Assessment of factors causing false alarm signals from detection equipment, and ways to mitigate this challenge

Transcription

1 Assessment of factors causing false alarm signals from detection equipment, and ways to mitigate this challenge REPORT by SENIOR RESEARCH FELLOW 12 CSRI OF THE MINISTRY OF DEFENCE OF THE RUSSIAN FEDERATION GRIGORIY SCHEVCHENKO GICNT Technical Workshop March 28-30, Ispra, Italy

2 MATRIX OF THE MSRMC USABILITY Tasks to solve Process or product control Hardware control Energy extraction control Detectors used Radiation fields control Spector and radionuclides control Scintillation Activity control Gas-discharge Aerosoles, vapours, gases control Radioactive liquids control Control of radioactive contamination Semiconductor Ionization chamber In-reactor direct-charge detectors Fission chamber Control of self-sustained chain reaction Thermoluminescent detectors, film and other memories Types of control Production in-process control Control of the industrial space of an object Scintillation detectors Gas-discharge meter Semiconductor detectors Emission and discharge monitoring Waste monitoring Environmental control Ionization chamber In-reactor direct-charge detectors Fission chamber Thermoluminescent detectors, film and other memories 1

3 USING OF THE MSMRC FOR ANALYSIS AND CONTROL OF THE NUCLEAR AND RADIOACTIVE MATERIALS SAFETY In case of detection of NM and RM In case of the safety control of NM and RM Identification Confirmation of an invariability of an object The quantitative analysis Express identifying of RM and NM type Monitoring systems of vehicles Analyzers of the isotopic composition of NM and RM Hand held gamma-spectrometers Active radiological control methods 2

4 USING OF THE MSMRC FOR DETECTION AND IDETIFICATION OF NUCLEAR AND RADIOACTIVE MATERIALS Detection of nuclear and radioactive materials Registration of the fact of existence of NRM Search and identification of NRM Portal monitors Hand held spectrometric means On vehicle checkpoints On railway checkpoints When loading vehicles When controlling traffic flow (non-stop) When controlling construction supplies When controlling food When controlling raw stuff (sugar beet at sugar-refinery), scrap metal Using of means of transport (vehicles, helicopter, motor boat) equipped with detection devices Using of a handheld search and spectrometer equipment (supervision of cargo modules of vehicles, monitoring of buildings and the territories) Using of equipment of invisible detection when monitoring vehicles, large-size cargoes and waste by the active radiation methods 3

5 FACTORS EFFECTING THE GENERATION OF THE MSRMC ALARM SIGNALS Control conditions Control method Object of control Mean of control Characteristic under control Operator 4

6 GENERALIZED CLASSIFICATION OF ERRORS DETERMINING THE CAUSES OF FALSE ALARM SIGNALS Errors of registration and analysis By the method of expression Absolute Relative By the nature of manifestation Systematic Accidental By origins Hardware Methodical Physical 5

7 BASIC REASONS OF ORIGIN OF FALSE ALARM OF MSRMC, CAUSED BY HARDWARE ERRORS Components of an instrument error registration (measurements) of γ-n radiations by MSRMC Constructive miscalculations in case of the MSRMC design Imperfection of the MSRMC element basis The errors caused by limited resolution capability of MSRMC Dynamic errors of MSRMC (stability of operation) Errors of communication of MSRMC with an object Errors of transmission of measuring information 6

8 BASIC REASONS OF ORIGIN OF FALSE ALARM OF MSRMC, CAUSED BY METHODYCAL ERRORS Components of a methodical error registration (measurements) of γ-n radiations by MSRMC Inadequacy of a model to an object Deviations of function arguments, connecting the registered (measured) value to value on MSRMC "input" Deviations of values of efficiency of registration of radiation and time of registration from optimum Error from quantization Difference of an algorithm of calculation from the set function Wrong choice of criterion for evaluation of results of registration Faults causing inconsistency of algorithms Of functioning of MSRMC subsystems 7

