where we left last time we were talking
about the genetics of radioactive decay
and we said that all radioactive decay
reactions nuclear reactions follow the
first order rate law and the first order
rate law integrated rate law here for
the first order and simply by using this
first order rate law integrated rate law
we can calculate the age of the old
objects and this is simply called radio
dating and for this we follow the decay
of carbon-14 a radioactive decay
radiative isotopes of carbon 14 or other
radioactive nucleus in fact and last
time remember we gave you an example how
we determine the age of an old object by
using carbon-14 dating methods actually
I picked up another example actually the
example given in the book and I will
just go through that before we leave
this dating radioactive dating now for
the again half-life first-order
reactions is given by this equation
again we know and we know what the
half-life is that's the time required to
reduce the initial reaction to the half
off it is initial value and in this case
in terms of ready activity simply decay
of the radioactive isotope in fact half
of it requires half the time T 1/2 we
call that
okay here we see some of the half-lives
of the radioactive isotopes Radio
isotopes actually and some of them are
very very long actually if you look at
the uranium for example 238 it is 4.5
times 10 to the 9 years they half-life
and the others and for example for
carbon 5,700 years and we used carbon-14
particularly in determining the age of
the radioactive isotopes and we believe
that it gives quite a reasonable age up
to 50,000 or lo 50,000 actually okay see
the example I picked up this is the
again I just took it from the book
example but it's a good example to go
through one more time here it says the
question here is Iraq contains 0.25 7
milligram of lead 206 for every
milligram of uranium 238
now the half-life for the decay of
uranium 238 is to the lead-206 actually
is given as two point five four point
five times ten to the nine year how old
is the rock now how can we determine the
age of the rock using these informations
again we will do the same things in
carbon-14 cases but remember in the
carbon-14 case we measure the activity
of the object carbon-14 activity decay
activity of the object and then also use
the decay activity of carbon dioxide
which contains carbon 14 in the
atmosphere today and we find out the
time
actually for the age of the object in
this case we simply assume that all
uranium-238 goes to lead-206 right now
remember this is a chain decay reactions
it's not only one step it starts from
the uranium-238 and it goes into the
other radioactive isotopes Radio
isotopes and then finally it reaches to
lead-206 because the led 206 is a very
very stable nucleus very stable nucleus
in fact so now what we assume here that
all of the lead-206
in this rock came from the decay of
uranium 238 and at the beginning
actually when the rock formed which
contain uranium 238 only but no lead
right no lead now then we simply find
out what was the amount of uranium at
the beginning actually when the at the
formations of the rock time right and we
calculate that again as follow every 1
milligram of uranium 238 we have and we
also have simply 0.25 7 milligrams of
uranium no lead actually 206 right over
here and we simply say how from how much
uranium 238
we got 0.25 7 milligrams of lead 206
right if the 206 lead 206 is obtained
from uranium 238 so we can calculate
that because the ratio of the uranium
mass 238 divided by the
led 206 this is multiplied by 0.25 7
will give us the amount of uranium which
decayed to give us lead 206 in this time
period right so then we simply add that
to 1 milligram that present time
presence of the uranium 238 in the rock
and find out that or we assume that when
the rock simply formed the amount of
uranium there was one point two nine
seven milligrams right and that is
actually reduced to one milligram
now once we know the amount of uranium
238 when the rock formed and also the
amount of uranium 238 when we determine
the age then we can simply make the
ratio of those use the first-order rate
low and the half-life to calculate the
rate constant then we can calculate the
age of the rock is this clear again this
is this is crucial again in this problem
that means we have to calculate the
amount of uranium 238 at the time when
the rock formed going from the you let
206 amount actually here and just the
molar masses of those or the atomic
masses now the problem now is more easy
so rate constant K will be equal to the
logarithm natural logarithm of 2 divided
by the half-life of uranium 238 this is
our rate constant and our equation turns
out to be T is equal to this is again -
remember 1 over K which is that value NT
M zero now NT is the amount of
uranium-238 at the present time and n0
is the amount of uranium when the rock
formed which we have calculated remember
in the previous step right and we just
simply put those here one milligram is a
