An atom consist of a nucleus ,which have protons and neutrons, and electrons surrounding the nucleus.
Isotopes are atoms that have the same number of protons but different amount of neutrons.
Early model of the atom is the plum pudding model but was then disproved by Rutherford's nuclear model.
The nuclear model shows an atom having 3 subatomic particles.
It shows protons and neutrons at the centre in the nucleus which is very small. Electrons surround the nucleus in different energy levels.
Protons have +1 charge and 1 relative mass
Neutrons have 0 charge and 1 relative mass
Electrons have -1 charge and almost 0 mass.
The number of electrons in an atom is always the same as the number of protons.
Atoms are neutral but can gain or lose electrons.
They form ions which are charged particles
losing electrons makes it positive
gaining electrons makes it negative
The plum pudding model consists of a sphere of positively charged protons and electrons dotted around inside it.
Ernest Rutherford fired a beam of alpha particles at a very thin gold foil
the particles was repelled at different angles which meant that the positively charged particle was deflected by positively charge in the atom.
The atomic number of an element is the number of protons
Isotopes have the same number of protons but different atomic mass as they have different number of neutrons
Background radiation
It is radiation all around us. It comes from natural and artificial sources
Natural
Cosmic rays- radiation from space
Rocks- radioactive rocks that release radon gas 50%
Living things- plants absorb radioactive material and is passed in the food chain
Artificial around 15%
Radioactive waste
Nuclear fallout
X-ray machines
Photographic film
Goes darker when radiation absorbed
Contains different material for different radiation to penetrate them
Contains aluminium/ lead and an open area
Geiger muller tube
Detects radiation by absorbing radiation
Each time it absorbs radiation, it transmits an electrical pulse to a counting machine
It makes a clicking sound or display a count rate
The greater the radiation, the higher the count rate
Types of radiation
Alpha
Identical to a helium atom but does not have electrons
2 proton 2 neutrons
Beta
Electrons are emitted from the nucleus of a radioactive atoms when neutrons split forming protons and electrons
Gamma rays
These are electromagnetic radiation with a short wavelength.
Alpha radiation is the least penetration, it can be absorbed by just a piece of paper or skin
Beta radiation can penetrate air and paper but absorbed by a thin sheet of aluminium
Gamma radiation is the most penetrating and can penetrate air, paper and metal, it can only be stopped by centimetres of lead.
The thicker the substance the more radiation is absorbed, radiation becomes less intense the further the distance from the radioactive material.
Detecting radiation
Electric fields
Alpha particles are positively charged and beta particles are negatively charged.
Gamma is neutral.
Alpha particles are attracted to negatively charged plates (Cathode) and beta particles will be attracted to positively charged plates (anode)
The radiation are deflected by electric fields but gamma radiation is not deflected.
The radiation are also deflected by magnetic fields but gamma remain unaffected
Hazards
When radiation collide with living cells it damage them. If the nucleus is damaged, the DNA might alter and become cancerous. The cell would divide rapidly and cause health problems.
The greater the dose of radiation the more chance it will be that the cell will become cancerous.
With a very high dose it will kill the cell. This property is used to kill cancer cells and also microorganisms.
Inside body
Alpha particles are the most dangerous as they are easily absorbed by cells - the most ionising.
Beta and gamma radiation are not as dangerous as they are not as ionising and will usually pass through cells.
Outside body
Alpha particles are not as dangerous as it is unlikely to reach inside the body as the body is protected by skin which will absorb the alpha particle.
Beta and gamma radiation are the most dangerous as they can penetrate the skin and damage the cells inside.
Half Life
Radioactive atoms have unstable nuclei, they break down to change into a different type of atom.
It is not possible to predict when an individual atom decay but it is possible to measure how long it takes for the half of the nuclei of a piece of radioactive material to decay.
This is called the half life of the radioactive isotope.
It is the time it takes for the number of nuclei of the isotope in a sample to halve.
It is also the time it takes for the count rate to half.
Half life varies in different isotopes one can last millions of years but some can only last a few seconds.
Use
Radiation can be used in smoke detectors
sterilising medical instruments
killing cancer cells
dating rocks and materials
chemical tracers to help medical diagnosis
measuring thickness of material
Tracers
Radioactive chemicals are ingested into the body and it concentrate in damaged parts of the body.
Radiation detectors are placed outside the body and detect radiation emitted inside the body.
A computer build up an image of the inside.
It usually isn't harmful as the substance has a short half life so it cannot do much damage before it decays and it is not poisonous.
Beta and gamma radiation are used as they pass out of the body and are less likely be absorbed by sells than alpha particles.
Thickness of material
It is used to monitor and control the thickness of material such as paper, plastic and aluminium.
A thicker material absorbs more radiation so less radiation reaches the detector
the detector sends signal to the equipment which adjusts the thickness of the material
Smoke detectors
Smoke detectors contain an ionisation chamber which has a cathode and an anode which an alpha source emitter radioactive substance. The alpha particles ionise the air which produce the current as it causes a flow of charge. The substance has a long half life so it won't run out.
When there is smoke, the alpha particle is unable to ionise the smoke particles so the current drops. The electric circuit triggers the alarm.
