What is Caesium-137


Caesium-137 is a radioactive isotope of caesium, which has a mass number (A) equal to 137, because it corresponds to the sum of the number of protons (55) and neutrons (82).

Caesium-137 is a radioactive isotope (radioisotope) of the chemical element Caesium (Cs), whose atomic number (Z), that is, the number of protons in the atomic nucleus, is equal to 55, and the number of neutrons is 82. Thus, the name “caesium-137” comes from its mass number (A), which corresponds to the sum of the atomic number and the neutrons (55 + 82 = 137). Thus, its representation is given by 55137Cs.

Cs-137 was discovered by means of a technique called spectroscopy by scientists Robert W. E. Bunsen (1811-1899) and Gustav R. Kirchhoff (1824-1887), who were professors of chemistry and physics, at the German university of Heildelberg.

This radioisotope emits radiation from its nucleus. As shown below, it disintegrates, releasing, for example, beta radiation (-10β), with the consequent formation of another, even more harmful radioactive element, barium-137:

55137Cs → -10β + 56137Ba


Caesium-137 is very dangerous to humans because:

  • It emits ionizing particles and electromagnetic radiation that can penetrate various materials, including human skin and tissue
  • Interact with molecules in the body, and have devastating effects

This interaction occurs because Cs-137, like all radioactive isotopes, emits radiation with sufficient energy to remove electrons from atoms and produce cations (positively charged particles). The cations are highly reactive and can in turn cause changes in the reactions that occur in the cells of living tissues. The reaction may alter DNA and possibly causing the appearance of cancer cells.

  • Beta particles released from caesium-137 penetrate up to 2 cm when they hit the human body and cause severe damage.
  • Gamma radiation (00γ) is also released. Gamma radiation has greater penetrating power and can completely penetrate the human body and cause irreparable damage.
  • Barium-137, which is formed from caesium-137, also releases gamma radiation.

Caesium-137 is an element of the alkali metal family (family 1 on the Periodic Table). Caesium is similar to potassium(K) (which also belongs to this family) and is able to replace it in living tissue.

Goiânia Caesium-137 accident

An example of how harmful this radioisotope can be was the incident that occurred in Goiânia – Goiás in September 1987. Two garbage collectors found a capsule containing caesium-137 (it actually contained about 19 g of caesium chloride (CsCl) in the rubble of a disused hospital. The scavengers took the capsule and sold it to a scrap yard.

When the capsule broke, radioactive material was released. The accident attracted the attention of many people because of the luminescence of caesium, a powder that glows bluish in the dark. In fact, the name of this element comes from the Latin word “caesius,” meaning bluish-gray sky. The result was:

  • The death of four people
  • More than 200 people got exposed to Cs-137
  • The creation of more than 7 tons of contaminated waste

Caesium-137 contamination can be prevented by isolating it with thick concrete walls.

However, caesium-137 has several useful uses, for example:

  • In industry
  • Food preservation
  • Medicine

The lead in the capsule prevents this radiation from penetrating and contaminating surrounding materials. Today, cobalt-60 is used instead of caesium-137.

Cs-137 is also absorbed by water and soil and has a half-life of about 30 years.

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