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 Half-Life: How Long Will It Last?

Although it seems like this post should include some commentary on zombies or video games, we’re going to focus on the term ‘half-life’ as it’s used in physics, this time. The reason for this is that important research has been published last month on geothermal heat produced by radioactive decay. 

But before all that complicated stuff let’s start at the beginning. ‘Half-life’ is actually shortened from ‘half-life period’ which refers to the time in which exactly half of a radioactive substance decays. This measurement is especially useful because radioactive materials decay exponentially – meaning that they decay much more quickly at first than later on, where the decay process drags on more slowly.  This decay rate is directly connected to the rate at which radioactive materials emit radiation.  

Let’s take iodine as an example. I-131 has a radioactive half-life of just over 8 days and gives off both alpha and beta radiation (for a discussion of these radiation types see this post). As I-131 atoms give off radiation they transform into atoms of Xe-131, a stable (and non-radioactive) isotope¹. That means if you start with a pure sample of I-131, after 8 days about half of the sample will be I-131 and half will be Xe-131. If you wait another 8 days, 1/4 of the sample will be I-131 and 3/4 will be Xe-131, and so on. As you may expect, the sample of I-131 will emit much more radiation right at first versus many days later on, when the majority of the sample is Xe-131. 

 Not all materials have a half-life short enough to notice. In fact, the half-lives of radioactive materials can vary from fractions of a second to billions of years. These differences lend themselves to varied applications. Isotopes with short half-lives (such as I-131, Tl-201, In-111, and Tc-99) are commonly used in medical imaging and therapy because they show up clearly in the body and become non-effective quickly so that the patient is not exposed to too much radiation². Isotopes with long half-lives (such as U-238, C-14, and K-40) are often used in radiometric dating, where scientists can measure the abundance of these isotopes in various materials to determine their age³.

Newly published research⁴ from Japanese and Italian scientists also suggests that over half of the internal heat produced by the earth is caused by long-lasting radioactive materials such as thorium, uranium, and potassium – a quantity that adds up to nearly twice as much energy used annually by everyone on the planet⁵. The fact that radioactive materials are responsible for the heat is important because it helps to explain why our earth is hot enough to produce volcanoes, mountain ranges, and general plate tectonics while other planets in our solar system have long since gone cold. The geothermal heat of our planet isn’t going to cool soon either, thanks to the fact that the isotopes producing the heat have half-lives of billions of years.    

So although the adage “all good things must come to an end” (and all bad ones, too!) may be a great application to radioactive materials, there’ll be plenty of radiation and geothermal heat for years to come.

1)http://epa.gov/radiation/radionuclides/iodine.html

2)http://www.world-nuclear.org/info/inf55.html

3)http://www.world-nuclear.org/info/inf55.html

4)http://www.eurekalert.org/pub_releases/2011-07/dbnl-wkt071311.php

   5)http://www.scientificamerican.com/blog/post.cfm?id=nuclear-  fission-confirmed-as-source-2011-07-18   

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

Isotope Identification: How Does it Work?

Although we can’t feel, see, or hear it, we live in a sea of radiation. Cosmic rays from outer space continually bombard our planet, natural radioactive materials produce a steady stream of radiation, and many man-made materials constantly emit radiation in our homes and vehicles. Although much of this radiation is weak and harmless, there are some sources, as well as elevated radiation levels, that are best avoided. This is the reason that isotope identification is so important.

The term isotope is often misunderstood: not all isotopes emit radiation. Rather,  the term isotope has to do with the number of neutrons in the nucleus of an atom. Each element is defined by a set number of protons (or atomic number), by which it is listed on the Periodic Table. Iodine, for example, has 53 protons. But there are different versions or isotopes of iodine with varying numbers of neutrons, which are denoted in the isotope name. I-127 is the most common isotope of Iodine and is stable, meaning that its atoms don’t give off radiation or change to other isotopes.  But I-129 and I-131, which are produced in nuclear processes, are unstable and give off radiation that can be dangerous.

