There are a several different units of measurement for radiation emitted and absorbed from radioactive materials. Exposure is measured in terms of a particular amount of radiation per a particular duration of time.

            A curie is a unit used to measure radioactivity. It is named for Madam Curie, an early pioneer in research into radioactivity. It is a measurement of the number of atoms in a group of radioactive atoms that are giving off radiation at a particular moment. One curie is equivalent to thirty seven billion radium atoms emitting radiation. One curie is about ten million times the usual amount of radiation in a human body. A picocurie is one trillionth of a curie. Curies are often measured in the number of curies per gram of a solid substance. Curies per liter measures the number of curies in a liquid substance.

            A becquerel is a unit of radioactivity named for Henri Becquerel who shared a 1903 Nobel Prize with Madam Curie for their research on radioactivity. It is defined as the quantity of radioactive material in which one nucleus decays each second. In a given amount of radioactivity the number of becquerels changes over time. When working with short live isotopes, it is necessary to note the exact date and time in the past or future for a particular becquerel count. There are 37 billion becquerels in one Curie.

            When using some sort of detector such as a Geiger counter to measure radioactivity, counts per second or counts per minute are often used. These measurements can be converted to becquerels by taking into account the radiation background, the efficiency of the detector, the sample size and the way that the sample may absorb its own radiation.

            A rem is a unit used to measure radiation exposure. It indicates how much radiation has been absorbed by someone or something. A calorie is a general measurement of energy. It takes one calorie to raise the temperature of one gram of water one degree centigrade at sea level. One rem is equivalent to two-millionths of a calorie. A rem is much more that people usually absorb from the natural environment each day. Rems are also broken down into millirems which are one-thousandth of a rem.

            A unit called a gray is also used to measure absorbed ionizing radiation. It is defined as one joule of ionizing radiation absorbed by one kilogram of matter. A joule of energy can produce one watt of energy for one second. We measure electric usage in our homes in terms of kilowatt hours or one thousand watts per hour. One gray is equivalent to one hundred rem.

            The most important unit for this blog is the sievert. It is a unit of dose equivalent radiation. It was developed in order to evaluate the biological effects of absorbed radiation instead of just the amount of radiation absorbed by the body. It is named for Rolf Maximilian Sievert, a Swedish scientist who worked on the biological effects of radiation. One sievert is equivalent to the effect of absorbing one gray of gamma radiation. Sieverts are measured by multiplying the grays of radiation by a weighting factor. Electrons and photons of all energies (beta and gamma particles) have a weighting factor of one. Protons have a weighting factor of two. Heavy ions and fission fragments (such as alpha particles) have a weighting factor of twenty. Neutrons have a weighting factor that is dependent on their linear transfer energy which can vary from less than ten for  a weighting factor of one, ten to one hundred with a weighting factor between one and thirty, and greater than one hundred for a weighting factor greater than thirty. Sieverts are also measured in millisieverts or one-thousandth of a sievert and microsieversts or one-millionth of a sievert. One sievert is equivalent to 100 rem.

            The effective dose of radiation absorbed by a person is found by taking the averages of all irradiated tissues whose weighting factors add up to one. Bone marrow, colon, lung, stomach, breast and other tissues each have a factor of twelve hundredths which combine to yield a factor of seventy two hundredths. Gonads weight as eight hundredths. Bladder, esophagus, liver and thyroid each have weights of four hundredths and collectively contribute sixteen hundredths. And finally, bone, brain, salivary glands and skin each have weighting factors of one hundredth which adds up to four hundredths. All together, these add up to one for the whole body.

            Radiation comes from many sources, natural and artificial. There are over 60 naturally occurring radioactive elements. In addition, there are many sources of radiation created by the human race for a variety of purposes.

            Unless radiation is very intense, we don’t notice it because we have no naturally evolved sense organs to detect alpha, beta and gamma radiation. Exposure is cumulative over time and can have effects that are not noticed until decades after exposure.

            There are many sources of gamma rays and highly energetic charged particles in space including our own sun, nova and supernova explosions, and other exotic astronomical phenomena such as pulsars which can direct beams to intense radiation toward the Earth. The Earth’s atmosphere filters out a lot of it but some makes it through to the ground. Because the atmosphere is thinner at higher elevations, there is more exposure at high altitudes.

            There are radioactive elements all around us. The amount of radioactivity in the soil under our feet varies with the type of soil, the mineral make-up, the density of the soil and the amount of water present. Radon is a colorless and odorless gas which is produced by the decay of natural radioactivity in soil and other materials. It seeps into homes and is the main source of natural radiation exposure. It is the second leading cause of lung cancer.

