As Francium is the most unstable element, how much more energy will it generate if it is split compared to, let’s say Uranium?



As Francium is the most unstable element, how much more energy will it generate if it is split compared to, let’s say Uranium?

In: Physics

Francium primarily decay via alpha decay, with average energies of ~6.5MeV. Comparing this to the fission of uranium, with average energies of ~200MeV, its about 30 times weaker. If Francium were to fission the energy release would likely be comparable to uranium if not slightly less due to the difference in mass.

The half-life of an element doesn’t really say anything about the energy release per-atom when fission occurs.

Fr223 to Ra223 produces 1.149 MeV of energy

Boring U238 to Th234 produces 4.270 MeV of energy, but only once every 5 billion years.

Shorter half-life isotopes release more heat overall because the decay is so much faster, but all this really does is make the material difficult to process and handle.

The heat buildup is often sufficient to melt or vaporize samples, rendering them useless.

About the same as uranium, but it is *much* harder to split because the nucleus is smaller. Half life from radioactive decays and energy released from fission are not related. You can’t split it with neutrons in the way you can split uranium, you would have to shoot particles at high energy into the francium nuclei. Not impossible but then you use more energy than you get out – even in a hypothetical scenario where you would have access to macroscopic amounts of francium. In fact, if you would have that by some magic then you could just use francium’s radioactive decays. No need to split anything.

The fissionability of an element is not he same as its radioactivity.

Fission is the splitting of a large atom into smaller atoms and free neutrons. If you add up the mass of the before and the after you find there is a mass defect. Some of the mass is missing. This mass was converted to energy (E=MC2).

Radioactive decay does not convert that much mass. There are elements across the entire periodic table that are radioactive, but are not fissile. For instance tritium is a proton and two neutrons. It is radioactive and does decay, but is obviously NOT fissile. There is really nothing to split it into.

It really is two different process. Splitting or fission and radioactive decay are not the same process. And with splitting or fission, both natural and induced, the amount of energy is dependant on the random resultant atoms that come from the split. There are averages for fission results for each fissile isotope, but they don’t really fully relate to energy generated by radioactive decay.

Natural radioactive decay tends to occur with small pieces breaking off of the atom. This include alpha decay (helium nuclei with an atomic mass of around 4) and beta decay (a neutron turning into a proton and loosing the mass of an electron). These small decay steps tend to put out smaller amounts of energy than the induced fission of Uranium, where the Uranium splits into several large pieces at once.

That said, the main reason that radioactive decay is hard to use for power generation is because of the rate at which it occurs. With a Uranium fission reactor, you can control the rate of fission and increase it to the point where you get useful power. With radioactive decay, the decay occurs at a fixed rate, which is usually too slow to generate useful power.

There are a number of isotopes which decay quickly and put out enough power to be useful. The most well known is Plutonium 238, which is used to power space probes. The problem is that these isotopes are difficult to come by, the only way to get them on earth is to make them inside a special nuclear reactor. Some radioactive isotopes decay so quickly that its impossible to create and gather much of it in one place so that you could use it for power generation. For instance Radon, which is a gas, is produced very slowly by natural uranium, but it decays within a few days, meaning there is never more than a tiny amount of it around, and if you tried to collect it, it would disappear faster than your could realistically gather more.