P4 Flashcards
What is the meaning of radioactive activity?
The number of unstable atoms that decay per second in a radioactive source
What is alpha radiation?
Alpha particles (two protons and two neutrons) emitted by unstable nuclei. It’s the most ionising but least penetrating
What can be used to stop alpha radiation?
A thin piece of paper
What is the atomic number?
The number of protons in an atom (sometimes called the proton number)
What is beta radiation?
A fast moving electrons emitted from unstable nuclei. It’s neither the most penetrating nor most ionising ray, and can be stopped by a sheet of aluminium
What is the count rate and how is it measured?
The Geiger-Muller Tube. It’s the number of counts per second
What is gamma radiation?
It’s an electromagnetic wave emitted from unstable nuclei in radioactive substances. It’s the most penetrating radiation and can be stopped by a thick wall of lead
What is the half life of a substance?
The average time taken for the number of nuclei of the isotope (or the mass of the isotope) in a sample to halve
What is ionisation?
Any process in which atoms become charged
What does it mean for a substance to be irradiated?
Exposed to radiation but it doesn’t become radioactive
What is the mass number of an atom?
The number of protons and neutrons
What is a moderator?
The substance in a nucleus reactor that slows down fission neutrons
What is nuclear fission?
Th process in which certain nuclei (U-235 and Pl-239) split into two fragments, releasing energy and two or three neutrons as a result
What is a nuclear fission reactor?
Reactors that release energy steadily due to the fission of a suitable isotope, such as Uranium-235
What is nuclear fusion?
The process where small nuclei are forced together to fuse and form a larger nucleus
What is a reactor core?
The thick steel vessel used to contain fuel rods, control rods and the moderator in a nuclear fission reactor
What is radioactive contamination?
The unwanted presence of materials containing radioactive atoms on other materials
What s the use of alpha radiation?
Smoke detectors- they send alpha particles across a gap which ionises the air so there’s a current across the gap. Smoke absorbs the current so the alarm is triggered when there isn’t a current
What are the uses of beta radiation?
Thickness monitoring- if the sheet doesn’t detect particles, it can tell you the right thickness of something
Leak detection- a radioactive tracer is added. If there is a leak, the count rate will increase
What are the uses of gamma radiation?
Irradiating food- cobalt-60 is a gamma emitter that is used to sterilises food because it kills the bacteria on it
What does it mean for something to be ionising?
It’s got an ability to create ions
What does it mean for something to be penetrating?
The ability for radiation to pass through substances
What are fuel rods made out of and why?
Made up of 2-3% of U-235. This ensures that there isn’t too many chain reactions
What is a chain reaction?
The process of neutrons emitted from fission reactions being absorbed by larger, more unstable nuclei which results in more fission
What is background radiation?
Radiation that is found in small quantities all around us and originates from natural sources such as rocks and cosmic rays, as well as from man-made sources such as nuclear weapons testing and accidents.
What are nuclear explosions?
Uncontrolled chain reactions, meaning large amounts of energy are produced in short periods of time
What is spontaneous fission?
The occurrence of nuclear fission without a neutron. It’s very rare
What are moderators and constant in a nuclear reactor?
Water or graphite- it slows down the neutrons for a successful fission reaction because it must be moving at the right pace for fission to occur
What do control rods do?
They absorb neutrons and are made of boron or cadmium. They can also be moved up and down- if lifted up, it speeds up the reaction due to less neutrons being absorbed and vice versa (lowered down to slow down reactions due to more neutrons being absorbed)
What are the uses of nuclear radiation in medicine?
Medical tracers and radiotherapy
Why is it important that the tracers and isotopes used in medicine have short half lives?
Tracers- so they only emit radiation for a short period and can stop being harmful
Isotopes- so they don’t emit radiation for too long
Why is it important that the tracers and isotopes used in medicine have short half lives?
Tracers- so they only emit radiation for a short period and can stop being harmful
Isotopes- so they don’t emit radiation for too long
Can radioactive decay be predicted?
No, it’s a completely random process
