Radioactivity Flashcards
What is induced nuclear fission?
Thermal neutron splitting nucleus -> 2 smaller + fast moving neutrons
What makes nuclear waste so dangerous ?
Radioactive for long time/long half life
Causes ionisation
What’s the size of a nucleus?
10^-14
Decay constant
Probability of decay of a nucleus per unit time
Why is it harder to fuse larger elements ?
Greater Q ∴ greater repulsive F
But fusion requires nuclei to get close
Why is there mass defect
- mass of nucleus < mass nucleons
- E released when nucleons combine
- E = mc²
Weak Nuclear Force
= F w/ short range + changes flavour of quarks
Background radiation
Weak level of nuclear radiation found everywhere
From naturally occurring isotopes, CMBR, man made sources
Activity definition
Rate of decay
Binding energy
Min E needed to separate all nucleons
In practice fusion occurs at much lower temperature suggest a reason why
Some nuclei will be travelling faster or have greater eK
Alpha particles
Few cm in air
0.2mm paper
Electron (beta minus)
1m in air
1mm Al/Pb
Gamma
Several km in air
1cm Pb/several m of concrete
Spontaneous
Decay cannot be induced
Random
Cannot predict when and which nucleus will decay next
Nuclear reactors
- Fission reactions -> fast n
- Moderators slowdown n ∵ n collides w/moderators nuclei + transfer eK
- Slower n = higher chance of fission
- Control rods absorb n to control RoR
- 1 n survives between successive reactions
Talk about fusion
- light nuclei -> fused together -> heavier nucleus
- 2 positron released = conserved Q
- mass reduction -> E released
- v.high temp to overcome EF (normally achieved in stars)
- E released in fusion > decay ∵ Δm is larger
- release of E from annihilation of positrons
What causes a nucleus to be unstable
- too many neutrons
- too few neutrons
- too many nucleons in total
- Too much energy in the nucleus
