Atomic structure

An atom has radius $1.0\times10^{-10}\,\mathrm{m}$ and its nucleus has radius $8.0\times10^{-15}\,\mathrm{m}$. Calculate how many times larger the atom's radius is.

Describe the positions and charges of the three subatomic particles in an atom, and state where nearly all the atom's mass is found.

An atom absorbs electromagnetic radiation and later emits electromagnetic radiation. Explain what can happen to one of its electrons in the two changes.

A neutral atom contains $17$ protons and $20$ neutrons. State its atomic number, mass number and number of electrons.

For the ion ${}^{27}_{13}\mathrm{Al}^{3+}$, determine the numbers of protons, neutrons and electrons.

Two isotopes of element $Q$ have mass numbers $63$ and $65$. An ion of the first isotope has charge $2+$ and contains $27$ electrons. Determine the atomic number of $Q$, the neutron number of each isotope, and explain why both are the same element.

Put these developments in chronological order: the nuclear model, the plum pudding model, evidence for the neutron, and electrons at specific distances from the nucleus.

In an alpha-scattering investigation, nearly all particles cross a thin metal sheet without changing direction, while a very small fraction turn through large angles. Explain two conclusions that caused the plum pudding model to be replaced.

A student says, 'Once the nucleus was proposed, the atomic model was complete.' Use later changes to the model to evaluate this statement.

Name the radiation described in each case: (i) two protons and two neutrons, (ii) electromagnetic radiation from a nucleus, (iii) a fast electron emitted when a neutron changes.

Radiation $P$ is stopped by card, $Q$ crosses card but is stopped by a thin aluminium sheet, and $R$ crosses both but is reduced by thick lead. Identify $P$, $Q$ and $R$, then state which has the greatest ionising power.

A sealed source must send radiation through several centimetres of tissue to a target while limiting ionisation of healthy tissue along the path. Compare alpha, beta and gamma, and choose the most suitable radiation.

Complete ${}^{218}_{84}X\rightarrow{}^{214}_{82}Y+\,?$ by giving the emitted particle in full nuclear notation.

Complete the beta-minus equation ${}^{131}_{53}X\rightarrow{}^{A}_{Z}Y+{}^{0}_{-1}\beta$ by determining $A$ and $Z$.

A nucleus ${}^{240}_{96}M$ emits one alpha particle and then two beta-minus particles. Determine the mass number and atomic number of the final nucleus, showing the change at each stage.

The activity of a sample falls from $640\,\mathrm{Bq}$ to $160\,\mathrm{Bq}$ in $10$ hours. Determine its half-life.

A detector records $420$ counts per minute beside a source at time zero and $70$ counts per minute $18$ minutes later. Background count rate is $20$ counts per minute. Calculate the source's half-life.

A detector beside a source reads $830$ counts per minute initially and $130$ counts per minute after $12$ minutes. Background is $30$ counts per minute. Determine the half-life, then explain why repeated one-minute readings taken at the same time would not all be identical.

A wrapped instrument is placed near a sealed gamma source and then removed. No radioactive material touches it. State whether this is contamination or irradiation, and whether the instrument becomes radioactive.

Compare the hazard from an alpha-emitting speck held outside the body with the hazard if the same speck is inhaled. Give a suitable precaution.

A small study reports that workers exposed near a sealed radiation source have a higher illness rate. Explain why publishing the method and results for peer review is important before concluding that irradiation caused the illnesses.

Classify each source of background radiation as natural or man-made: cosmic rays, radioactive rock, and fallout from a nuclear weapons test.

A detector averages $18$ counts per minute at sea level on sedimentary ground and $31$ counts per minute at a high-altitude site on granite. Suggest two reasons for the difference and explain why neither reading should be treated as zero-source error.

A cave guide receives $0.006\,\mathrm{mSv}$ per working week from surrounding rock and works $48$ weeks. An airline worker receives $0.009\,\mathrm{mSv}$ per working week from additional cosmic radiation for $48$ weeks. Calculate each annual occupational dose, compare them, and express the larger in sieverts.

Two contaminants have half-lives of $6$ hours and $24$ years. Which contaminant can remain a disposal hazard for longer? Explain your choice.

Samples $A$ and $B$ initially have the same activity and emit the same type of radiation. $A$ has half-life $3$ hours; $B$ has half-life $40$ years. Compare how their hazards change after the samples are securely stored.

Equal numbers of nuclei of isotopes $C$ and $D$ are spilled. $C$ has half-life $2.0\times10^2\,\mathrm{s}$ and $D$ has half-life $6.0\times10^7\,\mathrm{s}$. Compare the likely initial and long-term hazards, stating why half-life alone cannot determine the total risk.

Give two reasons why a gamma-emitting isotope can be suitable as a tracer for exploring an internal organ.

A doctor proposes directing nuclear radiation at a tumour to destroy unwanted tissue. A smaller dose will also reach nearby healthy tissue, and without treatment the tumour is likely to grow. Evaluate this use of radiation.

A hospital needs an internal tracer that will be measured by a detector outside the body during a four-hour investigation. Candidate $J$ emits alpha and has half-life $12$ years; $K$ emits gamma and has half-life $6$ hours; $L$ emits gamma and has half-life $30$ years. Select the best candidate and justify why the other two are less suitable.

State what usually starts a fission event and name two products other than the two smaller nuclei.

In a simplified chain reaction, every fission releases three neutrons and every released neutron causes one new fission. Starting with one fission in generation 1, calculate the numbers of fissions in generations 2, 3 and 4.

Sketch and label a chain-reaction diagram beginning with a neutron absorbed by one large unstable nucleus. Show that fission releasing two neutrons can cause the next generation, then explain how a controlled reactor prevents the number of fissions increasing each generation.

Complete the definition: nuclear fusion is the joining of two ______ nuclei to make a ______ nucleus.

Compare nuclear fusion with nuclear fission in terms of the nuclei before and after each process, and state one energy feature shared by them.

An experiment shows two light nuclei combining into one heavier nucleus while radiation leaves the reaction. The measured mass of the heavier nucleus is slightly smaller than the total mass of the two starting nuclei. Explain why the observations support fusion and account for the mass difference.