# Physics - Recall for Chapter 25: Radioactivity > Source: https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-25-radioactivity/ · Updated: 2022-04-20 · Tags: physics, a-level, school, recall-questions ## Flashcards ##### What is meant by ionising radiation?? Radiation with sufficient energy to ionise atoms. ##### What does it mean to ionise an atom?? Remove an electron. ##### What is an alpha particle?? 2 protons and 2 neutrons. ##### What is the charge of an alpha particle?? $$ +2e $$ ##### How ionising is alpha radiation?? Strongly ionising. ##### What is the range of alpha radiation in air?? Around 5cm. ##### What is alpha radiation typically absorbed by?? Paper. ##### What is a beta-minus particle?? A fast moving electron. ##### What is a beta-plus particle?? A fast moving positron. ##### What is the charge of a beta-minus particle?? $$ -e $$ ##### How ionising is beta-minus radiation?? Moderately ionising. ##### What is the range of beta-minus radiation in air?? Around 1m. ##### What is beta-minus radiation typically absorbed by?? 1-3mm of aluminium. ##### What is gamma radiation?? High frequency electromagnetic waves emitted from a nucleus. ##### How heavy is a gamma particle?? It has no mass. ##### What is the charge of a gamma ray?? It has no charge. ##### What is the typical speed of gamma radiation?? The speed of light. ##### How ionising is gamma radiation?? Weakly ionising. ##### What is gamma radiation typically absorbed by?? A few centimeters of lead. ##### What is the order of types of ionising radiation from most mass to least mass?? * Alpha * Beta-minus and beta-plus * Gamma ##### What type of nuclear radiation is not deflected by electric and magnetic fields?? Gamma. ##### What type of nuclear radiation is deflected the most by electric and magnetic fields?? Beta radiation. ##### Why is beta radiation the most deflected by electric and magnetic fields?? It has a very small mass. ##### When measuring the count rate of a radioactive source, what must be considered?? The background count rate. ##### How do you find the corrected count rate for a radioactive source from the measured count rate?? $$ \text{measured} - \text{background} $$ ##### Why is ionising radiation dangerous?? It can damage living cells and DNA. ##### What procedure is routinely used to minimise the dose when handling radioactive sources in the lab?? Use tongs and hold it far away from your body. ##### What are the three key steps for reducing radiation dose?? * Maximise distance * Minimise exposure * Use shielding ##### What do we call the nucleus before it undergoes radioactive decay?? Parent nucleus. ##### What do we call the nucleus after it undergoes radioactive decay?? Daughter nucleus. ##### Which type of nuclei are most likely to emit alpha particles?? Large, unstable nuclei. ##### What is normally true about the proton number of a nucleus likely to emit an alpha particle?? It has a proton number greater than 82. ##### What happens to the nucleon number and proton number when a nucleus emits an alpha particle?? * Nucleon number: -4 * Proton number: -2 ##### What type of nuclei are most likely to emit a beta minus particle?? Unstable nuclei with too many neutrons. ##### What type of nuclei are most likely to emit a beta plus particle?? Unstable nuclei with too many protons. ##### What happens to the nucleon number and proton number when a nucleus emits a beta-minus particle?? * Nucleon number: Same * Proton number: +1 ##### What happens to the nucleon number and proton number when a nucleus emits a beta-plus particle?? * Nucleon number: Same * Proton number: -1 ##### What else is emitted during either beta-minus or beta-plus decay?? An (anti)electron neutrino. ##### What type of nuclei are most likely to emit gamma radiation?? Nuclei with too much energy. ##### What happens to the nucleon number and proton number when a nucleus emits a gamma photon?? * Nucleon number: Same * Proton number: Same ##### What are two properties of natural radioactivity?? * Random * Spontaneous ##### Why is radioactive decay said to be random?? It is not possible to predict which nucleus will decay. ##### Why is radioactive decay said to be spontaneous?? It is not affected by any external factors. ##### What is the activity of a radioactive substance?? The rate at which nuclei decay. ##### What units are used to measure radioactive activity?? Becquerels. ##### What is 1 becquerel equivalent to?? One decay per second. ##### What is half life?? The average time taken for the activity of a sample to halve. ##### Why does the activity of a radioactive substance decrease with time?? Activity is directly proportional to the number of undecayed nuclei. ##### What pattern does the activity and the number of undecayed nuclei in a substance follow over time?? Exponential decay. ##### What is the decay constant of a radioactive substance?? The probability of a nucleus decaying per unit time. ##### What are some typical units of the decay constant $\lambda$?? $$ s^{-1}, h^{-1}, y^{-1} $$ ##### What is the relationship between the decay constant $\lambda$ and half life $t_{1/2}$?? $$ \lambda t_{1/2} = \ln(2) $$ ##### How can radioactive decay be modelled with iteration?? Repeatedly calculate the number of nuclei that decay in a very short amount of time and subtract this. ##### What happens to the ratio of carbon-14 to carbon-12 in an organism after it dies?? The carbon-14 decreases. ##### Why does the carbon-14 in an organism decrease after it dies?? Because the carbon-14 in the atmosphere can't get into it. ##### What is the basic principle of carbon dating?? Comparing the ratio of carbon-14 to carbon-12 in an organic sample to the ratio in a similar living organism. ##### Since rocks are too old to be dated with carbon-14, what element is used instead?? Rubidium-87. --- Olly Britton — https://ollybritton.com. Machine-readable index: https://ollybritton.com/llms.txt