What is Radiation

What is radiation?

Radiation is energy traveling through space. There are two main forms, electromagnetic radiation, which travels in rays or waves of energy, and particle radiation, comprised of highly energized sub-atomic particles traveling at fantastic speeds. The two forms differ significantly in the amount of energy they transmit.

Sunshine is the type of electromagnetic radiation we all know best. It gives us light and heat. Without it we could not survive. It is also the most lethal form of radiation, causing far more cancers and deaths every year than all other forms of radiation combined. Over time, people have learned how much of the sun’s rays we can tolerate, and how to deal with them. Most of us know very little about the other forms of radiation.

The variation in the strength of electromagnetic radiation is called the Energy Spectrum of Radiation. Figure one illustrates the range of the energy spectrum, and the relative strength of various types of radiation.

Figure 1

At the bottom of figure 1, the graph is plotted along the“frequency” of the various levels of radiation. Stronger radiation has higher frequencies; weaker levels correspond to lower frequencies. Wave forms of energy travel much like waves on a pond when you toss in a rock. They spread out from the source in all directions. The distance between the waves is the wavelength; the number of waves per second is the frequency. The higher the frequency, the more waves strike per unit of time.

Think of it like a spanking (which I realize is politically incorrect, but my father did not). For small transgressions I might get one pop on the butt. Unfortunately, I usually got multiple wacks (higher frequency) which imparted more energy and therefore more learning. For living tissues, higher frequency radiation has the potential to cause more damage.

In addition to wave forms, radiation can also travel as particles. These subatomic particles generally take one of three forms, alpha particles, beta particles and neutrons. All three carry much more energy than wave forms of radiation. If wave form radiation is like slowly pouring a bowl of bbs on your foot, particles are like dropping invisible bowling balls. They have more energy, and more potential for harm.

To understand radiation, you need to know a little about atoms. Everything is made up of atoms, and most atoms never really change. Take water for example. Every water molecule is made up of two atoms of hydrogen and one atom of oxygen (hence H2O). You can do a lot of things to water, but the hydrogen and oxygen atoms never really change.

But, some atoms do change; they are labeled “unstable.” Unstable atoms have excess energy, they are said to be in an “excited” state. Generally in nature (with the possible exception of teenagers) things in an excited state will move towards a less excited state. This is true for unstable atoms.

Unstable atoms are also called radioactive atoms or radioisotopes. Each time they change from an excited state to a less excited state, they give off their excess energy, or “radiate” energy in the form of radiation. This process of changing from an excited state, to a less excited state, is called radioactive decay. Uranium is the classic example of a radioactive atom. It has many decay steps, and each step releases a characteristic amount and type of energy.

When unstable atoms (radioisotopes) decay down to the next lower energy level, they may emit alpha particles, beta particles or gamma rays. Gamma rays and X-rays are essentially indistinguishable forms of electromagnetic radiation, except for their origin. Gamma rays are given off by radioactive decay. X-rays are produced from electrically powered devices, not natural decay.

Alpha particles are relatively large sub-atomic particles. They are made up of two protons which have a positive charge, and two uncharged neutrons. Because of their large size, they penetrate substances very poorly, depositing a lot of energy on the surface, like those invisible bowling balls. Beta particles are smaller, made up of one highly energized electron. They can penetrate tissue and water up to an inch, depositing their energy along the way.

Over the years physicists have figured out the decay rates and steps for most elements on earth. For a given quantity of an element, it is relatively straight forward to calculate how much radiation it will give off, what types of radiation will be there, how strong the radiation will be and how long the substance will be radioactive. This is important information, because it makes no sense to spend lots of money protecting ourselves from harmless levels and types of radiation.

Most things on earth are radioactive to one degree or another. Uranium gives off some strong forms of radiation. A pound of coffee is weakly radioactive. The human body is radioactive. Our homes are radioactive, some more than others, but we’ll cover this later in the section on radon. Man did not invent radiation; we have been surrounded by it for all time. A little over a century ago man (and woman) discovered radiation.

