Atomic Physics

Question 1

What did JJ Thompson believe and propose in what year?

Answer 1

In 1904 JJ Thompson proposed his infamous ‘plum pudding model’ of the atom.

It was believed that atoms were:

1. Spheres of positive charge.
2. With negative charges spread through it.

This resembled a plum-pudding, so it was called the ‘Plum–pudding’ model.

Question 2

Properties of the Alpha particle

Answer 2

Large mass
Very high Density
Small volume
Positive charge

Question 3

What did Rutherford expect to happen when he conducted the gold foil experiment?

Answer 3

To summarise, they expected;
1 – Little to no deflection.
2 – A very small loss in Ke.
3 – No loss of intensity

Question 4

What experiment did Rutherford conduct?

Answer 4

Ernest Rutherford got two undergrads to perform some experiments for him. He fired alpha particles at a very thin sheet of gold foil.

• Had the plum pudding model been true, the alpha
  particles should pass straight through a material with;
• No change in direction;
• Very little loss in kinetic energy.
• No drop in intensity

Question 5

What actually happened when Rutherford conducted the gold foil experiment

Answer 5

There was a drop in intensity. Also, the α particles that were detected had no drop in their Kinetic energy

Question 6

What were the results of Rutherford putting the gold foil on a moveable track.

Answer 6

The particles were spread out all over the
vacuum chamber right through 180 degrees

Most particles were unaffected or had very slight deflections with no loss of kinetic energy.

Some had unexpectedly large deflections, a few had deflections even greater than 90◦

Most unexpectedly of all, a very small number had deflections of 180◦

Question 7

How did Rutherford find out were the missing alpha particles went?

Answer 7

Rutherford decided to put the detector on a moveable track to find out where the alpha particles were going, now that the detector was moveable, he could find the missing particles

Question 8

How did Rutherford explain his results?

Answer 8

1st of all, to explain the high number of non deflected particles that retained all or most of their kinetic energy, Rutherford concluded that the atom must contain mostly empty space.

2nd of all, to explain the particles that were deflected, Rutherford concluded there must be a region of the atom that was very small and yet contained all of the positive charge. This region did not recoil by much and thus it must contain most of the mass

3rd the atom has a neutral charge, so all the electrons must be in orbit around the nucleus.

Question 9

What is the Mass and Charge of a Proton, Neutron and Electron?

Answer 9

Particle Mass Charge
Proton 1 +1
Neutron 1 0
Electron 1/1840th -1

Question 10

So what does our current model of our atom look like and is called?

Answer 10

Our current model of the atom was formed by
Rutherford; The NUCLEAR MODEL

Look in book for Diagram

Question 11

What is the Mass number?

Answer 11

The number of protons plus the number of neutrons in a neutral atom.

Question 12

What is the Atomic number?

Answer 12

The number of protons (which is the same as number of electrons) in a neutral atom.

Question 13

What are Isotopes

Answer 13

Atoms of the same element with the same number of protons and a different number of neutrons.

Question 14

What are Radioisotopes?

Answer 14

Isotopes that are unstable and emit radiation to become more stable

Question 15

What happens when the repulsion of protons become larger than the attractive forces

Answer 15

The nucleus emits radioactive
radiation to become a more stable nucleus

Question 16

Which isotopes will be radioactive and how will we
know, can we predict how they will decay?

Answer 16

They answer lies in the number of protons in comparison
to the number of neutrons of an isotope. We can use this
graph. (look in book)

• To be stable, an isotope must lie on the stability line shown.
• If above or below, it will give off radiation to get closer to it, and hence be more stable .

Question 17

What happens when an atom’s nucleus decays and releases an Beta
particle,

Answer 17

When an atom’s nucleus decays and releases a beta particle, a neutron turns into a proton, which stays in the nucleus, and a high energy electron, which is emitted.

Mass number remains the same & atomic number increases by 1

The decayed atom has gained a proton and so has changed into a new element.

Question 17

What does an Alpha Particles consist of?

Answer 17

An alpha particle consists of two protons and two
neutrons. It is the same as a helium nucleus.

Question 18

What happens when an atom’s nucleus decays and releases an alpha particle,

Answer 18

When an atom’s nucleus decays and releases an alpha
particle, it loses two protons and two neutrons.

Atomic number decreases by 2 & mass number decreases by 4

The number of protons has changed, so the decayed atom
has changed into a new element.

Note total mass number and atomic number is conserved!

Question 19

What does a Beta Particle consist of?

