Current regulations are too much stringent?

Like any other pollutant, radioactive materials and radiation are also present in our environment since the formation of earth.

The fear of radiation in everyone’s mind is due to the destruction caused by the effects of explosions of atomic bombs over Japan in 1945. The possible innumerable benefits of radiation in medicine and industry are simply not considered or exploited enough or publicized by the policy makers due to fear of negative reaction by the public. The ghost memories of the bombings and the Chernobyl disaster always remained fresh in the public mind! This is typical “Culture of fear” being promoted by various groups of people (so-called anti-nuclear lobby) with vested interests.

The organizations dealing with radiation protection also promote this culture by accepting the Linear Non-Threshold (LNT) approach for radiation protection and safety. Regulators have not much choice but to formulate regulations to address the acceptable dose limits which are based on the calculated risks assuming much debated LNT approach.

As such, the background radiation levels around us vary quite a bit from place to place and in some places it is of the order of the current dose limits. People are living in those places of high background radiation for ages. No abnormal health issues are observed.

At the Chernobyl accident site, the emergency workers (about 30 workers) who received doses above 4000 mSv have died within a few weeks due to Acute Radiation Syndrome (ARS). There were 140 workers who received less than 2000 mSv dose (which is 100 times more than the annual dose limit for radiation workers) and none died. In Fukushima (Japan), 30 workers received doses in the range of 100 and 250 mSv range in a few days and none is expected to die of the radiation exposure. In medical therapy, for the treatment of cancer, thousands of mSv doses are given to kill the cancer tissues.

There was no increased risk of cancer observed amongst the survivors of Hiroshima and Nagasaki whose exposures were below 100 mSv. Animal experiments could not prove the non-threshold theory to induction of cancer by radiation exposure assumed by the radiation protection fraternity.

Once we accept this fact, there is no need to have such stringent regulations for the applications of radiation and radioisotopes. One can save un-justified expenditure of resources, hardship and suffering to the population (based on the lecture given by Prof. Wade Allison, University of Oxford, August 2011).

Let us NOT say NO to the benefits of applications of radiation such as food irradiation, medical / industrial applications, pest control and electricity generation.

Radiation emission from towers

Since last three years, “I care for you” has been pursuing the issue of potential health hazard from exposure to radiation from mobile phones and towers through the blog: http://radsafe.blogspot.com. The potential hazards to the public from exposure to radiation from the towers are being highlighted. Periodically, articles are appearing in Mumbai Mirror, Times of India and DNA. But, there is no persistence in the reporting.

However, it is understood now that some actions are being taken in this direction by the Indian Government authorities to control this avoidable public health concern. DNA Navi Mumbai reported on September 4, 2011 that the radiation levels measured in certain areas of Navi Mumbai are 100 times higher than what is considered safe!

Is this not a matter of grave concern for every one of us?

NORM MANAGEMENT

The acronym NORM means all Naturally Occurring Radioactive Materials. Humans are continuously exposed to these materials such as potassium-40, uranium, thorium and their daughter products present in our environment. Some times, human activities such as uranium mining, phosphate mining, oil exploration, etc enhance the NORM concentration, which increases the potential of exposures of population groups to the radiation. Two important decay products of concern are Ra-226 and a radioactive gas - Radon-222. NORM received a global attention during last 4 decades.

Hence, it is important that the concentration of NORM is measured in suspected industrial activities and take appropriate measures to protect the workers and the environment. The industrial activities which generate NORM waste should be regulated to prevent environmental hazard from the disposal of the waste. Many countries have already aware of the issue and initiated remedial measures to control occupational exposures and to ensure environmental safety. NORM is discovered in the sludge being generated in deep oil well exploration /production activities. GM detectors or scintillation detectors are used for the NORM survey.

Radiation levels due to NORM are measured at the work sites. Personnel monitoring and personal protective equipments, if required are used to measure radiation exposures of the workers and its control. Thermoluminescence dosimeters (TLDs) are used to measure personal exposures and respirators (dust/gas), gloves, overalls, goggles are some of the personal protective equipments (PPEs) used. Above all, the workers should be made aware of the possible NORM exposures so that they follow proper and safe work procedures for the NORM management and environmental safety.

