AQA physics unit 5

Pregunta	Respuesta
Conclusions from the Rutherford scatttering	1. Atom is made up mostly of empty space --> alpha particles passed straight through 2. Nucleus must have a large positive charge --> alpha particles repelled/ deflected at large angles. 3. nucleus is very small 4. mass is concentrated in the nucleus.
nuclear decay	The process by which an unstable nuclei releases energy/ particles to become more stable.
Alpha radiation	1. 2 protons + 2 neutrons 2. absorbed by paper/ skin/ few mm of air 3. very strongly ionising 4. deflected in magnetic fields.
decay by alpha	nucleon number decreases by 4 proton number decreases by 2
Alpha uses	Because it is very ionising, it allow a current to flow in smoke alarms. When smoke is present, current no longer flows, leading to alarm
Beta - radiation	1. fast moving electron 2. stopped by a few cm of aluminium 3. medium ionising 4. deflected in magnetic fields
decay by beta	neutron turns into a proton proton number increases by 1 release of an anti-neutrino
beta uses	controlling paper thickness
Beta +	1. made up of a positron 2. almost immediately annihilates with electrons, so have 0 range
beta + decay	proton turns into a neutron proton number decreases by 1 release of a neutrino
gamma	1. EM wave 2. absorbed by many cm of lead 3. weakly ionising due to no mass 4. passes straight through magnetic fields due to no charge 5. Emitted due to daughter nucleus being in an excited state, which then de-excites, emitting gamma and becoming more stable.
gamma decay	proton and neutron numbers remain the same
gamma uses	medical tracers treatment of cancer
Why should it not have a short half-life?	So activity does not fall too low too quicky
why should it not have a long half-life?	to avoid damage long-term damage to the body
electron capture	1. nucleus captures and absorbs an orbiting electron 2. proton changes into neutron 3. neutrino is released
safe handling of radioactive sources	1. hold source as far away from body as possible (using long handling tongs). Due to gamma inverse square law and limited range of alpha and beta, this limits the amount of radiation that hits you. 2. store in a lead-lined container 3. should only be used for as long as necessary.
isotopes	elements with the same number of protons but different number of electrons
decay constant	probability of a specific nucleus decaying per unit time.
Activity	The number of nuclei that decay per second
Half-life	The average time it takes for the number of unstable nuclei to decay by half
mass defect	mass of the nucleus is less than the mas of its constituent nucleons
binding energy	The energy required to separate a nucleus into its constituent nucleons
nuclear fission	When large unstable nuclei randomly split to form two smaller nuclei
nuclear fusion	When two light nuclei combine to create a larger nucleus.

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	Creado por Will Welford hace casi 9 años