present amount and this is the initial
amount when the rock formed from there
we calculate the T the time passed since
that rock formed or the age of the rock
in other words and it turns out to be
one point seven times ten to the nine
years ten to the nine years so that is
one point seven billion years old
Rock old rock so this is how we use the
Radio isotopes again to determine the
age and this is called radio dating
actually very very useful as a matter of
fact okay now let's look at the how we
measure the radioactivity again the
activity is the rate at which the sample
decays now that's simply rate at which
the sample decays means it is the number
of disintegrations per unit time is
actually the rate of decay right number
of this integrations how many nuclei
actually decays in one second or yet per
unit time it that is the actually the
activity the units used to measure the
activity are as follow this is the Becca
L this is the guy who found the
radioactivity actually the first time
given its name French scientist one
disintegration per second is called one
bickerin and now we also use the Curie
and this is also another scientist lady
Polish lady and one Curie is equal to
three point seven times ten to the ten
dissing disintegration per second or we
can simply say one Puri is equal to
three point seven times ten to the
becquer all right because Becky Riley is
one disintegration per second actually
per second and again that simply comes
out from the radium decay and it says
which is the rate of the decay of one
gram of radium that means if you take
one gram of radium which is radioactive
and in one second there are three point
seven times ten to the ten
disintegrations off in that radium in
one gram radium in fact and it's called
one Curie now how do we measure the
radioactivity and there are instruments
one is using just film batches just like
we use we used to use actually for
taking photographs or x-ray films again
right so the decay particles simply when
hit to the films it makes it dark the
film contains silver bromide silver
iodide type things again and we also
have Geiger counters these are for
ionization in fact the the atoms are
ionized by decaying
radiation in fact and this is another
scintillation counters phosphorus in
this case again the decay particles when
hits to the surface it emits light and
by accounting those lights or measuring
conversion that to the electricity we
measure the radioactivity again actually
we measure the rate of this integrations
right that means how many disintegration
took place in one second now this is the
film batches again radioactivity was
first discovered by Henry Becker I'll
remember I told you because it's fogged
up the photographic plate this is
actually photographic plate film has
been used to detect radioactivity since
more exposure to the radioactivity means
darker spots and the developed film film
batches are used by people who work with
radioactivity to measure their own
exposure over time that means people
working in radioactive environment they
use the
batches in fact which contains film and
from that they measure how much
radioactivity they absorb their bodies
absorb now this is again Geiger counter
these are just instruments to determine
the radioactivity or rate of decay
measuring the amount of activity present
in radioactive samples radioactivity
enters the window and creates ions in a
gas and the ion results in an electric
current that is measured and recorded by
an instrument it is simply like this so
radioactive decay for example gamma rays
sent from here and this is we have a gas
in this case argon gas they are ionized
the gamma rays actually ionizes the
argon one gamma ray one argon and one
electron comes out and then we measure
the number of electrons and then we
convert it to the activity of the
radioactive substance now this is the
phosphorous it's not phosphorus the
element phosphorus it's fast first right
and some substances it says absorbs
radioactivity at and emit light they are
called phosphorus and the simply
well-known of these is zinc sulfide zinc
sulfide surfaces if you remember in
Alpha scattering experiment they used a
zinc sulfide surfaces to find out how
many alpha particles are simply coming
in what directions and so on an
instrument commonly used to measure the
amount of light emitted by a phosphor is
a scintillation counters called a
scintillation counter it converts the
light to an electrical response for the
measurement and simply counts out how
many simply disintegration and usually
alpha particles these are used for alpha
particle emissions yes no yes that's a
different little different but it's same
principle actually those are absorbs the
light in the visible sometimes and then
or
in the UV part and then emit the light
in the visible part and those are called
phosphorus phosphorescence and those
compounds are called phosphorescence
compound this is similar to that too
this is very similar now radio tape
traces again these radio isotopes are
used in a lot of applications actually
