Differences in Radioactive Elements
The form of the danger is an emanation of energy.
This will be the last week we spend on radiation (for now), so thank you for tuning in! I hope it’s as interesting to you as it is to me.
Below, I won’t be able to expand on all radioactive elements, but I’ve prioritized those that pop up the most in news around nuclear incidents and nuclear strategy. Let’s dig into it.
Uranium-235 and Plutonium-239
Uranium and plutonium both decay by alpha particles, meaning those bulky combinations of two protons and two neutrons which are easily stopped by solids like clothes and paper, but can cause serious damage if ingested.
Ingesting uranium particles can cause bone or liver cancer, along with damage to your kidneys. Inhaling it can somewhat predictably cause lung cancer; because of the relative weight of alpha particles, they cause damage where they come to rest in the body. Inhaling even one microgram of plutonium-239, an amount just barely visible to the eye, is a serious health hazard which can cause the formation of bone and lung tumors.
Both elements are very commonly used in all applications of radioactive materials, from weapons to power generation to medicine.
Uranium-235 has one of the longest half lives1 of all radioactive materials, at 703.8 million years. Plutonium-239 has a comparatively much shorter half life of “only” 24,400 years.
Strontium-90
Strontium decays into beta particles: high-speed electrons (or positrons) which might cause burns on bare skin, and can be stopped by something like a thin sheet of aluminum.
Strontium-90 is structurally similar to calcium; ingesting it can result in its harmful accumulation in bones, especially if the victim is still growing. Internal contamination can result in tumors, leukemia, and blood abnormalities.
Historically, strontium-90 mostly appears in the aftermath of nuclear power plant accidents, like Chernobyl and Fukushima. It’s a by-product of the fission of uranium and plutonium, which occurs in nuclear reactors as well as weapons. Its half-life is about 28.5 years.
Iodine-131
Like strontium-90, iodine-131 also releases beta particles. If ingested, it concentrates in the thyroid gland, where it can destroy all or a part of the gland. For this reason, many people associate this particle in particular, or perhaps radiation incidents more broadly, with the need to take supplemental potassium iodide in order to protect the thyroid. However, its positive health effects are extremely limited, mostly to people who are either pregnant or still growing, and should not be a source of concern in general. In fact, side effects of taking too much potassium iodide can be worse than your risk from iodine-131. If you’re curious, you can read more on this from the CDC.
Iodine-131 was released from the Chernobyl disaster, where a lot of our popular (not necessarily scientific) beliefs about the substance come from, and U.S. bomb tests in the 1950s. It has a half life of only 8 days, so poses a relatively short-term risk.
Tritium (hydrogen-3)
As you probably guessed, tritium also decays by beta particles. However, the beta particle that is emitted by tritium has a very low energy. As a result, these particular beta particles can only travel about 6 millimeters in air. A typical beta particle not from tritium can travel a meter or more.
Tritium is a radioactive isotope of hydrogen. It has the same number of protons and electrons as hydrogen but has 2 neutrons, whereas regular hydrogen does not have any. Tritium is produced in nature, and is also a by-product of nuclear reactors. As it is a form of hydrogen, it is very easy for tritium to replace one or both of the hydrogen atoms in water, and therefore it is very common for tritium to exist in the human body. It’s possible that an abundance of tritium in your body may slightly increase the probability of a cancer diagnosis later in life, but due to its weak radioactive emissions, tritium is one of the least harmful radioactive elements
The half-life of tritium is 12.3 years. As it decays, it changes into helium.
Cesium-137
Cesium-137 (or caesium-137) decays by both beta particles and gamma radiation. It’s structurally similar to potassium, which is more or less evenly distributed throughout the human body. Similarly, Cs-137 does not tend to collect in one region or another.
After its release during Cold War-era weapons testing, some of our low-level background radiation comes from cesium. About 27 kilograms of Cs-137 were also released into the atmosphere during the Chernobyl accident. Therefore, it would be very difficult to entirely avoid in everyday life. Luckily, these small amounts are relatively safe.
Cesium-137’s half life is 30 years. If I’m doing the math right, that means over half of the 27 kilograms from Chernobyl have decayed already; only what, 12 more to go?
Cobalt-60
Unlike the others, cobalt-60 decays mostly by gamma radiation, meaning external exposure can cause acute radiation sickness and death, in large quantities. Its half life of 5.3 years means that it decays slowly enough that it could widely disperse across a landscape, unlike iodine-131, but quickly enough to produce lots of harmful gamma radiation.
These qualities have given cobalt-60 a fearsome reputation which has thrived in fiction.2 While it has never been seriously built into weaponry, in 1950 Leó Szilárd first described its potential as a “salted bomb" which could deposit intense fallout, leading to mass casualties and the conversion of the landscape into an inhospitable wasteland. It would take over a hundred years for the dose rate to decay to something approaching the natural rate of background radiation.
In reality, cobalt-60 is mostly used in medicine, for radiation therapy, and food irradiation.
What is a half life?
Radioactive decay occurs exponentially; for every period of time, a fraction of the original number of atoms decays. A half life measures the period of time it takes for a number of atoms of a given substance to halve in quantity. So, if you take iodine-131’s 8 day half life, we know that after 4 days there would be 75% of the original quantity, and after 16 days there would be 25% of the original quantity of iodine-131. After 56 days, there would be less than 1% of the original quantity remaining.
On the Beach, Dr. Strangelove, Goldfinger…