Gamma radiation is the most penetrative type of energy currently known. Similar to X-rays, gamma rays can get past even some of the densest materials in use, making them both a great benefit and a hazard. Because the photons comprising gamma radiation are so energetic, their effect on human health is profound.
Research in the late 1890s produced much new information about gamma rays and their behavior. French scientists Henri Becquerel, Marie Curie and her husband, Pierre Curie, all experimented with materials such as uranium, polonium and radium, leading to the first observations of gamma radioactivity and its unique properties. It was determined that gamma rays far exceed the energy of alpha and beta radiation, and by the 1920s large-scale applications of gamma radiation became widespread.
Ironically, many of the scientists working on gamma radiation in those early stages became radiation sickness patients themselves due to poor shielding and little understanding of possible health ramifications.
Gamma radiation became even more important during WWII research into nuclear weapons. The release of intense gamma energy from nuclear explosions was noted as one of the most important and far-reaching consequences of such weapons.
Positive applications of gamma rays include cancer treatment through radiation, measurement and tracking of fluid flows, resource exploration, sterilization of medical equipment, pasteurization and geodesic surveys. All of these make use of gamma rays' high energy and ionization levels -- especially useful for ranged applications because gamma photons can travel long distances before decaying.
Conversely, it is these properties that make shielding against gamma radiation so difficult. Similar to X rays, gamma rays go through most materials and cause significant cell damage at even low dosage.
Gamma ray exposure is measured in millirem, or mrem. One-time exposure on a daily basis for most people is 25 mrem at most, while people working in radioactive environments with adequate protection may absorb up to 5,000 mrem at once. Anything more than 10,000 mrem is considered dangerous even if exposure is short. Beyond this point, health concerns become immediate and the risk of illness is very high. These numbers reflect studies into populations that survived the Japan bombings of WWII.
Unlike other types of radiation, gamma rays travel so fast they pass through the entire body very quickly, affecting all organs and tissue. Their ionizing patterns mean exposed body parts can become ionized, their properties changed even after the gamma radiation itself has long evaporated.
Soil and water, and therefore food sources, are primary vectors for gamma ray exposure, although levels are typically very low and do not pose a major risk. Most other sources are medical or industrial in nature. The general public may be exposed to gamma radiation through the use of medical scans and other investigative technology. Of course, nuclear detonation and accidents can be large-scale sources.
Effects -- Acute
The most immediately apparent effect are burns. Close contact with radioactive materials of an especially significant size causes damage to skin tissue. The burns are very painful and deep, making them hard to treat.
Acute effects of intense and sudden radioactive exposure are known as non-stochastic effects and are mostly related to skin damage. However, several other symptoms may occur -- nausea, hair loss and organ failure. In the event of acute exposure that causes these symptoms, treatment is well-nigh impossible and death is very likely.
These effects are associated with very close proximity to a gamma ray-emitting source such as handling of raw radioactive materials or literally touching a nuclear device.
Effects -- Long Term
The stochastic effects of gamma ray exposure are well-known to the public from coverage of nuclear fallout. The primary concern is cancer as a result of cell ionization and mutation. These cancers may appear months and years after exposure has occurred.
For women, birth defects when carrying to term is also a major concern, and a particularly long-lasting manifestation of radiation exposure that can take place even in subsequent generations. Genetic mutation can arise as a result of gamma ray poisoning, affecting people years after exposure.
Because building blocks of the human body such as calcium and iodine retain radiation for long periods of time, it's hard to clear the body of radiation poisoning and thus slow the damage. This is why people exposed to gamma radiation over time are more likely to develop thyroid and bone cancer.
Generally, burns occur almost instantly while nausea, fatigue and vomiting take hours to appear after exposure. Hair loss, incontinence and bleeding may take up to a few weeks to months. Doses of more than 1 million mrem are almost certain to kill a person within a couple of weeks, while 2 million mrem can do so in hours by destroying the central nervous system.