CHAPTER 13
The Wonderful World of Radiation
In science fiction TV and movies past, radiation is the great green glowing boogeyman that can do almost anything. In 1950s movies it fostered the growth of giant mutant ants, octopi, and grasshoppers. It created Godzilla (or Gojira), woke Gamera, attracted Kronos, and even gave a brachiosaurus the ability to distribute electric shocks. It gave Peter Parker spiderlike abilities, caused the hero to shrink in one movie and to melt in another. It influenced the genesis of the X-Men. There is perhaps no phenomenon in science that has been more misunderstood, or whose effects have been inaccurately portrayed, than radiation.
The general public has a bizarre love-hate relationship with radiation: we find it both incredibly cool and incredibly dangerous. We fry ourselves in tanning salons, then wear wide-brimmed hats and SPF 1,000,000 sunscreen outside.
We protest against “irradiated food,” then gleefully “nuke” something in a microwave oven. We’ve been conditioned to be wary of radiation by both science fiction and real-world events like Chernobyl, Three Mile Island, and Hiroshima.
Cylon Model Number Three D’Anna Biers.
Romo Lampkin.
I don’t want to be human. I want to see gamma rays, I want to hear X-rays, and I want to smell dark matter. Do you see the absurdity of what I am? I can’t even express these things properly, because I have to—I have to conceptualize complex ideas in this stupid, limiting spoken lan- guage, but I know I want to reach out with something other than these prehensile paws, and feel the solar wind of a super- nova flowing over me. I’m a machine, and I can know much more.
—John Cavil, Cylon Model Number One, “No Exit”
Yet radiation is essential to our very existence, and without it none of us would be alive. A cursory understanding of radiation would help us understand the physics behind some of the technology, weaponry, and astrophysical phenomena depicted on Battlestar Galactica.
Perhaps the main reason that radiation is so misunderstood is because several very different phenomena are collectively lumped into one term. Radiation can be separated into two different types: electromagnetic (EM) and particulate. The only real similarity between the two is that in each case something is being “radiated,” or sent outward, but that “something” is very different in each case. EM radiation is energy in the form of waves emitted by an atom or molecule when it undergoes a transition from a high-energy state to a lower-energy state. Particulate radiation is the release of (usually) high-speed subatomic particles from unstable atomic nuclei, or from nuclear processes like fission or fusion.
To understand either type of radiation, it helps to first understand the basic model of an atom. An atom is the smallest unit into which an element can be subdivided while still retaining the chemical properties of that element. The ancient Greek philosopher/scientist Democritus observed that when a stone is split, the pieces have the same properties as the original rock. If cleft in two again, the smaller pieces are still rocks. Democritus reasoned that there was a limit to this progression, and eventually you would be left with pieces so small that they could not be further subdivided. He called these pieces “atomos,” Greek for “indivisible.”
Democritus further believed that atomos could not be destroyed and were unique to the material that they comprised. In other words, he believed that the atomos of stone were unique to stone, and were different from the atomos of other materials such as wood and water—a line of reasoning that was, in many respects, more advanced than that of later philosophers like Aristotle. It wasn’t until the early twentieth century that science began to understand Democritus’s atomos.
While an accurate image of an atom is incredibly complicated, for nearly 100 years scientists and teachers have relied on the Bohr Model, the simple model of the atom proposed in 1913 by the Danish physicist Neils Bohr, which itself was based upon the even-more-simplified Rutherford model, proposed by the New Zealand physicist Ernest Rutherford in 1911.
Rutherford proposed that an atom was like a planetary system—with negatively charged “planets” (i.e., electrons) in orbit about a central “sun” (i.e., the nucleus). Just as the bulk of the mass of a planetary system is within the central star, the bulk of the mass of an atom is in the nucleus. The atomic nucleus consists of two different types of particles: protons and neutrons (collectively called nucleons). Protons and neutrons are similar in mass—a neutron has slightly more—but a proton has a positive charge and a neutron has zero charge.
The Rutherford model of the atom.
