How long can a 54-Ib child be exposed to 1.0 mCi of radiation from ²²²Rn before accumulating 1.0 mrad if the energy of each disintegration is 5.59MeV ?

The emission and propagation of energy in the form of waves, rays, or particles is known as radiation.

The becquerel (Bq) is the SI unit of radioactivity, defined as one disintegration per second $(d/s):1Bq=1d/s$. The curie (Ci) is a significantly bigger and more common unit of radioactivity, initially defined as the number of disintegrations per second in 1g of radium-226, but now a fixed quantity:

$1Ci=3.7x{10}^{10}\frac{di\sin t}{\sec }$

The millicurie (mCi) and microcurie (mCi) are regularly encountered since the curie is so enormous. A sample's radioactivity is frequently expressed as a particular activity, or the decay rate per gramme.

Binding energies are often measured in millions of electron volts, or mega-electron volts (MeV):

$1MeV={10}^{6}eV=1.602x{10}^{-13}J$

$Time=7.4079\sec$

$Mass=54lb\left(\frac{1kg}{2.2lb}\right)=24.5455kg$

$Energy=1mCi\left(\frac{{10}^{-3}}{1mCi}\right)\left(\frac{3.70x{10}^{10}\frac{di\sin t.}{\sec }}{1Ci}\right)\left(\frac{5.59MeV}{1di\sin t.}\right)\left(\frac{1.602x{10}^{-13}J}{1MeV}\right)$

$Energy=3.3134x{10}^{-5}\frac{J}{s}$

$Time=1mrad\left(\frac{{10}^{-3}}{1mrad}\right)\left(\frac{0.01\frac{J}{kg}}{1rad}\right)\left(\frac{24.5455kg}{3.3134x{10}^{-5}\frac{J}{\sec }}\right)$

$Time=7.4079\sec$