March, 2012

Nuclear Fusion

Let us look at the graph for the energy of various nuclei. Remember tht this graph is upside down and so Iron (Fe) has the lowest energy. We have seen when talking about alpha decay that some elements with atomic number higher than that of iron can decrease their mass by emitting an alpha particle […]

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About Uranium

It would be useful at this point to talk a bit more about Uranium and its isotopes. Uranium naturally occurs as two isotopes details of which are shown below. Atomic Mass Halflife Occurance 238 4.5×109years 99.3% 235 7×108 years 0.7% Of the two isotopes only Uranium-235 is fissile. However some of the Uranium-238 is converted […]

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The Rate of Decay

The rate at which these unstable isotopes undergo decay varies greatly between the different isotopes. The process is random for each atom. However there is a fixed probability that an atom will disintegrate over a fixed time scale. It is rather like throwing a dice – on an individual throw then you cannot be certain […]

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Gamma Radiation

When an atom undergoes alpha or beta decay it can leave the nucleus in a high energy state. The atom goes to a lower energy state by emitting light. This light is very high energy (high frequency – short wavelength) and is called gamma (γ) radiation. The nucleus stays the same i.e. its atomic mass […]

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Decay Chains

When an atom undergoes radioactive decay the isotope produced is not necessarily stable itself. If it is not then that can undergo radioactive decay. This can carry on in what are called decay chains. In the diagram above the atomic mass is along the bottom (204-240) and the atomic number up the side. Starting with […]

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Moderation

We have discussed fission and neutron capture. Now we are going to talk about how we can increase the likelihood that fission or neutron capture happening. What happens depends on the energy (speed) of the neutrons. The neutron induced fission process is much more likely to happen if the neutrons have a lower energy than […]

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Neutron Capture

Before we talk any further about fission it is useful to have a look at what other things can happen to the neutrons. One thing that can happen is that they can be captured by a nucleus. The atom that captures the neutron remains the same element (since the atomic number remains the same) but […]

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Very Heavy Atoms – Fission

Spontaneous Fission For heavy elements (greater than mass 232) the nucleus can split into two smaller elements and a few spare neutrons. This is called spontaneous fission. For example Uranium 235 can decay into Barium-141 and Krypton 92 With fission the atom can split in very many different ways although the ratio of the atomic […]

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Atomic Mass and Stability – Alpha Decay

As atomic mass increases the stability of the nucleus increases but after a while they become too heavy and the stability decreases. The graph above shows how the energy changes with atomic number. Note that the energy axis goes the other way to the way you would expect. I have shown the graph this way […]

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Proton to Neutron Ratios and the Stability of Nuclei – Beta Radiation

Adding more neutrons to the nucleus does not change the chemical properties of the atom. A hydrogen atom with one or even two neutrons has the same chemical properties as normal hydrogen. However the number of neutrons does affect the physical properties. As neutrons are added to the nucleus their energy increases with respect to […]

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