Radioactivity 🤩

How it all started

In 1896, A. H. Becquerel noticed that uranium salts could fog a photographic plate even when the salts were wrapped in black paper and shielded by silver. Something inside the uranium was always sending out invisible rays that zipped straight through the wrappers — the first peek at natural radioactivity. :contentReference[oaicite:0]{index=0}

What’s really going on?

Radioactivity is a nuclear effect. An unstable nucleus quietly reshuffles itself and spits out particles or energy to become more stable. This spontaneous change is called radioactive decay. 😊 :contentReference[oaicite:1]{index=1}

Three ways a nucleus can “let off steam”

  • Alpha (α) decay: the nucleus ejects a tiny helium nucleus, \(^{4}_{2}\text{He}\). Because this chunk is heavy, a sheet of paper can stop it. 📄 :contentReference[oaicite:2]{index=2}
  • Beta (β) decay: the nucleus shoots out an electron or its mirror-image twin, a positron. These lighter particles zoom faster and need a few millimeters of metal to block them. ⚡ :contentReference[oaicite:3]{index=3}
  • Gamma (γ) decay: after an internal shuffle, the nucleus relaxes by beaming out a high-energy photon (hundreds of keV or more). Thick lead is the go-to shield for these penetrating rays. 💥 :contentReference[oaicite:4]{index=4}

The energy story 🔋

The binding-energy-per-nucleon curve, \(E_{bn}\), stays almost flat at about 8 MeV for mass numbers \(30 \le A \le 170\). Nuclei that are much lighter or much heavier sit higher on the curve (meaning lower binding per nucleon). When such nuclei move toward the flat “valley” — either by fission (splitting a heavy nucleus) or fusion (fusing light ones) — energy bursts out. 🌟 :contentReference[oaicite:5]{index=5}

  • Fission of 1 kg uranium releases about \(10^{14}\,\text{J}\).
  • Burning 1 kg coal gives only \(10^{7}\,\text{J}\).
  • So, gram for gram, nuclear fuel is roughly a million times more energetic than chemical fuel! 🚀 :contentReference[oaicite:6]{index=6}

Quick symbols to remember 📑

  • \(^{4}_{2}\text{He}\) – the alpha particle emitted in α-decay.
  • \(E_{bn}\) – binding energy per nucleon.

NEET Spotlight 🌟

  1. Discovery of spontaneous radiation by Becquerel.
  2. Key features of α, β, and γ decays.
  3. Shape of the \(E_{bn}\) curve and why mid-mass nuclei are most stable.
  4. Huge energy gap between nuclear reactions (MeV scale) and chemical reactions (eV scale), with fission/fusion as prime examples.