OB: nuclear chem class #3

1. OB: nuclear chem class #3 Natural Radioactive Decay Modes, and Artificial Transmutations How does the Sun work, how does the chemistry inside a nuclear reactor work, and how donuclear bombs make energy?

2. Let’s first look at an example of alpha decay… 23892 U 42 He + 23490 Th Radioactive (unstable) uranium-238 naturally undergoes alpha decay and transmutes into thorium-234. An alpha particle is emitted from the original nucleus, leaving a “daughter” nucleus of thorium. And then, beta decay… 31 0-1 e 32 He H + Radioactive hydrogen (tritium, mass of three) undergoes natural beta decay. A beta particle is emitted as radiation, and an isotope of helium is formed as the daughter nucleus.

3. Positron decay example… 1910 199 F Ne 0+1 e + The radioisotope neon-19 undergoes natural positron decay, transmuting into fluorine-19 while emitting a positron particle from the nucleus. Note, this starts with a single radioisotope, and then comes the arrow. Nothing makes this happen, it’s natural. It just happens. Nothing can speed this process up, nothing can slow it down. Nothing can change it either. It just happens. If you were to see a different style of radioactive decay reaction, one where the original radioisotope has a neutron added to it, that would be artificially induced, not natural. Artificial transmutation comes next. It’s easy to spot since there’s a + sign on the left of the arrow, and the simple math of adding the top numbers (mass) and the bottom numbers (protons) still works.

4. Artificial transmutation is caused by humans. It is a forced reaction, and does not occur naturally. It usually involves the release of massive amounts of energy inside a nuclear reactor or a nuclear bomb. The first artificial transmutation reactions were carried out by some of the “regular” characters in our class, notable Earnest Rutherford (gold foil), James Chadwick (discovered the neutron), and the husband and wife team of Marie and Pierre Curie. 1919: Rutherford bombs some nitrogen atoms with alpha particles. 147 42 He 178 O + 11 H N + Nitrogen bombarded with alpha particles artificially transmutes into oxygen-17 and emits a proton

5. In 1932 Chadwick bombards beryllium-9 with alpha particles… 94 Be + 42 He 126 C + 10 n Alpha particles are blasted into beryllium atoms, transmuting artificially into carbon-12 and emitting a neutron in the process. In 1934 the Curie’s bombard aluminum with alpha particles, they form the first artificially created radioisotope in the process. 2713 Al + 42 He 3015 10 n P + Aluminum atoms are bombarded with alpha particles, causing the aluminum to artificially transmute into radioactive phosphorous while emitting a neutron. The radioactive phosphorous will undergo natural transmutation.

6. Those examples of artificial transmutation are relatively speaking minor concerning energy emitted. They were done in the lab, no explosions occurred. According to Albert Einstein, energy and matter are the same thing, just in different forms. His famous equation, E = mc2 Stands for energy equals mass times the speed of light squared. He proved that in a nuclear reaction, some matter could be converted into a lot of energy. This was the basis for nuclear reactors and nuclear bombs. In chemistry, matter cannot be created or destroyed. In nuclear chemistry that is not the case.

7. The artificial transmutation of U-235 by neutron bombardment into barium, krypton, and three more neutrons. Very strangely, there is a small loss of mass, and that mass is converted into energy. In the “second” round, three more U-235 nuclei are bombarded with the three newly formed neutrons, and this process occurs three more times, with three times the loss of a small amount of mass. (and again and again, until lots of energy can be released). This is called FISSION (the splitting of an atom). The mass of the Kr and Ba looks the same as the neutron and original U-235, but it is in fact slightly less. This slight amount of missing mass, the MASS DEFECT, is converted into energy. Lots and lots of energy!

8. The fission of uranium-235 is called a chain reaction, because one neutron causes the release of three neutrons plus some energy. These three neutrons cause the release of nine more neutrons, and more energy. Those nine cause the release of 27 neutrons and more energy. Those 27 neutrons cause the release of 81 neutrons, etc. The reaction becomes bigger and bigger quickly, releasing more and more energy all the while. With enough (a critical mass) of radioactive uranium-235, so much energy could be released it could cause an enormous explosion. Those are giant sized ships from a navy, watching a nuclear test explosion from a “safe” distance.

9. Fission splits larger isotopes into smaller ones. The Sun does something different, it fuses smaller atoms of hydrogen into larger helium atoms. In doing so some mass is lost (mass defect) and even more enormous amounts of energy are released. The Sun has an unbelievable mass and with that comes huge gravity and pressures. The heat and pressure allow it to squash hydrogen atoms into helium at the center, and it takes in excess of 10,000 years for that heat to escape to the surface to radiate out into space.

10. The Sun squashes four hydrogen's into helium to release energy this way: 4 H 11 42 He + 2 e + energy! 0-1 Also given off in this reaction is gamma radiation and neutrinos, which are very small particles that you will learn about in advanced physics if you are lucky enough to go there. For fusion to occur, crazy high temperatures and pressures must be acting. Fission reactions SPLIT atoms apart, Fusion reactions squish atoms together.

11. Nuclear bombs are either fission bombs that split atoms of uranium-235 and release huge amounts of energy, Or, they can be fusion bombs (hydrogen bombs). To make a fusion, or hydrogen bomb you have to first set off a fission bomb around the core of hydrogen, so enough heat and pressure can be exerted onto this hydrogen, to make that secondary fusion reaction occur. It’s hard to believe but fission reactions can be “controlled”, as in nuclear power plants, and the energy released can be harnessed and used. A fusion reaction is so much bigger that nothing can contain that energy. Fusion reactions are fine for the Sun, or for horrifically powerful bombs, but so far, not useable for human energy needs. Primary fission bomb. SecondaryFusion bomb