            The radioactivity in the air we breathe can be found in gases and in dust which may come from natural radioactivity in the soil in the form of particle or radon gas, mushroom clouds generated by nuclear explosions and releases of radioactive dust and vapors from nuclear accidents at power plants and waste facilities.

            The water we drink contains radioactivity in the form of natural particles from soil through which the water passes and dust washed out of the air by the rain. Radioactive materials are carried by streams and rivers to lakes and the ocean.

            Radioactivity finds its way into the plants we eat from the natural radioactivity in the soil and water used to grow them. Radioactivity from the soil and water consumed by animals and from the water, aquatic plants and other aquatic life that fish and crustaceans  consume.

            Our own bodies take up radioactive materials from the air, the water and the food that we consume. Some of the radioactive materials that we consume are passed out of the body but others accumulate in different tissues.

            Nearly half of radiation exposure of the people in the US comes from medical sources such as computer tomography (CT) scans, x-rays and nuclear medicine. Additional exposure can result from improper handling of consumer products that contain radioactive elements such as smoke detectors. Security procedures for transportation have begun to employ devices that produce radiation such as full body scanners at airports.

            The radiation produced by nuclear power plants is generally contained except for accidents such as Chernobyl and Fukushima which both released substantial amounts of radioactive materials into the environment that made their way around the world. In addition, the radioactive waste from nuclear power plants and the production of nuclear weapons when improperly handled can make its way into the environment.

            So the question is not whether or not we are exposed to radioactivity in the normal course of our daily lives but how much and what type.

           Radioactive decay occurs when an atomic nucleus of an unstable atom looses energy by emitting ionizing particles. There are many different types of radioactive decay. The result of decay is either that the nucleus enters a different state or that the number of nucleons (protons and/or neutrons) in the nucleus changes. The first types of decay processes that were discovered were alpha decay, beta decay and gamma decay.

            During alpha decay, the nucleus ejects what is called an alpha particle or helium nucleus. This particle contains two protons and two neutrons. It is the most common type of decay where the number of nucleon changes. (More rare types of nucleon emission include protons, neutrons or nuclei of elements other than helium.)

            Beta decay consists of a process where a nucleus emits an electron or a positron (the anti-matter version of the electron) and a neutrino (an almost massless particle.) This results in the conversion of a proton to a neutron or a neutron to a proton. (Orbital electrons can be captured which converts a proton into a neutron which is called electron capture.)

            Both alpha and beta decay change the nucleus into a different element. This is called atomic transmutation.

            Gamma decay does not transmute one element to another. Energy is carried away from the nucleus as a gamma ray which is a highly energetic photon or particle of energy. (An orbital electron can also be ejected from the electron cloud around the nucleus which is referred to as internal conversion.)

            A nucleus sometimes emits a neutron which results in a change from one isotope of the element to another isotope of the same element.

            Another type of radioactive decay that does not result in a well defined outcome is called spontaneous fission. This occurs when a large unstable nucleus breaks into two or three smaller nuclei. This is usually accompanied by emission of gamma rays, neutrons or other particles.

            So to recap, when a nucleus undergoes radioactive decay, the result can be the emission of an electron, a neutron, a proton, a gamma ray, a neutrino and/or one or more nuclei of elements with lower atomic numbers.

            At the level of an individual atomic nucleus, the time at which decay will occur is strictly statistical. That is to say, we don’t know when any particular nucleus in a group consisting of a specific isotope of a particular element will decay but the number of such nuclei that will decay in a specific period of time is always the same. For any given elemental isotope, this rate is predicted from the measured decay constant for that isotope. The time it takes for half the atoms in a specified number of identical atoms to decay is referred to as the half-life for that isotope. The half-life is a very important property of a particular isotope and one that we will be discussing further in future articles.

            The danger of radioactive decay lies in the effect of the emissions of decaying nuclei on living systems.

            People have been trying to figure out what the basic stuff of the material world is for thousands of years. An ancient Greek named Democritus said around 460 BC that there were tiny indivisible things he called atoms that made up all material objects. After that there were a lot of other ideas proposed that were not as advanced.

            In the early 19th Century, John Dalton built on earlier work to propose that chemical elements were made up of a single type of unique tiny objects or atoms. These elements combined in various ways to make up compounds. Elements and compounds constitute all material substances and objects.

            In the mid 19th Century, Dmitri Mendeleev developed the periodic table which arrayed all the elements in a grid based on increasing numbers of atoms which make up a particular element. The elements in each column shared similar chemical properties. The gaps in the grid have been steadily filled in until today we have a complete table containing elements with up to118 atoms.

