Free Nuclear Physics MCQs with Answers

• A. number of neutrons but different numbers of protons
• B. number of protons but different numbers of neutrons
• C. mass number but different atomic numbers
• D. number of protons and neutrons

Explanation: Atomic number fixes the element, so isotopes share chemical behaviour but differ in mass, as carbon 12 and carbon 14 do.

• A. 92
• B. 143
• C. 235
• D. 327

Explanation: Neutron number is mass number minus atomic number, so 235 minus 92 gives 143.

• A. the electrostatic force
• B. the gravitational force
• C. the strong nuclear force, which is short ranged and attractive
• D. the magnetic force

Explanation: The strong force acts over only a few femtometres but is far stronger than the electrostatic repulsion between protons at that range…

• A. a helium nucleus, two protons and two neutrons
• B. a fast electron
• C. a photon
• D. a proton

Explanation: Alpha emission therefore reduces the mass number by 4 and the atomic number by 2, moving the element two places back in the periodic…

• A. decreases by 1
• B. increases by 1, while the mass number is unchanged
• C. decreases by 2
• D. is unchanged

Explanation: A neutron converts into a proton, an electron and an antineutrino, so the nucleus gains a proton while the total nucleon count stays the…

• A. Alpha
• B. Beta
• C. Gamma
• D. All are equal

Explanation: Gamma rays are uncharged electromagnetic radiation and need several centimetres of lead or a metre of concrete to attenuate them…

• A. a change in mass number only
• B. a change in atomic number only
• C. no change in either mass number or atomic number
• D. a change in both

Explanation: A gamma ray carries away energy from an excited nucleus without removing any nucleons, so the nuclide is the same afterwards, simply in a…

• A. the whole sample decays
• B. half the undecayed nuclei present decay
• C. the activity becomes zero
• D. the mass of the sample halves

Explanation: Decay is a random process with a constant probability per nucleus per unit time, so a fixed fraction rather than a fixed number decays in…

• A. one half
• B. one quarter
• C. one eighth
• D. one sixteenth

Explanation: Twenty four days is three half lives, so the sample is halved three times, leaving one half multiplied by one half multiplied by one half…

• A. becquerel
• B. gray
• C. sievert
• D. coulomb

Explanation: One becquerel is one disintegration per second, so it measures how fast the source is decaying.

• A. carbon 14 is stable
• B. living things take in carbon 14 while alive, and it then decays with a known half life after death
• C. all carbon is radioactive
• D. carbon 14 is produced in the body

Explanation: While an organism lives it exchanges carbon with its surroundings and holds the atmospheric ratio of carbon 14 to carbon 12, but after…

• A. two light nuclei join to form a heavier one
• B. a heavy nucleus splits into two lighter nuclei, releasing energy and neutrons
• C. a nucleus emits an alpha particle
• D. an electron is captured by a nucleus

Explanation: Splitting a uranium 235 nucleus releases about 200 MeV together with two or three neutrons, and those neutrons can trigger further…

• A. absorb excess neutrons and shut the reactor down
• B. slow fast neutrons so that they are more likely to cause further fission
• C. cool the reactor core
• D. shield the operators from radiation

Explanation: Graphite or heavy water slows the neutrons through repeated collisions, because slow neutrons are far more readily captured by uranium 235…

• A. the chemical bonds between atoms
• B. the small loss of mass, converted according to E equals mc squared
• C. the kinetic energy of the electrons
• D. friction inside the nucleus

Explanation: The products of fission or fusion have slightly less total mass than the reactants, and that mass defect appears as energy, which is why…

• A. hydrogen
• B. iron
• C. uranium
• D. helium

Explanation: The curve of binding energy per nucleon rises steeply from hydrogen, peaks around iron and nickel at about 8.8 MeV, then falls slowly…

• A. alpha particles for imaging
• B. gamma rays for treating cancer
• C. neutrons for sterilising instruments
• D. X rays for dental work

Explanation: Its penetrating gamma radiation can be focused on a deep tumour from outside the body, and because dividing cells are more sensitive, the…

• A. a long half life and emit alpha particles
• B. a short half life and emit gamma rays that escape the body for detection
• C. a very long half life and emit beta particles
• D. no radiation at all

Explanation: Gamma radiation escapes the body so an external camera can detect it, and a short half life means the activity falls quickly once the scan…

• A. heats the tissue significantly
• B. ionises molecules, including DNA, producing reactive fragments
• C. makes the tissue radioactive
• D. changes the pH of the cells

Explanation: Ionisation breaks chemical bonds and generates free radicals that go on to damage DNA, which may kill the cell or, if it is repaired…

• A. gray
• B. sievert
• C. becquerel
• D. joule

Explanation: The sievert multiplies the absorbed dose in grays by a quality factor, which is 1 for beta and gamma but about 20 for alpha particles…

• A. uranium into lead
• B. hydrogen into helium
• C. helium into hydrogen
• D. carbon into oxygen

Explanation: Four hydrogen nuclei combine through the proton proton chain to give one helium nucleus, and the small mass difference appears as energy.