Radiation Detection Instrumentation Fundamentals

Radiation Detection Instrumentation Fundamentals

Radiation Detection Instrumentation Fundamentals
Includes Basic operation principles of different types of radiation detectors; Physical processes underlying the principles of operation of these devices, and Comparing and selecting instrumentation best suited for different applications.

General Principles of Radiation Detection

Outline Gas-Filled Detectors Scintillation Detectors
Solid State Detectors Others

Gas-Filled Detectors - Components
Variable voltage source Gas-filled counting chamber Two coaxial electrodes well insulated from each other Electron-pairs produced by radiation in fill gas move under influence of electric field produce measurable current on electrodes, or transformed into pulse

Gas- Filled Detectors - one example
wall fill gas Output Anode (+) End window Or wall A Cathode (-) or R

Indirect Ionization Process
wall e - e - e - e - e - e - e - e - Incident gamma photon

Direct Ionization Process
wall beta (β-) e - e - e - e - e - e - e - e - Incident charged particle

Competing Processes - recombination
+ e - Output + e - R

Voltage versus Ions Collected
Recom- bination region Ionization region Number of Ion Pairs collected Saturation Voltage 100 % of initial ions are collected Voltage

Saturation Current The point at which 100% of ions begin to be collected All ion chambers operate at a voltage that produces a saturation current The region over which the saturation current is produced is called the ionization region It levels the voltage range because all charges are already collected and rate of formation is constant

Observed Output: Pulse Height
Ions collected Number of ionizations relate to specific ionization value of radiation Gas filled detectors operate in either current mode Output is an average value resulting from detection of many values pulse mode One pulse per particle

Pulse Height Variation
Alpha Particles Pulse Height Beta Particles Gamma Photons Detector Voltage

Ionization Region Recap
Pulse size depends on # ions produced in detector. No multiplication of ions due to secondary ionization (gas amplification is unity) Voltage produced (V) = Q/C Where Q is total charge collected C is capacitance of the ion chanber

Ionization Chambers, continued
Chamber’s construction determines is operating characteristics Physical size, geometry, and materials define its ability to maintain a charge Operates at a specific voltage When operating, the charge collected due to ionizing events is Q = CΔV

Ionization Chambers, continued
The number of ions (N) collected can be obtained once the charge is determined: N = Q / k Where k is a conversion factor (1.6 x 10-19C/e)

Other Aspects of Gas-Filled Detectors
Accuracy of measurement Detector Walls composed of air equivalent material or tissue equivalent Wall thickness must allow radiation to enter/ cause interactions alpha radiation requires thin wall (allowed to pass) gammas require thicker walls (interactions needed) Sensitivity Air or Fill gas Pressure see next graph

Current vs. Voltage for Fill Gases in a Cylindrical Ion Chamber
Air at high pressure 100 Helium at high pressure Relative Current (%) 10 Air at low pressure 1.0 Helium at low pressure 0.1 Applied Voltage (volts)

Correcting Ion Chambers for T, P
Ion chambers operate in pressurized mode which varies with ambient conditions Detector current (I) and exposure rate X are functions of gas temperature and pressure as well as physical size of detector.

Correcting Ion Chambers for T, P
Detector current (I) and exposure rate (X) related by: k, conversion factor ρ detector gas density V detector volume STP standard temp and pressure (273K, 760 torr (1 atm)

Operating Regions of Gas-Filled Detectors
Proportional Region Pulse Height Ionization Region Recombination Region Continuous Discharge Region Limited Proportional Region Geiger-Mueller Region    Voltage

Values of k, Conversion Factor
Calculated as (2.58 x 10- 4C/kg-R)(1 h / 3600 s)( 1 A s / C) Yields 7.17 x A-h/R-kg

Examples CanberraL The portable Ground Monitor System comprises a beta/gamma detector assembly consisting of five pancake GM tubes mounted in a plastic housing attached to a lightweight adjustable carrying handle. Output of the detector assembly is connected to a battery operated ratemeter carried by a strap round the user's neck. A headphone connected to the ratemeter provides an audible output of the detector assembly. LND - examples of types of detector tubes - end window, pancake, etc.

Proportional Counters
Operates at higher voltage than ionization chamber Initial electrons produced by ionization are accelerated with enough speed to cause additional ionizations cause additional free electrons produces more electrons than initial event Process is termed: gas amplification

Pulse-Height Versus Voltage
Ionization Region Proportional Region Recombination Region Pulse Height   Voltage

Distinguishing Alpha & Beta
Proportional counters can distinguish between different radiation types specifically alpha and beta-gamma Differential detection capability due to size of pulses produced by initial ionizing events requires voltage setting in range of 900 to 1,300 volts alpha pulses above discriminator beta/gamma pulses too small

Alpha & Beta-Gamma Plateau
Ionization Current Beta-Gamma Plateau Alpha Plateau The location of the plateau of a proportional counter depends on the type of particles being detected. If a source emits two types of particles with significantly different primary ionization, two separate plateaus will be obtained, with the plateau corresponding to the more ionizing particles appearing first. The above graph shows such a plateau for a proportional counter detecting alpha and beta particles. Detector Voltage

Gas Flow Proportional Counters
Common type of proportional counter Fixed radiation detection instrument used in counting rooms Windowed or windowless Both employ 2 geometry essentially all radiation emitted from the surface of the source enters active volume of detector Windowless used for alpha detection

Gas-Flow Proportional Counter

Gas-Flow Proportional Counter
Fill gas outlet Fill gas inlet anode (window- optional) Detector O-ring sample Sample planchet

Gas Flow Proportional, continued
Fill gas selected to enhance gas multiplication no appreciable electron attachment most common is P-10 (90% Argon and 10% methane)

Geiger Mueller Detectors
Operate at voltages above proportional detectors Each primary ionization produces a complete avalanche of ions throughout the detector volume called a Townsend Avalanche continues until maximum number of ion pairs are produced avalanche may be propagated by photoelectrons quenching is used to prevent process

Geiger Mueller Detectors, continued
No proportional relationship between energy of incident radiation and number of ionizations detected A level pulse height occurs throughout the entire voltage range

Advantages/Disadvantages of Gas-Filled Detectors
Ion Chamber: simple, accurate, wide range, sensitivity is function of chamber size, no dead time Proportional Counter: discriminate hi/lo LET, higher sensitivity than ion chamber GM Tube: cheap, little/no amplification, thin window for low energy; limited life

Points to Remember for Gas-filled Detectors
Know operating principles of your detector Contamination only? High range? Alpha / beta detection? Dose rate? Alpha/beta shield?

