(nuclear) reactor 1. (average) time taken for number of nuclei to halve or (average) time taken for count-rate / activity to halve

Transcription

1 M. (a) (same) number of protons same atomic number is insufficient (i) nuclei split do not accept atom f nuclei / nucleus (ii) (nuclear) react (c) (d) beta any one from: atomic / proton number increases (by ) accept atomic / proton number changes by number of neutrons decreases / changes by mass number does not change (total) number of protons and neutrons does not change a neutron becomes a proton (average) time taken f number of nuclei to halve (average) time taken f count-rate / activity to halve (e) (i) 6.2 (days) Accept 6.2 to 6.3 inclusive allow mark f crectly calculating number remaining as allow mark f number of plus crect use of the graph (gives an answer of 0.8 days) 2 (ii) (iii) radiation causes ionisation allow radiation can be ionising that may then harm / kill healthy cells accept specific examples of harm, eg alter DNA / cause cancer benefit (of diagnosis / treatment) greater than risk (of radiation) accept may be the only procedure available Page 2

2 M2. (a) gravitational fce(s) () accept gravity balanced by (fce(s) due to) radiation pressure () accept equal 2 by (nuclear) fusion () of hydrogen to helium (other light elements) () allow low density f light accept hydrogen nuclei / atoms fm helium response must clearly link one element(s) producing others fusion to produce helium (2) heavy element / elements heavier than iron are only produced (by fusion) in a supernova () allow dense f heavy igne any reference to elements undergoing radioactive decay (to fm other elements) 3 [5] M3. beta reason may sce even if alpha gamma given any two from: mass number does not change total number of protons and neutrons does not change atomic / proton number increases by number of protons increases by number of neutrons goes down by allow f 2 marks a neutron splits / changes into a proton and electron / beta candidates that answer crectly in terms of why alpha and gamma are not possible, gain both marks 2 [3] Page 3

3 M4. (a) (fces due to) gravity and radiation pressure crect direction of fces (fces) are balanced / equilibrium / equal accept f 3 marks an answer in terms of sufficient hydrogen () to keep fusion reaction () reference to burn / burning negates this mark going at a continuous /steady rate () if fuel is used instead of hydrogen maximum of 2 marks the Sun will remain stable (f several billion years) based on evidence accept a specific example of evidence eg that the Sun has remained stable during the life of our planet / f 4.5 billion years still contains me than 50 % hydrogen by comparison with the lifecycle of (similar) stars allow a refutation eg not based on prejudice / whim / hearsay / folk law / histical religious authity [5] Page 4

4 M5. (a) gravitational attraction accept gravity accept (nuclear) fusion radiation pressure and gravity / gravitational attraction must be in crect context are balanced / in equilibrium accept are equal and opposite do not accept equal there is sufficient / a lot of hydrogen / fuel do not accept constant supply of hydrogen to last a very long time / f (nuclear) fusion this mark only sces if linked to the supply of hydrogen / fuel reference to burning negates both marks (c) (i) (conversion of) hydrogen to helium accept (conversion of) lighter elements to heavier elements by (nuclear) fusion note do not credit spelling of fusion which could be fission reference to burning negates both marks (ii) massive supply / lots of hydrogen (d) distributed throughout the Universe / space do not accept Solar System f Universe [7] Page 5

5 M6. (a) a protostar is at a lower temperature a protostar does not emit radiation /energy as (nuclear) fusion reactions have not started accept heat light f energy by (nuclear) fusion accept nuclei fuse (together) nuclear fusion and fission negates this mark of hydrogen to helium elements heavier than iron are fmed in a supernova accept a specific example e.g. heavier elements such as gold are fmed in a supernova accept heavier elements (up to iron) fmed in red giant/red super giant reference to burning (hydrogen) negates the first 2 marks [5] Page 6

6 M7. (a) (i) plutonium (239) accept Pu / Thium / MOX (mixed oxide) do not accept uranium-238 hydrogen (ii) (energy) used to heat water and produce (high pressure) steam the steam drives a turbine (which turns a generat) Neutron(s) shown hitting other U-235 nuclei one uranium nucleus is sufficient U-235 nuclei (splitting) producing 2 me neutrons (c) any two from: neutrons are absbed (by bon / control rods) there are fewer neutrons chain reaction slows down / stops accept fewer reactions occur 2 [8] Page 7

7 M8. (a) answers must be in terms of nuclear fuels concentrated source of energy idea of a small mass of fuel able to generate a lot of electricity that is able to generate continuously accept it is reliable can control / increase / decrease electricity generation idea of available all of the time / not dependent on the weather igne reference to pollutant gases the energy from (nuclear) fission is used to heat water to steam to turn turbine linked to a generat carbon dioxide is not released (into the atmosphere) but is (caught and) sted (in huge natural containers) [6] Page 8

8 M9. (a) fusion do not credit any response which looks like fission of hydrogen / H (atoms) credit only if st mark point sces fusion of other / lighter atoms / elements reference to big bang nullifies both marks during supernova / explosion of star(s) (c) the (available) evidence: suppts this ideadoes not contradict this ideacan be extrapolated to this idea(electromagnetic) spectrum from other stars is similar to sun [5] Page 9