Radioactivity is the spontaneous disintegration of heavy element without being affected by external means. The intensity of emitted radiation is measured in different available measuring units. The measuring units may be Becquerel (Bq), Curie (Ci) or Rutherford (Rd). **Standard** (**S.I**) unit of radioactivity is Becquerel.

## Units of Radioactivity

**a)** **Becquerel**

It is the S.I unit of radioactivity. It is represented by symbol ‘Bq’. 1 becquerel is defined as one disintegration per second.

1 Bq = 1 disintegration per second(dis/sec)

**b) Curie**

It is the CGS unit of radioactivity. It is represented by symbol ‘Ci’. 1 Curie is defined as 3.7 x 10^{10} disintegration per second. It is also equal to disintegration of 1gm of pure radium.

1 Ci = 3.7 x 10^{10} dis/sec

Also,

In terms of milli and micro, it can be represented as:

1 milli curie (mCi) = 3.7 x 10^{7} dis/sec

1 micro curie (µCi) = 3.7 x 10^{4 }dis/sec

**c) Rutherford**

1 Rutherford is defined as 10^{6} disintegration per second. It is represented by symbol ‘Rd’.

1 Rd = 10^{6} dis/sec

Also,

1 milli Rutherford (mRd) = 10^{3} dis/sec

1 micro Rutherford (µRd) = 1 dis/sec

**Read also**: Half life and mean life

## Relation between units of Radioactivity

Some mathematical relation can be drawn among different units of radioactivity.

1 Curie is equal to 3.7 x 10^{10} Bq

1 Rutherford is equal to 10^{6} Bq

1 Curie is equal to 3.7 x 10^{4 }Rutherford (Rd)

## FAQs

1) What is the S.I unit of radioactivity?

**Ans:** The S.I unit of radioactivity is Becquerel. It is represented by symbol ‘Bq’. One becquerel is equal to 1 disintegration per second.

2) 1 curie is equal to how many disintegrations per second?

**Ans:** 1 curie is equal to 3.7 x 10^{10} disintegration per second. That is, 37 billion disintegration per second.

3) 1 curie is equal to how many becquerel?

**Ans:** 1 curie is equal to 3.7 x 10^{10} disintegration per second. 1 becquerel I equal to 1 disintegration per second. So, 1 curie is equal to 3.7 x 10^{10} becquerel.

4) What is the CGS unit of radioactivity?

**Ans:** Curie is the CGS unit of radioactivity. In 1975, it was replaced by becquerel as S.I unit.

## References

https://radiopaedia.org/articles/curie-unit

https://www.nrc.gov/reading-rm/basic-ref/glossary/curie-ci.html

https://www.nrc.gov/reading-rm/basic-ref/glossary/becquerel-bq.html