Radioactivity Flashcards
(43 cards)
What is the basic structure of an atom?
A positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons arranged in fixed energy levels
When might the energy level of an electron change?
- When the atom absorbs electromagnetic radiation the electrons move to a higher energy level and further away from the nucleus
- When electromagnetic radiation is emitted the electron drops to a lower energy level
What is the atomic mass number/nucleon number of an atom?
The total number of protons and neutrons in an atom
What is the atomic number of an atom
The number of protons in an atom
What are isotopes
atoms of an element that have the same number of protons but different number of neutrons (same atomic number but different mass number)
What is ionising radiation
radiation that knocks electrons off atoms, creating positive ions. the ionising power of a radiation source is how easily it can do this
What did John Dalton think about the atom
that matter was made up of tiny spheres (atoms) that couldn’t be broken up and he reckoned that each element was made up of a different type of atom
Describe the plum pudding model
J.J Thomson suggested that atoms were spheres of positive charge with tiny negative electrons stuck in them (like the fruit in a plum pudding)
What would the results of Rutherford and Marsden’s experiment have been if the plum pudding model was correct?
the heavy positively charge alpha particles would not have passed straight through the thin gold foil
What did Rutherford and Marsden’s results show
Most particles passed straight through the foil and some alpha particles were deflected, so they must have come close to a concentration of charge
What did the alpha scattering experiment results shown
- Most particles passed through so the atom is mostly empty space
- Some deflected back so the mass of the atom was concentrated in a central nucleus which was positively charged
- Atoms are neutral so if the nucleus is positive, electrons must be on the outside of the atom
Describe Bohr’s model of the atom
Niel Bohr adapted this nuclear model by suggesting that electrons orbit the nucleus at specific distances called energy levels
What did later experiments (after Bohr) show about the atom
Later experiments led to the idea that the positive charge of the nucleus can be divided into a whole number of smaller particles with the same number of positive charge (protons)
What did Chadwick discover?
Chadwick’s experiments provided evidence that within the nucleus there was another particle called the ‘neutron’
What happens to unstable atomic nuclei
In some atoms binding energy is not strong enough to hold the nucleus together so the nuclei of these atoms are unstable. Unstable nuclei emit radiation (protons and neutrons and energy) in an attempt to become more stable. Emitting this radiation is spontaneous and a random process
What is the activity of a radioactive source and what is it measured in
the activity is the rate at which it is decayed and is measured in becquerels (Bq). One becquerel is equal to one decay per second. The count-rate is the number of decays recorded each second by a detector - a Geiger-Muller tube
What are the three types of nuclear radiation?
Alpha
Beta ß
Gamma
What is an alpha particle
Two neutrons and two protons ejected from the nucleus.
What are the ionising powers of the different radiations
Alpha - strong ionising power
Beta - reasonable ionising power
Gamma - weak ionising power
How far do alpha particles penetrate and what are they stopped by
They only travel a few centimetres in air and are absorbed by a few centimetres of air or a thin sheet of paper
What are beta particles
A fast-moving (high-energy) electrons that is emitted from the nucleus of an atom. This is made when a neutron changes into a neutron and a proton and the proton stays in the nucleus and the electron is emitted
How far does beta radiation penetrate and what absorbs it
They penetrate moderately far in air and have a range of a few metres (5-10m). They are absorbed by 3-5mm of aluminium
What is gamma radiation
Gamma rays are waves of electromagnetic radiation released by the nucleus
How far does gamma radiation penetrate and what stops it
They penetrate very far into materials without being stopped and travel a long distance in air. They are absorbed by many centimetres of lead or many metres of concrete.
