particles and radiation Flashcards
what’s the relative mass of an electron?
0.0005
what’s the atomic number?
number of protons in the nucleus, has the symbol Z.
the number that defines the element
what’s the nucleon number?
also called the mass number
has the symbol A
tells you how many protons and neutrons there are in the nucleus.
what’s the specific charge of a particle?
the ratio of its charge to its mass
what are isotopes?
atoms with the same number of protons but different number of neutrons
what’s isotopic data?
the relative amounts of the different isotopes of an element present in a substance.
what are all the forces that act on the nucleons in a nucleus.
electromagnetic
gravitational
strong nuclear
what does the electromagnetic force do in the nucleus of atoms?
causes the positively charged protons to repel from each other
what does the gravitational force do in the nucleus of atoms?
causes all the nucleons in the nucleus to attract each other due to their masses
why is the strong nuclear force needed to act on nucleons in the nucleus?
the repulsion from the electromagnetic force is much bigger than the gravitational attraction so there must be another force to hold the nucleus together.
what have experiments shown of how the strong nuclear force changes with distance and between different nucleons?
it has a very short range
it’s repulsive at distances smaller than 0.5fm to stop it crushing the nucleus.
becomes attractive past 0.5fm
it then reaches maximum attractive value and then falls rapidly towards 0 after 3fm
it works equally between all nucleons
what is nuclear decay?
when unstable nuclei emit particles to become more stable
what size atoms does alpha decay occur in?
very big atoms, more than 82 protons.
because they are too big for the strong nuclear force to keep them stable
how far can alpha particles travel in air?
only a few cm
how could you test the range of an alpha particle?
observing the tracks left behind in a cloud chamber
or use a Geiger counter or a spark counter by changing the distance it is from the alpha source
what is beta decay?
the emission of an electron from the nucleus along with an antineutrino
when does beta decay occur?
if isotopes are neutron rich. when a nucleus ejects a beta particle, one neutron is turned into a proton
how far can a beta particle travel in air?
several metres
name the 7 types of electromagnetic radiation in order of increasing frequency
radio waves, microwaves, infrared, visible light, UV, X-rays, gamma rays
name the 7 types of electromagnetic radiation in order of increasing wavelength
gamma rays, X-rays, UV, visible light, infrared, microwaves, radio waves
what happens to the energy of electromagnetic radiation as frequency increases?
energy increases
what is an antiparticle?
a particle with the same mass and rest energy but with opposite charge
what’s pair production?
when energy is converted into mass, you get equal amounts of matter and antimatter.
only occurs if there’s enough energy to produce the masses of the particles
always produces a particle and its corresponding antiparticle
what’s the minimum energy needed for pair production?
the total rest energy of the particles that are produced.
this is all the energy that would be produced if all its mass was transformed into energy
what’s the minimum energy you’d need for an electron-positron pair in pair production?
2x(0.510999)= 1.021998 MeV
when does annihilation occur?
when a particle meets its antiparticle
what is annihilation?
all the mass of the particle and antiparticle gets converted back to energy in the form of two gamma ray photons
how to work out the minimum energy of photon produced from annihilation
this is equal to the rest energy of particle type annihilated in MeV
how do PET scanners in hospitals work?
they put a position emitting isotope into the blood stream and detect gamma rays produced by electron-positron annihilation.
what’s a photon?
a packet of EM radiation/ energy
what are hadrons?
particles that can feel the strong nuclear force
they’re not fundamental particles
they’re made up of quarks
two types- baryons and mesons
what are baryons?
protons, neutrons, stigmas
they’re all unstable apart from free protons
do baryons decay?
all baryons apart from protons decay to become other particles
what’s the baryon number for an anti baryon?
-1
what’s beta decay caused by?
the weak interaction
what’s the equation for Neutron decay
n—-> p + e- + Ve (line on top)
where do you get loads of mesons?
in high energy particle collisions
are mesons stable?
no, they’re all unstable
what particles are mesons?
pions and kaons
what are leptons?
they are fundamental particles that don’t feel the strong nuclear force.
only interact with particles through the weak interaction
examples of leptons
electrons, muons
what type of interactions do neutrinos take part in?
weak
what needs to be conserved in particle interactions?
baryon number, both types of lepton number, charge, energy, momentum
what’s the quark composition of a baryon?
three quarks
what’s the quark composition of an antibaryon?
three antiquarks
what’s the quark composition of a proton?
uud
what’s the quark composition of a neutron?
udd
what’s the quark composition of a meson?
one quark and one antiquark
do pions have strangeness?
no, they’re only made up of u and d quarks and anti quarks
do kaons have strangeness?
yes they do
what’s quark confinement?
its not possible to get a quark by itself
what would happen if you blasted a proton to try and remove a quark?
the single quark would not be removed
a u and anti u pair will be produced in pair production instead
what happens to the quark composition during beta minus decay?
udd changes to uud (neutron into a proton)
what’s changing a quarks character?
a quark changing into another quark
what happens to the quark composition in beta plus decay?
uud changes to udd (proton to a neutron)
how can you get particles to travel at high speeds close to the speed of light?
use particle accelerators
what’s the disadvantage of particle accelerators?
very expensive to build and run
what are exchange particles?
how forces act between two particles
they are virtual particles
what are virtual particles?
they only exist for a very short time- long enough to transfer energy, momentum and other properties between particles in the interaction
what’s the electrostatic repulsion between two protons caused by?
the exchange of virtual photons (the exchange particles of the electromagnetic force)
what are exchange particles that cause 4 fundamental forces in nature called?
gauge bosons
for a strong interaction, what’s the gauge boson and particles effected?
gauge boson- pions
effects hadrons only
for an electromagnetic interaction, what’s the gauge boson and particles effected?
gauge boson- virtual photons
effects charged particles only
for a weak interaction, what’s the gauge boson and particles effected?