9 THE MAIN INDEX OF DETECTION OF NM OR RM WHEN MONITORING OBJECTS OF MSRCM Description of the result of detection Probability of a result of detection Name Specification 1 True Н0, choose Н0 probability of the correct nondetection Р0 =(1 - α) 2 True Н0, choose H1 error of the first type, significance value of criterion, probability of false alarm Рfa = α 3 True H1 choose H1 probability of detection (power of criterion) Рdetection = (1 - β) 4 True H1, choose Н0 Error of the second type, probability of fault β Н0 - hypothesis of absence of NM or RM on subject of monitoring; Н1 - hypothesis of existence of NM or RM on subject of monitoring. Neumann-Pearson's criterion has the largest capacity Рdetection =(1 β) (in case of the given error α, β is minimized). N пор = Nф + U1- pлт Nф Parameters of probabilities of false alarm α in case of different parameters of threshold determined by the natural background and the coefficient U1-α U1-α α 0,1587 0,0228 0,

10 THE BASIC REASONS OF "FALSE" ALARMS OF MSRCM CAUSED BY PHYSICAL ERRORS Components of physical errors of registration (measurements) Influence of the natural background and its variability from different objective factors Transportations of the materials and goods with increased concentration of natural radionuclides (NRN) The errors caused by a depression of the natural γ-background when passing through a zone of monitoring of a large object 9

11 THE MAIN CHARACTERISTICS OF THE NATURAL GAMMA BACKGROUND In the low layers of the atmosphere there are regular fluctuations of density of the background gamma-flow at different times : Daily (maximum in the morning, minimum in the afternoon) and seasonal (maximum in fall-winter, minimum in summer). Daily fluctuations in one and the same point in case of stable weather are from 10% to 150%; random waves (mostly from meteorological factors) are tens and more times; statistical fluctuations of a gamma flow in the ground atmosphere reach tens and hundreds percent. PARAMETERS OF THE NATURAL GAMMA BACKGROUND ARE CHARACTERIZED BY THE FOLLOWING: 1. Density of not scattered gamma flow, at the height of 1 m is for 208Tl (2,62 MEV) - 1,14; for 214Bi (1,76 MEV) - 1,7; and for 40K (1,46 MEV) - 20 quarter / (cm2 min) respectively. 2. The average flow of gamma radiation for energies of E=1,76 and 2,62 MEV fluctuates within 0,1-0,2 quantum./(cm2 sec); 3. Secondary space radiation provides contribution of 0,42 (part./cm2 min) for soft and 1 (part./cm2 min) for hard radiation and in general (in the field of energies of E =0-2,5 MEV) is equal to ~ 20% of the maximum soil component; 4. In case of stable weather intensity of the soft gamma background (Е=0,04 0,5 MEV)» 5 quantum./(cm2 sec)) in case of a range to 10 times, the dispersing relation (D[X]/M[X])» Intensity of the hard gamma background: 10-2 (Е=3-4 MEV), (4-5 MEV), (5-9 MEV) quantum./(cm2 sec) respectively, the dispersing relation (D[X]/M[X]» 4, and background variations due to change of solar activity and magnetic storms don't exceed 5-7% (daily <5% and monthly ~ 5%). Change of temperature on 20 oc or an atmospheric pressure on 10 mm of mercury. gives instability of 3-4%; 6. Changes of a gamma flow of the soil component are from 10-15% to 50%; 7. Heavy rains cause changes up to tens of percent, restoration to a norm requires for open terrain 6-12 hours, for woody terrain hours; 8. Snow cover reduces a gamma flow in several times; 9. In case of weather without any precipitations, the strong winds, atmospheric inverses of a variation of a gamma field at the surface are several tens of percent, for some regions in the morning the flow is 2-6 times more, than in the evening, maximum change in ~ 2 times in the morning; 10

12 MAIN CHARACTERISTICS OF THE NATURAL NEUTRON BACKGROUND 1. The flow density of the natural neutron background is (1-5) 10-3 n./(cm2 sec): (0,6-1,5) 10-3 for subcadmium neutrons (Ен<0,4 ev) and»2, n./(cm2 sec) for epicadmium neutrons (ЕN=0,4 ev - 20 MeV). 2. The background changes several times depending on the isotopic composition of the spreading surface (due to α-n reactions on Al, Si, O2) m away from big reservoirs of water the background changes 20 50%. 4. Upon transition from soil to water the thermal component increases in several times and the fast component decreases. 5. Changes of meteoconditions (rain, snow, humidity, cloudiness, etc.) make a significant effect. Solar flashes (magnetic storms and chromospheric flashouts) cause fluctuations of the background from 20% to n 10 times. 6. The general instability of the neutron background is comparable to the hard gamma radiation. 11

