beta particle, beta particle, beta--what's a beta particle? - electron. - electron. now we have to make the symbol for electron. e for electron, get it? mm-hmm. what's the atomic number of an electron? - negative one. - atomic number? negative one. what is atomic number, anyway? charge, right? what's the charge of an electron? - negative one. - negative one. what's the mass of an electron? zero. well, it's closer to zero than it is to one if one is the mass of a proton or neutron. and this has got, like, about 2,000th the mass. that's closer to zero than to one. so we round off atomic mass number, anyway. this is zero. now, what does the thorium become? well, what do we got over here for an atomic number? 91. do you see it's 91? yeah. 91. and what's the mass gonna be? - 89. - now, what has 91? protactinium. - is it gonna be 91, gang? - yeah. let's check. - 91 minus 1 equals 90. - correct. it's 91. that's interesting. some people think that radioactive decay, you start with uranium and work down, down, down, down the periodic table approaching hydrogen. not true. when

it emits a beta particle. okay. it emits a beta particle. and what does it turn into? how many people can figure out what the number is here that couldn't do it before but maybe now can? show of hands. four people. wonderful. now, how many? what is it gonna be, gang? it's 94. 94, 94. what is the second planet that we named after discovering by newton's laws? it wasn't neptune, it was what? - pluto. - pluto. guess what we'd be calling this, gang? plutonium. plutonium. pu239. and you know what plutonium will do? plutonium as well as uranium 235 will undergo fission when a neutron taps it. and so this is used for power production. u235, used for power production. historically, when the bombs were dropped back in world war ii, the bomb that devastated hiroshima was a uranium 235 bomb. you know how much uranium 235 was left after the bomb was detonated? almost none. the united states shot its arsenal, one bomb, none left to speak of. you know what the bomb that hit nagasaki was? plutonium. plutonium. does the same thing. plutonium is made from uranium 235--238, very plentif