ECE699 – 004 Sensor Device Technology Chapter 6 Radiation Detectors Fall 2018 George Mason University

Introduction N: number of nuclei still undecayed dN, the number of nuclei which decay in a small interval dt λ is a decay constant specific for a given substance It is defined as radioactivity, unit becquerel (Bq) = s-1 Absorbed dose is measured in grays (Gy) = 1 joule per kilograms (J/kg)

Scintillating Detectors -need photomultipliers to magnify the signal because the light intensity resulting from radiation is extremely small

The scintillation materials: When detecting 0 The scintillation materials: When detecting 0.662-MeV γ-rays, the energy resolution for sodium iodine scintillators is limited to about 6% - mean the energy required to produce a photoelectron is about 1000eV

A new design of photomultiplier

2. Ionization detectors Rely on the ability of some gaseous and solid materials to produce ion pairs in response to the ionization radiation 2.1 Ionization chambers -oldest and most widely used -ionizing particle causes ionization and excitation of gas molecules along its passing track

2.2 Proportional chambers – pulse mode and relies on gas multiplication

2.3 Geiger-Muller(G-M) counters -much higher applied voltage

2.4 Semiconductor detectors -radiation induces a large number of carriers: electron-hole pairs -good for γ-ray detection

Li-drifted (Ge/Li) detector

Materials: relatively high Z-value with a large bandgap semiconductor materials