Radioactivity (simpler) Flashcards
What did the discovery of electrons show scientists?
Atoms have an internal structure and are not spheres that cannot be divided as the ancient Greeks had believed
What was created after the discovery of electrons in 1897?
Plum pudding models
Atoms were a ball of positive charge with negative electrons embedded in it
What proved the plum pudding model wrong?
Alpha scattering experiment
What was the alpha scattering experiment?
Alpha particles (positive charge) fired at gold foil- only a few atoms thick
What happened during the alpha scattering experiment?
Most passed through the gold foil- this told scientists that the atoms are mainly empty space. This proved the plum pudding model wrong
Some were deflected- this told scientists that the centre of the atom must have a positive charge because the alpha particles came close to it and were repelled and changed direction
Some were bounced back- this told scientists that the that the centre of the atom must contain a great deal of mass. We call this the nucleus
What was the plum pudding model replaced with?
The nuclear model
What did the nuclear model show atoms as?
Mostly empty space
Positive centre
Negative electrons around edge
How was the nuclear model adjusted?
Bohr proposed electrons orbit the nucleus at specific distances in shells
scientists then discovered that the positive nucleus is due to protons
What was discovered after Bohr adjusted the nuclear model?
Protons- made nucleus positive
Chadwick discovered neutrons that make neutral charges in the nucleus
What happens to an electrons potential energy the further it is from the nucleus?
The further an electron from the nucleus, the greater its potential energy
How do electrons get excited?
An bound electron can be knocked from its lower orbit into a higher orbit by an electron that is free. This collision will raise it to a higher shell. The electron is in a state of excitation
What happens after an electron is in a state of excitation?
The electron is quickly drawn back toward the nucleus and returned to its original orbit. It will emit the energy it absorbed. Electromagnetic radiation carries this energy away
What are isotopes?
Atoms of the same element that have different numbers of neutrons. Some isotopes have an unstable nucleus
What does an unstable nucleus mean?
The isotope’s nucleus gives out radiation in order to become stable
Radioactive decay
The unstable nucleus of an isotope giving out radiation to become stable
Activity
The rate at which a source of unstable nuclei decay
How is the activity of a radioactive source measured?
A Geiger muller tube In becquerels (Bq) 1Bq= 1 decay per second
Control rate
The number of decays recorded each second by a detector
Why is count rate not the same as activity?
Background radiation
What happens if an isotope is radioactive?
Its nucleus decays and releases radiation
What are the 4 types of radiation given out by an unstable nucleus?
Alpha particles
Beta particles
Gamma radiation
Neutrons
Alpha particles features
Helium nucleus- 2 protons, 2 neutrons
Large
Travel 5cm in air before colliding with air particles and stopping
Stopped by a single sheet of paper
Strongly ionising- create a lot of ions when colliding with a material
Stopped by dead cells on the skin
Dangerous is inhaled or swallowed
What is a Beta particle?
An electron ejected at high speed from the nucleus
Formed inside nucleus when a neutron changes into a proton and an electron. The electron is then ejected
Characteristics of beta particles
Travel 15cm in air before stopping
Stopped by a few mm of aluminium
Quite ionising
Penetrates skin
What is gamma radiation?
A type of electromagnetic radiation from the nucleus
Characteristics of gamma rays
Travel several m in air
Stopped by several cm lead
Weakly ionising
Can penetrate the body but likely to pass straight through
What is ionisation?
When radiation collides with atoms, it can cause the atoms to lose electrons and form ions
What is the half life of a radioactive isotope?
The time it takes for half the number of nuclei of the isotopes in a sample to halve
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 irradiation?
Exposing an object to nuclear radiation
When an object is irradiated, why does it not become radioactive?
The object only comes into contact with the radiation, not the radioactive isotope itself
What can ionising radiation increase the risk of?
Cancer
What is gamma radiation used for?
Sterilising medical equipment
What can protect against alpha radiation?
Gloves
How can gamma and beta radiation be reduced?
Using lead aprons, walls and lead-glass screens
What do radiation monitors do?
Allow us to measure how much radiation has been received
Radioactive contamination
When unwanted radioactive isotopes end up on other materials
Why is radioactive contamination hazardous?
The radioactive atoms decay and emit radiation
