Energy and mass

Question 1

In 1905 Einstein published his theory of special relativity, which included the equation:

Answer 1

• E = mc²
• stating that the mass of an object increases by m when it gains energy
• For everyday energy changes, this increase in mass is usually insignificant compared to the mass of an object.
• However, on a nuclear scale it becomes much more important.

Question 2

For a spontaneous reaction, where no energy is supplied the energy released =

Answer 2

Q = Δmc²

Question 3

In α decay:

Answer 3

• The nucleus recoils when the α particle is emitted so the energy is shared between the α particle and the nucleus.
• Applying conservation of momentum to the recoil, the energy released is shared inversly proportional to their masses.

Question 4

In β decay:

Answer 4

• The energy released is shared in variable proportions between the β particle and the electron neutrino released in the decay.
• When β has max energy, the electron nuetrino has negligible Ek.
• The max energy of the β particle is slightly less than the energy released in the decay because of the recoil of the nucleus.

Question 5

In electron capture:

Answer 5

• The nucleus emits an a neutrino which carries away energy released in the decay.
• An X-ray photon is released when the innershell vacancy due to the electron is filled.

Question 6

Atomic mass unit, u

Answer 6

= 1/12 of mass of C₁₂ atom = 1.661 x10^-27

1u is equivalent to 931.3 MeV