3.8 Nuclear Physics

Question 1

Define Rutherford’s Experiment

Answer 1

Fired alpha particles at a very thin gold sheet.
They mostly passed through but some were deflected at large angles.
This disproved the ‘plum pudding’ model.
The deflections were caused by the electrostatic repulsion between the moisture nucleus and positive alpha particles.
Most passed through proving atoms are mostly free space.

Question 2

What are alpha particles?

Answer 2

Two protons and two neutrons (the equivalent of a helium nucleus).
Weakly penetrating.
Highly ionising.
Easily absorbed.
Positively charged.

Question 3

What are the applications of alpha radiation?

Answer 3

used in fire/smoke alarms:
alpha particles cannot penetrate through smoke, this is detected and sets off the alarm.

Question 4

What are beta particles?

Answer 4

electrons or positrons
moderately penetrative (cannot penetrate through about 5mm of aluminium/ 30cm of air)
fairly ionising
either positively or negatively charged

Question 5

What are the applications of beta particles?

Answer 5

used for gauging the thickness of paper in a paper mill
a beta plus emitter is used in medical PET scanning

Question 6

When are beta particles emitted?

Answer 6

beta-minus = by neutron-rich nuclei
beta-plus = by proton-rich nuclei

Question 7

What are some radioactivity protective measures?

Answer 7

wear protective goggles and gloves
point sources away
keep source at arm’s length
reduce exposure time
keep source in a lead-lined box

Question 8

What is gamma radiation?

Answer 8

part of the EM spectrum
highly penetrative
not very ionising

Question 9

What are some application of gamma radiation?

Answer 9

used in medical imaging, treating cancer by destroying tumorous cells, tracing, sterilising medical equipment
used to irradiate food to stop it from going bad

Question 10

What is background radiation?

Answer 10

radiation which is always present, even when there is no radioactive source

Question 11

What are some sources of background radiation?

Answer 11

radon gas
cosmic rays
medical procedures
food and drink

Question 12

What is radioactive decay?

Answer 12

when an object is radioactive it releases radioactive particles, but as time passes, the rate of particles decreases
it is random

Question 13

What is half-life?

Answer 13

the time taken:
for the number of radioactive nuclei in a sample, or for the activity (the number of decays per second) to halve

Question 14

What are the uses of half-life?

Answer 14

used in the dating of a substance.
-by knowing the original count rate, the current count rate and the half-life of the material, we can calculate the time passed:

Question 15

What are atomic excited states?

Answer 15

in an atom, an electron can gain energy and be promoted to a higher energy level
when the electron returns to the original level, the energy is released as EM waves

Question 16

What are nuclear excited states?

Answer 16

when the protons and neutrons rearrange to a lower energy state, the excess energy is released as gamma radiation

Question 17

What is binding energy?

Answer 17

A nucleus is made up of protons and neutrons
The mass of a nucleus is less than the mass of the individual protons and neutrons
This is because when the protons and neutrons combine, they release energy, which is the biding energy

Question 18

What is fission?

Answer 18

Nuclear fission is a reaction in which the nucleus is split:
Energy is released when heavy nucleus split apart
The new nuclei (daughter nuclei) have a larger binding energy per nucleon than the parent
This means that a large amount of energy is released

Question 19

What is a chain reaction?

Answer 19

Fission occurs when an unstable atoms splits, by absorbing a neutron
The reaction produces daughter nuclei, and releases energy and some neutrons
These neutrons will go on to cause more fission reactions, producing more neutrons

Question 20

What is fusion?

Answer 20

Nuclear fusion is a reaction in which two nuclei are combines to form a larger nucleus:
When an atom is formed, it releases binding energy