nuclear and particle physics Flashcards
what is meant by the unified atomic mass unit
1/12 of the mass of a carbon 12 atom. 1u=1.661x10^-27 kg
what is meant by the proton number
the number of nucleons inside the nucleus of the atom also known as the atomic number
deductions from the alpha particle scattering experiment
the vast majority of the mass of the atom is contained within a small volume called the nucleus
the nucleus has a positive charge
the nucleus of the atom is significantly smaller than the atom itself.
equate the energy lost to the electric potential energy at the distance of the closest approach
1/2mv^2=Qq/4π∑r
what is the strong nuclear force
acts between nucleons and holds the nucleus together against the electrostatic repulsion of the protons
what are the properties of strong nuclear force
-acts within the confines of the nucleus
-force acts between nucleons independent of charge
-provides a repulsive force between nucleons for distances of separation of around 0.5x10^-15
-it is attractive between distances of 3.0x10^-15 and 0.5x10^-15
is the relationship between nucleus size and nucleon number linear?
no, R=roA^1/3
ro=constan
calculate density
p=m/v
what is the equation for density of a nucleus
p=3m/4πr^3
what are fundamental particles
are particles that cannot be broken down into smaller components
what are hadrons
are particles consisting of a combination of quarks to give a net charge of zero or whole number. all experience the strong force
name two particles which are hadrons
neutrons and protons
what are leptons and two examples
fundamental particles. electrons and neutrinos
what are quarks
components of hadrons , and have a fractional electric charge. different types of quarks.
up, down and strange.
what is a neutrino
is a fundamental particle with almost no mass and zero charge. each neutrino has an antimatter particle called an antineutrino.
what is the weak nuclear force
felt by both quarks and leptons. It can change quarks from one type to another or leptons from one type to another is responsible for beta decay.
what is an antiparticle
is a particle of antimatter that has the same rest mass, but, if charged, the equal and opposite charge to its corresponding particle.
what two groups can subatomic particles
hadrons and leptons
what are antiparticles
the opposite charge to the associated particle
properties of quarks
spin, baryon number, lepton number, stangness and charm
the quark theory
up, down and strange quarks.
what is an alpha particle
is a particle comprising two protons and two neutrons ejected from nucleus during radioactive decay. it is identical to helium nucleus and is emitted due to its unusually high stability as a particle.
why did they do the alpha particle experiment in a vacuum
the alpha particles cannot travel too far without getting absorbed by the air.
what is a scintillator
when a high energy particle hits it, it gives out a flash of light.
how did the scattering experiment disprove the plum pudding model
alpha particles were passing through the gold leaf, meaning the majority of the atom was empty
some particles were deflected by an angle
some of the particles were deflecting backwards (more than 90º)
what were the inferences made about atoms after the scattering experiment
there is a large area of concentrated positive mass, which managed to repel the positive alpha particle.
there must also be neutrons because the protons couldn’t account for all the mass of the elements
what is the mass of a proton
1.673x10^-27KG
what is the mass of a neutron
1.675x10^-27KG
what is an alpha particle
comprised of two protons and two neutrons ejected from the nucleus during radioactive decay. it is identical to a helium nucleus and is emitted due to its unusually high stability as a particle.
what is beta particle
high speed electron emitted from the nucleus during beta decay. it is produced when a neutron changes into a proton
what is a gamma ray
form of electromagnetic waves, emitted from the nucleus during gamma decay.
what is radioactive decay
the spontaneous and random decay of an unstable nucleus. into a more stable nucleus by the emission of alpha, beta and gamma radiation.
why is radiation spontaneous
because it is not affected by external factors such as pressure and temperature or by chemical reaction.
what happens when alpha, beta and gamma goes through oppositely charged plates.
beta bends toward the positive terminal
gamma is not effected
alpha bends towards the negative terminal.
what is a beta-minus
a neutron in the nucleus breaks down into a proton under the influence of the weak nuclear force, and a beta minus particle and an electron antineutrino are emitted. a beta minus is an electron
what is a beta plus
in a decay where a proton breaks down into neutron under the influence of the weak nuclear force. a beta plus particle and an electron neutrino are emitted. a beta plus is also know as a positron
what is the elemental symbol for the an alpha particle
4
He
2
what is the elemental symbol for a beta minus decay
0
e
-1
what is the mass of an electron in terms of u
1/2000 u
what is the constant ro equal to
1.2fm or 1.2x10^-15m
why is an electron not attracted to the nucleus
the electron experiences the force in the direction of the nucleus, but the electrons velocity is at a right angle to the force, so the electron orbits.
why are two positive charges not repulsive inside the nucleus.
the strong force. If they get close enough the strong force will allow them to exist together
when the nucleus is in equilibrium, what is the strong for equal to?
the electrostatic repulsion
how do you calculate mass defect
predicted mass - calculated mass
how do you calculate Binding energy
e=mc^2
mass defect x speed of light^2
in terms of e, what is the charge of an alpha particle
2e
what is the range of an alpha particle
a few cm. 4
what is the range of beta-
up to 1m
what is the range of beta +
it will find another electron, and annihilate, so short
what is the range of gamma
very long distance
what stops alpha radiation
few mm of paper
what stops beta
few mm of aluminium 4-5mm
what stops gamma
lead, exponential curve, so many cm of lead.
what is annihilation
when a particle and its corresponding antiparticle collide, they annihilate each other and their combined masses are turned into energy, producing a pair of gamma photons. The energy of the photons must equal to intial kinetic energy and rest mass energy.
what is pair production
opposite of annihilation.
pair production is when one high energy photon spontaeneously turns into a particle-antiparticle pair
what do exchange particles do
push and pull particles together
what is the exchange particle in the electromagnetic forces
virtual photon
whats the exchange bosons for the weak nuclear force
W+,W-,Zo
what are baryons
particles containing three quarks
what are mesons
hardrons containing a quark and an anti quark
what baryon numbers do mesons have
0, because they are not baryons
what is strangeness
fundamental property of matter, a quantum number. The strangeness of a strange quark of -1.
the antistrange number is 1.
what are the six different types of quarks
up down, top bottom, strange charm
why is beta minus decay governed by the weak nuclear force
when neutron decays into a proton, its constituent particles change from udd to uud
so one down quark changes into an up quark
only the weak interaction can result into quarks changing type so the decay of a neutron into a proton must be governed by the weak force.
where do muons come from
cosmic rays
what is the electron lepton number of a muon antineutrino
0
