Basic Physics Of The Atomic Bomb (1951)

[Music] peeing off on the subject of the atomic bomb requires that you focus your attention properly keep your eyes where they belong on the ball because it serves to lead us into a minute Universe containing things so infinitesimal they are hard to imagine unless we change our concepts of size and space and the change comes Easier by taking a quick glimpse of golf a game involving the manipulation of a small sphere the ball or on the surface of another sphere about 300 million times as large the Earth for a golf ball is about 300 million times as large as each of the atoms which make up its elements if an atom is so small how can we know anything about it by observing its effects you can't see the wind either but you can see what it does and you know from recent history what the atom can do do it's a mighty might yet it becomes immense when we look inside it and compare the whole to its parts this an atom of hydrogen which is one of the principal elements found in a golf ball is the simplest of all atoms it consists of a negatively charged light particle called an electron which revolves in an orbit about a nucleus the nucleus of a hydrogen atom is made up of a single particle with a positive electrical charge and is known as a proton to reemphasize the submicroscopic nature of our subject if we could increase the size of the nucleus proton to that of a golf ball the route of the electron would be about a mile away hydrogen is one of the most common elements found in nature as a gas it has many uses one of them as fuel for welders torches scientists have classif IED and arranged elements according to their atomic structure and hydrogen with its single proton gets First Billing it is assigned the atomic number one which refers to the proton the ability of an element's atoms to form chemical compounds as hydrogen combined with oxygen to form water is governed by the atom's electrons in another form of hydrogen there is a second particle in the nucleus it carries no electrical charge however in the free natural state the number of electrons in protons is the same and the additional uncharged nuclear particle does not affect chemical behavior we can do it as superargo dead weight a passenger going along just for the ride it is called a neutron it gives this form of hydrogen an atomic weight of two the sum of the protons and neutrons in the nucleus different forms of the same element with different weights but carrying the same electrical charges and having identical chemical behavior are known as Isotopes for example adding this Neutron to a standard atom of hydrogen would produce this isotope of hydrogen known as dyum this is the hydrogen in heavy water adding another Neutron produces a third hydrogen isotope called tritium one rung above hydrogen on the ladder of elements is helium one of the uses for helium you're probably familiar with is in lighter than aircraft a helium atom has two electrons and a nucleus composed of two protons plus two neutrons so helium has the atomic number two same as the protons which it possesses and an atomic weight of four it's protons plus neutrons going up the ladder we find elements with atoms that become progressively complicated with more electrons and increased numbers of protons and neutrons in their nuclei for example a neutral carbon atom with an atomic number of six has six electrons in the nucleus are six protons plus six neutrons so the atomic weight is 12 carbon exists in many forms high and humble as diamonds and pencil points at the top of Nature's ladder is the most complex atom uranium with an atomic number of 92 naturally occurring uranium has three isotopic forms with Atomic weights of 234 235 and 238 uranium and its neighboring elements are maladjusted their atoms have an unstable number of protons and neutrons so observing Nature's law against lack of balance and symmetry they try to become stable by getting rid of their excess nuclear Freight the manifestation of this inner struggle is known as radioactivity the adjustment May release energy in three ways beta particles bearing a negative charge are expelled from the nucleus they are essentially high-speed electrons alpha particles may also be shot out they consist of two protons plus two neutrons and are positively charged they are the same as the nucleus of the helium atom or the energy may be in the form of gamma rays electromagnetic radiations like x-rays natural radioactivity causes these heavy unstable elements to Decay progressively down the ladder eventually reaching a stable form of lead the unit for measuring the rate of such changes or transmutations is the halflife the time required for 50% of a radioactive material to Decay to illustrate suppose you had a gallon of whiskey and each day you drank half the amount of the bottle the first day you drank half a gallon and the whisky's half life would be one day the second day assuming for the sake of science you'd be able to sit up and take it you'd knock all 50% of the remainder a one quart the third day a pint and so on but you'd never quite get to the bottom of the bottle there'd always be a half remaining the fact that some radioactive matter always remains is not so important as the time required for the half to Decay half life varies from isotope to isotope it takes 4 b500 million years for half a hunk of uranium 238 to become thorium 234 the half life of radium 226 is600 years that of radon is slightly less than 4 days while others have half lives of fractions of a second so so far we've been watching natural radioactivity man has stepped into the act however and in some cases outdone nature using as his gun cyclotrons and other accelerators and employing hydrogen and helium nuclei neutrons protons electrons and other minute bullets he has made stable matter unstable produced radioactive isotopes of many elements he transmutes lithium into helium with a hydrogen nucleus as the projectile by striking the nucleus of a chromium atom with a helium nucleus he changes it into Radioactive manganes with the emission of a proton manganes in turn decays to iron with the emission of a beta particle and gamma ray and scientists have gone up the ladder above uranium creating new elements by hitting the nucleus with a neutron if the neutron sticks the atomic weight goes to 239 a new artificial uranium isotope but the nucleus reacts by getting rid of a negatively charged beta particle thus raising the positive charge of the nucleus by one and becoming a new element with the atomic number 93 and called neptunium neptunium is a Mal content and it in turn emits a beta particle turning into element 94 plutonium even heavier elements have been developed but we can stop