Radioactivity Flashcards
What is a RADIOACTIVE ISOMER?
An element with:-
The same Proton (Atomic) number
The same Nucleon (Mass) number
A different energy state
What denotes that an element is metastable?
m next to the mass number to denote metastable.
What is NUCLEAR STABILITY?
There is a natural force of repulsion between the protons
Factors that affect nuclear stability?
1) Presence of neutrons- reduces the forces of repulsion (acts like a glue)
2) Short-range of attraction between nucleons- (neutrons, proton)
What happens as we go across the periodic table?
As Proton (Atomic) number increases then the number of neutrons increase to help maintain stability i.e. Help to overcome the forces of repulsion
What does the nuclear stability depend on?
Nuclear stability is dependent upon neutron:proton ratio:-
For low atomic number:-
Neutron/proton ratio = 1
For higher atomic numbers:-
Neutron/proton ratio = 1.3:1
What does radioactive disintegration result in?
Radioactive decay results in the emission of a particle and a gamma ray
Nucleus continues to undergo radioactive decay until a stable state is achieved
Important point - radioactivity cannot be ‘switched off’
What is Radioactivity?
Radioactivity is the rate of Decay of a nuclide
What are the two types of radioactivity?
There are two types of radioactivity:
Natural – certain elements have naturally occurring radioactive isotopes e.g.
12C (stable)
14C (radioactive)
Artificial – elements can be made radioactive by bombarding the nucleus with either:-
Neutrons – achieved in a nuclear reactor.
Proton Bombardment in cyclotron
What is the unit of radioactivity?
Unit of Radioactivity is the BEQUEREL (Bq)
1 Bequerel = 1 disintergration per Sec
Very low amount – therefore radioactive sources have activities of Mega or Giga Bequerels
1 MBq = 106 Bq
The rate of decay is specific (characteristic) for a radionuclide. What term/unit is used to denote this
This rate of decay is represented by the term;
half –life (T½)
What are the 3 types of half-life?
Physical half-life
Biological half life
Effective half-life
What does physical half-life mean?
Physical half-life – the time taken for the radionuclide to decay to half of its original activity. This is what is generally meant by half-life
What does biological half life mean?
Biological half life – the time taken for half of the activity to be removed from the body. This time depends upon:-
The radionuclide
The physiological functioning of the body, especially the “target organ”
What does Effective half-life mean?
his is calculated from the combined effects of the physical and biological half-lives
1 / Teff = 1 / Tbio + 1 / Tp
Or Teff = (Tbiol X Tp) / (Tbio + Tp)
This value is very important in calculating the radiation dose received by the patient
