Why Einstein Thought Nuclear Weapons Were Impossible
Why Einstein Thought Nuclear Weapons Were Impossible
Without neutrons, harnessing nuclear energy would be impossible.
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A few years ago I made a documentary about uranium, radioactivity and radiation. I always thought of the characters in our story as the scientists and maybe the uranium nucleus itself. It was only through making the documentary that I realized the real hero of the story is the neutron. Without a neutral nuclear particle, it would be virtually impossible to release the energy from the nucleus. But with it, and the idea of a chain reaction, nuclear energy went from science fiction to reality. That is something I had not grasped as clearly before and it motivated me to make this video.
Filmed by Raquel Nuno.
Content
0.03 -> Now that we have nuclear weapons and nuclear power plants you might think that it was always
4.69 -> Inevitable that we would be able to harness the energy inside the nucleus of atoms
9.01 -> But that was far from the case in fact serious scientists, thought the idea was laughable like Nobel laureate Robert
16.17 -> Millikan who in 1928 said there is no likelihood man can ever tap the power of the atom
21.46 -> The glib supposition of utilizing atomic energy when our coal has run out is a completely unscientific
27.55 -> Utopian dream or as Rutherford put it anyone who expects a source of power from the transformation of these atoms is talking moonshine
35.559 -> now there was good reason for their pessimism when Becquerel first observed to radioactivity he thought it was a phenomenon similar to
43.48 -> phosphorescence
44.05 -> That's when you shine radiation like light onto an object
47.129 -> And it absorbs that energy and later
49.84 -> Reradiates it in a different part of the spectrum now uranium ore was known to do this as I witnessed firsthand. Oh, yeah
57.52 -> X yes
59.26 -> fluorescent uranium ore
63.34 -> Yeah
64.72 -> Here, it's absorbing UV light and reradiating it as visible light in
69.88 -> 1896 Becquerel performed experiments where he placed uranium ore in the sunshine on top of some wrapped up
75.82 -> Photographic film he found that the film was exposed
78.909 -> Seemingly by invisible rays from the uranium ore that penetrated the paper when the uranium was excited by the sunlight
84.67 -> 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
91.18 -> Inside a drawer and a few days later even though the uranium hadn't seen the Sun
95.939 -> He decided to develop the film anyway
97.74 -> And what he found was that the photographic film had been exposed just as before
103.659 -> Even though the uranium was not excited by sunlight
106.869 -> So this was not a phosphorescence phenomenon some type of radiation and therefore energy was coming out of a rock
114.25 -> unprovoked
115.659 -> But how could a seemingly inert object like a rock give off energy
120.28 -> Where is it getting that energy from it was a mystery that seemed to violate the law of conservation of energy?
126.79 -> That is until Einstein published his famous e equals mc-squared
130.66 -> Which suggested a source of energy for the?
133.26 -> Might be the mass of the nucleus
135.629 -> 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
142.95 -> Imaginations run wild like HG Wells who in 1914 published the book the world set free
149.31 -> Which includes the first mention of the words atomic bomb he envisioned a uranium based hand grenade that would continue to explode
157.799 -> indefinitely but to scientists this was completely detached from reality as Einstein in 1933 put it there is not the
165.51 -> slightest indication that nuclear energy will ever be obtainable it would mean that the atom would have to be shattered at will and
172.68 -> That's just the thing people had no ability to make a nucleus do
176.76 -> Anything all we were observing was the natural process of radioactive decay atoms of a particular
182.579 -> Unstable isotope decaying at random with some characteristic half-life
187.079 -> And the energy given off although immense on the scale of an atom is pretty insignificant on the scale of people and the world
193.89 -> the fission of a single uranium atom releases
196.62 -> Twenty times less energy than the amount required to raise a grain of sand the thickness of a piece of paper
203.069 -> 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
210.78 -> Fire a proton at it
212.329 -> But since the nucleus and the proton are both positively charged they repel
216.599 -> 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
222.78 -> Even then if you're successful you've only affected one nucleus
225.709 -> Which at best can't even lift a grain of sand
228.69 -> So you can see why the Nobel Prize winners were saying nuclear weapons not gonna happen
233.639 -> But then comes the discovery of the neutron and the neutron changes everything
238.53 -> Because as an uncharged nuclear particle it can drift
242.489 -> Ghostly undeflected through matter until it hits a nucleus
246.12 -> Transforming it into something else and this leads to the Epiphany of a man named Leo Szilard
251.359 -> Now's a lard read the world set free, so he's already imagined a future in which nuclear energy is harnessed by weaponry
257.989 -> And he remembers the exact moment he comes up with this idea as he's crossing the street in London
263.7 -> 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
271.16 -> when it absorbed one Neutron then such an element
273.77 -> If assembled in sufficiently large mass could sustain a nuclear chain
278.25 -> reaction
278.97 -> In other words the neutron
280.62 -> Enables us to trigger
281.94 -> 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
289.07 -> Fission's and an exponentially increasing rate the nucleus that has this property is
295.02 -> uranium-235
296.06 -> In fact on average it releases two and a half neutrons every time it divides
300.06 -> Now all of a sudden you have the possibility of splitting zillions of nuclei
305.79 -> simultaneously releasing incredible amounts of energy all at once
309.68 -> That's an atomic bomb now if you want more control over this release of energy as in a nuclear power plant
315.15 -> well
315.65 -> Then you have to absorb a few neutrons so that the fission of one nucleus only
319.71 -> Causes the fission of one other nucleus on average
322.62 -> Then you have a steady chain reaction that emits the same amount of energy each instant the challenge is that this is like
329.34 -> 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
336.69 -> Increases exponentially and soon you're back to a bomb or Chernobyl so if not for the existence of the neutron a neutral
344.25 -> nuclear particle to trigger reactions that occurs in greater numbers relative to protons in the larger nuclei meaning
350.78 -> They're likely to be given off when a large nucleus splits well, then maybe as many brilliant scientists suspected
356.69 -> It would be impossible to harness the energy in the nucleus
359.67 -> But as it is in our universe the neutron is the hero or the villain of nuclear physics
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Source: https://www.youtube.com/watch?v=HD3k1hgbUXQ