Gas filled detectors!

ionization

creates ion pairs

ion pair is a ___________ and ____________

positively charged atom and negatively charged electron

excitation

atoms absorb energy

gas filled detectors are a chamber filled with ________, _______ ___________ with a voltage difference

gas; two electrodes

anode

positive charge

cathode

negative charge

how do gas filled detectors detect ionization?

radiation enters and ionizes gas, electrons go to the anode and ionized atoms go to the cathode which creates the electrical current

what are three types of gas filled detectors?

GM counter, dose calibrator, and ionization survey meter

what does a GM counter do?

check for contamination

what does a GM counter measure in?

mR/hr or cpm

what does a dose calibrator do?

measures activity

what does a dose calibrator meausre in?

Ci or Bq

what does an ionization survey meter do?

monitors exposure rates

what does an ionization survey meter measure in?

mR/hr

recombination occurs when _________ and ____________ recombine at ______ voltages

ions and electrons; low

most of the time the gas in the ionization chamber is ________

air

all types radiation detectors need an ____________ _____________

electric current

electric current is very _____________in ionization chambers

small

GM counters operate at __________ voltage, designed for gas amplification effect

high

GM is more __________

sensitive

current mode

number of electrons per sec to keep anode and cathode charged

pulse mode

electrons created by radiation interact as a group to create a single entity

advantages of gas filled detectors

easy to measure signals, wide range of intensities, good linearity, and simple/reliable

scintillation

process of giving off light

organic scintillators have a ________ atomic number and usually in _________

low; liquid

inorganic scintillators are __________

Na(TI) and and BGO and LSO

Na(TI) have __________ Z and _____________

high Z and dense

Na(TI) are very ____________

efficicent

50-200keV are _____________ inch

3/8

250+keV are ________________ inch

5/8

cons of Na(TI)- it is very ________________, must be away from _____________, and at greater than 250keV primary interaction is __________ _____________

fragile; moistures; compton scatter

PET scintillators prefer ______________ energies

high

PET scintillators include ______ and _________

BGO and LSO

considerations when choosing an inorganic scintillator:

high z material = more dense = more interactions, decay time, efficiency

examples of scintillation detectors:

thyroid probes, well counters, gamma cameras, PET cameras

PMT

electronic tubes that create a pulse of electrical current

photocathode

converts light to electrons

dynode

multiplies the electrons

anode

collects electrons and create a current/electrical signal

CZT is a solid state detector, is a ________ ____________ of a gamma ray to an electrical signal

direct conversion

CZT detectors are cameras such as __________ and _____________

MBI and DSPECT