Grade 10 physics – Radioactivity and Stability of Isotopes Quiz

Radioactivity is the process in which unstable nuclei lose energy by emitting particles (alpha, beta) or electromagnetic radiation (gamma).

Isotopes have the same proton (atomic) number but different neutron numbers, so they are the same element but with different mass numbers.

An alpha particle is a helium nucleus (2 protons, 2 neutrons) emitted by some heavy unstable nuclei during alpha decay.

Beta-minus decay converts a neutron to a proton and emits an electron (beta particle) and an antineutrino, increasing the atomic number by one.

An alpha particle (2 protons, 2 neutrons) leaves the nucleus, reducing the mass number by 4 and the atomic number by 2.

A neutron becomes a proton during beta-minus decay, so the atomic number (proton count) rises by one but the total nucleon number stays unchanged.

Gamma rays are high-energy photons emitted from excited nuclei; they have no rest mass and no electric charge and are very penetrating.

Alpha particles are stopped by paper, beta by thin metal, while gamma rays are most penetrating and need dense shielding like lead.

Half-life is the period over which half of the radioactive atoms in a sample undergo decay; it is characteristic of each isotope.

After 4 days one half remains; after another 4 days (8 days total) half of that half remains, which is 1/4 of the original.

Carbon-14 is taken up by living organisms and decays after death; measuring its amount estimates the age of formerly living material up to about 50,000 years.

Radiation exposure is reduced by minimizing time near the source, using appropriate shielding (lead, concrete) and maximizing distance.

A stable isotope has a nucleus that is not radioactive and therefore does not decay over observable timescales.

Carbon-12 has a well-balanced neutron-to-proton ratio near 1, which makes it stable; many heavy nuclei like uranium are unstable.

Mass defect is the lost mass when protons and neutrons bind; that mass converts to the binding energy that holds the nucleus together.

The becquerel measures activity as the number of radioactive decays per second; gray and sievert measure absorbed dose and biological effect, respectively.

A Geiger-Müller counter detects ionising radiation (alpha, beta, gamma) and gives counts proportional to activity; other instruments measure non-radioactive quantities.

Alpha particles are relatively large and highly charged, causing strong interactions with atoms in the paper and rapid loss of energy.

Radioactive decay is a random process for single nuclei, but large numbers follow statistical laws giving a constant probability and characteristic half-life.

Beta-plus decay converts a proton into a neutron and releases a positron and a neutrino, reducing the proton (atomic) number by one.

U-238 (atomic number 92) emits an alpha particle (2 protons, 2 neutrons), producing a nucleus with mass 234 and atomic number 90, which is Th-234.

Radioisotopes and radiation are used in medicine to kill cancer cells (radiotherapy) and for imaging; incorrect choices are unsafe or not practical uses.

Alpha particles are highly ionising because of their large charge and mass; they create many ion pairs along a short path before stopping.

In nuclear reactions and decay, the total number of nucleons (mass number) and total charge (atomic number) are conserved when accounting for emitted particles.

Activity quantifies how many nuclei decay each second (measured in becquerels); it is not a direct measure of mass, light, or temperature.