Session II.3.2 Part II Quantities and Measurements Module 3 Principles of Radiation Detection and Measurement Session 2 Proportional and GM Detectors IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources

Overview In this session we will discuss the principle of measuring radiation using proportional and Geiger Mueller detectors

Gas Filled Detectors As indicated in the previous lecture, ion chambers are the simplest of all gas filled detectors An electric field is used to collect all the ionizations (positive and negative charged particles) produced by the incident radiation in the gas volume

Regions of a Gas Filled Chamber Recombination Region The proportional region is located where the voltage is high enough to produce secondary ionizations. The voltage causes the electrons liberated by the incident radiation to have enough energy that they are able to ionize additional atoms. Since these secondary ionizations were not produced by the incident radiation they do not carry any information relating to the incident radiation. The signal produced by these and the originally liberated electrons is “proportional” to the energy carried by the incident radiation but not equal to it. When the voltage has been increased sufficiently, the electrons liberated by the initial incident radiation have enough energy to ionize other atoms and those electrons also are able to ionize additional atoms resulting in a chain reaction of ionizations until the entire volume has essentially been ionized. The result is an electronic pulse which is independent of the amount of energy initially deposited by the incident radiation. All types of radiation and all energies will produce the same effect if they interact with the atoms inside the chamber. This is the GM region.

Operating Regions of a Gas Filled Detector Recombination Ionization Proportional Limited Proportional Geiger Mueller Continuous Discharge

Gas Flow Proportional Chamber In this proportional chamber, a continuous flow of gas enters the chamber. This gas is ionized by the radiation emitted from the sample placed within the chamber. The liberated electrons are collected by the wire loop anode in the center of the chamber.

Directional and Energy Response This GM detector responds differently depending on the direction of the incident radiation. It also responds differently depending on the energy of the incident radiation. At low energies, the radiation cannot penetrate the walls of the detector. Since this type of detector has a very thin window at the end, radiation incident from that direction more readily enters the chamber. However, the detector over-responds to the low energy photons since it was calibrated with high energy photons from 137Cs.

Sample Geiger Muller (GM) Detectors

Bicron Surveyor 2000 0-0.2 mR/h to 0-2,000 mR/h 0-240 cpm to 0-240,000 cpm Exposure accuracy within 10% (per NRC reg. guide 10.8) Meets or exceeds 10CFR35 for nuclear medicine Surveyor 2000 is compact, with doserate and countrate scales and controls for response time and audio. X-ray and gamma ray exposures are measured by an internal GM detector, and alpha, beta, X- or gamma countrates using a suitable external probe operating at 900 V. High voltage check, anti-saturation and dead time compensation are included.

Bicron “Radiographer” A portable survey meter with an internal energy-compensated GM detector, the Radiographer also features automatic dead time compensation, anti-saturation circuit and HV and battery checks Three linear ranges: 0-10 mR/h to 0-1000 mR/h Response times optimized for each range Energy compensated: 40 keV to 1.2 MeV Weighs only 1 kg

Detector System (UWDS) Eberline Underwater Detector System (UWDS) Detects high gamma fields underwater. Underwater detector, 65' watertight cable and a Survey Meter which features a large, backlit digital display with analog bar graph. Data logging (up to 256 data points), adjustable alarms, and built in speaker with click rate proportional to the count rate. FEATURES - Energy compensated GM tube with a range of 10 mR/h to 10,000 R/h - Watertight detector down to 20m   Detector Size 3.5 cm diameter x 23 cm long Batteries - 2 standard "AA", 250 hrs with Alkaline, 500 hrs with Lithium Simultaneous internal and external detector rate measurements           OPTIONS - Stainless steel detector housing to facilitate easy decontamination  - "Smart Probe" with stored calibration parameters

