Radioactivity Flashcards
Why are radioisotopes used in biochemistry?
1- sensitivity
2- ease of detection
3- Ease of quantifying
4- Simple protocols
5- chemical properties of radioisotopically labelled biochemicals usually identical to non-labelled biochemicals.
6- studies can be carried out using intact living organisms
How does isotopes and radioactivity work?
Proteins are held together by short range nuclear energy attractive forces
Isotopes of different elements have different atomic masses but the same atomic number. A radioactive isotope is an unstoppable isotope
Nuclear instability
It’s enhanced by an increase in number of nucleons (P + N) which cause a increased electrostatic repulsion.
An uneven number of protons and neutrons or an excess of deficiency in neutrons
What are the isotope half life’s?
Natural. Radioactive. Half life
1H. 3H. 12.26 years
12C. 14C. 5730 years
31P. 32P. 14.28 days
31P. 33P. 25.4 days
32S. 35S. 87.9 days
What is radioactive decay?
Decay is where the nucleus disintegrates releasing energy and particles. It often converts atom of one isotope to an isotope of a different element
Decaying atoms can release A, B and G rays
What are Beta particles?
Negation (b-) emission is where an electron is lost when the neutron transforms to a proton
Positron emission is where a B+ particle is lost when a proton transforms to a neutron.
What are Gamma rays?
High energy rays, the resulting nuclei are often unstable and further decay
What is the Geiger-Muller tube?
This detects radiation that ionises has between electrodes across which a voltage is applied.
- useful for routine laboratory detection (checking contamination)
- disadvantages is that it’s not sensitive and not quantitive.
What is the scintillation counter?
This detects light flashes produces when radiation interacts with certain chemicals.
Different radioisotopes with different Emax can be measured simultaneously.
It’s the best method for liquid samples- cannot localise radioisotopes
Disadvantages is that it’s expensive
What is Autoradiography?
This is where an X-Ray film is exposed to isotopes. During developing silver grains form where the radiation has passed through the film leaves a black mark
It’s useful to detect radioisotopes where the location is critical (for example from sections of an organism).
It’s cheap but uses consumables and not as sensitive and quantitative as scintillation counting.
Not so good for low energy bets emitters (3H and 14C)
What is phosphorimaging?
The sample is placed against a phosphor screen composed of fine crystals of BaFBr:Eu+2 (barium:fluorobromide:europium)
Radiation excites the Eu+2 electrons to a state they move within the screen.
The Eu2+ is oxidised to Eu3+ and BaFBr is reduced to BaFBr-
These ions remain like this Acer the screen is removed and the phosphor stores the energy.
Laser scanning causes the reversal of the reaction and releases blue light. This is detected and quantified
Ionising radation
B particles and g rays are dangerous as they ionise and excite the molecules they interact with and the ionisation of DNA can cause damage and mutations
What is the standard unit of radioactivity
1 Bq = 1 disintegration per second
What is a curie?
It’s a non standard measurement of radioactivity.
One curie is the number of disintegration’s per second in a 1g sample of radium (=3.7 times 1010/s)
