Count Rate Variations Research Articles

Development of alternative methodology for normalization of the small animals PET scanner of LIM/CDTN

Normalization is a step taken to correct variations in count rates between detection channels of small animals PET scanners. In general, in laboratory practice, normalization is performed using a commercial source of germanium 68. Given the half-life of the Ge-68 isotope, the normalization source must be replaced every two years at most, which generates a significant spent for the Laboratory. The objective of this work was to develop and test an alternative rechargeable source to be used on normalization routine. The results indicated that the rechargeable source (18F-FDG) can be used to replace the commercial source.

Development of a neutron yield measurement system utilizing BF_3 detectors on the HL-3 tokamak

A neutron yield measurement system, comprising five BF3 proportional counters with excellent n/γ discrimination capabilities, has been meticulously developed and implemented on the HL-3 tokamak to provide time-resolved assessments of neutron emission rates. The size of moderator, optimized for the flat energy responses, was skillfully simulated and designed using the MCNP code. An in-depth analysis of measurement errors stemming from pile-up phenomena determined that the upper limit of the count rate, under the current electronics design, is 131 kcps with a relative error of less than 20%. Drawing from the pulse amplitude spectrum obtained from a 252Cf neutron source and experimentation on the HL-3 tokamak, the amplitude threshold for the BF3 neutron detector systems was judiciously established. Furthermore, it was conclusively affirmed that the neutron yield measurement system possesses the capability to effectively discriminate between neutron and gamma signals. During HL-3 discharges, deuterium-deuterium (DD) neutrons were reliably detected with a temporal resolution of 10 ms, and the variations in neutron count rates was found to be in alignment with the neutral beam injection. Ultimately, the total neutron yield was successfully estimated through the utilization of count rates from four BF3 detectors, thereby validating the robust performance of the neutron yield measurement system.

Wavelength calibration of a solar spectral irradiance radiometer and validation by correlation photon coincidence counting

Accurate wavelength calibration is the key to achieving accuracy observation of solar spectral irradiance. A wavelength calibration of solar spectral irradiance radiometer based on correlation photon radiation reference is proposed. The wavelengths of two channels of the solar spectral irradiance radiometer are calibrated by a Hg-Ar lamp and lasers. A collimating and focusing optics are designed to ensure that light can illuminate the slit vertically and without polarization. The optics can also keep the consistency of observing and self-calibration modes. The calibration equations of two channels are established. The wavelength deviations of two channels are −0.11 ∼ 0.07 nm and −0.085 ∼ 0.017 nm respectively. To validate the calibrated wavelength, channel 1 is selected as the inspection channel according to the spectral line number of the calibration lamp and the variation of the photon count rate. The motor position close to the calibration wavelength 763.511 nm is selected in channel 2, and the coincidence measurement is carried out to check the accuracy of wavelength calibration in channel 1. The deviation of wavelength around 408 nm is 1.139 nm. The experimental results show that the correlated photons self-calibration system can realize the calibration and validation of the system wavelength. The method can increase the number of calibration wavelengths and is suitable for both channels.

Study of Proton-Induced Defects in 40-nm CMOS SPADs

Defects induced by 62 MeV protons in SPADs are studied. A study of the Dark Count Rate (DCR) variation after irradiations for different biasing conditions underlines the predominance of field enhancement effects such as Poole-Frenkel effect and phonon-assisted-tunneling over band-to-band tunneling. Activation energy measurements below mid-gap value confirm the important contribution of these field effects. However, unexpected behaviors in these energies are seen: very low activation energies are extracted for SPADs with a DCR induced around 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> counts per second. We attribute them to the contribution of different groups of defects, with different energy level distribution. This analysis is completed with an annealing study between 100 °C and 300 °C. Results for high DCR SPADs correlate well with the presence of defect clusters. Moreover, histogram of the annealing temperature at which the DCR starts to drop displays two peaks at 170 °C and 250 °C. The first one is attributed to phosphorus vacancies and complex cluster of defects with an energy distribution inside the Si bandgap centered above mid-gap. The second one is attributed to clusters of divacancies that also anneal at temperatures around 250 °C.

