Achieve an A* in your A Level Physics exams with our expertly written notes on 'Nuclear Physics'. Created by a student who scored an A*, these notes are clear and easy to understand. Explore the fascinating world of the atomic nucleus, covering topics such as nuclear structure, radioactivity, and n...
3.8.1.1.
Who proposed the plum pudding model?
- J.J. Thompson
Descr. the plum pudding model?
- the plum pudding model stated that…
…the atom was made up of a sphere of positive charge
…with small areas of negative charge evenly distributed throughout like
plums in a plum pudding
Who conducted the alpha scattering experiment?
- Rutherford
Descr. the alpha scattering experiment?
- apparatus used:
● Alpha source
● An evacuated (so there’s a vacuum inside) chamber covered with fluorescent coating
● Gold foil in the evacuated chamber
● Microscope
- process:
● Alpha particles fired at the golden foil
● due to fluorescent coating you could see where the alpha particles hit the inside of
the chamber + microscope can be moved around the chamber to observe these
Results of the alpha scattering experiment?
1) most alpha particles passed straight the foil with no deflection
⇒ atom is mostly empty space
⇒ NOT uniform density, disproving the plum pudding model
2) small amount were deflected by a large angle (below 90 though)
⇒ centre of the atom is positively charged
3) very few particles were deflected backwards by more than 90 degrees
,⇒ the centre of the atom is very dense and small compared to the rest of the
atom
Conclusions deduced from the alpha scattering experiment?
- nucleus is much smaller than the separation between nuclei
- the vol. of the nucleus is much smaller than the vol. of the atom
- most of the mass is concentrated in the nucleus
- nucleus has a positive charge
Meaning of alpha particles being monoenergetic?
- they possess the same energy
Main interaction when an alpha particle is scattered by a gold nucleus?
- as in: one of the 4 fundamental forces/interactions
- electrostatic
- the nucleus' proton number (atomic no.) stays the same
==> the repulsive force stays the same
==> the scattering distribution stays the same
In which direction will the number of α particles per second be a maximum?
- deflection of 0 degrees
How does the deflection of an alpha particle change if the nucleus’ proton no.
decreases?
- less deflection
(deflection of lower angle)
Why is it necessary to remove the air from the chamber in a Rutherford scattering
experiment?
- to prevent the alpha particles from (colliding and) being absorbed/scattered by the air
particles
Explain why the gold foil should be very thin?
- the α particles must not be absorbed by the foil
+ the α particles must only be scattered once
Explain why there are more alpha particles passing straight through than particles
being deflected at large angles (more than 90 degrees)?
- atoms consist of mainly open space
- the nucleus is much smaller than the atom
- most of the mass of the atom is concentrated in the nucleus
- the nucleus is positively charged
((basically the conclusions of the alpha-scattering experiment/describe the atomic model))
+ most alpha particles don't pass close enough to be deflected
Why must all the alpha particles have the same speed?
, Why must the source of the alpha particles (the thing that decays, emitting alpha
particles) have a long half life?
Why must the beam of alpha particles be narrow?
History of the atom?
https://docs.google.com/document/d/1Gvtp7oiXvLLPOEmy_1kddWUR7B2Sf8GxFeWKY9Y
NJ48/edit?usp=sharing
3.8.1.2.
What does ionising radiation do to atoms?
- makes them into ions
Types of radiation from most to least ionising?
- alpha > beta > gamma
Range in air of diff. types of radiation?
- alpha - 0.04m
- beta - 0.40m
- gamma - infinite range that follows the inverse square law
Alpha, beta gamma rad. properties?
Experimental identification of diff. types of radiation?
~absorption experiments~
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