错误做法:

Swapping mass and atomic number position in nuclide notation, putting atomic number on top

原因:

Nuclide notation convention strictly places mass number (A) top-left and atomic number (Z) bottom-left; examiners penalise this heavily in equation questions

正确做法:

Always write nuclides as ${}_Z^{A}X$, and verify that total A and Z values balance on both sides of decay equations

错误做法:

Assuming beta-minus decay reduces atomic number by 1

原因:

Beta-minus decay occurs when a neutron turns into a proton and emits an electron, so the number of protons (atomic number) increases by 1

正确做法:

Remember the beta particle is ${}_{-1}^{0}e$, so to balance charge the product atomic number is original Z + 1

错误做法:

Using exponential decay formulas for half-life calculations

原因:

Exponential decay equations are out of scope for Edexcel IGCSE Physics, and all questions are designed to be solved with successive halving

正确做法:

Count the number of half-lives passed first, then divide the original activity by 2 once per half-life, or read values directly from the provided decay graph

错误做法:

Stating that irradiation makes an object radioactive

原因:

Irradiation only exposes an object to external radiation, with no transfer of radioactive material, so the object does not become radioactive

正确做法:

Only contamination (physical presence of radioactive material on/in an object) makes it radioactive; always check for contact with the source in question

错误做法:

Forgetting to subtract background count from measured activity

原因:

Background radiation contributes to the count measured by a GM detector, so unadjusted values give incorrect source activity leading to wrong half-life calculations

正确做法:

First measure background count with no source present, then subtract this value from all source activity measurements

错误做法:

Stating alpha radiation is the most dangerous in all scenarios

原因:

Alpha radiation cannot penetrate skin, so it is only dangerous if ingested, inhaled or enters the body through a wound; gamma is more dangerous for external exposure

正确做法:

Contextualise your answer: alpha is most dangerous inside the body, gamma is most dangerous for external exposure