Ludlum 44-9 “pancake” GM INDICATED USE: Alpha beta gamma survey DETECTOR: Pancake type halogen quenched GM WINDOW: 1.7 plus or minus 0.3 mg/cm2 mica WINDOW AREA: Active - 15 cm2 ; Open - 12 cm2 EFFICIENCY(4 geometry): Typically 5% - C14; 22% - Sr90/Y90; 19% - Tc99; 32% - P32; 15% - Pu239 SENSITIVITY: Typically 3300 cpm/mR/hr (Cs137 gamma ) ENERGY RESPONSE: Energy dependent DEAD TIME: Typically 80 microseconds COMPATIBLE INSTRUMENTS: General purpose survey meters, ratemeters, and scalers OPERATING VOLTAGE: 900 volts CONNECTOR: Series "C" (others available ) CONSTRUCTION: Aluminum housing with beige polyurethane enamel paint TEMPERATURE RANGE: -20oC to 50oC SIZE: 4.6 cm H X 6.9 cm W X 27.2 cm L WEIGHT: 0.5kg

Eberline Monitor 4 (pocket sized meter) FEATURES Compact Easy to Use Low Cost Carrying Case Included DETECTOR GM, uncompensated RANGES 0.5, 5, 50 mR/h and 500, 5k, 50k cpm OPTIONS Energy Compensated GM

Eberline HP-210 Series GM “pancake” Application/Type: Beta/Gamma surveys; GM, non energy compensated Dead Time: 50 usec nominal Mica Window Size/Thickness: 1.75 diameter (4.4 cm); 1.4 to 2.0 mg/cm2 Background Sensitivity: ~3,600 cpm/mR/h (137Cs) Beta/Gamma Efficiency: ~22% 137Cs, ~16% 60Co Beta Efficiency (4): ~ 32% 90Sr/90Y, ~ 15% 99Tc, ~ 6% 14C Alpha Efficiency (4): ~ 25% 241Am CONFIGURATIONS Model HP-210AL: Aluminum with 1:1 window to bkg ratio (0.7 kg) Model HP-210L: Lead shielded with 4:1 window to bkg ratio (1.9 kg) Model HP-210T: Tungsten shield with 4:1 window to bkg ratio (1.9 kg) Window Area: Active - 15 cm2 Open - 12 cm2 Window: 1.7  0.3 mg/cm2 mica Sensitivity: ~ 3,300 cpm/mR/hr (137Cs ) Beta Efficiency (4): ~ 22% 90Sr/Y; 19% 99Tc; 5% 14C; 32% 32P Alpha Efficiency (4): ~ 15% 239Pu Ludlum 44-40

Eberline HP-190A End Window GM Application: Alpha/Beta/Gamma surveys Detector Type: GM, non energy compensated, end window Operating Voltage: 900 V +/- 50 V Dead Time: 200 uSec nominal Mica Window Size: 1.1 diameter (2.8 cm) Mica Window Thickness: 1.4 to 2.0 mg/cm2 Gamma Sensitivity: ~ 2,500 cpm/mR/h (137Cs) Beta Efficiency (4): ~ 35% 90Sr/90Y, ~ 25% 99Tc, ~ 10% 14C Alpha Efficiency (4): ~ 6% 241Am Operating Temp: -30o to +60oC Housing: ABS plastic Connector: BNC Size: 3.9 x 12.4 cm Weight: 156 g

Eberline HP-271 Energy Compensated GM Application: Beta/Gamma exposure surveys Detector Type: Energy compensated GM Detector Range: 3 R/hr (with dead time correction) Energy Range: 30 keV to 6 MeV Operating Voltage: 900 V +/- 50V Dead Time: 100 uSec nominal Wall Material: Stainless steel Wall Thickness: 30 mg/cm2 (tube only) Gamma Sensitivity: ~1,200 cpm/mR/h (137Cs) Operating Temp: -40o to +63o C Housing: ABS plastic with sliding beta shield Connector: BNC Size: 3.5 x 15.2 cm Weight: 142 g

