General Overview of Radiation Detection and Equipment

Transcription

1 INL/MIS General Overview of Radiation Detection and Equipment International Nuclear Safeguards Policy and Information Analysis Course Monterey Institute of International Studies June 3, 2013 Mark Schanfein, Idaho National Laboratory

2 What is Radiation? Energy traveling through space in the form of particles or electromagnetic waves Examples include microwaves, x-rays, radio waves, and light Can be ionizing or non-ionizing Radioactive material emits ionizing radiation Alpha Beta (+/-) Neutron Paper Aluminium Lead Water Alpha Beta Gamma and X-rays Source: Neutron Source: ICx Technologies

3 Identifying Sources w/ Spectroscopy Nuclear materials emit unique radiation (alpha, beta, gamma, neutron) Gamma ray energies can identify material while intensity may provide insight into the amount of material. Source: Sodium iodide gamma spectrum of cobalt-60 Sodium iodide gamma spectrum of cesium-137 Gamma spectroscopy - quantitative study of energy spectra of gammasources

4 General Detector Types Gas tube detectors, Utilize small metal tubes filled with gas, containing an electrical lead down the center connected across a potential voltage. As ionized particles interact with gas molecules inside the tube, an electrical current is induced through the lead and outputted to a readout. Scintillation Crystal detectors Comprised of materials that fluoresce when hit by a photon. The induced florescence is then amplified, processed and outputted to a readout. Added ability to characterize energies observed. Solid-state semiconductor detectors Photons from a gamma ray hit the surface of a semiconductor, creating free electrons which can be detected as an electrical current, which is then processes and outputted to a readout.

5 Radiation Sensor: Ionization cut away ICAS /Page 5

6 Source: Wikipedia.org Basic Workings of Scintillation Based Detectors NaI(Ti) detector consists of an NaI (thallium doped) crystal optically mounted to a photomultiplier tube. Incident radiation interacting in the NaI crystal fluoresce or spark ( scintillations ). The emitted light are transmitted into the photomultiplier tube where the light produces electrons. Scintillation crystal surrounded by assorted detector assemblies Source: WikiBooks.org

7 Basic Workings of Scintillation Based Detectors The number of electrons is amplified within the phototube. The signal output of the phototube is processed electronically into a pulse that signifies the incidence of a photon: Circuitry consisting of high voltage supply, a resistor chain array and a load resistor, R L. Voltage is applied to the resistor divider array (each of same resistance), dividing up V dc into equal voltages which are supplied to dynodes Resulting charge from phototube amplifies from dynode to dynode within the array fed into the anode with a load resistor used to generate an output voltage, V out The pulse stream is outputted with V out directly proportional to energy deposited by radiation in Crystal Source: WikiBooks.org

8 HM-5 Components 8

9 Basic Components of a Typical Detector = Sensor (i.e. NaI(Ti)) Integrated Electronics Package Co-60 Integrated Software Package

10 identifinder HM5 by ICx Technologies The HM-5 is a handheld radiation detection, measurement, and analysis tool based on scintillation technology one of the most frequently used tools by IAEA inspectors Used to search for nuclear materials, identify isotopes present, and determine the level of uranium enrichment. Basic Features: NaI class instrument Easy to operate Automatic calibration & stabilization Digital signal processing Visible, audible, & tactile alarms Nuclear ID based on template matching Finder mode to locate source or possible contamination Integrated ancillary detectors Geiger- Mueller tube for high dose rates; He 3 tube for neutron detection. Source: IAEA

11 identifinder HM5 by ICx Technologies The gamma dose rate is displayed as a digital readout as well as a logarithmic analog bar graph For gamma only devices, gamma count rate is displayed or for identifinder s with neutron capabilities the neutron count rate is displayed. Both are in counts per second (cps) Gamma & Neutron Gamma Only Source: ICx Technologies

12 identifinder HM-5 by ICx Technologies One or several nuclides can be listed upon successful identification During data acquisition of the identification process the dose rate alarms are still active but the only indication will be audible tones, messages will not be displayed Nuclide identification is done by comparing spectra stored in the library with the measured spectra, if a mixture of isotopes is found then results could be unidentifiable because the spectrum is so different The result is rated between 1 (unlikely) and 10 (very likely) Nuclide Source: ICx Technologies

