atomic radiography Flashcards
1
Q
radioactivity def
A
- unstable atomic nuclei will spontaneously decompose to form nuclei with a higher stability
- decomposition process is called radioactivity
2
Q
strong nuclear force
A
- always attractive
- acts between p+p, n+n and p+n
- strong force is approx 137 times as strong as electromagnetism
- radius of n/p is 1fm means the n+p are packed together in nucleus so strong nuclear force is only effective between neighbours over short distance
3
Q
nucleus size
A
- if large enough, total electrical repulsion may be sufficient to overcome the attraction= nucleus may eject proton
- usually happens in alpha decay
4
Q
stability of nucleus
A
- depends of p:n ratio
- if p and n are equal then = max stability
5
Q
why does radioactivity occur
A
- for heavy nuclei, p:n increases due to dominance of number of neutrons
- stable nuclei have n:p between 1 and 1.6
- this is bcs for heavier nuclides, p+p repulsion’s start to offset the attractive forces and excess of neutrons over protons is required for stability
6
Q
alpha decay
A
- helium 4 nucleus
- form of nuclear fission (parent atom split into 2 daughter products)
- only seen in heavier nuclides ( atomic mass > 150)
- followed by gamma and characteristic x ray emission
- stopped by sheet of paper + much more easily shielded than other decay
7
Q
alpha particles
A
- safe externally cos kinetic energy is low quickly so dead skin cells can stop particle
- if enters body, alpha radiation is more effective at causing cancer/ cell death
- because it has high linear energy transfer (1 chem bond broken for every 10^-10 m travelled )
8
Q
beta minus decay
A
- occurs when n:p is too great in the nucleus
- neutron converts into proton inside atomic nucleus -> beta minus particle produced
- beta minus particle is an e- (carries neg charge and a high energy particle called anti-neutrino)
- p and n are more complex than e-, they aren’t fundamental particle but a combo of other particles
9
Q
why does beta minus decay occur
A
- nuclei that are rich in neutrons tend to decay by emitting an e- along with antineutrino
- so balance of n:p in nucleus is important
- force involved in this process is the weak nuclear force which acts to hold together the particles that make up p and n
10
Q
positron decay
A
- proton decays to become a neutron plus a positron (anti e- or beta particle) and an e- type neutrino
- positron decay increases N/Z ratio
- positron is an antimatter equivalent of an e-
- in this process, a proton is converted into a neutron
- as positron and neutrino are released along with energy in the form of electromagnetic radiation (gamma decay)
11
Q
beta particles
A
- medium penetrating power + ionising power because they’re charged particles
- more strongly ionising than gamma
- when passes thru matter, beta particle is decelerated by em interactions and may give off bremsstrahlung radiation
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12
Q
gamma decay
A
- occurs after alpha and beta
- radioactive particle alr released some particle so it just want to release energy burst of em radiations
- nuclei has come to stable state and releases energy in the form of gamma rays
- no p + n released= element before and after remain same
13
Q
gamma rays and x-rays
A
G: - high energy rays
- emitted in radioactive decays + very penetrating so require more substantial shielding
- produced from nucleus
X: - ionising radiation
- high energy
- virtually identical to gamma rays but not nuclear in origin (produced outside nucleus)
14
Q
radioactive decay
A
- spotaneous event which can’t be predicted
- can be predicted
15
Q
half life equation
A
N= No/2^n
N= number of particles
No= initial number
n= number of half lives
