Gamma Spectroscopy HPT001.204 TVAN Technical Training Health Physics (RADCON) Initial Training Program

Enabling Objectives - 1 Purpose of Gamma-Ray Spectroscopy Techniques for Measuring Photon Energy Mechanisms of Interaction Energy Range for Each Mechanism Minimum Energy for Pair Production Radiation Energy Measurement Unit TVAN Technical Training Health Physics (RADCON) Initial Training Program

Enabling Objectives - 2 Nuclear Decay Schemes Scintillation Detector Materials Components of Gamma Spectroscopy System NaI(Tl) Detector Shapes Features of Gamma-Ray Spectrum TVAN Technical Training Health Physics (RADCON) Initial Training Program

Enabling Objectives - 3 Differentiate Between Energy Efficiencies Calculate Energy Resolution Background Subtraction Identify Nuclides in Gamma Spectrum Materials Used in Solid State Detectors TVAN Technical Training Health Physics (RADCON) Initial Training Program

Gamma Rays Form of Electromagnetic Radiation Originate in Atoms Fixed Energy Values TVAN Technical Training Health Physics (RADCON) Initial Training Program

Cs-137 Gamma Energy TVAN Technical Training Health Physics (RADCON) Initial Training Program

Purpose of Gamma Ray Spectroscopy Measure: Energy of Photons Number of Photons Differentiate Photons by Energy TVAN Technical Training Health Physics (RADCON) Initial Training Program

Most Common Technique for Measuring Photon Energy Scintillation Material Creates Light Pulses Proportional to Photon Energy TVAN Technical Training Health Physics (RADCON) Initial Training Program

Gamma Interactions Photoelectric Absorption Compton Scattering Pair Production TVAN Technical Training Health Physics (RADCON) Initial Training Program

Interaction Processes TVAN Technical Training Health Physics (RADCON) Initial Training Program

Photoelectric Absorption TVAN Technical Training Health Physics (RADCON) Initial Training Program

Photoelectric Absorption Most Predominant Process for X-Ray Absorption Typical Energies ≤ 200 keV Enhanced for High Z Materials TVAN Technical Training Health Physics (RADCON) Initial Training Program

Compton Scattering TVAN Technical Training Health Physics (RADCON) Initial Training Program

Compton Scattering Predominately 200-500 keV Decreases with Increasing Gamma Energy Photon Still in Existance TVAN Technical Training Health Physics (RADCON) Initial Training Program

Pair Production TVAN Technical Training Health Physics (RADCON) Initial Training Program

Pair Production Requires at Least 1.022 MeV Gamma Most > 5 MeV May Result in Annihilation Radiation TVAN Technical Training Health Physics (RADCON) Initial Training Program

Electron Energy Measured in Electron Volts, eV Electron Vole - Energy Given to an Electron by Accelerating it Through 1 Volt of Electric Potential Difference. 1 eV = 1.602 * 10-19 Joules Usually Given in: keV (kilo eV), or MeV (mega eV) TVAN Technical Training Health Physics (RADCON) Initial Training Program

Electron Energy Equation E = h ν, Where, E = Photon Energy, eV h = Plank’s Constant, 4.135*10-15 eV-sec ν = Frequency, sec-1 TVAN Technical Training Health Physics (RADCON) Initial Training Program

Wavelength of Photon λ = 1.24 * 10-6/E, Where λ = Wavelength, meters E = Photon Energy, eV TVAN Technical Training Health Physics (RADCON) Initial Training Program

Decay Schemes Most Decay by Electron (Beta) Emission Beta Creates Excited State in Daughter Gamma Released to Return Excited State to Stable TVAN Technical Training Health Physics (RADCON) Initial Training Program

Cs-137 Decay Scheme TVAN Technical Training Health Physics (RADCON) Initial Training Program

Co-60 Decay Scheme TVAN Technical Training Health Physics (RADCON) Initial Training Program

Scintillation Detectors Zinc Sulfide Alpha Anthracene Crystals Beta NaI(Tl) Gamma TVAN Technical Training Health Physics (RADCON) Initial Training Program

NaI(Tl) Excellent Light Yield Nearly Linear Response Hygroscopic (Absorbs Water – Requires Sealing) TVAN Technical Training Health Physics (RADCON) Initial Training Program

Gamma Ray Spectroscopy TVAN Technical Training Health Physics (RADCON) Initial Training Program

Photomultiplier (PM) Tube TVAN Technical Training Health Physics (RADCON) Initial Training Program

Crystal Shapes Solid Right Cylinder Excellent Light Collection Accommodates Various Sample Geometries Well Crystal Efficiency can Approach 100 % Uniform Counting Efficiencies Excellent for Small Samples TVAN Technical Training Health Physics (RADCON) Initial Training Program

Solid Crystal with Marinelli Beaker TVAN Technical Training Health Physics (RADCON) Initial Training Program

