Deck 10 = Radio Activity Flashcards
Atomic Theory?
- Geiger and Marsden fired alpha particles at a very thin gold film.
Most alpha particles past through undetected - Conclusion?
Most of the atom is empty space.
Some were deflected through small angles - Conclusion?
Nucleus is positively charged.
Occasionally, an alpha particle would be deflected through a large angle. - Conclusion?
Tiny nucleus with a large mass, relative to alpha, so very dense.
What did Bohr add to the Rutherford model?
The Bohr Model added the idea of electron shells of energy (energy level shells).
Mass Number =
Protons + Neutrons
What is a Isotope?
An atom with the same number of protons but a different number of neutrons.
What is the difference between Rutherford’s model of the atom and Thomson’s plum pudding model?
The Rutherford model is made up of mostly empty space which the protons and neutrons are very small and dense in the middle. This is different to the ‘Plum Pudding’ as it just has a large sphere. The Rutherfod model also has orbiting electrons.
What is a radioactive isotope?
“A radioisotope is an atom with a unstable nucleus.” Like an unstable building or cliff.
Background Radiation is ………..
…….. everywhere, we are surrounded by it. Radioisotopes release particles when they fall apart.
Sources of background radiation?
Radon Gasses in the ground. Also buildings and medical facilities and Food and Drink, cosmic rays.
What is one thing we need to do when measuring the activity of a radioactive source?
We have to correct for background radiation. We can do this by first measuring for background radiation then subtracting this of the reading for the source.
Total counts =
counts from radio isotope + background radiation.
What is Ionising radiation?
When a radioisotope decays, ionising radiation may be released. These are dangerous because they can steel electrons from atoms. Which can lead to cancer. The three types are alpha, beta and gamma.
Structure of Alpha Particle?
Each particle is 2 protons + 2 neutrons (identical to nucleus of helium - 4)
Structure of Beta Particle?
Each particle is an electron (created when a nucleus decays)
Structure of Gamma Rays?
electromagnetic waves similar to X-rays.
Charge of alpha particles?
+2
Charge of Beta Particles?
-1
Charge of gamma rays?
0
Mass of alpha particles?
high, 4amu
Mass of beta particles?
low, weight of electron
Mass of gamma rays?
-
Speed of alpha partcle?
up to 0.1 x the spped of light.
Speed of a beta particle?
up to 0.9 x the speed to light
Speed of a gamma ray?
the speed of light.
Ionising effect of alpha particle?
Strong
Ionising effect of beta particle?
weak
Ionising effect of gamma ray?
very weak
Penetrating effect of Alpha Particle?
Not very penetrating, stopped by a thick peace of paper and skin, a few CM of air.
Penetrating effect of Beta Particle?
Penetrating, but stopped by a few mm of metal.
Penetrating effect of Gamma Ray?
very penetrating, never completely stopped, lead and thick concrete decreases intensity.
Effects of fields on Alpha Particles?
deflected by magnetic and electric fields.
Effects of fields on beta Particles?
Deflected by magnetic and electric fields?
Effects of fields on Gamma Rays?
Not deflected by magnetic and electric fields.
Name a radioactive isotope which occurs naturally in living things.
Carbon-12, 13-14
What is the difference between the atoms of an isotope which is radioactive and the atoms of an isotope that is not?
The atoms in an isotope that is not radioactive will be neutral, radioactive isotopes also radiate radioactive materials.
Example of Alpha emission?
Radium = Radon + alpha
226^88Ra = 222^86Rn + 4^2(ALPHA)
- Mass number reduced by 4
- Atomic number reduced by 2
Example of Beta Emission?
This is when a random neutron changes to a proton, emitting an electron.
Iodine = Xenon + beta
131^53I = 131^54Xe + 0^-1(beta)
Example of gamma Emission?
Atomic number remains the same.
What is a Half Life?
The time it takes for half of the sample of a radioisotope nuclei to decay.
Example of calculating half Life? A sample of a radioisotope has a mass of 250g. Calculate its mass after 64 minutes if it has a half life of 16 minutes.
64 minutes is 4 half lives. It is going to half every 16 minutes.
It will 1/2 four times, 250g, 125g, 62.5g, 31.25g = 15.625g
the bigger the radioisotope the …….
more stuff it will kick out.
The activity of a radioisotope is measured in ……….
Becquerels Bq
Mass left in sample is …….
proportional to activity (proportional = Jesus Fish)
If samples of Strontium - 90 and radium - 226 both had the same activity, which would have the lower activity in 10 years time?
- strontium - 90
If the activity of a sample of iodine -128 is 800 Bq, what would you expect the activity to be like after,
25 minutes -
50 minutes -
100 minutes -
400Bq
200Bq
50Bq
What is nuclear fission?
The splitting of an atom which releases energy.
Purpose of a moderator?
Graphite or water slows neutrons down so that they can successfully collide. to sustain reaction.
Purpose of control rods?
Made or Boron, limit the rate of fisson by absorbing accsess neutrons.
