Radioactivity Flashcards
What is activity of a radioactive source?
Number of decays.
How to calculate how many nuclei are left?
N = No / 2^n
where n is how many half lives have past.
What are Bequerels in SI base units?
s^-1
What is used in medical radioactive tracers?
Iodine - 123, gamma
What tracers are used in sterilising equipment?
Cobalt - 60, gamma radiation attacks microbial dna, stops them reproducing.
How are tracers used in manufacturing paper?
Radioactive source and detector on both sides of paper. If activity decrease, paper is not the right thickness and therefore the roller needs to squeeze harder.
What tracers are used in smoke screen detectors?
Americium alpha particles ionise the air, smoke interrupts streams of negative and positive ions, sounds alarm.
How is carbon-14 used in carbon dating?
Carbon-14 is formed in upper atmosphere by solar radiation when neutrons hit nitrogen-14 and trasmute it into carbon 14 + a proton. Carbon 14 is inhaled and is stored in plants and animals. Carbon 14 experiences beta minus decay and decays into Nitrogen 14 again. By using half life, you can determ the age by measuring proportion of nuclei.
What nuclei will undergo fission?
Nuclei heavier than iron.
What is critical mass? and what are the variables.
The minimum value of mass that a nuclei will undergo sustainable fission.
- mass < critical mass: more neutrons are escaped than produced.
- mass = critical mass: neutrons escaping = neutrons produced
- mass > critical mass: more neutrons produced than escaping.
What is induced fission?
Slow moving neutrons splits the nucleus into two smaller nuclei and fast moving neutrons.
What does the moderator do?
Slows down the fast moving neutrons to increase chance of more fission of Uranian 235.
What do the control rods do?
Absorbs some of the neutrons.
Why does helium need a higher temperature to fuse?
Higher net positive charge and therefore a large electromagnetic repulsion.
