A Bayesian Nuclide Identification Algorithm Based on the Energy Spectrum

Gamma-ray spectroscopy and gamma-ray imaging are two complementary techniques used for the localization and the identification of radioactive sources containing gamma-ray emitting radioisotopes. The radioactivity monitoring is focused on the detection of both artificial and environmental radioactive sources like Naturally Occurring Radioactive Materials (NORM). This kind of contamination becomes dangerous when the detection of the unwanted substances exhibits a concentration significantly above the environmental radioactive background radiation levels. For this purpose, we have developed, tested and shown a High Efficiency fast-Response GAmma (HERGA) detector useful for the identification of radionuclides and for gamma-ray imaging. A first version of the gamma detector prototype was composed of 16 CsI(Tl) scintillating crystals of 3x3x10 cm3 size, arranged in 4x4 matrix coupled with standard Photomultiplier tubes (PMTs). An image reconstruction of a radioactive gamma emitter source is possible using the coded mask technique, in which a 7x7 mask, made of Plastic and Tungsten tiles, is placed in front of the detector and a pattern recognition algorithm based on classical statistical methods (Kolmogorov Smirnov) is used to reconstruct the source position. The measurements carried out showed a point spread function (PSF) of a few mrad for pointlike sources. The Minimum Detectable Activity (MDA) was also determined in the case of pointlike radioactive sources. In this contribution we will present an update of the HERGA detector prototype in which Silicon Photomultipliers (SiPMs) are used in place of the PMTs. SiPMs provide similar or even better performance compared to the standard PMT sand provide benefits in terms of lower power consumption and reduced cost and compactness. The advantages of the SiPM technology are also characterized by the robustness of the photosensor that makes the new prototype compact, portable, ideal for in-situ and real-time. We will show a comparison between the results obtained with the newest SiPM read-out technology with respect to those obtained with the PMT one, in terms of energy and spatial resolution. The imaging performance is also in phase of testing in order to localize extended radioactive sources such as for example NORM samples or to detect inaccessible or hidden nuclear waste.

All living things are constantly exposed to background radiation. The presence of radioactive materials in the earth's crust and cosmic radiation are largely responsible for this exposure. The present study aimed to develop a new methodology of easy applicability and low cost to carry out measurements of environmental background radiation and to be able to establish a map of environmental radiation for primary monitoring of these exposures. For that, ionizing radiation measurements, Meteorological and Radiometric measurements were performed. Geiger Mueller Counter (GM) was used, as it is widely used in services that use radioactive sources and research centers. Measurements obtained showed that there were no statistically significant changes in the 24 hours of measurements with the GM, in relation to the variations presented in the Meteorological and Radiometric measurements that changed according to the time of day. The average value of the background radiation readings was 0.0194 mR/h, with an average variance of 1.8E-06 and an average standard deviation of 1.35E-03. GM proved to be useful for primary measurement of background radiation. The map was developed using open source libraries for the Python programming language. The map may be hosted on an open access website, so that professionals, students and researchers may contribute, sending new data from different locations. It is essential that the levels of radiation exposure are demonstrated and understood. Easy access to this information may contribute to health organizations, agriculture and research centers to establish a baseline for future research.

Absorbed doses in bricks and TL-dosimeters due to anthropogenic and natural environmental radiation sources

Delft Soil Mechanics Laboratory (Delft) has developed a nuclear density device to measure directly during penetration the in-situ density of saturated soils. A radioactive Source and radiation detector were built in a cone shaped probe with an effective area of 1500 mm2 for an offshore soil investigation. The nuclear density probe can assess directly the soil mass which is penetrated with standard cone penetration testing (CPT) methods and equipment. During penetration the in-situ density is continuously recorded. The tool has successfully been used for the first time offshore during the 1984 soil investigation for Statoil's Gullfaks 'C' gravity base platform in the North Sea. Tests were performed from the survey vessel Bucentaur in a water depth of 217 metres. The probe was pushed into the seabed to depths of about 34 metres using Fugro's cone penetration rig Seacalf. Density testing can be incorporated in routine site investigations, since it can be deployed from standard type CPT jacking units and drill rigs onshore and offshore. This paper describes the design of the tool the testing system, the performance of the offshore tests and the results of the in-situ density measurements. INTRODUCTION In 1984 a soil investigation program was carried out by NGI and Fugro at Statoil's Gullfaks field offshore Norway. Fugro contracted Delft Soil Mechanics Laboratory for the performance of in-situ density measurements. The purpose of the in-situ density tests was to establish the density of the upper 35 meters of soil at the location. his involved the deployment of Delft's new nuclear backscatter density probe. Generally in-situ density tools used for deeper penetrations appear bulky and are designed for borehole logging use. This involves measurement from inside a casing or drillpipe or in an open borehole. In the former method, the casing or drill pipe may influence the result. In the latter the borehole stability may be a restricting factor. Delft managed to miniaturize the device and the current probe has a diameter of 44 mm with an effective area of 1500 mm being identical to a 1500 mm cone (figure 1), Smits (1982). This allows the probe to be deployed in the same manner as a penetrometer cone. Direct contact between the instrument and the soil is thus realised. Four tests were carried out successfullyin water depths of 217 metres. On completion of the offshore phase, tests were performed onshore for calibration purposes. NUCLEAR BACKSCATTER DENSITY PROBE The in-situ density of a soil is an important geotechnical design parameter in foundation engineering calculations. Conventionally, density is determined destructively by weighing and measuring the volume of a small quantity of sediment taken from a sample. Because of the variable and unknown degree of disturbance involved in this process, there are distinct advantages to measuring the density in-situ. Representative papers on in-situ density measurement devices include Keller (1965), Preiss (1968) and Rose and Rooney (1971)