A brief history of radiation

On November 8, 1895, working alone in his lab at the Physical Institute of the University of Wurzburg, Wilhelm Roentgen discovered X-rays. He was experimenting with evacuated glass tubes when he discovered “a new kind of ray” emanating from the tube. Working alone for the next seven weeks, he figured out most of the characteristics of the rays, and immediately shared his discovery with the world. He gave them the name X-rays. In 1901 Roentgen received the Nobel Prize for his work.

Shortly after Roentgen’s discovery, Antoine-Henri Becquerel, professor of physics at the Polytechnical School in Paris began working with Uranium salts to see if they might emit radiation. Through a series of events he came to show that all forms of uranium gave off penetrating invisible rays. Unlike x-rays, which are produced using electrical current, the rays from uranium were a specific property of the uranium atom.

In the following years, Marie Curie, and her husband Pierre, built on these discoveries, separating purified forms of uranium and isolating additional radiation emitting substances. She called this form of energy coming from uranium and thorium“radioactivity.” At great personal sacrifice, they went on to discover radium and polonium. In 1903, the Curies and Becquerel shared the Nobel Prize in Physics for their work on radioactivity.

Almost immediately after their discovery, the medical applications of X-rays were being investigated around the world. And, within months, investigators soon realized over-exposure to X-rays was potentially harmful. Early equipment was crude, and protection was non-existent. Many early investigators suffered significant and sometimes lethal doses. Fairly quickly, people came to respect X-rays and radioactive materials. Some early investigators, such as Thomas Edison, left the field after seeing the effects on some of his coworkers. Others developed safer techniques and equipment, and the field of medical radiology was born.

Radiology, the medical specialty devoted to imaging the human body, has expanded the use of x-rays exponentially over the ensuing century. CT scanners use x-rays and computers to generate images of our bodies accurate down to sub-millimeter scales. A huge array of diagnostic and therapeutic procedures done inside living people are guided by various x-ray devices. Every year, thousands of lives are saved, and even more are spared from disease and suffering, by the medical uses of radiation.

Medical applications of X-rays were appreciated immediately, but since then hundreds of other applications, useful and not so useful, have developed. We do X-ray imaging of everything from small structures in laboratories to luggage on planes. Foods are irradiated to eliminate pathogenic bacteria and prolong their shelf life. For a brief time you could check the fit of your shoes with X-rays, relatively harmless, but still unnecessary exposure.

While the uses of X-rays have been expanding, so have applications of radioactive materials (remember, X-rays are radiation produced using electricity, radioactivity is radiation released spontaneously by various substances.)

In the early 1900s, researchers analyzed radioactive and non-radioactive matter, figuring out basic atomic structure in the process. The atom, with its positively charged nucleus and surrounding layers of negatively charged electrons, was established as the basic building block of the universe. Alpha and Beta particles were discovered and characterized. Physicists rapidly recognized the enormous amounts of energy and potential energy with which they were dealing.

In 1933 Leo Szilard, a Hungarian physicist, first conceived the idea of a nuclear chain reaction, where the energy released by the decay of one unstable atom, could split the nucleus of an adjacent atom, releasing twice the energy. The two particles released from the first split would split two more, doubling the energy again. These two spit atoms would split four more, and the process would continue, expanding exponentially.

Nine years later, in 1942, the first man-made nuclear reactor based on Szilard’s concept would be built at the University of Chicago.

On August 6, 1945, the first atomic bomb, also based on a nuclear chain reaction, was used over Hiroshima. Everyone’s view of radiation, radio-activity and science in general changed forever.

The first commercial nuclear power generator in the US began producing electricity 1951. There are now around 100 commercial nuclear power plants and 35 small research reactors in the United States.

In 1974 the first world-wide oil crisis hit. The French government responded by deciding to rapidly expand the nation’s nuclear power capacity. The US government did little of substance. France now supplies 90% of their power from nuclear and hydro sources, with consequently lower costs, lower CO2 emissions and relative energy independence.

March 1979, the “non-event” at Three Mile Island Unit 2 reactor. No one was hurt, no harm was done to the environment, and yet this event virtually killed nuclear power development in the United States. More on this later.

