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
[Show More]