Population distribution of doses from natural radiation in Finland

The technical details of a radiation measuring system based on a quartz torsion fiber electroscope and a pressurized ionization chamber are described. This equipment is designed to measure the radiation intensity from the carbon-14 contained in a sample introduced into the system as carbon dioxide. This system, including the shielding, is shown to be capable of measuring nuclear radiations of extremely low intensities, on the order of 1/200 of the normal laboratory background level, with a probable error of approximately l%. The background radiation intensity observed with the system including the shielding is also on the order of 1/200 of the normal laboratory background level. The nature of background radiation and its relation to the measurement of such low intensities is discussed. It is shown that the main limitation in accuracy, with the equipment described here, is due to cosmic ray bursts. It is also shown that the major source of background radiation is external to the equipment, being thus due to cosmic rays and/or local external gamma ray emitting material contamination. Although the evidence is not conclusive, the data indicates in addition that the cosmic rays are the major contributor to this background radiation. The main conclusion which may be drawn from these results is that the selection of an equipment location is very effective in reducing the level of background radiation, thus permitting the measurement of radiation fields of extremely low intensity. The final application of this equipment was to the well known carbon-14 dating method originated by W. F. Libby. Several samples of interest were dated and the results are given. Of particular interest, are the samples from the Santa Rosa Islands off the California Coast, concerning an Indian culture which existed there before Christ and after.

The environmental level multi-source air kerma rate calibration system

The localization of a radioactive source can be solved in closed-form using 4 ideal sensors and the Apollonius circle in a noise- and error-free environment. When measurement errors and noise such as background radiation are considered, a larger number of sensors is needed to produce accurate results, particularly for extremely low source intensities. In this paper, we present an efficient fusion algorithm that can exploit measurements from n sensors to improve the localization accuracy, and show how the accuracy scales with n. We report testbed results for a 0.911 μCi source to illustrate the effectiveness of our algorithm, in particular performance comparisons with state-of-the-art fusion algorithms based on Mean of Estimates (MoE) and Maximum Likelihood Estimation (MLE). We show that ITP is more accurate than MoE, whereas the choice between ITP and MLE is generally a tradeoff between accuracy and run time efficiency. Higher-intensity radioactive sources are not safe for actual experiments. In this case, we present simulation results based on a validated simulation model. We show that a low-intensity 400 μCi source, similar to the radioactivity of a concealed dirty bomb, can be localized to within 32.5 m using a sensor density of about 1 per 1100 m2 in a surveillance area.

To obtain the characteristic information of unknown radionuclides by analyzing the γ-energy spectrum of a low-resolution detector, and to improve the accuracy and validity of the analysis of overlapping and weak peaks in the γ-energy spectrum, in this paper we analyze the γ-energy spectrum of NaI(Tl) detectors based on the Boosted-Gold algorithm. A simulation model of NaI(TI) detector is established by using MCNPX, and a detector response matrix with dimension 201 × 200 is obtained. The γ-energy spectrum unfolding program is developed based on the Boosted-Gold algorithm. The detector response spectra of the γ radioactive sources <sup>22</sup>Na, <sup>133</sup>Ba, and <sup>152</sup>Eu are measured. Three groups of low-resolution γ spectra are constructed with different γ-ray energy, different energy differences (<inline-formula><tex-math id="M2">\begin{document}$ \Delta E $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20212429_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20212429_M2.png"/></alternatives></inline-formula>) and different relative intensities by simulation. Combining the response matrix and the unfolding procedures, the measured and simulated γ energy spectra are unfolded. The unfolding results are analyzed with the nuclide standard characteristics information from the IAEA database. The results show that the maximum unfolding error of the characteristic energy of the measured γ-energy spectrum is 2.17% (0.276 MeV for <sup>133</sup>Ba source) by the Boosted-Gold algorithm, and the maximum deviation between the unfolded intensity and the standard intensity is 0.197 (1.408 MeV for <sup>152</sup>Eu source). For the simulated γ energy spectrum, the characteristic energy of nuclide can be accurately analyzed, and the deviation between unfolded intensity and standard intensity maintains 0.01. When the enhancement factor <i>p </i>≤ 14, the Boosted-Gold algorithm is beneficial to the quantitative analysis of γ-radionuclides. For the relative intensity of γ-rays greater than 10%, this algorithm has better analysis accuracy.

