Suppose I have a volume of seawater that gets exposed to a heavy neutron flux. What changes would I expect to see in that water as a result?
I can imagine that neutron absorption would result in the formation of new isotopes, some stable and some radioactive, but I’m curious as to exactly what sort of changes to expect in a mixture like seawater. For example, seawater has a lot of H, a bunch of O, modest amounts of Na and Cl, and trace amounts of many other elements. I think I know that these various elements are not equally likely to absorb a neutron. So for all I know my irradiated seawater may end up full of deuterium or radioactive chlorine or stable gold isotopes. Maybe all the oxygen is activated but none of the hydrogen, for example. If I were to sample this water hours or years or eons after the irradiation, would I be able to determine that it had been irradiated?
In case it matters (does it?) consider neutrons from an atomic bomb test vs. a flooded nuclear reactor vs. the neutron source of your choice.
Seawater is a dog’s breakfast, and each element within the seawater (H, O, Cl, Mg, S, Na, Cl, C, Ca, K, and probably many more; those are just the more common ones that come to mind) will form different isotopes in a neutron flux. You’d really need to look up each one to see what things you’d get and in what ratios (is that your question?)
Hm, on the one hand, hydrogen is the most likely to interact with neutrons, but on the other, those interactions are going to be mostly elastic. I think that overall, the heavier nuclei are the more likely to absorb (and hold onto) a neutron. But you’ll still get at least some capture from all of them.
Yeah, I can look up the thermal neutron absorption cross-section of the elements and see that chlorine’s cross-section is 100 times that of hydrogen, while on the other hand the scattering cross-section for hydrogen is larger by a factor of about 5. But I don’t know what that would mean in real-world terms.
Like does the neutron irradiation produce a lot of deuterium from the abundant hydrogen while activating all the salts, or does it just ionize a lot of hydrogen while transmuting a lot of chlorine? I’ve read about a study of atmospheric radioactive sulfur isotopes after the Fukushima accident in which the sulfur was apparently a product of neutron irradiation of chlorine in seawater at the reactor site. And the mineral content of water samples can apparently be determined by brutal neutron bombardment to activate everything and count the resulting gamma decays. But the heavy minerals make up a small proportion of seawater compared to the hydrogen and oxygen content. What happens there? Plasma or transmutation?
Industrial production of heavy water seems to involve extraction from large volumes of ordinary water rather than irradiation followed by extraction, so it would seem to me that neutron irradiation of water doesn’t produce a lot of deuterium. But I could certainly be wrong.
The proportion of nuclei of each type that absorb a neutron is proportional to the cross-section for that nucleus. At least, in the low limit, where the proportions that absorb are small, but that’s going to be a good approximation for almost any real-world example. So if the chlorine cross-section is 100 times greater than the hydrogen cross-section, that means that the proportion of chlorine nuclei that get transmuted will be about 100 times greater than the proportion of hydrogen nuclei that get transmuted. On the other hand, it looks like seawater has about 200 times as many hydrogens as chlorines, so the absolute number of transmuted hydrogens will be about twice as much as the number of transmuted chlorines.
Of course, a nucleus that has absorbed a neutron may or may not be unstable. If it’s unstable, it’ll most likely beta decay, and turn into the next element up the table.
Flux effect equals time x distance x density. Can a neutron emitting source have a temporarily measurable effect on seawater (or anything else) in a lab? Yes.
If your concern is that said flux causes a significant and persistent radioactive discharge into the ocean from the cooling water of a nuclear electrical generator, the answer is: No
No, the question is more like a forensic one: if the seawater is neutron-irradiated, what altered isotopes would you expect to find, and in what rough amounts? Over time, any radioactive isotopes would be expected to decay to stable products, which might point toward irradiation in the distant past (future geologists examining the Anthropocene, for example).
I thought given the history of atomic bomb testing and use of water in spent fuel rod pools, etc., that there might be some actual researchable info about exactly what gets produced by the irradiation. Sadly, it doesn’t seem that there is.
From Chronos’ post above it sounds like you would expect twice as much deuterium as 36Cl, for example. The 36Cl would eventually decay to 36Ar or 36S, which could in principle be detected much later.