Isotope identification consists of finding out which radioactive isotopes are responsible for radiation. It is possible to figure this out by closely measuring the energy levels of radiation. Each radioactive particle or photon has a certain energy level, and each radioactive isotope emits a different set of energy levels. For example, here is a radiation measurement taken by a Rad-ID device:

Isotope Identification from the Rad-ID

As you can see, there are two energy peaks (at 25 keV and 88 keV) shown on the graph.  These two peaks appear because the isotope gives off a higher percentage of 25 keV and 88 keV radiation than radiation at other levels. By matching these measured energy peaks to pre-programmed energy peaks for known radioactive isotopes, isotope identifiers can narrow down and found out which isotopes are emitting the radiation.

There are a few difficulties that occur in the isotope identification process. First, no matter how well a radiation reading matches the pre-programmed energy levels, there is always at least a slight chance of an incorrect identification. This probability grows dramatically if the measured radiation levels can’t be matched very well. This is why it’s important to understand how good the match is and if there are lots of isotopes involved. Confidence bars can help out with this. Another problem is shielding. These two pictures show measurements an unshielded source on the left and a shielded source on the right:  

If you look closely at the two pictures you'll notice that a large energy peak on the left side of the first  (unshielded) reading is missing in the second. This  happens because shielding tends to block high-energy photons much better than the low-energy ones, which penetrate better. This can drastically change the shape of radiation measurements, and with enough shielding, completely block the radiation.

Measuring energy levels precisely enough to make an identification takes a very specialized instrument, different than a normal radiation detector. Identifiers usually have a LaBr3 or CZT detector, as does the Rad-ID.  These detectors are much more accurate than other types of radiation detectors. The Rad-ID also uses a large scintillation detector (NaI(Tl)), a Geiger-Mueller detector and an optional He3 tube to find a wide range of gamma and neutron radiation. In fact, the Rad-ID can identify 107 different radioactive isotopes, even if a measure sample is reading radiation from several isotopes.

With a good isotope identifier, you can be sure that you know what isotopes are in the environment and if you need to worry about them.

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

Protecting the Public from a Nuclear Power Plant Radiation Leak

How can you feel safe? How much warning will you have?

The ongoing battle to control the reactors at the Fukushima Nuclear Plant is terrifying to follow, but also leads millions that live near nuclear power plants to look over their shoulder and wonder “what if”? How many of us live within 50 miles of a nuclear power plant? In the U.S. alone, there are 104 nuclear power plants, most with multiple reactors.

When a leak is detected, there are two primary tools to measure the radiation: dosimeters and radiation detectors. Both provide different critical functions.

Dosimeters are the important instruments at the radiation leak. When worn on the body, often clipped to a pocket or belt, they measure how much radiation your body has absorbed. This is critical because the human body can absorb an amazing amount of radiation without damage, but there is a limit. A dosimeter shows when it is time to get away from the radiation before health consequences can occur. Everyone working in an area of high radiation needs to have a dosimeter. Especially the workers trying to stop a radiation leak.

Radiation detectors are faster and more sensitive than dosimeters, react instantly when radiation is detected, and indicate the amount of radiation.  If dosimeters are like a doctor looking over your shoulder to continually measure your health, radiation detectors are more like guard dogs. Radiation detectors are used just like guard dogs – they can monitor a perimeter and provide instant warning if that perimeter is violated. They can also be used to inspect people and vehicles for radiation. When people leave a contaminated area they are scanned with radiation detectors to quickly determine who needs to go through decontamination and who can be waved on.  Often contamination is in the form of dust present on skin, clothes and shoes. This contamination can be washed off once detected. The people who need radiation detectors are those who establish and guard the perimeter around ground zero, control the road blocks, evacuate the local population, control hospital admittance, and check people and vehicles for contamination as they leave the danger area.

How much warning will you have if a radiation leak occurs at the local nuclear power plant? Radiation detectors inform the authorities that a leak has happened within seconds.  Then it’s up to the authorities and the local emergency management team to determine how to respond and what the public needs to know.  And if a perimeter needs to be established and  an evacuation ordered.

After the leak is stopped, how can you feel safe living next to a Nuclear Plant? How do you know radioactive dust isn’t blowing around during windy days? Those same radiation detectors keep monitoring radiation levels 24/7.  They are sensitive enough to detect very small levels of radiation and can be set to alarm at far below hazardous levels. No radiation contamination can move without detection within a network of these devices.

Radiation is invisible to us, but we have the tools to track its every move.

