Binding energy 74-75

Question 1

What is the binding energy?

Answer 1

The energy needed to separate all of the nucleons in a nucleus is called the binding energy(measured in MeV), and it is equivalent to the mass defect.

Question 2

What is one atomic mass unit(u) equivalent to in Kg?

Answer 2

1 u = 1.66 x 10^-27

Question 3

What is a nuclear valley?

At what point on the graph do the most stable nuclei occur?

Answer 3

A graph of binding energy per nucleon against nucleon number, for all elements, shows a curve - sometimes called a nuclear valley.

The most stable nuclei occur around the minimum point on the graph- which is at nucleon number 56(Fe). Nuclei with a nucleon number close to 56 are bound most strongly.

Question 4

On a graph of binding energy per nucleon against nucleon number, how does the negative y-axis work?

Answer 4

The more negative the binding energy per nucleon, the more energy is needed to remove the nucleons from the nucleus.

Question 5

What is nuclear fusion?

Answer 5

Combining small nuclei is called nuclear fusion. This increases the size of the binding energy per nucleon dramatically, which means a lot of energy is released during nuclear fusion.

Question 6

What is nuclear fission?

Answer 6

Fission is when large nuclei are split in two - the nucleon numbers of the two new nuclei are smaller than that of the original nucleus, which means the size of the binding energy per nucleon increases. So energy is released during nuclear fission (but not as much energy per nucleon as in nuclear fusion.)

Question 7

If a ²³⁵U nucleus splits into ⁹²Rb and ¹⁴⁰Cs (plus a few neutrons.) during nuclear fission, the average change in binding energy per nucleon would be about 1.1 MeV.

What would be the energy relased from this fission?

Answer 7

There are 235 nucleons in ²³⁵U to begin with, so we can estimate the energy released as 235 x 1.1 = 260 MeV.