Role of Calcium-41 in Radiometric Dating

Why in news?

Recent study shows that Calcium-41 can be used the same way as Carbon-14 in carbon dating, but with several advantages.

What is radio carbon dating?

• Carbon-14 - Radiocarbon (Carbon 14) is an isotope of the element carbon that is unstable and weakly radioactive [The stable isotopes are carbon 12 and carbon 13]
• It has a half-life of 5,700 years, so the technique can’t determine the age of objects older than around 50,000 years.
• Radiocarbon dating – It is a method that provides objective age estimates for carbon-based materials that originated from living organisms.
• Plants and animals assimilate Carbon 14 from carbon dioxide throughout their lifetimes.
• When they die, they stop exchanging carbon with the biosphere and their carbon 14 content then starts to decrease at a rate determined by the law of radioactive decay.
• An age could be estimated by measuring the amount of carbon-14 present in the sample.
• There are 3 principal techniques used to measure carbon 14 content of any given sample.
  • Gas proportional counting
  • Liquid scintillation counting
  • Accelerator mass spectrometry (Advanced method)
• The method was developed 1940s by Willard Libby, who received the Nobel Prize in Chemistry to this work in 1960.
• The issue with carbon dating was to detect carbon-14 atoms, which occur once in around 10¹² carbon atoms.

What is Calcium-41?

• Calcium-41 is a rare long-lived radio-isotope of Calcium that has a half-life of 99,400 years.
• Calcium-41 is called a cosmogenic nuclide, because it is produced when cosmic rays from space smash into calcium atoms in the soil in a fission reaction, called spallation.
• It is found in the earth’s crust, opening the door to dating fossilized bones and rock.
• The issue is Calcium-41 is rarer, occurring once in around 10¹⁵ Calcium atoms.

How can the issue of detecting C-14 and CA-41 be resolved?

• Atom Trap Trace Analysis (ATTA) - Researchers at the University of Science and Technology of China pitched a technique called atom-trap trace analysis (ATTA) to spot these atoms.
• ATTA is both extremely sensitive and selective, and is based on the laser manipulation and detection of neutral atoms.
• Procedure - A sample is vaporised in an oven.
• The atoms in the vapour are laser-cooled and loaded into a cage made of light and magnetic fields.
• In ATTA, a laser’s frequency is tuned such that it imparts the same energy as required for an electron transition in Calcium-41.
• The electrons absorb and release this energy, revealing the presence of their atoms.
• Significance - It can spot one calcium-41 atom in every 10 ¹⁶ calcium atoms with 12% precision in seawater.
• ATTA also avoids potassium-41 atoms, which are similar to calcium-41 atoms but lack the same electron transition.
• It can also be modified to study isotopes of some noble gases that have defied techniques developed for carbon-14, such as argon-39, krypton-81, and krypton-85.

What are the applications of ATTA and Calcium-41?

• Opens the possibility of extension to other metal isotopes
• To study how long rocks has been covered by ice
• Open avenues for exploring Earth-science applications

References

1. The Hindu│About ATTA
2. The Hindu│About Radio Carbon Dating
3. Beta Analytic| Radiocarbon Dating