Ludlum Model 2401P “pocket meter” DETECTOR: Built-In Pancake GM SENSITIVITY: ~ 3,300 cpm/mR/hr (137Cs gamma) ENERGY RESPONSE: Energy dependent METER DIAL: 0 - 0.15 mR/hr; 0 - 500 cpm; BAT OK MULTIPLIERS: X1, X10, X100 LINEARITY: Reading within 10% of true value AUDIO: Built in speaker (quiet position on main switch to silence audio) CALIBRATION CONTROLS: Accessible from front of instrument RESPONSE: Typically 5 seconds from 10% to 90% of final reading POWER: 1 ea. 9 volt BATTERY LIFE: Typically 250 hours with alkaline batteries (battery condition can be checked on meter ) CONSTRUCTION: Aluminum housing with beige polyurethane enamel paint, and a recessed subsurface printed membrane front panel TEMPERATURE RANGE: -20 C to 50 C SIZE: 4.6 cm H X 8.4 cm W X 13.5 cm L WEIGHT: 0.4 kg including batteries

Ludlum Model 3-97EP Explosion Proof NaI(Tl) Gamma Scintillator & Energy-Compensated GM INDICATED USE: Gamma Survey DETECTORS: 2.5 cm X 2.5 cm NaI(Tl) scintillator SENSITIVITY: Typically 175 cpm/microR/hr (Cs-137 gamma) ENERGY RESPONSE: Energy dependent - Energy compensated GM ENERGY RESPONSE: Within 15% of true value from 60 keV - 3 MeV WORKING ENVIRONMENT: Explosion proof housing for extreme environments METER DIAL: 0 - 100 mR/hr, BAT TEST MULTIPLIERS: X0.1, X1, X10, X100, X1k LINEARITY: Reading within 10% of true value with detector connected CALIBRATION CONTROLS: Located in meter housing RESPONSE: 4 seconds from 10% to 90% of final reading RESET: Push-button to zero meter POWER: 2 each "C" cell batteries BATTERY LIFE: Typically 450 hours with alkaline batteries CONSTRUCTION: explosion proof housing TEMPERATURE RANGE: -20o C to 50o C SIZE/WEIGHT: 16.5cm H X 20.3cm W X 17.8cm L; 6.4 kg including batteries

Proportional Counters

Eberline E600 Survey Meter + NRD Detector GENERAL DESCRIPTION The model E600/NRD Combines E-600 Survey Meter with NRD neutron REM detector. The NRD is a 23 cm-diameter, cadmium-loaded polyethylene sphere with a BF3 tube in the center. Energy response closely follows the theoretical dose from neutrons over the energy range from 0.025 eV thermal to about 10 MeV. The BF3 tube allows excellent gamma rejection. FEATURES Measures Thermal Through Fast Neutrons Gamma Rejection Up To 500 R/h Direction Independent Measurements Background Subtraction Data Logging COMBINED DETECTOR/METER Size/Weight: 41.6 cm x 22.9 cm x 22.9 cm; 8.16 Kg Operating Temperature: -20oC to +50oC Operating Humidity: Up to 95% non-condensing

Eberline E600 Survey Meter + NRD Detector DETECTOR Detector: BF3 Tube in 23 cm cadmium loaded polyethylene sphere Plateau: Approximately 200 V with a slope of 5% per 100 V Operating Voltage: Dependant on sensitivity of counter and cable length; typically 1,600 to 2,000 V. Directional Response: Within 10% Energy Range: Thermal to approximately 10 MeV Gamma Rejection: Up to 500 R/h. Rejection is dependant on voltage selected. Factory default is 10 mR/h. Sensitivity: Approximately 45 cpm/mrem/h (3,000 counts per mrem) SURVEY METER (E-600) Count Range: 1 to 1.3 million cpm Response Times: Slow, Medium, Fast. Each time setting is programmable from 0 to 255 seconds. Dead Time Correction: 0 to 255 sec Operating Modes: Ratemeter, Scaler, Integration, Peak Trap, Background Accumulation.

