topic 7 - Radioactivity and particles Flashcards
what is a becquerel
unit for frequency of decay
structure of an atom
Atoms are made up of protons, neutrons and electrons.
Protons and neutrons are in the nucleus, electrons are in the shells
what is atomic number
number of protons in the nucleus of an atom.
what is mass number
the total number of protons and neutrons in the nucleus of an atom.
what is an isotope
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.
3 types of ionising radiation
Alpha (α), Beta (β) and Gamma (γ)
what is ionisation
when an atom loses or gains an electron, causing it to become an ion (an atom which is positively or negatively charged).
ionising power, range in air, what it’s stopped by and nature of radiation of alpha radiation
- strong
- a few cm
- paper or thin card
- helium nucleus
ionising power, range in air, what it’s stopped by and nature of radiation of beta radiation
- moderate
- about 1m
- 5 mm of aluminium
- fast moving electron
ionising power, range in air, what it’s stopped by and nature of radiation of gamma radiation
- very weak
- at least 1km
- 10 cm of lead
- electromagnetic wave
practical: investigating penetration powers of different types of radiation
- 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.
what happens in alpha decay
- 2 protons and 2 neutrons are lost.
- Mass number decreases by 4
- Atomic number decreases by 2
what happens in beta decay
- 1 neutron is converted to an electron (lost from the atom) and proton
- Mass number is unchanged
- Atomic number increases by 1
what is gamma decay
- Energy is lost from an atom in the form of an electromagnetic wave
- Mass number is unchanged
- Atomic number is unchanged
what is Geiger Müller detector
When connected to a counter, the detector will be able to measure radioactivity.
what is Photographic film
Radiation will cause photographic film to darken.
5 sources of background radiation from earth and space
- radon in air
- Granite in rocks
- Cosmic rays
- Medical equipment
- Food and drink
what happens to the activity of a radioactive source over time
The activity of a radioactive source decreases over a period of time
what does half-life mean
The Half-life is the time taken for the radioactivity of a specific isotope to fall to half its original value.
uses of radioactivity in industry and medicine
- 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
what is contamination
Occurs when material that contains radioactive atoms is deposited on materials, skin, clothing, or any place where it is not desired.
what is irradiation
The process by which an object is exposed to radiation.
danger of alpha sources and how to prevent
- heavy ionising radiation, but range is less than 1mm so it’s little problem if kept outside body
danger of beta sources and how to prevent
- medium ionising radiation, but range is a few cm in tissue, so keep away from body
danger of gamma sources and how to prevent
- little ionising radiation, but range is long. keep well away from body and use a lead vest if using.
what is nuclear fission
The process where heavy atoms are split into smaller, lighter atoms. This releases energy.
what is nuclear fusion
The process where lighter atoms are forced to join together to make heavier atoms. This releases energy.
what is radioactive decay
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.
what happens in the fission of U -235
- 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.
how can a chain reaction be set up if the neutrons produced by one fission strike other U-235 nuclei
- 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.
how does a moderator work
- 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
how do control rods work
- 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
what does shielding do
- Reactor vessel is made of steel and surrounded by a concrete layer about 5 meters thick.
- This prevents any radiation escaping, even neutrons.
what is the energy source for stars
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.
why doesn’t nuclear fusion occur at low temperatures and low pressure
- 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.
