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Summary Physics A level revision
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NUCLEAR3 8 I I Rutherford Scaltering
Plum pudding model Thomson stated that the atom
THOMSON was made up of a sphere
positive charge of positive charge with areas
o negativecharge of negativecharge evenly
yo 0 distributed
This was disproved and led to the
nuclear model being found
Rutherfords model
r alpha detector you could see
Fluroscentcoating which meant
where the alpha particles hit inside the
e goldfoil chamber
evacuated OBSERVATIONS of the model
I
ELIAS J chamber Mostalpha particles travelled straight through the
ha
beam
µ alphasource
v leadshield
foil with no detection suggesting the atom is
mostly empty space
some of theparticles were deflected at small
angles suggesting the centre of the atom is
positively charged
a
very few particles were deflected back at angles
of the
Yim isthanueeyao.snauYestandsthensemdms
JuD
Bueus
most of the mass must be in the nucleus as
the fast alpha particles with high momentum
were deflectedby the nucleus
38 l 2 x B and 8 radiation
constituent Range in air Ionising Deflectedby Mfields Mass u
Alpha 2protons 2neutrons o ol o Im Highly Yes 4
Beta Electron OZ im weakly Yes negligible
Gamma wave
Electromagnetic infinite veryweakly No o
lessdamage to our bodies so can be used in medicine
Gamma radiation weaklyionising
Detector a radioactive source with a snort nay life reducesexposure whichemits gamma
radiation can be injected into a patient in order to helpdiagnose patients
sterilisation gamma radiation can kill any bacteria present on surgicalequipment
, Radiation therapy
gamma radiation can be used to kill cancerous cells
As gamma radiation moves through the air it spreads out evenly in all direction
the iy ofgamma radiation follows an inverse square law
The intensity of a source is the radiation energy passing through a
unit area per second
I R_ Doubling the distance quadruples the area over which
I KZ distance from the same radiation is spread out
intensityof source
radiation Investigate by measuring the count rate of a gamma source at
different distances from the GM tube
Intensity Powery I nht
Area hour area of a sphere
at a distancerfrom
the source
I Kr k wht
ur
Background countshould be measured with the radioactive source in a lead
lined box Corrected Total count Background
count rate count
Radiation outside of the body Radiation inside of the body
Betaandgamma can penetrate the Alpha is highly ionising and can ionise
skin and muscle tissue body tissue
Alpha won't reach the cells Beta is less ionising but can still cause
damage to body tissue
Sources of background radiation
Radongas released from rocks emits alpha radiation
cosmicrays enter the atmosphere from space
Livingthings plants animals contain carbon some being radioactive carbon 14
Manmade radiation from medicalsources or nuclear meltdowns
Safety precautions
Long handled tongs will minimiseradiation absorbed by the body
Lead box storegamma in lead box so that win absorb the radiation
Don't pointsourcetowardsothers
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