DETECTION AND MEASUREMENT OF RADIOACTIVITY 1 NANIK DWI NURHAYATI,S.SI,M.SI

RADIATION DETECTORS Instruments used in the practice of health physics serve a wide variety of purposes one finds instruments designed specifically for the measurement of a certain type of radiation, such as low-energy X-rays, high- energy gamma rays. fast neutrons, and so on

The basic requirement of any such instrument is that its detector interact with the radiation in such a manner that the magnitude of the instrument's response is proportional to the radiation effect or radiation property being measured

Radiation Measurement Principles Detector Signal Physical Chemical Biological Reader Calibration Assessment Amplification

RADIATION DETECTORS

Type Radiation Detector Detector Gas Detector Scintilation Detector Semikonduktor

Radiation Detector Elektroskup (Electroscope) Kamar Ionisasi (Ionization Chamber) Proporsional Counter Geiger-Muller Counter Cloud Chamber Diffusion Chamber Bubble Chamber Nuclear Emulsion Scintillation Counter Solid State Detector The Spark Chamber Cerenkov Detecto

Examples 8

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” 10

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. 11

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 12