W+, W- bosons
effects all particles
what does the size of the exchange particle determine?
the range of the force
heavier exchange particles have a shorter range so the force itself also has a shorter range.
for the weak force, what is the range like and why?
very short range because W bosons have a mass about 100x a proton, so creating it uses so much energy that it can only exist for a very short time and can’t travel far.
for the electromagnetic force, what’s the range like and why?
range is infinite due to a photon having 0 mass
how are exchange particles represented on particle interaction diagrams?
wiggly lines
how to draw particle interaction diagrams
incoming particles start at the bottom of the diagram and move upwards
baryons stay on one side and leptons stay on the other
W bosons carry charge from one side of the diagram to the other
a W- boson to the left is the same as a W+ boson to the right
explain how to draw a beta minus particle interaction diagram
on left hand side, neutron in and proton out, wiggly line to right side with W- boson.
on right hand side, electron and antineutrino out
explain how to draw a beta plus particle interaction diagram
on left hand side, proton in and neutron out.
wiggly line to right side with W+ boson
on right hand side, positron and electron neutrino both out
explain how to draw a electron capture particle interaction diagram
on left hand side, proton in and neutron out
wiggly line to right side with W+ boson
on right hand side, electron in and electron neutrino out
explain how to draw an electron-proton collision particle interaction diagram
on left hand side, proton in and neutron out
wiggly line to the left with W- boson
on right hand side, electron in and electron neutrino out
explain how to draw an electromagnetic repulsion particle interaction diagram
left hand side, electron/ positron in and electron/ positron out
wiggly line in middle with photon
on right hand side, electron/ positron in and electron/ positron out
how are strange particles created
via strong interaction
whats the strangeness value of any leptons
0
what type of interaction do strange particles interact through?
weak interactions
is strangeness conserved in weak interactions?
not always
is strangeness conserved in strong interactions?
yes
what is conserved in all particle interactions?
charge, baryon number, electron lepton number, muon lepton number
A polonium-210 nucleus is formed when a stationary nucleus of bismuth-210 decays. A beta-minus (β−) particle is emitted in this decay.
Outline, with reference to β− decay, why bismuth-210 and polonium-210 have different proton numbers
A neutron decays into a proton
n—->p+e- + anti Ve
The kinetic energies of β− particles emitted from a sample of bismuth-210 are analysed. These β− particles have a range of kinetic energies.
The total energy released when each nucleus of bismuth-210 decays to a nucleus of polonium-210 is 1.2 MeV.
Figure 1 shows the variation with Ek of the number of β− particles that have the kinetic energy Ek.
Explain how the data in Figure 1 support the hypothesis that a third particle is produced during β− decay.
(Missing) energy carried off by third particle Or
(A third particle must be produced) for conservation of energy✔
Accept energy is converted into mass of third particle.
Where third particle is named must be a neutrino or an antineutrino.
There is missing energy (When) a beta (particle) has less than 1.2 MeV (of kinetic energy).
Or
The law of conservation of energy appears to be violated when beta (particle)
has less than 1.2 MeV ✔
This third particle is an electron antineutrino.
Explain why an electron antineutrino, rather than an electron neutrino, is produced during β− decay.
(It must be an electron antineutrino to) conserve lepton number✔
An electron and (electron) antineutrino have lepton numbers of opposite signs. Or
An electron and (electron) antineutrino have a (total) lepton number of zero. ✔
The positron produced in the interaction in Figure 2 slows down and collides with a lepton in a molecule of water.
Describe the process that occurs when the positron collides with this lepton. In your answer you should identify the lepton in the molecule of water.
Lepton (in the water molecule) is an electron ✔
Max 2 from
annihilation ✔
gamma photons are produced ✔
Two (gamma) photons are produced (that travel) in opposite directions. ✔
Deduce whether the positron or the electron antineutrino is likely to travel the shorter distance in the tank of water before interacting.
positron is charged and the (electron) antineutrino is neutral ✔
The antineutrino only interacts via the weak interaction / The positron interacts
via the electromagnetic interaction (and weak interaction)✔
The antineutrino’s (weak) interaction is shorter range / the antineutrino is less likely to get close enough to interact (with particles in the water so will travel further) / the antineutrino will interact with fewer particles✔
The positron’s (electromagnetic) interaction has a longer range / the positron does not have to be so close to interact (with particles in the water so will travel a shorter distance) / the positron will interact with more particles✔
