Radioactivity Flashcards
What did Rutherford observe in the deflection alpha particles in electric fields
They appeared to scatter (be deflected) at seemingly random small angles
Why could huge deflections of alpha particles not be described by Thomson’s model of the atom (where charge was distributed evenly throughout the atom)
For such large deflections all the positive charge had to be concentrated in a small mass greater than the mass of the alpha particles. The force that could cause it had to be large.
What did Geiger and Marsden observe during their experiment
Alpha particles bouncing straight back from a sheet of gold foil. The radioactive source produces alpha particles which are collocates (only particles going in straight direction allowed through) into a beam and directed at a gold foil. The alpha particles are scattered by the gold atoms and detected by a flash of light when they hit the fluorescent screen.
In the Geiger-Marsden experiment why are the apparatus in a vacuum
So the alpha particles are not effected/slowed by colliding with air molecules
What were the results of the Gieger-Marsdem experiment
- most of the particles went right through un deflected
- some were deflected by a small angle
- a few were deflected by very large angles
What was the conclusion of the Gieger-Marsden experiment
all the positive charge (repelled alpha particles) must be contained in a small region of large mass (bigger than mass of an alpha particle or it would have been knocked away by the alpha particle) at the centre of the atom
What did Rutherford’s nuclear model of an atom contain?
A massive nucleus containing all of its positive charge and that the much lighter electrons were outside this nucleus. But, most of the atom was empty space
When did scattering of the alpha particles at large angles occur
When the alpha particles came near the nucleus, but most alpha particles had been passing through large gaps between nuclei which is why many were not deflected
What does the amount of deflection depend on
The speed of the alpha particle (less deflection if it is traveling faster)
The nuclear charge (if the nucleus is strongly positive, the alpha particle will be more strongly repelled away)
How close the alpha particle gets to the positively charged nucleus (the closer it gets, the bigger the deflection)
What is nuclear energy
Energy that comes from the nucleus of an atom
What are the two processes in which nuclear energy is released from an atom
Nuclear fusion and nuclear fission
What was the “plum pudding” model
A sphere of positive charge containing electrons only one ten billionth of a metre across
What is nuclear fusion
When energy is realised when the nuclei of small atoms are combined or fused together. It is how the sun produces energy
What is nuclear fission
In nuclear fission energy is realised when the nuclei of large atoms are split apart. It is the only method currently used by nuclear plants to generate electricity
What is the fuel most widely used by nuclear power plants for fissioning
Uranium. It is heavy, fissile, and abundant but it is nonrenewable
What happens during fission
The (for example) uranium-235 atom absorbs a bombarding neutron, causing its nucleus to split apart into two smaller nuclei. At the same time, the fission reaction realises kinetic energy of the products, gamma radiation, and more neutrons. The neutrons bombard other uranium atoms and the process repeats. It is the heat produced that turns water into steam at high pressure which drives the turbine and generates electricity
Chain reaction during nuclear fission
Heat - heat - kinetic - electrical - electrical
What is a chain reaction
A process in which 2 or more neutrons realised in fission produce extra fissions in two further nuclei. These nuclei in turn produce 2 (or more) neutrons each, and a further four (or more) fissions, and the process repeats. It is involves the sudden release of lots of heat energy and radiation. It can be controlled or uncontrolled
What are nuclear power stations designed to do
Control nuclear processes in order to produce useful energy, so hewt energy is released over a longer period of time.
How does a pressurised ware reactor work
The reactor core contains fuel rods of enriched uranium. The heat produced in the core is used to hear water. The steam produced then drives turbines to turn generators.
How do you maintain a controlled nuclear reaction
For every 2 or 3 neutrons released, only one must be allowed to strike another uranium nucleus. If this ratio is less, it will die out and if it is greater it will grown uncontrolled and cause an explosion
How do you ensure safety in a PWR?
Reactors must be properly shielded
Waste must be disposed of carefully