Charge-Sign Dependent Cosmic-Ray Modulation Observed with the Calorimetric Electron Telescope on the International Space Station.

We present the observation of a charge-sign dependent solar modulation of galactic cosmic rays (GCRs) with the Calorimetric Electron Telescope onboard the International Space Station over 6yr, corresponding to the positive polarity of the solar magnetic field. The observed variation of proton count rate is consistent with the neutron monitor count rate, validating our methods for determining the proton count rate. It is observed by the Calorimetric Electron Telescope that both GCR electron and proton count rates at the same average rigidity vary in anticorrelation with the tilt angle of the heliospheric current sheet, while the amplitude of the variation is significantly larger in the electron count rate than in the proton count rate. We show that this observed charge-sign dependence is reproduced by a numerical "drift model" of the GCR transport in the heliosphere. This is a clear signature of the drift effect on the long-term solar modulation observed with a single detector.

Single-photon detector-based long-distance Brillouin optical time domain reflectometry

We present a long-range Brillouin optical time domain reflectometer (BOTDR) based on photon counting technology. We demonstrate experimentally the ability to perform a distributed temperature measurement, by detecting a hot spot in a thermal bath at 100 km, and the possibility to achieve measurement until 120 km with a spatial resolution of 10 m. We use the slope of a fiber Bragg grating (FBG) as a frequency discriminator, to convert count rate variation into a frequency shift. A performance study of our distributed sensor as a function of spatial resolution is also presented.

Long-term evolution of the neutron rate at the Canfranc Underground Laboratory

We report results on the long-term variation of the neutron counting rate at the Canfranc Underground Laboratory, of importance for several low-background experiments installed there, including rare-event searches. The measurement campaign was performed employing the High Efficiency Neutron Spectrometry Array (HENSA) mounted in Hall A and lasted 412 live days. The present study is the first long-term measurement of the neutron rate with sensitivity over a wide range of neutron energies (from thermal up to 0.1 GeV and beyond) performed in any underground laboratory so far. Data on the environmental variables inside the experimental hall (radon concentration, air temperature, air pressure and humidity) were also acquired during all the measurement campaign. We have investigated for the first time the evolution of the neutron rate for different energies of the neutrons and its correlation with the ambient variables.

The high energy spectrum of Proxima Centauri simultaneously observed at X-ray and FUV wavelengths

The M dwarf Proxima Centauri, the Sun’s closest stellar neighbour, is known to be magnetically active and it hosts a likely Earth-like planet in its habitable zone. High-energy radiation from the host star can significantly alter planetary atmospheres in close orbits. Frequent flaring may drive radiation-induced effects such as rapid atmospheric escape and photochemical changes. Therefore, understanding the characteristics of stellar radiation by understanding the properties of the emitting plasma is of paramount importance for a proper assessment of the conditions on Proxima Centauri b and exoplanets around M dwarfs in general. This work determines the temperature structure of the coronal and transition region plasma of Proxima Centauri from simultaneous X-ray and far-ultraviolet (FUV) observations. The differential emission measure distribution (DEM) was constructed for flaring and quiescent periods by analysing optically thin X-ray and FUV emission lines. Four X-ray observations of Proxima Centauri were conducted by the LETGS instrument on board of the Chandra X-ray Observatory and four FUV observations were carried out using the STIS spectrograph on board the Hubble Space Telescope. From the X-ray light curves, we determined a variation of the quiescent count rate by a factor of two within 20% of the stellar rotation period. To obtain the DEM, 18 optically thin emission lines were analysed (12 X-ray and six FUV). The flare fluxes differ from the quiescence fluxes by factors of 4–20 (FUV) and 1–30 (X-ray). The temperature structure of the stellar corona and transition region was determined for both the quiescence and flaring state by fitting the DEM(T) with Chebyshev polynomials for a temperature range log T = 4.25–8. Compared to quiescence, the emission measure increases during flares for temperatures below 0.3 MK (FUV dominated region) and beyond 3.6 MK (X-ray dominated region). The reconstructed DEM shape provides acceptable line flux predictions compared to the measured values. Using the DEM we provide synthetic spectra at 1–1700 Å, which may be considered as representative for the high-energy irradiation of Proxima Cen b during quiescent and flare periods. In future work these values can be used for planet atmosphere calculations which will ultimately provide information about how habitable Proxima Centauri b is.