Points to Remember for Gas-filled Detectors
Power supply requirements Stable? Batteries ok? Temperature, pressure correction requirements Calibration Frequency Nuclides

Issues with Gas Filled Detectors: Dead Time
Minimum time at which detector recovers enough to start another avalanche (pulse) The dead time may be set by: limiting processes in the detector, or associated electronics “Dead time losses” can become severe in high counting rates corrections must be made to measurements Term is used loosely - beware!

Issues with Gas Filled Detectors: Recovery Time
Time interval between dead time and full recovery Recovery Time = Resolving time- dead time

Issues with Gas Filled Detectors: Resolving Time
Minimum time interval that must elapse after detection of an ionizing particle before a second particle can be detected.

Correcting for Dead Time
For some systems (GMs) dead time may be large. A correction to the observed count rate can be calculated as: Where T is the resolving time R0 is the observed count rate and RC is the corrected count rate

Relationship among dead time, recovery time, and resolving time
100 200 300 400 500 Pulse Height Dead Time Recovery time Resolving time Time, microseconds

Geiger Tube as Exposure Meter
“Exposure” is the parameter measuring the ionization of air. Geiger tube measures ionization pulses per second - a “count rate”. The number of ionizations in the Geiger tube is a constant for a particular energy but is energy dependent.

COMPENSATED GEIGER DOSE RATE METERS
GMs have a high sensitivity but are very dependent upon the energy of photon radiations. The next graph illustrates the relative response (R) of a typical GM vs photon energy (E). At about 60 keV the response reaches a maximum which may be thirty times higher than the detector’s response at other radiation energies.

Energy Response of GM – Uncompensated
20 1.2 1.0 0.8 10 100 1000 E, keV

COMPENSATED GEIGER DOSE RATE METERS
Detector’s poor energy response may be corrected by adding a compensation sheath Thin layers of metal are constructed around the GM to attenuate the lower photon energies, where the fluence per unit dose rate is high, to a higher degree than the higher energies. The modified or compensated response, shown as a dashed line on the next graph, may be independent of energy within ± 20% over the range 50 keV to 1.25 MeV. Compensation sheaths also influence an instrument’s directional (polar) response and prevent beta and very low energy photon radiations from reaching the Geiger tube.

Energy Response of GM – Uncompensated and Compensated
10 100 1000 E, keV R 20 1.2 1.0 0.8

Example Polar Response

Example of Compensated GM
RadEye component

RadEye Pocket meter Number of optional components low power components
automatic self checks essential functions accessed while wearing protective gloves. Alarm-LED can be seen while the instrument is worn in a belt-holster. Instrument also equipped with a built in vibrator and an earphone-output for silent alarming or use in very noisy environment. Number of optional components

RadEye Options RadEye PRD - High Sensitivity Personal Radiation Detector The RadEye PRD is times more sensitive than typical electronic dosimeter. The RadEye PRD uses Natural Background Rejection (NBR) technology. It is the only instrument of its type and size to achieve this. Probably a plastic scintillator – more about this later

RadEye Options RadEye G - Wide Range Gamma Survey Meter for Personal Radiation Protection linearity over 6 decades of radiation intensity: from background level to 5 R/h overrange indication up to 1000 R/h. RadEye G incorporates a large energy compensated GM-tube for dose rate measurement for gamma and x-ray. NBR = Natural Background Rejection The NBR measurement technology has been developed by Thermo Electron for the supression of alarms caused by variations of the natural background.

SCINTILLATION DETECTORS
CANBERRA; Scintillation Detectors A gamma ray interacting with a scintillator produces a pulse of light, which is converted to an electric pulse by a photomultiplier tube. The photomultiplier consists of a photocathode, a focusing electrode and 10 or more dynodes that multiply the number of electrons striking them several times each. The anode and dynodes are biased by a chain of resistors typically located in a plug-on tube base assembly. Complete assemblies including scintillator and photomultiplier tube are commercially availabl. The properties of scintillation material required for good detectors are transparency, availability in large size, and large light output proportional to gamma ray energy. Relatively few materials have good properties for detectors. Thallium activated NaI and CsI crystals are commonly used, as well as a wide variety of plastics. NaI is the dominant material for gamma detection because it provides good gamma ray resolution and is economical. However, plastics have much faster pulse light decay and find use in timing applications, even though they often offer little or no energy resolution.

Scintillators Emit light when irradiated Can be promptly (<10-8s)
fluorescence delayed (>10-8s) phosphorescence Can be liquid solid gas organic inorganic

Basis of Scintillation - Energy Structure in an Atom
Excited state Ground state, last filled (outer) orbital

Basis of Scintillation - Energy Structure in a Molecule
Excited state A1 EA1 Ground state EB1 B1 EB0 Bo EA0 Ao Interatomic distance

Scintillator Properties
A large number of different scintillation crystals exist for a variety of applications. Some important characteristics of scintillators are: Density and atomic number (Z) Light output (wavelength + intensity) Decay time (duration of the scintillation light pulse) Mechanical and optical properties Cost

Liquid scintillation counting
Standard laboratory method for measuring radiation from beta-emitting nuclides. Samples are dissolved or suspended in a "cocktail" containing an aromatic solvent (historically benzene or toluene, and small amounts of other additives known as fluors. Beta particles transfer energy to the solvent molecules, which in turn transfer their energy to the fluors; Excited fluor molecules dissipate the energy by emitting light. Each beta emission (ideally) results in a pulse of light. Scintillation cocktails may contain additives to shift the wavelength of the emitted light to make it more easily detected. Samples are placed in small transparent or translucent (often glass) vials that are loaded into an instrument known as a liquid scintillation counter.

