Relative Biological Effectiveness - What Kind of Radiation is the Most Risky?

As you read this right now, you are being bombarded by radiation – cosmic rays flying in from the dark reaches of space, photons streaming out of the hot core of the earth, and miniscule particles issuing from your computer and other objects around you. But not all radiation is created equal. A new field of study has unearthed the fact that different kinds of radiation affect us differently.  

Although quite a mouthful, this study is called Relative Biological Effectiveness (abbreviated RBE). It seeks to put all radiation on an equal plane and find out what kind poses the highest risk to our organism. Higher values of RBE mean that certain types of radiation are more harmful. Ionizing radiation, which is made up of alpha, beta, and gamma rays, constitute electrically charged particles that interact with matter. These interactions can cause ionization, which refers to changes within the structure of an atom that can cause it to destabilize or behave differently.

Alpha particles are the largest kind of ionizing radiation, each consisting of two protons and two neutrons. Because they are highly charged and quite large, they are quickly stopped by as little as 4 cm (1.4 inches) of open air or a sheet of paper¹. Beta particles are much smaller, meaning they can penetrate further: through 9 meters (19 ft) of open air or 11 mm (.4 inches) of body tissue. Gamma rays are high-energy photons, meaning that they penetrate much further and interact differently with matter than alpha or beta particles. Thick, dense materials such as lead are necessary to block gamma rays. Another related form of radiation is neutron radiation, which is commonly referred to as indirectly ionizing radiation. Free neutrons, which are emitted from nuclear materials such as uranium and plutonium, have about a quarter of the mass of an alpha particle². Neutrons are not charged but readily cause ionization by knocking away electrons or slamming into atomic nuclei. The neutral charge of these fast-traveling neutrons also allows them to penetrate much further into most materials than other types of ionizing radiation, even through many feet of concrete.

Source: American Nuclear Society

 To test how damaging different types of radiation is on the human body, scientists expose living tissue to equal amounts of energy from each type. Surprisingly enough, scientists have found that beta and gamma radiation are nearly equally damaging, so the RBE value of beta and gamma radiation is 1. It gets more complicated from here, though. Alpha and neutron radiation have different RBE values depending on what kind of cells are exposed to them. The RBE for bacteria is 2-3, but can be 6-8 for more complex cells like those found in the human body. This means that a certain amount of alpha radiation is 6-8 times more damaging then the same amount of beta radiation. Neutrons are even more damaging with a RBE of 4-6 for bacteria and 12-16 for complex cells³.  

The high RBE values of alpha and neutron radiation should make us think twice about how we deal with these types. Because incoming alpha particles are stopped by a single layer of skin, they can’t do much damage unless they get in our bodies. That’s why breathing in alpha radiation (from radon or radioactive dust) or ingesting it (in contaminated food or water) is so dangerous. When alpha particles get to really important cells in our organs, the RBE can shoot up: scientists have measured RBE values of 1,000 for alpha radiation inside hamsters⁴. Neutron RBE values are more constant because neutrons penetrate just about everything, but they are also much harder to contain. That’s why materials that emit neutrons are highly controlled, very hard to transport, and large neutron sources are only found in research facilities and power plants.

The Rad-ID device by D-tect Systems has a special way of finding neutron radiation. A container filled with Helium-3, a rare and stable gas, is included with other radiation detectors inside the Rad-ID. As neutrons shoot through the detector, they collide with some of the He-3 atoms, causing them to change into charged particles. These particles are quickly identified and counted by a detector and a measurement of this radiation is sent to the user. Since neutron sources give off varying levels of gamma radiation, the Rad-ID can also identify these materials and let the user know what they are dealing with.

The Rad-ID can detect neutron radiation sources.

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D-tect Systems is a supplier of advanced radiation and chemical detection equipment sold around the world. www.dtectsystems.com.

  

Radioactive Fossils!

Last week one of our engineers took a trip down to Moab, Utah which is about a 4 hour drive south from our facility. For those of you who have never visited southern Utah, Moab is a world-famous mountain biking destination. It’s also known for dinosaur bones – the bright red sandstone in the area has produced some amazing ancient remains. While checking out one of the shops in town, our engineer noticed that the MiniRad-D (a portable radiation detector) he brought with him alarmed when he passed a row of fossils. I was surprised to find that this isn’t an anomaly: fossils often have radiation levels much higher than the environment around them. Robert Bekker, a world famous paleontologist, referred to this phenomenon when he said "you wouldn't want to leave some bone fragments in your pocket all day long."

An enthusiast checks the radiation levels of a dinosaur bone near Denver (source).

