Paul Jacks05/06/06NMT1002Prof Marshel Gas Filled Radiation Detectors
What you should learn about the equipment you are using • How it works. • How to operate it. • How to perform maintenance and quality control. • How to repair it.
Gas Filled Used for non-imaging applications Three types used in nuclear medicine Ionization Chambers Proportional Counters Geiger-Mueller Detectors Scintillation Used in nuclear medicine for radiation detection when imaging is being performed Radiation DetectorsGas Filled vs. Scintillation
Ionization • When an atom becomes ionized, it forms a pair of ions that are oppositely charged. This is called an ion pair. • The ion pair consists of a positively charged atom and negatively charged electron • Radiation causes ionization
Neg Neg Neg Ionization Neg
Construction • Gas filled detectors contain Helium, Argon, Neon, or Hydrogen • At one end of the chamber is a positive anode, at the other end is a negative cathode. Power Source Alarm Anode Cathode Measurement Gas
Ionization Chamber • 100-400V • Radiation causes ionization • Electrons are attracted to positive anode • Positive ions are attracted to negative cathode • Ion pairs pulled apart and a current forms • Current is measured and determines how much radiation is deposited in chamber
Proportional Counter • Similar to Ionization chamber • Higher Voltage 400-800V • Ions gain kinetic energy and “bump” into gas molecules causing them to become ionized in a chain reaction. • More ions form than in an ionization chamber, but measurement of current is proportional to amount of energy deposited from radiation.
Geiger-Mueller Counter • Higher Voltage 1000-1500V • Even small amount of radiation sets off a chain reaction of ionization from the ions bumping into gas molecules with tremendous kinetic energy. • Works like a yes/no detector since even small amounts of radiation cause large current.
Application • Ionization chamber and proportional counters can be used to measure activity of a dose to be given to patient • Geiger-Mueller Detectors can be used to survey the lab for radiation in unknown places.