Kind: captions
Language: en
now that we have nuclear weapons and
nuclear power plants you might think
that it was always inevitable that we
would be able to harness the energy
inside the nucleus of atoms but that was
far from the case in fact serious
scientists thought the idea was
laughable like Nobel laureate Robert
Millikan who in 1928 said there is no
likelihood man can ever tap the power of
the atom the glib supposition of
utilizing atomic energy when our coal
has run out is a completely unscientific
utopian dream or as Rutherford put it
anyone who expects a source of power
from the transformation of these atoms
is talking moonshine now there was good
reason for their pessimism when
Becquerel first observed to
radioactivity he thought it was a
phenomenon similar to phosphorescence
that's when you shine radiation like
light onto an object and it absorbs that
energy and later reradiates it in a
different part of the spectrum
now uranium ore was known to do this as
I witnessed firsthand oh yeah X yes
fluorescent uranium ore yeah here it's
absorbing UV light and reradiating it as
visible light in 1896 Becquerel
performed experiments where he placed
uranium ore in the sunshine on top of
some wrapped up photographic film now he
found that the film was exposed
seemingly by invisible rays from the
uranium ore that penetrated the paper
when the uranium was excited by the
sunlight but one day when he went to do
his experiment the weather in Paris was
lousy so he put the uranium and the
photographic film inside a drawer and a
few days later even though the uranium
hadn't seen the Sun he decided to
develop the film anyway and what he
found was that the photographic film had
been exposed just as before even though
the uranium was not excited by sunlight
so this was not a phosphorescence
phenomenon some type of radiation and
therefore energy was coming out of a
rock unprovoked but how could a
seemingly inert object like a rock give
off energy where is it getting that
energy from it was a mystery that seemed
to violate the law of conservation of
energy that is until Einstein published
his famous e equals mc-squared which
suggested a source of energy for the
might be the mass of the nucleus just a
tiny bit of mass can give you a lot of
energy and this premise was enough for
science fiction writers to let their
imaginations run wild like HG Wells who
in 1914 published the book the world set
free which includes the first mention of
the words atomic bomb he envisioned a
uranium based hand grenade that would
continue to explode indefinitely but to
scientists this was completely detached
from reality as Einstein in 1933 put it
there is not the slightest indication
that nuclear energy will ever be
obtainable it would mean that the atom
would have to be shattered at will and
that's just the thing people had no
ability to make a nucleus do anything
all we were observing was the natural
process of radioactive decay atoms of a
particular unstable isotope decaying at
random with some characteristic
half-life and the energy given off
although immense on the scale of an atom
is pretty insignificant on the scale of
people and the world the fission of a
single uranium atom releases twenty
times less energy than the amount
required to raise a grain of sand the
thickness of a piece of paper now up
until 1932 the only known particle in
the nucleus was the proton so if you
wanted to alter a nucleus you could
conceivably fire a proton at it but
since the nucleus and the proton are
both positively charged they repel so
you'd have to fire the proton in with
such high speed and accuracy to get it
to hit and stick to a target and even
then if you're successful you've only
affected one nucleus which at best can't
even lift a grain of sand so you can see
why the Nobel Prize winners were saying
nuclear weapons not gonna happen but
then comes the discovery of the neutron
and the neutron changes everything
because as an uncharged nuclear particle
it can drift ghostly undeflected through
matter until it hits a nucleus
transforming it into something else and
this leads to the Epiphany of a man
named Leo Szilard
now soulard read the world set free so
he's already imagined a future in which
nuclear energy is harnessed by weaponry
and he remembers the exact moment he
comes up with this idea as he's crossing
the street in London
he says it suddenly occurred to me that
if we could find an element which is
split by neutrons and which would emit
two neutrons when it absorbed one
Neutron then such an element if
assembled in sufficiently large mass
could sustain a nuclear chain reaction
in other words the neutron enables us to
trigger nuclear reactions at will and if
there's a nucleus which when it splits
in this way releases two neutrons it
could trigger more and more fission's at
an exponentially increasing rate the
nucleus that has this property is
uranium-235
in fact on average it releases
two-and-a-half neutrons every time it
divides now all of a sudden you have the
possibility of splitting zillions of
nuclei simultaneously releasing
incredible amounts of energy all at once
that's an atomic bomb now if you want
more control over this release of energy
as in a nuclear power plant well then
you have to absorb a few neutrons
so that the fission of one nucleus only
causes the fission of one other nucleus
on average then you have a steady chain
reaction that emits the same amount of
energy each instant the challenge is
that this is like balancing on a
knife-edge absorb too many neutrons and
the chain reaction quickly decays to
nothing absorb too few and the rate of
reactions increases exponentially and
soon you're back to a bomb or Chernobyl
so if not for the existence of the
neutron a neutral nuclear particle to
trigger reactions that occurs in greater
numbers relative to protons in the
larger nuclei meaning they're likely to
be given off when a large nucleus splits
well then maybe as many brilliant
scientists suspected it would be
impossible to harness the energy in the
nucleus but as it is in our universe the
neutron is the hero or the villain of
nuclear physics
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