Organic Scintillators
Examples Differences Energy CH3 Excited state A1 EA1 Toluene Ground state EB1 The materials that are efficient organic scintillators belong to the class of aromatic compounds. They consist of planar molecules made of of benzene rings. Two examples are toluene and anthracene, having the structure shown above. Organic scintillators are mixtures of compounds that consist of a solvent and solute(s). Examples of solvents (the substance with the highest concentration) include benzene, toluene, and p-Xylene. There are many others. Examples of solutes include p-Terphenyl, PPO (2,5-diphenalyoxazole), and PDB ((2-Pheny l, 5-(4-biphenyl)-1,2,4-oxadiazole). There are primary and secondary solutes and solvents. Light production in organic scintillators is the result of molecular transitions. The potential energy of a molecule (which comes from electronic, vibrational and translational energies) changes with interatomic distance. The ground state is at point A0. Ionizing radiation passing through the scintillator can raise the molecule to an excited state (A1). The molecule wants to return to the ground state, and loses energy through vibrations (heat) to move to point B1. This is still not at the lowest energy state, and so the molecule will emit energy (a photon) to move it to point B0. This transition is rapid (10-8 s), and results in a measurable photon of energy different than the incident one. B1 EB0 Bo EA0 Ao Anthracene Interatomic distance

Inorganic (Crystal) Scintillators
Most are crystals of alkali metals (iodides) NaI(Tl) CsI(Tl) CaI(Na) LiI(Eu) CaF2(Eu) Impurity in trace amounts “activator” causes luminescence e.g., (Eu) is 10-3 of crystal The high Z of iodine in NaI gives good efficiency for gamma ray detection. A small amount of Tl is added in order to activate the crystal, so that the designation is usually NaI(Tl) for the crystal. The best resolution achievable ranges from 7.5%-8.5% for the 662 keV gamma ray from 137Cs for 3 in. diameter by 3 in. long crystal, and is slightly worse for smaller and larger sizes. Figure 1.6 shows, respectively, the absorption efficiencies of various thicknesses of NaI crystals, and the transmission coefficient through the most commonly used entrance windows.

Organic vs. Inorganic Scintillators
Inorganic scintillators have greater: light output longer delayed light emission higher atomic numbers than organic scintillators Inorganic scintillators also linear energy response (light output is  energy absorbed)

Solid Scintillators Solids have Lattice structure (molecular level)
Quantized energy levels Valence bands Conduction bands

Crystal Lattice e- Ge As+ Shared electron pair

Creation of Quantized “Bands”
Conduction Band Valence Band + - Eo Eo + Eg EF

Introduction of Impurities
Conduction Band Donor impurity levels ~0.01 eV ~1 eV ~ 0.01eV Acceptor impurity levels Valence Band

Detecting Scintillator Output:- PhotoCathode & Photomultiplier Tubes
Radiation interaction in scintillator produces light (may be in visible range) Quantification of output requires light amplification and detection device(s) This is accomplished with the: Photocathode Photomultiplier tube Both components are placed together as one unit optically coupled to the scintillator

Cutaway diagram of solid-fluor scintillation detector

Cutaway diagram of solid-fluor scintillation detector
Photocathode Scintillation event Photomultiplier tube Gamma ray Dynodes Photoelectrons Fluor crystal NaI (Tl) Reflector housing

Major components of PM Tube
Photocathode material Dynodes electrodes which eject additional electrons after being struck by an electron Multiple dynodes result in 106 or more signal enhancement Collector accumulates all electrons produced from final dynode Resistor collected current passed through resistor to generate voltage pulse

Generalized Detection System using a Scintillator
(Crystal & Photomultiplier) Scaler Detector Amplifier Pre- Amp Discriminator Multi- Channel Analyzer High Voltage Oscilloscope

Liquid Scintillation Systems
Used to detect low energy (ie., low range) radiations beta alpha Sample is immersed in scintillant Provides 4  geometry Quenching can limit output chemical color quenching optical quenching

Chemical Quenching Dissipation of energy prior to transfer from organic solvent to scintillator Reduces total light output Common chemical quenching agents Dissolved oxygen is most common Acids Excessive concentration of one component (e.g., primary fluor) Too little scintillation media halogenated hydrocarbons

Color Quenching Absorption of light photons after they are emitted from the scintillator Reduces total light output Common color quenching agents: light absorbing contaminants blood urine tissues samples

Optical Quenching Absorption of light photons after they are emitted from the scintillator liquid and before they reach the PMT Reduces total light output Common optical quenching agents: fingerprints condensation dirt on the LS vials

Circuitry in LSC systems
Shielded counting well Two (or more) PMT’s optically coupled to sample well Coincidence circuitry to compare PMT pulses Pulse Summation Circuit adds signals from PMTs gates single pulse to amplifier summation circuit doubles height of signal

Coincidence Circuitry
Used to reduce noise Limit thermionic emissions spontaneous emissions from within the PMT Directly opposing PMT tubes connected to coincidence circuit gated outputs from both tubes only simultaneous signal from both will be accepted only one signal is not accepted simultaneous signals are summed Applied to Liquid Scintillation Systems

Coincidence & Anticoincidence Circuitry
Sometimes desirable to discard pulses due to some radiations & accept only those from a single type of particle. Examples: detection of pair-production events (accept only simultaneous detection of 180° apart photons) detection of internal conversion electrons radioisotopes with IC electrons emit gammas & X-rays. A single detector counts IC and compton electrons. Use X-rays that are emitted simultaneously with IC & block Compton events

A simple coincidence circuit
Amplification Timing Multi-channel Analyzer Detector Source Coincidence Unit Gate Detector Scaler Amplification Timing After Tsoulfanidis, 1995

Basic LSC System Beckman LS 6500 Liquid Scintillation Counting System.

Single & summed pulse spectra
With pulse summation Counts/ Min Without pulse summation Pulse Height

Correcting for Quench Quench correction Techniques
any quenching that occurs in sample results in shift of pulse height spectrum toward lower values Techniques purge sample with N2, CO2, or Ar (removes O2 chemical quench bleach or decolorize sample (reduces color quench) handle LSC vials by top/bottom & wiping vials clean prior to counting (reduces optical quenching)

Alternative Methods Channel ratio method Disadvantage
two energy windows established known amount of radioactivity is added to varying concentrations of quenching agent ratio of net counts in upper channel over lower channel vs quench correction is plotted Disadvantage low count rates require longer counting times multiple calibration curves may be required for range quenching agents

Alternative Methods Internal standard method Most accurate method
older technique sample is counted known quantity of radioisotope is added sample recounted Efficiency = (cpm(std+sample) – cpm(sample))/dpm(std) Most accurate method requires ability to add same amount of radionuclide each time more costly & time consuming

Alternative Methods External standard method Disadvantages
relies on gamma source (226Ra or 133Ba) adjacent to sample two sets of calibration curves are derived sample standard count is plotted versus amount of quench agent Net External Counts - [External & Sample Std cpm] - [Sample Standard cpm] Disadvantages least accurate of available methods samples must be counted twice sample uniformly dispersed in counting vials

