Past papers- 5. nuclear Flashcards
Explain what is meant by nuclear fission.
large unstable nucleus OR neutrons hit nucleus OR neutrons are released (from nucleus)
(large) nucleus splits (into smaller nuclei)
(large) release of energy
The isotope X1 is a beta emitter that decays to the stable isotope X2.
(i) Describe how a nucleus of X2 differs from a nucleus of X1.
(ii) Suggest why isotope X2 is stable whereas X1 is not stable
(X2 has) one more proton more and one fewer neutron (than X1) OR (X2 has) 6 protons and 6 neutrons
(X2) has fewer (excess) neutrons (in its nucleus)
(i) Define the term half-life.
(ii) Suggest one reason why isotopes with very short half-lives are especially hazardous.
time (taken) for number of (radioactive) nuclei / atoms (in a sample of X1) to halve OR for rate of decay to halve
large number of particles produced in short time OR high / large decay rate OR high dose (of radiation) in short time
State two safety precautions taken when moving, using or storing radioactive sources in a laboratory.
limit time of exposure
store sources in lead boxes
keep distance from sources
avoid contact OR use tongs OR wear gloves
During β-decay, one of the neutrons in the nucleus changes.
(i) State what happens to this neutron.
(ii) Explain how charge is conserved during this change.
(neutron) becomes proton and electron OR (neutron) becomes proton and β particle
charge on neutron = 0 OR total charge on products = 0
charge on proton = +1 AND charge on electron =
–1
Describe how the americium-241 ionises air.
alpha (particles emitted from americium)
move close to / hit molecules in the air (between the metal plates)
removing electrons (out of the molecules)
Suggest and explain two reasons why smoke detectors use an isotope that emits α-particles rather than an isotope that emits γ-radiation.
- alpha not penetrating / short range AND alpha (particles) stopped by smoke particles
- alpha (particles) more highly ionising (than gamma) AND ionise air more easily
- range of alpha particles is short / alpha is not penetrating AND alpha less harmful (to humans)
Explain why an extremely high temperature is needed when forcing two hydrogen nuclei together for nuclear fusion.
(high temperature produces) high (kinetic) energy / momentum / speed / ability to do large quantity of work
they repel each other
are positively charged / have like charges or need to come close together
The substance emits α-particles and γ-rays. The student suggests that it is safe to store the substance in a plastic container of thickness 2mm. State and explain whether the student’s suggestion is correct
container / (2 mm) plastic does not absorb / stop / block / is penetrated by γ
- container / (2 mm) plastic absorbs / stops α
- partially correct as statement
- need lead to stop γ
- γ is dangerous / harmful
β-particles ionise the air they pass through less strongly than the same number of α-particles. Suggest why this is so
- β-particles have charge of smaller size
- β-particles have smaller mass
- β-particles have less energy
- β-particles travel faster/ less time near to air molecule
- effect / force on electrons in air molecules less
The lead cylinder has a narrow central hole. State and explain the effect of the lead cylinder.
(beam) narrow OR straight OR in one direction
radiation in other directions absorbed
movement of alpha when in magnetic field
alpha move in direction of current (F- LHR)
beta moves opposite to alpha as it moves in opposite direction to current
(γ) uncharged OR not equivalent to current
State two differences between nuclear fission and nuclear fusion.
nuclear fission – nucleus / atom splits (into two)
AND nuclear fusion– two nuclei / atoms join together
- {nuclear fission –large(r) mass (number) OR heavy nuclei / atoms involved OR neutrons involved / emitted}
AND nuclear fusion – small(er) mass (number) OR light nuclei / atoms involved OR no neutrons - fission in a nuclear reactor AND fusion in Sun / stars
- fission produces very radioactive / long lasting waste
- fission makes lighter new elements AND fusion makes heavier new elements
- fission at normal p / T AND fusion at high p / T
- fusion produces more energy (than fission)
Radioactive tracers emitting γ-rays can be used in medicine. The half-life of the source of these γ-rays is 6 hours.
(i) Explain why a source of γ-rays used in this way should not have a half-life shorter or
longer than about 6 hours.
longer half-life – radioactive substance active in body for a long time B1
shorter half-life – might be insufficient time for investigation OR it takes time / hours for the tracer to spread round the
body
State another use of radioactive nuclides in medicine.
State and explain one practical application of γ-rays
sterilisation of equipment, treatment of cancer, gamma for diagnosis, radiotherapy
suitable application e.g. sterilisation of equipment, medical diagnosis / treatment, thickness control, detecting leaks / cracks, food preservation
explanation e.g. destroys bacteria, destroys cancer cells, lower amount of radiation detected if thickness too large, radiation detected at site of leak, destroys microbes in food
