Question

The activity of a radioactive sample
A. Can be increased by heating it
B. Is independent of the physical parameter
C. Cannot be increased by any method
D. Both (b) and (c)

Answer 1

Hint: The activity of a sample relies on the aggregate number of radioactive molecules, N, and the probability of every single atom experiencing radioactive decay. Activity has units of dps or disintegrations per second.



Complete answer:
The activity of a sample of radioactive matter is determined by the number of disintegrations that take place at its core at any time. The activity also indicates the number of radiations emitted. Thus, the numbers of alpha, beta, and gamma rays that are emitted are in proportion to the number of disintegrations. These activities are basic characteristics of the radioactive sample and of the kind of radiation emitted. They represent its ‘baseline radioactivity’. When the sample includes more than a single item, the overall activity is the sum of the individual activity values. The activity cannot be raised or lowered by any method. Radioactivity is a spontaneous phenomenon. It is independent of external physical conditions such as pressure, temperature, etc

In most cases, disintegrations cause the emission of a beta or alpha ray. Then the numbers are equal. If specific decays are accompanied by the emission of gamma rays, a gamma activity is introduced which is proportional to the emission frequency of these gamma rays.

The activity of a radio element is in inverse proportion to its lifespan. Higher the half-life of a substance, the smaller its activity. An analogy can be done with a soft-burning candle, whose lower flame burns for a longer period. Thus, in uranium 238, which has a half-life of 4.5 billion years, only a single nucleus out of 65 million will decay each century.
Therefore the correct answer is Option D.



Note: One describes the activity of a sample of radioactive material as the number of disintegrations occurring every second. The basic unit of activity is the becquerel (Bq) named after Henri Becquerel, the first man to find out about radioactive radiation. Historically, activity values were calculated in Curies (Ci) for several years: a Curie is the activity of a standard source of a single gram of radium.