Context: Researchers have detected proton emission from 188At (astatine) isotope and measured its half-life. The isotope is currently recognised as the heaviest known proton emitter found till date.
Relevance of the Topic:Prelims: Key concepts- basics of an atom; half life; Applications of radioisotopes.
Key Concepts
Basics of an Atom
- An atom contains a nucleus (with protons and neutrons) and electrons revolving around the nucleus.
- Almost all of the mass of the atom is concentrated in the nucleus.
- The number of protons (Z) in an atom determines the atomic number of an element.
- The total number of protons and neutrons, called Nucleons, is called the Atomic Mass Number (A).
- Atoms can be unstable (radioactive) due to imbalance in the number of protons and neutrons (proton-neutron ratio) inside the nucleus.
- All elements with atomic numbers greater than 83 are considered radioactive, including Astatine (85), Uranium (92), Plutonium (94), and Thorium (90) etc.
- These elements have unstable atomic nuclei, and over time, the unstable nuclei decay by releasing energy and radiation to reach a more stable configuration. They release energy in the form of three types of radiations: alpha, beta, and gamma.
Radioactive Half-life:
- For a given radioisotope, the radioactive half-life is the time for half the radioactive nuclei in any sample to undergo radioactive decay.
- After two half-lives, there will be one fourth the original sample, after three half-lives one eighth the original sample, and so forth.
188Astatine isotope
- For the first time that an Astatine isotope decaying by proton emission was detected and its half-time was measured in a lab.
- 188Astatine (At-188) isotope decayed by emitting a proton. While isotopes often undergo radioactive decay by emitting alpha, beta, and gamma particles, rarely do they emit a proton. The measured half-life for the 188At is 190 microseconds.
- At-188 isotope emits a proton and becomes 187-polonium isotope, which in turn decays via alpha decay into 183-lead and so on, until it reaches a stable nucleus.
Targeted Alpha Therapy (TAT):
- TAT is an emerging and highly promising form of radiopharmaceutical therapy that involves the use of alpha-emitting isotopes to target and destroy cancer cells in the human body. In the therapy alpha particle-emitting radionuclides are injected into the tumor tissue.
- One isotope of Astantine (Astatine-211) is one of the most promising alpha emitters for TAT of cancers.