Another Reef Chemistry Question of the Day: Radioactive Seawater

[Christoph]

Hi Reefers,

Randy, i hope you dont mind that im hijacking this category for a single question

So here we go:

Natural seawater contains about 3 µg/l of Uranium (this is way more compared to several other trace elements such as Selenium, Chromium, Iron, Manganese & co).

Since Uranium has only unstable isotopes this uranium content makes seawater radioactive. The radioactivity caused by the uranium is in the range of 0,04 Bq/l (Becquerel per litre). However, the real radioactivity of natural seawater is by orders of magnitude higher (~12 Bq/l), so there must be some other contributors besides Uranium.

Which element is the major contributor to the radioactivity of seawater?

A) Caesium
B) Strontium
C) Potassium
D) Carbon

Have fun!
all the best, Christoph

 

[Court_Appointed_Hypeman]

Oh heck yeah, love this question

Following.

Will I need to get a Geiger counter on my contriller and dose to keep it in line with natty sea water? The answer may surprise you.

 

[Randy Holmes-Farley]

I'm guessing carbon from C14 made in the atmosphere..

That brings up an old story.

Back in graduate school, the prof assigned me the task of cleaning out the chemical storage room. Plenty of issues, including expired cylinders of certain organometallic compounds that were very flammable, and being expired, were hard to get rid of.

But most troubling was a small plastic bottle of uranium acetate. I did not know anyone in the group had used uranium, and it may have been around for a while. I mistakenly assumed that for it to be stored this way, it must be some sort of isotope that was depleted of the most radioactive isotopes, but no....

I double checked with a Geiger counter the lab had, and was greeted with a machine staccato of clicks when I held the probe up to the bottle. Lesson learned: be more careful. lol

 

[John Bolden]

I'm guessing carbon from C14 made in the atmosphere..

That brings up an old story.

Back in graduate school, the prof assigned me the task of cleaning out the chemical storage room. Plenty of issues, including expired cylinders of certain organometallic compounds that were very flammable, and being expired, were hard to get rid of.

But most troubling was a small plastic bottle of uranium acetate. I did not know anyone if the group had used uranium, and it may have been around for a while. I mistakenly assumed that for it to be stored this way, it must be some sort of isotope that was depleted of the most radioactive isotopes, but no....

I double checked with a Geiger counter the lab had, and was greeted with a machine staccato of clicks when I held the probe up to the bottle. Lesson learned: be more careful. lol

Let us know if you start growing another leg

 

[John Bolden]

What if we use uranium to alter the corals to get new growth patterns?

 

[Court_Appointed_Hypeman]

What if we use uranium to alter the corals to get new growth patterns?

Or 5G

 

[Randy Holmes-Farley]

Well, neither I nor ChatGPT got this one right.

ChatGPT did not even pick one of the choices until I gave it the choices. Then it got it right.

 

[Christoph]

Its a tricky one ;-) lets wait another day for suggestions, then we will lift the mystery

By the way, the radioactivity level is (extremely) far from dangerous. Also every human has a significant level of natural radioactivity. Typically around 4-5 kBq (4000-5000 Becquerels). The main reason is the same as it is in seawater!

 

[gbroadbridge]

Hi Reefers,

Randy, i hope you dont mind that im hijacking this category for a single question

So here we go:

Natural seawater contains about 3 µg/l of Uranium (this is way more compared to several other trace elements such as Selenium, Chromium, Iron, Manganese & co).

Since Uranium has only unstable isotopes this uranium content makes seawater radioactive. The radioactivity caused by the uranium is in the range of 0,04 Bq/l (Becquerel per litre). However, the real radioactivity of natural seawater is by orders of magnitude higher (~12 Bq/l), so there must be some other contributors besides Uranium.

Which element is the major contributor to the radioactivity of seawater?