Pulse Height Discrimination
Light produced per disintegration of a radioactive atom: is related to particle type (alpha, beta, gamma), and energy (keV - MeV). Pulse height increases with energy Example (follows) beta emitters of varying energies: 3H, max 18.6 keV 14C, max 156 keV 32P, max 1.71 MeV

Pulse Height Discrimination for three common beta emitters
Count Rate Pulse Height

Background & Efficiency Checks on LSC
Essential - LSC’s are essentially proportional counters; change in potential impacts gain Efficiency depends on several variables: temperature quenching ( determine counting efficiency for every sample) Background & efficiency checks needed with every run contamination efficiency changes

Field Applications for Liquid and Solid Scintillation Counters
Solid Scintillators in-situ measurement of low to high energy gammas laboratory systems spectroscopy SCA or MCA mode Liquid Scintillators wipe tests contaminants in solids (concrete) contaminants in aqueous/organic liquids

Selecting Scintillators - Density and Atomic number
Efficient detection of gamma-rays requires material with a high density and high Z Inorganic scintillation crystals meet the requirements of stopping power and optical transparency, Densities range from roughly 3 to 9 g/cm3 Very suitable to absorb gamma rays. Materials with high Z-values are used for spectroscopy at high energies (>1 MeV).

Linear Attenuation of NaI

Relative Importance of Three Major Interaction Mechanisms
The lines show the values of Z and hv for which the two neighboring effects are just equal

Light output of Scintillators
Scintillation material with a high light output is preferred for all spectroscopic applications. Emission wavelength should be matched to the sensitivity of the light detection device that is used (PMT of photodiode).

Decay time Scintillation light pulses (flashes) are usually characterized by a fast increase of the intensity in time (pulse rise time) followed by an exponential decrease. Decay time of a scintillator is defined by the time after which the intensity of the light pulse has returned to 1/e of its maximum value. Most scintillators are characterized by more than one decay time and usually, the effective average decay time is given The decay time is of importance for fast counting and/or timing applications

Mechanical and Optical Properties
NaI(Tl) is one of the most important scintillants. Hygroscopic Can only be used in hermetically sealed metal containers Some scintillation crystals may easily crack or cleave under mechanical pressure CsI is “plastic” and will deform. Important aspects of commonly used scintillation materials are listed on the next 2 slides. The list is not exhaustive, and each scintillation crystal has its own specific application. For high resolution spectroscopy, NaI(Tl), or CsI(Na) (high light output) are normally used. For high energy physics applications, the use of bismuth germanate Bi4Ge3O12 (BGO) crystals (high density and Z) improves the lateral confinement of the shower. For the detection of beta-particles, CaF2(Eu) can be used instead of plastic scintillators (higher density).

Commonly Used Scintillators
Material Density [g/cm3] Emission Max [nm] Decay Constant (1) Refractive Index (2) Conversion Efficiency (3) Hygro-scopic NaI(Tl) 3.67 415 0.23 ms 1.85 100 yes CsI(Tl) 4.51 550 0.6/3.4 ms 1.79 45 no CsI(Na) 420 0.63 ms 1.84 85 slightly CsI undoped 315 16 ns 1.95 4 - 6 CaF2 (Eu) 3.18 435 0.84 ms 1.47 50 6LiI (Eu) 4.08 470 1.4 ms 1.96 35 6Li - glass 2.6 60 ns 1.56 CsF 4.64 390 3 - 5 ns 1.48 5 - 7 (1) Effective average decay time For g-rays. (2) At the wavelength of the emission maximum. (3) Relative scintillation signal at room temperature for g-rays when coupled to a photomultiplier tube with a Bi-Alkalai photocathode.

Conversion Efficiency (3)
Commonly Used Scintillators Material Density [g/cm3] Emission Maximum [nm] Decay Constant (1) Refractive Index (2) Conversion Efficiency (3) Hygroscopic BaF2 4.88 315 220 0.63 ms 0.8 ns 1.50 1.54 16 5 no YAP (Ce) 5.55 350 27 ns 1.94 GSO (Ce) 6.71 440 ns 1.85 BGO 7.13 480 0.3 ms 2.15 CdWO4 7.90 470 / 540 20 / 5 ms 2.3 Plastics 1.03 1 - 3 ms 1.58 (1) Effective agerage decay time For g-rays. (2) At the wavelength of the emission maximum. (3) Relative scintillation signal at room temperature for g-rays when coupled to a photomultiplier tube with a Bi-Alkalai photocathode.

Afterglow Defined as the fraction of scintillation light still present for a certain time after the X-ray excitation stops. Originates from the presence of millisecond to even hour long decay time components. Can be as high as a few % after 3 ms in most halide scintillation crystals . CsI(Tl) long duration afterglow can be a problem for many applications. Afterglow in halides is believed to be intrinsic and correlated to certain lattice defects. BGO and Cadmium Tungstate (CdWO4) crystals are examples of low afterglow scintillation materials

Scintillators - Neutron Detection
Neutrons do not produce ionization directly in scintillation crystals Can be detected through their interaction with the nuclei of a suitable element. 6LiI(Eu) crystal -neutrons interact with 6Li nuclei to produce an alpha particle and 3H which both produce scintillation light that can be detected. Enriched 6Li containing glasses doped with Ce as activator can also be used.

Neutron Detection

Neutron Detection Conventional neutron meters surround a thermal neutron detector with a large and heavy (20 lb) polyethylene neutron moderator. Other meters utilizes multiple windows formed of a fast neutron scintillator (ZnS in an epoxy matrix), with both a thermal neutron detector and a photomultiplier tube.

Radiation Damage in Scintillators
Radiation damage results inchange in scintillation characteristics caused by prolonged exposure to intense radiation. Manifests as decrease of optical transmission of a crystal decreased pulse height deterioration of the energy resolution Radiation damage other than activation may be partially reversible; i.e. the absorption bands disappear slowly in time.

Radiation Damage in Scintillators
Doped alkali halide scintillators such as NaI(Tl) and CsI(Tl) are rather susceptible to radiation damage. All known scintillation materials show more or less damage when exposed to large radiation doses. Effects usually observed in thick (> 5 cm) crystals. A material is usually called radiation hard if no measurable effects occur at a dose of 10,000 Gray. Examples of radiation hard materials are CdWO4 and GSO.

Emission Spectra of Scintillation Crystals
Each scintillation material has characteristic emission spectrum. Spectrum shape is sometimes dependent on the type of excitation (photons / particles). Emission spectrum is important when choosing the optimum readout device (PMT /photodiode) and the required window material. Emission spectrum of some common scintillation materials shown in next two slides.