13 Basic Workings of Scintillation Based Detectors Outputted pulse stream to screen, log, etc Typical plot graph (gamma spectrum) of count rates (Y) vis-à-vis voltage pulse height (X) for each gamma energy emitted from source Output quality Inherent limitations given inefficient conversions of radiation to light and subsequent generation of electrical current Statistical spread / the higher the resolution (quality) the more narrow the spread Source: WikiBooks.org

14 Safeguards Verification Activities Attribute test Pu, U and Th Materials Confirms the presence of plutonium in low-grade mixed plutonium/uranium mixed oxide (MOX), MOX scrap, and waste Presence/Absence/Enrichment of LEU, natural, and depleted U UF6 cylinders, process materials, scrap, and waste Detects the presence of natural, depleted, and LEU in containers of process materials, scrap, and waste at LEU fuel fabrication plants Verify % U-235 in samples (enrichment) Distinguish between natural (0.7% U-235), depleted (ca. 0.2% U-235), LEU (0.7 20% U-235), and HEU (> 20% U -235) Confirm that fresh low-enriched uranium (LEU) fuel is in fact, lowenriched fuel 15

15 Safeguards Verification Activities Cont. Verification of Active Length of Nuclear Fuel Used to determine boundaries of the nuclear fuel zone in fuel pins and assemblies Note the nuclear fuel zone boundaries should be measured carefully - to determine the total uranium and U-235 content of the fuel Detecting Undeclared Nuclear Activity In dose-rate mode, permits detection of gamma radiation from undeclared nuclear material processing Including: Fuel reprocessing, enriching uranium, and production of HEU Detecting Undeclared Nuclear Material In isotope identifier mode, permits detection of undeclared nuclear materials, which aids in identifying undeclared nuclear activities Including: Pu-239, U-235, Cs-137, Sr-90, Th-232, and Am-241 Note To confirm the presence of undeclared nuclear material, the inspector should collect a sample of the material or an environmental (swipe) sample Note Secure the unknown material with an IAEA seal 16

16 Raider Hand-Held Radionuclide Identifier A Main Display B A D B Gamma/Neutron Detectors C Left Control Buttons (1 & 2) D Right Control Buttons (3 & 4) E Communication LEDs C E F F Speaker G Microphone G I H J K H Detection LEDs I Power Button J Secondary Display K Alarm Beeper

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18 False Alarms The verification of unknown containers and materials can lead to false (positive) alarms Inspectors need to be aware of common commercial materials and equipment that contain small amounts of radioactive substances, including: Orange/yellow/green glassware colored with uranium minerals Orange/yellow/green ceramic ware colored with uranium minerals Natural phosphate fertilizer containing uranium Large porcelain and ceramic objects containing thorium and/or radium Radium painted night-glow instruments and watch faces Smoke detectors containing Am-241 (ionization type) Natural Th (camera lenses, lantern mantels, welding rods) Radon People and Bananas (K 40 ) 19

19 Germanium Detectors InSpector 2000 Multi-channel Analyzer (Germanium). Pictured laptop used to record readings from the detector. Source: IAEA

20 Germanium Detectors

21 Uranium Spectral Features 60 kev ( 241 Am) kev ( 235 U) Ge High-Enriched uranium spectrum at high-(ge) and low- (NaI) energy resolution U, Th X rays NaI 22

22 Plutonium Spectra Relative Comparison 23

23 Considerations for Gamma-Ray Measurements Detector Type? Content of Source? Single Isotope? Multiple Isotopes? Distance to Source? Dead Time Poor Statistics Measurement Time with Source? Instrument Count Time? Your Radiation Exposure? Shielding? Collimation? Location of Source within Container? Nearest Neighbors?

24 Summary The HM-5 is a small, portable, and very powerful gamma dose-rate meter and gamma spectrometer The HM-5 is used by safeguards inspectors on routine inspections and Complementary Access under the Additional Protocol Despite the fact that it is small and portable it is an important tool if the user is properly trained The HM-5 is used to Determine the presence of Pu, U, and Th in samples Determine uranium enrichment Determine the active length of nuclear fuel pins and assemblies Detect undeclared nuclear activities Detect undeclared nuclear material and identify that material The IAEA is looking into the Raider System 25

25 May the Force be with you.. (Image Source Angela Durst, DNE) 26