Isotopes of thallium

Thallium (Tl) has several isotopes, which are variants of the element with the same number of protons but different numbers of neutrons. Naturally occurring thallium has two stable isotopes: 1. **Thallium-203 (Tl-203)**: - Number of protons: 81 - Number of neutrons: 122 - Natural abundance: About 29.5%.