Observation of variations in cosmic ray single count rates during thunderstorms and implications for large-scale electric field changes

We present the first observation by the Telescope Array Surface Detector (TASD) of the effect of thunderstorms on the development of cosmic ray single count rate intensity over a 700 km2 area. Observations of variations in the secondary low-energy cosmic ray counting rate, using the TASD, allow us to study the electric field inside thunderstorms, on a large scale, as it progresses on top of the 700 km2 detector, without dealing with the limitation of narrow exposure in time and space using balloons and aircraft detectors. In this work, variations in the cosmic ray intensity (single count rate) using the TASD, were studied and found to be on average at the ∼(0.5–1)% and up to 2% level. These observations were found to be both in excess and in deficit. They were also found to be correlated with lightning in addition to thunderstorms. These variations lasted for tens of minutes; their footprint on the ground ranged from 6 km to 24 km in diameter and moved in the same direction as the thunderstorm. With the use of simple electric field models inside the cloud and between cloud to ground, the observed variations in the cosmic ray single count rate were recreated using CORSIKA simulations. Depending on the electric field model used and the direction of the electric field in that model, the electric field magnitude that reproduces the observed low-energy cosmic ray single count rate variations was found to be approximately between 0.2 GV–0.4 GV. This in turn allows us to get a reasonable insight on the electric field and its effect on cosmic ray air showers inside thunderstorms.2 MoreReceived 19 November 2021Accepted 3 January 2022DOI:https://doi.org/10.1103/PhysRevD.105.062002© 2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtmospheric scienceCosmic rays & astroparticlesInterdisciplinary PhysicsParticles & Fields

A Swift study of long-term changes in the X-ray flaring properties of Sagittarius A

ABSTRACT The radiative counterpart of the supermassive black hole at the Galactic Centre, Sagittarius A*, displays flaring emission in the X-ray band atop a steady, quiescent level. Flares are also observed in the near-infrared band. The physical process producing the flares is not fully understood and it is unclear if the flaring rate varies, although some recent works suggest it has reached unprecedented variability in recent years. Using over a decade of regular X-ray monitoring of Neil Gehrels Swift Observatory, we studied the variations in count rate of Sgr A* on time-scales of years. We decomposed the X-ray emission into quiescent and flaring emission, modelled as a constant and power-law process, respectively. We found that the complete, multiyear data set cannot be described by a stationary distribution of flare fluxes, while individual years follow this model better. In three of the ten studied years, the data is consistent with a purely Poissonian quiescent distribution, while for 5 yr, only an upper limit of the flare flux distribution parameter could be determined. We find that these possible changes cannot be explained fully by the different number of observations per year. Combined, these results are instead consistent with a changing flaring rate of Sgr A*, appearing more active between 2006–2007 and 2017–2019, than between 2008–2012. Finally, we discuss this result in the context of flare models and the passing of gaseous objects, and discuss the extra statistical steps taken, for instance, to deal with the background in the Swift observations.

Amplitude of One-Minute Fluctuations of Secondary Cosmic Rays as a Marker of Environmental Factor Determining Ultradian Rhythms in Body Temperature of Laboratory Rats.

