Radioactivity Flashcards
Define nuclear fission.
When large, unstable nuclei split into smaller nuclei, releasing energy in the form of radiation. This normally happens when the nucleus absorbs a neutron.
Define nuclear fusion.
Two light nuclei are joined together to form a heavier nucleus. Some of the mass of the nuclei is converted into energy, which is released as radiation.
Which process releases the energy in stars?
Nuclear fusion.
What causes nuclear fission?
Nuclear fission is triggered when a neutron is absorbed by a nucleus. It can also happen spontaneously, but this is incredibly rare.
What does a nucleus release during nuclear fission?
Gamma radiation, two or three neutrons and two identical daughter nuclei are formed. Energy is also released by the reaction. All of the fission products have kinetic energy.
How is nuclear fission a chain reaction?
For nuclear fission to occur, a nucleus must absorb a neutron. When a nucleus splits during nuclear fission, alongside forming two identical daughter nuclei, it releases gamma radiation and two or three neutrons. These neutrons go on to be absorbed by other nuclei, which then undergo nuclear fission and repeat this process. This is a continuous chain reaction.
Why does fusion produce so much energy?
Some of the mass of the original nuclei is being transferred to energy instead of the new nucleus.
What is controlled nuclear fission used for, and why?
Controlled nuclear fission is used to generate electricity in nuclear reactors, as the chain reaction releases a lot of energy very quickly. Controlling this chain reaction allows us to convert the kinetic energy released to electricity.
Give two uses of nuclear fission.
Nuclear weapons (uncontrolled)
Generating electricity (controlled)
Why would nuclear fusion be beneficial as an alternative energy source?
It produces great amounts of energy quickly. The hydrogen required for it to occur is easy to obtain. But most importantly, it does not produce any radioactive waste.
Why can’t nuclear fusion happen on earth?
It can only occur at extreme temperatures and pressures, the likes of which cannot be achieved on Earth. (10 000 000°C)
How can we work out the energy released by nuclear fusion?
With Einstein’s E=mc^2 formula.
Define an isotope.
Atoms of the same element with the same number of protons and electrons, but different numbers of neutrons.
What is radioactive decay? Is it controlled or random?
Radioactive decay is when some isotopes’ nuclei are unstable, so they release forms of radiation to become stable. It is a completely random process.
What are the three forms of radiation?
Alpha, Beta, Gamma.
What does Alpha radiation consist of?
Alpha particles are two protons and two neutrons - the same as a helium nucleus.
What does a beta particle consist of?
A beta oarticle is a single electron ejected from the nucleus at very high speed.
How is a beta particle formed?
It is formed when a neutron changes into a proton and an electron.
What is gamma radiation?
It is an electromagnetic wave.
State the properties of an Alpha particle.
- Large
- Can travel up to 5cm in air before they collide with particles and stop
- Very high ionising power
- Very low penetrative power. Can be stopped by a sheet of paper.
State the properties of a Beta particle.
- Can travel up to 15cm in air.
- Quite strongly ionising, but not very.
- Relatively strong penetrative power, stopped by a few millimeters of aluminium.
State the properties of Gamma rays.
- Weakly ionising.
- Can travel several metres in air before stopping.
- Highest penetrative power, stopped by a few centimeters of lead.
What can each form of radiation be stopped by?
Alpha particles- at sheet of paper.
Beta particles- a few millimeters of aluminium.
Gamma rays - a few centimeters of lead.
What is the change to the element’s atomic number and mass number if it decays and releases gamma radiation?
There is no change. They are just an electromagnetic wave.
What is the change to an element’s atomic number and mass number if it decays and releases a beta particle?
Nothing is added to the mass number as a neutron forms a protons and an electron, so the number of protons and neutrons hasn’t changed. However, 1 is added to the atomic number as another proton has been formed.
What happens to an element’s atomic number and mass number is it decays and releases an alpha particle?
Atomic number - decreases by 2
Mass number - decreases by 4
State the two definitions of half-life.
The half-life of a radioactive isotope is the time taken for the number of nuclei of the isotope in a sample to halve.
The half-life of a radioactive isotope is also the time taken for the count rate (activity) to fall to half its initial reading.
A radioactive isotope has a half-life of 15 days and an initial count rate of 200 counts for second. Determine the count rate after 45 days.
Half-life = 15 days
45 ÷ 15 = 3, so 3 half-lives have been spent.
200 ÷ 2 = 100
100 ÷ 2 = 50
50 ÷ 2 = 25
The count rate will be 25.
Why are sources with longer half-lives more dangerous?
A longer half-life will mean that the source will be able to ionise its surroundings for longer, as its activity (count rate) will take much longer to fall.
Define contamination.
When unwanted radioactive isotopes end up on other materials.
Define irradiation.
Irradiation - when an object is exposed to nuclear radiation.
Which type of radiation would be best for sterilising medical tools?
Gamma rays. They have the highest penetrative power, so would kill the most bacteria present on the tool.
How are workers kept safe from radiation?
When tools are sterilised, workers are kept safe with lead shields.
Radiation monitors will measure how much radiation a person has received, and can tell us if someone has received too much. If this is the case, then that person will stop working with radiation.
Why don’t objects become radioactive if they are irradiated?
They don’t become radioactive if they are irradiated because they only come into contact with the radiation and not the radioactive isotope itself.
Why must precautions be taken if people regularly work with radioactive isotopes?
Radioactive isotopes can emit ionising radiation. Ionising radiation increases the risk of cancer in humans, which is highly dangerous. This means that workers must be protected if they regularly work with radioactive substances to prevent the accumulation of ionising radiation in their body over time and by extension the risk of cancer.
Which kinds of radiation can penetrate into the body?
Beta and Gamma. Gamma rays are able to pass straight through.
Alpha particles are too large, and are blocked by dead cells on the skin’s surface.
How does ionising radiation cause cancer?
Alpha particles are extremely ionising. This is because they can crash into living cells and damage their DNA - which can cause mutations and, from that, cancer.
Give two natural sources of radiation.
- Cosmic rays from space. These are very high-energy particles that trav from space and crash into the Earth’s atmosphere. They come from supernovae.
- Certain rocks, such as granite, are radioactive.
Give two man-made sources of background radiation.
- Fall out from nuclear weapons.
- Nuclear accidents.
What is used to measure count rate?
A Geiger-Muller tube.
How would nuclear radiation be used to explore internal tissue?
They would be able to explore internal organs using a tracer. The patient would swallow the tracer and a radiation monitor would be used to measure how much radiation from the radioactive isotope ingested the afflicted area absorbs. A diagnosis would be produced from this.
How would nuclear radiation be used to control or destroy unwanted tissue, e.g. in cancer?
In radiotherapy, certains cancers are destroyed using ionising radiation. Gamma rays are passed through the body and destroy the tumour.
What is a disadvantage to radiotherapy?
The gamma rays passed through the patient could also damage healthy tissue. This is amended, however, by the radiation being targeted precisely to the tumour.
Explain why some atoms emit radiation.
Most isotopes are unstable, meaning that over time they decay into atoms of other elements to become stable.They emit radiation as this happens.