Revision of the Basic Safety Standards (BSS)

The IAEA International Basic Safety Standards for Protection Against Ionizing Radiation and for the Safety of Radiation Sources is in the final stage of revision.

A review of the Basic Safety Standards (the BSS) was carried out in 2006 in cooperation with the cosponsors (FAO, ILO, NEA, PAHO and WHO) and potential cosponsors UNEP and EC. The review concluded that, while there was no major issue requiring urgent revision, there was a case to be made for the revision of the BSS in order to take account of the many improvements that have been suggested. The International Atomic Energy Agency (IAEA), in cooperation with the co-sponsoring and potential co-sponsoring organizations, initiated the revision of the BSS in 2007.

The revised International Basic Safety Standards was endorsed by the Commission on Safety Standards (CSS) at its meeting from 25-27 May 2011. The CSS has asked that Member States be consulted about the change (Draft 5.0) to the dose limit for the lens of the eye. Member States are invited to on this change by 7 July 2011. This is a major milestone in the development process of the revision. The revised BSS will now be submitted to the Board of Governors for approval at its meeting to be held from 12-16 September 2011 (IAEA News).

Risk of radiation exposure – ICRP Recommendations

The International Commission of Radiological Protection (ICRP) provides recommendations on radiation protection standards. Since the ICRP-60, there has been significant progress in understanding the genetic risk associated with the induction of mutations in germ cells. The clearer understanding is that the genetic risk is much lower than the earlier estimates. In ICRP-103 (2007), the risk estimates considered only two generations rather than the all generations (theoretical equilibrium) considered in ICRP-60. The overall contribution to the detriment (total harm) from genetic effects works out to be 3-4% as compared to 18% considered in ICRP-60. Hence, the tissue weighting factor was reduced from 0.2 (ICRP-60) to 0.08 (ICRP-103).

The radiation detriment (overall harm to stochastic effects) was assessed (ICRP-60) taking in to account the cancer incidence, mortality, length of life lost if cancer occurs and the morbidity and quality of life lost due to suffering in incidences of non-fatal cancers. The ICRP-103 considered the detriment based on lethality and life impairment weighted on cancer incidence data.

The detriment values were assessed for both genders and also for working (18 to 64 years) the whole population (0 to 85years). The detriment adjusted nominal risk coefficients for cancer and hereditary effects combined have been estimated to be 5.7 and 4.2% per Sv for the whole population and working population respectively.

Based on the new risk assessments, the Tissue Weighting Factors (WT) for specific organ/tissue are the fractional harm associated with the stochastic effect (gender averaged relative detriment) were also reviewed by the ICRP in ICRP-103. The important changes in ICRP-103 are the upgrading the value of risk for breast from 0.05 (ICRP-60) to 0.12 and for gonads, the WT was reduced from 0.12 (ICRP-60) to 0.08.

Conclusion

In-spite of the some changes in the nominal risk coefficients and in WT values, the total detriment remains close to 5% per Sv. In view of this, the dose limits for occupational and public exposures remain same at an average of 20mSv/y and 1mSv/y respectively as in ICRP-60 (1991).

ICRP - Statement on Tissue Reactions

As per the ICRP communication, it has approved “Statement on Tissue Reactions” in April 21, 2011. The effects of radiation which was called as deterministic effects previously are now referred as Tissue Reactions. Based on the data various aspects of the effects with very late manifestation such as cataract of the eyes, the threshold in absorbed dose is now considered as 0.5Gy.

Similarly, for occupational exposure in planned exposure situations the Commission now recommends an equivalent dose limit for the lens of the eye of 20mSv in a year, averaged over defined periods of 5 years, with no single year exceeding 50mSv.

The Commission continues to recommend that optimization of protection be applied in all exposure situations and for all categories of exposure, including patient’s exposure during some complex interventional procedures, With the recent evidence, the Commission further emphasizes that protection should be optimized not only for whole body exposures, but also for exposures to specific tissues, particularly the lens of the eye, and to the heart and the cerebrovascular system.

