Heuristic techniques for maximum likelihood localization of radioactive sources via a sensor network

Maximum likelihood estimation(MLE)is an effective method for localizing radioactive sources in a given area.However,it requires an exhaustive search for parameter estimation,which is time-consuming.In this study,heuristic techniques were employed to search for radiation source parameters that provide the maximum likelihood by using a network of sensors.Hence,the time consumption of MLE would be effectively reduced.First,the radiation source was detected using the k-sigma method.Subsequently,the MLE was applied for parameter estimation using the readings and positions of the detectors that have detected the radiation source.A comparative study was performed in which the estimation accuracy and time consump-tion of the MLE were evaluated for traditional methods and heuristic techniques.The traditional MLE was performed via a grid search method using fixed and multiple resolutions.Additionally,four commonly used heuristic algorithms were applied:the firefly algorithm(FFA),particle swarm optimization(PSO),ant colony optimization(ACO),and artificial bee colony(ABC).The experiment was conducted using real data collected by the Low Scatter Irradiator facility at the Savannah River National Laboratory as part of the Intelligent Radiation Sensing System program.The comparative study showed that the estimation time was 3.27 s using fixed resolution MLE and 0.59 s using multi-resolution MLE.The time consumption for the heuristic-based MLE was 0.75,0.03,0.02,and 0.059 s for FFA,PSO,ACO,and ABC,respectively.The location estimation error was approximately 0.4 m using either the grid search-based MLE or the heuristic-based MLE.Hence,heuristic-based MLE can provide comparable estimation accuracy through a less time-consuming process than traditional MLE.

COMMONLY USED RADIOACTIVE SOURCES

Table 36.1. Revised November 1993 by E. Browne （LBNL）.＂Emission probability＂ is the probability per decay of a given emission; because of cascades these may total more than 100%. Only principal emissions are listed. EC means electron capture,

Multi-Energy Gamma-Ray Attenuations for Non-Destructive Detection of Hazardous Materials

We present a non-destructive method (NDM) to identify minute quantities of high atomic number (Z) elements in containers such as passenger baggage, goods carrying transport trucks, and environmental samples. This method relies on the fact that photon attenuation varies with its energy and properties of the absorbing medium. Low-energy gamma-ray intensity loss is sensitive to the atomic number of the absorbing medium, while that of higher-energies vary with the density of the medium. To verify the usefulness of this feature for NDM, we carried out simultaneous measurements of intensities of multiple gamma rays of energies 81 to 1408 keV emitted by sources 133Ba (half-life = 10.55 y) and 152Eu (half-life = 13.52 y). By this arrangement, we could detect minute quantities of lead and copper in a bulk medium from energy dependent gamma-ray attenuations. It seems that this method will offer a reliable, low-cost, low-maintenance alternative to X-ray or accelerator-based techniques for the NDM of high-Z materials such as mercury, lead, uranium, and transuranic elements etc.

Study on dynamic characteristics of fission products in 2 MW molten salt reactor

In this study,a numerical flow model of the fission products(FPs)in the primary loop system of a molten salt reactor(MSR)was established and solved using Mathematica 7.0.The simulation results were compared with those of the ORIGEN-S program in the static burnup mode,and the deviation was found to be less than 10%,which indicates that the results are in good agreement.Furthermore,the FPs distribution in the primary loop system under normal operating conditions of the 2 MW MSR was quantitatively analyzed.In addition,the distribution phenomenon of the FPs under different flow rate conditions was studied.At the end of life,the FPs activity in the core region(including active region,and upper and lower plenum regions)accounted for 77.3%,and that in the hot leg #1,main pump,hot leg #2,heat exchanger,and cold leg region accounted for 1.2%,16.15%,0.99%,2.5%,and 1.9%,respectively,of the total FPs in the primary loop under normal operating conditions.The proportion of FPs in the core decreased with the increase in flow rate in the range of 2.24-22,400 cm^3 s^-1.The established analytical method and conclusions of this study can provide an important basis for radiation safety design of the primary loop,radioactive source management design,thermal-hydraulic safety analysis,and radiochemical analysis of FPs of 2 MW MSRs.

Influence of Chemical Effect on the Kβ/Kα Intensity Ratios and Kβ Energy Shift of Co, Ni, Cu, and Zn Complexes

Chemical effects on the Kβ/Kα intensity ratios and △E energy differences for Co, Ni, Cu, and Zn complexes were investigated. The samples were excited by 59.5 keV γ-rays from a ^241Am annular radioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV. We observed the effects of different ligands on the Kβ/Kα intensity ratios and △E energy differences for Co, Ni, Cu, and Zn complexes. We tried to investigate chemical effects on central atoms using the behaviors of different ligands in these complexes. The experimental values of Kβ/Kα were compared with the theoretical and other experimental values of pure Co, Ni, Cu, and Zn.

