAFFT) project is developing a low-cost simple fluorescence detector (FD). The simple structure of the CRAFFT detector will reduce the cost to about 1/10 of the current FD. We also aim to realize a fully automated observation system. A prototype of the CRAFFT detector has been successfully used to detect cosmic ray air showers. Since the spatial resolution of the simple FD is rougher than that of the current FD, we are developing a new air shower reconstruction method using the waveform fitting method. In this presentation, we report the performance of the CRAFFT detector, detector optimization, and future prospect.

Energy Spectrum Measured by the Telescope Array Surface Detectors

Located in the west desert of Utah, USA, the Telescope Array experiment is the largest ultra-high energy cosmic ray observatory in the northern hemisphere. It consists of two types of detectors: scintillator surface detectors (SDs) and air fluorescence detectors (FDs). A total of 507 SDs consisting of two-layer plastic scintillation counters is deployed with 1.2 km spacing, making measurements over an area of approximately 700 km2. There are 3 FD stations, having 38 fluorescence telescopes viewing 3°–31°in elevation, overlooking the SD array. In this work, we update the Telescope Array energy spectrum as measured by the SD array for 14 years. We verify the linearity in TA SD energy reconstruction using three different energy comparisons: Monte Carlo comparison, FD/SD comparison, and Constant Intensity Cut method. The spectral features of ankle, softening, and GZK cutoff are seen in 14 years of TA SD data. Also, we consistently observe that the cutoff energy depends on declination.

The FlashDC project: Development of a beam monitor for FLASH radiotherapy

FLASH Radiotherapy is currently being studied and actively explored by medical and radiobiology communities as one of the most promising technological break-through in the future of cancer treatment as it could considerably improve the sparing of healthy tissues when compared to conventional radiotherapy. However, the FLASH effect activation mechanism still needs a thorough investigation before the characteristics of a therapeutic beam could be properly defined. In this manuscript, a new method for the on-line monitoring of therapeutic beams at FLASH intensities, based on air fluorescence and developed within the FlashDC project, is presented.

Optimal focal curve of spherical mirrors used in a high resolution UV-A spectrograph

The present study concerns the determination of the optimal focal curve of the reflected beam from a spherical mirror. This study has been used in a stigmatic high resolution UV-A spectrograph operating in UV-A region. As a light source we have used a low pressure air discharged lamp while the light detector was a cooled CCD camera with a resolution of 1600×1200 pixels. Locating it on the optimal position along the useful spectral range allows us to exploit the full resolution provided by the spectrograph. An analytical expression of the focal curve has been derived as a function of the main geometrical parameters of the spectrograph and the focusing spherical mirror. A set of experimental validation tests have been performed recording several band heads and the associated molecular rotational lines of nitrogen provided by the lamp. The obtained result has been used in high resolution spectroscopy relevant to air fluorescence yield determination in Ultra High Energy Cosmic Ray research.

Status and prospects of the CRAFFT project for the next generation UHECR observation

Recent observations by TA and Auger have advanced our understanding of ultra-high energy cosmic rays, but their origin is still unclear. As a future approach, it will be effective to obtain the directional energy spectra and compositional distributions by observing even larger statistics, and there are active discussions on future large-scale experiments. In order to realize such a huge observation area, the Cosmic Ray Air Fluorescence Fresnel lens Telescope (CRAFFT) project has started to develop a cost-effective fluorescence telescope with Fresnel lenses. We have succeeded in observing cosmic ray induced air showers by simultaneous observations with TA using prototype telescope. We are currently working on the development of an event reconstruction method using waveforms, optimization of the focal plane, development of a calibration system, and development of an autonomous observation system for future large-scale deployment. The current status and future prospects of the CRAFFT project are discussed.

The POEMMA (Probe of Extreme Multi-Messenger Astrophysics) observatory

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is designed to accurately observe ultra-high-energy cosmic rays (UHECRs) and cosmic neutrinos from space with sensitivity over the full celestial sky. POEMMA will observe the air fluorescence produced by extensive air showers (EASs) from UHECRs and potentially UHE neutrinos above 20 EeV. Additionally, POEMMA has the ability to observe the Cherenkov signal from upward-moving EASs induced by Earth-interacting tau neutrinos above 20 PeV. The POEMMA spacecraft are designed to quickly re-orientate to follow up transient neutrino sources and obtain currently unparalleled neutrino flux sensitivity. Developed as a NASA Astrophysics Probe-class mission, POEMMA consists of two identical satellites flying in loose formation in 525 km altitude orbits. Each POEMMA instrument incorporates a wide field-of-view (45∘) Schmidt telescope with an optical collecting area of over 6 m2. The hybrid focal surface of each telescope includes a fast (1 μs) near-ultraviolet camera for EAS fluorescence observations and an ultrafast (10 ns) optical camera for Cherenkov EAS observations. In a 5-year mission, POEMMA will provide measurements that open new multi-messenger windows onto the most energetic events in the universe, enabling the study of new astrophysics and particle physics at these extreme energies.