to study for example the chemical
reactions particularly the mechanism of
chemical reactions we used for example
oxygen-18 and labeled water that simply
means we prepare water molecule with the
oxygen 18 isotope and then we follow
that oxygen 18 or some other Radio
isotopes as a matter of fact an element
can be followed through a reaction to
determine its path and better understand
the mechanism of chemical reaction this
is one application now medical
applications of radio ice traces you've
probably heard about these when you go
to the hospitals you know they might
apply these radiotracers applications
medical applications radio charities
have found why diode misdiagnose stick
used in medicine again Radio isotopes
are administered to a patient that means
given to the patient usually
intravenously from the blood actually
injection from the blood and then
followed since it's radioactive you can
follow it by measuring its activity in
the body and where it goes through your
body certain elements collect more in
certain tissues so an organ or tissue
type can be studied based on where the
radioactivity collects again this is
just the applications medical
applications actually so some of the
radio nuclei used in radio tracers are
given here for example iodine 131 iron
59 and phosphorus now this is the L
phosphors actually and technetium-99
talia and sodium particularly the iodine
31 is used for thyroid disease and to
put the diagnosis on that actually now
they're positron emission tomography
again a compound labeled with a positron
emitters is injected into the patient
blood flow oxygen and glucose metabolism
and other biological functions can be
studied from those and again labeled
glucose is used to study the brain as
seen in the figure to the right here
again and from that the medical doctors
you know put the diagnosis and evaluate
that and do whatever they're supposed to
do again to treat that disease now
energy in nuclear reactions again we
said that the nuclear reactions are much
much more energetic than the chemical
reactions or the energy involved in
nuclear reactions like usually thousand
at least thousand or more times of the
chemical reactions very very energetic
reactions these nuclear reactions now
what we actually are we calculate the
energy involved in chemical nuclear
reactions by using this equation here i
unsigned famous equation z is equal to
MC square and this relates directly to
the calculations of this energy actually
if there as I said in chemical reactions
the mass change between the reactants
and the products is very very small
negligible we never think about the mass
change what we say actually that the
mass of the reactants exactly equal to
the mass of the product they're not
exactly equal but very very small
difference again it's not so important
so we neglected but for nuclear
reactions the mass balance is important
again
the mass of the reactants that enter in
nuclear reactions are not equal to the
mass of the product that comes out
usually when the energy is released
actually the mass of the product is less
than the mass of the reactant so we can
calculate the energy that is released if
you know how much mass change between
the reactants and the products in a
nuclear reactions this is simply based
on that and using this equation this is
the mass this is the speed of light and
we can calculate what is the energy
involved in a nuclear reactions again if
you know the masses of reactants and the
products now again to show the enormous
difference in energy for nuclear
reaction the mass changes associated
with alpha decay of one mole of uranium
238 to thorium 234 is about minus 0.004
six grams that means to 38 grams that
much decrease in the mass of the
reactant as it goes to the product again
now this minus means that the mass
reduced that means that the mass of the
product is less than the mass of the
reactants now where is that mass gone
that is actually converted to the energy
which is released as a result of this
nuclear reaction and we can calculate
that once we know that that change and
we just put it over here and one thing
that we have to remember the unit of
mass in SI unit system is kilograms and
we usually talk about grams here when we
talk about the mass molar mass of the
substances so we have to convert that to
kilograms and then multiplied by the
square of the speed of light and that
gives us minus four point one times 10
to the 11 joules this is really big very
very large amount of energy comes out
again when you
actually 238 is converted to thorium-234
just this is just for one mole that
means to 38 grams and if you have twice
as much the energy release will be twice
as much also right okay I have simply
take another example from the book this
is a gain word example it says how much
energy is lost or gained when one mole
of cobalt-60 undergoes to cop out nickel
60 and beta particle right here like
this alright now we will simply take
this equation this is our nuclear
