Nuclear Reactions, Radioactivity, Fission and Fusion

Nuclear Reactions, Radioactivity, Fission and Fusion

October 15, 2019 100 By Ewald Bahringer


hey guys its professor Dave, let’s learn
about nuclear reactions the electromagnetic force is responsible for
the entirety of chemical phenomena. that positively charged protons and
negatively charged electrons are attracted to one another is the reason
that atoms form, the reason that chemical bonds and therefore molecules form, the
reason that those chemical bonds have differing polarities which lead to
differing reactivities as well as a method for enzyme recognition of
substrate and DNA base pairing which leads to life itself. but there are three
other fundamental forces in the universe the four forces are as follows: there’s gravity which is the weakest but
it operates on astronomical distances so when you’re looking at planets and stars
and galaxies this is the only force that matters electromagnetism as we mentioned is what
makes chemistry happen and it operates on the scale of atoms and molecules but
the other two forces operate on a scale even smaller than that, the scale of the
atomic nucleus. these are called the strong nuclear force and the weak
nuclear force. the strong nuclear force is what keeps the nucleus together
preventing positively charged protons from pushing each other away and
splitting up the nucleus, and the weak nuclear force is what facilitates
nuclear decay. these are instances in which the nucleus of an atom changes in
some way. they’re called nuclear processes and though there are more in
the realm of physics they are important for chemistry because they often cause
transmutation of elements. that’s when an atom will change from one element to
another so we need to know a bit about them. to reiterate in a chemical reaction
only the valence electrons in atoms are rearranging when chemical bonds break
and form, the identity of each individual atom remains unchanged in a nuclear reaction changes occur to
the fundamental particles in the nucleus of an individual atom which means it
will change from one element to another these reactions are some kind of nuclear
decay where something in the nucleus disintegrates giving off some form of
radiation in the process radioactivity was first discovered by
Henri Becquerel in 1896. he noticed that photographic plates had bright spots
when they were exposed to uranium minerals. this radiation was found to be
composed of three types when exposed to a magnetic field since they were
deflected in different manners. at the time we didn’t know about the subatomic
particles the radiation was comprised of so we just name them with Greek letters
and discovered their identities later. an alpha particle is essentially a helium
nucleus, two protons and neutrons. emitting an alpha particle will result
in transmutation as seen here. a beta particle is an electron. a positron is the
anti-matter particle of the electron which has the same mass as the electron
but a positive charge, and a gamma particle is a photon of light this is the same as the electromagnetic
radiation from the Bohr model just no longer associated with the transition of
an electron. let’s quickly learn the ways that we can notate these particles so
that we can write nuclear reactions remember that when we write nuclide
symbols the lower number is atomic number, or number of protons and the
upper number is atomic mass, or the protons + neutrons. so a proton and
neutron will be signified this way with a p and an n each with mass one but
only the proton has atomic number one. an alpha particle can be represented as
helium or with alpha symbol, an electron can be either an e or beta symbol and
the atomic number will be negative one while the mass though technically not
zero is negligible so we call it zero a positron will be the same but with a
positive one here and a photon will be gamma, both numbers zero as it
legitimately has zero mass. so if we want to describe the emission of say an alpha
particle we would write it this way show the first particle the arrow
signifies the reaction and then show the alpha particle. to figure out the
resulting nucleus after a mission we just do some arithmetic. because the
atomic numbers and mass numbers have to add up to the same number on both sides kind of like how we need the same number
of atoms on both sides of a chemical equation, if the atomic number is 86 on
the left and there’s a two on the right we need 84 for it to work out. again with
mass 222 on the left, four on the right we need the other particle to be 218. any
atom with eighty four protons is polonium so the resulting nuclide symbol
must be this. again the numbers on each side of the arrow add up to the same
thing. now that we are aware of these processes, why do they occur? it’s always
due to some instability in the nucleus one reason might be that the nucleus is
just too large. you see the strong nuclear force which is mediated by
particles called mesons is very strong and it keeps the protons and neutrons
fused together with a hundred times greater force than the electromagnetic
propulsion that wants to push the protons apart. but the strong nuclear
force drops off with distance more quickly than the electromagnetic so if
the nucleus gets too big all of a sudden the strong nuclear force
is too weak over the diameter of the nucleus to keep it all together and the
protons will push apart. so for atoms larger than bismuth the nucleus is just
too big to be stable. nuclei like these will often rapidly emit an alpha particle
to try to get a little smaller and a little more stable but even if the
nucleus isn’t too large it may have a number of protons or neutrons that isn’t ideal. the shell
