T5

Observations of radioactive sources (natural and artificial), their activities, and possible effects on our biology:


Internal radiation; in particular, that of potassium-40, is one source that no one escapes.

• It is a particularly interesting isotope, as it is capable of undergoing all forms of Beta deacay
• Beta minus decay gives us calcium-40 (89.28%)
• 1.33 MeV
• Electron capture ends in argon-40 (10.72%)
• 1.46 MeV
• And very rarely will it go through Beta plus to leave us with argon -40 (around 0.001%).

Due to the energy released is the form of gamma rays, potassium-40 is monitored closely by our bodies, with a biological half-life of 30 days. Homeostatic controls in the body are not affected by changes in our environment, resulting in a very constant level of potassium-40 in our body at any given point in time.

• After thorium-232 and uranium-238, potassium-40 is the largest source of radiogenic heat: heat from radioactive decay. In our case, from the outer core of the Earth.
• It is the largest source of natural radioactivity in humans.
• A 70 kg person, on average, contains 160 g of potassium
• => 0.000117 (natural abundance) * 160 g = 0.0187 g of potassium-40
• The activity of potassium-40 in natural potassium is calculated to vary between 27.33-31.31 Bq/g of potassium. 
• Data used in this summary reports an average activity of 0.1 microcuries
• =3700 Bq, at all times, in an average human male. 

This results in a yearly dose to organic tissue between 0.14 mSv - 0.18 mSv: the rough equivalent to the dose received from a mammogram, for the women reading this. This falls where one would expect; that is, as part of the natural dose humans receive each year from natural radiation. In time, however, it is no wonder we would all eventually die of cancer. Perhaps our inescapable fate is written in that we die because we have lived. 

One example of artificial radiation would be one that is found in a common household item: the smoke detector, which uses americium-241 to detect smoke.

• Obtained as a decay product of plutonium-241
• Half-life of 432 years
• Undergoes Alpha decay as well as Gamma emission
• Has a measured activity of 127 GBq/g
• Average detector contains 0.29 micrograms
• => 127 GBq * 0.29 micrograms = 37000 Bq per gram @ 60 keV

In the gamma emission pathway, americium-241 has a dose constant of 3.14 mSv per hour at a one meter distancefor the given amount of 37 GBq activity, we can conclude the dose received, yearly, from a smoke detector is around 27 microSv. Which is several magnitudes below the natural background radiation dose of 2.4 mSv

The takeaway message from studying data and claims about everyday life, like these, is that key words like "radiation" and "radioactive" are often used to scare people into buying some product or simply to inspire needless fear. Stay smart, stay radioactive.




Further reading and References 

Diapositivas http://ibioii16n.blogspot.com.es/

Efectos biologicos del potasio http://phi.nmsu.edu/~pvs/teaching/phys593/potassium.pdf

Mas info sobre potasio-40 http://www.radioactivity.eu.com/site/pages/Potassium_40.htm

Half-life de potasio en nuestra biologia http://iopscience.iop.org/article/10.1088/0031-9155/42/2/012/meta;jsessionid=69F544D2B72F61FFF764B56817095B43.c3.iopscience.cld.iop.org

Americium en detectores http://www.world-nuclear.org/information-library/non-power-nuclear-applications/radioisotopes-research/smoke-detectors-and-americium.aspx