An atom’s chemical properties are a result of a value known as its atomic number—a count of the number of protons within its nucleus. Different elements have different atomic numbers. Hydrogen, the simplest atom, which comprises over 90 percent of the visible mass in the universe, has just one proton. Helium has two protons, lithium three, and so on. The number of neutrons in an atom’s nucleus has no bearing on the chemical properties of that element, but as we’ll see next, the count of neutrons can affect the way that atom behaves in other ways.
Planets are bound to their star by the force of gravity, but in an atom the force of electromagnetic attraction between negatively charged electrons and positively charged protons (usually) keeps electrons in bound orbits. For nearly all of the matter that you come into contact with on a daily basis—solids, liquids, and gases—the atoms have an equal number of protons and electrons. The positive charges of the protons equal the negative charges of the electrons; the atom is balanced, content, and dull. On those rare occasions when an atom has a net imbalance between its number of protons and electrons—when it gains or loses an electron—its behavior changes drastically. It becomes disruptive, a danger to all the other atoms around it. Ready at all times for the subatomic equivalent of a fight or a frak, such an atom searches desperately for the balance all the other atoms have, a balance it will achieve only at the expense of another. It becomes an ion.
The Bohr Model of the atom has yet another similarity with a planetary system: the distance between objects is vast. Just as the distance from, say, Earth to the Sun is much larger than the size of either object, the distance from the nucleus to the closest electron orbit is equally staggering. If the nucleus of a simple atom were the size of a grape, the nearest electron would be on the order of half a kilometer away. Since electron orbits of adjoining atoms don’t overlap, electrons usually do not like to share their orbits with other electrons—a phenomena known as the Pauli Exclusion Principle, formulated by the Austrian physicist Wolfgang Pauli in 1925. Because of this, and because the distances between nuclei and electron orbits are vast, most matter with which we come into contact on a daily basis is just empty space. Remember the Second Law of The Science of Battlestar Galactica: “Space is mostly empty. That’s why it’s called ‘space.’” It turns out that stuff is mostly empty, too!
In all of our discoveries of exoplanets—planets orbiting other stars—we’ve learned that planets can orbit at just about any distance from the central star. That isn’t the case in an atom. To address difficulties with Rutherford’s model, Bohr’s model postulated that electrons can be found in only particular discrete orbits—which correspond to particular discrete orbital energies—around the nucleus. To move outward from the nucleus, an electron has to gain energy. To move closer to the nucleus, an electron has to lose energy.
There are many processes that can knock electrons to more distant orbits: collisions between atoms, electrical current flowing through a wire, even the absorption of light energy. Electrons, like Gaius Baltar, tend to like to stay at the lowest energy level possible; when they’re externally energized, they will spontaneously, and usually immediately, drop back down to their original orbit.
In chapter 9 we saw that energy can neither be created nor destroyed. Since the outer electron orbit had a higher energy than the inner orbit, when an electron “drops down,” where does that energy go? It gets radiated away from the atom in the form of a tiny packet
of energy called a photon.
A photon is the fundamental “particle” of electromagnetic (EM) energy. EM energy comes in many “flavors,” each comprised of photons with different energies. The entire range of EM radiation is known as the electromagnetic spectrum. EM radiation at the low end of the spectrum—whose photons have the lowest energies—is known as radio waves. The cell phone in your pocket is constantly radiating a small number of photons to various towers spread throughout your town. The word RADAR was originally an acronym that stands for RAdio Detection And Ranging. To determine the distance to other objects, a radar system radiates a pulse of radio photons, then measures the time it takes for that pulse to be reflected back. We can probably assume that Colonial and Cylon DRADIS systems radiate in this portion of the EM spectrum as well. (We’ll elaborate on this much more in chapter 26.)
Photons that are slightly higher in energy than radio are called microwaves—the kind of radiation generated by microwave ovens when you “nuke” a burrito. The radar used by law enforcement to catch you speeding actually broadcasts in the microwave portion of the EM spectrum. Microwave transmissions are also used for satellite, spacecraft, and even Wi-Fi communications.
