What are isotopes?
Atoms with the same number of protons but different numbers of neutrons are called isotopes.
Why is it easy for a nucleus to become unstable?
The nucleus is under the influence of the strong nuclear force holding it together and the electromagnetic force pushing the protons apart. It's a very delicate balance.
When will a nucleus becomes unstable?
A nucleus will be unstable if it has:
1) Too many neutrons
2) Too few neutrons
3) Too many nucleons altogether, ie it's too heavy.
4) Too much energy.
What is a stability graph?
Roughly sketch the line of stability on the graph. Make sure the axes are clearly shown.
You can get a stability graph by plotting Z (atomic number) against N (number of neutrons.).
The line of stability is found by plotting N against Z for stable nuclei.
When a heavy nuclei decays what is emitted and how many protons/neutrons does the nuclei loose?
Heavy nuclei release alpha emission.
The proton number decreases by two, and the nucleon number decreases by four. (because alpha has a mass of 4.)
Why does alpha emission only happen in very heavy atoms?
How heavy do the atoms need to be to decay?
Alpha emission only happens in very heavy atoms ( with more than 82 protons.), like uranium and radium.
The nuclei of these atoms are too massive to be stable.
Write the equation for uranium(u) decaying to thorium(Th)
What is beta-minus decay?
It is the emission of an electron from the nucleus along with an antineutrino.
What does beta decay occur?
Beta decay happens in isotopes that are " neutron rich" (have more neutrons than protons.)
What happens to the structure of the nucleus during beta-plus emission(in terms of protons/neutrons)?
A proton gets changed into a neutron. The proton number increases by one, and then nucleon number stays the same.
When does gamma emission occur from a nuclei?
A nucleus with excess energy is said to be excited, this energy can be lost by emitting a gamma ray. This often happens after an alpha or beta decay.
How is the nucleus changed after a gamma emission?
During gamma emission, there is no change to the nuclear constituents - the nucleus just looses excess energy.
In every nuclear reaction what is consereved?
In every nuclear reaction energy, momentum, proton number/ charge and nucleon number must be conserved.
The nucleon numbers must balance.
The proton numbers must balance.
Explain why the mass of an alpha particle is less than the individual masses of two protons and two neutrons.
The difference in mass is called the mass defect. Mass doesn't have to be conserved because of Einstain's equation: E = mc2.
This says that mass and energy are equivalent. The energy released when the nucleons bonded together accounts for the missing mass - so the energy released is the same as the magnitude of the mass defect x c2.