Nuclear Physics Flashcards
what is Rutherfords scattering experiment?
firing alpha particles at a piece of gold foil, surrounded by a fluorescent screen
- if alpha particles stuck it would glow green
- it was done in a vacuum
what were the 3 conclusions form the scattering experiment?
- most of the atom is empty space
- most of the mass is contained in once space (nucleus)
- (nucleus) mass is positively charged
what is the closest approach
firing an alpha particle at a nucleus, the particle repels, kinetic energy turns into potential. so where v=0, gives an overestimate of the radius
what is the closest approach equation
initial Ek= 1/4 πε*Qq/r
what are the disadvantages of the closest approach method
- its an overestimate
- needs thin samples
- needs mono energetic beams
- affected by SNF at close ranges
what is the electron diffraction method for measuring radii
firing electrons at foil to create a diffraction pattern. So you can measure the interference pattern
what is the electron diffraction equation for measuring radii
sinθ=1.22λ /d
what are advantages and disadvantages for electron diffraction
advantages
-electrons aren’t affect by SNF
disadvantages
-need very high speeds for wavelength to be same order of magnitude as diameter
-first minima difficult to detect
-needs mono energetic beams
what’s the relationship between nucleons and radius
not linear adding 1 nucleon to 4 significantly increases it but adding 1 nucleon to 225 doesn’t
how can you make the relationship linear
radius is directly proportional to the cube root of the nucleon number
what’s the nuclear radius equation
r=r0*A^1/3
what is the number of r0
1.4x10^-15(1.4fm)
calculating nuclear density
nuclear density is aways the same , as if you have 2 balls of the same material, regardless of size, they will always have the same density
atomic density vs nuclear density
nuclear- 10^17
atomic-10^3
What are the properties of alpha radiation
-Helium nucleus
- relative charge +2
-relative mass +4
- range in air 3-5cm
-blocked by paper
what are the properties of beta minus radiation
- electron
-relative charge -1
-relative mass 1/2000
-range in air 1-2m
-blocked by aluminium foil
what are the properties of beta plus radiation
- positron
-relative charge +1
-relative mass 1/2000
-Range in air 0m - blocked by electron (annihilation)
what are the properties of gamma radiation
- EM wave
-relative charge 0
-relative mass 0
-range in air infinite
-blocked by lead/ concrete
What makes an atom radioactive
if the nucleus is unstable
-too much mass
-too much energy
- proton/neutron imbalance
What are the three experiments to test types of radiation
-penetrating power
-Range in air
-Deflection in a magnetic field
What radiation is used in smoke alarms
alpha
What radiation is used in pipe leak detection
Gamma
what radiation is used in medical tracers
Gamma (technitium 99m)
What radiation is used in monitoring material thickness
Beta
Name 4 natural sources of radiation
cosmic rays
Radon gas
Food/drink
The ground
Name artificial sources of radiation
medical equipment
Buildings
How does the inverse square law relate to nuclear physics
intensity is inversely proportional to the square of the distance from the centre of the gamma source
What is background radiation
natural radiation that occurs. This could ruin experiments results so make sure to take readings and subtract that off of any readings you have to improve accuracy
describe the activity of a radiation source
radioactive decay is random, so its impossible to predict which atom will decay next. however there is a pattern with larger atoms. the same proportion decay every second
what is the decay constant
it tells you the probability of decay. the larger the decay constant, the faster the decay.
what is activity
the number of atoms that decay each second. measured in Bq. also called rate of decay
what is special about a rate of decay graph
its exponential, following the half life rule
what is molar mass
mass of 1 mole of that substance
1mol of uranium is 235g
what is half-life
the time taken for half of the unstable nuclei to decay
why is nuclear waste so serious
its half life is 1000s of years so it needs to be stored in geologically safe areas to prevent people and places getting radiation poisoning from exposure
what is carbon dating
measuring the age of an object through the decay of carbon-14, an isotope of carbon that trees absorb alive but stop after death, decaying constantly from that point.
