Lecture 7 Flashcards
What does Ionising mean
Ionizing is the process by which atoms gain or lose one or more electrons, resulting in the formation of ions with a net electrical charge
What is alpha radiation and is it penetrating or ionising
a Helium nucleus (some gamma is also released)
not penetrating
ionising
What is beta radiation and is it penetrating or ionising
an electron/positron (antielectron)
moderately penetrating
moderately ionising
What is gamma radiation and is it penetrating or ionising
electromagnetic waves (short wavelength) emitted by an excited nucleus
very penetrating
not very ionising
What is neutron radiation and is it penetrating or ionising
free neutrons
very penetrating
not very ionising
Absorbed dose
measure of the energy deposited in joules/kg by radiation which is incident on a material that absorbs it.
what is attenuation and what is the use of the term
different materials will adsorb radiation with different efficacy
describes the best materials to shield from radiation
What is specific activity
amount of radioactivity found in a gram of material
Do radioactive materials with long or short half lives have low specific activity
and why
Long half lives
because the activity is very low because the decay is slow and the radiation emitted at a slower rate
What is the unit of radioactivity
Bequerel (1 disintegration peer second)
What is the unit of equivalent dose
Sievert (8 = death)
What is used to detect radiation
Friction
In terms of detection what does more charge mean
More friction
In terms of detection what does more massive mean
More friction
In terms of detection what does more friction mean
A shorter range
In terms of collisions what causes the biggest damage to lattices (think cricket explaination)
Bigger and more charged particles will cause more damage (meaning alpha does lots of damage and gamma does not a lot)
How far can you detect alpha vs gamma
Alpha not far at all
Gamma very very far
What are good shielding materials
Lead, concrete, polyethalyne
What are good shielding materials for neutrons
Something hydrous like concrete and water
Describe the attenuation mechanism - photoelectric effect
low energy gamma radiation, kicks out an electron, electron from higher shell drops down, this emits a characteristic energy which can be detected
all gamma is absorbed creating peak
Describe the attenuation mechanism - compton scattering
medium energy gamma, more energy than photoelectric effect, (like billiards), gamma hits an electron in a higher shell which becomes a scattered electron, the gamma becomes a lower energy scattered gamma ray, the energy gained by the electron is equal to the energy lost by the gamma ray
not all gamma is absorbed so can continue to hit other electrons and so the signal released is not as simple
Describe the attenuation mechanism - pair production
A very high energy photon (gamma) interacts with the nucleus to create an electron/positron pair. The positron then hits another electron and causes an anihilation creating a distinct peak
Types of detectors
Gas and Solid state
Example of gas detectors
Postives
geiger counter
clicks to tell you if there is radiation but not what type
Electric field induces ionisation which causes a cascade and therefore it clicks
Example of solid state detectors
Postives
Scintillator - flash of light when something interacts with it
What are the three regions on the gas aplification curve
1) Recombination regaion
2) Ionisation region
3) Proportional region
4) Limited proportional region
5) Geiger-Mueller region
6) Continuous discharge region
What are the advantages and disadvantages of the Geiger-Muller Gas-Filled detectors
ADV
highly sensitive
less insulation required to decrease noise interferance
DISADV
no single detector setup can discriminate between alpha, beta and gamma
no energy discrimination
entire gas volume ionises
limited use in extreme intensity radiation fields
