nuclear physics

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plum pudding
they believed the atom was made up of a positive dough spread evenly with negative electrons scattered throughout.electrons within the atom were very small compared to the entire atom.
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Rutherford's scattering experiment
1.Fired alpha particles (positively charged) at a thin sheet of gold foil 2.this was done in an vaccum container 3.with a zinc sulphate screen all around-which emits light when an alpha particle hits it 4observed using a moving microscpe in a dark ro
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results:
almost all alpha particles passed through with little or no deflection. 1 in every 8000 were reflected or scattered through angle +90 and some slightly deflected
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the nuclear model
1. most mass must be gathered in one small volume - the NUCLEUS which can repel fast moving alpha particles 2.nucleus must be positively charged - repel positive alpha particles 3. most of atom is empty space 4.negative electrons orbit far away
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Geiger counter tube (GM)
The counter consists of a tube filled with an inert gas that becomes conductive of electricity when it is impacted by a high-energy particle. When a Geiger counter is exposed to ionizing radiation, the particles penetrate the tube and collide with th
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IONISATION
removal of one or more electrons from an atom. when radiation enters a gm tube it may ionise the atoms insie, the electrons are then attracted to a positive wire nd a current flows
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the inverse-square law
from a source gamma radiation will spread out - can be considered the same in all direction (isotropic). as we move away the amount of energy is spread over a bigger surface area - therefore the less intense it is I=KIo/x^2
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do not always need intensity of source Ia(x^2)=Ib(x^2)
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background radiation
REMEMBER to subtract background raditation from recorded radiation to get a true reading. 87%natural gas 13% man-made
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radioactive decay
it happens randomly and spontaneously: there is no was of predicting when a nucleus will decay and external factors do not influence it at all (e.g. p and temp)
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DECAY CONSTANT (Y)
every radioactive isotope as its on probability that a nucleus will decay
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ACTIVITY (A)
number of decays that will happen every second - 1 becquerel (Bq) is equal to one decay per second
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change in number of nuclei + activity
-ΔN/Δt=YN + A=-YN
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Exponential decay
As time passed the number of nuclei that decay will DECREASE N=Noe^-Yt A=Aoe^-Yt
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HALF-LIFE
time it takes for half of the substance to decay. half-life is linked to the decay constant. if there is a high probability that a nuceus will decay (Y=BIG) - if there is a low probability (Y=SMALL) T/2=ln2/Y where T/2 - half-life
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what does the N against Z graph look like?
1.follows N=Z around Z=20 2.curves up to N=120 Z=80 3.B- above and B+ below
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explain the N against Z graph
it shows stable and unstable nuclei. alpha emmiters are the 'valley of stability' - b+ and b- bothe represent radioactive nuclei
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why doesn't it follow the N=Z?
protons repel with the electrostatic force but the strong nuclear force is stronger between 0.5-3fm. line of stability follows N=Z at low values. as nucleus gets bigger there are more protons, when they become over 3fm apart they ONLY feel
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electrostatic force. to keep the nucleus together we need more neutrons which feel no electrostatic repulsion ONLY attraction of the strong nuclear force.
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alpha decay
loss:2 protons, 2 neutrons. alpha particle is a helium NUCLEUS (NOT ATOM). energy is released in the decay most of it being KE. the velocity of the alpha particles is much greater than the nucleus
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beta minus decay
neutron is transformed into a proton (that says in the nucleus) and an electron (which is emitted).
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beta plus decay
a proton is transformed into a neutron and a positron
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electron capture
a nucleus can capture an orbiting electron - proton then turns into a neutron
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nucleon emission decay - is it possible for an unstable isotope to emit a nucleon from the nucleus?
in proton rich nuclei it is a possible for a proton to be emitted in neutron rich nuclei is it possible for a neutron to be emitted THESE ARE BOTH VERY RARE CASES
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gamma ray emission
alpha emission is often followed by gamma emission. the daughter nuclei is left in an excited state so when the electron falls back to ground state - it emits a gama photon. no nuclear structure change just a change in ENERGY
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where does the energy come from in gamma ray emission?
it comes from the MASS DEFECT. at nuclear level mass and energy are interchangable
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gamma rays have two important medical applications:
RADIOTHERAPY - a cobalt 60 source is aimed at a cancerous tumour. the genetic material of caners is generally unstable, the gamma photon can have sufficient interaction to the rend the cells nonviable. however, it can effect normal cells aswell
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TRACERS - e.g. technetium-99 can be injected into the body and used to monitor blood flow using a gamma camera.
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explain the closest approach of alpha particles experiment
1. rutherford fire alpha particles at gold atoms in a piece of foil. 2.they aproach the nucleus but slow down as the electrostatic replusion forces gets stronger. 3.eventually they stop, and all the KE is transferred to potential energy. 4.they come
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nuclear radius
R=r0A^1/3
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mass and energy
(mass of protons + neutrons) - mass of nucleus =
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explain binding energy and state formula
as protons and neutron come together they are pulled together by the strong nuclear force. energy must be done again the strong nuclear force to seperate the nucleus into the nucleons it is made of - binding energy E=
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BINDING ENERGY PER NUCLEON
the energy required to remove one proton or neutron from the nucleus
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binding energy gragh - state important features
Fe (iron) at 8.8eV and 56 - requires the most energy to remove and electron meaning it is the most stable. before the peak = fusion after peak = fission
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INDUCED NUCLEAR FISSION
Fission occurs when a nucleus splits into to two smaller nuclei. it happens by firing slow moving neutrons at uranium 235, platonium 239 and thorium 232. the nucleus absorbs a neutron and splits into two smaller nuclei releasing energy and 2-3 spare
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CHAIN REACTION
the spare neutrons realeased in the fission experiemnt may go on to be anbsorbed by other heavy nuclei which could cause further fission's and so on
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CRITICAL MASS
for a chain reaction to happen the mass of the fissionable material much be greater than a certain minimal value - the critical mass. 1.if mass
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FUSION
protons and neutrons feel the attraction of the strong nuclear force but only protons feel repulsion. for light nuclei, adding and extra proton increases the strong nuclear force to pull the nucleon together. this is because he range of snf is greate
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FISSION
adding a proton the to nuclei adds to the electrostatic repulsion. the bigger the nucleus becomes to the less the outter protons feel the snf - binding enegery decreases for heavier nuclei. a big nucleus will break into smaller more stronly bonded nu
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FUEL RODS
this is where nuclear fission reactions happen. they are made of uranium spread out in a grid like pattern. natural uranium is a mixture of different isotopes. thr one used in fuel rods is said to be enriched - so more reactions take place
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Rutherford's scattering experiment

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1.Fired alpha particles (positively charged) at a thin sheet of gold foil 2.this was done in an vaccum container 3.with a zinc sulphate screen all around-which emits light when an alpha particle hits it 4observed using a moving microscpe in a dark ro

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results:

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the nuclear model

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Geiger counter tube (GM)

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