Emission Spectra of Scintillators

Temperature Influence on the Scintillation Response
Light output (photons per MeV gamma) of most scintillators is a function of temperature. Radiative transitions, responsible for the production of scintillation light compete with non-radiative transitions (no light production). In most light output is quenched (decreased) at higher temperatures. An exception is the fast component of BaF2 where intensity is essentially temperature independent.

Temperature Influence on the Scintillation Response

Choosing a Scintillator
Following table lists characteristics such as high density, fast decay etc. Choice of a certain scintillation crystal in a radiation detector depends strongly on the application. Questions such as : What is the energy of the radiation to measure ? What is the expected count rate ? What are the experimental conditions (temperature, shock)?

Material Important Properties Major Applications NaI(Tl) Very high light output, good energy resolution General scintillation counting, health physics, environmental monitoring, high temperature use CsI(Tl) Noon-hygroscopic, rugged, long wavelength emission Particle and high energy physics, general radiation detection, photodiode readout, phoswiches CsI(Na) High light output, rugged Geophysical, general radiation detection CsI undoped Fast, non-hygroscopic, radiation hard, low light output Physics (calorimetry) CaF2(Eu) Low Z, high light outut b detection, a, b phoswiches CdWO4 Very high density, low afterglow, radiation hard DC measurement of X-rays (high intensity), readout with photodiodes, Computerized Tomography (CT) Plastics Fast, low density and Z, high light output Particle detection, beta detection

Material Important Properties Major Applications 6LiI(Eu) High neutron cross-section, high light output Thermal neutron detection and spectroscopy 6Li - glass High neutron cross-section, non-hygroscopic Thermal neutron detection BaF2 Ultra-fast sub-ns UV emission Positron life time studies, physics research, fast timing YAP(Ce) High light output, low Z, fast MHz X-ray spectroscopy, synchrotron physics GSO(Ce) High density and Z, fast, radiation hard Physics research BGO High density and Z Particle physics, geophysical research, PET, anti-Compton spectrometers CdWO4 Very high density, low afterglow, radiation hard DC measurement of X-rays (high intensity), readout with photodiodes, Computerized Tomography (CT) Plastics Fast, low density and Z, high light output Particle detection, beta detection

PRACTICAL SCINTILLATION COUNTERS
Highly sensitive surface contamination probes incorporate a range phosphors Examples include: zinc sulphide (ZnS(Ag)) powder coatings (5–10 mg·cm–2) on glass or plastic substrates or coated directly onto the photomultiplier window for detecting alpha and other heavy particles; cesium iodide (CsI(Tl)) that is thinly machined (0.25 mm) and that may be bent into various shapes; and plastic phosphors in thin sheets or powders fixed to a glass base for beta detection.

PRACTICAL SCINTILLATION COUNTERS
Probes (A and B previous slide) and their associated ratemeters (C) tend not to be robust. Photomultipliers are sensitive to shock damage and are affected by localized magnetic fields. Minor damage to the thin foil through which radiation enters the detector allows ambient light to enter and swamp the photomultiplier. Cables connecting ratemeters and probes are also a common problem. Very low energy beta emitters (for example 3H) can be dissolved in liquid phosphors in order to be detected.

43-93 Alpha/Beta Scintillator
The Model is a 100 cm² dual phosphor alpha/beta scintillator that is designed to be used for simultaneously counting alpha and beta contamination

INDICATED USE: Alpha beta survey SCINTILLATOR: ZnS(Ag) adhered to 0.010" thick plastic scintillation material WINDOW: 1.2 mg/cm² recommended for outdoor use WINDOW AREA: Active cm² Open - 89 cm² EFFICIENCY (4pi geometry): Typically 15% - Tc-99; 20% - Pu-239; 20% - S-90/Y-90 NON-UNIFORMITY: Less than 10% BACKGROUND: Alpha - 3 cpm or less Beta - Typically 300 cpm or less (10 µR/hr field ) CROSS TALK: Alpha to beta - less than 10% Beta to alpha - less than 1%

COMPATIBLE INSTRUMENTS: Models 2224, 2360 TUBE: 1.125"(2.9cm) diameter magnetically shielded photomultiplier OPERATING VOLTAGE: Typically volts DYNODE STRING RESISTANCE: 100 megohm CONNECTOR: Series “C” (others available ) CONSTRUCTION: Aluminum housing with beige polyurethane enamel paint TEMPERATURE RANGE: 5°F(-15°C) to 122°F(50°C) May be certified to operate from -40°F(-40°C) to 150°F(65°C) SIZE: 3.2"(8.1 cm)H X 3.5"(8.9 cm)W X 12.2"(31 cm)L WEIGHT: 1 lb (0.5kg)

44-2 Gamma Scintillator The Model 44-2 is a 1" X 1" NaI(Tl) Gamma Scintillator that can be used with several different instruments including survey meters, scalers, ratemeters, and alarm ratemeters

44-2 Gamma Scintillator INDICATED USE: High energy gamma detection
SCINTILLATOR: 1" (2.5 cm) diameter X 1" (2.5 cm) thick sodium iodide (NaI)Tl scintillator SENSITIVITY: Typically 175 cpm/microR/hr (Cs-137) COMPATIBLE INSTRUMENTS: General purpose survey meters, ratemeters, and scalers TUBE: 1.5:(3.8cm) diameter magnetically shielded photomultiplier OPERATING VOLTAGE: Typically volts DYNODE STRING RESISTANCE: 100 megohm CONNECTOR: Series "C" (others available ) CONSTRUCTION: Aluminum housing with beige polyurethane enamel paint TEMPERATURE RANGE: -4° F(-20° C) to 122° F(50° C) May be certified for operation from -40° F(-40° C) to 150° F(65° C) SIZE: 2" (5.1 cm) diameter X 7.3" (18.5 cm)L WEIGHT: 1 lb (0.5kg)

Scintillation Detectors
Best: Measure low gamma dose rates Also: Measure beta dose rates (with corrections) However: Somewhat fragile and expensive CANNOT: Not intended for detecting contamination, only radiation fields

Semi-Conductor Detectors

Idealized Gamma-Ray Spectrum in NaI
theoretical Counts per Energy Interval Actual Energy Eo

Components of Spectrum
Compton edge Backscatter Peak Photopeak Counts per Energy Interval X-ray Peak Annihilation Peak Energy Eo

