A sample of a radioactive isotope is monitored in a laboratory. After a duration equivalent to exactly two half-lives, what percentage of the original unstable nuclei will remain undecayed?

$25\%$

$50\%$

$12.5\%$

$75\%$

Question

When a nucleus of $^{238}\text{U}$ captures a neutron to become $^{239}\text{U}$ , how are its atomic and mass numbers affected?

Which of the following statements best describes the nature of radioactive decay for a specific individual nucleus?

A radioactive source has an activity of $1600\ \text{Bq}$ . After $40\ \text{minutes}$ of observation, the activity is measured at $100\ \text{Bq}$ . What is the half-life of this isotope?

In an industrial process designed to monitor the thickness of thin aluminium foil, a beta-emitting source is typically used. Why would a gamma-emitting source be less effective than a beta source for this specific application?

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Both the atomic and mass numbers stay the same

The atomic number increases but the mass number stays the same

The mass number increases but the atomic number stays the same

Both the atomic and mass numbers increase by 1

It is triggered only when the external temperature exceeds a specific threshold.

It can be slowed down by increasing the external pressure on the sample.

It occurs at fixed, regular intervals determined by the isotope's mass.

It is completely random and impossible to predict exactly when it will occur.

$5\ \text{minutes}$

$10\ \text{minutes}$

$8\ \text{minutes}$

$20\ \text{minutes}$

Gamma radiation would be completely absorbed by even the thinnest layer of aluminium, preventing any signal from reaching the detector.

Gamma radiation is so highly penetrating that it would pass through the foil with almost no absorption, making it difficult to detect small variations in thickness.

Gamma radiation consists of large, heavy particles that would cause physical damage to the surface of the foil as it passes through.

Gamma radiation is too ionizing and would cause the aluminium foil to become radioactive during the manufacturing process.