3.Nuclear

Question 1

U10PH5 Explain why 1.0 kg of caesium-137, although it has an activity of 3 × 1015 Bq, would be quite safe in a sealed metal box of thickness 1 cm.

Answer 1

[All] β absorbed [however expressed] or no γ present [implies β absorbed]

Question 2

U16PH5 Explain without calculation, whether the total binding energy of Si and He is greater or less than that of O nuclei.[3]

Answer 2

1) The reaction releases [9.594 MeV of] energy or is exothermic (some mention must be made of the energy on the RHS) Don’t accept 9.594 MeV is lost or left over
2) Products are more stable OR mass must have been lost or PE is lost
3) Binding energy of [RHS / Si and He] greater or converse

Question 3

U16PH5 Explain why 4.22 × 10–11 kg of polonium-211 could be highly dangerous even though it emits alpha particles which cannot penetrate human skin. [2]

Answer 3

[Can be] ingested (accept inhaled) Large activity / short half-life) and [alpha highly] ionising Accept high equivalent dose Don’t accept high dose only (needs ionising too) and treat reference to daughter nuclei as neutral.

Question 4

U16PH5

Answer 4

1） conservation E

2）KE=16.5>0

3)contravene Conservation p

Question 5

U16PH5 An electron-positron pair is produced by a photon of energy 1.04MeV.State what happens to the remaining 0.02MeV of the photon energy in this electronpositron pair production. [1]

Answer 5

KE [of particles]

Question 6

C3 When the paper is marketed as being “Hi-tech beta radiation” paper, sales figures of the paper decrease rapidly. A scientist claims that this is a reflection of the ignorance of society. Explain briefly whether the scientist is justified in making this statement. [2]

Answer 6

Society should realise that the paper is not radioactive or society doesn’t know if paper is radioactive or society thinks paper is radioactive (1) Radioactivity needs to be linked to health issues e.g. society should realise the paper is harmless or society doesn’t know whether or not the paper might cause cancer or people think the radioactive paper is harmful / carcinogenic etc (1)

Question 7

C3 The beta particles produced have a kinetic energy of 0.55 MeV. Explain why using your A level Physics knowledge will not provide an accurate value of their kinetic energies. Your explanation should be reinforced by a calculation. [3]

Answer 7

c

Question 8

Scientists claim that this reaction is extremely important for life in the universe. Explain whether or not this claim is true.

Answer 8

Scientists have gathered evidence for carbon being essential to life (1) 《Scientists have discovered that this is the process in stars that produces carbon (1)

Question 9

C3 8. (a) (i) State three differences (other than mass) in the properties of down quarks and electrons. [3]

Answer 9

d has charge ⅓ that of e–

d feels strong force; e– doesn’t

d cannot be isolated; e– can or equivalent

Question 10

State two other features of the decay which point to it being a strong interaction.

Answer 10

π meson formed

× v γ

No neutrino nor gamma emission (accept either) No change in quark flavour [and no gamma]

Question 11

A10PH2 Explain in terms of quarks, why the is classed as a meson but the Δ– as a baryon. [2]

Answer 11

A meson is a quark-antiquark (1) pairing. A baryon is a triplet of quarks [accept antiquarks] (1)

Question 12

Answer 12

v_e

Must be neutral or lepton number conserved (1) by considering charge and lepton number (1)

Question 13

(ii) Hence explain how the quark version of the interaction is equivalent to the version given at the beginning of the question. [2]

Answer 13

In version at top, neutron is lost and proton is gained. (1)

[or − n ν +→+ e p e] We can regard this as a neutron losing a d [quark] and gaining a u [quark] (1)

Question 14

Answer 14

1st mark : π+ (1)

x y can’t be a lepton [violates lepton conservation]

x y must be positive

x y can’t be a baryon

OR y must have u quark number [2-1] = 1 (1)

and d quark number [1- 2] = -1 (1)

Question 15

(a) Describe an experiment that uses various absorbers to identify the type(s) of radiations emitted by a radioactive sample. Justify all steps in the experiment. [4]

Answer 15

Diagram showing source, absorber and detector or equivalent stated in words (1)

I. Take measurement with no source and no paper/aluminium – [to measure the background radiation] or show awareness of background.

II. Measure count rate with no paper/aluminium. (1 for both I and II)

III. Insert [a few sheets of] paper between the source and receiver and take measurement. If reduction from count in II then alpha particles present. (1)

IV. Insert [a few mm of] aluminium between the source and receiver and take measurement. If reduction in the count from that in III then beta particles are also present and if count is still above the background level, then γ

Question 16

fusion or fission

Answer 16

The most stable nuclei (or reference to elements near to peak i.e. Fe, Ni Ca) are therefore where the curve (or binding energy per nucleon) reaches its BEpn maximum. (1)

Nuclei of small atomic mass number (lhs of graph) can combine to produce species of larger atomic mass number, [hence larger binding energy per nucleon. Energy is released]. Fusion. (1)

Nuclei of large atomic mass number (on rhs of graph) break down to produce species of smaller atomic mass number, [hence larger binding energy per nucleon. Energy is released]. Fission. (1)

Reference anywhere to there being energy released, when a reduction in mass occurs i.e. mass converted to energy. (1)

Question 17

Nuclear power pros and cons

Answer 17

Benefit: routine supply of energy (i.e. does not depend on weather) or jobs or no CO2 emission (1)

Issue: needs secure storage of radioactive waste (products) over a extended time period or reference to long half-lives or long build time or building extra transmission power lines (1)