Detector Surface Research Articles

Identification and quantification of a 60Co radiation source under an intense 137Cs radiation field using an application-specific CeBr3 spectrometer suited for use in intense radiation fields

ABSTRACT Passive γ-ray spectroscopy is a useful technique for surveying the radioactive wastes and spent nuclear fuels under nuclear decommissioning. However, this method depends on material properties such as the activity, density, element, scale, and (especially) for low-energy γ rays from 235U and 239Pu. The γ-decay lines of 134Cs, 137Cs, 60Co, and 154Eu occur at greater energies (than those of 235U and 239Pu), and these nuclides provide significant information on spent nuclear fuel and radioactive wastes. A CeBr3 spectrometer with a small-volume crystal has been previously developed for use in intense radiation measurements. We exposed the spectrometer to radiation dose rates of 0.025, 0.151, 0.342, 0.700, and 0.954 Sv/h under a standard 137Cs radiation field. A 6.38 MBq 60Co calibration source was placed in front of the detector surface. Identification of the full energy peak at 1173 keV was impossible at dose rates higher than 0.700 Sv/h. However, subtraction of the 137Cs radiation spectra from the γ-ray spectra enabled the identification of the full energy peaks at 1173 and 1333 keV at dose rates of up to 0.954 Sv/h; the relative energy resolution at 1173 and 1333 keV was only slightly degraded at this dose rate.

Sequence-Feature Detection of Small Targets in Sea Clutter Based on Bi-LSTM

In the complex and changeable marine environment, it is difficult to achieve high-performance detection based on statistical theory for small sea surface detectors in practical applications. In this work, a method for detecting small targets on the sea surface based on sequence-features is proposed from the perspectives of feature extraction and feature classification on a basis of real data. The sequence-feature method firstly extracts three sequence-features from the radar echo sequence, namely, the instantaneous phase, Doppler spectrum entropy, and short-time Fourier transform (STFT) marginal spectrum. The features are used to train the bidirectional long short-term memory networks (Bi-LSTM) model so that it has the ability to distinguish the target and the sea clutter. The measured dataset verifies that the proposed detector can achieve the detection of sea surface targets with controllable false alarm rate, and the performance is better than several existing detectors.

Photoelectric detector surface damage state polarization imaging type detection system

Photoelectric detector surface damage state polarization imaging type detection system

Compensated differential Zernike fitting method for wavefront aberration metrology based on grating lateral shearing.

Lateral shearing based on the grating is one of the classical configurations when measuring the wavefront aberration of optical systems such as the lithographic projection lens. Because the wavefront under test is spherical, but a detector surface is a plane, the coordinate of the wavefront surface will be distorted on the detector surface. As the numerical aperture (NA) of the optics under test increases, the shear ratios at different positions within the shearing region are significantly different due to the coordinate distortion. Therefore, the reconstructed wavefront from the traditional lateral-shearing reconstruction method designed for a fixed shearing ratio will contain a non-negligible error. In this work, we use the ray-tracing method to calculate the shearing ratio distribution in the shearing region and propose a compensated differential Zernike fitting method to solve the coordinate distortion and shearing ratio variation problem. The relative error of the uncompensated result will increase as the NA increases. This error is around 1% for a 0.1 NA, 10% for a 0.3 NA, and over 100% for an NA above 0.7. Compensation for the shearing ratio variation is necessary when the NA is larger than 0.3. The proposed method has been validated by simulations and experiments.