Spend national resources in proportionate to the risks. Say no for over-protection.

WHO report is sighted in Indian News Papers show that out of 57 million global deaths in 2008, 36 million deaths are due to non communicable diseases (NCDs) like cancer, stroke, diabetes and cardio-vascular diseases, and it is increasing! Assumed to be old-age diseases, the NCDs are now taking toll at younger ages (below 60 y) also. Cancer kills 7.6 million people a year; tobacco use kills about 6 million and alcohol 2.5 million a year.

Bhopal gas-leak tragedy, in the year 1984, killed over 3000 people, within days. In Chernobyl nuclear reactor accident, only 47 people died of acute radiation dose and fire burns. Some more may die of cancer over the years. Similarly, over 9000 people died of Tsunami in Japan and the on-going nuclear situation in Fukushima may also cause some fatalities over the years. These deaths are not due to acute radiation doses.

Over 1.5 lakh deaths a year are reported due to accidents on Indian roads. Today, while driving from Belapur, Navi Mumbai to Chembur (18 km), I met near-death situation on the road at least 5 times. This is not due to my fault but due to other’s faults such as: cutting lanes, drunken driving and three wheeler nuisance. Road discipline simply does not exist in Mumbai roads.

Under such scenarios, some vested interests and politicians are creating nuisance everywhere criticizing against developmental projects, particularly nuclear power plants at Jaitapur. Reason is safety! If they are so much concerned about safety, what they are doing about safety on the roads, high pollution levels, floods, crime, etc?

If one sees the risks in proper perspective, it is unimaginable to understand why the designers are spending so much money on safety in nuclear power plants? How many thousands are spend to save ONE life in nuclear power sector?

Let us spend our resources in proportionate to the risks. Say no for over-protection.

ICRP New publication - ICRP-113, 2009, Education and Training in Radiological Protection

Title: Education and Training in Radiological Protection for Diagnostic and Interventional Procedures, ICRP Publication 113, ICRP, Ann. ICRP 39 (5), 2009 - New Publication from ICRP

Abstract: In view of the increase in the number of diagnostic and interventional medical procedures using ionizing radiations, there is compelling need for education and training of medical staff (including medical students) and other healthcare professionals in the principles of radiation protection.

Based on the current ICRP basic recommendations (2007) for such education and training of these individuals, the ICRP is providing guidance through ICRP-113 regarding the necessary radiological protection education and training for use by various categories of medical practitioners and other healthcare professionals who perform or provide support for diagnostic and interventional procedures utilizing ionizing radiation and nuclear medicine therapy.

The publication is useful for regulators, health authorities, medical institutions, and professional bodies with responsibility for radiological protection in medicine; an the industry that produces and markets the equipment used in these procedures and universities and other academic institutions responsible for the education of professionals involved in the use of ionizing radiation in health care.

Advice is also provided on the accreditation and certification of the recommended education and training. The accredited organization is required to meet standards that have been set by the authorized body (based on ICRP News).

Important of Exclusion Zone in safety of public

Exclusion Zone is one of the five and the last barriers before radioactive releases from nuclear power plants reach the public domain. This is not a physical barrier. However, no permanent residence is allowed within the 1.6 km radius from nuclear reactor. This ensures significant dilution of an airborne radioactive release before it reaches any public habitation, thus reducing the resulting public dose. Radiation dose to the public at the distance of 1.6km is calculated for the releases during normal/abnormal working of the nuclear reactors, to check compliance with the regulatory limits for releases to the public domain.

Thus Exclusion Zone is an important barrier which has prevented large public doses during the on-going nuclear emergency situation at Fukushima nuclear power reactor in Japan.

In spite of the best possible design and safety records, accidents can still occur and hence the concept of defense-in-depth should never be compromised.