NaI(Tl) vs. HPGE

Semiconductor Detectors
Solids have lattice structure (molecular level) quantized energy levels valence bands conduction bands Semiconductors have lattice structure similar to inorganic scintillators composed of Group IVB elements ability to easily share electrons with adjoining atoms Solids have allowed and forbidden bands of energy values which the most loosely bound (valence) electrons can possess. The origin of the band of energy levels is a consequence of the splitting of discrete atomic energy levels when multiple atoms are brought together into a regular array. When the number of atoms is very large, a continuous energy band results, and you have the formation of the conduction and valence bands for the solid. The valence band can be considered the outermost electron level around the atom which is still held to the atom. The conduction band loosely encompasses all the atoms in the solid. If an electron is promoted to the conduction band, then it can freely migrate across the solid. An electron promoted from the valence band leaves behind a positively charged “hole”. This hole can similarly migrate across all the atoms in the solid. The gap between the valence and conduction band is called the “forbidden gap”. Electrons will have a continua of energy values in the valence and conduction band. No states with energies that fall within the forbidden band will exist. If the valence band is full, and the forbidden gap is large (> 5 eV), then the material will be an insulator.

Crystal Lattice e- Ge As+ Shared electron pair
Addition of a small quantity of pentavalent As to Ge crystal lattice produces very loosely bound “extra” electrons that have a high probability of being thermally excited into the conduction band at room temperatures. Arsenic is called a donor impurity because it has five valence electrons whereas germanium only has four. There is one electron left over after the As “sits” in the lattice and all the covalent bonds have been formed. The loop respresents the orbit of the extra electron. Because it is not tightly bound to the As ion it can be excited into the conduction band. The conductivity of the doped Ge is therefore much higher than the pure material. Arsenic is the “dopant” in this lattice and donates an extra electron. As a result, this semiconductor is called an n-type (for negative charge). Shared electron pair

Basic Nature of Semiconductors
Schematic view of lattice of Group IVB element Si Dots represent electron pair bonds between the Si atoms Si

Basic Nature, cont’d Schematic diagram of energy levels of crystalline Si. Pure Si is a poor conductor of electricity Conduction Band 1.08 eV Energy Forbidden Gap Valence Band

Basic Nature, cont’d Schematic view of lattice of Group IV element Si, doped with P (Group VB) as an impurity – note extra electron Si P

Basic Nature, cont’d Schematic diagram of disturbed energy levels of crystalline Si. Si with Group V impurities like P is said to be an n-type silicon because of the negative charge carriers (the electrons) Conduction Band 0.05 eV Donor level Energy Valence Band

Basic Nature, cont’d Schematic view of lattice of Group IV element Si, doped with B (Group IIIB) as an impurity – note hole in electron orbital Si Si Si B Si Si

Basic Nature, cont’d Schematic diagram of disturbed energy levels of crystalline Si with B impurity. Si with Group III impurities is said to be a p-type silicon because of the positive charge carriers (the holes) Conduction Band Energy Acceptor level 0.08 eV Valence Band

Occupation of energy states for n and p-type semiconductors
As donor impurity levels Conduction Band 0.013 eV 0.67 eV 0.011eV The energy level diagram for a p-type Ge semiconductor with Ga acceptor atoms added, and for an n-type semiconductor with As donor atoms added When the crystal is doped with an electron donating material, the electrons can enter the conduction band, greatly increasing the conductivity of the material. When the crystal is doped with a hole donating material (such as Ga), the dope crystal contains positively charged holes which can accept electrons. Holes in the valence band move like positive charges as electrons from neighboring atoms fill them. This also results in enhanced conductivity of the crystal.. Ga acceptor impurity levels Valence Band After Turner

Operating Principles of Semiconductor detectors
Si semiconductor is a layer of p-type Si in contact with n-type Si. What happens when this junction is created? Electrons from n-type migrate across junction to fill holes in p-type Creates an area around the p-n junction with no excess of holes or electrons Called a “depletion region” Apply (+) voltage to n-type and (-) to p-type: Depletion region made thicker Called a “reverse bias”

Energy-level diagram for n-p junction
Conduction Band n-type Semiconductors are useful as radiation measuring devices because of special properties that occur at a junction where n- and p-type semiconductors are brought together. If they are placed in good contact they form a single system. This system has its own Fermi energy. Because it is just below the conduction band in the n-region, and just above the valence band in the p-region, the bands must be deformed over the region of the junction. When the two materials are initially placed in contact, electrons flow from the donor levels to the acceptor side. As a result, negative charge accumulates on the p side and positive charges are left on the n side. There is a net separation of charges (indicated by + and - in the figure). This region is called the depletion region, because, initially, there are no mobile charges. As a result of depletion in this region, the detector behaves much like a parallel plate ionization chamber. When ionizing radiation creates ion pairs in this region of the crystal, they will migrate according to sign, and give rise to an electrical signal. A bias voltage can also be placed on the system to prevent recombination and to limit noise. Junction region Valence Band p-type After Turner

Detector specifics Depletion region acts as sensitive volume of the detector Passage of ionizing radiation through the region Creates holes in valence band Electrons in conduction band Electrons migrate to positive charge on n side Holes migrate to negative voltage on p side Creates electrical output Requires about 3.6 eV to create an electron hole pair in Si

Detector Specifics, cont’d
Reverse bias n-p junction is good detector Depletion region Has high resistivity Can be varied by changing bias voltage Ions produced can be quickly collected Number of ion pairs collected is proportional to energy deposited in detector Junction can be used as a spectrometer Types of detectors: HPGe GeLi (lithium drifted detectors) Surface barrier detectors Electronic dosimeters

SOLID STATE DETECTORS RECAP
Solid state detectors utilize semiconductor materials. Intrinsic semiconductors are of very high purity and extrinsic semiconductors are formed by adding trace quantities (impurities) such as phosphorus (P) and lithium (Li) to materials such as germanium (Ge) and silicon (Si). There are two groups of detectors: junction detectors and bulk conductivity detectors.

SOLID STATE DETECTORS Junction detectors are of either
diffused junction or surface barrier type: an impurity is either diffused into, or spontaneously oxidized onto, a prepared surface of intrinsic material to change a layer of ‘p-type’ semiconductor from or to ‘n-type’. When a voltage (reverse bias) is applied to the surface barrier detector it behaves like a solid ionization chamber. Bulk conductivity detectors are formed from intrinsic semiconductors of very high bulk resistivity (for example CdS and CdSe). They also operate like ionization counters but with a higher density than gases and a ten-fold greater ionization per unit absorbed dose. Further amplification by the detector creates outputs of about one microampere at 10 mSv·h–1

Solid State Counters A - very thin metal (gold) electrode.
P - thin layer of p-type semiconductor. D - depletion region, 3–10 mm thick formed by the voltage, is free of charge in the absence of ionizing radiations. N - n-type semiconductor. B - thin metal electrode which provides a positive potential at the n-type semiconductor.

