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Half-Life Of Radioactive Elements

What is the half-life?

The half-life is the period of time required for one half of the atoms in a radioactive substance to decay. This concept is fundamental for understanding the stability and longevity of radioactive materials.

Radioisotopes and their significance

Radioisotopes are unstable atoms that emit radiation when they decay into more stable forms. They are utilised in medicine, archaeology and environmental science.

Applications of radioisotopes

  • Medical imaging and treatment: Radioisotopes, such as Iodine-131, are employed in the diagnosis and treatment of thyroid disorders.
  • Archaeological dating: Carbon‑14 is used to determine the age of ancient artefacts.
  • Environmental monitoring: Caesium‑137 is applied for tracking pollution and contamination.

How is the half-life calculated?

To calculate the half-life of a radioisotope, its decay rate must be known. Although the process is based on exponential decay, the decay can be approximated by measuring the substance’s quantity over time.

  1. Measurement of the initial quantity: Determine the starting amount of the radioisotope.
  2. Monitoring the decay: Record the reduction in quantity over specified time intervals.
  3. Application of the decay constant: The constant decay rate is used to estimate the time required for the substance to reduce by half.

Half-lives of common radioactive elements

Element

Isotope

Half-life

Decay type

Carbon (C)

Carbon‑14

5 730 years

Beta decay

Uranium (U)

Uranium‑238

4.468 billion years

Alpha decay

Uranium (U)

Uranium‑235

703.8 million years

Alpha decay

Radon (Rn)

Radon‑222

3.8 days

Alpha decay

Thorium (Th)

Thorium‑232

14.05 billion years

Alpha decay

Plutonium (Pu)

Plutonium‑239

24 100 years

Alpha decay

Iodine (I)

Iodine‑131

8.02 days

Beta decay

Cobalt (Co)

Cobalt‑60

5.27 years

Beta decay and gamma radiation

Polonium (Po)

Polonium‑210

138.4 days

Alpha decay

Radium (Ra)

Radium‑226

1 600 years

Alpha decay

Strontium (Sr)

Strontium‑90

28.8 years

Beta decay

Caesium (Cs)

Caesium‑137

30.1 years

Beta decay

Krypton (Kr)

Krypton‑85

10.76 years

Beta decay

Neptunium (Np)

Neptunium‑239

2.36 days

Beta decay

Tritium (H)

Tritium‑3

12.3 years

Beta decay

Zinc (Zn)

Zinc‑65

243 days

Beta decay

Chlorine (Cl)

Chlorine‑36

301 000 years

Beta decay

Molybdenum (Mo)

Molybdenum‑99

65.6 hours

Beta decay

Radon (Rn)

Radon‑220

55.6 seconds

Alpha decay

Iron (Fe)

Iron‑60

2.26 million years

Alpha decay

Further information can be found atStanford Advanced Materials (SAM).

Frequently Asked Questions

Which factors influence the half-life of a radioisotope?

The half-life is determined by the nuclear properties of the radioisotope, including the forces within the nucleus that affect its stability.

Why is knowledge of the half-life important in medicine?

It assists in determining the dosage and scheduling of radioisotope treatments to ensure efficacy and minimise risks.

Can the half-life of a radioisotope be altered by external influences?

No, the half-life is an intrinsic property and remains constant regardless of environmental conditions.

How is the half-life used in environmental science?

It is utilised for tracking the persistence and migration of radioactive contaminants over time.

What occurs with a radioisotope after several half-lives have elapsed?

The quantity of the radioisotope decays exponentially. Consequently, after several half-lives, the remaining amount becomes negligible.

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About the author

Chin Trento

Chin Trento holds a bachelor's degree in applied chemistry from the University of Illinois. His educational background gives him a broad base from which to approach many topics. He has been working with writing advanced materials for over four years at Stanford Advanced Materials (SAM). His main purpose in writing these articles is to provide a free, yet quality resource for readers. He welcomes feedback on typos, errors, or differences in opinion that readers come across.

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