<span>Heavy water acts as a neutron moderator. The neutrons formed by fission come off at high velocity, but U-235 absorbs neutrons much more strongly when they are slowed down, so all so-called thermal reactors use a moderator to slow them down until they achieve the average velocity appropriate to the atoms of the moderator which is at approx 300 deg C in a water reactor. Other moderators can be light water or graphite. Heavy water has the advantage over light water that it absorbs fewer neutrons so natural uranium can be used, whilst light water requires enriched uranium fuel. Graphite in a very pure form is also a good moderator but requires a gas coolant, carbon dioxide has been used in magnox and agr reactors, but there is a time limit on the life of the reactor due to graphite corrosion, and these are now obsolete as far as new builds are concerned. The Soviet RBMK reactors used graphite but with a water coolant inside pressure tubes, but after Chernobyl there will certainly be no more of these built
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I think the answers to this is d
<span>B.The oxygen isotopes contain 8 electrons but each contains a different number of neutrons and protons - 8 and 10 respectively.</span>
Answer:
Tides . hope this helps
Explanation:
the tidal force causes earth and its water to bulge out on the side closest to the moon
Answer:
Photoelectric effect, pair production and Compton scattering
Explanation:
Gamma rays, having no charge, can be slowed slowly by ionization as a material passes through. They suffer other mechanisms that eventually make them disappear, transferring their energy, they can cross several centimeters of a solid, or hundreds of meters of air, without undergoing any process or affecting the material they cross. Then they suffer one of the three effects and deposit much of their energy there. The three mechanisms of interaction with matter are: the photoelectric effect, the Compton effect and the production of pairs.
The photoelectric effect is that the photon meets an electron in the material and transfers all its energy, disappearing the original photon. The secondary electron acquires all the energy of the photon in the form of kinetic energy, and is sufficient to separate it from its atom and convert it into a projectile. This is stopped by ionization and excitation of the material
In the Compton effect the photon collides with an electron as if it were a clash between two elastic spheres. The secondary electron acquires only part of the energy of the photon and the rest takes it with another photon of lesser energy and diverted.
When an energy photon approaches the intense electric field of a nucleus, the production of pairs can happen. In this case the photon is transformed into an electron positron pair. Since the sum of the mass of the pair is 1.02 MeV, it cannot happen if the photon's energy is less than this amount. If the energy of the original photon is greater than 1.02 MeV, the surplus is distributed by the electron and the positron as kinetic energy, and the material can be ionized. The positron at the end of its path forms a positronium and then annihilates producing two annihilation photons, 0.51 MeV each.