Still higher in energy is infrared (IR) radiation, sometimes called thermal radiation, which we normally associate with heat. Thermal radiation is emitted from objects when the energy of collisions between atoms and molecules is converted to electromagnetic radiation, with warmer objects radiating more energy than cooler objects. Any object whose temperature is above absolute zero (—459 degrees Fahrenheit) radiates photons in the infrared part of the spectrum. Yourself included.
There are many varied ways in which infrared radiation affects our day-to-day lives. IR radiation from an electric space heater can warm a room. Heat sinks on electronic components are designed to cool the devices by radiating heat away as thermal radiation. A tympanic ear thermometer determines a person’s temperature by measuring the thermal radiation generated within the ear cavity. There have even been numerous instances over the run of Battlestar Galactica when we have seen Cylons fire heat-seeking missiles at Colonial Vipers and Raptors. Heat-seeking, or IR-seeking, missiles are programmed to home in on the thermal radiation emitted from the hot tailpipes of an adversary’s spacecraft.
The spectrum of visible light ranges from red at the low-energy end of the EM spectrum to violet at the high-energy end. Many physical processes give off photons in this part of the EM spectrum—basically every method humans have used to create light, from fire to fluorescence. It’s no accident that our eyes have their peak sensitivity at almost precisely the same wavelength as the Sun’s peak visible light output.
Still more energetic than violet in the EM spectrum is ultraviolet (UV) radiation. UV radiation can be damaging to living tissue, and it is the primary reason why pale-skinned redheads fry like bacon at the beach. Although a type of oxygen molecule called ozone (O3) shields Earth’s surface from most of the UV radiation emanating from our Sun, enough gets through to be a concern.
At the upper end of the spectrum are very-high-energy forms of EM radiation: X-rays and gamma rays. As anybody who has ever had a dental exam knows, X-rays are used to look deep inside skeletal and dental frameworks. X-rays are generated by the radioactive decay of unstable atomic nuclei. They are also generated by astrophysical phenomena such as neutron stars, pulsars, and black holes. At the very-high-energy end of the EM spectrum are gamma rays—the same gamma radiation that mutated comic book (and movie) character Bruce Banner into the Hulk! Gamma rays are generated by radioactive nuclei, thermonuclear explosions, the nuclear fusion processes that generate power within the cores of stars, and supernovae. Gamma rays can do extreme damage to the cells of living tissue; parents, don’t buy that gamma-ray generator on eBay thinking it’ll make a good toy for the kids.
Visible light, at least visible for humans, corresponds to a narrow portion of the entire EM spectrum. There are many cosmic and astrophysical phenomena that are more clearly seen in portions of the EM spectrum outside of the visible, which explains why NASA’s four Great Observatories—space-based telescopes—are geared to see in the infrared (Spitzer Space Telescope), visible (Hubble Space Telescope), X-rays (Chandra X-ray Observatory), and gamma rays (Compton Gamma Ray Observatory). Colonel Tigh alluded to this in the episode “Water” when he said, “Optical and X-ray telescopes say we’ve got five systems within our practical jump radius. All five have planetary bodies.” (How would Colonel Tigh use X-ray telescopes to find planets? Repeat the First Law of The Science of Battlestar Galactica to yourself: “It’s just a show, I should really just relax.”)
This also clearly explains Brother Cavil’s overwhelming frustration with his basic design, as well as that of all the humanoid Cylon models: they can’t “see gamma rays” nor can they “hear X-rays.” Keeping the basic human form constrains them to observing the same narrow portion of the EM spectrum as their Colonial counterparts. As machines, nothing would prevent them from seeing the entire EM spectrum—giving them the ability to observe the universe in a way that no human lacking special instrumentation ever could.
