topic 7 - Radioactivity and particles

Question 1

what is a becquerel

Answer 1

unit for frequency of decay

Question 2

structure of an atom

Answer 2

Atoms are made up of protons, neutrons and electrons.

Protons and neutrons are in the nucleus, electrons are in the shells

Question 3

what is atomic number

Answer 3

number of protons in the nucleus of an atom.

Question 4

what is mass number

Answer 4

the total number of protons and neutrons in the nucleus of an atom.

Question 5

what is an isotope

Answer 5

an atom of the same element, i.e. it has the same number of protons/same atomic number, but has a different number of neutrons/different mass number.

Question 6

3 types of ionising radiation

Answer 6

Alpha (α), Beta (β) and Gamma (γ)

Question 7

what is ionisation

Answer 7

when an atom loses or gains an electron, causing it to become an ion (an atom which is positively or negatively charged).

Question 8

ionising power, range in air, what it’s stopped by and nature of radiation of alpha radiation

Answer 8

• strong
• a few cm
• paper or thin card
• helium nucleus

Question 9

ionising power, range in air, what it’s stopped by and nature of radiation of beta radiation

Answer 9

• moderate
• about 1m
• 5 mm of aluminium
• fast moving electron

Question 10

ionising power, range in air, what it’s stopped by and nature of radiation of gamma radiation

Answer 10

• very weak
• at least 1km
• 10 cm of lead
• electromagnetic wave

Question 11

practical: investigating penetration powers of different types of radiation

Answer 11

• Detect using a Geiger Müller Tube.
• Try the three different materials in order, paper then aluminium then lead.
• Count rate will significantly decrease if radiation is stopped.

Question 12

what happens in alpha decay

Answer 12

• 2 protons and 2 neutrons are lost.
• Mass number decreases by 4
• Atomic number decreases by 2

Question 13

what happens in beta decay

Answer 13

• 1 neutron is converted to an electron (lost from the atom) and proton
• Mass number is unchanged
• Atomic number increases by 1

Question 14

what is gamma decay

Answer 14

• Energy is lost from an atom in the form of an electromagnetic wave
• Mass number is unchanged
• Atomic number is unchanged

Question 15

what is Geiger Müller detector

Answer 15

When connected to a counter, the detector will be able to measure radioactivity.

Question 16

what is Photographic film

Answer 16

Radiation will cause photographic film to darken.

Question 17

5 sources of background radiation from earth and space

Answer 17

• radon in air
• Granite in rocks
• Cosmic rays
• Medical equipment
• Food and drink

Question 18

what happens to the activity of a radioactive source over time

Answer 18

The activity of a radioactive source decreases over a period of time

Question 19

what does half-life mean

Answer 19

The Half-life is the time taken for the radioactivity of a specific isotope to fall to half its original value.

Question 20

uses of radioactivity in industry and medicine

Answer 20

• Medical tracer - radioactive tracer put in body, detector put around body, computer generates an image
• Radiotherapy - high doses of radiation are directed at cancer cells, cancer cells are killed
• Sterilisation - medical equipment irradiated, kills all living matter on tools (e.g. bacteria)
• Gauging - coal absorbs a lot of radiation, if only a small amount of radiation is detected back after it is reflected by what you are trying to gauge, lots of coal is present.
• Carbon dating

Question 21

what is contamination

Answer 21

Occurs when material that contains radioactive atoms is deposited on materials, skin, clothing, or any place where it is not desired.

Question 22

what is irradiation

Answer 22

The process by which an object is exposed to radiation.

Question 23

danger of alpha sources and how to prevent

Answer 23

• heavy ionising radiation, but range is less than 1mm so it’s little problem if kept outside body

Question 24

danger of beta sources and how to prevent

Answer 24

• medium ionising radiation, but range is a few cm in tissue, so keep away from body

Question 25

danger of gamma sources and how to prevent

Answer 25

• little ionising radiation, but range is long. keep well away from body and use a lead vest if using.

Question 26

what is nuclear fission

Answer 26

The process where heavy atoms are split into smaller, lighter atoms. This releases energy.

Question 27

what is nuclear fusion

Answer 27

The process where lighter atoms are forced to join together to make heavier atoms. This releases energy.

Question 28

what is radioactive decay

Answer 28

Within the core of the Earth, radioactive isotopes of elements such as uranium, thorium and potassium provide a large proportion of the heat within the Earth through radioactive decay.

Question 29

what happens in the fission of U -235

Answer 29

• a slow moving neutron is absorbed by a uranium 235 nucleus.
• The resulting uranium 236 nucleus is unstable.
• It splits to form two smaller daughter nuclei, three neutrons and gamma radiation.

Question 30

how can a chain reaction be set up if the neutrons produced by one fission strike other U-235 nuclei

Answer 30

• The three neutrons produced by the fission may hit other nuclei of uranium 235, causing the process to repeat.
• For a chain reaction to occur, there is a minimum mass of uranium 235 required. This is known as the critical mass.

Question 31

how does a moderator work

Answer 31

• the purpose of the moderator is to absorb some of the kinetic energy of the neutrons to slow them down.
• this is because slow neutrons are more easily absorbed by uranium 235 nuclei.
• made of graphite

Question 32

how do control rods work

Answer 32

• The purpose of the control rods is to absorb neutrons and completely remove them from the fission process.
• Helps adjust the rate of nuclear fission in the reactor.
• made of boron or cadmium

Question 33

what does shielding do

Answer 33

• Reactor vessel is made of steel and surrounded by a concrete layer about 5 meters thick.
• This prevents any radiation escaping, even neutrons.

Question 34

what is the energy source for stars

Answer 34

Nuclear fusion is the source of energy for our sun and all stars.
In the case of the sun, it is typically hydrogen undergoing fusion to create helium.

Question 35

why doesn’t nuclear fusion occur at low temperatures and low pressure

Answer 35

• For nuclear fusion to occur, very high temperatures are required to overcome the repulsive force between the positively charged nuclei of each isotope.
• High pressures are also needed to increase the chance of fusion between the nuclei.