7.3 Nuclear physics - IB

the splitting of a heavy nucleus into lighter nuclei. releases energy

nucleus is struck by neutron - splits into nuclei and more neutrons are ejected, colliding with other nuclei and continuing fission, lasting until all material is used up

a certain minimum mass of an element (uranium-235) that must be present, otherwise neutrons escape without causing further reaction

joining of two lighter nuclei to produce a heavier nucleus. energy is released due to mass defect

kinetic energy of the nuclei has to be very high to overcome electrostatic repulsion

alpha particles were directed at thin gold foil in vacuum chamber. the number of particles deflected at different angles were recorded

because attractive nuclear forces between nucleons dominate over repulsive electrostatic forces between protons

the mass of nucleus created is slightly less than total combined mass of original nuclei. the mass defect is equal to binding energy released since the nucleus formed is more stable

repulsive electrostatic forces between protons begin to dominate, and these forces tend to break apart the nucelus

an unstable nucleus is converted into stable nuclei with lower total mass - the mass defect is equal to binding energy released

fusion releases more energy per kg. the gradient of binding energy per nucleus much stepper at lower A values (when fusion occurs), meaning larger binding energy per nucleon is released

the atom is mainly empty space

there is a pos nucleus at the centre, repelling the positively charged alpha particle

that the nucleus is extremely small and chrage of atom is concentrated

particles not made up of any smaller components

fundamental particles that make up other subatomic particles, eg neutron and proton

particle made up of quarks

up u, charm c, top t, down d, strange s, bottom b

+2/3

-1/3

same mass but all properties are opposite, eg charge, baryon number, strangeness…

uud

ddu

particle made of three quarks (no anti quarks)

pair of quark and anti quark

+1/3 (antiquarks have -1/3)

strange quark has -1, anti strange has 1, everything else 0

weak interaction

charge, baryon number, lepton family number always, strangeness sometimes

fundamental particle, not made up of quarks

electron, muon, tau, electron neutrino, muon neutrino, tau neutrino

tau heaviest, then muon, then electron. neutrinos have negligible amost zero mass

all weak nuclear force/interaction, those that have charge also with electromagnetic interaction

all leptons have lepton number of +1, just belongs to different families

strong, electromagnetic, weak

the most stable baryon, has the longest half life and is lightest - cannot decay into lighter particle

neutron turns into proton - the down quark turns into an up quark, antineutrino and electron also emmitted

proton turns into neutron - up quark turns into down quark + positron + neutrino

pos (u and anti d), neg (anti u and d) and neutral (u and anti u or d and anti d). lightest mesons, most stable. exchange particle of strong force

pos (u and anti s), neg (anti u and s) and neutral (anti d and s or d and anti s). heavy and unstable, decay into pions. long lifetimes (characteristic of particles w strange quarks). decay through weak interaction

contain strange quark. produced through strong interaction, decay through weak

holds the nucleus together against electromagnetic repulsion. very short range. keeps quarks bound within nucleus

repulsive until 0.5fm

attractive from 0.5 to 3fm

max attractiveness at 1fm

zero after 3fm

pion (between nucleons) and gluon (between quarks) - hadrons subject to interaction since made up of quarks

leptons cannot interact w strong force since not made of quarks

responsible for radioactive decay of atoms

w-, w+, z0 bosons - depends on type of interaction

w- boson

w+ boson

gluons and mesons

photon

graviton

it is impossible to have isolated quarks - they have never been found on their own, only in mesons or baryons

a particle responsible through its interactions for the mass od the particles od the standard model, in particular for masses of w and z bosons

an electron is absorbed by a proton in the nucleus, resulting in release of a neutron and electron neutrino - mediated by w+ boson

an electron collides with a proton, and a neutron and electron neutrino is emmitted - mediated by w- boson

no mass, no charge, its own antiparticle

virtual particles/bosons that mediate/carry/transmit the fundamental force between interacting particles - when two particles exert a force on each other, a virtual particle is created

only theoretical, no mass, no charge, its own anti particle