Mark Kaspersen is the Director of Engineering of D-tect Systems, producers of radiation 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.

Radiation Detector Overview

“The only thing constant in life is change.” -  François de la Rochefoucauld

Although they report on thousands of different stories each day, the covers of newspapers in recent weeks have all carried a similar theme – instability.  On-going political changes in many parts of the world, as well as the rapid power transfers and challenges in the Egypt, Yemen, Libya, and many bordering countries have made it clear that political unrest is on the rise.  Recent upheavals have also made it clear that finding security in an increasingly unstable world is a difficult task. 

Adding to political turmoil, terrorist organizations have become increasingly aggressive in both their tactics and technology.   The release of diplomatic cables lays bare new plans by terrorist organizations, such as the Taliban, to construct ‘dirty bombs’ – weapons designed to spread radioactive material over large areas.  We here at D-tect Systems focus on this increasingly relevant area of that security effort: radiation detection. 

With dozens of detector types utilized of literally thousands of radiation detection products, matching the right technology to a threat is a daunting task.  To make this search a little easier, we’ve compiled a general overview of some of the main radiation detectors currently in use.

Geiger-Mueller Tubes, with low sensitivity and a wide range, are the most commonly used detectors on the market.  Available in sizes from ring-worn dosimeters to giant cargo scanners, Geiger-Mueller detectors can pick up certain types of alpha, beta, and gamma radiation.  The downside to these kind of detectors is that they are much less sensitive to radiation than other detector types and cannot differentiate between radiation types.  They are also too slow to detect moving radiation, but are cheap and durable.

Sodium Iodide (NaI(Tl)) and Cesium Iodide (CsI(Tl)) are among the most common gamma radiation detectors.  These two types of materials are commonly referred to as inorganic scintillators because of their composition and method for detecting radiation.  Unlike Geiger-Mueller Tubes, they are fast, sensitive, and can measure the actual energy of gamma rays.  D-tect Systems’ MiniRad-D and MiniRad-V devices uses CsI(Tl) detectors equipped with photo-multiplier tubes that allow the operator to detect radiation from tens of meters away.  

CsI(Tl) detectors, like those used in the MiniRad-D, can detect gamma radiation from even some shielded sources.

Plastic Scintillators (PVT) use the same detection method as NaI(Tl) and CsI(Tl) detectors but usually require much larger detector sizes the achieve the same sensitivity.  They are commonly used in high-volume portal monitors and come in a variety of shapes and sizes.

Lanthanum Bromide (LaBr3) detectors are capable of finding energy peaks more quickly (known as detector efficiency) than a corresponding NaI(Tl) detector, but LaBr3 detectors exhibit internal radioactivity that reduces its spectral resolution at energies below 100 keV.  The current cost of LaBr3 detectors is generally much higher than that of comparable NaI(Tl) detectors. 

 

High Purity Geranium (HPGe) detectors figure into the top end of radiation detection and identification.  Devices using HPGe detectors are able to identify isotopes 2-3 more quickly than NaI(Tl) partly because they need sense far less radiation to come up with an identification.  The downside to this type of detectors is that HPGe detectors must be cooled with liquid nitrogen to operate, which makes HPGe devices bulky and much more expensive than scintillator units.

Cadmium Zinc Telluride (CZT) detectors have higher resolution and stability (for gamma rays and x-rays) than NaI(Tl), but are expensive in large crystal volumes.  Many CZT systems contain arrays of multiple small CZT detectors because the detection sensitivity increases with volume and some directionality can be established this way.  The Rad-ID device by D-tect Systems is available in configurations that contain four or eight CZT crystals, as well as a large NaI(Tl) detector. The combination of multiple detector types allows the Rad-ID to quickly and accurately identify over 110 radioactive isotopes.

Detection systems for neutron radiation (extremely high-energy radiation produced by elements such as Uranium and Plutonium) are also critical for security.  This type of radiation only comes from a few highly-controlled materials. The most commonly used neutron radiation technology involves the use of He3 tubes and requires relatively large volumes.  D-tect Systems’ Rad-ID device has neutron radiation detection capabilities with an optional He3 tube.

So whatever kind of radiation detection you need, we hope this short overview allows you to make informed decisions to help ensure security in an unstable world.