A proposed method for measurement of absolute air fluorescence yield based on high resolution optical emission spectroscopy

In this work, we present a method for absolute measurement of air fluorescence yield based on high resolution optical emission spectroscopy. The absolute measurement of the air fluorescence yield is feasible using the Cherenkov light, emitted by an electron beam simultaneously with the fluorescence light, as a “standard candle”. The separation of these two radiations can be accomplished exploiting the “dark” spectral regions of the emission band systems of the molecular spectrum of nitrogen. In these “dark” regions the net Cherenkov light can be recorded experimentally and be compared with the calculated one. The instrumentation for obtaining the nitrogen molecular spectra in high resolution and the noninvasive method for monitoring the rotational temperature of the emission process are also described. For the experimental evaluation of the molecular spectra analysis we used DC normal glow discharges in air performed in an appropriate spectral lamp considered as an air-fluorescence light emulator. The proposed method and the associated instrumentation could be tested and used in thin or thick target experiments in electron beam accelerators as a candidate optical system for this purpose.

The Cosmic-Ray Composition between 2 PeV and 2 EeV Observed with the TALE Detector in Monocular Mode

Abstract We report on a measurement of the cosmic-ray composition by the Telescope Array Low-energy Extension (TALE) air fluorescence detector (FD). By making use of the Cherenkov light signal in addition to air fluorescence light from cosmic-ray (CR)-induced extensive air showers, the TALE FD can measure the properties of the cosmic rays with energies as low as ∼2 PeV and exceeding 1 EeV. In this paper, we present results on the measurement of distributions of showers observed over this energy range. Data collected over a period of ∼4 yr were analyzed for this study. The resulting distributions are compared to the Monte Carlo (MC) simulated data distributions for primary cosmic rays with varying composition and a four-component fit is performed. The comparison and fit are performed for energy bins, of width 0.1 or 0.2 in , spanning the full range of the measured energies. We also examine the mean value as a function of energy for cosmic rays with energies greater than 1015.8 eV. Below 1017.3 eV, the slope of the mean as a function of energy (the elongation rate) for the data is significantly smaller than that of all elements in the models, indicating that the composition is becoming heavier with energy in this energy range. This is consistent with a rigidity-dependent cutoff of events from Galactic sources. Finally, an increase in the elongation rate is observed at energies just above 1017 eV, indicating another change in the cosmic-ray composition.

Intensity of muon bundles according to the NEVOD-DECOR cosmic ray experiment

Data of NEVOD-DECOR experiment on investigations of inclined cosmic ray muon bundles for a long time period (May 2012 – May 2020) are presented. Their comparison with the results of calculations based on simulations of extensive air shower hadron and muon components is carried out. The analysis showed that the observed intensity of muon bundles at primary particle energies of about 1018 eV and higher can be compatible with the expectation only under the assumption of an extremely heavy mass composition of cosmic rays. On the contrary, measurements of the depth of the shower maximum in the atmosphere in the experiments using air fluorescence technique, favour a light mass composition of primary cosmic rays at these energies.

Space-based extensive air shower optical Cherenkov and fluorescence measurements using SiPM detectors in context of POEMMA

Developed as NASA Astrophysics Probe-class mission, the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is designed to identify the sources of ultra-high energy cosmic rays (UHECRs) and to observe cosmic neutrinos. POEMMA consists of two spacecraft flying in a loose formation at 525 km altitude, 28.5°inclination orbits. Each spacecraft hosts a Schmidt telescope with a large collecting area and wide Field-of-View (FoV). A novel focal plane is employed that is optimized to observe both the UV fluorescence signal from extensive air showers (EASs) and the optical Cherenkov signals from EASs. In UHECR stereo fluorescence mode, POEMMA will measure the spectrum, composition, and full-sky distribution of the UHECRs above 20 EeV with high statistics along with remarkable sensitivity to UHE neutrinos. The POEMMA spacecraft are designed to quickly re-orient to a Target-of-Opportunity (ToO) neutrino mode to observe transient astrophysical sources with unique sensitivity. In this mode, POEMMA will be able to detect cosmic tau neutrino events above 20 PeV by measuring the upward-moving EASs for τ-lepton decays induced from tau neutrino interactions in the Earth. In this paper, POEMMA’s science goals and instrument design are summarized with a focus on the SiPM implementation in POEMMA, along with a detailed discussion of the properties of the Cherenkov EAS signal in the context of wide wavelength sensitivity offered by SiPMs. A comparison of the fluorescence response between SiPMs and the MAPMTs currently planned for use in POEMMA will also be discussed, assessing the potential for SiPMs to perform EAS fluorescence measurements.

