Mr Litvinenko died in 2006 after he was apparently poisoned with the radioactive substance polonium-210.
BBC: Alexander Litvinenko murder was 'London nuclear terror'
Tritium is a radioactive substance produced by the reactors from nuclear-powered submarines based at the Devonport yard.
Meanwhile, Japan's recall of Meiji baby formula because of pollution by a radioactive substance has also raised a lot of concern.
Accordingly, by observing how much of a radioactive substance has decayed, scientists are able to determine how old that substance is.
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Physicists have long held the view that the rate of breakdown - or decay - for any given radioactive substance is constant.
Alexander Litvinenko, a renegade Russian security officer living in London, was killed by poisoning with polonium, a rare radioactive substance, in 2006.
On that day Litvinenko fell sick, suffering (it eventually turned out) the effects of poisoning by polonium, a rare radioactive substance that killed him three weeks later.
Radioactive decay happens when a radioactive substance emits a particle.
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Tritium is a low level radioactive substance, considered one of the least dangerous by the EPA. State and federal regulators say that tritium leaks pose no threat to public health and safety.
The researchers fired a beam of calcium ions, each containing 20 protons, into a target of californium, a highly radioactive synthetic substance with 98 protons.
The test uses a chemical called florbetapir, known by the brand name Amyvid, which is a radioactive agent that tags clumps of a sticky substance called an amyloid.
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