The Most Dangerous Rock in the World

this is the most dangerous rock in the world it's called pitch blend and it comes from the yawkenstall mines in the northern Czech Republic in 1789 the German Apothecary Martin claproth extracted a medal from these rocks that was widely used to color Ceramics and glass 60 years later in 1852 George Stokes showed that this glass would fluoresce under ultraviolet light in the late 1800s the physicist on rebeccarell tried to figure out if this metal generated x-rays when it fluoresced he hypothesized that he placed some small bits of metal on top of a photographic plate wrapped in black paper and put the whole Contraption out in the sun that the UV rays from the Sun would cause the metal to fluoresce generating x-rays which would pass through the black paper and expose the photographic plate in the regions close to the metal pieces after running the experiment and developing the plate beckrell saw exactly what he expected but his hypothesis was actually wrong and what has to be one of the luckiest moments in science the next week it was cloudy in Paris and instead of rewriting the experiment beckrell put it in a drawer and forgot about it when he came back a week later he decided to develop the plate just for fun expecting to see nothing he instead found very strong silhouettes on the plate this metal was emitting radiation all by itself this was an entirely new phenomena where was the energy even coming from what was this metal extracted from these rocks doing this mystery attracted the interest of some of the best scientists in the world including Maurice gladoska Curie Pierre Curie and Ernest Rutherford they discovered something remarkable the metal extracted from these rocks uranium was transmuting it was turning into other elements and releasing huge amounts of energy as it did this contradicted Decades of science that showed that atoms were the unchanging building blocks of our universe the word Adam literally and incorrectly means indivisible in the summer of 1903 Rutherford and his wife visited the curies in Paris and happened to arrive on the day that Marie received her PhD that night after the ceremony the group gathered in the garden to celebrate Pierre brought out a party trick a test tube coated in zinc sulfide and full of radium gas radium is a product of uranium Decay and itself is another radioactive element as the tube glowed in the Paris night Rutherford noticed Pierre's hands were covered in radiation burns from months of laboratory work an early sign of the power of their Discovery a new secret of the universe radioactive uranium had been unlocked hiding in these rocks what the Curious in Rutherford know that night in Paris was that uranium had one more lurking secret uncovering the secret would require a new generation of scientists and a complete rejection of Rutherford's understanding of the nucleus these Revelations would come in waves the first hit Leo silard 30 years later as he crossed the street in London one day a recent Refugee from Nazi Germany Seiler had just left his hotel lobby where he'd read a speech from Rutherford in his morning paper it had recently been shown that instead of waiting around for nuclear reactions to happen spontaneously it was possible to create these reactions by bombarding atoms with high-speed protons two of Rutherford's colleagues had shown that lithium atoms bombarded by protons would split into two alpha particles releasing huge amounts of energy in the process splitting just one kilogram releases 2.35 Terra joules enough to power modern day London for 14 hours as excitement around harnessing nuclear energy grew Rutherford now Lord Rutherford remained dismissive in the speech he said that anyone who looked for a source of power in the transformation of the atom was talking moonshine Rutherford argued that while splitting a single atom would release more energy than the incoming proton would provide that on average this was a very poor and inefficient way to produce energy to split the incredibly dense and positively charged lithium nucleus required accelerating protons in an electric field of 250 000 volts and only one in a billion of these high energy protons would actually crack the nucleus scilard thought this was that it was possible to harness nuclear energy and that Rutherford and his colleagues were just doing it wrong as he walked asylard realized that the proton was a poor choice of projectile its positive charge was intensely repelled by the positive nucleus overcoming the coulomb barrier to reach the nucleus was precisely the reason protons had to be accelerated to such high speeds in the first place a recent discovery from one of Rutherford's colleagues the neutron with no electrical charge would be much more effective but it wasn't clear how to make a strong enough source of neutrons or how much energy this would require a cylard moved across the street a new thought occurred to him what if we didn't have to provide the neutrons at all what if they came from the reaction itself what if there is some type of atom that when bombarded by a neutron would break apart releasing energy while simultaneously ejecting two new neutrons the resulting neutrons would then fly off to spawn two new reactions and so on the resulting nuclear Chain Reaction would be catastrophic one reaction becomes two two becomes four four becomes 8 and just 40 steps later we've split a trillion atoms did such an element exist and what would later become Nobel prize-winning work Enrico Fermi picked up this line of questioning and over the next couple years systematically bombarded every element on the periodic table with neutrons Fermi observed fairly consistent Behavior with most elements either not reacting or losing a proton or alpha particle and decaying into a neighbor on the periodic table a source of neutrons next to a sample of aluminum for example would chip away alpha particles converting some of the aluminum atoms into sodium notably none of fermi's experiments showed multiple neutrons being released per reaction making cylard's idea of a nuclear Chain Reaction seem impossible however for one element in fermi's experiments nothing made sense when Fermi reached the very last element on the periodic table at the time our old friend uranium extracted from Pitch blend he couldn't find chemical evidence that uranium was decaying into any of its neighbors observing a wide range of radioactive decay half-lives Fermi hypothesized that uranium was transmuting into a heavier yet to be discovered element this controversial claim to the tension of some of the best scientists in the world including Marie and Pierre curie's daughter Irene who began connecting experiments aimed at understanding exactly what was happening inside the uranium nucleus in 1938 the German nuclear chemist Otto Han would beat her to the punch observing that his bombarded uranium samples were turning into barium Han was alarmed and ran the experiment again and again looking for some mistake finding nothing 100 alerted to his collaborator Elise mightner on December 19 1938 asking for some insight into his frightful conclusion barium has atomic number 56. for Uranium to turn into barium the entire nucleus would have to split apart a decade of nuclear research had only ever shown atoms losing very small pieces at a time the accepted mathematical probability of such a large fragment