by Willem Post
Background radiation comes from outer space, the earth, natural materials (including natural foods), and even other people.
US natural background radiation exposure is an average of 3.6 mSv/yr; Australia 2.4mSv, Ramsar (Iran) 260mSv
US total radiation exposure, background plus all other sources is an average of 6.2 mSv/yr per person, increased from 3.6 mSv/year about 20 years ago when CT scans were much less common.
Background (3.6 mSv/yr): radon, cosmic, solar, terrestrial (K, U, thorium)
Human-made (2.6 mSv/yr): CT scans 55%, other diagnostic & therapeutic 24%, other 21%;
A gray (Gy) is a unit of radiation dose absorbed by biological matter. To gauge biological effects the dose is multiplied by a ‘quality factor’ which is dependent on the type of ionizing radiation. Such measurement of biological effect is called “dose equivalent” and is measured in Sievert (Sv). For electron and photon radiation (e.g. gamma), 1 Gy = 1 Sv.
0.1 mSv dose: increased risk of death from radiation induced cancer about 1 in 1,000,000; i.e., one millimort
100 mSv dose: death of radiation induced cancer increased by 0.8%, two 100 mSv doses 1.6%, etc.
1,000 to 2,000 mSv dose: 0 to 5% fatal
8,000 to 30,000 mSv dose: 100 % fatal
BANANA EQUIVALENT DOSE, BED
All foods are slightly radioactive, some more than others. All food sources combined expose a person to around 0.4 mSv per year on average.
The average radioactivity of bananas is 130 Bq/kg, or about 19.2 Bq per 150 gram banana. It contains about 450 mg of potassium of which the isotope potassium-40 makes up 0.0117%, or about 53 ugram.
Eating 1,000 bananas, or 40 tablespoons of peanut butter, or smoking 1.4 cigarettes equals a dose of 0.1 mSv, or one millimort. Cigarettes smoke does radioactive damage to a person’s body, especially the lungs
Bananas are radioactive enough to regularly cause false alarms on radiation sensors used to detect possible illegal smuggling of nuclear material at US ports.
For comparison: Human adult 100 Bq/kg, carrots 126 Bq/kg, bananas 130 Bq/kg, brazil nuts 207 Bq/kg
In the International System of units (SI), the becquerel (Bq) is the unit of radioactivity. One Bq is 1 disintegration per second (dps).
1 becquerel = 1 disintegration per second
1 curie = 3.7 x 10 to the power 10 disintegrations per second
1 millicurie (mCi) = 37 megabecquerels (MBq)
1 rad = 0.01 gray (Gy)
1 rem = 0.01 sievert (Sv)
1 roentgen (R) = 0.000258 coulomb/kilogram (C/kg)
A becquerel, Bq, equals one atomic decay (disintegration) per second; 1 Bq = 27 pCi.
EPA limit on drinking water = 20,000 pCi of tritium/liter = 740 Bq of tritium/liter A luminous EXIT sign (1970s) contains about 1,000,000 million Bq (1 TBq), or 27 Curies of tritium. They often end up in landfills causing the leacheate to be contain up to 250,000 pCi/liter, which may be similar to some nuclear plant tritium leaks.
SOME INTERESTING Bq VALUES
1 human adult 100 Bq/kg x 70 kg = 7,000 Bq
1 kg of coffee 1,000 Bq
1 kg superphosphate fertilizer 5,000 Bq
The air in a 100 sq meter Australian home (radon) 3,000 Bq
The air in many 100 sq meter European homes (radon) up to 30,000 Bq
1 household smoke detector (with americium) 30,000 Bq
Radioisotope for medical diagnosis 70 million Bq
Radioisotope source for medical therapy 100,000,000 million Bq (100 TBq)
1 kg of 50-year old vitrified high-level nuclear waste 10,000,000 million Bq (10 TBq)
1 luminous EXIT sign with tritium (1970s) 1,000,000 million Bq (1 TBq), or 27 Curies
1 kg uranium ore (Canadian, 15%) 25 million Bq
1 kg uranium ore (Australian, 0.3%) 500,000 Bq
1 kg low level radioactive waste 1 million Bq
1 kg of coal ash 2,000 Bq
1 kg of granite 1,000 Bq, as in kitchen counter tops.
RADIATION DOSES FROM VARIOUS SOURCES
The below table indicates additional radiation above average background exposure:
– One backscatter wave scan at an airport = 0.001 mSv for about 5 seconds of full body exposure
– One bitewing X-rays, F-speed film = 0.007 mSv for about 0.4 seconds of part body exposure
– Living near a nuclear plant = 0.01 mSv/yr of full body exposure
– One dental X-ray, Panorex, digital = 0.014 mSv for about 18 seconds of part body exposure
– Sleeping next to another person = 0.02 mSv/yr of full body exposure
– One airplane cross-country flight = 0.03-0.05 mSv of full body exposure
– Eating one banana per day for a year = 0.036 mSv/yr of full body exposure
– Nuclear plant design target at perimeter fence = 0.05 mSv/yr of full body exposure
– Brick house compared with a wood-frame house = 0.1 mSv/yr of full body exposure
– One skull X-ray = 0.1-0.2 mSv for about 0.4 seconds of part body exposure
– One chest X-ray = 0.1-0.5 mSv for about 0.4 seconds of part body exposure
– One mammogram = 0.3 mSv for about 0.4 seconds of part body exposure
– One abdomen X-ray = 0.6-1.7 mSv for about 0.4 seconds of part body exposure
– Airline crew, short flights = 2.2 m Sv/yr of full body exposure
– One head CT scan = 2.0-4.0 mSv for about 10 minutes of part body exposure
– One barium X-ray = 3.0-8.0 mSv for about 0.4 seconds of full body exposure
– Airline crew, non-polar flights, 900 hrs/yr = 3 to 6 mSv/yr of full body exposure
– Cooking with natural gas (radon) = 10 mSv/yr of full body exposure
– One full body CT scan = 5.0-15.0 mSv for about 20 minutes of full body exposure
– One chest CT scan = 6.0-18.0 mSv for about 10 minutes of part body exposure
– Airline crew, polar flights, such as NYC-Tokyo, 900 hrs/yr = 9 mSv/yr of full body exposure
– Smoking one pack of cigarettes per day for a year = 13 mSv/yr of full body exposure
– Limit for nuclear plant workers = avg 20 mSv/yr for 5 years, or 50 mSv for one year of full body exposure,
– Cardiac catheterization, coronary angiogram, other heart x-ray studies = 50 mSv for about 60 minutes.
– Lowest clearly carcinogenic level = 100 mSv/yr of full body exposure.
Willem Post BSME New Jersey Institute of Technology, MSME Rensselaer Polytechnic Institute, MBA, University of Connecticut. P.E. Connecticut. Consulting Engineer and Project Manager. Performed feasibility studies, wrote master plans, and evaluated designs for air pollution control systems, power plants, and integrated energy systems for campus-style building complexes. Currently specializing in energy efficiency in buildings.