Radioactivity

Question 1

What is induced nuclear fission?

Answer 1

Thermal neutron splitting nucleus -> 2 smaller + fast moving neutrons

Question 2

What makes nuclear waste so dangerous ?

Answer 2

Radioactive for long time/long half life

Causes ionisation

Question 3

What’s the size of a nucleus?

Answer 3

10^-14

Question 4

Decay constant

Answer 4

Probability of decay of a nucleus per unit time

Question 5

Why is it harder to fuse larger elements ?

Answer 5

Greater Q ∴ greater repulsive F

But fusion requires nuclei to get close

Question 6

Why is there mass defect

Answer 6

• mass of nucleus < mass nucleons
• E released when nucleons combine
• E = mc²

Question 7

Weak Nuclear Force

Answer 7

= F w/ short range + changes flavour of quarks

Question 8

Background radiation

Answer 8

Weak level of nuclear radiation found everywhere

From naturally occurring isotopes, CMBR, man made sources

Question 9

Activity definition

Answer 9

Rate of decay

Question 10

Binding energy

Answer 10

Min E needed to separate all nucleons

Question 11

In practice fusion occurs at much lower temperature suggest a reason why

Answer 11

Some nuclei will be travelling faster or have greater eK

Question 12

Alpha particles

Answer 12

Few cm in air

0.2mm paper

Question 13

Electron (beta minus)

Answer 13

1m in air

1mm Al/Pb

Question 14

Gamma

Answer 14

Several km in air

1cm Pb/several m of concrete

Question 15

Spontaneous

Answer 15

Decay cannot be induced

Question 16

Random

Answer 16

Cannot predict when and which nucleus will decay next

Question 17

Nuclear reactors

Answer 17

1. Fission reactions -> fast n
2. Moderators slowdown n ∵ n collides w/moderators nuclei + transfer eK
3. Slower n = higher chance of fission
4. Control rods absorb n to control RoR
5. 1 n survives between successive reactions

Question 18

Talk about fusion

Answer 18

• 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

Question 19

What causes a nucleus to be unstable

Answer 19

• too many neutrons
• too few neutrons
• too many nucleons in total
• Too much energy in the nucleus