AQA A Level Physics Paper 1 2019 Mark scheme|

Iodine-131 has 6 more neutrons (than iodine-125)  Condone iodine-131 has 78 neutrons and iodine-125 has 72 neutrons. Condone “6 fewer/less neutrons than iodine-131” Do not credit nucleons. Suggestion of difference ...

Iodine-131 has 6 more neutrons (than iodine-125)  Condone iodine-131 has 78 neutrons and iodine-125 has 72 neutrons. Condone “6 fewer/less neutrons than iodine-131” Do not credit nucleons. Suggestion of difference in number of protons loses the mark. 1 01.2 131 (nucleons)  If more than one number is given, the nucleon number must be explicit. 1 01.3 The tellurium has 1 more neutron (than iodine-125)  The tellurium has 1 fewer proton (than iodine-125)  Accept reverse arguments. Accept tellurium has 73 neutrons Accept tellurium has 52 protons Condone “proton number”. Condone “number of neutrons/protons have increased/decreased by one" Treat any nuclear reactions as neutral. Discussion of electrons in nucleus scores max 1. Accept answer in terms of quarks (one more down and one fewer up). Ignore references to nucleons/mass number. 2 MARK SCHEME – A-LEVEL PHYSICS – 7408/1 – JUNE 2019 5 01.4 A (internal conversion: only electron released); beta-decay: (electron and) anti-neutrino released;  B (both statements required for mark) internal conversion: all electrons released will have similar/discrete energies/momenta beta-decay: electrons will have a range of energies/momenta  C (internal conversion: no change in constituents of nucleus/element does not change) beta-decay: neutron converted to proton (allow in terms of quarks)/element changes (to one with (one) more p, different Z, different proton number/different atomic number))  D (internal conversion: orbital electron lost) beta-decay: electron comes from nucleus / no change in orbital electrons  E (both statements required for mark) internal conversion: mediated by electromagnetic force / virtual photons beta-decay: mediated by weak interaction / W–  Any 3. Treat each difference, as delimited by the answer book, as a single independent mark. Contradiction within a difference cancels the mark for that difference (on list basis). For a contradiction between separate differences treat the incorrect difference as neutral. Allow: F (both statements required for mark) Internal conversion: may be accompanied by X-ray photon Beta-decay: may be accompanied by gamma photon  Allow “shells” for “orbitals”. Do not award separate marks for force and exchange particle Condone “W boson” or “W particle” but not W+ and W ......................CONTINUED