A new method for correction of temperature changes in scintillation detector without using a radioactive source

An area radiation monitoring system was designed using the solid state technology replacing the traditional GM tubes. Unlike the GM tubes, PIN silicon photodiodes require relative low bias voltage, have smaller detector size, respond more linearly to radiation, and are capable detecting wider radiation range. A microprocessor is also incorporated in this design to enable the operator to screen out unwanted low energy gamma rays, and an electronic bug source is also used to eliminate a possible down scale trips from statistical uncertainty from radioactive bug source and background radiation. This system is currently installed through out the nuclear plants to monitor radiation levels.

APDs (Avalanche Photodiodes) referred to in this Chapter differ by their construction and characteristics from those commonly used in long-distance optical communication. Common to both applications is the usage of an internal gain mechanism that functions by applying an adequate reverse voltage. In the optical communication industry one is mainly interested in small diameter devices to be coupled to optical fibres in near infrared domain. In nuclear physics they are used to convert light pulses, induced by particles and photons in scintillating crystals, into electronic signals. These emit at shorter wavelengths, moreover, it is advantageous to cover up to several cm2 of scintillator exit face with the sensing element to maximize the detector signal for low energies deposited in the scintillator. Therefore, progress in large area APDs in short-wavelength domain has been mainly driven by nuclear physics applications. A vast amount of research and development work invested by the joint CERN + Hamamatsu Photonics team resulted in a 5x5 mm2 device (S8664-55), which paved the way to larger area APDs. A notable feature of S8664-55 is its outstanding radiation hardness, so that by its application, the CMS-ECAL expects 10 years of failureless operation in a hostile radiation environment of the CERN-LHC. Let numbers illustrate the volume of APD usage: the barrel part of CMS-ECAL has 122400 pieces and the ALICE-PHOS 35840 of them. The meaning of the term High-Energy Gamma-Ray used in the title and meant in the rest of this chapter is related roughly to the maximum antiproton energy of 14 GeV from the HESR accumulator at the future FAIR facility in Darmstadt. The electromagnetic calorimeter (EMC) (Erni et al., 2008) of the PANDA detector, to be used in studies of hadron physics in antiproton-proton annihillations, will thus deal with photons in the energy range extending nearly from zero up to the maximum energy of the order of 10 GeV. Low-Energy Photon does not have its common meaning of a photon emitted from a radioactive source but rather is related to the practically achievable EMC low-energy detection threshold of several MeV. The results reported in Sect. 7 refer to a study intended to investigate detector resolution with 4 20 MeV photons, relevant for the latter energy range. Low-energy proton capture reactions are used to generate these gamma-rays. A reader interested in medical application of APDs, for example in Positron Emission Tomography (PET), which uses photons emitted in annihilation of positrons from radioactive Low-Energy Photon Detection with PWO-II Scintillators and Avalanche Photodiodes in Application to High-Energy Gamma-Ray Calorimetry

Infrared imaging characteristics of space-based targets based on bidirectional reflection distribution function

Background: Boron neutron capture therapy (BNCT) is a potential radiation therapy for treating refractory cancers. Measuring the neutron energy spectrum is important to evaluate the biological effect of BNCT. We have developed a novel low-energy neutron spectrometer with a 3He position-sensitive proportional counter. The effectiveness of this spectrometer remained unvalidated due to the inadequate response function.Materials and Methods: The response function of this spectrometer was evaluated by Monte Carlo simulation to perform the validation experiment of this spectrometer. The 3He(n,p)3H reaction rate for each monochromatic neutron (energy range, 0.5 eV–10 keV) was calculated. Numerical experiments were conducted to investigate the performance of this spectrometer. Several estimated values of the energy spectrum were obtained and compared with a calculated energy spectrum at the exit of the epithermal column by the Monte Carlo simulation by preparing several candidates for signals. The Bayesian estimation algorithm was utilized for the estimation.Results and Discussion: The results indicate that the spectrometer and the evaluated response functions can be utilized to measure the energy spectrum of neutrons in the low-energy range. However, the energy spectrum could not be well represented >4 keV due to the poor response function, including uncertainties in response function calculation as well as the poor energy resolution of this detector in the high-energy region.Conclusion: The response function of the low-energy neutron spectrometer for the epithermal energy region can be assessed by the Monte Carlo simulation. The numerical experiments reveal that the effectiveness of this spectrometer can be shown in the range of 0.5 eV.

In the present work, we have made Monte Carlo simulations of the response of 1″ × 1″ LaCb(Ce) and 1″ × 1″ LaBn(Ce) scintillation detectors using the radioactive sources emitting two gamma rays in cascade, namely, 60Co, 94Nb, 46Sc and 24Na for different values of source-detector separation. These simulations were done using GEANT4 toolkit that include radioactive decay module and general particle source (GPS) module. Energy spectra were generated for each of these double gamma emitters and absolute activities were calculated using conventional sum-peak method and modified sum-peak method proposed very recently. In order to validate the simulated results, we have carried out experimental investigations using a calibrated 60Co source. The measured activities are found to be in very good agreement with the simulated activities.