Quality Assurance Purity control Polycrystalline Ingots
1 Gamma Spectrometry Nuclide Identification Detection of Impurity Traces 1.1 Nuclides Notation: Atomic Mass Atomic Number Element Neutron Atomic Mass Atomic Number Element Proton 1 1 1 H 1 4 2 4 He 2 12 6 12 C 6
1.1.1 Chart of the Nuclides Isotopic Nuclides Atoms which have the same atomic number but different mass numbers He 4,002602 σ abs < 0,05 H 1,00794 σ 0,332 H-1 99,985 σ 0,332 He-3 0,000137 σ 0,00005 H-2 0,015 σ 0,00052 He-4 99,99986 3β 0,02 H-3 12,323 a β 0,02 He-5 99,99986 n He-6 806,7 ms β - 3,5 Z n 1 10,25 m β 0,8 N 1.1.2 Radio Nuclides Disintegration of atomic nucleus Radioactivity phenomena Emission of alpha-, beta-, gamma-rays Halflife of radio nuclides Detection of activity
1.1.3 Electromagnetic Waves Electromagnetic waves such as the photon - are transverse waves: The electric fields (E) and the magnetic field (M) both oscillate at right angles to the direction of wave propagation (travel). The two fields also oscillate at right angles to each other. 1.1.4 Electromagnetic Spectra
1.2 Activity Activity of a radio nuclide: A( t) ln 2 t t 1/ 2 = A e 0 A(t) A 0 t 1/2 activity of a given time t activity at time t=o nuclide half life Unit: 1 Bq = 1 decay per second = s -1 3,7. 10 10 Bq = 1 Curie (Ci) 1.2.1 Decay Diagram Co-60 Decay Diagram Co-60 (III) transient probability energy transients energy in kev
1.2.2 Nuclide Characterization e.g. I-131 atomic number I (Z = 53) mass number I-131 physical halflife 8,02 d decay type beta to Xe-131 radiation energy 0.971 MeV biological halflife 40-140 d effective halflife: =? T eff Tp Tb = T + T p b 1.3 Photon Matter Interactions Photon Interactions
1.3.1 Photo Effect Incoming photon Photo electron 1.3.2 COMPTON Effect Scattered photon Incoming photon COMPTON electron
1.3.3 Pair Effect Incoming photon Positron Electron 1.5 Nuclide Detection Measurements single Channel multiple Channel γ -Spectrometry semiconductor detector (Ge) scintillation detector NaI(Tl ) Detection limits 10-13 -10-12 g Co 10-12 -10-12 g Mn 10-10 -10-9 g As
1.5.1 Radiation Counter hν + - Argon R Sperrspg. (3-5kV) Preamplifier 1.5.2 Scintillation Detector h ν 3 1 2 R R R R R R Electron Multiplier 1 scintillator 2 photo cathode 3 anode pulsecounter
1.5.3 PIN Diode hν e - e - e - P I + + N R Sperrspg. (3-5kV) Preamplifier 1.5.4 Detector Properties Diffusion Ion Implant Surface Barrier PIPS Substrate P-Type N-type or P-type N-type or P-type N-type Donation Phosphorus Phosphorus / Boron Aluminium / Gold Boron Donation layer 10um 200um 15um 50um 10um 20um 5um Leek Currant >1uA >1uA >1uA 10nA - 100nA Resolution >50keV >40keV >18keV >16keV Ruggedness good good good very good Stability good good in vacuum good very good PIPS = passivated implanted planar silicon detector Leek currant and resolution at 450mm 2 surface
1.5.6 Ge Detector 3,5kV + - + + + - + + + + - - - + + - - - - - - - - pulsecounter 1.6 Gamma Spectrometer Analogue Digital Converter Detector Pulses MCA Input Measuring Time Pulse Height Pulse Counts MCA Channels MCA Output Memory
NIM Electronics 1 2 3 1 2 3 High Voltage Amplifier for Ge Detectors Analogue Digital Converter NIM Electronics 1 2 3 1 2 3 Signal Height Research Amplifier Mod 2025 AFT A/D Converter
Detector and Shielding 1 2 3 Sensor Dewar with liquid nitrogen Pb Shielding (surrounding gamma protection) 3 1 2 Measuring Place
γ Spectrometer Sample Detector Preamplifier Screen Cryostate Amplifier Impulse Height Analyser Oscilloscope Printer γ - Spectra Background X Detection Limit NG = X± 3σ Probability that signal is no noise : 50 % Estimation Limit BG = X± 6σ Probability that signal is no noise : 99,7 %
Nuclide Identification 1. Calibration Channel to energy conversion Calibration standards: Co-60 E1 = 1332,50 kev E1' = 1173,24 kev Cs-137 E2 = 661,66 kev 2. Background Measurements Spectrum without sample 3. Spectra Recording Impulse probability histograms (intensities, energies) 4. Spectra Evaluation Comparison with nuclide libraries Spectrum of a Wafer after n- Activation 1
Spectrum of a Wafer after n- Activation 2 γ-spectra with Ge Detector Photon Intensity [cps] backscattering peaks COMPTON continuum photo peaks pair peaks Detector: : Ge 500 1000 Photon Energy [MeV]
γ-spectra with Scintillation Counter Photon Intensity [cps] backscattering peaks COMPTON continuum photo peaks pair peaks Detector: NaI (Tl) 500 1000 Photon Energy [MeV] Spectra Comparison Photon Intensity [cps] Ge: NaI(Tl) higher resolution more expensive more fragile higher sensitivity better for mobile equipment 500 1000 Photon Energy [MeV]