Radioactivity Flashcards
(35 cards)
Describe the basic structure of an atom.
Nucleus containing protons and neutrons, around which electrons orbit in fixed energy levels/shells.
Describe the plum pudding model of the atom.
Sphere of positive charge with negative electrons embedded in it.
What charges do protons, neutrons, and electrons carry?
Protons = positive, neutrons = no charge, electrons = negative.
Why do atoms have no overall charge?
Equal numbers of positive protons and negative electrons.
What is the radius of an atom?
Around 1x10-10 m.
What is ionisation?
Process which adds or removes electrons from an atom.
What is the mass number of an element?
Number of protons + number of neutrons.
Which particle do atoms of the same element always have the same number of?
Protons.
What are isotopes?
Atoms of the same element (same number of protons) with different numbers of neutrons.
What were the two main conclusions from the alpha particle scattering experiment?
Most of the mass of an atom is concentrated in the nucleus; nucleus is positively charged.
What are the three types of nuclear radiation?
Alpha, beta, and gamma.
Which type of nuclear radiation is the most ionising?
Alpha.
What is the range in air of alpha, beta, and gamma radiation?
A few cm, 1m, and unlimited, respectively.
What are the equation symbols for alpha and beta particles?
α and β.
What is meant by the half-life of a radioactive source?
Time taken for half the unstable nuclei to decay or the time taken for the count rate to halve.
What is radioactive contamination?
Unwanted presence of substances containing radioactive atoms on or in other materials.
Where does background radiation come from?
Rocks, cosmic rays, fallout from nuclear weapons testing, nuclear accidents.
Why are gamma-emitting sources used for medical tracers and imaging?
Gamma rays pass through the body without causing much damage to cells.
What is nuclear fusion?
When two light nuclei join to make a heavier one.
How does nuclear fission occur?
An unstable nucleus absorbs a neutron, it splits into two smaller nuclei, and emits two or three neutrons plus gamma rays.
The ionising power of alpha beta and gamma particles
Alpha -highest
Beta-high
Gamma-low
Dalton’s model description
A tiny solid neutral sphere that cannot be divided into small parts
What changes in the nucleus when different types of radiation happen?
Alpha-nucleus loses two protons and two electrons
Beta-a neutron changes into a proton and an electron
Gamma-some energy is transferred away from the nucleus
What is an example of a detector of rate of decay of an unstable nucleus?
Geiger-Müller tubes