Answer 19

An beta particle consists of a high energy electron,
which is emitted by the nucleus of the decaying atom.

Question 20

What is the law of conservation of Charge

Answer 20

Conservation of charge - in any process, charge before = charge after.

Question 21

What does Gamma particle consist of?

Answer 21

Gamma radiation is a form of electromagnetic radiation, not a type of particle.

Question 22

What happens when an atom’s nucleus decays and releases an Gamma particle,

Answer 22

When an atom’s nucleus decays and emits gamma radiation,
it releases energy in the form of electromagnetic radiation.

There is no change to the make up of the nucleus and so a new element is not formed.

Gamma rays are usually emitted with alpha or beta particles. For example, cobalt-60 decays releasing a beta particle. The nickel formed is still not stable and so emits gamma radiation.

Question 23

What is Ionisation

Answer 23

When an atom has sufficient energy, or indeed radiation
directed upon it, its electrons may be given sufficient
energy (the ionisation energy) to free electrons.

• This leaves a positively charged ion as it has lost an
  electron.

Question 24

How can radiation be detected?

Answer 24

The effects of radiation can be seen and so it can detected using instruments such as a Geiger-Müller tube. This is a device that can detect and measure radiation.

Radioactivity can also be detected by the presence of photographic film, which darkens when struck by radiation. This effect lead to the initial discovery of radioactivity more than one hundred years ago.

Question 25

What is the electric charge of a Alpha particle

Answer 25

+2

Question 26

What is the electric charge of a Beta particle

Answer 26

-1

Question 27

What is the Relative atomic mass of an Alpha Particle

Answer 27

4

Question 28

What is the electric charge of a Gamma particle

Answer 28

0

Question 29

What is the Relative atomic mass of an Beta Particle

Answer 29

1/1840

Question 30

What is the Relative atomic mass of a Gamma Particle

Answer 30

0

Question 31

What is the Penetrating power of an Alpha particle

Answer 31

Stopped by paper or a few
centimetres of air

Question 32

What is the Penetrating power of a Beta particle

Answer 32

Stopped by a few millimetres of
aluminium or several metres of
air

Question 33

What is the Penetrating power of a Gamma particle

Answer 33

Stopped by several centimetres of
lead or several metres of concrete

Question 34

What is the ionizing power of an Alpha particle

Answer 34

Strongly ionizing

Question 35

What is the ionizing power of a Beta particle

Answer 35

Weakly ionizing

Question 36

What is the ionizing power of a Gamma Particle

Answer 36

Very weakly ionizing

Question 37

What is the speed of an Alpha particle?

Answer 37

6 percent C

Question 38

What is the speed of an Beta particle?

Answer 38

90 percent C

Question 39

What is the speed of an Gamma particle?

Answer 39

C

Question 40

What does the symbol C stand for?

Answer 40

The speed of Light

Question 41

What is background activity?

Answer 41

Background radiation is the radiation all around us and is detected when no radioactive sources are present

Question 42

What are the main forms of background activity?

Answer 42

Background radiation main forms;

Radon gas – emitted from granite rock.’

Potassium – 40 from food is absorbed by our
body.

Cosmic rays from outer space.

Question 43

What are the dosage levels of background radiation like?

Answer 43

The dosage levels from these are safe and not aconcern.

However if we get exposed to dangerously high levels, the story is very much different.

Question 44

How do you measure the activity of the source?

Answer 44

When measuring the activity of a source, we
must ‘correct’ the count for background
radiation.

First – measure the background radiation 3
times for 1 minute, take average background
radiation.

Measure the activity for your source. You then
must take background count away from all your
readings.

Question 45

Table of finding the corrected Count

Answer 45

Look in book

Question 46

How does radiation go up the food chain?

Answer 46

Gas, living things and plants absorb radioactive materials from the soil which are then passed along the food chain

Question 47

What to homes in areas with high background radiation have to do?

Answer 47

Due to radon gas, homes are required to be well ventilated to remove the gas

Question 48

How does human behaviour expose us to radiation?

Answer 48

Medical X-rays
Radioactive waste from nuclear power plants
Nuclear fallout from nuclear weapon

Question 49

How are radioactive emissions dangerous?

Answer 49

They cause dangerous ionisations by removing electrons from atoms when this happens with molecules in living cells, the genetic material of a cell is damaged and the cell may become cancerous

Question 50

What happens if radiation is incident upon a living cell?

Answer 50

Radiation can ionise cells which causes cellular damage

If the exposure is high, it can kill the cell.

