detection Flashcards
which two radiation sources will have continuous energy spectra?
beta particles and bremsstrahlung
relate energy and wavelength.
E = hc/lambda
What are the differences between fast electrons and heavy charged particles?
Fast electrons lose energy at a slower rate. They may be lost by radiative processes as well as coulomb interactions.
What energy is typical for bremssahlung photons?
It’s generally very low and is absorbed close to point of origin.
What does the transmission curve for beta particles look like?
It is near exponential.
What is backscattering and when does it usually happen?
When an electron entering an absorber is deflected enough to go back the way it came. Most pronounced with electrons that have low incident energy and absorbers with high atomic number.
What are common statistical models used in detection experiments?
Binomial distribution, poisson distribution, gaussian or normal distribution.
What is the difference between the binomial, poisson, and gaussian distributions?
Gaussian distribution is a special case of poisson which is a special case of the binomial distribution. All must have constant p. In poisson p is also small, in gaussian we have a relatively large number of successes (>20 or 30)
what is rise time? what is it dependent on?
the time it takes to recognize charge, dependent on reactor
what is the sequence of machines from source to computer?
source - detector - preamp - linear amplifier - pulse shaper - multichannel analyzer - computer
what does the detector do?
Turns radiation into electric charge
how much energy does it take to ionize one atom in a gas detector?
order of 30 ev
how much energy does liberated charge usually have?
pico coulombs
what does the preamp do?
converts charge into current or voltage
what is the gain for a preamp?
G = V_out/Q_in
What does the linear amplifier do?
makes signal bigger so it is easier to see for MCA. produces gaussian to optimize signal to noise ratio.
what does the pulse shaper do?
turns curved signal into square pulse (easier for computer to read)
what does MCA do?
digitizes signal
What are the four general types of atomic or nuclear radiation?
Fast electrons, Heavy Charged Particles, Electromagnetic Radiation, Neutrons
What is a fast electron?
Beta particles (positive or negative) emitted in nuclear decay, as well as energetic electrons produced by other processes.
What are Heavy Charged Particles?
All energetic ions with mass of 1 amu or greater. ie alpha particles, protons, fission products.
What type of electromagnetic radiation is of interest?
X rays emitted in the rearrangement of electron shells of atoms, gamma rays.
At what energy is radiation ionizing?
10ev
Arrange typical forms of radiation in terms of “hardness” from soft to hard .
Alpha/low energy xrays; beta particles; gammas and neutrons