Photons propagate through a vacuum at 299,792,458 meters per second (a value for which we normally use the variable c). The key phrase is “in a vacuum.” Photons travel more slowly through other transparent media (air, glass, and water being examples) than they do through a vacuum. The speed of photons in a vacuum is, as far as we know, the upper speed limit in our universe. Photons have zero mass and travel at c; any object that has mass must travel more slowly. We’ll examine how this rule may be broken, or at least severely bent, in chapter 22.
The vehicle for electromagnetic radiation is the massless photon. The vehicles for other types of radiation are the many varieties of subatomic particles, all of which have mass. Generally these forms of radiation are generated as a result of processes within an atomic nucleus, or processes involving the interaction of multiple nuclei. To understand these forms, we must delve into the nature of the atomic nucleus just a trifle more.
The three most common forms of radiation emitted are called alpha, beta, and gamma radiation.
Alpha particles consist of two protons bound to two neutrons, and are equivalent to a nucleus of helium. When a radioactive element such as uranium gives off alpha particles, it’s a sign that one of the atoms of uranium-238 has decayed into an atom of thorium-234. Alpha particles outside the body are relatively harmless; alpha particles inside the body are deadly.
Beta particles are nothing but free electrons.bg When that thorium-234 atom subsequently gives off a beta particle, for instance, it becomes an atom of protactimium-234. Beta particles are slightly more energetic than alpha particles, but are also relatively safe as long as they’re outside the body; inside the body they can rearrange DNA molecules to turn a harmless cell cancerous.
Gamma rays, as we have previously discussed, are extremely dangerous high-energy photons.
Another type of subatomic particle that can be radiated by unstable nuclei is the neutrino. Neutrinos travel very close to the speed of light, have an almost nonexistent amount of mass, and do not have an electric charge. Neutrinos do not easily interact with normal matter, so they can pass through ordinary matter unperturbed; they are also extremely difficult to detect. Every second, over 50 trillion neutrinos generated within the core of the Sun pass through your body. In addition to being by-products of radioactivity, neutrinos are also emitted in staggering amounts by nuclear fusion reactions—the kinds of reactions that power stars—and in even more staggering amounts when a star explodes in a supernova.
Finally, we return to the concept of the ion. Depending upon how it interacts with atoms, radiation can be classified as either ionizing or non-ionizing. Radiation, either particulate or electromagnetic, that has enough energy to strip electrons from an atom—enough energy to create ions—is called ionizing radiation. The three most common types of radioactive decay products—alpha, beta, and gamma radiation—are all
forms of ionizing radiation.
Some forms of radioactive decay even emit subatomic particles called positrons. Positrons are not ionizing per se. They are electrons that have a positive charge instead of the negative charge to which we’re accustomed. This means that positrons are a type of antimatter. Most of us have read or watched enough science fiction to know (or think we know) that when matter and antimatter come into contact, there is an explosion. That actually occurs only when large amounts of matter and antimatter come into contact, on the order of about one gram or so. When a particle and its antiparticle collide, the entirety of their mass is converted into energy (by E = mc2) in the form of gamma rays—which are ionizing.
Ionizing radiation can do severe damage to living tissue by creating free radicals—highly reactive atoms or molecules that readily form chemical bonds and form numerous different compounds—within your tissues. While organisms require a certain level of free radicals to perform basic biological functions, when the concentration of free radicals gets too high, beyond a body’s ability to regulate, bad things happen, like wrinkles, old age, and cancer.
Ionizing radiation can damage or alter the DNA sequences within an organism’s cells. Changes to the genetic code of an organism are called a mutation, and any substance that causes the mutation is called mutagenic. Since DNA is the genetic code that, among many functions, tells cells how to divide, some mutations can have very profound effects. Most mutations are harmful, but normally a healthy body can either repair damaged DNA or kill an unhealthy cell through a process called apoptosis. On occasion, though, radiation can disable the DNA repair mechanism and block apoptosis. Any resulting mutated cells will pass their damage on to subsequent cell divisions, which in turn frequently lead to various forms of cancer. We’ll further discuss the harmful effects of radiation in much more (gory) detail in chapter 14.
The Science of Battlestar Galactica Page 10