If the exposure is lower it can cause cancer.

The higher the exposure, the higher the risk of cancer.

Alpha is the most ionising radiation, gamma is the least.

Question 50

Why isn’t alpha radiation as dangerous as beta and gamma radiation if the radioactive source is outside the body?

Answer 50

It cannot pass through the skin and is unlikely to reach cells inside the body while beta and gamma radiation can penetrate the skin and cause damage to cells

Question 51

When can alpha radiation be dangerous to cells in the body?

Answer 51

If it is breathed in or swallowed

Question 52

What steps should be taken when handling radioactive sources to minimise the risk of those using them?

Answer 52

• Wearing protective clothing
• Keeping the source as far away as possible by using tongs
• being exposed to the source for as short a time as possible
• Keep the radioactive materials in lead-lined containers

Question 53

What is radioactive decay?

Answer 53

Radioactive decay is a spontaneous process that cannot be controlled and is not affected by temperature.

Question 54

What does the term half-life mean and what would happen if the half-life of the isotope iodine-131 was 8 days

Answer 54

The half-life of a radioactive element is the time that it takes half the atoms in a sample to decay.

For example, the half-life of the isotope iodine-131 is 8 days.

This means that after 8 days half the atoms in a sample of iodine-131 have decayed. 8 days later half the remaining atoms have decayed and so on.

Question 55

How is the half-life calculated from a decay curve?

Answer 55

Find the time taken for the activity to half in counts/s
Do this multiple times to find an average
This is the half- life of the radioactive sample

Look in book to see example

Question 56

How is radioactivity used in Industry?

Answer 56

They are used as tracers to find out what is happening inside an object without the need to break the object e.g.

To find the route of underground pipes using a gamma ray emitter

To control the thickness of metal as it is rolled into thin sheets

Gamma rays are used to sterilise plastic objects such as syringes

Radioactive isotopes are used to monitor the function of organs

Alpha radiation can be used in smoke alarms

Question 56

What particle is used in finding underground pipes, monitoring organs, smoke alarms and controlling metal thickness?

Answer 56

Gamma radiation is used in finding pipes and beta particles are used in monitoring organs and controlling the metal thickness and alpha radiation is used in smoke alarms

Question 57

How is radiation used to control metal thickness in a mill?

Answer 57

Look in book for diagram

A beta particle passes through the material and through to a detector and based on whether it can pass through or not we can decide if the material is too thick or not.

If the radiation cannot pass through the bottom roller moves up to make the material thinner and if the radiation passes through to easily the roller moves down and the materials becomes thicker.

Question 58

How is alpha radiation used in smoke alarm?

Answer 58

Look in book for diagram

Smoke alarms contain a weak source of alpha radiation as it ionizes a few cm into the air

If there is smoke present, it interacts with the ions produced by the the alpha particles and ionization is reduced. This means that less current is flowing through the air, which causes the alarm to sound

Question 59

What is nuclear fission?

Answer 59

Nuclear fission is the splitting of a large atomic nucleus into smaller nuclei.

After a slow moving neutron hits the nucleus the entire nucleus splits into two large fragments called daughter nuclei.

In addition to the ‘daughter’ products, two or three neutrons also explode out of the fission reaction and these can collide with other uranium nuclei to cause further fission reactions.

This is known as chain reaction

Question 60

What happens to the neutron during nuclear fission in a nuclear reactor?

Answer 60

In a nuclear reactor, a slow-moving neutron is absorbed into a nucleus (typically uranium-235). This causes the nucleus to become uranium-236, which is unstable.

Question 61

How is the energy produced by nuclear fission used in nuclear reactors?

Answer 61

Their energy is passed on to other components in the nuclear reactor, which is used to heat water to drive the turbines that turn the generators.

Question 62

Nuclear reactor diagram

Answer 62

Look in book for diagrams it explains it well

Question 63

What is the nuclear fuel used in nuclear reactors?

Answer 63

The uranium or plutonium isotope that will split when triggered by an incoming neutron. The fuel is held in rods so that the neutrons released will fly out and cause nuclear fission in other rods.

Question 64

What is the moderator used in nuclear reactors?

Answer 64

A graphite core, for example, slows the neutrons down so that they are more likely to be absorbed into a nearby fuel rod.

Question 65

What are the control rods used in nuclear reactors?

Answer 65

These are raised and lowered to stop neutrons from travelling between fuel rods and therefore change the speed of the chain reaction.

