Summary OCR A level Physics A 6.5 Medical Physics

6.5 Medical
Physics

, ✗ rays -




•

Can be plane polarised
•

Diffracted by atoms in
crystals
Short ( 10-8-10 -13m)
wavelength
•




•

Electromagnetic waves -
travel at speed of light
Photons have 10-10000 than visible
more
energy light photons
•
×

•

Harmful to living cells /used for cancer treatment
•
cathode acts as a heater and
produces electrons by thermionic emission
•
electrons accelerated through evacuated
tube towards the anode by large p d- .




•
anode made from a target metal with
a high melting point e.
g. tungsten
X
ray photons produced when electrons
• -




are decelerated by hitting the anode
oil is circulated around the 1% of the
energy output of photons is
• <


kinetic
anode to cool it
energy of the electrons
anode is rotated to spread the heat
anode is shaped to deflect the photons
in the desired direction
through a
window
tobe tired with lead to shield the
X-ray
radiographer from Krays emitted in other
directions


One electron releases one X
ray photon Therefore from the principle of
-
.



,



conservation of energy :




maximum energy of X-ray photon =
maximum kinetic
energy of electron

✗
¥ er
÷
=
✗