balanced nuclear reaction equations
right so we simply find out the mass of
the nickel 60 and the mass of the
electrons and subtract from that the
mass actually subtract from that the
mass of the cobalt 60 we can work in
molar quantities for example and find it
out now here it says the mass of carbon
60 atoms is this and the mass of nickel
60 atoms is this here is a point when
they say that this is the mass of the
carbon 60 atoms means that this atom has
27 protons and 33 neutrons in a nucleus
right that's it but the this mass
corresponds to 27 protons and 33
neutrons and 27 electrons so when we
simply calculate the energy involved in
nuclear reactions we only consider the
nucleus not the electrons right so this
is important again so as we see here
when we calculate for example we just
take one mole of cobalt 60 and
them to get one mole of nickel 60 like
this so to find out the mass of the
nickel 60 right here we take the mass of
the nickel
simply given here write that and then
subtract from that the mass of 27
electrons right the electrons remember
27 electrons is outside of the nucleus
they are the simply electrons that is
involved valence electrons only involved
in the chemical reactions Oh core
electrons and the valence electrons and
then we find out the mass of the nickel
in fact per mole here in atomic units it
is this and per mole it that simply
means 59.91 gram per mole less than that
how much less 27 electrons subtracted
the mass of the 27 electrons subtracted
from the mass of the atoms and then we
do the same things for the nickel and
the cobalt the same things again here
then we can calculate the mass change so
the mass change in that chemical
reaction will be mass of the electron
now this is the beta particles which
comes out from the nuclear reactions
this is the mass of the nickel 60 that
we have calculated in previous steps
without electrons right without
electrons and then this is again the
mass of cobalt 60 without electrons that
will be calculated in previous by
subtracting 27 electrons off the cobalt
and the mass difference again is equals
to this and this is simply means if we
work for one mole of cobalt 60 and
nickel 60 means that the mass change in
this nuclear reaction will be equal to
this and what is the energy the energy
just Delta e is equal to C square Delta
M and it is minus two point seven three
times 10 to the 11 joules again huge
amount of energy so this is how we
calculate the energy involved in nuclear
reactions the energy involved in nuclear
reactions gained using the Einstein
equations again now here is another
things we said that some of the nuclei
are stable some are not stable can we
find out or somehow can we find a
measure to predict the stability of a
nucleus stability of any quiz and the
answer to this question is yes there is
a way in fact to predict the stability
of a nucleus stability of a nucleus
remember when we say nucleus we mean the
center of the atom which consists of
protons and neutrons right that's it
now here we know that at the nucleus we
have protons and neutrons for example if
we simply take a helium right in a
helium nucleus there are two protons and
two neutrons can we calculate the mass
of one helium atom or the mass of one
helium nucleus yes we can calculate it
how if I know for example the mass of a
proton and the mass of a neutron I can
simply calculate the mass of two proton
and the mass of two neutrons and add
them up that will give me the mass of
the helium right but when I do that I
find out that the calculated mass of
helium is always greater than the
measured mass of helium nucleus now what
does that means that means is this
when you have the two protons and two
neutrons infinitely apart they have a
mass right
certain amount each proton has a mass
and neutrons has a mass we know that now
when you bring those two neutrons and
two protons to form a helium nucleus
huge amount of energy is released and
that released energy corresponds to the
mass loss as the two neutrons and two
protons from infinitely apart brought
together to form a helium nucleus energy
is released so this energy that released
is exactly the amount of energy required
if I would like to take that nucleus of
helium and separate do put two protons
and two neutrons infinitely apart I have
to give the same amount of energy right
so what does that mean that means that
the energy released as that nucleus
formed shows the stability of that
nucleus the larger the energy released
the more stable the nucleus we can say
why because the larger the energy
released means that it will require more
energy to disintegrate that nucleus into
the protons and neutrons actually right
protons and neutrons so by using this
approach we can calculate how much
energy is released if I would like to
make that nucleus starting from the
protons and neutrons infinitely apart
right bring them together and now
dividing that energy release to the
number of nucleons that means total
number of protons and neutrons I find
out an energy which I call the binding