PRACTICAL SOLID STATE DETECTORS
The main applications for semiconductor detectors are in the laboratory for the spectrometry of both heavy charged (alpha) particle and gamma radiations. However, energy compensated PIN diodes and special photodiodes are used as pocket electronic (active) dosimeters. PIN diode: Acronym for positive-intrinsic-negative diode. A photodiode with a large, neutrally doped intrinsic region sandwiched between p-doped and n-doped semiconducting regions. A PIN diode exhibits an increase in its electrical conductivity as a function of the intensity, wavelength, and modulation rate of the incident radiation. Synonym PIN photodiode.

PIN Diodes Ordinary Silicon PIN photodiodes can serve as detectors for X-ray and gamma ray photons. The detection efficiency is a function of the thickness of the silicon wafer. For a wafer thickness of 300 microns (ignoring attenuation in the diode window and/or package) the detection efficiency is close to 100% at 10 KeV, falling to approximately 1% at 150 KeV(3). For energies above approximately 60 KeV, photons interact almost entirely through Compton scattering. Moreover, the active region of the diode is in electronic equilibrium with the surrounding medium--the diode package, substrate, window and outer coating, etc., so that Compton recoil electrons which are produced near--and close enough to penetrate--the active volume of the diode, are also detected. For this reason the overall detection efficiency at 150 KeV and above is maintained fairly constant (approximately 1%) over a wide range of photon energies. Thus, a silicon PIN diode can be thought of as a solid-state equivalent to an ionization-chamber radiation detector. Ordinary Silicon PIN photodiodes can serve as detectors for X-ray and gamma ray photons. The detection efficiency is a function of the thickness of the silicon wafer. For a wafer thickness of 300 microns (ignoring attenuation in the diode window and/or package) the detection efficiency is close to 100% at 10 KeV, falling to approximately 1% at 150 KeV(3). For energies above approximately 60 KeV, photons interact almost entirely through Compton scattering. Moreover, the active region of the diode is in electronic equilibrium with the surrounding medium--the diode package, substrate, window and outer coating, etc., so that Compton recoil electrons which are produced near--and close enough to penetrate--the active volume of the diode, are also detected. For this reason the overall detection efficiency at 150 KeV and above is maintained fairly constant (approximately 1%) over a wide range of photon energies. Thus, a silicon PIN diode can be thought of as a solid-state equivalent to an ionization-chamber radiation detector. DC Current-Mode Operation The DC-current response to gamma radiation incident on a PIN diode detector can be estimated as follows: Let A = area of the diode in cm2 N = flux of incident gamma rays (gamma's / second-cm2) r = detection efficiency (assume constant = .01) Ê = average energy of recoil electrons in detector, expressed in eV s = ionization constant in silicon = 3.6 eV / electron-hole pair(1) e = electronic charge = 1.6 x coulombs Then the average current produced in the diode is given by: I = N A r Ê e / s Example--Consider a 10 mCi point-source of ß+- emitting activity (gamma-ray energy = 511 KeV annihilation radiation) at a distance of 10 cm from a type PDC 24S PIN diode detector (Detection Technology, Inc., Micropolis, Finland). The diode area is .057 cm2. The flux at the detector, N = (2 x 10 x 3.7 x 107) / (4 pi x 102 ) = 588,870 gamma photons / cm2-second. This is equivalent to an exposure doserate at the face of the detector of 0.54 roentgens / hour. An exact expression for the average energy of a Compton recoil electron may be found in (6). An approximate formula -- accurate enough to be useful over a wide range of gamma ray energies* -- is given by Ê = 1/2 Emax, where Emax is derived from Compton's formula for the energy of the 180o (backscattered) photon:(4) Emax = hv {2 hv / (m0c2 + 2 hv)} hv = the energy of the incident photon (expressed in eV) m0c2 = 511,000 eV In this example hv = 511,000 eV, so that Emax = 340,000 eV, and Ê = 170,000 eV. The radiation-induced current in the diode is therefore 588,870 x .057 x .01 x 170,000 x 1.6 x / 3.6 = 2.53 x amperes. Thus the scale factor relating current to exposure doserate in this example is (2.53 picoamperes) / (0.54 roentgens per hour), or 1.68 x 10-8 coulomb / roentgen. One roentgen produces, by definition, 3.33 x coulombs in 1 cm3 of standard air(5). Thus, our .057 cm2 diode has the same radiation-induced-current sensitivity as a (1.68 x 10-8) / (3.33 x ) = 50 cm3 standard air-ionization chamber. *The estimate, Ê, is ~ 2% high at 80 KeV, dropping to ~3% low at 511 KeV, dropping further to ~10% low at 1000 KeV. Pulse-Mode Operation--Radiation Survey and Monitoring Applications Stable, reliable operation at low-to-medium exposure doserates in general radiation survey and monitoring applications is enhanced by operating the PIN diode detector in AC-coupled pulse-mode. This essentially eliminates drift and instability due to changes in system parameters, such as diode leakage current, with time and temperature. In this mode of operation the diode is closely coupled to a charge-integrating preamplifier of our own design (USA patents 5,990,745 and 6,054,705), so that individual x-ray or gamma-ray photon interactions are detected as discrete pulses of current. The preamplifier gain, expressed in units of "volts per unit charge" is 1 / Cint, where Cint is the value of the integrating capacitor which, in this implementation, is of the order of 2 x farads. Example: Assume that an incident 511 KeV photon produces a 340 Kev recoil electron in the diode. This, in turn, produces a charge of 340,000 x 1.6 x / 3.6 = 1.51 x coulombs deposited in 2 picofarads, or a voltage pulse whose amplitude = 7.55 millivolts. Individual voltage pulses are then further amplified, thresholded, and integrated. We eliminate system noise by introducing a low-energy threshold before the input to a bipolar junction transistor - charge-pump. This, in turn, is followed by an RC-integrating filter with a time-constant nominally = 1 second. The overall system gain beyond the preamp is set so that a 1.33 mV preamp-output pulse (60 KeV photon energy) just exceeds the threshold. The input current to the charge-pump is set by a series resistor. The output of the charge pump / filter is a DC current proportional to doserate in the detector which may be read by a meter, chart recorder, or computer data-acquisition system. In addition, a current-to-pulse-rate converter provides a TTL-compatible output for convenient interfacing to computer process-control and monitoring systems. Spectroscopy Applications In addition to general survey and monitoring applications, the same basic system detector and amplifier concept can be used for spectroscopy applications, where the detector diode is optically-coupled to a scintillating crystal such as CsI(Tl) for gamma-ray spectroscopy, or where the detector diode is used directly to detect x-rays below 60 KeV. Spectroscopy applications demand the best in low-noise performance from the detector and its amplifying system. The circuit components and active devices must be selected specifically to match the application at hand. In particular, the amplifying transistors (JFET's) at the input of the charge-integrating preamplifier must be chosen to match the junction capacitance of the detector diode in order to achieve the lowest possible noise and best pulse-height resolution. In addition, the time constant(s) in the shaping amplifier must be optimized to minimize line-broadening effects due to noise and from "ballistic deficit" effects due to non-uniform charge-collection times in the diode detector. Below is an example of a gamma-ray / x-ray spectrum from an 241Am check-source attached to the surface of a 2.7 mm x 2.7 mm diode (Cj = 15 pF, Vbias = 24 VDC). The prominent source peaks are: Energy (KeV) Percent Abundance(2) 13.9 KeV_________13.2 17.8 KeV_________19.25 20.8 KeV__________4.85 26.35 KeV_________2.4 59.54 KeV________35.9 The large peak at 8 KeV is due to x-ray fluorescence from a thin copper foil attenuator placed between source and detector. Spectral measurements are done at room temperature. The shaping-time is 8 µsec. The pulse-height resolution is 2.07 KeV (FWHM) at 59.5 KeV. The second trace, whose peak is shown centered at 43 KeV, is from a pulser and shows the line-broadening effects of electronic noise in the diode detector and preamplifier. The pulser-peak is 1.80 KeV wide (FWHM), which corresponds to an equivalent noise charge in the system "front end" of 212 e- rms. References: Knoll, Glenn F., Ch. 13 in Radiation Detection and Measurement John Wiley and Sons, New York, 1979 ibid. Silicon Photodiodes and Charge Sensitive Amplifiers for Scintillation Counting and High Energy Physics Hamamatsu Photonics K.K., Solid State Division, Catalog #KOTH0002E02, June,1993 Evans, R.D., Ch. 23 in The Atomic Nucleus McGraw-Hill, New York, 1955 Fitzgerald, J.J., Brownell, G.L., Mahoney, F.J., Ch 2 in Mathematical Theory of Radiation Dosimetry Gordon and Breach Science Publishers, New York, 1967 op. cit., Chapter 4

