Dr. Tsubokura's Radiation Lecture Vol.76

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

151. Radioactive uranium and plutonium could be used as ingredients for nuclear weapons

When radioactive uranium 235, which accounts for less than 1% of natural uranium, collides with a neutron, radioactive uranium becomes unbalanced and split, which results in a release of heat. Furthermore, fission of uranium also results in the production of a new neutron, which will then collide with more radioactive uranium and produce another fusion reaction and more heat.

Radioactive uranium produces this chain reaction when predetermined conditions are met. At a nuclear power plant, this chain reaction is gradually carried out in sealed containers to produce heat and results in the production of plutonium.

There are also several forms of plutonium produced by nuclear reactors, but along with uranium 235, plutonium 239 is particularly prone to fission.

The fuel utilized in nuclear power generation is approximately 3-5% concentrated radioactive uranium 235, while uranium used for a nuclear bomb is concentrated to more than 90%. Since plutonium 239 is also prone to initiating fission, it could be used as an ingredient for a nuclear bomb as well.

There are several kinds of atomic bombs; the one dropped on Hiroshima was a uranium atom bomb, and the one dropped on Nagasaki was a plutonium atom bomb.

152. The number after radioactive substances indicates the sum of protons and neutrons

When it comes to radioactive substances, a number (e.g., 100 or 200) is placed after them, as in cesium 134 or 137 and uranium 235 or 238. This article is going to explain what these numbers indicate.

All materials are composed of small particles called protons, neutrons, and electrons. When the numbers of each type of particles are unbalanced, the substance as a whole becomes unstable and is called a radioactive substance.

The numbers after the names of radioactive substances indicate the total number of protons and neutrons. For example, cesium 137 is composed of 55 protons and 82 neutrons for a total of 137. Furthermore, the names of radioactive substances, such as cesium and uranium, are determined by the number of protons in their core, regardless of the number of neutrons. The number of protons is the same for every type of cesium; therefore, cesium 134 contains 55 protons and 79 neutrons.

In the same vein, uranium 235 contains 92 protons and 143 neutrons, while uranium 238 contains 92 protons (the same number of protons as uranium 235) and 146 neutrons.

The nature of a substance varies depending on the balances of these numbers of particles. Radioactive substances have unbalanced numbers of particles; they emit excessive protons, neutrons, electrons, and energy to stabilize themselves. These emitted substances are radiation.


The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on 3rd and 11th November 2017 was reproduced for MRIC Global under the author's permission.

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