Pyroelectricity

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my site; wellness [continue reading this..] The curie (symbol Ci) is a non-SI unit of radioactivity, named after Marie and Pierre Curie. It is defined as

1 Ci = 3.7 × 10¹⁰ decays per second.

While its continued use is discouraged by NIST and other bodies, the curie is widely used throughout the US government and industry.

One curie is roughly the activity of 1 gram of the radium isotope ²²⁶Ra, a substance studied by the Curies.

The SI derived unit of radioactivity is the becquerel (Bq), which equates to one decay per second. Therefore:

1 Ci = 3.7 × 10¹⁰ Bq = 37 GBq

and

1 Bq ≅ 2.703 × 10⁻¹¹ Ci

Another commonly used measure of radioactivity is the microcurie:

1 μCi = 3.7 × 10⁴ disintegrations per second = 2.22 × 10⁶ disintegrations per minute

A radiotherapy machine may have roughly 1000 Ci of a radioisotope such as caesium-137 or cobalt-60. This quantity of radioactivity can produce serious health effects with only a few minutes of close-range, unshielded exposure.

Ingesting even a millicurie is usually fatal (unless it is a very short-lived isotope). For example, the LD-50 for ingested polonium-210 is 240 μCi.

The typical human body contains roughly 0.1 μCi (14 mg) of naturally occurring potassium-40. A human body containing 16 kg of carbon (see Composition of the human body) would also have about 24 nanograms or 0.1 μCi of carbon-14. Together, these would have an activity of approximately 2×0.1 μCi or 7400 decays (mostly from beta decay and rarely from gamma decay) per second inside the person's body.

Curies as a measure of quantity

Curies are occasionally used to express a quantity of radioactive material rather than a decay rate, such as when one refers to 1 Ci of caesium-137. This may be interpreted as the number of atoms that would produce 1 Ci of radiation. The rules of radioactive decay may be used convert this to an actual number of atoms. They state that 1 Ci of radioactive atoms would follow the expression:

N (atoms) × λ (s⁻¹) = 1 Ci = 3.7 × 10¹⁰ (Bq)

and so,

N = 3.7 × 10¹⁰ / λ,

where λ is the decay constant in (s⁻¹).

We can also express a Curie in moles:

$\begin{array}{rl}\text{1 Ci}& =\frac{3.7\times 10^{10}}{(\ln 2)N_{\mathrm{A}}}\text{ moles}\times t_{1/2}\text{ in seconds}\\ & \approx 8.8639\times 10^{-14}\text{ moles}\times t_{1/2}\text{ in seconds}\\ & \approx 5.3183\times 10^{-12}\text{ moles}\times t_{1/2}\text{ in minutes}\\ & \approx 3.1910\times 10^{-10}\text{ moles}\times t_{1/2}\text{ in hours}\\ & \approx 7.6584\times 10^{-9}\text{ moles}\times t_{1/2}\text{ in days}\\ & \approx 2.7972\times 10^{-6}\text{ moles}\times t_{1/2}\text{ in years}\end{array}$

where N_A is Avogadro's number and t_1/2 is the half life. The number of moles may be converted to grams by multiplying by the atomic mass.

Here are some examples:

Isotope	Half life	Mass of 1 Curie
238U	Template:Val years	2.977 tonnes
40K	Template:Val years	140 kg
129I	Template:Val years	5.66 kg
99Tc	Template:Val years	58 g
239Pu	Template:Val years	16 g
14C	5730 years	0.22 g
226Ra	1601 years	1.01 g
137Cs	30.17 years	12 mg
90Sr	28.8 years	7.2 mg
60Co	1925 days	883 μg
210Po	138 days	223 μg
131I	8.02 days	8 μg
123I	13 hours	0.5 μg

The number of Curies present in a sample decreases with time because of decay.

See also

• Geiger counter
• Ionizing radiation
• Radiation exposure
• Radiation poisoning
• United Nations Scientific Committee on the Effects of Atomic Radiation

References

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