It is probable that all heavy matter possesses – latent and bound up with the structure of the atom – a similar quantity of energy to that possessed by radium. If it could be tapped and controlled, what an agent it would be in shaping the world’s destiny! The man who puts his hand on the lever by which a parsimonious Nature regulates so jealously the output of this store of energy would possess a weapon by which he could destroy the Earth if he chose. ~ English radiochemist Frederick Soddy in 1904, anticipating atomic weaponry
French physicist Henri Becquerel accidentally discovered radioactivity in 1896 while investigating the glow of phosphorescence. These radiations were, for a while, called Becquerel Rays.
Radiation pervades the universe, differing only in source and energy intensity. Radiation may be an energetic display of electromagnetism. It is otherwise a decay of atomic stability: the weak force overcoming the strong.
Weak interaction effects can be observed in decays and in collisions only when they are not hidden by the presence of strong or electromagnetic forces. ~ Italian particle physicist Alessandro Bettini
There are 2 forms of radiative emission, corresponding with radiation types: waves and particles. Electromagnetic radiation is massless, traveling as photonic waves of energy at some frequency. Light is an electromagnetic radiation.
Particulate radiation consists of high-speed particles. Such radioactivity emanates from atomic decay: neutrons shedding something of themselves while heading toward entropy. (The lightest of baryons, protons do not decay.) Atomic decay is an interplay of the strong and weak nuclear forces, along with the electrostatic force, with hd quantum phenomena conducting.
Atomic radiation rearranges a nucleus, something normally hindered. hd forces are thought to kick off the reaction, as a quantum fluctuation forces a nucleus to a lower energy state. This relaxation is a decay event, caused by quantum tunneling. A particle under duress overcomes its 4d classical confines, and cuts loose a particle or energetic wave.
An atom receives a burst of energy which may come in a flush of heat. An electron absorbs the energy bit, boosting it to a higher orbital, farther from the nucleus. But the electron cannot hold that position for more than a fraction of a second, and so it falls back to its original shell.
An electron losing energy, as happens when dropping to a lower orbital shell, results in releasing that energy as a photon. How much energy a released photon has depends upon how far the electron dropped between orbitals. That determines the photonic wavelength.
In this case, wavelength is spatial period of an energy wave: the point-to-point distance between wave repetitions. Mathematically, wavelength (l) is the spatial period of a sine wave.
The energy of a single wavelength is a product of its mass, angular frequency, and amplitude (height). The mass of a wave defines its momentum.
The wavelength gives the angular frequency, which is the rate of change in the wave. The shorter the wavelength, the higher its frequency and greater its energy.
Electromagnetic radiation is a wave of radiant energy. The photon is its quantum poster child.
Newton coined the term spectrum to describe the rainbow of colors when sunlight is split by a prism. The electromagnetic spectrum is a continuum of increasing energy intensity. High-energy wavelengths are shorter than low-energy wavelengths.
Radio waves have the longest wavelength in the EM spectrum, and so are the least energetic. A single radio wave may be up to 100 kilometers long. The shortest radio wave is 1 millimeter.
Befitting their name, microwaves are more energetic than radio waves, with a shorter wavelength: 30 centimeters to 3 millimeters. The entire universe has a faint background radiation of microwaves (cosmic background radiation (CMB)), generally considered a lingering effect of the universe’s origin. (This assertion of CMB being an artifact of cosmic origination is a conjecture connected with the Big Bang hypothesis.)
Microwaves can penetrate smoke, haze, or clouds, making them useful for transmitting information. Radar, a common tool for weather forecasting, uses microwaves.
At a shorter wavelength lies infrared (IR), which touches upon the EM spectrum detectable by living organisms. IR extends from 300 micrometers (µm) down to 0.74 µm.
Humans feel infrared radiation from the Sun as heat, both in the eyes and skin. Snakes can sense infrared radiation, allowing them to locate endothermic prey in total darkness.
The small slice of the EM spectrum that can be seen by humans is anthropomorphically referred to as visible light. EM radiation between 400–700 nanometers is visible. The Sun is the natural source of most visible light.
Just beyond our visibility is ultraviolet (UV) light, which ranges between 10–400 nanometers. Some insects, including spiders and honeybees, see UV. Consequently, flowers look much different to a bee than a human, with intricate patterns and subtle colorations undetectable by us; even more beautiful to their intended audience than they are to our eyes.
