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Nuclear Fusion

Q1. The fusion of two deuterium nuclei produces a nuclide of helium plus a neutron and liberates 3.27 MeV of energy. How does the mass of the two deuterium nuclei compare with the combined mass of the helium nucleus and neutron?

The liberated energy will be the 'mass difference' between the reactants and products. You therefore have to change that into mass. On your data sheet you have the energy/mass conversion factor: 1u is equivalent to 931.3 MeV

1 u = 931.3 MeV so 1 Mev = 1/931.3 u - Note that you are already dealing with MeV !!

Therefore 3.27 MeV = 3.27/931.3 u

Now the 'u' to 'kg' conversion - 3.27 MeV = 3.27 x 1.661 x 10-27/ 931.3 = 5.8 x 10-30 kg

The fused nucleons are more stable - have higher binding energy per nucleon. The released energy shows this! Mass was converted to energy to attain this state - so the mass after fusion will be lower.

A
 It is 5.8 × 10-30 kg greater before fusion.
B
 It is 5.8 × 10-30 kg greater after fusion.
C
 It is 5.8 × 10-36 kg greater before fusion.
D
 It is 5.8 × 10-36 kg greater after fusion.

 

Q2. In the reaction shown, a proton and a deuterium nucleus, H, fuse together to form a helium nucleus,

What is the value of Q, the energy released in this reaction?

mass of a proton = 1.00728 u

mass of a H nucleus = 2.01355 u

mass of a He nucleus = 3.01493 u

Before fusion: 1.00728 u + 2.01355 u = 3.02083 u

After fusion: 3.01493 u

Mass difference = 3.02083 u - 3.01493 u = 0.0059 u = 0.0059 x 931.3 = 5.49 MeV

A
 5.0 MeV
B
 5.5 MeV
C
 6.0 MeV
D
 6.5 MeV

 

 

Q3. The reaction shown below occurs when a proton and a deuterium nucleus, H, fuse to form a helium nucleus.

If the energy released, Q, is 5.49 MeV, what is the mass of the helium nucleus?

mass of H nucleus = 2.01355 u

mass of proton = 1.00728 u

Before fusion: 1.00728 u + 2.01355 u = 3.02083 u

Mass difference: 5.49 / 931.3 = 0.00589 u - this will be mass that has been converted into Q (energy) - therefore it will be missing after fusion.

After fusion: 3.02083 u - 0.00589 u = 3.01494 u

A
 0.00589 u
B
 3.01494 u
C
 3.02083 u
D
 3.02323 u

 

Q4. A deuterium nucleus and a tritium nucleus fuse together to form a helium nucleus, releasing a particle X in the process, according to the equation

Which one of the following correctly identifies X?

Nucleon numbers don't balance, but proton numbers do - it is therefore a neutron!

A
 electron
B
 proton
C
 positron
D
 neutron