Which is not emitted by radioactive substance? — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

Step 1 - Standard Modes of Radioactive Decay Naturally occurring radioactive substances emit the following particles/radiations: - $\alpha$-particles: $\ce{^4_2He^{2+}}$ — very common in heavy nuclei ($Z > 83$) - $\beta^-$-particles: high-speed electrons ($\ce{^0_{-1}e}$) — from neutron-rich nuclei - Positrons ($\beta^+$): $\ce{^0_1e^+}$ — from proton-rich nuclei - $\gamma$-rays: high-energy photons from excited nuclear states Step 2 - Analysis of Each Option - (A) $\alpha$-rays: emitted by heavy radioactive elements like $\ce{^{238}U}$, $\ce{^{226}Ra}$ — standard decay ✓ - (B) $\beta$-rays: emitted by neutron-rich nuclides — standard decay ✓ - (C) positron: emitted by proton-rich artificial nuclides — standard decay ✓ - (D) proton: spontaneous proton emission is extremely rare, occurring only in exotic artificially-created nuclides far beyond the proton drip line. It is NOT a standard mode of radioactive decay in naturally occurring or typical radioactive substances. $$\boxed{D}$$