nuclear physics (some stuff missed out that i already know) Flashcards
discribe thomeses sugestion (plum pudding modle)
atoms are sphears of positive charge with tiny e- stuck in them (like fruit in a plum pudding)
draw a diagram of the rythoford scattering diagram and simple description
see pg 154
- an alpha souce fired a beem of alpha particals a a thin (few atom thick) peice of gold foil
- any deflected atoms were then detected by a circular detector screen serounding the source and the foil
what was the expected outcome of ruthurfords experoment?
what was observed (2)?
what does this mean (4)?
- the positivly charged alpha particals would be deflected by a very small amount by the e- within the atom
- most aplha particals went straight through the foil with no deflection
- small number of alpha particals were deflected by a large amount (some even more the 90 degrees)
- most of the atom must be empty space as most alpha particals went straight through the foil
- the nuclues must be very small as very few alpha particals were reflected back
- the nuclues must have a large positive charge, as some positivly charged alpha particals were repelled by large amounts
- most of the atoms mass must be in the nucues, since fast moving paricals with high momentum were deflected by the nuclues
- atom mostly empty space
- nuclease very small
- nucluease has a large positive charge
- nulcleus dense
you can calculate the closest aproch of the alpha partical to the nucluease (thereofre an estimation of the raduis) when the alpha partical is deflected ___
give closest approach equation
180 degrees
Ek=E (electifc field strenth) at closest aproach
therefore
E=kQ1Q2/r^2 in this equation
closest aproach:
r=rootKQ(1)Q(2)/mv^”
what is the de broglie wavelenth for a moving e- when taking into account relevistic effects?
(this is used for ellectron diffrection to estimate nuclear radius)
(not given)
λ ~ hc/E
(this is close to the E=hc/λ equation of enegy of a photon)
if a beem of ___ ____ __ is directed onto a thin film of meterial in front of a screen, a ________ ______ will be seen on the screen.
give equation for where the first minimum appeares
high enegy e-, diffraction pattern
sinθ ~ 1.22λ/2R
where R is the raduis the e- has been scattered by
draw intensity over angle of diffraction for ellectron diffraction
see pg 156
(very prenounced and fast decrease in intensity) (intensity never actually reaches 0)
what is the raduis of:
an atom
a nucleus
0.05nm (5x10^-11m))
1fm (1x10^-15m)
(some times you are surposed to use 1.4fm as R(0)=1.4fm)
R∝
R=
where R(O) =
R∝A^1/3
where A is nucluen NO.)
R=R(O)A^1/3
R(O) = 1.4fm
R(O) is just a constent
what are the reasons a nuclues may be unstable
(dubble check)
(not sure)
- too many neutrons - (every parical is unstable so too many uneeded nuetrons will also make something more unstable)
- too many protons - (if there are too many neutrons the electrostatic force will become greater then the strong force making the nuclues unstable)
- too much enegy - (releses a gamm photon)
for each give there ionisation, speed, penetrative power
1.α
2.B-
3.B+
4. γ
- strong, slow, paper or few cm in air
- weak, fast, few mm of aluminuim
- annialated imediatly
- very weak, speed of light, many cm of lead or few m of concrete
what do you use to record count rate
geiger counter
explain an experoment you can preform to detemin the type of radiation form a souce
- recored the backroud radiation with no source present
- place source next to geiger counter and recored count rate
- place a piece of paper between the source and the geiger counter and record count rate (if it has substatialy decreased then the source emitted α radiation)
- palace a few mm of aluminuim bewteen th geiger counter and teh cource (if there is a substantial drop in count rate then the source produced B- radiation)
- if there has been no drop in count rate then the source produced y radiation)
explain how you can controle how thick a meterial is using radiation
- a meterial is flattened as it is fed through rollers…
see pg 158 if u really dont know
ionisation is….
α particalls are ionising as they ____ __ ___ _____.
B- are ionising as they…
and y are ionisiong because of the…
the addition or removal of electrons to an atom to creat ions
pull e- off atoms
knock electroins off atoms
photoelectric effect
α particals cant _____ ______, so they are only dangerus if you _____ them. tho if you do they _____ ______ body tissue and are very ______.
B- radiation is ______ _______ so do _____ ______ to body tissue.
