Section 7 - Radioactivity and Particles Flashcards
Describe the structure of an atom
There is a proton (+) and neutrons in the nucleus of an atom. Electrons (-) orbit on shells (or orbitals) around the nucleus
What does atomic number mean?
The number of protons in the nucleus
What does mass number mean?
The total number of protons and neutrons in the nucleus
What is an isotope?
Isotopes are atoms with the same atomic number, but different mass number
Describe the characteristics of an alpha particle
They are made up of 2 protons and 2 neutrons - helium nucleus and are highly ionising
They don’t penetrate far into materials (can’t penetrate paper)
They decrease the atomic number by 2 and mass number by 4
Describe the characteristics of a beta particle
A beta particle is an electron which has been emitted from the nucleus of an atom when a neutron turns into a proton and an electron.
They penetrate moderately (won’t penetrate aluminium) and ionise moderately
They increase the atomic number by 1
Describe the characteristics of a gamma ray
They can penetrate a long way into materials (won’t penetrate lead)
They are weakly ionising.
They have no charge and no effect on the atomic or mass number
It occurs after beta or alpha decay
How can a Geiger-Muller detector be used to detect ionising radiations?
Geiger-Muller detectors beep when ionising radiation is detected. The faster the beep, the more ionising it is.
How can photographic film be used to detect ionising radiation?
Photographic film is white and absorbs radiations. When it does, it will turn black
What are some sources of background radiation?
- Substances on Earth - air, food, building materials, soil, rocks …
- Radiation from space (mostly from the Sun)
- Living things - there is a little bit of radioactive material in all living things
What happens to the activity of a radioactive source over a period of time?
It decreases. Each time decay happens, a little bit more of the radioactive nucleus has disappeared. As the unstable nuclei disappear, the activity as a whole will decrease.
The amount of radiation given out is measured in becquerels
What is half-life?
Half-life is the time taken for half of the radioactive atoms now present to decay
How is radioactivity used in non-medical tracers?
A radioactive source is put into a system (like a piping network). It will build up where there is a blockage and this can be detected.
How is radioactivity used in medical tracers?
A radioactive source is put into a body and will build up at a blockage so the area of the problem can be detected
How is radioactivity used in radiotherapy?
Radiation is used to destroy unwanted cells (cancerous cells)
How is radioactivity used in radioactive dating / carbon dating?
The amount of radiation from an object is measured. the half life of the carbon is then used to see how old the object is.
Archaeologists use this to tell the age of an object
What are the dangers of ionising radiation?
- It can cause mutations in living organisms
- It can damage cells and tissues
- The problems arising in the disposal of radioactive products
How does ionising radiation cause mutations in living organisms?
Radiation can damage the structure of a cells DNA. When the cells replicate, the changes will be passed on. this can be how cancer is caused
How does ionising radiation cause damage to cells and tissues?
Atoms can be changed by radiation. This prohibits them functioning properly. This can mean cells and tissues are damaged
How does ionising radiation cause problems arising the disposal of radioactive waste?
The waste emits radiation that can be dangerous.
If the waste is put into water, it can poison ecosystems.
Radioactive waste tends to be buried underground with the thinking that it would be less harmful.
What precautions can be made to make an individual safer from ionising radiation?
Minimise your exposure:
- never allow skin contact (use tongs)
- store radioactive sources in a sealed lead box
For those working with radioactive materials:
- use lead aprons and stand behind lead screens
- industrial nuclear workers wear full protective suits
- workers can also use remote-controlled robot arms to carry out tasks
Describe the results of Geiger and Marsden’s experiments with gold foil and alpha particles
Alpha radiation was beamed at a sheet of gold foil. A sheet of zinc sulphide surrounding the foil showed where the alpha particles ended up.
A few went straight through, but many were deflected at angles.
Describe Rutherford’s nuclear model of the atom
A central nucleus with positive protons and neutral neutrons surrounds by orbiting negative electrons
Explain the results of Geiger and Marsden’s experiments with gold foil and alpha particles
Previously, the plum pudding model was used (a positive sphere contained with negative electrons dotted inside). However, if this was true, then the alpha particles would have gone straight through the gold foil
Instead, there are positive alpha particles being repelled by a positive charge and others were going through the spaces between the charged areas.. The faster the they hit the positive charge, the faster they were repelled.
What is nuclear fission and what does it produce?
Nuclear fission is the splitting of a nucleus of Uranium-235 by collision with a neutron, which releases kinetic energy.
It produces two daughter nuclei and a small number of neutrons
How can a chain reaction be set up during the fission of U-235?
If the neutrons (a product of a fission reaction) strikes another U-235 nuclei to cause another fission reaction
What role do the control rods and moderators play during the fission reaction of U-235?
Control Rods (boron) - limit the rate of fission by absorbing excess neutrons
Moderator (graphite or water) - slows neutrons so that they can successfully collide with uranium nuclei and sustain the chain reaction