Uranium in drinking water and chemical toxicity

As per US-EPA (US-DOE, 2007) the maximum concentration level (MCL) in drinking water is 0.03mg/L or 27pCi/L for natural uranium. Level of 67pCi/L of natural uranium in drinking water is also suggested by some authors. It is assumed that 02 to 5% of the intake is absorbed in to the blood stream of which 22% is deposited on bone, 12% in kidneys and rest excreted. The uranium deposited in kidneys is excreted within few days. The mean U concentration in drinking water detected in some SU cities is 2.55 micro-g/L

WHO threshold value to prevent sub-clinical renal effects is 0.002mg/L.

The chemical toxicity value for soluble salts of uranium is 0.003mg /kg-day. This is the highest dose that can be taken every day, over a life time without causing adverse health effects. This is generated based on animal studies and normalized to humans using an uncertainty factor of 1000. Lowest observed adverse health effect is at an intake level of soluble uranium of 3mg/kg-day. Daily intake of uranium by adults (60kg) through air, water and food is 2.2 micro-g and total body burden of uranium in humans is 40 micro-g. At equilibrium, the excretion rate through urine is 4.4 micro-g per day.

In alkaline conditions in the kidney, uranium hydrogen carbonate complex is most stable and hence uranium is excreted out from the kidney. In acidic conditions the uranium (as uranyl ion) gets deposited in the tubular wall in the kidney. The most common renal injury caused by uranium in experimental animals is damage to the proximal convoluted tubules in kidney. Nephritis is the primary induced effect of uranium in humans.

The threshold uranium concentration for chemical toxicity is 1 micro-g/g of kidney tissue. For protection of the public, further safety factor of 10 is applied and values in the range of 0.1 to 0.3 micro-g/g of the tissue are reported as threshold limits for public by some authors.

Physical Barriers to Environmental Release of radioactive releases in case of reactor accidents: Defense-in-Depth concept

The following five barriers are built into the reactor design to prevent radioactivity escaping from the reactor to the public:

1. Ceramic Fuel - The ceramic uranium dioxide fuel in pellet form entraps most of the fission products generated due to the fission reaction in the fuel. These fission products would be released if the fuel were to melt. The fuel has a high melting point, but continuous cooling is required so that the fuel is not over-heated resulting in melting of the fuel. Another safety feature of the ceramic fuel is that it is relatively chemically inert with the heavy water coolant.

2. Fuel Sheath (cladding) - The fuel pellets are enclosed in a high integrity, welded zircalloy sheath. This sheath contains the gaseous and volatile fission products which escape from the pellets. The sheath is designed to withstand the stresses resulting from pellet thermal expansion, gaseous fission product build-up and external hydraulic pressure.

3. Heat Transport System Boundary - The high integrity pressure tubes, piping, and vessels contain most fission products escaping via sheath defects until they are removed via the coolant purification system.

4. Containment Boundary - This is designed to withstand the pressure surge of a worst case LOCA, with a small ‘puff release’ during the overpressure transient. Post LOCA containment venting via a filtered, monitored pathway minimizes the environmental radioactive release.

5. Exclusion Zone - No permanent residence is allowed within a 1.6 km radius from nuclear reactor. This ensures significant dilution of an airborne radioactive release before it reaches any public habitation, thus reducing the resulting public dose.

Inadequate fuel cooling due to cooling system failure, the situation which is prevailing now at Fukushima nuclear power reactor in Japanese, results in overheating of the fuel, with potential for large scale fuel failures. In the event of large scale fuel failures, at least two of the five physical barriers would be breached, i.e., the fuel and the fuel sheath. In the case of a LOCA, the third barrier, the heat transport system is also breached, leaving only the containment and exclusion zone barriers.

In the case of a LOCA coincident with containment failure (dual failure), only the exclusion zone would remain as a physical barrier. Thus, the Containment boundary is a very strategic defense-in-depth barrier to fission product release in to the public domain. .

Contamination of foods and feedstuffs by the nuclear disaster

The releases from the damaged reactors are contaminating food and feedstuffs in the nearby areas in Japan. Radioactive iodine will be seen quickly in the milk. As most of the radioactive particles may end up in the ocean it is imperious to avoid sea foods of any kind. Water sources are likely to be contaminated. The Japan government declared that the tap water in Tokyo is contaminated with radioactive iodine and is unsafe for infants.

