P2.5 Flashcards
Where do radioactive substances emit radiation from
The nuclei of their atoms all the time
What can new evidence cause
A theory to be re-evaluated
What are most atoms
Empty space
What is the basic structure of an atom
A small central nucleus composed of protons and neutrons surrounded by electrons
Why does an atom have no overall charge
The number of protons = the number of electrons
Where does some substances give out radiation
From the nuclei of their atoms all the time
Origins of background radiation
Rocks
Cosmic rays from space
Nuclear weapons test
Nuclear accidents
Nucleic structure of alpha particle
Same as helium
2 protons
2 neutrons
What is gamma radiation
Type of electromagnetic radiation
What is the difference between gamma with alpha and beta
Alpha and beta are deflected by both electric and magnetic fields
What is the difference between beta and alpha
Alpha are deflected less than beta and in opposite direction
Types of nuclear radiation
Beta
Alpha
Gamma
What is a half life of a radioactive isotope
The average time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate from a sample containing the isotope to fall to half its initial level
Who came up with the nuclear model of the atom
Rutherford and Marsden
Mass of an electron
1/2000
Examples of isotopes
Carbon 12 and Carbon14
How many stable isotopes of an element are there
One or two
What does it mean that an isotope is unstable
They are radioactive so they decay and give off radiation
What do radioactive substances spit out
One or more of alpha,beta and gamma radiation
What is background radiation
Radiation that is present all the time
Properties of alpha particles
Big
Heavy
Slow moving
What does it mean that an alpha particle is strongly ionising
They bash into a lot of atoms and knock electrons off them before they slow down which creates lots of ions
Why are alpha particles strongly ionising
They are big
What are beta particles
Electrons
Properties of a beta particle
Quite fast Quite small Penetrate moderately Long range in air Moderately ionising
What happens when a beta particle is emitted
A neutron turns into a a proton.
Why does a beta particle have a charge of -1 and a small mass
It is an electron
Properties of a gamma ray
Penetrate far into materials without being stopped Pass straight through thin air Weakly ionising No mass No charge
Why don’t gamma rays get deflected by electric or magnetic fields
They are electromagnetic waves and have no charge
The older a sample of a radioactive substance becomes
The less radiation it will emit
Why do u have to use the idea of half life to measure how quickly the activity drops off
The activity never reaches zero
What does a short half life mean
The activity falls quickly because lots of the nuclei decay quickly
What does a long half life
The activity falls slowly because most of the nuclei don’t decay for a long time