Solid and Well Crystals Solid Crystal Well Crystals TVAN Technical Training Health Physics (RADCON) Initial Training Program

Components of a Gamma Spectroscopy System Detector – Detects the Radiation Energy Photocathode–Converts Light to Electrons Photomultiplier Tube – Multiplies the Number of Pulses Amplifier – Amplifies & Shapes the Pulses Analog-to-Digital Convert (ADC) Converts the Pulses to Numbers Multi-Channel Analyzer (MCA) – Sorts and Stores the Pulses & Their Amplitudes TVAN Technical Training Health Physics (RADCON) Initial Training Program

MCA Output Numbers Correlate with the Activity Amplitudes Correlate with Gamma Energy Expectation: Single Vertical Line at the Energy of the Gamma Ray TVAN Technical Training Health Physics (RADCON) Initial Training Program

Gaussian Distribution 38 Symmetrical about the mean One  includes 68.3% of area under curve TVAN Technical Training Health Physics (RADCON) Initial Training Program

Ideal Gamma Ray Spectrum TVAN Technical Training Health Physics (RADCON) Initial Training Program

Spectrum TVAN Technical Training Health Physics (RADCON) Initial Training Program

Energy Resolution - Diagram TVAN Technical Training Health Physics (RADCON) Initial Training Program

The Gamma Spectrum Distribution of the Data (Resolution) Energy Resolution, “R” R = (FWHM * 100)/Ho, where FWHM = Full Width, Half Max, (eV) Ho = Location of Peak Centroid (eV) TVAN Technical Training Health Physics (RADCON) Initial Training Program

Energy Resolution Assume FWHM = 50 keV Ho = 662 keV, then, For NaI(Tl), R Typically 5-10 % TVAN Technical Training Health Physics (RADCON) Initial Training Program

The Gamma Spectrum Compton Scattering Compton edge TVAN Technical Training Health Physics (RADCON) Initial Training Program

The Gamma Spectrum X-Ray Escape Peaks Photoelectric Absorption near Surface X-Rays Escape Detector Results in Loss of Energy Most Prominent at Low Incidence Gamma-Ray Energies TVAN Technical Training Health Physics (RADCON) Initial Training Program

The Gamma Spectrum Annihilation Radiation Occurs When Positron Emitted Positron Expends Energy & Combines with an Electron Two 0.511 MeV Photons Emitted from the Annihilation of the Positron Adds a Peak at the 0.511 MeV Line TVAN Technical Training Health Physics (RADCON) Initial Training Program

The Gamma Spectrum Bremsstrahlung Many Gamma Interactions Release Beta Particles Beta Particles Create Secondary Bremsstrahlung These Radiations Added to the Continuum TVAN Technical Training Health Physics (RADCON) Initial Training Program

The Gamma Spectrum Backscatter Results from Compton Scattering in Shielding Material Some Gamma Rays Reflected Back into the Detector Usually ≤ 0.25 MeV TVAN Technical Training Health Physics (RADCON) Initial Training Program

The Gamma Spectrum Characteristic X-Rays Photoelectric Absorption in Shield Material Generates Characteristic X-Ray From the Shield Material Especially Prominent with High Z Material Compensate by Graded Shielding: High Z Material for Primary Shielding Low Z Material for Lining of Shielding TVAN Technical Training Health Physics (RADCON) Initial Training Program

The Gamma Spectrum Summation Effects Occurs When Two Photons are Counted at the Same Time Detector Sees them as One Event Energy is the Sum of the Two Photon Energies Results in Sum Peak (Example, Co-60 & Sc-46) TVAN Technical Training Health Physics (RADCON) Initial Training Program

Sum Peak, Sc-46 TVAN Technical Training Health Physics (RADCON) Initial Training Program

The Gamma Spectrum Background Radiation Terrestrial Cosmic Laboratory Example: K-40 TVAN Technical Training Health Physics (RADCON) Initial Training Program

Potassium-40 Spectrum TVAN Technical Training Health Physics (RADCON) Initial Training Program

Single Channel Analyzer Spectrum LLD ULD TVAN Technical Training Health Physics (RADCON) Initial Training Program

Components of a Gamma Spectrum Photopeak Backscatter Peaks Compton Continuum Compton Edge Annihilation Peak Escape Peaks Sum Peaks Bremsstrahlung Background Peaks TVAN Technical Training Health Physics (RADCON) Initial Training Program

Spectrum with Components TVAN Technical Training Health Physics (RADCON) Initial Training Program

Detector Efficiency Measured Efficiency from Known Activity 1. Same or Similar Geometry as Unknown 2. Separate Efficiency for Each Geometry Calculated Efficiency Based on Knowledge of Gamma Ray Interactions TVAN Technical Training Health Physics (RADCON) Initial Training Program

Detector Efficiency – Solid Right Cylinder TVAN Technical Training Health Physics (RADCON) Initial Training Program