Radon Monitoring by Alpha Track Detection Using Cn–85 Plastic Track

Radon sources can be found in external and internal radiation. Lead pencil (LP) is often used for drawing, sketching, etc. regardless of age nowadays. Paracetamol (PC) is commonly used around the world especially to treat fever, headache, menstrual pain, and common pain. Hence, the aim is to study the procedures for determining the radon gas comes out from different types of lead pencil and paracetamol. Eight and five samples were collected from different companies of lead pencil and paracetamol, respectively. The samples were measured using the sealed technique in cylindrical plastic containers with CN–85 detectors. After irradiation, the detectors were chemically etched using 2 N sodium hydroxide (NaOH) solution at a temperature of 70 ºC for 62 min. The alpha track density on the surface of detectors was measured using an optical microscope at a magnification of 100×. Tracks on detectors were counted using Image software. Radon concentration values including all samples in this study are within the limits of international which is 1000 Bq/m3. The concentration of radium in LP and PC samples are lower than those reported in previous study. The result of the uranium concentration of both samples is quite low compared with the allowed limit which is 11.7 ppm. Annual effective dose levels are all below the dose limit which is 10 mSv/y. Lastly, there was a linear relationship between radium activity and radon exhalation rate. Therefore, using LP and eating PC cause no danger to humans. All results showed in this study are within internationally permissible limits, and therefore not a threat to human health.

Re-construction of a HPGe detector precise modeling for efficiency calibration

High purity germanium (HPGe) detector is a preferred choice for determining the activity of the radioactive samples for nuclear diagnostics of Inertial Confinement Fusion (ICF) experiments. Although the amounts of the radiochemical sample are limited, activity measurement at a close distance between the detector window and the radioactive source is a feasible method. Efficiency calibration of gamma rays at a close distance from the surface of a HPGe detector is crucial. Considering the problem of the coincidence at a close distance, the alternative way is to construct a precise model of the HPGe detector and then to calculate efficiency accurately at an arbitrary distance from the surface of the HPGe detector using Monte Carlo method. In this paper, internal geometry and structure except for dead layers of the HPGe detector is obtained by X-ray radiography and 3D reconstruction. The optimal dead layers of the germanium crystal are determined by tracing the minimal sum squared residual (SSR) of gamma-ray efficiencies between calculations and measurements for standard planar sources. Nonhomogeneous distribution of the dead layer is supposed according to the inner structure on the Ge crystal. The final results show that the corrected model improves the accuracy of the calculated efficiencies.

Medipix3 proton and carbon ion measurements across full energy ranges and at clinical flux rates in MedAustron IR1

The Medipix3, a hybrid pixel detector with a silicon sensor, has been evaluated as a beam instrumentation device with proton and carbon ion measurements in the non-clinical research room (IR1) of MedAustron Ion Therapy Center. Protons energies are varied from 62.4 to 800 MeV with 104 to 108 protons per second impinging on the detector surface. For carbon ions, energies are varied from 120 to 400 MeV/amu with 107 to 108 carbon ions per second. Measurements include simultaneous high resolution, beam profile and beam intensity with various beam parameters at up to 1000 FPS (frames per second), count rate linearity and an assessment of radiation damage after the measurement day using an x-ray tube to provide a homogeneous radiation measurement. The count rate linearity is found to be linear within the uncertainties (dominated by accelerator related sources due to special setup) for the measurements without degraders. Various frequency components are identified within the beam intensity over time firstly including 49.98 Hz with standard deviation, σ = 0.29, secondly 30.55 Hz σ = 0.55 and thirdly 252.51 Hz σ = 0.83. A direct correlation between the number of zero counting and noisy pixels is observed in the measurements with the highest flux. No conclusive evidence of long term radiation damage was found as a result of these measurements over one day.

Multimessenger Astronomy of Transient Point Sources at the Pierre Auger Observatory

One of the key challenges in astroparticle physics is the identification of the sources of cosmic rays at the highest energies (above 1018 eV). In this context, the search for neutral messenger particles in the ultra-high energy (UHE) regime is of high interest. The sources of the gravitational waves (GWs) that can be observed with the current generation of GW detectors provide extreme astrophysical environments that are most likely to be unique in the universe. Another extraordinary source candidate is the anomalous blazar TXS 0506+056 which has been found to be coincident with two periods of enhanced high-energy neutrino flux in 2014/15 and 2017 as reported by the IceCube Collaboration. Due to their distance and transient nature, the capabilities of these sources to produce UHE radiation can only be studied through neutral messengers like photons and neutrinos. The Pierre Auger Observatory near Malargue, Argentina, is the largest air shower experiment for the detection of ultra-high energy cosmic rays. With its surface detector, consisting of a grid of 1660 water-Cherenkov detectors covering an area of 3000 km2, it has a unique exposure to UHE photons and neutrinos and has published first constraints on these particles from GW sources and TXS 0506+056.

