P7 Radioactivity Flashcards
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 to the power of -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, 1 m, and unlimited, respectively
What are the equation symbols for alpha and beta particles?
alpha particles (α) beta particles (β) gamma rays (γ)
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 fussion occur?
an unstable nucleus absorbs a neutron, it splits into two smaller nuclei, and emits two or three neutrons plus gamma rays
