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NEED FOR SIRADS
Need for SIRAD: Ionizing radiation such as X-ray and neutrons need to be monitored because they can cause cancer. TLD (ThermoLuminescence Dosimeters), film (silver halide based X-ray film) and OSL (Optically Simulated Luminescence) are most widely used for monitoring personal exposure to radiation. TLD and OSL can monitor radiation over a very wide range, e.g., 0.1 mrem – 1,000 rem. For a tissue equivalent material 1 rem = 1 rad. However, they are not instant and self-reading. They need to be sent to a laboratory/vendor for determination of the dose, which may take days. Electroscope or ionization camber dosimeters, often called quartz fiber dosimeters are instant and self reading but they are the most fragile dosimeters. There are small electronic dosimeters but they are expensive, need batteries and are not resistant to severe conditions, such as very high or low temperatures and water (e.g., laundry cycle). Hence, there is a need for a dosimeter, especially when the threat of radiological terrorism is high, which is (1) instant, (2) simple and self-reading, (3) light weight that can be carried with us all the time, (4) inexpensive and disposal, (5) practically non-destructible, (6) can withstand severe ambient and environmental conditions such as laundry cycle, (7) tamper resistant and evident, (8) does not need any external power, such as a battery, (9) integrates the dose for at least one year, (10) tissue equivalent so no dose correction required, (11) retains the dose and the results/dose can be archived, (12) monitors wide dose range (1 – 1,000 rads) which is harmful, (13) monitors all kinds of harmful radiation, such as X-ray, neutrons and high energy electrons over a very wide temperature range (e.g., -20oC to 60oC), and (14) independent of energy and dose rate. SIRADTM family of dosimeters are such dosimeters.
Objective of Monitoring Hazardous Agents: We are exposed to a wide variety of toxic chemicals and biological agents, through air, water and food which are hazardous to our health, e.g., can potentially induce cancer. Our exposure to these hazardous agents is usually at very low levels. These agents at low levels of exposure either cause little harm to us or the harm is within the acceptable risks. Hence, they are not monitored. However, when the exposure level is expected to be high, which exceeds the acceptable risks, toxic chemicals and biological agents are monitored. It is clear that we need to monitor a hazardous agent when it exceeds the acceptable risks.
There are selective detectors/monitors for monitoring exposure to some individual hazardous chemicals and biological agents. As we are exposed too many hazardous chemicals and biological agents, it is not possible to monitor them individually. However, it is possible to monitor radiation selectively. Typically, we monitor exposure to radiation way below the acceptable risks. Should we not use a dosimeter which instantly monitors hazardous dose so preventive measures can be taken?
Radiation Hazard: There is no doubt that radiation can cause cancer. The question is what level of radiation it takes to cause cancer. Some believe that this low level is about 20 rads. Below this dose it is not possible to detect adverse health effects. The Health Physics Society has issued a position statement: There are no observable health effects below 10 rem but that health risks, if they exist below 10 rem, are too small to be observed. (Note: 1 rem is almost equivalent to 1 rad for tissue equivalent materials). However, the data suggest that risks in the 15-20 rem dose range are very small and difficult to measure. Above 10 rems, there appears to be a significant risk of thyroid cancer due to radio-iodine exposure in children, 15 years of age and younger. The general consensus of opinion for the radiation induction of cancer is 10% increase in cancer rate/100 rem when the dose is given over a short time with a decrease to 5% when the dose is protracted over an extended time period. This raises an interesting question; what dose range is more important to monitor, low dose (1 mrem to a few rems) which is not harmful to us or high dose (1 – 1,000 rems) which could harms us?
Dose range to be monitored: Tens of millions dosimeters, such as TLD, OSL and film are used for monitoring low dose every year. We believe that only a very tiny fraction of a percent of OSL/TLD/film badges users are exposed to one rad or above during the monitoring period, usually three months. Even if a person is exposed to a high dose (e.g., above 1 rad), it takes days for users of OSL/TLD/film badges to know their exposure. Out of those who receive high dose, e.g., between 1 and 5 rads per year or per incidence, how many are given any special medical treatment for the exposure to high dose? In addition to the conventional low dose, what we need to monitor is (1) high dose instantly and (2) legally allowed dose, e.g., 5 rads/year or 25 rads for the life time for nuclear/radiation workers. What is required is to monitor harmful high dose instantly and total dose per year and/or life time.
Best Alternative: Instead of using only SIRAD or TLD/OSL/film dosimeters, it is better to use both the dosimeters. SIRAD being light weight, which can also be in form of a tape or sticker (RADStick-on or Stick-on SIRADTM), can be applied on the top or back of a TLD/OSL/film or other dosimeters/detectors. As stated above, SIRAD has the most of the desired properties to monitor an accidental high dose (higher than 1 rad) instantly.
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