physics - radioactivity Flashcards
(36 cards)
How big is an atom?
Atoms are about 1 x 10^-10 m in diameter.
What is the structure of an atom?
Atoms are made up of a positively charged nucleus containing protons and neutrons surrounded by negatively charged electrons.
Where are the electrons in an atom?
Electrons are arranged at different distances from the nucleus in different energy levels.
What happens to electrons when electromagnetic radiation is absorbed?
Electrons move further from the nucleus to a higher energy level.
What happens to electrons when electromagnetic radiation is emitted?
Electrons move closer to the nucleus to a lower energy level.
What is an atom?
An atom has an equal number of electrons and protons, resulting in no overall electrical charge.
What notation is used to describe atomic nuclei?
All atoms of a particular element have the same number of protons (atomic number) and the total number of protons and neutrons is called the mass number.
What is an isotope?
Atoms of the same element with different numbers of neutrons are called isotopes.
How is an ion formed?
Atoms turn into positive ions if they lose one or more outer electron(s).
Why do scientists look for new evidence?
New experimental evidence may lead to a scientific model being changed or replaced.
How was our current model of the atom developed?
It evolved from the plum pudding model to the nuclear model due to discoveries by J.J. Thomson, Rutherford, Niels Bohr, and James Chadwick.
What is radioactive decay?
Radioactive decay is a random process where unstable atomic nuclei emit radiation as they change to become more stable.
What is activity in the context of radioactive decay?
Activity is the rate at which a source of unstable nuclei decays, measured in becquerel (Bq).
What are the types of nuclear radiation emitted?
The types of nuclear radiation may include:
* Alpha particles (α)
* Beta particles (β)
* Gamma rays (γ)
* Neutrons (n)
What are the penetrative properties of alpha particles?
Alpha particles are strongly ionising, have a short range in air, and are stopped by a thin sheet of paper.
What are the penetrative properties of beta particles?
Beta particles are less ionising and have a greater range in air, stopped by a few mm of aluminium.
What are the penetrative properties of gamma rays?
Gamma rays ionise weakly, have an unlimited range in air, and can be stopped by thick concrete or lead.
What are common uses for alpha particles?
Alpha particles can be used in smoke detectors.
What are common uses for beta particles?
Beta particles can be used to check the thickness of paper and thin metals.
What are common uses for gamma rays?
Gamma rays can be used to sterilise medical equipment, treat cancer, and find leaks in pipes.
What are nuclear equations used for?
Nuclear equations represent radioactive decay and may show changes in mass and/or charge of the nucleus.
What is the half-life of a substance?
The half-life is the time it takes for the number of nuclei of a radioactive isotope in a sample to halve.
How do you determine half-life from a graph?
Find half of the original value on the y-axis and draw lines to intersect the curve and the x-axis.
What is contamination?
Contamination is the unwanted presence of materials containing radioactive atoms on other materials.
