Atomic structure COPY Flashcards
what is the radius of an atom?
1 x 10^-10 metres
when does the energy level of an electron change?`
when the atom emits or absorbs electromagnetic radiation
what is the radius of a nucleus
1/1000 the radius of an atom
what happens when atoms absorb electromagnetic radiation
electrons to a higher energy level
what happens when atoms emit electromagnetic radiation
electrons drop to a lower energy level
What is radioactive decay?
when isotopes are unstable and decay into other elements and give out radiation as they try to become more stable
what does the type of radiation depend on?
why the nucleus is unstable and is spontaneous
what are 4 types of nucleur radiation?
alpa beta gamma neutron
What is ionising radiation?
radiation that creates positive ions. *the ionising power of radiation source is how easily it can do this
What is activity?
the rate at which a source of unstable nuclei decays.
what is activity measured in?
becquerel (Bq)
What is the count-rate?
the number of decays recorded each second by a detector (eg Geiger-Muller tube).
What do alpha particles consist of?
two neutrons and two protons the same as a helium nucleus
What is alpha radiation?
when an alpha particle is emitted from the nucleus
What are the features of alpha radiation?
- they don’t penetrate very far into materials and are stopped quickly
- they can only travel a few cms in air and are absorbed by a sheet of paper
- because of their size they are strong ionising
What is a beta particle?
a high-speed electron ejected from the nucleus as a neutron turns into a proton
What are features of beta radiation?
- they are moderately ionising
- they penetrate moderately far into materials before colliding and have a range in air of a few metres.
- they are absorbed by a sheet of aluminium
what is a gamma ray?
electromagnetic radiation from the nucleus
What are features of gamma radiation?
- they penetrate far into material without being stopped and will travel a long distance through air
- they are weakly ionising because they pass through rather than collide with atoms
* eventually they hit something and do damage
- they can be absorbed bu thick sheets of lead or metres of concrete
What happens during beta decay?
a neutron in the nucleus turns into a proton and releases a fast-moving electron
because the nucleus has lost a neutron and gained a proton the mass doesnt change
Gamma rays don’t change the charge or mass of the nucleus.
What do they do instead?
They get rid of excess energy from a nucleus
Radioactive decay is spontaneous, however, with a _______________ it is possible to predict how many decay in a certain time period
large enough number of nuclei