The study examined association between oscillations of body temperature of laboratory Wistar rats maintained under constant illumination with the amplitude of fluctuations of secondary cosmic rays reported by neutron count rate provided by neutron monitors and geomagnetic undulations. In contrast to geomagnetic undulations, neutron count rate variations and body temperature oscillations in rats assessed by spectrum analysis of the corresponding step functions at 1-min intervals demonstrated almost permanent variations with the periods ranging from 100 to 400 min. Under conditions of constant illumination inducing changes in the period of circadian rhythm and predominance of the ultradian rhythms, an association between neutron count rate fluctuations and body temperature oscillations was observed perpetually during the day- and nighttime.

Developmental challenges to internationalizing the higher education sector: a critical inquiry of business schools in Kerala

PurposeKerala is one of India's most advanced states in human development and other social indices. This study aims to look at the management education scenario in Kerala from a macro-perspective and examines the existing trends, major issues and present challenges facing the sector.Design/methodology/approachThe study is driven by previously unexplored secondary data published by India's apex technical education regulator–All India Council for Technical Education (AICTE). Qualitative and quantitative assessments are assimilated from the organization, dissection and categorization of unit-level data.FindingsBusiness schools (B-schools) in the state are facing acute distress in enrolments. There are intra-regional variations in institution count and occupancy rates. The vast majority of the institutions have no accreditation at all. The entire sector is facing a protracted decline.Research limitations/implicationsThe study has relied primarily on descriptive statistics considering a single discipline within the higher education sector in Kerala. Future studies should look at other disciplines (engineering, medicine) simultaneously. Use of statistical methods like panel data regression would be beneficial to find hidden trends in cross-sectional and longitudinal time-series data.Practical implicationsManagement education in Kerala is facing an existential crisis. This has implications for the state's economic development. The paper creates strong imperatives for government policymaking to forestall the complete decline of the sector.Social implicationsA highly literate state with advanced human development indices need not be a suitable location for building a knowledge-based economy. Government policy has strong implications for the development and sustenance of higher education. The relationship between government and business schools are symbiotic.Originality/valueThe paper maps the progression of B-schools from local to global. A typology of privately funded B-schools is proposed. The conceptual framework advanced in this study can contribute to further literature development. The suggested policy initiatives are applicable not only to Kerala but also to other tightly regulated markets.

Метод автоматической коррекции данных нейтронного монитора на осадки в виде снега в реальном времени

We have carried out an experimental study of the influence of precipitation in the form of snow on measurements of the neutron flux intensity near Earth's surface. We have examined the state of the snow cover and its density, and found out that the density depends on the depth of the snow cover. Using the experimental results, we estimate the neutron absorption path in the snow. Changes in snow cover by 10–12 cm at a depth of 80 cm are shown to cause variations in the monitor count rate with an amplitude of 0.9 %. At the snow depth of 80 cm, the neutron monitor count rate decreases by about 8 %. The observed variations should be attributed to the meteorological effects of cosmic rays. The absorption coefficient of neutrons in the snow was also found from the correlation between the count rate of the neutron monitor and the amount of snow above the detector. We propose a real-time correction of the neutron monitor data for precipitation in the form of snow. For this purpose, we implement continuous monitoring of the amount of snow cover. The monitoring is provided by a snow meter made using a laser rangefinder module. We discuss the results obtained.

Method of automatic correction of neutron monitor data for precipitation in the form of snow in real time

We have carried out an experimental study of the influence of precipitation in the form of snow on measurements of the neutron flux intensity near Earth's surface. We have examined the state of the snow cover and its density, and found out that the density depends on the depth of the snow cover. Using the experimental results, we estimate the neutron absorption path in the snow. Changes in snow cover by 10–12 cm at a depth of 80 cm are shown to cause variations in the monitor count rate with an amplitude of 0.9 %. At the snow depth of 80 cm, the neutron monitor count rate decreases by about 8 %. The observed variations should be attributed to the meteorological effects of cosmic rays. The absorption coefficient of neutrons in the snow was also found from the correlation between the count rate of the neutron monitor and the amount of snow above the detector. We propose a real-time correction of the neutron monitor data for precipitation in the form of snow. For this purpose, we implement continuous monitoring of the amount of snow cover. The monitoring is provided by a snow meter made using a laser rangefinder module. We discuss the results obtained.