Ultraviolet is biologically significant in several ways. UV irradiation of interstellar ice, such as in comets, assisted creation of organic compounds in prebiotic times. Ultraviolet radiation may have produced a disequilibrium in biomolecular chirality, creating an evolutionary impetus to the L-amino acids and D-sugars common in terrestrial life forms.
At 290 to 400 nanometers, the ultraviolet radiation reaching Earth’s surface now is non-ionizing. Wavelengths shorter than 200 nm are invariably ionizing.
Solar radiation fluxes reaching Earth’s surface have changed over geologic time. Part of the flux has been from photochemical reactions, most notably in recent decades from the depletion of stratospheric ozone.
Ultraviolet radiation (UVR) played an important, almost ironic role in prebiotic chemistry and habitat creation before life arose. In energizing O2 to O3, UVR initiated the photochemical processes that led to the formation of ozone (O3) in the paleoatmosphere (the atmosphere before life arose).
The formation of a stratospheric ozone layer was critical to life evolving, as ozone strongly absorbs 220–330 nm solar radiation. These wavelengths can be hazardous to life.
Ultraviolet radiation is a photochemical catalyst for the formation of hydrogen peroxide (H2O2), which produces reactive oxygen species (ROS) that can damage DNA. DNA naturally absorbs UV.
Ultraviolet photochemistry might have been essential in developing the biosynthetic pathway of chlorophyll. Photosynthesis may have initially evolved from a mechanism to protect cells from UVR, at a time when atmospheric oxygen was scant, and the ozone shield not in place.
Anaerobic prokaryotes (single-celled organisms not respiring oxygen) are intrinsically resistant to UV radiation, and are able to repair DNA damage from ultraviolet radiation. They arose when such sunscreen protection was essential.
Biochemical UV protection mechanisms may have been instrumental in the evolution of eukaryotic life via ploidy: the number of sets of chromosomes in a biological cell. Diploid cells, as in animals, are more resistant to radiation damage than haploid bacteria and yeast cells.
(A haploid organism has only 1 set of chromosomes (genetic packaging). A diploid has 2.)
Early life not only learned to deal with reactive oxygen species (ROS); it was even harnessed as a biochemical tool. Macrophages, a key actor in vertebrate immune systems, employ ROS bursts to blast microbial invaders to oblivion.
In a subtler application, ROS is used in inter-cell signaling. It is an axiom of evolution that adaptive mechanisms are often redeployed for applications different from those to which an initial response developed (what is termed pre-adaptation).
ROS accumulates in animal cells with age. Cells in older animals have a harder time warding off oxidative stress; hence, senescence: growing old.
UV may have provided the pressure for evolution of human skin color. Skin color closely correlates to latitude, as does solar ultraviolet. Human skin is protected from ultraviolet radiation by 2 means: the pigment melanin, and the thickness of the uppermost skin layer (the stratum corneum).
Plants too can suffer senescence via ROS. But some plants ward off oxidative stress and live for hundreds or thousands of years.
By depleting the ozone layer via pollution, especially chlorofluorocarbons (CFCs), surface-level UV radiation at damaging wavelengths has increased. Skin cancer is stimulated by overexposure to ultraviolet light.
X-rays range from 10 to 0.01 nanometers. X-rays naturally occur in space, but generally don’t travel to the Earth’s surface in the present eon, as they are absorbed in the upper atmosphere. Lightning on Earth generates X-rays. Peeling back clear office-supply sticky tape emits X-rays.
In 1895, German physicist Wilhelm Röntgen accidentally created X-rays in the lab while experimenting with electron beams in a gas discharge (vacuum) tube. In the process, he accidentally founded radiology, by seeing an image of the bones of his hand illuminated by X-rays.
Not long on imagination or ego, Röntgen coined the term X-ray and stuck to it, even as the penetrating new rays would come to bear his name in several languages: Röntgen rays.
Röntgen died of intestinal carcinoma, but his X-ray work is not generally considered causal, because he was one of the few pioneers in the field who routinely used protective lead shields during experimentation.
