Dr. Tsubokura's Radiation Lecture Vol.77

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

153. There are dozens of types of cesium

All materials are composed of small particles called protons, neutrons, and electrons. The number after the name of radioactive substances, as in cesium 134 and 137, indicates the sum of protons and neutrons. The nature of a substance varies depending on the balance of these numbers of particles. Radioactive substances have unbalanced numbers of particles, and they emit excessive protons, neutrons, electrons, and energy to stabilize themselves. These emitted substances are called radiation.

Furthermore, names of radioactive substances, such as cesium and uranium, are determined by the number of protons contained in their cores. That is to say, the substance named cesium always contains 55 protons.

There are several types of cesium containing various numbers of neutrons. For example, when a cesium core contains 60 or 90 neutrons, those substances are called cesium 115 and 145, respectively. Similarly to cesium 134 and 137, which are of critical concern to our daily lives, cesium 115 and 145 also emit radiation, as they contain unbalanced numbers of particles.

On the other hand, when a cesium particle contains 78 neutrons, the balance between the number of neutrons and protons becomes stable; therefore, it will not emit radiation. This balanced cesium is called cesium 133, which is the sum of 78 neutrons and 55 protons. There are dozens of types of cesium with various numbers of neutrons.

154. “Tri-” in tritium means three

All materials are composed of small particles called protons, neutrons, and electrons. The number after the name of radioactive substances, as in cesium 134 and 137, indicates the sum of protons and neutrons in their cores.

Generally, there is a number after the name of most radioactive substances, such as 134 or 137, but there are some radioactive substances that do not have such numbers. For example, tritium, which has often appeared in articles related to liquid radioactive waste released from the nuclear power plant, does not have a number after its name.

Tritium is composed of 1 proton and 2 neutrons (total of 3). Its chemical nature is the same as the hydrogen, which also has only one proton. The English prefix “tri-” in tritium means three; therefore, it is also called hydrogen 3. Similar to other types of hydrogen, tritium is generally found in liquid form in nature.

The level of radiation given off by tritium is very low. Besides, since tritium has similar characteristics to water, it does not accumulate in a specific part of the body even when ingested. This is one of the reasons the effect of tritium on our bodies is much smaller compared to other radioactive substances.

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The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on 17th and 24th November 2017 was reproduced for MRIC Global under the author's permission.