Nuclear Energy (not quite done!)

Question 1

Where do stable nuclei lie on the graph of N against Z?

Answer 1

The centre of the band, central belt that curves upwards. For Z < 20, N ~= Z, For Z > 20, N/Z > 1.

Question 2

When do particles start emitting alpha radiation?

Answer 2

USUALLY when Z > 60 or so, as the strong nuclear force cannot then overcome the electrostatic repulsion between protons.

Question 3

When does beta minus decay occur?

Answer 3

On isotopes to the left of the stability belt who are too neutron-rich

Question 4

When does beta plus decay occur?

Answer 4

On isotopes to the right of the stability belt who are too proton-rich

Question 5

When does electron capture occur?

Answer 5

To the right of the stability belt, as it turns a proton into a neutron and removes an electron.

Question 6

What do the different decays look like on an N-Z graph?

Answer 6

Alpha is 2 down and 2 left; beta + is 1 up and 1 left, beta - is one down and 1 right.

Question 7

How are radioactive decay series represented?

Answer 7

Chains of decays on the N-Z graph.

Question 8

What are excited states in nuclear energy?

Answer 8

Atoms being left in an excited state after a radioactive decay; they then emit gamma radiation before returning to the ground state,

Question 9

What are metastable states?

Answer 9

Stable states that last for at least 1 nanosecond, can be useful in medicine as they can be sources that only emit gamma.

Question 10

What is the typical radius of a nucleus?

Answer 10

Around 1fm, 1 x 10 ^-15 m

Question 11

How can you estimate the nuclear radius using an alpha particle?

Answer 11

Use the distance of closest approach of an alpha particle to a nucleus of charge Qn. EPE will be equal to Ke.
So r = Qn Qa / 4pi e0 x E(k)

Question 12

How can you determine nuclear radius from diffraction?

Answer 12

First minimum, theta min, is given by sin theta = 1.22 lambda / d where lambda is de broglie of an electron and d is diameter.

Question 13

How do you determine nuclear radius from nucleon number?

Answer 13

R = R0 A^1/3 , A is nucleon number, R is radius and R0 is 1.05 x 10^-15

Question 14

What is the mass defect, and what does it allow you to calculate?

Answer 14

The difference in the mass before and after a reaction or decay where energy is released; allows you to calculate the energy released through E = mc^2.

Question 15

What is the mass defect of a nucleus?

Answer 15

Difference in mass between the separated nucleons and the mass of the nucleus, equal to the energy released when the nucleus forms from all these separate neutrons and protons.

Question 16

What is nuclear fission?

Answer 16

A large unstable nucleus splitting into 2 smaller nuclei

Question 17

What is nuclear fusion?

Answer 17

Small nuclei joining together to form a larger nucleus.

Question 18

What is induced nuclear fusion?

Answer 18

Splitting heavy nuclei by firing slow-moving thermal neutrons at them (in thermal equi. with their surroundings)

Question 19

What is the binding energy of a nucleus equal to?

Answer 19

mass defect x c^2, deltam x c^2. A measure of the stability of the nucleus - the higher the binding energy the more stable the nucleus.

Question 20

How can you calculate the energy released from fission or fusion?

Answer 20

The change in binding energy per nucleon.

Question 21

What is the most stable nucleus?

Answer 21

Iron-56

Question 22

What does increasing the binding energy do?

Answer 22

Release energy.

Question 23

What is the equation for fission in a reactor?

Answer 23

n + U -> Kr + Ba + n + n + n

Question 24

What are some safety features of reactors?

Answer 24

Thick concrete walls to absorb radiation
Rad. fuel rods inserted and removed using remote handling devices
Control rods fully inserted in emergencies

Question 25

How are spent fuel rods disposed of?

Answer 25

Removed with remote handling devices, placed in cooling ponds. Then reprocessed so some products can be used for other things.

Question 26

How is radioactive waste disposed of?

Answer 26

Stored, usually in stainless steel containers in concrete vaults to isolate it from the environment.

Question 27

What are the advantages and disadvantages of nuclear power?

Answer 27

Can produce huge amounts of energy without producing greenhouse gases, but produces waste and is extremely expensive and time-consuming to commission, maintain and decommission.

Question 28

What are control rods usually made of?

Answer 28

Boron or cadmium, absorb neutrons and so control the rate of the reaction.