Step-scan Michelson Fourier-transform spectrometer for optical emission spectroscopy in UV-VIS spectral range.

We present the design, construction, and first spectra of a step-scan Michelson Fourier-transform spectrometer for optical emission spectroscopy in the UV-VIS spectral range. The mirror motion mechanism is based on a long-travel piezo-based linear translation stage with built-in position feedback. The step-scan arrangement allows for signal integration, making the instrument suitable for measurements of less intensive radiation sources and for the photon-counting technique. The spectrometer consists of two coupled Michelson interferometers, one for the spectrometer itself and the other to provide positional reference for the mirror stepping mechanism using interference fringes of a stabilized 635 nm laser diode. Using interpolation of the laser interferogram and taking advantage of the translation stage precision in linear-piezo mode, the mechanism is capable of performing 79 nm steps, which puts the Nyquist wavelength at ∼320 nm. The spectrometer was tested by measuring the spectra of HgAr cold-cathode fluorescent lamp and electron-induced fluorescence of ambient air. Two different detectors were used, an amplified photodiode detector and a photomultiplier tube module in photon counting mode. The highest achieved experimental spectral resolving power was ∼4000 using 1 mm of total mirror travel and the highest achieved noise-free dynamic range was 103. Test results show that the instrument is suitable for use with moderate-to-low intensity signal sources such as small gas discharges and spectroscopic measurements at astronomical telescopes.

Current status and future prospects of the CRAFFT project for the next generation UHECR observatory

A key to understand the origin of the Ultra High Energy Cosmic Ray (UHECR) is higher statistics with the composition information. One of the concepts to realize the future huge observation is an array of simple and low cost fluorescence telescopes. The fluorescence telescope can measure not only the arrival direction and energy spectrum but also the mass composition which is the important information to understand the origin of UHECR. A concept of a simple FD is to reduce the cost by changing from the imaging with multiple PMTs to the time information of a few PMTs, and minimization of the optical system by focusing the high energy events. In order to demonstrate this concept, we are developing Cosmic Ray Air Fluorescence Fresnel lens Telescope (CRAFFT), which further reduces the cost by using Fresnel lens and stand alone system without telescope hut unlike existing fluorescence detector in present UHECR observatory. We have constructed four prototype CRAFFTs and observed air showers by simultaneous observation with Telescope Array. By those study, the cost of a simple FD reaches 1/10 of that of a present FD.

Air shower observation by a simple structured Fresnel lens telescope with a single pixel for the next generation of ultra-high-energy cosmic ray observatories

Improved statistics and observations sensitive to mass composition are required to clarify the origin of ultra-high-energy cosmic rays (UHECRs). Inevitably, in the future UHECR observatories will have to be expanded due to the small flux; however, such upgrades will be expensive with the detectors currently in use. Hence, we are developing a new fluorescence detector for UHECR observation. The proposed fluorescence detector, called a cosmic ray air fluorescence Fresnel lens telescope (CRAFFT), has an extremely simple structure and can observe the longitudinal development of an air shower. Furthermore, CRAFFT has the potential to significantly reduce costs for the realization of a huge observatory for UHECR research. We deployed four CRAFFT detectors at the Telescope Array site and conducted a test observation. We have successfully observed ten air shower events using CRAFFT. Thus, CRAFFT can be a solution to help realize the next generation of UHECR observatories.

EAS longitudinal development distribution parameters for different extrapolations of the nuclei intaraction cross section to the very high energy domain

Determination of the primary particle mass using air fluorescence or a Cherenkov detector array is one of the most difficult task of experimental cosmic ray studies. The information about the primary particle mass is a compound of the produced particle multiplicity, inelasticity, interaction cross-section and many other parameters, thus it is necessary to compare registered showers with sophisticated Monte-Carlo simulation results. In this work we present results of the studies of at least three possible ways of extrapolating proton- Nucleus and Nucleus-Nucleus cross sections to cosmic ray energies based on the Glauber theory. They are compared with experimental accelerator and cosmic ray data for the proton-air cross section. We also present results of the EAS development with the most popular high-energy interaction models adopted in the CORSIKA program with our cross section extrapolations. The average position of the shower maximum and the width of its distribution are compared with experimental data and some discussion is given.