model of the nucleus describes nucleons as existing in levels or shells kind of
the way electrons do. as it happens there are so-called magic numbers for each
nucleon that correspond to a special type of stability kind of like a full
valence shell of electrons. these are the magic numbers. in addition most stable
isotopes of a given element have even numbers of both protons and neutrons and
most of the rest have at least one of them in even numbers. and lastly an atom
will tend to want a certain neutron to proton ratio in the nucleus. for smaller
atoms this is roughly one-to-one which is represented by this line but for
larger atoms this becomes closer to 1.5 to 1. more neutrons than
protons. this ratio gives a nucleus balance so if an atom veers too much in
one way or the other nuclear decay will allow it to adjust the ratio. so as we
said if a nucleus is too large it will emit an alpha particle or it can undergo
spontaneous fission where it breaks into multiple lighter nuclei and usually a
few neutrons. in beta emission the reason an electron is emitted is because a
neutron spontaneously transforms into a proton. remember before how we said that
protons and neutrons both weigh one atomic mass unit even though technically the
neutron is slightly heavier? well it is heavier by exactly the mass of the
electron which is why a neutron is neutral, it’s a proton and electron
combined. so when the neutron becomes a proton it will emit an electron in the
process a nucleus would do this if the neutron
to proton ratio is too high meaning too many neutrons, as this
would adjust that ratio favorably positron emission is just the opposite.
when a proton becomes a neutron this will emit a positron because this is the
process that is the opposite of beta emission and the positron is the
opposite of an electron. this would happen if the
neutron to proton ratio was too low meaning too many protons. with both of
these types of decay there is also a tiny particle called a neutrino that is
emitted. in beta and mission it’s an anti neutrino and with positron emission
it’s a regular neutrino. more on that in particle physics. another process that
can occur is electron capture, this is similar to positron emission in that a
proton becomes a neutron but it does so by absorbing an electron rather than
emitting a positron. once again a proton plus an electron makes a neutron. the
electron in question will tend to come from one of the inner orbitals of the
atom and the electron will be a reactant since it is absorbed by the proton to
give a new particle. and lastly if a nucleus is in an excited state it can
emit a high-energy gamma photon. in this process there is no transmutation
because we don’t change around any protons and neutrons. so we can predict
what kind of nuclear decay a nucleus might undergo by looking at its
condition. is it too large? what’s the proton neutron ratio? each
decay process has its typical cause. too many protons: positron emission or
electron capture. too many neutrons: beta emission. too big: alpha emission or a
spontaneous fission. excited: gamma emission. an unstable atom can undergo a
radioactive decay series, over multiple emissions generate a stable nucleus
like uranium 238 which eventually becomes lead 206. so now we know what
radiation is. its unstable nuclei emitting high energy particles. the
reason this is bad for biological organisms is that these high-energy
particles can tear through our cells and if one strikes a DNA molecule it can
potentially change the genetic code at that location resulting in a potentially harmful
mutation. most elements have naturally occurring isotopes that do decay over
time, even carbon, hydrogen, and oxygen so there are radioactive nuclei decaying all over your body every
second. luckily we have enzymes that repair DNA damage as it happens. but
if we were to be in the presence of highly radioactive substance that is
emitting particles at a high frequency this would do much more damage than our
bodies can repair so we have ways of detecting radiation like geiger counters.
we will often talk about radioactive material in terms of a half-life. this is
the time it takes for a material to be depleted to half the original amount.
after two half lives there would be one fourth the original amount. after three
half-lives 1/8, etcetera. half-life is given by the following formula where k
is a constant specific to the material by learning about nuclear processes
we can harness the massive energy that are contained. with nuclear processes matter is
converted directly into energy as is given by Einstein’s famous equation e=mc^2 squared. here c is the speed of light which is very big, so with this
equation says is that matter is simply extremely dense energy, the densest form
there is. we have harnessed this power already with atomic bombs much to the
dismay of mankind. these worked by bombarding unstable uranium nuclei with
neutrons which caused them to split generating more neutrons which collide
with other uranium nuclei causing a chain reaction that releases tremendous
energy. an even more powerful process is nuclear fusion. this is where small
nuclei combine to give larger ones, a process that involves a loss of mass
which is converted into even more energy efficient nuclear reactors that harness
the power of fusion promise to solve all kinds of problems regarding renewable
energy sources and could be the key to the next step in societal advancement.
maybe you can aid in the advancement of this or other important technologies.
let’s check comprehension thanks for watching guys subscribe to my
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