basule, welcome to the Dope! A well written and reasoned OP.
I do feel free to question just how much knowledge you have about rad health physics: that is how radiation and radioactive contamination affects tissues and whole organisms. At the moment while everyone will say that minimizing dose is a good thing, no one can quantify how great the effect of [sup]210[/sup]Po contamination of cigarette tobacco might be.
One of the problems with quantifying the hazard from [sup]210[/sup]Po for smokers is that it’s not the only environmental source of particulate alpha particle emitters that your average smoker will be exposed to. The household Radon gas remediation industry may be something of a scam, but it’s based on a real phenomenon. Radon does outgas from the earth and the particulate decay daughter do accumulate in low-flow areas, such as basements, and the lungs of people who breathe in the particulate. Given that atmospheric temperature inversions are fairly common (more so in some areas than others, of course) local, temporary high concentrations of Ra and Ra decay daughters can occur. And like the [sup]210[/sup]Po for contaminated tobacco, the particulate decay daughters will accumulate in the brachiations of the lung. Where they’ll shoot alpha particles at the cells forming those tubes.
Now, alpha particles (or alpha rays) are basically Helium nuclei moving at some fraction of the speed of light. As subatomic particles go, they’re highly charged, and very heavy. Because of those two traits, they tend not to penetrate very far, but they do transfer a great deal of energy to the material they hit during their short travels. But before you can say that they do a great deal of damage, instead of simply talking about the quantity of energy transferred, one has to consider what radiation damage to living tissues really means. The short, and dirty answer is that all forms of radiation (with the exception of neutron radiation) cause damage to living tissues by the creation of free radicals, or ions, in the cells of the living tissues. These free radicals then interfere with the normal metabolic processes of the cell, and if enough free radicals are concentrated in a single cell, it will die. If the damage is not that extensive, but still significant, it may affect the RNA or DNA of the cell to the point where it’s no longer operating within the normal framework for such a cell - which is one way that cancers may start.
But you can’t assume that all the energy deposited into the lungs of a smoker (or non-smoker) will be causing actual damage to their cells. The lungs have a mucous layer that serves to help filter and then remove particulate contaminants from the air we breathe. Because of the short distance that alpha particles travel, the thin layer of this mucous layer may be enough to shield the living tissue behind it from the alpha particles. This question is hotly debated in rad healthy physics circles, and so far I’ve not seen a consensus answer. It’s also one of the reasons that estimated dose levels for Ra and Ra decay daughters varies so wildly - no one has a model that has been universally accepted for just how much self-shielding the mucous layer may account for.
What I have seen accepted as generally being beyond debate is that any dose from [sup]210[/sup]Po that smokers may receive is, unless we’re talking about someone who’s smoking like a chimney, going to be overshadowed by the dose that the average person will receive from Ra and Ra decay daughters.
A caveat - the last time I researched this issue was back in 2004 or 2005. There may be new knowledge that makes what I’m saying outdated. (I doubt it, strongly, but I do want you to be aware of the possibility.) I’m not currently working in rad health physics, and only pay attention to the field as something of a hobby, so feel free to take what I’m saying with a grain of salt.