decora said:

“the radio-toxicity of plutonium is not all that high and the spread of such material would be fairly local. “

this is why ‘debunker scientists’ websites fail. this question is incredibly important, but in this article is has been glossed over as if it were unimportant.

then the author proceeds to scream at everyone with ALL CAPS about how stupid they are.

‘proof by intimidation’, as an old professor used to say.

please remind me which part of the scientific method involves screaming at people.

I don’t need to tell people how stupid you are, you did a better job at it than I ever could.

Yes, it’s a little bit simplified, because that’s the nature of addressing the general public on an internet site. If you want they details please feel free to look them up for yourself.

I’ll provide some:

Plutonium is an alpha emitter. It’s only dangerous when it is internal (within the body) as would be the case if ingested or inhaled.

It has a reasonably low activity. The half-life of Pu-239 (the most common form in reactor generated plutonium) is 24,000 years. That’s fairly long. Therefore the specific activity isn’t very high. Pu-240, the second most common is about 6,500 years – also fairly long.

This is quite long and thus the radio-toxicity is relatively low as compared with much shorter lived isotopes.

Take for example Po-210, the stuff that Alexander Litvinenko was poisoned with – plutonium is literally tens of thousands of times less radio-toxic because it is also an alpha emitter but Po-210 has a halflife of only 138 days.

Short and medium fission byproducts also have much higher radio-toxicity.

Additionally, the biological uptake of plutonium is not especially high.

If you really want, you can look up the relative toxicity in various tables. It’s out there.

Good enough for you?

this is why ‘debunker scientists’ websites fail. this question is incredibly important, but in this article is has been glossed over as if it were unimportant.

then the author proceeds to scream at everyone with ALL CAPS about how stupid they are.

‘proof by intimidation’, as an old professor used to say.

please remind me which part of the scientific method involves screaming at people.

        Anon said:

⁹⁰Sr also has a lower energy density than ²³⁸Pu so you’d need more of it (and every kilogram costs thousands with a space probe, a centimetre of cladding would also add more mass).

Thanks, I checked the info on the two isotopes again — each one of ²³⁸Pu’s alpha particles carries ten times the punch of a ⁹⁰Sr beta particle, so I guess that explains the difference in power densities.

The shorter half life of ⁹⁰Sr also means that the probe would need even more to last the same amount of time before they don’t have enough power to operate (though it’d probably work pretty well).

When it comes down to it they also tend to launch those space probes on their most powerful rockets and so saving a couple of hundred kilograms on the RTG can allow them to carry an extra couple of hundred kilograms of scientific instruments (which is what the probe is built to carry anyway).

When launch costs come down enough ⁹⁰Sr could make sense for more space missions and might even end up dominating over ²³⁸Pu but probably not right now (though ²⁴¹Am (longer half life but lower power density), ²¹⁰Po (short high power use only, make sure you cool it well because it has enough heat to vaporise itself) as well as ²⁴²Cm and ²⁴⁴Cm (need lots of shielding) could also be used in RTGs).

        George Carty said:

Why do space probes use (hugely expensive) plutonium-238 in their RTGs, rather than (much cheaper as found in spent fuel) strontium-90?

Sure Sr-90 is a beta emitter while Pu-238 is an alpha emitter, but Sr-90 doesn’t emit appreciable quantities of gamma rays, and wouldn’t cladding it with about a centimetre thickness of non-radioactive metal should prevent the betas doing damage to the rest of the spacecraft?

Or is Sr-90’s half-life (28.8 years, rather than Pu-238’s 87 years) too short for space probes?

A couple of reasons:

1. You would need more of it, because it has a lower power density. Mass is the enemy in space flight.
2. It would require more shielding. Sr-90 is a beta emitter, but it produces secondary x-rays as a result and this would require quite a bit of shielding ionizing radiation is an issue for space probes because it could interfere with sensitive instruments.
3. Half-life could potentially be an issue, depending on the mission. If it’s something like Voyager, which is still functioning decades after launch then the halflife could definately be an issue. Probably would not be an issue for something like the Mars Science Laboratory though.

Sure Sr-90 is a beta emitter while Pu-238 is an alpha emitter, but Sr-90 doesn’t emit appreciable quantities of gamma rays, and wouldn’t cladding it with about a centimetre thickness of non-radioactive metal should prevent the betas doing damage to the rest of the spacecraft?

Or is Sr-90’s half-life (28.8 years, rather than Pu-238’s 87 years) too short for space probes?

        George Carty said:

If the pockets of the anti-nukes are THAT deep, couldn’t they shut out pro-nuclear public support by buying all the main political parties so that all the election candidates are anti-nuclear? That’s my big worry — that nuclear energy will be suppressed by undemocratic means…

Well to a certain extent they HAVE bought the leadership of most major parties. However despite the fact that the lower echelon elected members (what we call back-benchers in the Commonwealth system) normally have little influence, they still need to be elected, and have in the past forced change because of public opinion. The fact is no amount of lobbying or slush funding is going to outweigh the threat of a significant number of them losing their seats.

Look at the history of most hot-button issues, and you will see politicians voting to save their asses, regardless of party position.