The Search for Ultra-High Energy Neutrinos through Highly Inclined Air Showers in the Pierre Auger Observatory

The Surface Detector of the Pierre Auger Observatory for the detection of ultra-high energy cosmic rays, an array of 1600 water-Cherenkov stations in a triangular grid with 1500 m separation between stations, has also the capability to detect neutrinos with energy above 1017eV. The identification, through the special characteristics of highly inclined showers, is efficiently performed for neutrinos of all flavours interacting deep in the atmosphere at large zenith angles as well as for τ-neutrinos skimming the Earth crust. In this talk I review the status of the neutrino search at the Observatory using about 15 years of data. Restrictive upper bounds on the neutrino flux from diffuse sources and from point-like steady sources were stablished, placing strong constraints on several models of neutrino production at EeV energies and on the properties of the sources of ultra-high-energy cosmic rays. Unrivaled sensitivity in searches for transient sources has been also achieved.

Method to Improve the Detection Accuracy of Quadrant Detector Based on Neural Network

The quadrant detector (QD), has developed into a core detector in the free space optical communication system. The light power received by the detector surface will be very weak after long distance transmission of laser, it brings great challenges to the high precision spot position detection of the detector. Therefore, this letter proposes a method to improve the spot position detection accuracy of the QD through artificial neural network. The neural network can solve the impact of multiple different factors on the detection accuracy of the detector at one time, which can save a lot of time and cost. Moreover, the test results of the detection accuracy of the network show that the neural network has significantly improved the detection accuracy of the spot position of the QD.

144Ce - 144Pr spectrum measurement with 4π semiconductor β-spectrometer

Precision β-spectra measurement always had a great importance in some fundamental physics problems including neutrino physics. Magnetic and electrostatic spectrometers have high resolution, but at the same time usage of such kinds of equipment involves the size and cost issues. Since electron mean free path at the energy of 3 MeV (which is basically the maximum energy of a β-transition for the long-lived nuclei) does not exceed 2 g/crn2 , electron registration could be effectively performed with the solid state scintillators and semiconductors. A strong probability of backscattering from detector surface is present in case of semiconductor detectors and is dependent upon the detector material. Such problem can be solved with 4π geometry detector development, which fully covers the radioactive source and is able to register the backscattered electrons. In this work we present the newly developed technology of 4π geometry β-spectrometer based on two semiconductor detectors. This spectrometer was used for measurement of the 144Ce - 144Pr spectrum, that is the perspective anti-neutrino source due to endpoint energy at 3 MeV and can be used for the sterile neutrino search experiments. The form-factor parameters that were obtained are: C(W) = 1 + (-0.02877 ± 0.00028)W + (-0.11722 ± 0.00297)W-1. The measurement accuracy was sufficiently enhanced with respect to the previous results.

The energy spectrum of cosmic rays beyond the turn-down around varvec{10^{17}}\xa0eV as measured with the surface detector of the Pierre Auger Observatory

We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the spectrum is observed, confirming the presence of the so-called second-knee feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays.

