Nuclear Physics

Question 1

What does the nucleus of an atom consist of? Mention charges

Answer 1

Protons +1 charge
Neutrons 0 charge

Question 2

What orbits the nucleus of an atom?
Mention charge

Answer 2

Electrons -1 charge

Question 3

What is the bottom number of an element? (Smaller number)

Answer 3

Atomic number, total protons/electrons

Question 4

What is the top number of an element?
(Bigger number)

Answer 4

Mass number, total of protons and neutrons

Question 5

What determines which element an atom is

Answer 5

The number of protons it has

Question 6

What are isotopes?

Answer 6

Atoms with the same number of protons but different amounts of neutrons
(Different versions of the same element)
- Have the same atomic number

Question 7

What is radioactive decay?

Answer 7

When unstable isotopes decay into other elements by emitting radiation
(Alpha, beta or gamma)
Or sometime they just emit neutrons

Question 8

What makes an isotope unstable?

Answer 8

When it’s nucleus has a different amount of protons and neutrons

Question 9

What does it mean when an electron becomes excited?

Answer 9

The electron gains enough energy to increase its energy level (jump to the next shell)
- the energy comes from electromagnetic radiation

Question 10

How is electromagnetic radiation formed?

Answer 10

When an electron get excited and jumps up and energy level, it soon falls back down to the lower energy level and will re emit the energy as electromagnetic radiation

Question 11

What is ionization?

Answer 11

Occasionally one of the outer most electrons can gain enough energy to leave the atom completely, giving the atom a positive charge
(It’s now a positive ion)

Question 12

What is ionizing radiation?

Answer 12

Able to knock electrons off atoms turning them into ions

Question 13

What does it mean when we say a material is radioactive?

Answer 13

It consists of unstable isotopes that can decay.

Question 14

What are the 4 types of nuclear radiation?

Answer 14

Beta particles, alpha particles, gamma rays, neutrons

Question 15

Describe alpha particles

Answer 15

• made up of 2 protons and 2 neutrons
  (Like helium, He)
• don’t have any electrons so have 2+ charge
• large so can’t penetrate very far into other materials
  (Can travel few cm in air, absorbed by a single sheet of paper)
• large size and charge makes them strongly ionising (able to knock off electrons on atoms they collide with)

Question 16

Describe beta particles

Answer 16

• electrons
• no mass and -1 charge
• not emitted from an atom’s shell; one of the atom’s neutrons decays into a proton and an electron. The proton stays in the nucleus but the electron is emitted out at high speed
• tiny so are moderately ionising and penetrate moderately far into materials
  ( takes several meters of air or 5mm of aluminum to stop them)

Question 17

Describe gamma rays

Answer 17

• waves of electromagnetic radiation
  ( often emitted after alpha or beta radiation as a way for the nucleus to remove any extra energy)
• no mass or charge
• passes straight through materials so moderately ionising
• can penetrate far into materials before being stopped ( long distances through air, thick sheets of lead to stop it)

Question 18

Describe the emission of neutron

Answer 18

If a nucleus contains too many neutrons it can emit one to increase stability

Question 19

What is activity?

Answer 19

Overall rate of decay of all isotopes in a samples
- measured in Becquerels
( 1Bq = 1 decay per second)
- as time passes the activity decreases as there are less nuclei that need to decay

Question 20

What is half life?

Answer 20

The time taken for the no of radioactive nuclei in a sample to halve

Question 21

What is equipment is used to measure activity?

Answer 21

Geiger counter
(Records all the decays that reach them each second)

Question 22

What is irradiation?

Answer 22

The process by which objects are exposed to radiation

Question 23

What is contamination?

Answer 23

When radioactive particles get onto other objects
- contamination isn’t a problem but likely the particles will decay will lead to irradiation
(Increased risk of irradiation)

Question 24

What determines how harmful radiation is?

Answer 24

Ionising = more dangerous as they can enter living cells, ionise our dna and cause mutations

Ionising radiation:
Alpha, beta, gamma, x ray

If source of radiation is outside the body:
- alpha isn’t harmful as it can’t penetrate through skin
- beta and gamma can penetrate the skin so are very dangerous

If source is on or inside the body:
- alpha radiation would be the most dangerous

Question 25

Explain nuclear fission

Answer 25

The splitting of a large unstable nucleus and the release of energy

• there are 2 fissionable substances commonly used in nuclear reactors:
  Uranium-235 and plutonium-239

1) we start of with large unstable nuclei (uranium 235) and fire a slow moving neutron at it
2) this addition of a neutron causes the nuclei to become even less stable, causing it to split apart into 2 smaller nuclei (daughter nuclei)
3) this process also releases 2 or 3 more neutrons and loads of energy in the form of gamma radiation
4) a neutron released is then fired onto another unstable nuclei for the same process to repeat ( chain reaction)
5) in a nuclear reactor, control rods absorb fission neutrons to ensure that on average only one neutron per fission goes on to produce further fission and energy transfer

Waste:
Nuclear reactions produce waste which may be dangerous due to its radioactive nature and can remain so for a long time depending on half life.
The disposal for such waste needs to be managed with care making it a factor influencing the use of nuclear power for electricity

Question 26

Explain nuclear fusion

Answer 26

When 2 lighter (positive) nuclei fuse to form a single larger nuclei
- releases tons of energy

The reason fusion produces so much energy:
Some of the mass from the lighter nuclei is being converted into energy rather than transferred to the larger nuclei

• doesn’t produce any radioactive waste
• only happens at very high temperatures and pressures as the force of repulsion between the 2 positive nuclei must be overcome for them to fuse
• the process by which energy is released in stars