separating from the uranium nucleus was impossibly small had to be a mistake when ottohan's letter arrived at least mitner desperately needed a distraction as an Austrian of Jewish descent Miner had been forced to flee when Hitler annexed Austria earlier that year might and her sister and brother-in-law had been sent into cow concentration camp leaving mightner and her nephew the physicist Otto fresh to celebrate the winter holidays alone in Kung Gulf Sweden when Frisch came down the stairs the morning of Christmas Eve meitner insisted that they get to work how could their German colleague Otto Han have possibly found barium setting out in the snow fresh on skis and nightner walking briskly they began to discuss the most complete nuclear mathematical model at the time treated the nucleus as a liquid drop each proton and neutron inside the nucleus is equally attracted by all of its neighbors while the particles on the surface of the nucleus only have neighbors on one side resulting in a net force a surface tension directed Inward and along the surface of the nucleus unlike a liquid drop however the positively charged protons inside the nucleus also repel each other adding an outward coulomb Force to the balance the balance of these forces accounts nicely for one of the most important observations we've made about the nucleus when physicists compare the mass of a given atom to the mass of the particles that make it up the math never comes out quite right the atom always has some Mass missing the answer to this puzzle lies in Einstein's discovery of mass energy equivalence his famous E equals MC squared equation the missing mass is converted into the binding energy that holds the nucleus together this discovery gave physicists an accurate way to measure the binding energy of each element by taking the differences in the measured mass and plugging into Einstein's equation when plotting these energies against the number of protons and neutrons in each atom an interesting curve emerges elements towards the center of the periodic table like 10 have the most strongly bound nuclei while lighter and heavier elements have less tightly bound nuclei initially no one was able to produce a satisfactory explanation for this trend why would elements towards the center of the periodic table have the strongest nuclear bonds as first shown by George gamawa in 1930 the balance of the forces in the liquid drop model nicely explains this curve the average attractive nuclear force between protons and neutrons is constant across all elements since the protons and neutrons on the surface of the nucleus have fewer neighbors this results in less overall attractive force and we need to reduce our overall binding energy by a factor proportional to the surface area of the nucleus this explains the lower binding energy of smaller atoms the ratio of surface area to volume increases as atoms become smaller finally the repulsive coulomb Force also reduces The Binding energy of the nucleus by a factor proportional to the number of protons squared divided by the radius of the nucleus this explains why heavier elements have weaker nuclear bonds the coulomb force has a much larger range than the nuclear force so its relative effect is larger in large atoms the net effect of these forces known as the semi-empirical mass formula amazingly matches observation with less than 1.5 percent error with all this in mind friction mightner stopped and set on a log to do some math despite the surface and coulomb terms reducing the overall binding energy of uranium it still has significant binding energy way more energy than the incoming Neutron that apparently split apart the nucleus and Otto Hans experiment then came a flash of insight what if the nucleus was more like a water drop that anyone had previously assumed what if it could oscillate fresh quickly sketched this picture with a nucleus deformed and stretched to a Breaking Point splitting into two but did the mathematics actually support this mitner and fresh realized that for this model to work they didn't need to overcome the full binding energy of the nucleus they only needed to check how much energy was required to make the nucleus wobbly deforming the nucleus increases the surface area and requires energy to push interior particles away from their neighbors into the surface this is why liquid drops are spherical a sphere minimizes the surface area for a given volume however unlike a liquid drop the particles in the nucleus are also repelled by the coulomb force if the coulomb force could push outward with a force equal to the inwardly pooling surface attention there would no longer be any net force preserving the drops spherical shape and the geometry of the nucleus would become unstable setting the change in energy as the liquid drop to formed equal to zero and solving for the mass number a and the atomic number Z fresh found that for large atoms around atomic number 100 the surface and coulomb terms would cancel out uranium is not too far away with atomic number 92 suggesting that the extra energy from the incoming Neutron may be sufficient to kick off oscillations and ultimately splitting as soon as the nucleus separated the very short-range nuclear force would no longer be in play leaving only the coulomb force to eject the two halves in this case a barium and Krypton nucleus with a huge amount of energy Frisch was able to quickly compute this energy coming up with around 200 Mega electron volts an impossibly large number at the atomic scale could this really be the case and if so where would this energy come from the answer again came down to Einstein's equation equals mc squared the higher binding energies of the resulting barium and Krypton produced by splitting uranium meant that more mass was converted into energy mitner had a version of The Binding energy curve memorized and sitting on that log in the middle of the snow she was able to show in a scrap of paper that an average change of a little under one Mega electron volt per proton and neutron multiplied by the 238 protons and neutrons in uranium which results again in around 200 Mega electron volts all the pieces fit fish would later say within weeks Frisch had experimentally validated these results and even given the new splitting phenomena a name nuclear fission word quickly spread across the globe of the Breakthrough when news reached versus Mentor Niels Bohr he said what fools we have been when news reach graduate student Louise Alvarez made haircut in California he ran out before his haircut was even over to let his advisor Robert Oppenheimer know within months he had another member of the Curie family was able to show that uranium fission released two or more neutrons making cylard's vision of a nuclear Chain Reaction a real possibility 200 Mega electron volts per atom one kilogram of uranium would release around 81 terrajoules of energy 20 million times the energy released by one kilogram of TNT if this energy could be released using a nuclear Chain Reaction the results would be catastrophic this possibility was not lost on governments as World War II loomed within much the United States Germans and Japanese began research work on building the atomic bomb the race had begun [Music]

Channel: Welch Labs

Views: 2,448,953

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Id: y-FuqptTZow

Length: 13min 10sec (790 seconds)

Published: Sat Jun 24 2023