In 1984 the publicity surrounding the discovery of high radon levels in the Watras home in Pennsylvania brought Radon into the public eye. This radioactive gas, undetectable to human senses, has been around since man first sat on a rock, and our current reactions to it are worth an entire post.

In April, 1986, there was a real nuclear disaster at the Chernobyl power plant in Ukraine. There were a few real victims from the radiation. Unfortunately, there were far more victims of radiation phobia. This too we will cover in more detail.

In March 2011 a massive tsunami struck Japan. It severely damaged the three nuclear reactors at the Fukushima Daiichi nuclear power station. A few workers in the site received potentially dangerous doses of radiation. Elsewhere the Tsunami killed 10,000 people and destroyed billions of dollars in property. Not surprisingly, the American media concentrated on the reactors.

From 1986 until today, due primarily to mammography, angiography and CT scanning, the medical uses of radiation have expanded, with a subsequent increase in public anxiety over radiation. Individuals, organizations and governments are asking how much radiation are we getting, and is it safe. To know ”how much,” you have to know a little about radiation measurement.

Radiation measurement

Measuring radiation is like measuring music. Consider a symphony orchestra as our radiation “source.” Which notes are being played, corresponding to the frequency of the sound waves being produced, can be determined by a simple device, or an elegant one like the human ear. It is also relatively easy to count the number of notes being produced each second, and how loud the music is being played. My 12 year old could do these measurements with a lap top and a microphone.

Quantifying how much of the music the audience hears, and how it affects them is not so straight forward. My 12 year old might measure the output of the orchestra, but having been woefully corrupted by his mother, he would be far more affected by a Black Eyed Peas or Usher performance. Like different audiences, every person, and each human tissue, has its own response to radiation.

Heat is also radiated energy, and like electromagnetic radiation, it affects us differently. How often have you been in a setting where one person feels cold and another feels hot? The measured temperature of the room is the same for both, but the effect of the temperature varies.

In 1928 The International Commission on Radiologic Units proposed the first units for measuring exposure to radiation, the Roentgen(R). Prior to this, exposure was discussed in terms of the machine settings used to produce the X-rays such as time, voltage and current applied to the x-ray tube. They just ignored the vast differences in machines and tubes.

A Roentgen is the amount of X or gamma radiation (remember , the two are similar, but are produced differently) required to produce a specific amount of ionization in a unit of air. With an ionization chamber, the amount of radiation in an exposure can be measured. Because the usual dosages are much smaller than 1 R, exposures are usually given in milliroentgens. At our concert this would be similar to measuring the loudness of the orchestra in decibels (dB).

The tougher questions of how much of the exposed dose is actually absorbed, and its potential effect, were tackled later.

In 1953 the Rad (radiation absorbed dose) was proposed. It quantifies the energy absorbed per unit of tissue. Finally, came an attempt to adjust for the different types of radiation and their varying effects on living tissue, the Rem (Roentgen equivalent in man). Here again, the Rem is too high for discussing typical human exposures, so the term millirem ( 1 mRem=one thousandth of a Rem) is commonly used.

A newer international system, using the terms Sieverts and Grays, where 1 Sievert equals 100 mRem , has been developed. I trained with the old system. When I make furniture, I measure in units of inches and feet, not meters and centimeters. There is nothing wrong with the new system, but I will use mRem.

Henceforth, we will primarily quantify radiation dose in mRem. When I compare exposure from nuclear waste to exposure from a chest X-ray, the fact that these are two entirely different forms of radiation has already been included in the calculation, at least as well as it can be. Ditto radon versus a CT scan. The system is far from perfect, but it is the best way we have of comparing apples to oranges. When the system breaks down in these comparisons, I will point it out.

Now, equipped with that most dangerous of tools, a little bit of knowledge, let us move on to the actual effects of radiation on humans.

For a far better and more thorough discussion of what radiation is, use the link provided to Dr. Eric Halls book, Radiation and Life.

http://www.world-nuclear.org/education/ral.htm

Another explaination can be found at the MIT news website.

http://web.mit.edu/newsoffice/2011/explained-radioactivity-0328.html