Characterization of stilbene and EJ-276 scintillators coupled with a large area SiPM array for a fast neutron dose rate detector

A 1-inch stilbene and EJ-276 (plastic) organic scintillators were characterized in view of their use in a portable survey meter for fast neutron detection and dose rate measurements in radiation protection. They were coupled with a large area Silicon Photomultiplier (SiPM) array and characterized in terms of neutron/γ–ray (n/γ) discrimination capability, count rate linearity, count rate saturation effects, temperature stability and neutron detection efficiency. A Pile-Up Rejection (PUR) algorithm was developed and tested to increase their count rate linearity with increasing dose rate. Results show that the stilbene exhibits better performance compared to the plastic in terms of: Pulse Shape Discrimination (PSD) with a Figure Of Merit (FOM) of 1.5 vs. 1.1, energy resolution (15% vs 20% at 662 keV) and fast neutron efficiency (12% vs. 9% with an AmBe source). For both scintillators, the dose rate response is linear up to 1 mSv/h with a 137Cs γ-ray source. With a neutron source, the response is linear, and the FOM is almost constant for dose rates up to 1.5 mSv/h. The PUR reduces the false neutron events by one order of magnitude when the detectors are irradiated with a γ-ray source up to 10 mSv/h, and it correctly works when irradiated with an AmBe source at 1.5 mSv/h together with a 137Cs source up to 60 μSv/h. The proposed PUR algorithm is promising but needs to be tested with a higher intensity mixed n/γ field. The temperature stability of both detectors was also studied in the temperature range from −10 °C to ＋40 °C. The light yield increases by around 25% for both detectors when reducing the temperature. The variation of the neutron count rate is around 10% in the same temperature range. This work provides a complete overview of the performance of these detectors and a coherent comparison between the two types of scintillators with the same experimental setup.

Study on the stability of 20 inch photomultiplier tubes based on microchannel plate

The normal working stability of 20-inch MCP-PMTs are studied by random triggering, in this paper. The variation of dark counting rate and gain in the long-term (∼400 days) aging process is mainly analyzed. It is found that the variation trend of the dark counting rate is consistent with the temperature, and the dark counting rate increases by about 15%/∘C at room temperature (20–28∘C). Moreover, the gain of PMTs began to decline after 5 months of continuous operation. After the gain is reduced by about 15%, the gain reaches a steady state.

Monitoring of Particle Count Rate and LET Variations With Pulse Stretching Inverters

This study investigates the use of pulse stretching (skew-sized) inverters for monitoring the variation of count rate and linear energy transfer (LET) of energetic particles. The basic particle detector is a cascade of two pulse stretching inverters, and the required sensing area is obtained by connecting up to 12 two-inverter cells in parallel and employing the required number of parallel arrays. The incident particles are detected as single-event transients (SETs), whereby the SET count rate denotes the particle count rate, while the SET pulsewidth distribution depicts the LET variations. The advantage of the proposed solution is the possibility to sense the LET variations using fully digital processing logic. SPICE simulations conducted on IHP's 130-nm CMOS technology have shown that the SET pulsewidth varies by approximately 550 ps over the LET range from 1 to 100 MeV ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·mg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The proposed detector is intended for triggering the fault-tolerant mechanisms within a self-adaptive multiprocessing system employed in space. It can be implemented as a standalone detector or integrated in the same chip with the target system.

