# Atomic Weight Atomic number (Z) Goal: To understand the basics of nuclear physics

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## Atomic Weight Atomic number (Z) Goal: To understand the basics of nuclear physics

Bethel College McKenzie, US has reference to this Academic Journal, Goal: To understand the basics of nuclear physics Objectives: To learn about Atomic number in addition to weight To be able so that find the Size of nucleus To understand Fusion in addition to Fission To learn about Binding Energy To learn about How all the elements are made To learn about the Hydrogen Bomb in addition to other uses in consideration of nuclear power such as power plants Atomic number (Z) The atomic number is the number of protons an atom has in its nucleus (and electrons if it is not ?ionized?). Each different element has its own atomic number. Atomic Weight Each atom has some number of neutrons. The # of neutrons is N. Most atoms lighter than iron have 1 neutron per proton. Atoms alongside a lot more neutrons than protons tend so that be unstable.

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Size of a nucleus Each proton in addition to neutron gets squeezed together. The nucleus will almost always have the same density which is the density of matter. This is 1014 g/cm3 or 100 trillion times the density of water. As in consideration of the radius, since the volume of the nucleus depends on the cube of the radius in addition to the number of particles therefore: r = r0 * A1/3 And r0 = 1.2 fm Atoms The density in consideration of the total atom includes the electrons, so it is mostly empty space (like finding the density of our solar system). Larger atoms have their electrons closer so that the atoms, so their densities are larger. So, while atoms all have the same density of nucleus, they do not have the same density. Fusion + Fission Fusion is taking two atoms in addition to combining them together. This is the power source that powers stars. Fission is breaking an atom into more than 1 atom. This is what powers nuclear plants. Often time an ?alpha? particle is released ? which is just a helium nucleus.

Binding energy It takes some amount of energy so that glue the atoms together. If you slam them together or break them apart you can either loose energy or gain energy depending on what the new atom needs so that be formed. Each element has some amount of binding energy. If you divide this energy by the # of particles in its nucleus you get a binding energy per nucleon. Which so that do? If you go so that higher binding energy alongside larger atoms you gain energy through fusion. If you go so that higher binding energy alongside smaller atom you gain energy through fission. At what point are you no longer able so that get energy?

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How the elements are made: There are a few different methods so that make different elements. Hydrogen was formed in the big bang when energy formed into quarks ? in addition to the quarks formed into Hydrogen. Nuclear fusion in the early universe created most of the Helium. For all of the other elements iron in addition to lighter they were all formed via fusion in the cores of massive stars! Heavier than Iron Once you get so that Iron other processes take over. The first involves a massive bombardment of neutrons onto a Iron atom. This is called the fast process. The neutrons then decay in addition to emit an electron so that become a proton. This is called beta decay. Reverse Sometimes a neutron can capture an electron in addition to become a proton. This is called electron capture. So, a heavy Nitrogen atom can capture an electron in the nucleus in addition to become a light oxygen atom.

Alpha Decay Some atoms are radioactive. What this means is that in some given time (called a half life) half of the atoms will release a particle (we have seen the beta decay example already). Usually though a mean lifetime is used, after which only 37% of the original atoms stay original. Many radioactive materials release a helium nucleus (2 protons + 2 neutrons) in an attempt so that become more stable. A problem alongside this is that the nucleus is bigger than it should be in size. This is called an ?excited state?. To unexcite itself it will usually emit one or more gamma rays. Uses We have shown that stars use fusion in consideration of power. However it is very tough. In the core of our sun it is 100 million degrees in addition to 100 times the density of water. What usually happens when 2 protons find themselves on a collision course? NOTHING! Even at that temperature their energy is still not enough so that collide. Eventually their repulsive force brings both so that a screeching halt in addition to then they go the other way. But, it turns out that there is some small chance that they are really located somewhere else in addition to can fuse ? thank you quantum mechanics.

Our uses in consideration of fusion Well, not much. We have tried, but we cannot generate a sustained burst which gives more energy that it takes. Heck, even in consideration of the sun it takes an average of 10 billion years in consideration of each Hydrogen atom so that fuse. Fission We use it in consideration of nuclear power. We use it in consideration of bombs. The bombs that were used in WWII would have been pure fission bombs. Basically you have some radioactive material that you hit alongside a neutron. That makes it split into 2 atoms + 3 neutrons. The resulting neutrons then hit other atoms making them split. This gives a runaway affect. But only Uranium 235 reacts this way (neutron in means 3 neutrons out). Difficulties If you had pure U235 this would be pretty easy, but luckily in consideration of us U235 comes alongside a LOT of U238 ? which is pretty harmless. Also the U238 absorbs neutrons, so if you have a normal breakdown (99.3% U238) then the neutrons quickly all get eaten up by U238 atoms in addition to the chain reaction ends. To get it so that work you have so that ?enrich? the U235 so that make it a few percent. But this is EXPENSIVE!

Nuclear plants Now you have what you need so that generate power. However, the fissioning U235 atoms fire neutrons which move too fast. The U235 atoms can absorb them in addition to not fission! So, you have so that have some substance so that slow down the neutrons (such as water). Reactor at Critical! Now, how many neutrons do you want? If you get less than 1 on average, your reactions won?t last long in addition to will die out. This is called subcritical. If you get on average exactly 1 neutron then you can keep it going at a constant pace. This is called critical ? in addition to a reactor at critical is actually a GOOD thing ? don?t listen so that Hollywood. Will it blow? Well if you produce more than 1 the reaction rate will INCREASE alongside time. Other than when it is turned on ? this is very bad. If this happens you need so that absorb some neutrons by inserting a ?control rod?. This is called supercritical. The Worry about N. Korea Here is why there is concern about nuclear power being used in countries that cannot be regulated by the UN? Sure, you produce energy without greenhouse gasses. This is good, but: When the U238 absorbs a neutron (and it will from time so that time ? there is a LOT more of it) then it will become U239 ? which is not stable. The U239 beta decays into plutonium 239. Pu239 can be used so that make nuclear weapons! This is NOT a good thing clearly. These can be called ?breeder reactors?

H bomb The modern version of the atomic bomb uses both fission in addition to fusion. The first part of the bomb is a fission bomb (U235 or Pu239). This generates a lot of energy ? enough so that fuse a lighter element such as Hydrogen (which you can provide using water). Yes this takes hundreds of millions of degrees! This fusion reaction is an uncontrolled reaction in addition to generates even more energy than the original bomb. This type of bomb destroyed the Bikini atoll. Stronger bombs than this were banned by the Geneva convention because any stronger than this in addition to the blast wave would reach outer space in addition to throw some of our atmosphere into space. Conclusion We learned everything there is so that know about the basics of nuclear power. We can now all apply in consideration of Homer Simpson?s job ? (picture from wikipedia)

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