energy per nucleon actually the energy
released is called the binding energy of
the nucleus and if I divided that to the
number of protons and neutrons that
means total number of nucleons and it
will give me the binding energy of the
nucleus per nucleon actually right
curr nuclei so here is the the values
that are calculated for helium for
example helium 4 and the mass of nucleus
in atomic mass unit only the nucleus not
remember this is not the mass of atom
mass of nucleus what does that means
that means it is the mass excluding the
two electrons of the helium right it's
actually alpha particle as a matter of
fact now this is the mass of that and
the mass of individual nucleons atomic
masses again that means if I simply
calculate the mass of helium by using
the mass of each nucleon proton and
neutrons it turns out to be this
you see it's larger than it's actually
okay this is larger than that right you
see that's larger now the mass defect is
this and then when we convert it to the
energy this is called the binding energy
right again we just use again Einsteins
e is equal to MC square equations to
convert that mass defect to the energy
that is the binding energy of helium
nucleus if I divide it by for number of
nucleons this will give me the binding
energy per nucleon right so if I do this
for all nuclei and it will give me
actually a measure of stability of the
nuclei the more the energy binding
energy or binding energy per nucleon
that means it's more stable than nuclei
right or that nucleus and more stable
means that means it will not be very
active right it will not be radioactive
as a matter of fact okay now here is the
graph it's done for all elements all
nuclei actually and you see again this
is the mass number of the nuclei and
this is the binding energy per nucleon
divided by the total number of protons
and neutrons what we see here that when
we have light atoms the binding energy
is not very high for example consider
the hydrogen in its hydrogen is right
over here
right somewhere over here it's not hot
not large at all
now as the atomic mass increases of a
nucleus the binding energy increases and
then becomes maximum here at ayran what
does that mean that means that iron-56
actually is the most stable isotope
right it will be very very stable it has
a very high binding energy per nucleon
actually the maximum point now from that
point on again decreases what does that
means that simply means that the light
nuclei are not stable as well as the
heavy ones are not stable so we will
simply find the radioactive nuclei small
atoms small nuclei and also very heavy
ones over here now what will happen if
the uranium-235 for example which has a
binding energy about that this
integrates into smaller nuclei that
means the energy will be released now
energy will be released means that the
uranium-235 will be converted to more
stable nuclei right now if you have
light atoms like hydrogen if we combine
the hydrogen to form helium that means
that the binding energy will also
increase what does that means energy
will be released right energy will be
released so these two processes actually
this is dividing off one nucleus into
two or three coming from this side to
this direction is called fission right
you take one nucleus divided into two or
three smaller one is called fission now
when we simply combine light nuclei to
to get the heavier ones they gain energy
will be released and that process is
called fusion so we have fission and
fusion process
fission and fusion now both process will
be exothermic process but that means
energy will be released again fission is
simply means going in this graph from
this side to that directions and fusion
simply combinations of smaller light
nuclei to get heavier going from this to
that
okay so let's simply look at here it
says alright the same things here heavy
nuclei again stability and give off
energy when they split into two smaller
nuclei this is fission as we said here
and the lighter nuclei emits great
amount of energy by being combined in
fusion this is called the fusion fission
and fusion okay here are the simply
examples of nuclear fission let's look
at what this slide says commercial
nuclear power plants uses fission
nuclear power plants remember are the
power plants generates electricity by
using nuclear substances radioactive
substances as fuel right and the fuel
used in those is uranium-235 again now
as we see this is the fuel that is used
in nuclear power plants uranium-235
remember the uranium has uranium 238
isotope uranium-235
and also uranium 237 I guess yes 237 but
the most abundant one is 238 now the
abundance of uranium 235 in uranium 238
rocks is about 0.7 I guess about 0.7
percent somewhere about 0.7% very low
but this is the reaction nuclear fission
reactions now again this reaction is
started with bombardment of a neutron we
have a neutron slow-speed neutron and
sent it to uranium 235 92 at it
disintegrates like this divides into the
smaller nuclei and this gives you the
