Gamma Decay

Unit 2

Gamma Decay

The Weak Force is most known by Modern Physics for particle decay.

Juan Juan
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Gamma decay is a radioactive decay where an excited atomic nucleus releases excess energy by emitting a high-energy photon called a gamma ray.

We call this as an upgrade.

Unlike alpha and beta decay, gamma decay does not change the number of protons or neutrons in the nucleus.

Instead, the nucleus transitions from a higher energy state to a lower energy state, much like an electron dropping between orbitals.

Gamma decay often occurs immediately after alpha or beta decay.

The Process

After undergoing alpha or beta decay, a daughter nucleus is often left in an excited (metastable) state, denoted with a superscript m.

The nucleus then releases this excess energy almost instantly (within (10^{-12}) to (10^{-9}) seconds) as a gamma photon with an energy range of ~10 keV to ~10 MeV.

Examples

Parent Excited Isotope Gamma Decay Daughter Isotope Half-life (excited state) Typical Use
Technetium-99m 4399mTc→4399Tc+γ ^{99m}_{43}Tc \rightarrow ^{99}_{43}Tc + \gamma Technetium-99 6.01 hours Medical imaging
Cobalt-60 (excited nickel) 2860Ni∗→2860Ni+γ1+γ2 ^{60}_{28}Ni^* \rightarrow ^{60}_{28}Ni + \gamma_1 + \gamma_2 Nickel-60 10.5 minutes (preceded by beta decay of Co-60) Cancer radiotherapy
Barium-137m 56137mBa→56137Ba+γ ^{137m}_{56}Ba \rightarrow ^{137}_{56}Ba + \gamma Barium-137 2.55 minutes Industrial gauges
Cesium-137 (via Ba-137m) (Ba-137m decays as above) - 30.17 years (parent Cs-137 half-life) Food irradiation

Gamma vs. Other Decays

Feature Alpha ((\alpha)) Beta ((\beta)) Gamma ((\gamma))
Particle Helium nucleus ((^4_2\text{He})) Electron/positron ((e^-)/(e^+)) Photon ((\gamma))
Mass ~4 u ~0.0005 u 0
Charge +2 ±1 0
Penetrating power Low (stopped by paper) Medium (stopped by plastic/metal) High (stopped by thick lead/concrete)
Changes atomic number? Yes (-2) Yes (±1) No

Practical Applications

  • Medical imaging – Technetium-99m emits 140 keV gamma rays detectable by SPECT scanners for organ imaging (heart, brain, bone).
  • Cancer treatment – Cobalt-60 gamma rays (Gamma Knife) destroy tumors without surgery.
  • Sterilization – Gamma rays from Cesium-137 or Cobalt-60 sterilize medical equipment and food.
  • Industrial inspection – Gamma radiography detects flaws in welds and pipelines.
  • Astrophysics – Gamma-ray bursts (GRBs) from supernovae and neutron star mergers are the most energetic events in the universe.

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