Initiating a Fission Chain Reaction: What is Critical Mass?

Physics, Technology
[caption id="attachment_19651" align="alignright" width="600"] One basic fission reaction[/caption] What is critical mass? Before we answer that question, we want to discuss the topic of fission, itself. When we speak of atomic bombs, we do not usually mean hydrogen bombs or fusion bombs in which the nuclei of hydrogen atoms fuse together.¹ Rather, we mean fission bombs, in which large atoms of radioactive (unstable) elements are torn apart to produce smaller atoms with the release tremendous energy. One simple atomic explosion reaction is written, 1 n + 235U → [236U] → 92Kr + 141Ba + 3 n The above equation informs us that one energetic neutron properly striking an atom of uranium, isotope 235, produces, first and temporarily, an ordinarily stable atom of uranium, isotope 236. [caption id="attachment_19652" align="alignleft" width="300"] Uraninite…
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Why All Helium Has Not Escaped Earth’s Atmosphere

Geology, Physics
[caption id="attachment_14665" align="alignright" width="440"] Hydrogen or Helium?[/caption] Ninety of the elements occur in nature. The smallest and lightest of the elements is hydrogen. Yet, it is abundant in Earth. Almost no hydrogen gas escapes Earth’s atmosphere. This is partly because hydrogen is reactive and exists almost exclusively in combination with other, heavier elements. Helium, too, is a gas. It is the second lightest element. However, it is neither reactive nor abundant. It does not occur in nature in compound form. Why doesn’t it all escape Earth’s atmosphere? Comparing Hydrogen and Helium Although hydrogen is the lightest element and atom, it almost never exists, even as a gas, in atomic form. It assumes, not monatomic form, H, but diatomic form, H₂. The weight of that is twice the weight of an…
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