barium 142 Krypton 91 and three neutrons
from this fission this is again a
fission reaction three neutrons comes
out from there and now this way two
neutrons comes out tellurium and
zirconium now if those three neutrons
hits two another three uranium-235 then
there will be another fission and then
each of those will emit three neutrons
and if we can have those three neutrons
and hit another three uranium-235
this is a chain reaction and the amount
of energy that relieves from this chain
reaction if we do not control that will
be huge amount huge amount of energy
actually but in the power plant as we
will see the amount of fission actually
or the rate of this reactions is control
certain ways and that way we keep the
amount of heat that released from the
reactions and we control it just enough
to produce the electricity actually
we will talk about that okay so this is
again the genetic diagram how it shows
the chain reaction in nuclear fission
238 you see again one proton one uranium
238 235 remember this is uranium 235 I
should talk and then hitch to that and
another two neutrons comes out from
there and they hit this one and that
gives two neutrons and so this continues
like this and that chain reaction take
place now bombardment of the radioactive
nuclei within neutrons starts the
process right there Neutron released in
the transmutation strike other nuclei
chosen their decay and the productions
of more neutrons this process continues
in what we call a nuclear chain
reactions and the amount of energy
involved huge huge amount of energy
alright now what we need for this
nuclear fission again remember we can we
can use the uranium-235 as a fuel in
nuclear power plant to generate
electricity but we can also use
uranium-235 to make an atomic bomb
atomic bomb is nothing but huge amount
of energy is released in a very short
time right and that's the bomb actually
made use you know she may negotiate
macro sake in 1945 right and it's made
from the uranium-235 now we have to
remember that if you want to use the
uranium-235 as a fuel in part in in in
power plants to generate electricity the
amount of uranium-235 has to be up to
3.5 to 4 percent right so that means
that in natural uranium ore contains
point O 7 I guess
abundance of the uranium-235 that means
we have to increase the amount of
uranium-235 and that process is called
enriching uranium that means we enrich
in the amount of uranium-235 there are
certain different ways of that remember
if you the problem that Iran has with
the other nations particularly the
United States because Iran was enriched
in the uranium 235 Ryan there's special
centrifuges now why this is important
because first of all if you want to use
the uranium-235 as a fuel it has to be
enriched how to three to four percent
but if you want to make uranium use the
uranium-235 to make a bomb it has to be
almost 100 percent uranium-235 right but
if you can enrich it to 3.5 to 4 percent
that means you can get pure from that to
continuing enriched in that and now for
one actually there is another things
here let's look at this this slide this
says that there is a minimum mass that
must be present for a chain reaction to
be sustained is called the critical mass
that means for the chain reaction to
continue there has to be a certain
amount of uranium-235 certain amount of
uranium-235 for the atomic bomb I guess
it's about 50 kilograms about 50
kilograms now why it is so because if
you have small mass of uranium-235 you
can start the chain reaction here let's
say and then the two neutron comes out
here and hits two these and these also
goes into fission then the you lose the
neutrons most of the neutrons comes out
from the fission because the neutrons
comes out of fission are used in the
next fission processes right if you
don't have enough neutrons
actually if you lose your neutrons
before they hit another uranium-235 that
means a chain reaction will not continue
now so you have to have a critical mass
and that critical mass simply is the
amount of mass where the rate of fission
reaction kept constant right that means
that if you have simply one
disintegration one fission of
uranium-235 let's say three neutron
comes out only one of them is hit
another uranium-235 and also one neutron
comes from out there and so on this way
we can keep the rate of the radioactive
fission reaction actually the fission
the same now if more than critical mass
is present it is called supercritical
mass an explosion will occur this is the
case for the atomic bump in any
construction of the atomic bomb it has
to be more than the supercritical mass
actually greater than the critical mass
we call it super critical mass weapons
were created by cos and smaller and
bounds to be forced together to create
this mass this is the shape of the
atomic bomb again here we have the
uranium-235 some amount here some amount
there and here we have a chemical
explosives and when you simply have this
chemical explosive hit those two
together you start the chain reactions