what are the 5 major problems with carbon dating
- you find the age of the material, not the object
- the object could become contaminated
3.high background radiation obscures readings - sample size maybe to small
- unsure of amount of carbon-14 in the atmosphere previously
what decay happens when there’s too much mass
alpha
(more than 62 protons)
what decay happens when there’s too much energy
gamma
what decay happens when there’s too many neutrons
beta minus
what decay happens when there’s too many protons
beta plus or electron capture
how to draw a stability curve
(draw stability curve, check on century)
why are more neutrons good
Most stable nuclei have more neutrons then protons
Protons are the destabilising particle, as the electromagnetic force is trying to push them apart
Whereas neutrons only produce the strong nuclear force which binds the nucleus together
what is u
1/12th of the mass of carbon 12
how do you split a nucleus into its constituents
you put in energy to overcome the SNF. similar to putting work into a spring. this is binding energy
what are the 3 binding energy definitions
The energy required to separate a nucleus into its individual constituents
The energy released when combining individual nucleons are combined to form a nucleus
This energy is equivalent to the mass defect converted into energy
what 3 elements should you know of on a biding energy graph
iron-56
hydrogen-2
uranium-238
what’s the most stable element
iron
what does a binding energy graph tell us
The higher the binding energy per nucleon the more stable the element is
-Earlier we saw how when individual nucleons are combined into a nucleus they get lighter
-Meaning each nucleon gets a bit lighter
-A nucleon in an iron nucleus is the lightest
how to create energy
there needs to be less mass in the end products than the start
binding energy is proportional to mass defect
creating energy with fission and fusion
in fission and fusion, number of nucleons stay the same before and after, so the mass defect per nucleon changes
what is nuclear fission
nuclei with more than 62 protons split into 2 smaller stable nuclei. this happens by firing a low speed Neutron at it
what element is usually used in fission
uranium 238 (referred to as parent nuclei). the 2 more stable are the daughter nuclei. it also releases 2/3 neutrons and energy.
differences in the parent and daughter nuclei in fission
the binding energy is higher in the daughter nuclei. and therefore higher mass defect. so due to the number of nucleons not changing, the mass defect increases as the nucleons in the daughter nuclei are lighter. (this is released as energy).
what is nuclear fusion
2 smaller nuclei combing into a more stable one. however its harder for this to happen as they need to be very close to work and overcome the SNF. this happens naturally in the sun. fusion requires a huge amount of energy and has yet to be replicated on earth
what element is usually used in fusion
isotopes of hydrogen called deuterium and tritium
differences in the daughter and parent nuclei in fusion
binding energy in daughter nuclei is still higher, therefore mass defect has grown (daughter nucleons are lighter). this gets released as energy. this is due to them being even more stable now (closer to iron)
what are the 5 key components of a nuclear reactor
fuel rods
coolant
control rods
shielding
moderator
what is a fuel rod
contains uranium or plutonium. 5% uranium-235 which fissions easily the rest is uranium-238 which doesn’t.
uranium undergoes treatment before used as its 1% when mined
what is coolant
its used to remove heat that’s produced by fission, needs to be high specific heat capacity. ( most use water now). its important it keeps circulating. hot water uses steam to spin turbine
what are control rods
usually made of boron to absorb neutrons. this slows down fission reactions. can be lowered or raised to increase or decrease fission.
what is shielding
reactors are surrounded in thick layers of concrete to protect the reactor from external factors and to prevent radiation from getting out.
what is a moderator
fuel rods must be placed in a moderator. graphite and water are examples. they both slow down neutrons producing fission.
what does supercritical mass mean
every fission event causes more than 1 event, increasing amount of power released
what does critical mass mean
every fission event causes 1 more event, causing steady amount of power released
what does subcritical mass mean
every fission event causes less than 1 event, decreasing amount of power released
what happens to neutrons in a nuclear reactor if it doesn’t undergo fission
-hit U-235 too quickly and scatter
-hit U-238 and be absorbed
-hit a U-238 and scatter
-hit the reactor wall
-be absorbed by a control rod
how to reduce speed via collision
neutrons are slowed down via collisions with moderator molecules, releasing energy. works best when moderator atoms are close in mass to neutrons. about 50 collisions are needed to slow down a neutron enough, causing it to become in thermal equilibrium. getting the name thermal neutrons
what’s the benefit of multiple fuel rods
neutrons pass through a moderator between events ( one couldn’t stand this)
control rods need to fit inbetween
increases surface area (improves heat dissipation)
fuel rods can be replaced in stages
what are the differences in used and unused fuel rods
unused rods contain Uranium (an alpha emitter) so its easy to block
Daughter nuclei are neutron rich so are gamma/beta emitters, therefore a lot more dangerous.
daughter nuclei are also very hot when removed from the reactor.
how to dispose of nuclear waste
its initially left in cooling ponds for a number of years and handled by robots.
plutonium/uranium is recycled
waste is then stored in concrete boxes, deep underground in geologically safe areas for 1000s of years to wait out is very long half-life.
transporting it is dangerous to the public so it kept in crash resistant casing.