Goofing with X-rays continued well past Röntgen. From the 1920s to the 1960s in the United States, and into the mid-1970s in Britain, X-ray fluoroscopes were employed to fit shoes. Called pedoscopes, their use was a sales gimmick: claiming a better fit, and more fun for the kids at the shoe store. The traditional method was equally effective, more convenient, and much less hazardous to health.
The danger of the pedoscope was belatedly revealed in the US in 1949. The machines were quietly phased out as the next decade wore on. Pedoscopes may not have resulted in gross overexposure to customers but did take a toll on shoe clerks who regularly used them.
The EM spectrum energetically ends with gamma rays, with wavelengths less than 10 picometers (10–12 meters): less than the diameter of an atom.
In deep space, gamma ray bursts occur regularly. The Sun powers low-energy gamma rays (up to 1010 eV). Midrange rays are energized by the shock waves of supernovae. The origin of high-energy rays, above 1015 eV, is a mystery.
Planet-side, radioactive atoms and nuclear blasts create gamma rays. Gamma rays readily kill living cells.
Particulate radiation comes from subatomic particles carousing about. An atom with too many or too few neutrons makes for an unstable nucleus. The nucleus becomes radioactive. A disintegrating atom produces particulate radiation, including alpha and beta particles.
When radium, uranium, and polonium decay, they effervesce alpha particles: 2 protons and 2 neutrons. Alpha particles are relatively chunky and slow. Protons and neutrons that can travel only short distances.
Alpha particles can be stopped by a piece of paper, or skin. Inhaling or ingesting alpha particles is dangerous, in exposing sensitive internal tissues to radiation.
Beta particles are hightailing electrons or positrons. Beta decay may be β−: where a neutron converts into a proton, an electron, and an electron-type antineutrino, or β+: where a proton transforms into a neutron, a positron, and an electron-type neutrino.
Lower-energy beta particles can be slowed, or even stopped, by clothing or aluminum foil. Higher-energy beta decay can reach speeds that are ultrarelativistic: approaching the speed of light.
When passing through matter, particulate radiation ionizes whatever it encounters, incrementally losing energy in the process.
The distance to where a charged particle is spent is called the range of the particle. Range depends on particle type, initial energy, and what matter is in the way.
Similarly, energy loss per path length, stopping power, depends on the particle’s type and energy, and the material bombarded. Stopping power, which equates to density of ionization, increases until it reaches an apex, the Bragg peak, just before the energy drops to zero. English physicist William Henry Bragg discovered the elemental dynamics of ionizing radiation in 1903.
Earth’s Age Via Isotope
The heaviest elements are naturally radioactive. They readily shed to get down to lead, the heaviest steady-state metal.
For his 1948 dissertation project, American geochemist Clair Cameron Patterson determined the duration of Earth by measuring the age of meteorites found on the planet, using a technique developed by his academic mentor, American chemist Harrison Brown: counting lead isotopes in igneous rocks.
Patterson calculated Earth to be 4.55 billion years old, give or take 70 million years. The number stands still, though the margin of error has been whittled down to 20 million years.
Ionization is the energetic process of converting an atom or molecule into an ion with randy electrons.
Radiation may be ionizing or non-ionizing. Both can be harmful to living organisms and change the natural environment. Non-ionizing forms of radiation are at the low end of the electromagnetic spectrum. They include radio waves and visible light. While non-ionizing radiation is considered less dangerous than ionizing radiation, overexposure or long-term exposure to non-ionizing radiation can degrade health.
Long-term exposure to transmission power lines affects health, especially infants and youngsters during early development, but it took decades of research for scientists to come to even a tentative acceptance of that. Cell phones alter brain function on the side of the head used.
Overexposure to infrared radiation can result in burns. Ultraviolet radiation overexposure can be insidious, because there are no immediate symptoms of overexposure. Sunburn is exemplary.
Besides sunlight, sources of UV include black lights and welding tools. UV overdoses can lead to cataracts and skin cancer, as well as compromising the immune system.
But nothing is simple. Ultraviolet radiation in the eyes, and on the skin, is essential to stimulate the body to producing vitamin D. As little as 5 to 15 minutes, 3 times a day, is more than enough.
Higher-energy radiation can ionize atoms: strip electrons off by knocking them out of their shells. This leaves a cation: an atom with a net positive charge. At higher energy, the nucleus of an atom can be destroyed.