and that chain reactions especially when
the amount of masses above the critical
mass we have that super critical mass
huge amount of energy is released now
but we can control the amount of energy
released from the fission reaction of
uranium-235 and use it in a power plant
to generate electricity remember I said
that there we only need about three
percent abundance enrichment of the
uranium-235
so in nuclear reactors the heat
generated by the reaction is used to
produce steam that turns a turbine
connected to a generator
otherwise the
plant is basically the same as any power
plants in fact the coal power plants we
use coal to boil water actually obtain
vapor in high pressure and use those to
turn the turbines and create electricity
so this part is exactly the same and
nuclear power plants the fuel is the
radioactive uranium 235 which is here
there are some rods but we have to
control the reaction nuclear reaction
chain reactions by using these control
and rods we simply put push them down
here and that way we prevent the
neutrons emitted from the fission to hit
another uranium-235 and cause the chain
reactions as a matter of fact so this
way we get the heat and that heat went
through the heat exchanger and we get
vapor actually right here steam very
high pressure goes to turbine and we
produce electricity now this is the
reactive part of the nuclear this is
what I was fuel these are the fuel
elements these are fuel elements they
are actually uranium oxide but uranium
is 235 enriched actually 235 up to 3 to
4 as a gain percent as I said and
remember I said that the nuclear
reactions is not affected by any
environmental conditions pressure
temperature or whatever the radioactive
isotopes in what molecule it really
doesn't matter so these are just the
uranium oxides uranium-235 oxides here
and then we have the control rod which
are simply boron made of boron they
absorb actually the neutron access
neutrons so by simply pushing it down
like this or taking it out we control
the amount of energy that comes out from
the chain
reaction from the fishin actually by
controlling deficient chain reactions
and the power plans simply works and
generates electricity produces
electricity now unit says water acts as
moderator and coolant that means here we
have water and there are different types
of nuclear reactors some use heavy water
for example those are called heavy
waters now the functions of this
moderator is actually to slow down the
speed of the neutron comes out from a
fission process because if the energy of
the neutron if the neutrons are very
fast they don't really absorb by another
uranium-235 and cause the chain
reactions they have to slow down so that
when they hit two uranium-235 absorbed
by a chain fission reaction take place
now the problem with this is the waste
actually what we do with the waste and
still a big problem after you use those
fuels rods which contains the
radioactive substances right remember
again the product of fission reaction
also gives radioactive radioisotopes
they are also radioactive to not only
the remaining uranium-235 in the fuel
rods are harmful but the products there
are also harmful so after you use that
fuel actually you can't use all the
uranium-235 you have to remember that
the half-life is very long so you have
to somehow store it somewhere that will
not cause any environmental problem by
giving those high energy radiations and
it's still a problem today and I guess
the most important problem with the
energy production by nuclear reactions I
should say nuclear power plants
okay now Fusion is as we see again the
lighter nuclei combines to form little
heavier ones this is again one of the
reaction that taken place in the Sun
actually the energy of the Sun is
produced from this fusion reactions
because almost nineteen ninety-two
percent of the Sun is hydrogen and seven
percent is helium and only one percent I
guess if I remember correctly is other
elements so it's Sun is mainly made of
hydrogen and helium right and
continuously the hydrogen combines in
this fusion reaction and forms the DT
reom and that combines to form the
tritium and that combines to form
finally helium right and that huge
amount of energy is released right huge
amount of energy is released but the
problem again to be able to use this
fusion reaction instead of fission
because fusion reactions do not give you
you know like radioactive products as
inefficient reactions so they are more
appropriate to use to generate the
electricity actually are used in a power
plants but the problem is for the fusion
reaction to take place the temperature
should be like forty thousand Kelvin
somewhere about there very very high you
need a very high pressure and very high
temperature for the fusion reaction to
take place the huge amount of energy is
simply released from that too but to get
that to start you need very high
temperature and very high pressure again
now atomic bump based on the fishing of
two uranium-235 hydrogen bump is based
on the fusion of this it is possible to
