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Date May 2019 Marks available 2 Reference code 19M.2.SL.TZ2.6
Level Standard level Paper Paper 2 Time zone 2
Command term Determine Question number 6 Adapted from N/A

Question

Deuterium, 1 2 H , undergoes fusion according to the following reaction.

1 2 H + 1 2 H 1 3 H + X

 

The following data are available for binding energies per nucleon.

1 2 H = 1.12 MeV

1 3 H = 2.78 MeV

 

Particle Y is produced in the collision of a proton with a K- in the following reaction.

The quark content of some of the particles involved are

Identify particle X.

[1]
a.

Determine, in MeV, the energy released.

[2]
bi.

Suggest why, for the fusion reaction above to take place, the temperature of deuterium must be very high.

[2]
bii.

Identify, for particle Y, the charge.

[1]
ci.

Identify, for particle Y, the strangeness.

[1]
cii.

Markscheme

proton /  1 1 H / p ✔

a.

«3 x 2.78 − 2 × 2 × 1.12»

See 3 × 2.78/8.34 OR 2 × 2 × 1.12/4.48✔

3.86 «MeV» ✔

 

bi.

the deuterium nuclei are positively charged/repel ✔

high KE/energy is required to overcome «Coulomb/electrostatic» repulsion /potential barrier

OR

high KE/energy is required to bring the nuclei within range of the strong nuclear force ✔

high temperatures are required to give high KEs/energies ✔

 

bii.

−1 / -e ✔

 

ci.

−3 ✔

cii.

Examiners report

At HL this was well answered with the most common wrong answer being ‘neutron’. At SL however, this was surprisingly wrongly answered by many. Suggestions given included most smallish particles, alpha, positron, beta, antineutrino and even helium.

a.

The majority of candidates missed the fact that the figures given were the binding energies per nucleon. Many complicated calculations were also seen, particularly at SL, that involved E = mc2.

bi.

The most common mark to be awarded here was the one for linking high temperature to high KE. A large number of candidates talked about having to overcome the strong nuclear force before fusion could happen.

bii.

At SL many answers of just ‘negative’ were seen.

ci.

This was poorly answered at both levels with the most common answer being zero.

cii.

Syllabus sections

Core » Topic 7: Atomic, nuclear and particle physics » 7.2 – Nuclear reactions
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