Fission and Fusion

Question 1

what is the mass of a proton and neutron

Answer 1

1.67x10-27 kg

Question 2

what is the mass of an electron

Answer 2

9.11x10-31 kg

Question 3

what did we discover about the masses of a nucleus compared to the sum of masses of the nucleons that formed it

Answer 3

the measured mass of the nucleus is always less than the total mass of the nucleons that form it

Question 4

what is this difference called

Answer 4

mass deficit / defect

Question 5

how would you calculate the mass deficit of a carbon-12 atom with a mass of 12u

Answer 5

• subtract the mass of all its electrons from 12u
• giving you the mass of the nucleus
• work out the total mass of protons and neutrons
• add them together to the the theoretical mass of the nucleus
• subtract the theoretical mass from the real nucleus mass
• multiply it by the mass value of 1u (given you were going the calculations in terms of u)

Question 6

where does this loss of mass go

Answer 6

its converted into the binding energy of the nucleus

Question 7

what is binding energy

Answer 7

• the energy used to hold a nucleus together

- converted from the mass deficit

Question 8

what is the equation that shows this relationship between mass deficit and energy

Answer 8

E = mc^2

Question 9

if you have calculated the mass deficit in terms of kg, you would simply multiple it by c^2 to get E. however,if you have mass deficit in terms of u, how would you work out E

Answer 9

• 1u = 931.5 MeV

- so you multiply what you have in terms of u by 931/5 MeV

Question 10

how do you calculate binding energy per nucleon

Answer 10

• work out the binding energy of the nucleus in MeV
• and the number of nucleons within it
• divide one by the other

Question 11

in the graph for binding energy per nucleon against mass number, what does the graph look like

Answer 11

• very steep line the beginning, almost vertical
• then it becomes jagged as it reaches a peak
• then the line slowly tapers off with a vert shallow gradient

Question 12

what element is at the very peak of the line

Answer 12

iron

Question 13

how can you relate this to the life cycle of a star

Answer 13

• this is why the core of a star can only fuse up to iron
• it has the largest binding energy
• so fusion cannot happen anymore when its reached

Question 14

what do elements to the left side of iron tend to do

Answer 14

fuse (nuclear fusion)

Question 15

what do elements to the right side of iron tend to do

Answer 15

split up (nuclear fission)

Question 16

when you fuse two light nuclei together, why is energy released

Answer 16

• the heavier nucleus will have less mass than the sum of the daughter nuclei
• as some of the mass has been converted into energy
• however not all of it converted into binding energy
• so the remaining energy will be released from the nucleus

Question 17

what is the first stage of proton-proton fusion

Answer 17

two protons fuse

Question 18

what is the second stage

Answer 18

• one proton changes into a neutron
• by emitting a b+ particle and a neutrino
• leaving a deuterium nucleus

Question 19

what is the third stage

Answer 19

• another proton fuses with the nucleus

- making a helium-3 nucleus

Question 20

what is the fourth stage

Answer 20

two helium-3 nuclei fuse

Question 21

what is the last stage

Answer 21

• two protons break off

- leaving a helium-4 nucleus

Question 22

why have we not been able to use nuclear fusion as a source of energy on earth

Answer 22

• because it is extremely difficult
• and the amount of energy required to do it is extremely high
• in most cases youd lose more energy than you gained

Question 23

what is the main problem that makes nuclear fusion so hard

Answer 23

• forcing the oppositely charged protons to fuse

- the kinetic energy they need to overcome their electrostatic repulsion requires temps in the millions of degrees

Question 24

what is the other problem you run into

Answer 24

• you need enough collisions to be happening in order to a good amount of energy to be produced
• but youd require very high densities of protons
• which is also very hard to do and maintain

Question 25

what is nuclear fission

Answer 25

• the splitting up a larger nuclei into smaller nuclides

- releasing energy in the process

Question 26

how are man-made fission reactions triggered

Answer 26

• when a nucleus absorbs a slow moving neutron

- making it unstable and causing it to break down