make the hydrogen bomb that means to
carry out the fusion reactions and
release the energy from that but to
start the
atomic bomb the hydrogen bomb they use
the atomic bombs small amount
uranium-235 and that creates the
temperature and the pressure required to
start the fusion actually fusion
reactions but economically not feasible
them again to use these in the power
plants as a fuel hydrogen in fact is not
at the moment is not feasible yet
now radiation in the environment let's
see what we have here we are constantly
exposed to radiation yes at least we
know that all radio frequencies of the
TVs and the mobiles right phones so we
are exposed to a lot of radiations but
the radiations that we exposed our low
energy radiations they don't really make
much harm to the living organisms or the
environment but if the living organisms
are exposed to the high energy
radiations like beta particles gamma and
alpha and so on and which are called
ionizing radiations and that is a
problem a big problem actually right why
because the ionizing radiation simply
ionizes the water right which almost 70%
of living organisms are water right and
when you have the water ionized water
like this this ionized water reacts with
another water to form the hydronium ion
and all H radical and this Oh H radical
causes all kinds of problem in the
living organisms it is a very reactive
species and reacts with a lot of
biological molecules and causes all kind
of problems so we should be aware that
we should not be exposed to the ionizing
radiations ionized
now the damage to the cells of the
ionizing radiations now again alpha
particles beta particles and gamma
particles you see again the penetration
power of alpha particles is not very
high they can't really penetrate through
the skin so if the alpha particles is
outside of the living organisms the
damage is not large but if the alpha
particle if you're radioactive
substances inside your body for living
organisms and if it gives alpha particle
that is very bad that's really bad now
beta particles they simply penetrate you
see some extent now the gamma particles
can go through the body actually and
that is very very dangers to be exposed
about a certain limit of gamma rays
particularly because they simply break
the bonds between the atoms in the body
in the biological molecules and that
means the end of the life there right
now let's look at here again the damage
to the cells depends on the type of
radioactivity that means alpha beta or
gamma the length of the exposure and the
whether the source inside or outside the
body see that means the radioactive
source inside and outside outside the
body gamma rays are most dangerous
because they can go through inside the
body alpha radiation can cause most harm
right so now the exposure and again we
are constantly exposed to the radiation
but what amount is safe this is another
things set in the standards for safety
is difficult low level long-term
exposure can cause health issues damage
to the growth regulation mechanism of
the cells results in cancer this is the
worst part of that actually if you're
exposed to the radiations finally you
know may take years and years but cancer
may be seen not
living organisms actually now uh now
these are the average abundances
activities of natural radio nuclides are
given here I guess the next is radiation
those are given and short term exposures
like 60 REM is fatal to most humans
average exposure per year is about 360
million this is REM this is milligram
that means every person is exposed to
the radiation about 60 360 milligram per
year and that's okay I mean considered
okay agree
now the radon-222 is a decay product of
uranium 238 which is found in the rock
formation and soil it's most of the
decay product of uranium remain in the
soil but radon is a gas when breathing
it in if you take the radon gas in it
can cause much harm since it produces
alpha particles which have high R b/a
that means effectiveness and it is
estimated to continue to about 10% of
all lung cancers that in the United
States actually in the United States
they there are a lot of rocks that
contain radon and that radon comes from
the uranium 238 a activity of uranium
238 reactor to be rhenium 238 and since
it's a gas it goes into the air you
simply inhale that and very very
dangerous and in the States particularly
in these parts here they usually have
measuring of radioactivity in their
homes in their living rooms in somewhere
because it comes out from the ground
right from the rocks every year or every
six months depending on where they are
to make sure that the amount of radon in
the air below the safe limit actually
before blow the safe okay
in the last part I will advise you to
read the last part particularly
those things than radioactivity and this
like meaning of RBA and so on
and this would be the end of chapter 21
next week we will start chapter 24
not all chapter but part of it in three
hours actually finished before the final
exam okay question