Particles

Page 1

RUTHERFORD'S EXPERIMENT:

Firing alpha particles at thin gold foil

Zinc sulphide scintillates when hit by alpha particles

Most particles passed straight through foil (A)

One in a while, knocked off course (B)

Small proportion (1 in 8000) bounced off gold foil (C)

Since most particles passed straight through foil, most of gold atom must be empty space

Mass must be concentrated in very tiny volume in centre of atom called nucleus

Deflections and rebounds because positive charged on alpha particles repelled by positive charges on nuclei

Amount of deflection depends on:

Speed of alpha particle - deflected less if faster travelling

Nuclear charge - if strongly positive, more strong repelled away form it

How close alpha particle gets to positively charged nucleus

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NUCLEAR FISSION:

Uranium-235 used as fuel in nuclear reactor because U-235 nuclei can be split by neutron

Fission - process of splitting atom

U-235 fissile material because goes through fission easily

Slow-moving neutron absorbed by nucleus of U-235

Resulting nucleus of U-236 becomes unstable, splits part

Fragments of decay - two daughter nuclei produced

Gamma radiation and three more neutrons produced

Huge amount of energy produced because some of mass of U-236 nuclei converted to energy

Most carried away as KE of two daughter nuclei

CHAIN REACTION:

Three neutrons produced by fission hit three nuclei of U-235 so process repeats

1 neutron to 3 to 9 to 27, etc, known as chain reaction

If done in uncontrolled way, gives enormous TE and radiation

Nuclear reactor - controlled so TE released over long period f time

Heat produced in core of reactor used to heat water

Steam produced drives turbines

Turbines turn generators

Page 3

NUCLEAR REACTOR:

Fuel rods - provide fuel for nuclear reactors

Graphite used as moderator

Moderator - absorb some of KE of neutrons to slow them down so more easily absorbed by U-235

Control rods - absurd neutrons and taken them out of fission process completely

If fully inserted into core, chain reaction almost full stopped so rate of heat production low

If withdrawn, rate of fission increases, heat produced at higher rate

Some reactors designed to produce plutonium

Plutonium - very radioactive artificial element

Fissile material

Production of nuclear weapons

Serious health hazard, even in small amounts