22 Feb 2019

Actinium - rare & radioactive

From Elemental, 8:00 am on 22 February 2019

The first alphabetical element in the periodic table is actinium. It is a heavy radioactive element, as we discover in episode 1 of Elemental, with Professor Allan Blackman from AUT.

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Photo: RNZ

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Find out more about events during the United Nation’s International Year of the Periodic Table.

Nights with Bryan Crump is also celebrating the chemical elements during their Friday night Sonic Tonic and Element of the Week.

Professor Allan Blackman is at Auckland University of Technology.


In the audio we mistakenly said that Cherenkov radiation happens when particles travel faster than the speed of light. Listener Jennifer Narang wrote in with this helpful and correct explanation:

"Cherenkov radiation is not the result of a particle traveling faster than the speed of light (which is physically impossible). It's due to a particle traveling faster than the PHASE SPEED, which is a totally different animal.

Imagine I were singing scales, going up and down and up and down with my voice. How fast I ran through the notes and returned to my original note, that would be my phase speed. That's completely unrelated to how fast those sound waves--whatever their frequency--are traveling from my mouth to your ears.

Hope this explanation helps shed light on Cherenkov radiation!"

It certainly does help - many thanks.