The Radioactivity of Nuclei &Solar Oscillations: New Experiments

The experimental detection of the hidden periodicities in the activity of various radioactive sources which were observed by different instruments and which coincided with the period of the free oscillations of the Sun gave an impetus to the further research. The simultaneous recording of gamma rays from two radioactive sources revealed the elements of synchronism and the periods of solar oscillations as well as the phase delay for the different sources in the obtained time series. A neutrino detector has been designed and tested, the advanced schemes for neutrino detection are developed, and the impact of the neutrino source on the radioactive matter is explored. The search for the new principles for creating the emitters of neutrino beams is conducted.

K Shell Fluorescence Parameters by Impact of 5.96 keV Photons on Ti and Its Compounds

K shell fluorescence parameters of pure Ti and some of its compounds have been determined experimentally using an Ultra-LEGe detector with resolution 150 eV at 5.9keV.The samples were excited 5.96 keV photons emitted from a ^(55) Fe radioisotope source with 50 mCi activity.The experimental values of the K shell fluorescence parameters have been compared with the experimental and theoretical values available in the literature for pure Ti.

Implementation of safety and security standards for high dose rate brachytherapy sealed radioactive source used in a medical radiation facility

Objective:To provide guidance on basic concepts and elements for radiation safety and security measures for a HDR brachytherapy sealed radioactive source in a medical radiation facility.Methods:Brachytherapy sources are Category 2(High risk-very dangerous)radioactive source and Security Level B applied to cover the range of security measures needed for the associated risk with remote afterloading HDR brachytherapy sources.These security measures were applied based on a risk informed graded approach.A series of in-build and operational safety measures were implemented for equipment and radiation installation.Results:The medical radiation facility equipped with adequate radiation protection,detection and monitoring equipment such as survey meter,digital contamination monitor,gamma zone monitor,digital radiation monitor,personnel dosimeter,pocket dosimeter,long handled forceps,shielding material and emergency source storage container etc.to deal with radiological incidences.The contingency plan with security objectives for incidents and procedures for action was prepared in order to implement response function to fulfill the goal of adequate security of radioactive source.The emergency response plan documented against emergency scenarios during transport,loss of radioactive source,theft,sabotage,natural calamities/disasters such as fire,flood and earthquake.Conculsions:The paper provides various radiation safety and security aspects for the HDR brachytherapy.The HDR brachytherapy radioactive sources are Type A packages.Transport of radioactive material is the responsibility of consignors,consignee and carriers under the legislation,supervision and control of regulatory authority.

An approach to evaluate the efficiency of γ-ray detectors to determine the radioactivity in environmental samples

This work provides an approach to determine the efficiency of T-ray detectors with a good accuracy in order to determine the concentrations of either naturally occurring or artificially prepared radionuclides. This approach is based on the efficiency transfer formula （ET）, the effective solid angles, the self- absorptions of the source matrix, the attenuation by the source container and the detector housing materials on the detector efficiency. The experimental calibration process was done using radioactive （Cylindrical ＆ Marinelli） sources, in different dimensions, that contain aqueous 152Eu radionuclide. The comparison point to a fine agreement between the experimental measured and calculated efficiencies for the （NaI ＆ HPGe） detectors using volumetric radioactive sources.

Review of the 5·7 Nanjing^(192)Ir source radiological accident

This paper gives a detailed description of a radiological accident of ^(192)Ir source occurring on May 7,2014 in Nanjing,China(the 5⋅7 accident),encompassing a combination of accident overview,emergency response,investigation process and results,dose estimation,medical treatment,experience and lessons learnt.The investigation showed that the accident was mainly caused by insufficient attention to the radiation safety,non-compliance with licensing conditions and employment of untrained temporary radiographer without equipped with alarm dosimeters.Additionally,no area radiation survey meter was used to verify whether the source would have retracted to radiography camera after every exposure.It therefore is the important means to strengthen the management of radioactive source safety and put the strict management measures in place,implement the requirements for personnel qualification management,strengthen regulatory inspection and actively poster safety culture,which are necessary to avoid accidents.This paper aims to provide experience and reference for the emergency response and countermeasure of radiological accidents involving industrial radioactive sources.