with plutonium because it's one of the basic ingredients of an atomic explosion in trying to bring about such an explosion scientists had two recipes two blueprints to follow the first call for nuclear fusion to illustrate here are four hydrogen atoms if fused brought together under proper conditions they form one helium atom but loss of weight occurs during the process in other words the parts are heavier than the whole why because when the fusion takes place this extra mass or weight is converted to and released as energy energy which might be put to some use the sun has the key to this combination it is continually converting hydrogen into helium and sending the resulting energy earthward that's the princip Le which might make a hydrogen bomb work but to the scientists who wanted a quick solution releasing a piece of the sun on Earth for the moment of Devastation seemed a bit impractical so they went to the upper end of the ladder and set about getting Atomic power through the reverse of fusion by breaking heavy elements into lighter ones by a process called fishing like this when hit by a neutron traveling at a certain speed the nucleus of a uranium 235 atom breaks up into two much lighter elements with a tremendous release of energy from that which held the tightly packed nucleus together like this while it seems inconsistent that both building up and breaking down of atoms releases energy this is only possible at the far ends of our ladder of elements where Fusion produces energy through the combination of the lightest elements and fishing splits only the heaviest the products of fishing and fusion tend toward the middle of the ladder in the case of fishion the possibility seem immense and workable the scientists knew that the fishing of one pound of uranium would produce as much energy as the combustion of 1,400 tons of coal or 250,000 gallons of gasoline the question was how to do it how to produce the breaking up of the millions of atoms in a comparatively massive hunk of uranium and do it instantaneously so that instead of a gradual release of smooth power as demonstrated by a moving locomotive the energy would be built up then let loose in a violent explosion a path was indicated by the fact that fishing of a uranium 235 nucleus by one Neutron creates in addition to the fishing products in energy two or three new neutrons perhaps these neutrons could be put to work in developing a chain reaction this is an example of the Chain Reaction sustaining itself this is one that builds up to a big finish if several neutrons could be produced in a single fishion of a uranium atom and these neutrons in turn could be used for further the fishs then a chain reaction would be developed which would reach a colossal climax the energy liberated by each fishion step would be let loose in a mighty explosion they knew that uranium 235 was good fishable material they also knew it was scarce one part in 140 of natural uranium is 235 an insignificant amount is 234 and the rest is 238 which wasn't a suitable ingredient it was hard to extract the good from the bad because being Isotopes both had the same atomic number of 92 therefore the same chemical behavior the very slight difference in atomic weights however made possible several ways of achieving The Separation by physical means if natural uranium gas is passed along one side of a porous barrier with a greater vacuum on the other the the lighter 235 atoms will go through the barrier a bit faster than the 238 by this process it is possible to enrich the uranium with the 235 isotope enrich it enough for fision purposes the Manhattan engineer District team of scientists engineers industrialists labor and Military built huge plants to produce the stuff by this and other means the scientists went further taking advantage of the fact that uranium 238 instead of visioning tends to capture neutrons to ultimately become plutonium and plutonium is as effective for fishing as uranium 235 the Manhattan engineer District team built a plutonium plant at Hanford Washington our bomb Builders were nearing the goal they had the substance now for the shape this isn't it and the reasons because obvious when we hit the block with a neutron and follow the careers of the three neutrons we assume are formed by the initial atom split this Neutron enters a nucleus without causing fishing it's captured it's a dud these two escape this is then a hunk of fishable material in which the neutrons accomplish nothing and in which a chain reaction can't even get started it's called a subcritical mass the problem of the scientist became clear to make fullest use of all neutrons produced in a single fishion a big step toward their goal was to prevent The Escape of the neutrons here one of three neutrons makes good visioning another atom and starting a chain our material is now called a critical mass this would be fine for an atomic power plant but it isn't enough for an explosion to get that we must keep the birth rate of the neutrons well above the death rate one Neutron must produce two two must produce four and so on then we'll be in business one way to cut down Neutron loss and increase the number of fishion is to give them more working room yet since we are dealing with bomb material we must economize on size so the best shape is a sphere which has minimum surface area through which Neutron can escape with maximum volume in which they can work and we can further decrease Neutron loss by covering our bomb with a special mirror which will reflect the neutrons turn them back into the field of play when we get a successful Chain Reaction growing we have what is called a supercritical mass and our situation is also super critical because we aren't ready for an explosion we must keep our supercritical Mass divided into subcritical Parts until the proper time when the explosion is desired the parts are brought together quickly and kept together long enough for a great number of fishs to occur the time for our bomb to explode is less than a millionth of a second in building our bomb we've been playing a game toying in a broad General way with theories already worked out in detail and executed by those who during World War II developed and produced the most destructive weapons of all time theirs was a dramatic role and a precarious position they couldn't experiment realistically along the way they couldn't conduct small safe tight siiz tests there's no such thing as a small safe atomic explosion below critical size the bomb is a bust above it's a burst compromise wasn't possible to those who early on the morning of July 16th 1945 awaited the setting off of their first atomic bomb it had to be all or nothing but [Music] which the answer left no [Music] doubts