So why are fossils so ‘hot’? The reasons for this are not completely known, but one possible reason is that naturally-occurring radiation tends to concentrate in the living tissue of plants and animals. This is especially true with ocean-dwelling creatures such as shellfish and snails. Particles containing  isotopes such as U-238 and Th-232 and other isotopes often coalesce on the seafloor where the living organisms are exposed to them. Over long periods of time, the collected isotopes decay into other radioactive isotopes, making even small concentrations stand out. Also, In a process known as permineralization, living materials are replaced at times by deposits of denser materials with greater concentrations of radioactive isotopes.

These concentrations are usually fairly low, however, and it’s easy to see why people miss them. There’s often no visual difference between a rock containing a fossil and other ancient rocks. And because Geiger counters respond slowly to radiation, they would be ineffective at finding radiation at such low levels unless the operator knows what they are looking for. Scintillation detectors like the Cesium Iodide crystal used in the MiniRad-D will have a much better chance of finding these materials because they react quickly to radiation and can be up to 100 times more sensitive to radiation.

Also found in southern Utah, this rock contains measurable levels of Th-232.

Has anyone else had luck finding fossils or bones with a radiation detector? All this talk has made me want to get out into the late-spring sunshine and go searching. Who knows how many hot dino bones are still down there?  

D-tect Systems is supplier of advanced radiation and chemical detection equipment sold around the world. www.dtectsystems.com.

Radiation Contamination in Food and Water: What's the Risk?

As Japanese emergency workers continue to pump out thousands of gallons of contaminated water from the damaged reactors of the Fukushima Power Plant, radiation contamination in food and water has emerged as a new focus of the international media.  

Before explaining the risks of food and water contamination, it’s important to understand the difference between radiation exposure and radiation contamination.  The United States Center for Disease Control (CDC) defines exposure and contamination with the following:

A person exposed to radiation is not necessarily contaminated with radioactive material. A person who has been exposed to radiation has had radioactive waves or particles penetrate the body, like having an x-ray. For a person to be contaminated, radioactive material must be on or inside of his or her body. A contaminated person is exposed to radiation released by the radioactive material on or inside the body. An uncontaminated person can be exposed by being too close to radioactive material or a contaminated person, place, or thing.”

Source: U.S. Department of Health

As the CDC implies, there are many ways that radiation can enter the body for contamination to occur.  Radioactive materials that enter into digestive tract can do damage while they reside in the body, but most of these materials pass through quickly. Radiation that gets trapped in other areas of the body, such as radioactive dust being breathed in and lodged in the lungs, can cause serious threats because the longer the radiation resides in the body, the more harm it can do.

So what are levels of radiation we actually need to worry about in food or water? The unit of measurement used for quantifying radiation in food and water is the Becquerel (Bq) and defined as the activity of a radioactive material in which one nucleus decays per second. More dangerous sources of radiation give off higher readings, and amounts decrease as radioactive isotopes decay. The Becquerel is a very small quantity of radiation; the human body itself produces over 4000 Bq per second. The standards set by the United States Food and Drug Administration (FDA) for food and water is about 375 Bq/lb (170 Bq/kg).

Recently Japan reported a reading of 463 Bq/lb (210 Bq/kg) in Tokyo’s tap water, leading to widespread fear and a government advisory against giving tap water to children (who are more susceptible to radiation and have lower exposure limits). Since this incident, the radiation in Tokyo’s tap water has returned to safe limits. Radiation in food has also been a problem, especially since much of the Fukushima Prefecture near the crippled nuclear plant is dedicated farmland.  Widespread bans have gone into place on the sale and consumption of crops from affected areas, as well as seafood caught in the ocean near the plant. Much of the radiation present in the contaminated food and water is Iodine-131, which has a half-life (meaning that half of a quantity of the material has broken down and is not longer radioactive) of only 8 days. This means that this type of radiation won’t be around for long, but the fear of radiation is more likely to hurt the Japanese economy as buyers shy away from food that they think might still have some contamination.

Source: Associated Press

Although the fear that Japanese radiation in dangerous amounts will end up in other countries is often unfounded, we can’t let down our guard just yet. Japan provides 4% of US food imports, including many seafood products that can have concentrated levels of radiation, such as shellfish and seaweed.

So how can we assure that our food and water is contamination free? Finding trace amounts of radiation in food and water is often difficult because products are usually shipped in large containers that shield radiation. Common radiation detectors such as Geiger Counters just aren’t sensitive enough to detect radiation at these levels. The FDA works to safeguard our food supply by using the MiniRad-D, a hand-held radiation detector, to search for radiation. The MiniRad-D uses a scintillation detector, which is over 100 times more sensitive than a Geiger counter, and because it can pick up radiation from tens of meters away, it can be used to scan whole containers of food at once. 