Spectral analysis of χ class data of GRS 1915+105 using TCAF solution

The class variable source GRS 1915+105 exhibits a wide range of time variabilities on timescales of a few seconds to a few days. Depending on the count rates in different energy bands and the nature of the conventional color-color diagram, the variabilities were classified into sixteen classes that were later sequenced in ascending order of Comptonization Efficiency (CE), which is the ratio of power-law and blackbody photons. However, CE estimation is based on an empirical model which does not provide us with a comprehensive picture regarding accretion flow dynamics around the central source. In reality, the accretion flow is comprised of two components: the high angular momentumKeplerian flow in the form of a radiatively efficient disk and a low angular momentumradiatively inefficient sub-Keplerian halo enveloping the disk. These two components contribute differently to the overall flux due to the differences in their radiative efficiencies. Therefore, it is necessary to analyze the spectral behaviors and time variabilities in terms of accretion rates. In χ class, X-ray flux is steady with no significant variation, however various χ subclasses are observed at different X-ray fluxes and variations of count rates across different χ subclasses must be linked to the variation of flow parameters such as the accretion rates, be it the Keplerian disk rate and/or the low angular momentum halo rate. This motivated us to analyze the spectra of the χ class data implementing the physical Two Component Advective Flow (TCAF) solution which directly extracts these two rates from spectral fits. We find that in the χ 2,4 classes, which are reportedly devoid of significant outflows, the spectra could be fitted well applying the TCAF solution alone. In the χ 1,3 classes, which are always linked with outflows, a cutoff power-law model is needed in addition to the TCAF solution. At the same time, the normalization required by this model along with the variation of photon index and exponential roll-off factor provides us with information on the relative dominance of the outflow in the latter two classes. TCAF fit also supplies us with the size and location of the Compton cloud along with its optical depth. Thus by fitting with TCAF, a physical understanding of the flow geometry in different χ classes of GRS 1915+105 has been obtained.

Gross Alpha-Based Continuous Air Monitor: Mathematical Modeling, Measurements, and Interpretation

The detection and measurement of transuranic activity in ambient air by counting alpha particles is confounded due to the presence of short-lived alpha-emitting isotopes due to radon and thoron. This paper describes an algorithm intended for use in a gross alpha-based continuous air monitor. The algorithm is capable of generating the variation of gross alpha count rate with time from air filter samples using in situ–measured radon progeny data. The required input of atom concentration can be obtained from a simple experimental technique, which is discussed here.

Computational model for detector timing effects in Compton-camera based prompt-gamma imaging for proton radiotherapy

This paper describes a realistic simulation of a Compton-camera (CC) based prompt-gamma (PG) imaging system for proton range verification for a range of clinical dose rates, and its comparison to PG measured data with a pre-clinical CC. We used a Monte Carlo plus Detector Effects (MCDE) model to simulate the production of prompt gamma-rays (PG) and their energy depositions in the CC. With Monte Carlo, we simulated PG emission resulting from irradiation of a high density polyethylene phantom with a 150 MeV proton pencil beam at dose rates of 5.0 × 108, 2.6 × 109, and 4.6 × 109 p+ s−1. Realistic detector timing effects (e.g. delayed triggering time, event-coincidence, dead time, etc,) were added in post-processing to allow for flexible count rate variations. We acquired PG emission measurements with our pre-clinical CC during irradiation with a clinical 150 MeV proton pencil beam at the same dose rates. For simulations and measurements, three primary changes could be seen in the PG emission data as the dose rate increased: (1) reduction in the total number of detected events due to increased dead-time percentage; (2) increase in false-coincidence events (i.e. multiple PGs interacting, rather than a single PG scatter); and (3) loss of distinct PG emission peaks in the energy spectrum. We used the MCDE model to estimate the quality of our measured PG data, primarily with regards to true and false double-scatters and triple-scatters recorded by the CC. The simulation results showed that of the recorded double-scatter PG interactions 22%, 57%, and 70% were false double-scatters and for triple-scatter interactions 3%, 21%, and 35% were false events at 5.0 × 108, 2.6 × 109, and 4.6 × 109 p+ s−1, respectively. These false scatter events represent noise in the data, and the high percentage of these events in the data represents a major limitation in our ability to produce usable PG images with our prototype CC.