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<h2>SL Paper 3</h2><div class="specification">
<p>Nuclear fission of <sup>235</sup>U is one source of electrical energy that has a minimal carbon footprint.</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Natural uranium needs to be enriched to increase the proportion of <sup>235</sup>U. Suggest a technique that would determine the relative abundances of <sup>235</sup>U and <sup>238</sup>U.</p>
<div class="marks">[1]</div>
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Explain how <sup>235</sup>U fission results in a chain reaction, including the concept of critical mass.</p>
<div class="marks">[3]</div>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Suggest one reason why there is opposition to the increased use of nuclear fission reactors.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p>mass spectrometry/mass spectroscopy/MS</p>
<p> </p>
<p><em>Accept “analysis of radiation emitted”.</em></p>
<p><strong><em>[1 mark]</em></strong></p>
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p><em>critical mass: </em>mass required so that <strong>«</strong>on average<strong>» </strong>each fission/reaction results in a further fission/reaction</p>
<p><em>Any two for </em><strong><em>[2 max]</em></strong><em>:</em></p>
<p>neutron captured by <strong>«</strong><sup>235</sup>U<strong>» </strong>nucleus</p>
<p>fission/reaction produces many neutrons/more than one neutron</p>
<p>if these cause further fission/reaction a chain reaction occurs</p>
<p> </p>
<p><em>Accept “minimum mass of fuel needed </em><em>for the reaction to be self-sustaining”.</em></p>
<p><em>Accept answers in the form of suitable </em><em>diagrams/equations.</em></p>
<p><strong><em>[3 marks]</em></strong></p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>produce long lived/long half-life radioisotopes/radioactivity</p>
<p><strong><em>OR</em></strong></p>
<p>could be used to produce nuclear weapons</p>
<p><strong><em>OR</em></strong></p>
<p><strong>«</strong>nuclear<strong>» </strong>accidents/meltdowns can occur</p>
<p> </p>
<p><em>Accept “long lived/long half-life </em><em>radioactive waste”.</em></p>
<p><strong><em>[1 mark]</em></strong></p>
<div class="question_part_label">b.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
[N/A]
<div class="question_part_label">a.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
[N/A]
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
[N/A]
<div class="question_part_label">b.</div>
</div>
<br><hr><br>