penetrate skin, ingest, quickly ionise, dangerus
less ionisiong, less damage
give 3 sources of backround radiation
- radon gass in air - (largest contrebuter)
- cosmic rays
- living things - (contain carbon and some of this will be radioactive carbon 14)
(or medical equipment)
the intensity of gamma radiation obayes the _______ _____ ___
give this equation
inverse square law
I=k/x^2
A (activity) is…
what is the unit
λ (decay constent) is…
what is the unit
therefore
A =
A can aslo be called the…
therefore
-λN=
- the number of radioactive nuclei (N) that decay per second
- Bq (becuerels) (1Bq=1 decay per second)
- the probability of a given radioactive nucleus decaying per -second
- s-1
A=λN
nomber of nuclie that decay per second = probability that a nuclie decays x
rate of change of N
-λN=ΔN/Δt (- as the nomber of atoms left is decreasing)
half life (T1/2) is…
give T1/2 equation
the avarge time it takes for the nomber of unstable nuclie to half
T1/2 = ln(2)/λ
what is the graidient of a ln(N(0)) over t graph
-λ
give the number of unstable nuclei equation (not A=λN)
N=N(0)e^-λt
give the activity equation (not A=λN)
A=A(0)e^-λt
carbon 14 has a T1/2 of…
5730 years
draw the N (nomber of noutrons) Z (nomber of protons) graph and annotate annotate where this is what decay
see pg 164
α decay happens ______ nuclie
B- decay happens in ________ _____ nuclei
B+ decay happens in _______ _____ nuclei
y decay happens when nuclei have _____ _____ _____
heivy
neutron rich (n=p+B++Ve)
proton rich (p=n+B-+antiVe)
too much enegy (or through electron capture)
nuclear fission is where a ______ nuclei _____ into ____ ______ nuclei
this happens ___________ or can be ______
large, splits, two smaller
spontaniasly, induced
how can you induce nuclear fission?
(this is used in nuclear reactors)
fire a low enegy (low speed) neutron at a U-235 nucleus.
these low energy neutrons are called thurmal neutrons
why is enegy released during nuclear fission?
because the new smaller nuclei have a higher binding enegy per nucleon
the ______ the nuclues the more _______ it will be. thereofre the nuclueas will be more likley to ____________ _____.
this means that ___________ _____ limits the _______ __ _________ that a nucleus can contain. therefore _______ the possible ________.
larger, unstable, spontaneously fission
spontaneouse fission, nomber of noucluns, limiting, elements
(big flash card)
explain how nuclear reactors produce useful power
- rods of unranium that are rich in U-235 are used as ‘fuel’ for fission reactions
- these are placed into the reactor remotly to keep workors far away and reduce exposure
- rods of unranium that are rich in U-235 are used as ‘fuel’ for fission reactions
- some U-235 undergo spontaneously fission, this produces some neutrons
- these emitted neutrons are then slowed through elastic collisions by a moderator (like water) to enable U-235 nuclei to be able to capture the now thurmal nuetrons
- the U-235 undergo induced fission as a result of capturing the thermal neutron and produce more neutrons
- this causes a chain reaction
3.- a super critical mass of U-235 is normally used. the rate fission reaction and the chain reaction is then controled using controle rods
- coolent (wich is usally the same water used as the moderator) is sent around the reactor to remove heat produced during fission.
- the steam produced is then used to power electrical-generators turbines.
- coolent (wich is usally the same water used as the moderator) is sent around the reactor to remove heat produced during fission.
5.- the nucluear reactor is surrounded bu a thick concreat case that acts as sheilding. preventing radiation from excaping
nuclear waste need to be disposed of carfully as it has a _____ half life.
long
what is an example of a moderator?
why is this one used?
water
particals of similar mass are more efficient at slowing down neutrons through eleastic collisions. water is used as it contains hydrogen.
what is critical mass within nuclear reactors?
the mass of fuel (U-235) that is needed to ensure a chain reaction at ‘steady rate’ were 1 fission follows another
what do controle rods do in the reactor?
what meterial is usally used?
they absorbing some of neutrons that are released by U-235 fission therefore limitilng the number of thermal neutrons avalible to be captured by other U-235 nuclei therefore controling the rate of fission and the chain reaction.
boron
how many neutrons are released during U-235 fission?
3
why is enegy released during nuclear fussion?
because the new heavier nuclei have much higher bindnig enegy per nucleon
fussion requiers a lot of ______ as the _______ ______ between the 2 nuclei must be overcome to get close enough for the ______ _____ to attract the nuclei.
the enegy need is about…
enegy, electrostatic repulsion, strong force
1Mev
binding enegy is…
the enegy needed to seperate a nuclues into its constituent parts
mass defect of 1u =
931.5 MeV
binding enegy (B) =
avarge binding energy per nucleuon (MeV) x Nucleon number (A)
what is the most stable nuclei and its nucleuon nomber?
Fe-56 (iron)
draw the avarge binding enegy per nucleon over nucleon number graph
see pg 169
an increase in binding energy after an interaction results…
this means…
a mass defect
enegy will be released (E=Δmc^2)
energy released as a result of a mass defect =
E=Δmc^2
how does a moderator slow down neutrons?
through elastic collisions between the nutrons and the particals within the moderator
what are some poroblems with dealing with nuclear waste and how to we deal with thses problems (2)
nuclear waste is initially very hot
we deal with this by putting the waste in colling pools untill they cool to temptreture that eneble the waste to be moved
radioactive waste has a lomg half life thereofre it ts radioactive for a hundreds or thoudends of years
therefore the waste is placed deep underground in geological stable areas
what is the most dangurus waste
(dubble check)
spent fuel rods
