Nuclear Models?

Question

Explain each of the following in terms of nuclear models:

1. The mass of an atom of 4He is less than the sum of the masses of 2 protons, 2 neutrons, and 2 electrons

2. Alpha radiation penetrates a much shorter distance into a piece of material than does beta radiation of the same energy

3. Products from a nuclear fission of a uranium atom such as 90Sr and 137Ce are highly radioactive and decay by emission of beta particles.

4. Nuclear fusion requires large amounts of energy to get started, whereas nuclear fission can occur spontaneously, although both processes release energy

Answer 1

1) Atomic mass is sum of protons and neutron, electrons don't count.

2) Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus; hence, it can be written as He2+, Beta particles are high-energy, high-speed electrons. The higher mass of the Alpha particle collides with matter faster than free electrons so it has lower penetrating power.

3) Well that is just how those isotope decay. By the way where are you getting this information. Fission of Ur235 gives Kr92 and Ba141 As little as 15 lb (7 kg) of uranium-235 can be used to make an atomic bomb.[6] The first atomic bomb worked by this principle (nuclear fission)

ref http://en.wikipedia.org/wiki/Uranium

4) Fission occur because the element is unstable to begin with. Isotope decides to naturally relax (decompose) intop a more satble isotope) it will release two neutrons. Each of these neutrons can then hit another Ur atom could is to release 2 each (total 4), etc, etc, chain reaction.

In nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus. It takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen. But the fusion of lighter nuclei, which creates a heavier nucleus and a free neutron, will generally release more energy than it took to force them together — an exothermic process that can produce self-sustaining reactions. The energy released in most nuclear reactions is much larger than that for chemical reactions, because the binding energy that holds a nucleus together is far greater than the energy that holds electrons to a nucleus.

Answer 2

1. Whenever you do a reaction that gives off energy, the total energy of the products will have less energy than the reactants. This energy is equal to the difference in mass times the speed of light squared (Einsteins E=mc^2 forumla) Potential energy has mass.

2. Alpha particles(helium nucleus) are much heaver than beta particles(electron) and for the same energy they would be moving much slower so they are more able to interact with matter.

3. Heavier nuclei such as Uranium have a higher neutron to proton ratio than lighter elements. This is because as elements have more protons, the electromagnetic force pushing them apart gets stronger. The additional neutrons help by binding via the strong nuclear force and spreading out the protons. When lighter elements are created by fission, these extra neutrons are not needed anymore and prefer to decay into the lighter proton by giving off an electron.

4. When positively charged nuclei are pushed together, kinetic energy in the form of heat is required to overcome the repulsion due to the electromagnetic force. The strong nuclear force which binds protons and neutrons together cannot take effect until the nuclei are very close together. However, the energy created by fusing nuclei together via the strong nuclear force exceeds the energy needed to bring the nuclei close enough so overall the process gives off energy. In nuclear fission no heat energy is required to start the reaction.

Answer 3

1) When you form an atom, you must have some energy to keep all the particles together; The source of energy is a loss of mass converted to energy in order to keep the staff together

2) The mass of an alpha ray is about 7000 times that of an electron(beta ray) . So , with the amount of energy of the radiation about the same, the particle alpha which is very heavy can not penetrate the matter as the electrons

3) When you brake an heavy atom as Uranium, the products have more odds to be radioactive than stable. The emission of alpha is mainly the fact of very heavy atoms with high Z . Sr and Cs (you have made a mistake) show a beta emission

4) The fusion requires very high temperature (as in the inner of the sun) to begin

Answer 4

1) Just because you have flour, eggs, sugar and milk doesn't mean you have a cake; you need to put some work into it to make a cake. Same goes for this problem here. There is some amount of energy required to make the protons and neutrons stay together instead of just going off their separate ways. The way you get this nuclear binding energy is to convert some of your mass into the energy required ( you know, Einstein's E=mc^2??) 2) A simple way to think about this is that an alpha particle is also ~7200 times larger than a beta particle. As a result, a beta particle should be more nimble through a given material. 3) No clue 4) no clue. Though you may want to check out an graph of energy vs. atomic distance to help with the nuclear fusion aspect.