Continuous monitoring for radioactivity of the food products, milk and drinking water is being done to ensure that the radiation exposure of the public does not exceed the acceptable limits prescribed by the WHO. Since some of the radioactive isotopes released are having half lives in years, the food chain safety will be compromised in the next decades by the situation in Fukushima.

The WHO guideline levels in drinking water, for the most predominant radio-nuclides, Iodine-131 and Cesium-137, in the releases from the reactors are: 0.01 Bq/mL. These guideline levels of radionuclides in drinking water were calculated on the basis of an annual dose criterion of 0.1 mSv (10mR) from drinking 2 liters of water per day. The average natural background radiation to which we are all exposed is 2 mSv in a year.

The International Atomic Energy Agency (IAEA) has also been monitoring the environment for radioactivity and radiation levels at the nearby areas from the Fukushima plant in Japan. As per IAEA update, the dose-rate results ranged from 0.8 to 9.1 micro-Sievert per hour. The beta-gamma activity contamination measurements ranged from 0.08 to 0.9 MBq per square metre.

The Agency continues to receive data confirming high levels of radioactivity (above permissible limits) in food, notably spinach, in samples taken from 37 locations in the vicinity of five cities south of the Fukishima site. Higher levels of both Iodine-131 and Caesium-137 have been measured by the Japanese authorities in milk, water, in spinach and some other fresh vegetables. In view of this, it is reported that distribution of food from the areas affected has been restricted. The Japanese authorities are monitoring the situation in the rest of the country.

Further radioactivity releases from the stricken reactors in to the environment should be controlled somehow to keep the public exposures as low as possible.

Radiation dose control from releases from “damaged” nuclear reactors

The recent nuclear crisis in Japan where four nuclear power reactors were damaged due to earthquake has raised questions with respect to the public exposures. In such accidental situations, the atmospheric releases from the damaged reactor core are mainly radio-nuclides in vapour form, such as of Iodine. Let us take an example of radioactive Iodine isotope, I-131.

The half-life - the time required for the radioactivity to reduce by one-half - for I-131 isotope is 8 days. Since the half life is considerably long, the isotope can travel long distances along the direction of the wind. On the way, the iodine isotope gets deposited on the soil, on water surfaces and on grass and “contaminates” them. Human consumption of such contaminated items results in radiation dose to the exposed population. Biologically, the thyroid hormone contains iodine in stable (not radioactive) form. If one is exposed to radioactive iodine, it will get uploaded into the thyroid and gets deposited there, giving radiation dose. Prophylaxis is a process where the thyroid is deliberately saturated by “stable” iodine and hence the uptake of “radioactive” iodine from the releases is minimized. A tablet of Potassium iodide/iodate (around 130 mg) is consumed, just before or just after the releases, for “blocking” the thyroid from radioactive iodine uptake.

In general, staying indoors, use of proper respirators and consumption of stable iodine tablets (if advised), reduces exposure of people from the atmospheric releases of radioactive isotopes/materials.

Public needs to be sensitized on this aspect for their protection.

ICRP Publication 104 (2007): Scope of Radiological Protection Control Measures

In this report, the ICRP recommends approaches to national authorities for their definition of the scope of radiological protection control measures through regulations, by using its principles of justification and optimisation. The report provides advice for deciding the radiation exposure situations that should be covered by the relevant regulations because their regulatory control can be justified, and, conversely, those that may be considered for exclusion from the regulations because their regulatory control is deemed to be unamenable and unjustified.

It also provides advice on the situations resulting from regulated circumstances but which may be considered by regulators for exemption from complying with specific requirements because the application of these requirements is unwarranted and exemption is the optimum option. Thus, the report describes exclusion criteria for defining the scope of radiological protection regulations, exemption criteria for planned exposure situations, and the application of these concepts in emergency exposure situations and in existing exposure situations. The report also addresses specific exposure situations such as exposure to low-energy or low-intensity adventitious radiation, cosmic radiation, naturally occurring radioactive materials, radon, commodities, and low-level radioactive waste.