The MiniRad-D radiation detector

The procedure of scanning food is becoming increasing popular as Japan increases its exports. According to a recent New York Times article, even some fish markets and high-end restaurants have begun radiation detection procedures to ensure the safety of their customers. Knowing for sure that food and water is clean is a big draw for these businesses as Japan’s nuclear clean-up continues to make headlines.

So, although the direct danger of radiation contamination in food and water is very low, the effects of the nuclear crisis are sure to be felt for years to come. And as many companies involved with food imports are discovering, peace of mind is not only attainable, but extremely valuable. With the right equipment, good information, and correct procedures, this peace of mind is truly available to everyone.

D-tect Systems is supplier of advanced radiation and chemical detection equipment sold around the world. www.dtectsystems.com.

 

Radiation Exposure: What Can I Do?

Experiencing the front line of a crisis is a terrifying experience, especially in the face of uncertainty and fear of the unknown.  This point is especially well illustrated in Japan’s ongoing nuclear crisis.  For over a week now, rescue workers in Japan have dealt with floods, fires, power outages, and infrastructure damage, all compounded with the threat of an escalating nuclear crisis.  Radiation levels are at elevated levels for miles around the Fukushima Dai-ichi nuclear complex and scientists are scrambling to determine how much radiation has already been released into the environment.  In the interest of providing a little peace of mind to security personnel across the globe whose line of work brings them into contact with critical situations, we have a few basic suggestions on how to avoid radiation risks.

The way the public views radiation has been shaped by some of the most horrific incidents in modern history: Chernobyl and Hiroshima.  These extreme cases have influenced many to assume that radiation is an exotic and deadly phenomenon.  In reality, our environment is steeped in radiation that our bodies absorb without any proven ill effect.  The most important factor in understanding the impact of radiation is quantity – how high radiation levels are and how these levels translate to risk. 

Security personnel are key and assist as the first line of defense against these varying dangers of radiation.  Organization is extremely important in crisis situations, and even just a few informed individuals can drastically change the outcome of a hazardous situation.  Security personnel have to act quickly to mitigate and ascertain the amount of radiation in the environment.  Two tools that are absolutely essential to security personnel in a radiation crisis are the dosimeter and radiation detector. 

A dosimeter is a small badge worn on the body or a small handheld device used to measure how much radiation the person has been subjected to.  Security personnel are often exposed to more radiation in their line of work, and must carefully monitor their dosimeters to tell them when they are approaching risk levels and must leave the danger area.  To give some idea of safe radiation levels, natural background radiation – the radiation that we are exposed to every day from cosmic rays and naturally-occurring radioactive materials – is about 370 millirems per year in the United States.  A coast-to-coast airplane trip will expose you to about 12 millirems, and a year of watching four hours of television per day adds up to about 2 millirems.  These quantities are miniscule compared to a federal occupational limit of exposure at 5000 millirems per year. Children and pregnant women have much lower exposure levels, and very high levels of radiation can cause serious health risks in a short time. 

Radiation detectors are indispensable to security efforts because they allow personnel to find contaminated areas and people quickly.  A common detector that has been used in the past is a Geiger-Mueller detector, or a Geiger counter. A Geiger counter is a very low cost detector, typically less than $500 USD, and provides very basic detection of large levels of radiation. However, they have significant limitations in a radiation crisis including limited to no detection of lower levels of radiation that can still be dangerous, as well as slower response time. One of the best detection technologies on the market is called a scintillation detector.  These detectors, on average, are 100 times more sensitive than Geiger counter and respond more rapidly to radiation, usually within one second, and typically cost around $1,200 USD.  The much greater sensitivity of scintillation detectors is important in situations like the Japanese nuclear crisis because the heightened environmental levels of radiation in the ocean near the complex (which are 127 times normal background levels) would not even show up on a typical Geiger counter.  The information scintillation detectors gather from radiation can even be used to identify different radioactive isotopes.  Devices such as the D-tect Systems MiniRad-D (a personal handheld detector) and Rad-ID (a handheld radiation detector and identifier) and regularly used by security personnel and individuals in such situations to detect and, where necessary, identify the types of radioactive materials a person has been exposed to.

The procedures outlined by government agencies are carefully adapted to each dangerous situation and should be strictly adhered to.  These procedures aim to limit the spread of radiation and minimize risk to exposed areas.  Although the specific instructions given out for each incident vary, here are a few general guidelines that should always be followed. 

First, in case of radiation contamination, get people (including yourself) out of harm’s way as quickly as possible and notify authorities. Radiation spreads easily though blowing dust and smoke, so radiation-free secure zones must be established by sealing off areas from the outside environment by closing and weather-proofing doors and windows and placing food and water in well-insulated areas such as basements.

