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Chapter 14: Radon's half-life

Updated: Jun 28, 2023

...They walked in the door and headed for the library to study and to think about the mystery they had just discovered...


As Holmes and Watson delved deeper into the mystery, they found themselves confronted with a peculiar case involving a hidden danger lurking within the shadows: radon and its enigmatic half-life. The great detective, renowned for his astute observations, explained to Watson the significance of this elusive concept.


"The half-life of radon," Holmes began, his keen eyes narrowing, "is the duration in which this perilous gas and its decay products must disperse into the environment. Some of these decay products possess short half-lives, rendering them hazardous if inhaled, as they unleash harmful radiation upon the delicate lungs of unsuspecting victims."


Watson listened attentively, his mind processing the intricate details of radon's half-life. Holmes continued, his voice measured and precise.


"Each radionuclide exhibits a unique rate of radioactive decay, encapsulated within its radioactive half-life. It signifies the time required for half of the radioactive atoms to disintegrate from their initial count. Remember, Watson, it is not a fixed number, but merely a fraction of the atoms that undergo this transformation."


He then presented a simple example, illustrating the essence of half-life. "Consider a radionuclide with 100 atoms and a half-life of one minute. After one minute, only 50 atoms remain. The count decreases further to 25 atoms after the second minute, demonstrating that the concept of half-life is applicable to the vast number of atoms within even the smallest samples of radioactive materials. A hundred atoms would hardly emit any significant radiation."


Holmes emphasized the significance of comprehending the half-life process in their investigation. "It is within this temporal realm that radon and its decay products disperse into the environment. A duration of 3.8 days allows radon to traverse the soil, but be wary, for the initial decay products possess fleeting half-lives, endangering the lungs before they can be expelled."


As Holmes and Watson unraveled the mysteries surrounding radon's half-life, they uncovered a web of intricacies. Little did they know that the key to unlocking the enigma of their case lay hidden within the delicate dance of atoms and the passage of time.


Here is the graphic they found on the Uranium Decay Chain and radon's half-life.

The Uranium Decay Chain with half-life
The Uranium Decay Chain with half-life

• Rn-222, 3.8 days, alpha decaying to...

• Po-218, 3.10 minutes, alpha decaying to...

• Pb-214, 26.8 minutes, beta decaying to...

• Bi-214, 19.9 minutes, beta decaying to...

• Po-214, 0.1643 milliseconds, alpha decaying to...

• Pb-210, which has a much longer half-life of 22.3 years, beta decaying to...

• Bi-210, 5.013 days, beta decaying to...

• Po-210, 138.376 days, alpha decaying to...

• Pb-206, stable.



Holmes and Watson studying radon's half-life
Holmes and Watson studying radon's half-life

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