The quantitative criteria in the report are intended only as generic suggestions to regulators for defining the regulatory scope, in the understanding that the definitive boundaries for establishing the situations that can be or need to be regulated will depend on national approaches (From ICRP Site).

The ICRP draft report on Early and late effects of radiation in normal tissues and organs----at its site for comments

The International Commission on Radiological Protection (ICRP) invites comments on the draft document: “Early and late effects of radiation in normal tissues and organs: threshold doses for tissue reactions and other non-cancer effects of radiation in a radiation protection context” which can be downloaded through the consultations page of the ICRP web site. The last date for receiving the comments is April 1, 2011.

This radiation protection related draft report provides a review of early and late effects of radiation in normal tissues and organs considering recent advances in the scientific results. It follows the ICRP Publication 103, and provides updated estimates of dose responses and threshold doses for tissue reactions (deterministic effects). Estimates are given for morbidity and mortality endpoints in all organ systems following acute, fractionated or chronic exposure.

In light of the new information, ICRP may consider how best to manage and control exposures to ionizing radiation to protect human health with respect to certain tissue reactions

ICRP Committee 4 meeting

Committee 4 of the International Commission on Radiological Protection (ICRP) met in Geneva, Switzerland, from 15 to 19 November 2010. The meeting was hosted by the World Health Organization headquarters (WHO) which is an official observer organization to ICRP Committees.

The Committee devoted significant time to further clarifying how the basic radiation protection principles and the dose criteria recommended in the new recommendations of the Commission apply to protection of the public and workers according to the three exposure situations defined in Publication 103, i.e. planned, existing and emergency exposure situations.

The Committee also reviewed several draft reports under preparation:

• Protection against enhanced exposure from industrial processes using NORM, prepared by Task Group 76 chaired by Peter Burns (Australia)
• Protection in disposal of long lived solid radioactive waste prepared by Task Group 80 chaired by Wolfgang Weiss (Germany)
• Protection against radon exposure prepared by Task Group 81 chaired by Jean-François Lecomte (France)
• The ICRP approach to integrate human and environmental protection prepared by the joint Committee 4 – Committee 5 Task Group 82 co-chaired by Jan Pentreath (UK) and Jacques Lochard (France)

The Committee also discussed the general orientation to be given to Task Group 83 on the protection of aircraft crew from cosmic radiation exposure chaired by Jacques Lochard (France). The next meeting of the Committee will take place in Bethesda, Maryland, USA, from 24 to 28 October, 2011 (Extract from ICRP Site).

Exposure to radiation from mobile phones and towers

Bloggers like me have been relentlessly calling attention of the authorities to the health effects of exposure from radiation from the cell phones. Like most us, endocrinologist Dr. Shashank Joshi also says the mobile phone should be used only as an emergency toll to pass on messages. Some reports say that the mobile phones can cause cancer. This is over-exaggeration. Cancer is a multi cause disease with a latency period of 10 to 30 year after exposure. Nobody can say for sure that the EMF radiation exposure can cause cancer.

Mobile towers are particularly more dangerous due to the emission higher levels of EM radiation for 24x7 basis. Ideally, the towers should be put up at a sufficient height away from populated areas. The guidelines specified should be followed by the service providers. Instead of erecting separate towers, the existing towers should be shared by the service providers. The city areas should be monitored frequently by the designated agencies to ensure that the levels are below the prescribed guidelines. Specific Absorption Rate (SAR) values of mobile phones should be displayed continuously on the screen to caution or alert the user in case of any over-exposure. Keep the mobile phones away from the children.

As regards to the standards, India also should follow the International Standards Specified by International Commission for Non-ionizing Radiation (ICNIRP), a non-governmental expert body to recommend permissible limits for exposures to non-ionizing radiations such as electromagnetic radiation. The guidelines are based on science and should be respected by one and all.

