P7 Atomic Structure Flashcards
What is the entire history of the atom
Atoms thought to be tiny undividable spheres
Discovery of electron led to plum pudding model
Alpha particle scattering experiment led to the discovery of nuceus, nuclear model replaced plum pudding
Niels Bohr suggested electrons orbit the nucleus in specific shells
Proton was later discovered after it was suggested that the positive charge of nucleus could be seperated into subatomic particles
James Chadwick provided evidence of neutrons
What is radioactive decay
When an unstable nuclei gives out radiation as it changes to become more stable
What is activity and what is it measured in
The rate at which a source of unstable nuclei decays
Measured in Becquerels ( Bq )
What is count rate
The number of decays recorded each second by a detector ( eg geiger - muller tube )
What are the compositions of: an alpha particle, a beta particle, a gamma ray
Alpha particle: 2 neutrons and 2 protons
Beta particle: a high speed electron efected from the nucleus as a neutron turns into a proton
Gamma ray: electromagnetic radiation from the nucleus
What are alpha, beta and gamma stopped by
Alpha: 5cm of air or thin paper
Beta: thin aluminium
Gamma: thick lead or thick concrete
What are the range in air of alpha, beta and gamma
Alpha: 5cm
Beta: 1m
Gamma: unlimited
What is the ionising power of alpha, beta and gamma
Alpha: most
Beta: medium
Gamma: least
What is the equation for alpha decay
A A-4 4
X = D + α
Z Z-2 2
What is the equation for beta decay
A. A. 0
X = D + B
Z. Z+1. -1
What is the halflife of a radioactive isotope
The time it takes for the number of radioactive nuclei of the isotope in a sample to halve, or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level
What is radioactive contamination
The unwanted presence of materials containing radioactive atoms on other materials
What is irradiation
Irradiation is the process of exposing an object to nuclear radiation. The irradiated object does not become radioactive
What are some examples of background radiation
natural sources such as rocks and cosmic rays from space
man-made sources such as the fallout from nuclear weapons
testing and nuclear accidents.