Eberline E600 Survey Meter Eberline E600 Survey Meter + NRD Detector Eberline E600 Survey Meter + SHP-400A (Data Logging RO-20)

Ludlum Model 15 (---) End Window GM Detector for Alpha Beta and Gamma BF3 Proportional Detector with Moderator for Neutron 4 Ranges - Total Counting Range from 0 - 500,000 cpm INDICATED USE: Fast and thermal neutron, alpha, beta-gamma survey DETECTORS: Controlled by selector switch NEUTRON: Model 42-9 BF3 proportional detector with 7.6 cm diameter cadmium lined moderator for fast neutrons (remove detector from moderator for thermal neutrons) ENERGY RESPONSE: Count response is not linear throughout energy spectrum (0.025 - 8 MeV) SENSITIVITY: Typically 60 cpm/mrem/hr (AmBe fast neutrons) GAMMA REJECTION: Less than 10 cpm through 10 R/hr ALPHA BETA-GAMMA: Model 44-7 thin end window GM detector WINDOW: 1.7 0.3 mg/cm2 mica WINDOW AREA: Active - 6.4 cm2 Open - 5.2 cm2 EFFICIENCY(2 geometry): Typically 5% - 14C; 20% - 90Sr/90Y; 15% - 239Pu SENSITIVITY: Typically 2100 cpm/mR/hr (137Cs gamma)

Ludlum Model 15 METER DIAL: 0 - 500 cpm, 0 - 2.5 kV, BAT TEST MULTIPLIERS: X1, X10, X100, X1000 LINEARITY: Reading within 10% of true value RESET: Push-button to zero meter AUDIO: Built in speaker with ON/OFF switch (greater than 60 dB at 0.6 m) CALIBRATION CONTROLS: Accessible from front of instrument (protective cover provided) RESPONSE: Toggle switch for FAST (4 seconds) or SLOW (22 seconds) from 10% to 90% of final reading POWER: 2 each "D" cell batteries (housed in sealed compartment that is externally accessible) BATTERY LIFE: Typically 600 hours with alkaline batteries (battery condition can be checked on meter) METER: 6.4cm arc, 1 mA analog type CONSTRUCTION: aluminum with beige polyurethane enamel paint TEMPERATURE RANGE: -20oC to 50oC SIZE: 31.8cm H X 8.9cm W X 21.6cm L WEIGHT: 3.7 kg including batteries

“air proportional alpha” Ludlum Model 43-44 “air proportional alpha” INDICATED USE: Alpha survey WORKING ENVIRONMENT: Splashproof shields and desiccant vented chamber for outdoor use WINDOW: 0.4 mg/cm2 aluminized mylar WINDOW AREA: Active - 76 cm2 Open - 50 cm2 EFFICIENCY(4 geometry): Typically 8% 239Pu COMPATIBLE INSTRUMENTS: Models 12, 16, 18, 2000,2200, 2221, 2241, 2350 OPERATING VOLTAGE: Altitude sensitive Sea level - 2050 volts 2000 feet - 2000 volts 5000 feet - 1925 volts 7000 feet - 1875 volts CONSTRUCTION: Anodized aluminum body with aluminum screen (65% open) TEMPERATURE RANGE: -20 C to 50 C SIZE: 10.2 cm H X 6.4 cm W X 22.9 cm L WEIGHT: 0.5kg

Ludlum Model 44-110 The Model 44-110 is a windowless 100 cm2 gas proportional detector for tritium detection INDICATED USE: Tritium surface survey WINDOW: Windowless WINDOW AREA: Active - 126 cm2 Open - 100 cm2 EFFICIENCY (4): Typically 25% - H3 BACKGROUND: Typically 400 cpm OPERATING VOLTAGE: Typically 1700 volts COUNTER THRESHOLD SETTING: Typically 4 mV RECOMMENDED COUNTING GAS: P-10 (10% methane, 90% argon) GAS PURGE TIME: Approximately 20 seconds CONNECTOR: Series "C" CONSTRUCTION: Anodized aluminum housing TEMPERATURE RANGE: -20o C to 50o C SIZE: 12.4cm H X 11.7cm W X 22.9cm L WEIGHT: 0.9kg

Where to Get More Information Cember, H., Introduction to Health Physics, 3rd Edition, McGraw-Hill, New York (2000) Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8th Edition, 1999 update), Wiley, New York (1999) International Atomic Energy Agency, The Safe Use of Radiation Sources, Training Course Series No. 6, IAEA, Vienna (1995)