Atomic mass = number of protons + neutrons
Atomic number = number of protons
Alpha decay
2 protons and 2 neutrons are lost when a nucleus emits an alpha particle
Atomic mass decreases by 4
atomic number decreases by 1.
Beta decay
A neutron changes into a proton and an electron.
The proton stays in the nucleus but the electron leaves as a beta particle
The atomic mass number stays the same
Atomic number increases by one
Nuclear fission
Nuclear fission means to split a nucleus.
Uranium -235 and plutonium-239 are most commonly used.
They must first absorb a neutron.
The nucleus splits into two smaller nuclei
The split releases 2 or 3 neutrons and energy is released
The neutrons released may be absorbed by other uranium or plutonium nuclei which causes them to split.
This is called a chain reaction.
Nuclear fusion
This is when two atomic nuclei join to make a large nucleus and this also releases energy.
Sun and starts use nuclear fusion.
Hydrogen nuclei join to form helium nuclei.
Hydrogen-1 join with hydrogen-1 to form helium-3
Alpha radiation is the least penetration, it can be absorbed by just a piece of paper or skin
Beta radiation can penetrate air and paper but absorbed by a thin sheet of aluminium
Gamma radiation is the most penetrating and can penetrate air, paper and metal, it can only be stopped by centimetres of lead.
The thicker the substance the more radiation is absorbed, radiation becomes less intense the further the distance from the radioactive material.
Detecting radiation
Electric fields
Alpha particles are positively charged and beta particles are negatively charged.
Gamma is neutral.
Alpha particles are attracted to negatively charged plates (Cathode) and beta particles will be attracted to positively charged plates (anode)
The radiation are deflected by electric fields but gamma radiation is not deflected.
The radiation are also deflected by magnetic fields but gamma remain unaffected
Hazards
When radiation collide with living cells it damage them. If the nucleus is damaged, the DNA might alter and become cancerous. The cell would divide rapidly and cause health problems.
The greater the dose of radiation the more chance it will be that the cell will become cancerous.
With a very high dose it will kill the cell. This property is used to kill cancer cells and also microorganisms.
Inside body
Alpha particles are the most dangerous as they are easily absorbed by cells - the most ionising.
Beta and gamma radiation are not as dangerous as they are not as ionising and will usually pass through cells.
Outside body
Alpha particles are not as dangerous as it is unlikely to reach inside the body as the body is protected by skin which will absorb the alpha particle.
Beta and gamma radiation are the most dangerous as they can penetrate the skin and damage the cells inside.
Half Life
Radioactive atoms have unstable nuclei, they break down to change into a different type of atom.
It is not possible to predict when an individual atom decay but it is possible to measure how long it takes for the half of the nuclei of a piece of radioactive material to decay.
This is called the half life of the radioactive isotope.
It is the time it takes for the number of nuclei of the isotope in a sample to halve.
It is also the time it takes for the count rate to half.
Half life varies in different isotopes one can last millions of years but some can only last a few seconds.
Use
Radiation can be used in smoke detectors
sterilising medical instruments
killing cancer cells
dating rocks and materials
chemical tracers to help medical diagnosis
measuring thickness of material
Tracers
Radioactive chemicals are ingested into the body and it concentrate in damaged parts of the body.
Radiation detectors are placed outside the body and detect radiation emitted inside the body.
A computer build up an image of the inside.
It usually isn't harmful as the substance has a short half life so it cannot do much damage before it decays and it is not poisonous.
Beta and gamma radiation are used as they pass out of the body and are less likely be absorbed by sells than alpha particles.
Thickness of material
It is used to monitor and control the thickness of material such as paper, plastic and aluminium.
A thicker material absorbs more radiation so less radiation reaches the detector
the detector sends signal to the equipment which adjusts the thickness of the material
Smoke detectors
Smoke detectors contain an ionisation chamber which has a cathode and an anode which an alpha source emitter radioactive substance. The alpha particles ionise the air which produce the current as it causes a flow of charge. The substance has a long half life so it won't run out.
When there is smoke, the alpha particle is unable to ionise the smoke particles so the current drops. The electric circuit triggers the alarm.
Atomic mass = number of protons + neutrons
Atomic number = number of protons
Alpha decay
2 protons and 2 neutrons are lost when a nucleus emits an alpha particle
Atomic mass decreases by 4
atomic number decreases by 1.
Beta decay
A neutron changes into a proton and an electron.
The proton stays in the nucleus but the electron leaves as a beta particle
The atomic mass number stays the same
Atomic number increases by one
Nuclear fission
Nuclear fission means to split a nucleus.
Uranium -235 and plutonium-239 are most commonly used.
They must first absorb a neutron.
The nucleus splits into two smaller nuclei
The split releases 2 or 3 neutrons and energy is released
The neutrons released may be absorbed by other uranium or plutonium nuclei which causes them to split.
This is called a chain reaction.
Nuclear fusion
This is when two atomic nuclei join to make a large nucleus and this also releases energy.
Sun and starts use nuclear fusion.
Hydrogen nuclei join to form helium nuclei.
Hydrogen-1 join with hydrogen-1 to form helium-3
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