Calculation of the Effective Energy Release Centerʼs Position of Inorganic Scintillation Detectors for Calibration at Small “Source–Detector” Distances

Inorganic scintillation detectors are widely used to measure of dose rate in the environment due to their high sensitivity to photon radiation. A distinctive feature when using such detectors is the need to take into account of the position of the effective energy release center. This peculiarity is actual when using measuring instruments with inorganic scintillation detectors as working standards during calibration at short “source–detector” distances in conditions of low-background shield or using a facility with protection from external gamma radiation background in the dose rate range from 0.03 to 0.3 μSv/h (μGy/h). The purpose of this work was to calculate the position of the effective energy release center of NaI(Tl) scintillation detectors and to take it into account when working at short “source–detector” distances.An original method of determining the position of the effective energy release center when irradiating the side and end surfaces of inorganic scintillation detector with parallel gamma radiation flux and point gamma radiation sources at small “source–detector” distances using Monte Carlo methods is proposed. The results of calculations of the position of the effective energy release center of NaI(Tl) based detectors of “popular” sizes for the cases of parallel gamma radiation flux and point sources of gamma radiation at small “source–detector” distances are presented. The functional dependences of the position of the effective energy release center of NaI(Tl) based detectors on the distance to the point gamma radiation sources and the energy of gamma radiation sources are presented.As a result of the study it was found that for scintillation NaI(Tl) detectors of medium size (for example, Ø25×40 mm or Ø40×40 mm) the point gamma radiation source located at a distance of 1 m or more, creates a radiation field which does not differ in characteristics from the radiation field created by a parallel flux of gamma radiation. It is shown that approaching the point gamma radiation source to the surface of scintillation detector leads to displacement of the position of the effective energy release center to the surface of the detector.

Alpha particles detection using P3HT conducting polymer-coated DAM-ADC

For radiation detection applications, Raman analysis, photoluminescence (PL), and UV–Vis spectroscopy are thoroughly studied using the DAM-ADC (diallyl maleate - allyl diglycol carbonate) detector coated with poly(3-hexylthiophene-2,5-diyl) (P3HT) conducting polymer. A thin Am-241 disk that emits alpha particles with an activity of 340 kBq was used to irradiate the surface of DAM-ADC detector. After irradiation with different fluencies of alpha particles, the spectroscopic analysis confirms that the effects of alpha particles on the DAM–ADC detector coated by P3HT conducting polymer are detectable in Raman spectra and PL spectral emission. Furthermore, the photoluminescence and UV–Vis responses of the DAM–ADC samples are influenced by the track density of the irradiated samples. For Raman, UV–vis, and PL analysis, the spectral peak heights and the area under the peaks show a correlation with the fluencies of alpha particles. For the irradiated samples, all the techniques displayed major spectral alterations, suggesting that they could be used to establish sensitive alpha particle detection methods. For both direct and indirect transitions, the optical band gap was found to decrease with increasing the alpha fluencies.

New statistical model of track overlap in solid state nuclear track detectors

Solid state nuclear track detector are commonly used as passive radon dosimeters. Radon exposure is directly linked to the etched track density measured on the detector surface. Due to their finite size, separate tracks can overlap, and this effect can result is a severe underestimation of the actual track density. In the present work a new statistical model to calculate the probability of overlap between tracks in solid state nuclear track detectors is presented. This model can be used to calculate the actual track density from the one measured in the presence of track overlap. The new model provides a full statistical description of the overlapping process and does not require any prior knowledge about the particles originating the tracks, the etching process or the reading system. The model has been validated trough Monte Carlo simulations and experiments.

A [formula omitted] bend curved light-guide for TOF scintillating detectors

We report here a bench study of TOF resolution using a 90° bend curved solid light-guide (LG) used to transport the light from a plastic scintillator counter to a photomultiplier (PMT). The 90° LG allows the rotation of the PMT axis to be vertical to the detector axis, in an environment featured by a strong magnetic field along the detector surface, or other geometrical constrains. We show that with a TOF counter of 2000×100×60 mm3 and light read-out by PMTs at its two 100 × 60 mm2 sides, when 90° LG benders are used between the scintillating bar and the PMTs on both sides, the TOF resolution is worsen, by 5–10%.