Detector Efficiency – Well Crystal TVAN Technical Training Health Physics (RADCON) Initial Training Program

Detector Efficiency Critical Data Category of Efficiency 1. Absolute – Based on Radiation Emitted 2. Intrinsic – Based on Radiation Incident on Detector Size & Shape of Crystal Example – Solid or Well Geometry of Sample Absorption Between Source & Detector TVAN Technical Training Health Physics (RADCON) Initial Training Program

Peak Area Determination B TVAN Technical Training Health Physics (RADCON) Initial Training Program

Peak Area Determination- Equation B Peak Area = ∑ Ci , i=A Where, Ci = Number of Counts in ‘i’ Channel A & B = Channels Marking Either Side of the Peak Area TVAN Technical Training Health Physics (RADCON) Initial Training Program

Peak Area Determination – Background Subtraction Peak Area = ∑ Ci – (B - A)[CA + CB)/2] i=A Where, A & B = Channels Marking Either Side of the Peak Area Ci = Number of Counts in ‘i’ Channel CA = Counts in Channel ‘A’ CB = Counts in Channel ‘B’ TVAN Technical Training Health Physics (RADCON) Initial Training Program

Background Subtraction - Spectrum Stripping Accumulate a Background Spectrum Subtract Background Channel Counts from Respective Sample Channel Counts Analyze Resulting Spectrum Photopeak TVAN Technical Training Health Physics (RADCON) Initial Training Program

I-131 Spectrum, With Background TVAN Technical Training Health Physics (RADCON) Initial Training Program

Background Spectrum TVAN Technical Training Health Physics (RADCON) Initial Training Program

I-131 Spectrum, Background Subtracted TVAN Technical Training Health Physics (RADCON) Initial Training Program

Identifying Gamma Emitters Unknown Spectrum TVAN Technical Training Health Physics (RADCON) Initial Training Program

Identifying Gamma Emitters Solution Spectrum TVAN Technical Training Health Physics (RADCON) Initial Training Program

Comparison of NaI(Tl) and GeLi Spectra TVAN Technical Training Health Physics (RADCON) Initial Training Program

Other Detectors – Advantages Solid State GeLi HPGe More Efficient Compact Size Fast Timing Characteristics Effective Thickness can be Varied to Match Requirements of Applications TVAN Technical Training Health Physics (RADCON) Initial Training Program

Other Detectors – Disadvantages Must be Cooled to Liquid Nitrogen Temperatures GeLi – Continuously Cooled HPGe – Cooled Only While in Use TVAN Technical Training Health Physics (RADCON) Initial Training Program

Practical Exercises Problem # 1 TVAN Technical Training Health Physics (RADCON) Initial Training Program

Practical Exercises Problem # 1 - Solution TVAN Technical Training Health Physics (RADCON) Initial Training Program

Practical Exercises Problem # 2 TVAN Technical Training Health Physics (RADCON) Initial Training Program

Practical Exercises Problem # 2 - Solution TVAN Technical Training Health Physics (RADCON) Initial Training Program

Practical Exercises Problem # 3 TVAN Technical Training Health Physics (RADCON) Initial Training Program

Practical Exercises Problem # 3 -Solution TVAN Technical Training Health Physics (RADCON) Initial Training Program

Practical Exercises Problem # 4 TVAN Technical Training Health Physics (RADCON) Initial Training Program

Practical Exercises Problem # 4 - Solution TVAN Technical Training Health Physics (RADCON) Initial Training Program

Practical Exercises Problem # 5 TVAN Technical Training Health Physics (RADCON) Initial Training Program

Practical Exercises Problem # 5 - Solution TVAN Technical Training Health Physics (RADCON) Initial Training Program

Summary - 1 Gamma Rays: 1. Form of Electromagnetic Radiation 2. Energy Levels from 0.01 to 10 MeV 3. Measured by Scintillation Detectors 4. Interactions with Matter: a. Photoelectric Absorption b. Compton Scattering c. Pair Production TVAN Technical Training Health Physics (RADCON) Initial Training Program

Summary - 2 Gamma Ray Spectrum: Components 1. Photopeak 2. Backscatter Peak 3. Compton Continuum 4. Annihilation Peaks 5. Escape Peaks 6. Sum Peaks 7. Bremsstrahlung 8. Characteristic X-Rays 9. Background Radiation TVAN Technical Training Health Physics (RADCON) Initial Training Program

Summary - 3 Gamma Ray Detection Efficiency: 1. Absolute – Based on Radiation Released from the Source 2. Intrinsic – Based on Radiation Incident on the Detector TVAN Technical Training Health Physics (RADCON) Initial Training Program

Summary - 4 Other Gamma Ray Detector Systems 1. GeLi 2. HPGe Advantages 1. Compact 2. More Efficient 3. Faster Disadvantage – Operate at Liquid Nitrogen Temperatures TVAN Technical Training Health Physics (RADCON) Initial Training Program