Definitions for the 'P6: Radioactivity' topic of the GCSE OCR Gateway Spec.
Fully detailed, easy to understand & perfect definitions for use in the exams.
Alpha particle- a positively charged particle consisting of two protons and two neutrons.
They are highly ionising, but can be stopped by a few centimetres of air.
Atomic number- the number of protons found in an atom of a specific element. Each
element has a different atomic number.
Beta particle- a high speed electron that a nucleus emits when a neutron converts into a
proton. They are ionising but can be stopped by a thin sheet of aluminium.
Chain reaction- the process of neutrons released by a fission reaction, being absorbed by
another unstable, large nuclei, and inducing further fission.
Contamination- the unwanted presence of radioactive atoms on other materials. It is
hazardous due to the decay of the contaminating atoms.
Electrons- a negatively charged subatomic particle of the atom, that are found in different
energy levels, around the nucleus.
Energy levels- the stable states in which electrons are found in around a nucleus. Electrons
can transition to a higher energy level through the absorption of electromagnetic radiation
and can transition to a lower energy level through the emission of electromagnetic
radiation.
Fission products- fission produces two smaller nuclei, two or three neutrons and gamma
rays. All these products are released with kinetic energy.
Gamma ray- electromagnetic radiation emitted from a nucleus. They have a very high
penetrating power and require several centimetre of lead to absorb them.
Geiger-Muller tube- a device used to detect ionising radiation.
Half-life- the time it takes for the number of unstable nuclei of an isotope in a sample to
halve, or the time it takes for the initial count rate of a sample of the isotope to halve.
Ions- atoms with a resultant charge due to the loss or gain of electrons.
Irradiation- the process of an object being exposed to nuclear radiation. The object doesn’t
become radioactive.
Isotopes- atoms with the same number of protons but different numbers of neutrons. The
atomic number is the same, but the mass number is different.
Mass number- the number of protons and neutrons in an atom.
Negative ions- atoms that gained electrons and so have a resultant negative charge.
Neutrons- a neutrally charged subatomic particle of the nucleus.
Nuclear fission- the splitting of a large and unstable nucleus into two smaller and more
stable nuclei to produce energy. This is the method currently used in nuclear power
stations.
Nuclear fusion- the joining of two small, light nuclei to form a larger, heavier one and
release energy. It cannot happen at low pressures and temperatures since in these
conditions the electrostatic repulsion of protons in the nucleus cannot be overcome.
PET scanner- a medical imaging device that uses radioactive tracers and detectors to form
internal body images.
Positive ions- atoms that have lost electrons and so have a resultant positive charge.
Protons- a positively charged subatomic particle of the nucleus.
Radioactive decay- the random process involving unstable nuclei emitting radiation to
become more stable.
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