Radiation Protection and Environment

: 2011  |  Volume : 34  |  Issue : 3  |  Page : 215-

The SI unit of radioactivity (Bq) is too small for public consumption!

 Ex. RSSD, India

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How to cite this article:
Pushparaja. The SI unit of radioactivity (Bq) is too small for public consumption!.Radiat Prot Environ 2011;34:215-215

How to cite this URL:
Pushparaja. The SI unit of radioactivity (Bq) is too small for public consumption!. Radiat Prot Environ [serial online] 2011 [cited 2021 Jan 15 ];34:215-215
Available from: https://www.rpe.org.in/text.asp?2011/34/3/215/101729

Full Text

Henri Becquerel discovered radioactivity in 1896, and 2 years later, in the year 1898, the Curies (Pierre Curie, Marie Curie) announced the existence of the element - Radium. In 1903, the Royal Swedish Academy of Sciences awarded all the three the Nobel Prize in Physics for their work on naturally occurring radioactive elements.

The classical unit to express amount of radioactivity is Curie (Ci). A 1 Ci radioactive source is the activity of 1 g of 226 Ra. The SI unit for radioactivity is Becquerel (Bq) and 1 Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays or disintegrates per second (1 dps). The factor to convert Curie into Bq is: 1 Curie = 3.7 Χ 10 10 Bq = 37 billion Bq. Bq is a very small unit indeed.

1 milli Curie (mCi) = 3.7 Χ 10 7 Bq1 micro Curie (΅Ci) = 3.7 Χ 10 4 Bq, and 1 nano Curie (nCi) = 37 Bq1 Bq = 2.703 Χ 10−11 Ci

Over the years, due to extensive research and development work, the radioactivity measurement systems are so much advanced that we are able to detect Bq level of activity in a given material.

Radioactive content of any material is given in terms of Specific Activity in the units of Becquerel per gram (Bq/g) of the material. To know the mass equivalent of 1 Bq, we need to know the term, Specific Activity. The specific activity of any radionuclide depends on the mass number, and its half-life, i.e., the time taken by the radioactive material to reduce its radioactivity by one-half of the initial value. The half-lives of different radionuclides vary from fraction of a second to billions of years.

Given below are the relevant data which gives the mass equivalent of 1 Bq of the given radionuclide.

As could be seen from the below table, the Bq equivalent of mass is such a small fraction of a gram that if it were not radioactive element, no existing instrument would have even detected the presence of the element. In fact, many of the naturally occurring, low specific activity radionuclides such as Potassium-40 ( 40 K) and Uranium-238 ( 238 U) are present in our day-to-day diet and they have become part and parcel of our body. These radioactive elements can also be detected by the sensitive detection systems available.


High specific activity radionuclides, with very short half-lives are used in nuclear medicine procedures for diagnosis of diseases. Since the actual physical quantity of the element is very small, the element is not expected to cause any biologically toxic reactions.

Members of the public always get frightened by large numbers. The risk perception is: smaller the number, lower is the risk level and it is less frightening. It is suggested here that for public awareness/communication purposes, one may use micro (10 -6) or milli (10 -3 ) Ci as the units and not kilo (10 3 ), Mega (10 6 ), or Giga (10 9 ) Bq. Being a much smaller number, reporting in the unit of micro/milli Curie, and when expressed in equivalent mass in terms of nano (10 -9 ) gram, will create less panic among the public.