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Protactinium-231 arises naturally from the decay of natural uranium-235, and artificially in nuclear reactors by the reaction 232 Th + n → 231 Th + 2n and the subsequent beta decay of 231 Th. It was once thought to be able to support a nuclear chain reaction, which could in principle be used to build nuclear weapons ; the physicist Walter ...
231 Pa makes up nearly all natural protactinium. The primary decay mode for isotopes of Pa lighter than (and including) the most stable isotope 231 Pa is alpha decay, except for 228 Pa to 230 Pa, which primarily decay by electron capture to isotopes of thorium. The primary mode for the heavier isotopes is beta minus (β −) decay.
However, the 231 Pa (with a half-life of 3.27 × 10 4 years) formed via (n,2n) reactions with 232 Th (yielding 231 Th that decays to 231 Pa), while not a transuranic waste, is a major contributor to the long-term radiotoxicity of spent nuclear fuel. While 231 Pa can in principle be converted back to 232
In physics, there are equations in every field to relate physical quantities to each other and perform calculations. Entire handbooks of equations can only summarize most of the full subject, else are highly specialized within a certain field. Physics is derived of formulae only.
Theoretical chemistry requires quantities from core physics, such as time, volume, temperature, and pressure.But the highly quantitative nature of physical chemistry, in a more specialized way than core physics, uses molar amounts of substance rather than simply counting numbers; this leads to the specialized definitions in this article.
The "Six-factor formula" is the neutron life-cycle balance equation, which includes six separate factors, the product of which is equal to the ratio of the number of neutrons in any generation to that of the previous one; this parameter is called the effective multiplication factor k, also denoted by K eff, where k = Є L f ρ L th f η, where ...
The distances relevant to the physics expressed in SI units are naturally on the order of , while expressed in atomic units distances are on the order of (one Bohr radius, the atomic unit of length). An additional benefit of expressing quantities using atomic units is that their values calculated and reported in atomic units do ...
How much gas is present could be specified by giving the mass instead of the chemical amount of gas. Therefore, an alternative form of the ideal gas law may be useful. The chemical amount, n (in moles), is equal to total mass of the gas (m) (in kilograms) divided by the molar mass, M (in kilograms per mole): =.