Second, since human skin generally acts a good barrier against low-level radiation, the biggest threat is breathing in radioactive materials or somehow ingesting them.  Make sure to wear a face mask in areas that may be contaminated and wash hands regularly.  If you suspect someone has been exposed to radioactive dust, the best solution is usually as simple as discarding contaminated clothing and washing with soap and water, as this will rid the body of radiation before it can cause damage.  As an additional guard against significant amounts of radiation, potassium iodide tablets are sometimes given to protect to the thyroid gland.

Third, preparation is vital when it comes to any kind of disaster, and we recommend everyone keep an emergency kit close at hand so that they can be personally prepared in case of any crises.  This kit should include such things as food and water for a few days, water filtration kit, emergency blanket, rain gear, batteries for radios and detectors, dust mask, extra clothing, flashlight, candles, waterproof matches, cooking utensils, necessary medications, and a first aid kit.  Although we generally take these supplies for granted, shortages can occur quickly in crisis situations.   

Although the current nuclear crisis is fraught with unanswered questions, appropriate preparation will enable you to minimize potential risks and provide you the ability to safely navigate through any crises, including potential radiation exposure.

Japan's Nuclear Crisis

Last week one of the largest earthquakes on record shook Northern Japan and triggered a devastating tsunami.  The damage is extensive: so few roads and runways are open that even humanitarian supplies have been seriously delayed.  But the greatest fear of the country isn’t the washed out roads or flattened villages.  It’s an invisible phenomenon with huge historical significance to the Japanese: the threat of nuclear radiation is rising like a ghost recalled from the past.

Nuclear power doesn’t make many headlines these days.  Until last Friday, nuclear plants have been considered in many parts of the world to be the best economical solution to growing power needs.  Japan has 55 nuclear reactors, providing approximately a quarter of the country’s power.  Advancing nuclear technologies have made power more efficient and seemed to invalidate radiation risks illustrated so horrifically by incidents at Chernobyl and Three-Mile Island.  But it is clear that innate nuclear power risks, however diminished, remain.

Japanese security personnel at the nuclear complex.  Photo credit cnn.com.

 The setting for the nuclear showdown in Japan is the Fukushima Dai-ichi nuclear complex.  Although this reactor, as well as two others, ceased operations as soon as the magnitude 9.0 earthquake hit, consequent damage to the structure has destabilized the normal cooling operation of the plant and lead to an atomic crisis.  Three hydrogen gas explosions have already rocked the plant, providing evidence that the fuel rods are at above normal temperatures.  Japanese authorities have already announced that steam from a nuclear cooling pond (used to cool the fuel rods) has been released into the atmosphere, meaning that some radiation has already leaked from the plant.  At this point, quantities of released radiation are unknown, but could rise dramatically if cooling of the reactor core is unsuccessful or a breach in the reactor wall occurs. 

But what is the real danger of nuclear radiation?  Unlike other forms of radioactive materials, such as those used commonly in hospitals and industry, nuclear materials are very heavily controlled throughout the world, and for good reason.  Nuclear materials, such as plutonium and uranium, give off neutrons at extremely high energy levels as their nuclei decay.  This kind of radiation easily passes through most matter, but can affect body tissues enough to cause serious medical problems. Short-term nuclear exposure can cause infections, hair loss, and fevers, and in extreme cases, organ failure and death.  Long-term exposure can cause cancer, tumors, and genetic damage.  Even shielded nuclear radiation sources can emit gamma radiation, which brings other health risks. 

The nature of this nuclear crisis, as well as many related scenarios, requires the use of a combination of radiation detectors all working together to minimize risks.  Our products are designed for just this.  In case of a radiation release, a perimeter could be set up using small, handheld MiniRad-D devices.  These pager-sized radiation detectors can sense radiation from tens of meters away.  The MiniRad-D could also be used to check personnel leaving the nuclear zone to determine if decontamination is needed.

The MiniRad-D is self-calibrating and uses a high-sensitivity scintillation detection system.

 The Rad-D unit is ideal for placement in unmanned locations to monitor ambient changes to radiation levels.  The system requires no maintenance and sophisticated neutron detectors can be configured into the system as well as gamma detectors. 

At the forefront of the crisis, specialized equipment designed for finding and identifying the type of radiation is needed.  The high-energy nature of nuclear radiation tends to saturate detectors and is hard to differentiate from gamma radiation.  Special neutron detector systems, such as the Helium-3 gas-filled tubes used by D-tect Systems in both the Rad-ID and Rad-D systems, sort out gamma rays and detect and identify neutron radiation.  The Rad-ID also contains a combination of detector types to find radiation over a wide range of energies, and from large amounts of radiation to sources emitting just above background radiation.

The Rad-ID can identify over 110 radioactive isotopes.

 We hope for the best in the Japan’s current nuclear crisis and that future wise decisions will mitigate the risks involved with nuclear power.