Surface detectors of the TAx4 experiment

Telescope Array (TA) is the largest ultrahigh energy cosmic-ray (UHECR) observatory in the Northern Hemisphere. It explores the origin of UHECRs by measuring their energy spectrum, arrival-direction distribution, and mass composition using a surface detector (SD) array covering approximately 700 km2 and fluorescence detector (FD) stations. TA has found evidence for a cluster of cosmic rays with energies greater than 57 EeV. In order to confirm this evidence with more data, it is necessary to increase the data collection rate. We have begun building an expansion of TA that we call TAx4. In this paper, we explain the motivation, design, technical features, and expected performance of the TAx4 SD. We also present TAx4’s current status and examples of the data that have already been collected.

Modeling the impact of defects on the charge collection efficiency of a Cadmium Telluride detector

Cadmium telluride is a favorable material for X-ray detection as it has an outstanding characteristic for room temperature operation. It is a high-Z material with excellent photon radiation absorption properties. However, CdTe single crystals may include a large number of extended crystallographic defects, such as grain boundaries, twins, and tellurium (Te) inclusions, which can have an impact on detector performance. A Technology Computer Aided Design (TCAD) local defect model has been developed to investigate the effects of local defects on charge collection efficiency (CCE). We studied a 1 mm thick Schottky-type CdTe radiation detector with transient-current technique by using a red laser at room temperature. By raster scanning the detector surface we were able to study signal shaping within the bulk, and to locate surface defects by observing their impact on the CCE. In this paper we present our TCAD model with localized defect, and compare the simulation results to TCT measurements. In the model an inclusion with a diameter of 10 μm was assumed. The center of the defect was positioned at 6 μm distance from the surface. We show that the defect has a notable effect on current transients, which in turn affect the CCE of the CdTe detector. The simulated charge collection at the position of the defect decreases by 80 % in comparison to the defect-free case. The simulations show that the defects give a characteristic shape to TCT signal. This can further be used to detect defects in CdTe detectors and to estimate the overall defect density in the material.

Influence of pre-exposure thermal annealing on etch rates of CR-39 nuclear track detectors: New findings

The influence of pre-exposure thermal annealing on CR-39 etch rates has been studied here thoroughly. Annealing experiments were conducted on CR-39 detectors prior to their exposure to 252Cf fission fragment source. The bulk etch rates were measured by using the weight loss method (WLM) and the fission track diameter method (FTDM). We report here a new quantitative result that the bulk etch rate decreases from the original surface of each CR-39 detector initially rapidly and then more slowly along the depth mimicking the exponential trend. These quantitative results are more pronounced for cases of higher annealing temperatures and larger annealing time intervals. This exponential drop of the bulk etch rate suggests that the interior of the CR-39 detector material is almost out of pre-exposure annealing. Our results reveal that the etch rates and the registration properties of the heavy ions are considerably altered in the near-surface layer of the annealed PADC.

Extraction of the muon signals recorded with the surface detector of the Pierre Auger Observatory using recurrent neural networks

The Pierre Auger Observatory, at present the largest cosmic-ray observatory ever built, is instrumented with a ground array of 1600 water-Cherenkov detectors, known as the Surface Detector (SD). The SD samples the secondary particle content (mostly photons, electrons, positrons and muons) of extensive air showers initiated by cosmic rays with energies ranging from 1017eV up to more than 1020eV. Measuring the independent contribution of the muon component to the total registered signal is crucial to enhance the capability of the Observatory to estimate the mass of the cosmic rays on an event-by-event basis. However, with the current design of the SD, it is difficult to straightforwardly separate the contributions of muons to the SD time traces from those of photons, electrons and positrons. In this paper, we present a method aimed at extracting the muon component of the time traces registered with each individual detector of the SD using Recurrent Neural Networks. We derive the performances of the method by training the neural network on simulations, in which the muon and the electromagnetic components of the traces are known. We conclude this work showing the performance of this method on experimental data of the Pierre Auger Observatory. We find that our predictions agree with the parameterizations obtained by the AGASA collaboration to describe the lateral distributions of the electromagnetic and muonic components of extensive air showers.