A) Caesium
B) Strontium
C) Potassium
D) Carbon

Have fun!
all the best, Christoph

Potassium

 

[taricha]

If you had given me a choice of Radon, I think I might have guessed that one.
I'm going to blindly guess C)
Potassium at a few hundred ppm is so many times more abundant than the other more radioactive elements that I think it wins in terms of most contributed radioactivity.

 

[Christoph]

Well done, nobody stepped into the Caesium or Strontium trap (Both have prominent radioisotopes that are sometimes released in nuclear accidents: strontium-90 and caesium-137. Both are absent from natural sewater far from nuclear desasters)

Carbon has a radioisotope, Carbon-14, that makes a small constant portion of all carbon that is in equilibrium with the athmosphere (which is likely the case with the oceans). However, the C-14 radioactivity in seawater is very low.

However, natural potassium contains the radioisotope Potassium-40. The amount in potassium is low (0,012% mass fraction) - the majority cosists of stable potassium-39 and potassium-41 - but enough to consider potassium measurably radioactive. If you happen to have a geiger counter or dose rate monitor you can easily measure the radioactivity in several kg of potassium salts (Potassium chloride for example) yourself. So the correct answer is C.

For the technically interested: K-40 is a beta minus and beta plus emitter. Using a gamma spectrometer you can see the 511 keV annihilation photons and also the 1460 keV gamma line. Since potassium is present almost everywhere the 1460 keV occurs in almost every gamma spectrum if recorded long enough.

Edit: Another interesting thing: Uranium is low in almost all aquaria, but fairly constant at 3 ppb in natural sewater. Using uranium (and some other elements) we can easily distinguish between natural and artificial seawater.

All the best,
Christoph

 

[taricha]

Edit: Another interesting thing: Uranium is low in almost all aquaria, but fairly constant at 3 ppb in natural sewater. Using uranium (and some other elements) we can easily distinguish between natural and artificial seawater.

So any likely explanation why the source material for salt mixes is lower in uranium than the material in the ocean?

 

[Randy Holmes-Farley]

Well done, nobody stepped into the Caesium or Strontium trap (Both have prominent radioisotopes that are sometimes released in nuclear accidents: strontium-90 and caesium-137. Both are absent from natural sewater far from nuclear desasters)

Carbon has a radioisotope, Carbon-14, that makes a small constant portion of all carbon that is in equilibrium with the athmosphere (which is likely the case with the oceans). However, the C-14 radioactivity in seawater is very low.

However, natural potassium contains the radioisotope Potassium-40. The amount in potassium is low (0,012% mass fraction) - the majority cosists of stable potassium-39 and potassium-41 - but enough to consider potassium measurably radioactive. If you happen to have a geiger counter or dose rate monitor you can easily measure the radioactivity in several kg of potassium salts (Potassium chloride for example) yourself. So the correct answer is C.

For the technically interested: K-40 is a beta minus and beta plus emitter. Using a gamma spectrometer you can see the 511 keV annihilation photons and also the 1460 keV gamma line. Since potassium is present almost everywhere the 1460 keV occurs in almost every gamma spectrum if recorded long enough.

Edit: Another interesting thing: Uranium is low in almost all aquaria, but fairly constant at 3 ppb in natural sewater. Using uranium (and some other elements) we can easily distinguish between natural and artificial seawater.

All the best,
Christoph

Thanks for the nice learning experience!

 

[Christoph]

So any likely explanation why the source material for salt mixes is lower in uranium than the material in the ocean?

I can only guess. Since the majority of salt mixes is blended from more or less pure salts, i´d say that there is just no (or very little) uranium contained in this raw materials.

It would also be interesting to fill a reef tank with natural seawater and evaluate if the concentration of Uranium declines (maybe there is some co-precipitation going on, etc). Since uranium measurement is extremely sensitive it would also be possible to evaluate the concentration in dissolved coral skeleton fragments. Maybe we find the "fingerprint" there aswell and can evaluate which portion of the coral grew in the ocean, and which in artificial seawater.

Many things to explore... ;-)

all the best,
Christoph