Chapter 5: Radioactive Materials

"What are the three main subatomic particles and their properties?"

"Proton: relative mass 1, charge +1. Neutron: relative mass 1, charge 0. Electron: relative mass 0 (0.0005), charge -1."

"What is the typical radius of an atom?"

"1 × 10⁻¹⁰ metres."

"How does the radius of the nucleus compare to the atom?"

"The nucleus radius is about 10,000 times smaller."

"Where is most of the mass of an atom concentrated?"

"At the nucleus."

"What are electron energy levels?"

"Electrons orbit the nucleus at different distances (energy levels) and can change arrangement by interacting with EM radiation."

"What was Dalton's atomic model (1800)?"

"Atoms are tiny indivisible spheres."

"What did JJ Thomson discover in 1897?"

"The electron, leading to the Plum Pudding Model."

"What did the Plum Pudding Model suggest?"

"Negative electrons embedded in a positive 'pudding', overall neutral."

"What was discovered in Rutherford's gold foil experiment (1911)?"

"Most particles went through = mostly empty space; some deflected = nucleus is charged; few deflected >90° = nucleus is dense with most mass."

"What did Rutherford's model show?"

"A central positive nucleus with negative electrons in a cloud."

"What problem did Rutherford's model have?"

"Electrons in a cloud should spiral into nucleus, making atom collapse."

"How did Bohr's model (1913) solve this?"

"Electrons exist in fixed orbitals (energy levels)."

"Who discovered the neutron and when?"

"James Chadwick, about 20 years after the nucleus model."

"What defines an element?"

"Number of protons."

"What is an isotope?"

"Atoms of the same element with the same protons but different neutrons."

"Give an example of isotopes."

"Carbon-12, Carbon-13, Carbon-14."

"What do A

Z, and N represent in atomic notation?","A = mass number, Z = proton number, N = charge."

"What is radioactive decay?"

"A random process where unstable nuclei emit radiation to become more stable."

"What is activity?"

"Rate of decay of unstable nuclei, measured in Becquerels (Bq)."

"What is count-rate?"

"Number of decays detected per second by a device like a Geiger-Muller tube."

"What are the main types of radiation?"

"Alpha (helium nucleus), Beta minus (electron), Gamma (EM radiation), Neutrons."

"What are the properties of alpha radiation?"

"Highly ionising, weak penetration (~5 cm of air)."

"What are the properties of beta radiation?"

"Medium ionising, medium penetration (~50 cm of air, stopped by aluminium)."

"What are the properties of gamma radiation?"

"Low ionising, highly penetrating (stopped by thick lead)."

"What changes happen in alpha decay?"

"Mass and charge of nucleus both decrease."

"What changes happen in beta decay?"

"Mass unchanged, charge increases."

"What changes happen in gamma decay?"

"No change in mass or charge."

"What is half-life?"

"Time for half of nuclei to decay, or for activity/count rate to halve."

"Can we predict when one nucleus will decay?"

"No, decay is random, but half-life is constant and predictable for large samples."

"Example: if 80 atoms reduce to 20 in 10 minutes

what is the half-life?","5 minutes (two half-lives)."

"How do you calculate net decline after X half-lives?"

"Initial number halved X times; net decline = (initial - remaining) / initial."

"What is contamination?"

"Unwanted presence of radioactive atoms on materials. Hazard: contaminated atoms decay and release radiation. Example: radioactive dust on skin."

"What is irradiation?"

"Exposure to radiation without becoming radioactive. Example: medical equipment sterilised with gamma rays."

"What is the main hazard of contamination?"

"The decaying of radioactive atoms on or in the material."

"What is the main hazard of irradiation?"

"Damage caused by radiation exposure, but no long-term contamination."

"How are radioactive tracers used?"

"Technetium (half-life 6 hrs) injected/swallowed, gamma emitter so passes through body, short-lived to reduce harm."

"How is radioactivity used in cancer treatment (radiotherapy)?"

"Gamma rays directed at cancer cells, killing them. Healthy tissue may also be damaged, causing side effects."

"How do smoke alarms use radioactivity?"

"Americium (half-life 432 years) emits alpha particles. Smoke reduces alpha detected, triggering alarm. Safe because alpha is weakly penetrating."

"What are the advantages of short half-life sources?"

"Very radioactive initially but quickly decay, posing less long-term risk."

"What are the risks of long half-life sources?"

"Remain weakly radioactive for a long time, posing a long-term hazard."

"What is nuclear fission?"

"Splitting of a large, unstable nucleus (e.g. uranium, plutonium) after absorbing a neutron, releasing energy, neutrons and gamma rays."

"What happens during a fission chain reaction?"

"Released neutrons cause further nuclei to split, releasing more neutrons and energy."

"What are the dangers of an uncontrolled chain reaction?"

"Exponential increase in energy release, like in nuclear weapons."

"What is the energy output of fission due to?"

"Kinetic energy of daughter nuclei and neutrons, plus gamma radiation."

"What is nuclear fusion?"

"Two small nuclei fuse to form a heavier nucleus, releasing a large amount of energy."

"Why does fusion release energy?"

"The mass of the fused nucleus is less than the sum of its parts; missing mass is converted to energy."

"Where does nuclear fusion naturally occur?"

"In stars like the Sun."

"Why is fusion not yet used on Earth for power?"

"No design yet achieves positive net energy output sustainably."