Mobile phones - a health risk

Finally, the much awaited report from the India Government Inter-ministerial Panel’s study is out. Radiation from mobile phones and towers poses serious health risks, says the Panel. The study also attributed disappearances of bees, insects, sparrows and butterflies from cities for the EMF radiation emission from the towers. The reported health risks are memory loss, lack of concentration, sleep disruptions, etc. The eight-member panel recommended that mobile phones not adhering to the international standards be barred. It is also recommended that mobile towers should not be installed near high density residential areas, schools, hospitals, etc.

Precautions: Use wireless hand-free system, keep your calls short- use for sending messages only and do not use mobile phones for gossip and long chats. Do not give mobiles to children. They are more sensitive to radiation.

Note: There are many posts in this blog since last two years calling authorities to take urgent action against this public health concern.

Handle radioactivity carefully and not fearfully

Half-life is a term used to express the rate at which a given radionuclide gives up its radioactivity. With time, the radioactivity comes down, but not the mass. More or less, the mass of the radioactive material remains the same even after very many years of radioactive decay. And Specific Activity is the term used to express the quantity of radioactivity per gram of a material.

Take an example of a source of Cobalt-60 (Co-60). The source is generally used in gamma irradiators/chambers used in industry and medicine. The half life of Co-60 is 5.27 years. This means, in 5.27 years the radioactivity of the source reduces by one-half. The mass of the source remains the same. A typical irradiator source of strength 1000 Curie (Similar to sources recovered in Mayapuri, Delhi) will give gamma radiation dose rate of 13.25 Gray per hour. After say, 25 years of decay, the dose rate of the source will reduce to 0.4 Gray per hour. If some one is exposed to this source (the so-called decayed source) for about 10 hours, the person is likely to get dose of 4 Gray which is in the range of Lethal dose -50 (LD-50).

Lethal dose – 50/60 means, if 100 people are exposed to the dose of 4 to 5 Gray, 50 persons will die in 60 days’ time after the exposure.

That is precisely the reason why the “decayed sources” just lying in some cup-boards in laboratories or in hospitals for over 25 to 30 years can still be dangerous and can deliver fatal doses if the sources are not properly shielded, or not handled with care. The decayed sources should be disposed off by strictly following the procedure suggested by the national regulators. In India, the regulator is Atomic Energy Regulatory Board (AERB), located at Anushaktinagar, Mumbai, 400094.

Handle radioactivity carefully and not fearfully.

Handle radioactivity carefully and not fearfully

Half-life is a term used to express the rate at which a given radionuclide gives up its radioactivity. With time, the radioactivity comes down, but not the mass. More or less, the mass of the radioactive material remains the same even after very many years of radioactive decay. And Specific Activity is the term used to express the quantity of radioactivity per gram of a material.

Take an example of a source of Cobalt-60 (Co-60). The source is generally used in gamma irradiators/chambers used in industry and medicine. The half life of Co-60 is 5.27 years. This means, in 5.27 years the radioactivity of the source reduces by one-half. The mass of the source remains the same. A typical irradiator source of strength 1000 Curie (Similar to sources recovered in Mayapuri, Delhi) will give gamma radiation dose rate of 13.25 Gray per hour. After say, 25 years of decay, the dose rate of the source will reduce to 0.4 Gray per hour. If some one is exposed to this source (the so-called decayed source) for about 10 hours, the person is likely to get dose of 4 Gray which is in the range of Lethal dose -50 (LD-50).

Lethal dose – 50/60 means, if 100 people are exposed to the dose of 4 to 5 Gray, 50 persons will die in 60 days’ time after the exposure.

That is precisely the reason why the “decayed sources” just lying in some cup-boards in laboratories or in hospitals for over 25 to 30 years can still be dangerous and can deliver fatal doses if the sources are not properly shielded, or not handled with care. The decayed sources should be disposed off by strictly following the procedure suggested by the national regulators. In India, the regulator is Atomic Energy Regulatory Board (AERB), located at Anushaktinagar, Mumbai, 400094.

Handle radioactivity carefully and not fearfully.