13 MOST PROBABLE LEVELS OF GAMMA RADIATION OF LEGAL TRANSPORTATIONS OF CARGOES BY VEHICLES п/п Cargo type А eff, Bq/kg Total activity (MBq) of cargo for truck transport Large-capacity Low-tonnage CONSTRUCTION MATERIALS 1 scobs 176 4,5 0,45 2 gravel from 30 to 300 from 0,75 to 7,5 from 0,075 to 0,75 3 concrete ,4 4 keramzit ,4 5 brick from 175 to 360 from 4,5 to 9 from 0,45 to 0,9 6 ceramic tiles 300 7,5 0,75 7 road building materials from 740 to 4000 from 18 to 100 from 1,8 to 10 FOOD 8 flour, grain, bread, pasta from 15 to 60 from 0,4 to 1,5 from 0,04 to 0,15 9 Milk ( including dehydrated), milk food from 5 to 500 from 0,13 to 12,5 from 0,013 to 1,3 10 Meat from 13 to 300 from 0,3 to 7,5 from 0,03 to 0,8 WOOD 11 Industrial from 9 to 3700 from 0,23 to 93 from 0,02 to products from wood and wood materials from 8 to 190 from 0,2 to 5 from 0,02 to 0,5 13 SCRAP METAL from 0,2 to 1 µsv/h 12

14 RADIO PHARMACEUTICALS MEDICAL RADIONUCLIDES: F-18, Cr-51, Ga-67, Se-75, Sr-89, Tc-99m, Pd-103, In-111, I-123, I-131, Cs-131, Sm-153, Tl-201, Mo-99, I-125, Xe-133 GAMMA-ENERGIES OF COMMON RPM, COINCIDING (IN RESOLUTION CAPABILITY LIMITS OF MSRMC) WITH GAMMA-ENERGIES OF NUCLEAR MATERIALS Nuclide Energy, kev 1 Fe ,648; 192,344; 334,8; 1099,22; 1291,56 2 Ga-67 91,266; 93,311; 184,577; 208,951; 300,219; 393,529; 887,693 3 Tc-99m 140,466 4 I ,97; 528,96; 538,54 5 I ,1829; 284,298; 325,781; 364,48; 636,973; 722,893 6 Xe ,62; 81; 160,6 7 Tl-201 1,57; 5,84; 32,19; 135,34; 167,43 13

15 PROGRAM AND TECHNICAL MEASURES OF MINIMIZING FALSE ALARMS CAUSED BY INSTRUMENTAL ERRORS Technical solution 1 Use of coincidence pattern 2 Separation of energetic windows 3 Use of position sensitive detectors Expected efficiency, % Up to 25 Not determined 4 Optimization of Тexp and eс Right choice of the working body of the detector Protection of the detector against the natural background: 6 - shielding; - chart of anticoincidences 7 Deduction of the background 8 Elimination of mutual shielding of gas-filled counters 9 Use of sensors of presence Up to 20 Up to 25 Not determined

16 PROGRAM AND TECHNICAL MEASURES OF MINIMIZING FALSE ALARMS CAUSED BY METHODICAL ERRORS Methodical solution 1 Optimum filtering of the registered radiation 2 Application of nonparametric methods of information processing 3 Application of the digital method of processing of a signal 4 Application of methods of multiparameter registration of signals 5 Evaluation of difference of times Expected efficiency, % Up to Up to Up to Up to Taking into account depression of the natural background and restoration of an undisturbed background Not determined 7 Increase of accuracy in approaching the distribution law of radiation to the Gaussian distribution Not determined 15

17 PROGRAM AND TECHNICAL MEASURES OF MINIMIZING FALSE ALARMS CAUSED BY PHYSICAL ERRORS Pb 16

18 GICNT Technical Workshop Thank you for your attention! March 28-30, Ispra, Italy