Beta Rays and Their Transmission in Different Isotopes

ß rays are not transmitted by which one of the isotopes given below?
(A) 14C
(B) 3H
(C) 32P
(D) 125 I

Correct Answer: (D) 125I (Iodine-125)

Understanding Beta (β) Radiation

Beta radiation (β) consists of high-energy electrons or positrons emitted from the nucleus of a radioactive atom during beta decay. There are two types of beta decay:

• Beta-minus (β-) decay: A neutron converts into a proton, releasing an electron and an antineutrino.
• Beta-plus (β+) decay (positron emission): A proton converts into a neutron, releasing a positron and a neutrino.

Beta particles are more penetrating than alpha particles but can be stopped by materials like plastic, glass, or lead.

Beta Emission of Given Isotopes

Let’s analyze the given isotopes:

1. 14C(Carbon-14)
   • Undergoes β- decay.
   • Used in radiocarbon dating.
   • Emits low-energy beta particles that can penetrate thin materials.
2. 3H(Tritium)
   • Undergoes β- decay.
   • Used in radioactive labeling and luminescent devices.
   • Emits low-energy beta radiation that does not travel far.
3. 32P(Phosphorus-32)
   • Undergoes β- decay.
   • Used in biomedical research and molecular biology (e.g., DNA labeling).
   • Emits high-energy beta radiation that requires shielding.
4. 125I(Iodine-125)
   • Does not emit beta (β) radiation.
   • Undergoes electron capture, emitting gamma rays (X-rays) instead.
   • Used in medical imaging and radio immunoassays.

Correct Answer: (D) 125I (Iodine-125)

Why?

• Iodine-125 does not emit beta (β) particles; instead, it undergoes electron capture where an electron is absorbed by the nucleus, leading to the emission of gamma rays.
• Other isotopes (14C, 3H, and 32P) all undergo β- decay and emit beta particles.

Conclusion

Among the given isotopes, 125I (Iodine-125) does not transmit beta rays because it undergoes electron capture instead of beta decay. Understanding beta radiation is essential in nuclear medicine, radiochemistry, and molecular biology, where different isotopes serve specific applications based on their emission properties.