(c) fission and fusion

nuclear reactions are sources of .? (7.17)

energy

explain nuclear fission (7.18 / 7.19 / 7.20)

fission is the splitting of a large, unstable nucleus into two smaller nuclei

• a neutron collides with the unstable nucleus

  • these are the reactants

• and the nucleus splits into two daughter nuclei and two or three neutrons

  • these are the products

  • the neutrons then go on to collide with other unstable nuclei which splits into more neutrons which collide with more nuclei etc.

• gamma rays are also emitted

• this releases kinetic energy

use of control rods and the moderator during the fission process (7.21)

control rods:

• made of boron or cadmium

• absorbs neutrons

  • completely removes them from fission process

• this helps to adjust the rate of fission in the reactor

moderator:

• made of something like graphite

• absorbs some of the kinetic energy of the neutrons to slow them down because slower neutrons are more easily absorbed by uranium 235 nuclei

role of shielding around a nuclear reactor (7.22)

the vessel is made of steel and surrounding by a 5m layer of concrete, meaning no radiation escapes

explain nuclear fusion (7.24)

the creation of larger nuclei resulting in a loss of mass from smaller nuclei, accompanied by a release of energy

differences between fission and fusion (7.23 / 7.26)

fusion: two light nuclei join to form a heavier nucleus

fission: a neutron collides with a large and unstable nucleus, sending out daughter nuclei, a few electrons, gamma rays. this has to happen under intense pressure and very high temperatures to force the nuclei together, since nuclei are positive particles and like charges repel, meaning than a lot of energy is needed to overcome the electrostatic repulsion

fusion is the energy source for..? (7.25)

stars