Atoms and nuclei

In addition to the radiactive process we already know about there are two more:

• neutron radiation
• β+ decay (a proton becomes a neutron plus an positron)

We have seen that nuclei contain and . It is the number of that determines how a atom behaves and therefore how an element behaves. , on the other hand, are difficult to detect because they are neutral. Neutron radiation was discovered as a result of observing a beryllium nucleus interacting with an alpha particle. It transformed into a carbon nucleus and emitting a neutron:

9	Be	+		α	→		C	+		n
4						6

Neutron radiation is very , because it has little with other atoms. This is because it has no .

It does not directly ionise atoms, but as we have seen with nuclear fission, it can trigger other froms of radiation, which can lead to the ionisation of atoms. Because of this, it is considered as dangerous as the other forms of radiation.

Radation	Mass	Charge	Pentration	Ionising Ability
Alpha
Beta (β-)
Positron (β+)
Neutron
Gamma

Radation	Change in number of Protons (Z)	Change in number of Neutrons (N)	Change in mass (A)
Alpha
Beta (β-)
Positron (β+)
Neutron
Gamma

In addition as a result of β- or β+ decay nuclei often undergo rearrangement with a loss of energy as radiation

You need to know the qualitative features of the curve obtained when the number of neutrons (N) is plotted against the number of protons (Z) for stable isotopes:

This graph allows us to identify radioactive isotopes because if an isotope does not lie within this band it will be and therefore radioactive.

It also allows us to predict how an isotope will decay:

• an isotope that lies above the curve has too ) neutrons to be stable and will undergo β- decay (emit an )
• an isotope that lies below the curve has too ) neutrons to be stable and will undergo β+ decay (emit a )
• nuclei with more than 82 protons usually undergo α decay

Revision Questions