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Begum et. al. 2012  (Alz and IR) p. 1Begum et. al. 2012 (Alz IR) p. 2Begum et. al. 2012 Alz IR p. 3Begum et. al. 2012 Alz IR, p. 4Begum et. al. 2012 Alz IR p. 5Begum et. al. 2012 Alz IR p. 6Begum et. al. 2012 Alz IR p. 7
Begum et. al. 2012 Alz IR p. 8
Original available here, without green highlight, which we have added: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3483841/

Our postscript:
The BEIR VII report is well-known for its Linear No-Threshold Model (LNT), i.e. no safe dose: “the risk of cancer proceeds in a linear fashion at lower doses without a threshold and that the smallest dose has the potential to cause a small increase in risk to humans.” However, BEIR only “focuses on the health effects of low levels of low linear energy transfer (low-LET) ionizing radiation such as x-rays and gamma rays.” And, as they point out “Most radiation sources have a mixture of high- and low-LET radiation. Compared to high-LET radiation, low-LET radiation deposits less energy in the cell along the radiation path and is considered less destructive per radiation track.” Original here: http://www.dep.state.pa.us/brp/radon_division/BEIR%20VII%20Preliminary%20Report.pdf Emphasis added.

In other words, ionizing radiation from high LET alpha particles, which may be inhaled, ingested and even absorbed through skin, is even more dangerous than the low LET described by BEIR as having no safe dose! The above Alzheimer’s Disease study focuses on low LET x-ray and gamma-ray exposure, which is considered less dangerous and destructive, than the high LET internal alpha radiation. This is both because high LET alpha is more “destructive per radiation track” and because it stays in the body over time (A time which varies according to radioisotope and the amount of the radioisotope in the outside environment). Low LET gamma-ray exposure can also occur over time either internally, or externally in a contaminated environment, but will be still “less destructive per radiation track” than internal high LET alpha. Low LET Beta radiation is also “less destructive per radiation track” than alpha, but stays in the body over a time period, which varies according to type of radioisotope and according to its presence in the external environment. In other words, if the environment is contaminated the internal radioisotopes will enter into a steady-state condition within the body.

Hence, in a real world exposure scenario, including high LET alpha emitters, such as Plutonium and Americium 241, the impacts may be worse than described in this article on Alzheimer’s Disease.

(Note that 239Pu is an alpha emitter with a half-life of 24,110 years, 240Pu is an alpha emitter with a half life of 6,561 years, 241Pu is a Beta emitter with a half-life of 14.325 years, but which becomes 241 Americium, which is itself a strong alpha emitter with a half-life of 432 years, and 242Pu is an alpha emitter with a half-life of 373,300 years. http://en.wikipedia.org/wiki/Isotopes_of_plutonium http://en.wikipedia.org/wiki/Isotopes_of_americium#Americium-241 Plutonium has a half-life in the body of about 20 to 50 years (some authors give 60 or 70 years or more. Basically it stays a lifetime.)

Some additional information: https://www.osha.gov/SLTC/radiation_lectures/ion_rad_20021007.ppthttp://www.ncbi.nlm.nih.gov/pubmed/10363986 http://ec.europa.eu/energy/nuclear/radiation_protection/doc/scientific_seminar/2007/beta_emitters.pdf https://www.osha.gov/SLTC/radiationionizing/introtoionizing/ionizinghandout.html http://www.atsdr.cdc.gov/toxprofiles/tp149-c2.pdf
On High vs. Low LET:
The amount of energy that the radiation transfers per unit of path length is called its linear energy transfer (LET) and is measured in units of MeV/µm. This feature reflects a radiation’s ability to produce biological damage. Radiation is classified as either high linear energy transfer (high LET) or low linear energy transfer (low LET), based on the amount of energy it transfers per unit path length it travels. Alpha radiation is high LET; beta and gamma radiation are low LET. Alpha particles are classified as high LET radiation because their large +2 charge and relatively large mass (about 7,200 times that of an electron) cause them to move relatively slowly and interact strongly with any material they pass through, producing dense ionization along its path. Beta particles, which are energetic electrons, are classified as low LET radiation. Even though they interact with matter in a manner similar to alpha particles, their smaller +1 or -1 charge and smaller mass result in a greater distance between ionizing collisions and, thus, a lower rate of energy transfer“. http://www.atsdr.cdc.gov/toxprofiles/tp149-c2.pdf
[ Note that the much maligned potassium 40, in bananas, is not only a very tiny part of the very necessary non-radioactive potassium, but is a low energy beta emitter. It is also a form of potassium, so does not act as a poison as some radioisotopes such as caesium do. We are still waiting for the banana growers and companies to sue MIT-WHOIS and Ken Buessler over defamation of bananas. ]