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Scintillation Counter


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What's a scintillation counter?
an atom that is specified by its atomic number, atomic mass, and energy state.
what is an isotope?
an instable
what's an isotope?
2 atoms with the same number of protons, but different # of electrons and/or neutrons; thus different mass numbers.
what are the 3 types of radioactivity?
What do we want to know about radioactive decay?
1. Mode - what type it is
2. Half life - tells how much is in the sample/how old it is.
3. Interaction with matter.
How do we measure radioactivity?
by the energy it emits
How can we detect radioactive emission?
It transfers energy through matter via excitation and ionization. The detection indicates -Presence and -Quantity.
What are 3 methods for measuring radioactivity?
1. Gas ionization
2. Scintillation
3. Photographic
What is a common use of gas ionization method?
the geiger counter; radioactive emission will ionize gas, and the geiger counter detects it.
What is scintillation?
production of light flashes in relation to a flour.
What is a flour?
a compound that flashes when it gets excited.
What is the definition of a scintillation counter?
A modified spectrophotometer with a PMT.
Why is it a modified spectrophotometer?
Because the energy to be measured is actually given off as energy, not light. Thus the flour is excited by it, and the light from the flour is what's detected by the PMT.
In a scintillation counter, what is the
-Input transducer?
-Output transducer?
Input = PMT
Output = Electronic counter that counts light flashes.
What are the 2 types of fluors?
What's the difference?
-Solid: physically attached to the PMT.
-Liquid: detects low energy Beta emittors that can't excite a solid fluor.
What's the most common solid flour?
Sodium iodide crystal coupled with thallium. Energy strikes, excites the salt, electrons excite/fall and emit lite.
What's the most common liquid flour?
-PPO - an organic substance mixed with toluene/xylene. -Solvent gets excited.
-Not in physical contact w/ PMT and it holds the sample.
What are 2 signal modifications you might do for scintillation?
-another PMT
-Gater to reduce background signals of small dust, etc.
What is the readout on the scintillation counter?
-Counter - of flashes/time
What are 3 problems encountered with scintillation?
1. Quenching - interference with light production.
2. Coincidence - 2 rays excite flours that emit lite as one.
3. Waste disposal - environmental hazards.
How do you fix coincidence?
dilute the sample.
When is scintillation counting used?
In nuclear medicine. Or, imunoassay w/ radioactive tag.
-Red cell survival studies
-Hormone levels
-Therapeutic drug levels.

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