A count rate meter shows a count of $240$ per minute from a given radioactive source. One hour later the meter shows a count rate of $30$ per minute. The half-life of the source is ..........$min$
$120$
$80$
$30 $
$20$
The '$rad$' is the correct unit used to report the measurement of
A certain radioactive material can undergo three different types of decay, each with a different decay constant $\lambda_1$, $\lambda_2$ and $\lambda_3$ . Then the effective decay constant is
A radioactive substance has a half-life of $1$ year. The fraction of this material, that would remain after $5$ years will be
The half life period of a radioactive substance is 60 days. The time taken for $\frac{7}{8}$ th of its original mass to disintegrate will be $......days$
Write down the definition and formula of half life of radioactive substance.