4: NUCLEAR PHYS

Question 1

order of atomic discovery:

Answer 1

greeks - matter is made of indivisible particles
jj thomson - plum pudding
rutherford - nucleus is small and positively charged after finding most alpha particles went through a gold leaf but some got deflected back
bohr - electrons exist in shells and orbit the nucleus
chadwick - neutrons exist

Question 2

why do nuclei decay

Answer 2

if they are unstable they will decay to restabilise, emitting radiation in the process, which can ionise other particles and be dangerous

Question 3

alpha vs beta vs gamma radiation

Answer 3

alpha: helium nucleus (2p and 2n)
mass of 4
charge of 2
high ionising power
low penetrative ability
used in smoke detectors
beta: high speed electron
mass of 0
charge of -1
med ionising power
med penetrative ability
used to gauge thickness
gamma: high energy EM wave
mass of 0
charge of 0
low ionising power
high penetrative ability
used in radiotherapy and sterilisation

Question 4

all abt background radiation

Answer 4

eg cosmic rays, nuclear weapons, medical equipment
background count should be taken first then taken away from resultant count to give correct count

Question 5

what is radioactivity

Answer 5

the rate of decay in a sample of radioactive material

Question 6

why does radioactivity decrease over time

Answer 6

fewer unstable nuclei are left

Question 7

fission vs fusion

Answer 7

fission: the splitting up of a bigger nuclei (eg uranium-235) into two daughter nuclei releasing energy that can generate electricity
when a neutron is absorbed by another neutron, making it more unstable, releasing three neutrons and causing a chain reaction
fusion: the joining together of two lighter nuclei, releasing energy. happens in the sun but it is difficult to harness the energy produced by fusion in reactors being developed

Question 8

the rutherford experiment:

Answer 8

1. fired alpha (positively charged) particles towards a thin gold leaf
2. most went through, some were deflected
3. shows every atom has mostly empty space but small positive charge at the centre