PRACTICAL SOLID STATE DETECTORS
Specially combined thin and thick detectors provide the means to identify charged particles. used to monitor for plutonium in air, discriminating against alpha particles arising from natural radioactivity, and for monitoring for radon daughter products in air. Small physical size and insensitivity to gamma radiation have found novel applications: inside nuclear fuel flasks monitoring for alpha contamination and checking sealed radium sources for leakage. Bulk conductivity detectors can measure high dose rates but with minute-long response times. A Ge(Li) detector operated at –170°C is capable of a very high gamma resolution of 0.5%. The temperature dependence and high cost add to their impracticality.

Another type of Solid State / Scintillation system
Thermoluminescent Dosimeters

Thermoluminescence (TL) is the ability to convert energy from radiation to a radiation of a different wavelength, normally in the visible light range. Two categories Fluorescence - emission of light during or immediately after irradiation Not a particularly useful reaction for TLD use Phosphorescence - emission of light after the irradiation period. Delay can be seconds to months. TLDs use phosphorescence to detect radiation.

Thermoluminescence Radiation moves electrons into “traps”
Heating moves them out Energy released is proportional to radiation Response is ~ linear High energy trap data is stored in TLD for a long time Conduction band Valence band Forbidden energy gap Trapping centres

Electron trap (metastable state)
TL Process Conduction Band (unfilled shell) Electron trap (metastable state) - Phosphor atom Valence Band (outermost electron shell) Incident radiation

TL Process, continued - Conduction Band Thermoluminescent photon
Heat Applied Phosphor atom Valence Band (outermost electron shell)

Output – Glow Curves A glow curve is obtained from heating
Light output from TLis not easily interpreted Multiple peaks result from electrons in "shallow" traps Peak results as traps are emptied. Light output drops off as these traps are depleted. Heating continues Electrons in deeper traps are released. Highest peak is typically used to calculate dose Area under represents the radiation energy deposited in the TLD

Trap Depths - Equate to LongTerm Stability of Information
Time or temperature

TLD Reader Construction
DC Amp To High Voltage To ground PMT Recorder or meter Filter TL material Heated Cup Power Supply

Advantages Advantages (as compared to film dosimeter badges) includes:
Able to measure a greater range of doses Doses may be easily obtained They can be read on site instead of being sent away for developing Quicker turnaround time for readout Reusable Small size Low cost

TLD Disadvantages Lack of uniformity – batch calibration needed
Storage instablity Fading Light sensitivity Spurious TL (cracking, contamination) Reader instability No permanent record

NON-TL Dosimeters LUXEL DOSIMETER
"Optically Stimulated Luminescence" (OSL) technology Minimum detectable dose 1 mRem for gamma and x-ray radiation, 10 mRem for beta radiation.

Non TL Dosimeters, continued
Uses thin layer of Al2O3:C Has a TL sensitivity 50 times greater than TLD-100 (LiF:Mg,Ti) Almost tissue equivalent. Strong sensitivity to light Thermal quenching. Readout stimulated using laser Dosimeter luminesces in proportion to radiation dose.

Summary Wide range of detection equipment available
Understand strengths and weaknesses of each No single detector will do everything We’ll get to selection issues in the next two days

Suggested Reading Glenn F. Knoll, Radiation Detection and Measurement, John Wiley & Sons. Hernam Cember, Introduction to Health Physics, McGraw Hill. Nicholas Tsoulfanidis, Measurement and Detection of Radiation, Taylor & Francis. C.H. Wang, D.L.Willis, W.D. Loveland, Radiotracer Methodology in the Biological, Environmental and Physical Sciences, Prentice-Hall

Radiation Detection Instrumentation Fundamentals

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