Ionizing radiation may be particulate or by high-energy electromagnetic rays.
The noble gas radon, found underground, is a natural ionizing radioactive material. Radon is one of the densest elements that remains gaseous under atmospherically ambient conditions.
X-rays and gamma rays are a common man-made ionizing radiation. Bones are examined using X-ray photography.
As a shotgun therapy, gamma rays are blasted for radiation treatment to kill cancer cells. The stopping power Bragg peak effect allows gamma radiation therapy to work on tumors without demolishing a large swath of nearby healthy tissue.
X-rays and gamma rays are much the same, but from a different origin. Whereas gamma rays emanate from inside an atom’s nucleus, X-rays are stirred from discombobulating the electrons of an atom. X-rays are less penetrating, and so can be stopped by a few millimeters of lead, which absorb the energy.
Overexposure to ionizing radiation can cause genetic mutations, raising the risk of cancer. At higher exposures, burns or radiation sickness results.
Besides the gentle echo of EM background radiation from the universe’s distant past, cosmic radiation continues. Highly charged particles are ejected from supernova explosions: ersatz atoms, stripped of their electrons by the extreme temperatures within these giant furnaces.
Supernova-borne particle types vary: primarily hydrogen nuclei (protons) (85%) and helium nuclei (alpha particles) (12.5%), but also heavier nuclei, such as iron and nickel (1%). There is also a smattering of electrons (1.5%) in the cosmic radiation broth. Their scurry is ultrarelativistic (near the speed of light). The radiation is isotropic: coming from all around, and so constantly bombarding Earth’s vicinity.
Solar wind is the constant, fluxing flow of particulate released from the Sun’s atmosphere. A portion of the galactic radiation is deviated by the magnetic field carried by the solar wind. So, the more intense the solar wind, which runs in an 11-year cycle, the less the galactic cosmic radiation in the neighborhood of the Sun.
Between 10 and 100 keV, in a stew of mostly electrons and protons, the emissions from the solar wind are less energetic than cosmic radiation. Few solar wind emissions reach Earth’s surface and they are not evenly distributed. The rotating ball with an iron core called Earth creates a magnetosphere that deviates most of the solar wind and cosmic radiation. But determined particles breach the magnetosphere and reach the upper layers of the atmosphere, where the ions socialize with local atoms. These collisions create less energetic secondary radiation that sometimes manages to reach the ground.
There are also solar flares which dust up the solar wind and can cause disruption in communications satellites in orbit. The largest solar flares originate in complex formations of sunspots, the dynamics of which are little understood.
On average, only ~11% of the ionizing radiation that strikes Earth’s surface is cosmic in origin.
More radiation emanates from natural land-based sources than from the sky. Radon, the gaseous descendant of earthbound natural uranium, concentrates in enclosed areas, such as houses.
Soil-based radiation comes from surface rocks, granite in particular, which totes radioactive elements dating from the formation of the planet. Water and foods consumed have bits of radioactive elements. Finally, potassium-40, naturally present in human tissue, completes the story of radiation coming from everywhere. It’s a miracle anything lives, what with all the atomic noise going on.
Watch That Dial
Wrist watches became popular during World War I. A few years later, quite a few companies came up with the bright idea of rendering watches easier to read, and even glow in the dark, using radium-laced paint. The Radium Dial Company of Ottawa, Illinois was one; U. S. Radium Corporation of Orange, New Jersey another.
All told, 4,000 young women were hired for the painstaking painting by hand. They were encouraged to make a fine point on their brushes by rolling the tips on their tongues before dipping them in the paint.
Their bosses told them “not to worry. If you swallow any radium, it’ll make your cheeks rosy.” All the while, staff doctors routinely checked dial painters for radioactivity exposure, though the employees weren’t informed.
Many died, and the companies lied. Workers were exposed to more than 1,000 times the amount of radiation scientists considered safe at the time.
In a Chicago court in 1938, after a worker sued, a supervisor explained why the company didn’t post the results of the physical exams: “My dear girls, if we were to give a medical report to you girls, there would be a riot in the place.”
The radium scattered from the Ottawa factories when the buildings were bulldozed in 1969 and 1984. No precautions were taken.