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Rutherford to Becquerel Converter

Enter an activity in rutherfords to convert to becquerels.

How it is calculated

The conversion has two steps. A rutherford is defined as one million decays per second, so Bq = Rd × 1,000,000. The becquerel value is shown as a whole number. The curie value comes from the becquerel result using the definition 1 Ci = 3.7 × 1010 Bq: Ci = Bq ÷ 3.7×1010, printed to 9 decimal places. Because of that fixed precision, a very small activity (a fraction of a rutherford) shows only a few significant digits in curies, or even rounds to 0.000000000, while the becquerel figure stays exact. Negative input is not rejected and passes straight through, which has no physical meaning for an activity. The tool does not apply decay or half-life corrections; it converts units only.

Worked example

A source is listed in an old paper at 5 Rd. In becquerels, 5 × 1,000,000 = 5,000,000 Bq. For the curie value, divide by 3.7 × 1010: 5,000,000 ÷ 37,000,000,000 = 0.000135135 Ci. So a 5 Rd source equals 5,000,000 Bq, or about 135 microcuries. As a check, 37,000 Rd corresponds to exactly 1 Ci, since 37,000 × 1,000,000 = 3.7 × 1010 Bq.

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Common mistakes

  • Confusing the rutherford with the roentgen. The roentgen measured exposure to radiation, not the number of decays per second, so the two cannot be converted into each other.
  • Treating 1 Rd as 1 Bq. It is one million becquerels, and the missing factor makes the result a million times too small.
  • Reading the curie figure for tiny sources. It is cut off at 9 decimals, so use the becquerel value for small activities.
  • Mixing it up with the millicurie or microcurie. The displayed curie value is in full curies, so 0.000135135 Ci is 135.135 µCi.
  • Expecting the result to show the activity today. The conversion is purely of units; the activity of a source falls over time according to its half-life.

About this calculator

The rutherford (Rd) was a unit of radioactivity introduced in 1946 and named after physicist Ernest Rutherford, defined as 10⁶ disintegrations per second, i.e. 1 Rd = 10⁶ Bq. It was proposed as a more convenient, round-number alternative to the curie for laboratory-scale sources, but never gained wide traction and was largely abandoned within a couple of decades once the SI adopted the becquerel (1 Bq = 1 decay/second) as the standard unit of activity in 1975.

Anyone reading older nuclear-physics or radiochemistry literature from the mid-20th century encounters the rutherford and needs to convert it to becquerels or curies (1 Rd = 1/37,000 Ci) to compare against modern measurements, which is essentially the only context this converter is used in today.

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