[12markkram34]

I know that radiation damages cells. The question is, how? I know that beta particles are electrons and that alpha particles are helium nuclei. Do radioactive particles damage cells by simply ripping through them, or in a far more advanced method?

[408]

"Polonium-210, made famous in a recent poisoning en.wikipedia.org/wiki/Litvinenko, has an LD50 of 0.7ng/kg by injection [current wikipedia is misleading in this figure, as is to be expected of a constantly editable source] – which is 30 times more poisonous than botulinum, and 1.4 million times more poisonous than cyanide! Moreover it destroys all body cells rather than disabling a small set, and its effects are irreversible. 50ng are sufficient to kill an average human - this amount of matter is invisible to the naked eye.

Polonium releases a total 3*10^9 J/gm in the form of radioactivity.


J/gram = a-energy * eQ * Av / Mw

= 5 *10^6 * 1.6 * 10^-19 * 6 * 10^23 /210

=2.5 * 10^4 * 10^5 = 2.5 * 10^9, that is approximately 3 billion joules/gm.


Converting this to Sieverts for a 100kg man we have

20 * 2.5 * 10^7 Sv/g = 5 * 10^8 Sv/g

A dose of 4.5Sv is generally considered to be LD50

Hence for polonium an LD50 is 4.5/5 * 10^-8g = 10 ng


However, the amount of energy released by 50ng (150J) of Po-210 can only heat the body by 150/(4000*80kg) = 1/2000 of a degree! Yet it produces complete shutdown of all vital systems in a matter of weeks with a failure of organs whose total mass exceeds that of the poison by 10kg/0.05ug = 200 billion. What massive amplifying effect, making the human body an exceptionally sensitive radiation detector is at work here?

It turns out that the mammalian cell is so sensitive to radiation that 200rad - an amount of energy sufficient to raise its temperature by only 0.0005C if delivered thermally - if delivered in the form of a hard charged particle is sufficient to kill it. Since nuclear processes are small scale, they are quantum processes, and most process energy is typically ranged fairly narrowly, with emitted particles having energies in the range of several MeV - about several 10^-13J per particle. But
this means a single radioactive particle (several nucleides maximum) can kill a cell consisting of 10^-9/10^-24 particles. Therein the massive amplification factor of 10^15!

To irradiate all cells in a 100kg human body the amount of Po-210 needed is roughly

100kg * 10^-15 (mass particle/mass cell) * 210 (mass Po-210/mass particle) = 20ng

In excellent agreement with observed results!

What exactly happens on the chemical level is not fully understood - but the basics are known to come about from the fact that cells contain a suicide mechanism (apoptosis) whose seat lies at the atomic level. A single atom incorrectly placed can lead to chemical reactions which on completion (this ‘amplification’ or ‘developing’ takes several weeks) in the cell lead to apoptosis. It also explains the existence of a 'walking ghost' phase of several weeks where en.wikipedia.org/wiki/Walking_ghost_phase people who are definitely going to die from radiation go thru a period when they are apparently well - their cells are still functioning - even though they have been irreversibly programmed to die. Death is inevitable as there is no known method of reversing the apoptosis process once it has been started. [[en.wikipedia.org/wiki/Louis_Slotin]]

This amplification is not evenly spread among cells, Many bacteria cells can sustain an enormous amount of radiation before dying, to the extent that they fry thermally first (completely the opposite of the case for human cells) and this explains why radiation can not be used as an effective disinfectant - we are far more sensitive to it than anything else - radiation is good for homicide - it can rid wheat of people without spoiling it - but not for insecticide or bactereocide (antiseptic). Even within the humans body not all cells are equally susceptible - cells stop replicating at levels of radiation www.iaea.org/Publications/Magazines/Bulletin/Bull023/02305892124.pdf well before apoptosis is triggered - probably due to the huge DNA molecule essential to replication, being sensitive to a single atomic change. This explains why radiation sufferers en.wikipedia.org/wiki/Litvinenko display loss of hair and immuno deficiency (death of fast dividing cells) before system shutdown symptoms appear (massive cell apoptosis).

From the toxicological viewpoint there is nothing special to Po-210. Poisoning by radioactive materials is essentially all of the same type. What is important is how long the average Po atom takes to decay with respect to how long on average it takes to be eliminated from the body, and its detectability. In physical terms the important characteristics are the half-life (138days), type of radiation whether: electromagnetic-gamma, electron-beta, neutron, helium nulceus (only alpha), and radiation energy range hard or soft (hard). Radium for instance, is on half life alone 1680yrs/138days ~ 4400 less poisnous than Polonium-210. Uranium is more toxic chemically than radioactively, being 4*10^9yrs/138days = 10 billion less toxic than Po-210. On the other hand a very short half life, seconds or days typical for many isotopes, is detrimental to toxicity since the toxin would be essentially non-radioactive before having a chance to be administered. Still there are hundreds of isotopes with a half-life in a suitable range, Even more isotopes emit the most toxic hard alpha particle radiation (in converting the dose in J/kg to the Sievert, the empirical biological effectiveness of radiation, alpha particles have the highest multiplication factor of 20).

Po-210 is perhaps most unusual in its detectability characteristics. Unusually there is no gamma or beta radiation (former occurs in one in 10^5 decays), while alpha being charged has a mean free path measured in microns in fluids and solids. So Geiger counters will not detect it. Its radiation will not even pass through paper (100um thick). It can be taken through airport detectors. An invisible amount [en.wikipedia.org/wiki/Lugovoi] 15ug of Po-210 will kill everyone on a plane, yet can not be detected on embarkation. Resonance spectroscopy which can detect nitrates for instance, is not sensitive enough to detect such small amounts of matter, which can be inconspicuously EM shielded, in say a pin head."

From: https://www.sciencemadness.org/whisper/viewthread.php?tid=11940

[Borek]

I believe ionization is a key word.

Po case is a special one - we are talking about radiation occuring inside cells. The same amount of alpha radiation can be safely stopped by the skin, without any adverse effects.

[renge ishyo]

I believe ionization is a key word.

That it is sir.

Whether you have particle radiation, UV or gamma radiation, etc. the effect is for the radiation to ionize a particle in the body that in tern can become a radical starting a chain reaction of destruction. Your body has things that can stop such chain reactions (glutathione for one), but if you are exposed to too much radiation at a time your defenses can't "put out the fires fast enough" and the damage can become very large and widespread and perhaps even fatal.