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| EDITORIAL |
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| Year : 2012 | Volume
: 35
| Issue : 2 | Page : 57-58 |
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Radioactivity in human body and its detection
DD Rao
Internal Dosimetry Section, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
| Date of Web Publication | 21-May-2013 |
Correspondence Address:
D D Rao
Internal Dosimetry Section, Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0972-0464.112337
How to cite this article:
Rao D D. Radioactivity in human body and its detection. Radiat Prot Environ 2012;35:57-8 |
Human body and some elements of the periodic table are critically linked to the general well-being of the human through the metabolic function. Some of these elements have radioisotopes with them that emit ionizing radiation and are inseparable from each other in the body. A few of the elements are critical for the proper functioning of several organs/tissues such as the requirement of element iodine for thyroid. The radioactive elements enter into the body through inhalation of air via breathing and the consumption of food via ingestion.
The most important natural radionuclides that are found in the human body are 238 U, 234 U, 232 Th, 210 Po, 210 Pb, 40 K, 226 Ra, 228 Ra, 14 C, 7 Be, 22 Na, and the last three being cosmogenic in nature. In addition to these natural and cosmogenic types, the artificial radionuclides such as 137 Cs and 90 Sr and many others can also be found in an extremely small level. The concentration of the gamma emitting radionuclides, except for 40 K, in human is so small that none of them can be detected using normal whole body counters available to measure any intakes of radionuclides by occupational workers.
The potassium content, distributed uniformly in the human body is about 0.18% and the radioactive isotope 40 K is 0.0117% of total potassium, and the rest is stable 39 K. The average 40 K content in a human body weighing 70 kg is 4400 Bq, meaning that it emits 4400 radiations within the body per second. Out of 4400 radiations/s, 470 are gamma rays part of which come out of the body due to their higher penetrating power and 3930 are beta radiations most of which are absorbed in the tissues. Potassium in the human body is homeostatic, a property of the system to regulate potassium content to equilibrium or constant value. However, its content depends on the body height and weight and a large number of studies have already been conducted to establish a kind of correlation between the body size and food habits. It has also been observed that most of these studies using the medium sized scintillation detectors have not considered the uncertainties involved in the 40 K evaluations while performing the correlations.
Average concentration of 238 U is in the range of 0.7 - 1 Bq in a 70 kg reference body and about 70% of the content is retained in skeleton. Natural uranium in equilibrium consists of equal activity concentration of 234 U and 238 U. The detection limits of natural uranium using a sensitive whole body counter located above the skull region is generally about 50 Bq for 238 U compared to the 0.5-0.7 Bq present in the skull. The natural U-content retained in the body can be estimated by indirect method of urine analysis and using the bio-kinetic models. Similarly, 232 Th, 230 Th, 210 Pb also get accumulated in the bone up to an extent of 70%. The average concentration of 232 Th and 230 Th in the human body is 0.07 Bq, and 0.21 Bq, respectively. The concentration of 210 Pb and 210 Po in the body is 21 Bq and 18 Bq, respectively. The average radioactivity contents of 226 Ra and 228 Ra in the human body of 70 kg weight are 1.86 Bq and 0.70 Bq, respectively.
The detection of the radionuclides such as 238 U, 232 Th, 234 U, 235 U, 7 Be is not possible with the existing laboratory whole body counters as the levels of these radionuclides are very small. The only radionuclide that can be detected with the normal sensitive whole body counters is 40 K. Large number of scientific papers have already been published to study the 40 K trends in the human body with respect to food habits and body physical standards. 40 K, on the other hand, can be interference in the measurements of actinides deposited in the lungs or other tissues. A paper in this issue discusses certain aspects of identifying the 40 K interference along with others. The fact that many radionuclides present in the human body cannot be detected due to their extremely low concentration leaves ample scope for the development of sensitive monitoring systems particularly for natural Uranium, Radium, Lead, and Polonium isotopes.
The effective radiation dose due to the body 40 K content is 0.165 mSv, and due to the Uranium and Thorium series of radionuclides, it is 0.12 mSv in a year. Cosmogenic radionuclides such as 14 C, 22 Na, 7 Be, including 3 H, which have metabolic roles in the human body also emit radiation. The 14 C content in a 70 kg reference body is 2700 Bq, which emits 2700 low energy beta radiations per second and exposes the body to 0.012 mSv of annual effective dose. The annual effective doses from 22 Na, 3 H, and 7 Be are 0.15 μSv, 0.01 μSv, and 0.03 μSv respectively.
The total annual effective dose from different natural radionuclides present within our human body works out to be about 0.3 mSv. The annual effective dose recommended for a member of public by International Commission on Radiological Protection (ICRP) due to the operation of nuclear facilities and from the applications of radiation and radioisotopes is 1 mSv. Dose from background exposure to naturally occurring radionuclides and medical exposure is not included in the dose limit for the members of the public. The activity concentration of natural radionuclides in human body mentioned in this article are taken from United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR 2008).
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