            In the early 20th Century, it was discovered that the “indivisible” atoms were actually made up of smaller units. These were call electrons, protons and neutrons. It turned out that atoms were mostly empty space with a cloud of electrons surrounding a tiny nucleus containing protons and neutrons. The electrons carry a negative charge, the protons carry a positive charge and neutrons are neutral. (Actually neutrons are composed of an electron and a proton.) The number of protons in the nucleus of an atom uniquely identifies that atom as a particular element.

            While the number of protons in the atoms of a particular element is a fixed number, the number of neutrons can vary. An atom of a particular element that contains a specific number of neutrons is referred to as an isotope of that element. The term nuclide is often used in place of isotope when the focus is on the behavior of the nucleus in nuclear chemistry as opposed to the behavior of the element in conventional chemistry. The neutron number can have a big influence on nuclear properties but has very little effect on the chemical properties of an element.

            Elements are identified by their atomic number which corresponds to the number of protons in their nucleus. The combination of the protons and neutrons in a nucleus is referred to as the mass number. So a particular element will always have the same atomic number but the isotopes or nuclides of a particular element will have different mass numbers.

            Some isotopes are radioactive and are referred to as radioisotopes or radionuclides. This means that they can decay. There are several different types of decay including spontaneous fission, alpha decay and double beta decay. The time it takes for half of the atoms of an isotope to decay is known as the half-life of that isotope. Half-lives can vary from nanoseconds to trillions of years. Many of the naturally occurring isotopes are considered to be stable and to never undergo any type of decay. Other naturally occurring isotopes have estimated half-lives longer than the estimated life span of the universe. I will be primarily concerned with naturally occurring and man-made isotopes which have half-lives from nanoseconds to millions of years.

            The particles of energy and matter emitted by an isotope when it undergoes decay are the types of radiation that I will be discussing in this blog.

Welcome to Nucleotidings. This is a blog about radiation. Radiation is a general term with different meanings. This is a blog about dangerous radiation in our environment. There are different types of dangerous radiation and there are multiple sources. I will be most concerned with radioactive emissions from man-made sources.

The greatest current man-made source of radiation is from nuclear reactor accidents. The recent earthquake and tsunami in Japan that destroyed the reactors at Fukishima has released a great deal of radiation into the environment, some of which has made its way to the United States.

Nucleotidings will contain a broad variety of articles dealing with various aspects of dangerous radiation including science, history, politics, economics, etc. There are two related blogs that I will also be producing. www.rad-links.com will contain links that deal with current news about dangerous radiation. www.geigerthis.com will contain daily radiation readings from my home in Seattle, Washington.

My name is Burt Webb. I am a retired software engineer who now has time to write and publish novels, non-fiction books and blogs posts. Many years ago I was a founding member of the Evergreen Chapter of the World Future Society here in Seattle. One of the things that we spent a lot of time discussing was the benefits and dangers of technology. I was very concerned with environmental issues and looked into the pros and cons of different sources of energy.

Nuclear power has been advertised as a safe, clean and inexpensive source of energy. Unfortunately, none of these qualities have proven to be true.  The disaster at Fukushima has illustrated how unsafe nuclear power can be. The enormous problem of how to dispose of accumulating radioactive waste belies of the claim of clean energy. And the rising cost of plant construction, clean up, uranium, etc. have shown us that it is not really inexpensive.

Long ago during an argument about nuclear power, I said “I am sure that the engineers could design a safe, clean and cheap nuclear power plant. The problem is that we would have to be able to trust government and industry to be 10 times as honest and capable as they have ever proven to be in the past.” Nothing that has happened since that conversation has convinced me that I was wrong. Government has been woefully incompetent at monitoring and policing the nuclear industry. The nuclear industry has often put profits over safety and failed to deal adequately with many risks and problems associated with nuclear power. We still have no permanent solution for how to deal with waste products from nuclear power plants. And many of the functioning nuclear power plants are reaching the end of their projected life-spans and will have to be decommissioned.

Since Fukishima some countries like Germany have decided to build no more nuclear power plants and to decommission the ones that are currently operating. Here in the United States we don’t seem to really be getting message and there is a new effort to promote the licensing and construction of more power plants.

One of the big problems with engaging the public in the debate over the pros and cons of nuclear power is that fact that biological radiation damage can be invisible and take decades to manifest itself as cancer and other illnesses. Nucleotidings and its companion blogs are an attempt to increase public awareness and knowledge of the dangers of radioactive contamination of our environment.