SP4i Nuclear Fusion

Question 1

Radioactive decay?

Answer 1

the radiation (e.g., alpha, beta) emitted by the unstable nuclei releases energy.

Question 2

Nuclear fission?

Answer 2

large nuclei such as uranium-235, break up to form smaller nuclei and release energy.

Question 2

energy = ?

Answer 2

mass lost x speed of light² (3 x 10⁸)²

Question 3

Nuclear fusion?

Answer 3

.two small nuclei join together to form a larger nucleus
.if the two light nuclei that go into a fusion reaction have an atomic number below26(the atomic number of iron), the nuclear reaction can release energy

Question 4

Why is energy released in fusion?

Answer 4

because when the new nucleus forms its mass is slightly less than the total of the masses of the two smaller nuclei, that loss of mass has been converted into energy.

Question 5

Why does fusion occur in stars?

Answer 5

.because of the extremely high temperatures and pressures at their centres
.high temperatures mean nuclei are moving very fast, high pressures due to their strong gravitational fields mean they are much closer and more likely to collide

Question 6

What are advantages and disadvantages of generating electricity in fusion reactors?

Answer 6

.adv - produce no green house gases, and produce significantly less radioactive waste than in fission reactors
.disadv - very expensive and is taking a long time to build

Question 7

What is electrostatic repulsive force and how can it be overcome?

Answer 7

.two positive nuclei are prevented from fusing because they repel
.the electrostatic repulsive force increases as the distance between them decreases
.if the nuclei are moving very fast, (over 1 000 000 m/s) the electrostatic force can’t stop them, they get close enough (10-15m) to fuse into a single nucleus, under the action of the strong nuclear force