By Ron B. Davis Jr., Georgetown University
Alpha particles are large, and travel shorter distances than the other common forms of radiation, and that makes pure alpha particles also a more targeted radiological weapon. They are also safer for a poisoner to carry. How? Read on to find out more.
The Perfect Radiological Poison
Alpha particles are devastating once ingested or inhaled, since any alpha particles emitted inside the body are free to smash into nearby tissue and organs, causing radiation sickness and eventual death. They also do not penetrate the skin, making them safer for a poisoner to carry.
Combine that with a convenient half-life—just long enough to be produced, transported, and administered, before it decays away—and we have a recipe for the perfect radiological poison.
Polonium
The assassin’s choice of radioactive poison is polonium. Named for Poland, the homeland of its famed discoverer, Marie Curie, it was extracted from a uranium ore known as pitchblende. Given all the other radioactive substances that are more readily available, what is it that’s so special about polonium-210.
Polonium, much like the metalloid astatine, decomposes so quickly that it leaves no significant isotopic abundance to report. Interestingly, in 2006, it was polonium-210 that was implicated in the assassination of former Russian spy, Alexander Litvinenko. It was estimated that less than 1 microgram of polonium-210 had been administered to Litvinenko by dissolving it in a cup of tea, ensuring that it was ingested by the victim.
Polonium-210 and not uranium or thorium was used as it decays to stable lead-206 in a single step, releasing only alpha radiation as it decays.
Thallium and Lead’s Toxicity
When it comes to thallium and lead’s toxicity, the reasons behind it might seem a shock at first. The key is the ability of these heavy metals to impersonate potassium and calcium. This is because both potassium and thallium share a diagonal relationship, as do calcium and lead on the periodic table.
Thallium, as a member of the boron group, can lose its entire allocation of valence electrons from the fifth energy level to become what is called thallium (III). Or, thallium can compromise by losing just one electron to empty its 5p subshell and become thallium (I), with a charge of 1+.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Thallium (I)
It’s this ‘thallium (I)’ form that makes thallium so poisonous. It has a charge of plus one, just like potassium. And with four times as many protons in its nucleus, thallium pulls its electron cloud in, making thallium’s ionic radius about the same size as potassium! The result is that thallium (I) ions can go just about anywhere in the body that the essential element potassium can.
This highly efficient uptake is what also made thallium (I) sulfate the rodenticide of choice in the mid-20th century—until its analogous toxicity in humans led many governments to ban or restrict its use.
Lead
Similarly, part of lead’s toxicity lies in its ability to substitute for calcium, both in bones and in the nervous system. Lead that has lost only its two 6-p electrons becomes lead (II)—which is remarkably similar to calcium (II) ions in size and charge. Hence, once ingested, lead can impersonate calcium ions in the body, much the way strontium ions can, taking up residence in our bones and nervous system.
Lead has what can be called a ‘biological half-life’ of about 25 years. This means that lead exposure at high levels can effectively cause life-long medical problems—particularly for anyone exposed at an early age, when bone growth and nervous system development is at its greatest.
The Engine Knock
Lead’s toxicity and its properties as a weak but heavy metal have had many consequences in human history. For example, in the early days of automotive engineering, when there were still many challenges yet to be overcome, one of those challenges was what was known as ‘engine knock’. This was a pesky problem in which gasoline detonated prematurely in an engine cylinder. That produced an annoying noise, and it ultimately increased engine wear or damage.
But a bright chemist working for General Motors in the 1920s, Thomas Midgley Jr. made a discovery that changed the automobile fuel industry.
Leaded Gas
Thomas Midgley Jr. created a gasoline formulation that reduced knocking in engines. He called his creation ‘leaded gas’, a very unusual creation of gasoline with lead dissolved in it.
Midgley’s creation, however, did not contain naked lead atoms or ions. Rather, this was a compound of hydrocarbons chemically bonded to lead called, tetraethyl lead.
In this compound, lead itself acted more like how carbon might. That is, the lead bonded to four hydrocarbon ‘ethyl’ groups. This surrounded the lead with gasoline-like groups, disguising the metal and helping it dissolve into gasoline.
Tetraethyl Lead
Unfortunately, the toxic nature of lead left a trail of sickness and death in the wake of this product, first in Midgley’s research labs, then in the plants in which his tetraethyl lead was produced, and later in the worldwide health consequences of lead emissions.
As the environmental historian J.R. McNeil once quipped, Midgley may have “had more impact on the atmosphere than any other single organism in Earth’s history”. From environmental calamities to political assassination, weak metals have caused their fair share of problems.
Common Questions about Alpha Particles and Deadly Poisons
The assassin’s choice of radioactive poison is polonium. Named for Poland, the homeland of its famed discoverer Marie Curie, it was extracted from a uranium ore known as pitchblende.
The reasons behind thallium and lead’s toxicity might seem a shock at first. The key is the ability of these heavy metals to impersonate potassium and calcium. This is because both potassium and thallium share a diagonal relationship, as do calcium and lead on the periodic table.
Thomas Midgley Jr. created a gasoline formulation that reduced knocking in engines. He called his creation ‘leaded gas’, a very unusual creation of gasoline with lead dissolved in it.