Question 66

What is the coolant used in nuclear reactors?

Answer 66

This is heated up by the energy released from the fission reactions and is used to boil water to drive turbines in the power station.

Question 67

Why do nuclear reactors have a concrete shield?

Answer 67

The daughter products of the fission reaction are radioactive and can be a hazard.

Question 68

Why are the features of a nuclear reactor controlled?

Answer 68

Many of the features of the reactor are designed to control the speed of the reaction and the temperature inside the shielding.

An uncontrolled fission reaction is the basis of an atomic bomb.

Question 69

Advantages of nuclear power stations

Answer 69

Produces no polluting gases.

Does not contribute to global warming.

Very low fuel costs.

Low fuel quantity reduces mining and transportation effects on environment.

High technology research required benefits other industries.

Power station has very long lifetime.

Question 70

Disadvantages of nuclear power stations

Answer 70

Waste is radioactive and safe disposal is very difficult and expensive.

Local thermal pollution from wastewater affects marine life.

Large-scale accidents can be catastrophic.

Public perception of nuclear power is negative.

Costs of building and safely decommissioning are very high.

Cannot react quickly to changes in electricity demand.

Question 71

What is nuclear fusion?

Answer 71

Nuclear fusion is when two small, light nuclei join together to make one heavier nucleus. Fusion reactions occur in stars where, for example, two hydrogen nuclei fuse together under high temperatures and pressure to form a nucleus of a helium isotope. Look in Book for diagram

Question 72

Where does nuclear fusion occur naturally?

Answer 72

There are a number of different nuclear fusion reactions happening in the Sun. The simplest is when four hydrogen nuclei become one helium nucleus.

Question 72

Why does nuclear fusion produce energy?

Answer 72

The combined mass of four hydrogen nuclei is 6.693 × 10-27 kilograms (kg). The mass of one helium nucleus is 6.645 × 10-27 kg. This means that there is a missing amount of mass equalling 0.048 × 10-27 kg.

The missing mass is converted to energy, which radiates away. This is seen happening in the Sun.

In all nuclear reactions, a small amount of the mass changes to energy. This may not seem like a lot of energy but this energy is a result of the fusion of only four hydrogen nuclei.

Question 73

Why is nuclear fusion difficult?

Answer 73

However, the issue with fusion is that it requires the fusing of nuclei, which are positive particles.

As two nuclei approach each other, they will repel because they have the same charge. The fusion of the nuclei has to happen under intense pressure and very high temperatures in order to force the nuclei together and overcome this electrostatic repulsion.

This need for a very high temperature and pressure makes it very difficult to build a practical and economic fusion power station. For fusion to occur at the lower pressures in a reactor on Earth, the temperature would need to be between 100 and 200 million degrees.

Question 74

Where has nuclear fusion been achieved on earth.

Answer 74

Fusion has been successfully achieved by scientists at the JET experiment near Oxford but so far they have been unable to create a financially viable reactor.

Question 75

How is gamma radiation used in industry?

Answer 75

Gamma rays are used in agriculture to kill the bacteria on food, prolonging its shelf life

Gamma radiation of food has many opponents but would be valuable in hot climates where refrigeration is not always possible

Question 76

What isotopes of hydrogen are used in nuclear fusion and their source?
Also why is fusion environmentally friendly?

Answer 76

That the isotopes of hydrogen,deuterium and tritium are widely available as the constituents of seawater and so are nearly inexhaustible; and

That fusion does not emit carbon dioxide or other greenhouse gases into the atmosphere as its major by-product is helium, an inert, non-toxic gas;

Question 77

How many more times energy is released from fusion than by burning coal or fission.

Answer 77

• fusing nuclei together in a controlled way releases four million times more energy per kg than a chemical reaction such as burning coal, oil or gas; and

• fusing nuclei together in a controlled way releases four times as much energy as nuclear fission reactions per kg;

Question 78

When may nuclear fusion become viable?

Answer 78

There are many difficulties to over come before nuclear fusion provides electricity on a commercial scale and it may be another 50 years before that happens

Question 79

Why are nuclear fusion reactors unviable?

Answer 79

Nuclear fusion reactors will be expensive to build, and the system used to contain them will be equally expensive because of the very high temperatures needed for the nuclei to fuse

Question 80

What work is being done to make nuclear fusion economically viable and how are multiple countries involve?

Answer 80

Demonstrate an appreciation of the work being carried out at the ITER project (International Thermonuclear Experimental Reactor) and an understanding that such research requires international co-operation.