Arsene M. Thidimu

College Physics

Nelson Kilmer

April 21, 2003

Gamma Rays

It's sometimes misunderstood when we're talking about the differences between gamma rays, x-rays, and other kinds of radiation in our nature because they're all characterized as being electromagnetic radition. Why are X-rays and Gamma rays different in nature? It is a question that's being asked by many of us, especially physics students, because they're both high-energy elecromagnetic radiation. In the following report, I will explore the question above to give a better understanding of Gamma rays and also define some other special features of it.

A gamma ray is packet of electromagnetic energy, commonly called a photon. In other words, accoding to Tom Swanson, Ph. D. Physics at Oregon State University, Gamma rays refer to electromagnetic radiation from nuclear interactions, while X-rays come from atomic interactions. Professor Tom also supported his idea by saying that even tough Gamma and X-rays are both high energy electromagnetic radiation and, if you didn't already know the source, you couldn't tell for sure if a particular photon was a gamma ray or an X-ray.

Flashes of gamma-rays coming out of the 
bottom of storm clouds

It's also important to acknoweldge that Gamma photons are the most enernetic photons in the electromagnetic spectrum. Besides Professor Tom, the U.S. Environmental Protection Agency state that Gamma rays originate in the nucleus and X-rays in the electron fiels surrounding the nucleus. Click on the link below to have a better understanding of differences in terms of Frequency (Hz), Wavelength (m), Photon Energy (electon Volt (eV)), and Photon Energy (Joule), between all kinds of radiation found in the electromagnetic spectrum.

Electromagnetic Spectrum

It always has been a good discussion to know who discover gamma radiation. According to many physicists, Paul Villard, A French physicist working in Paris at the same time as Marie and Pierre Curie, is credited with discovering gamma rays. Paul Villard's main interest was in chemistry, which guided him into his studies of cathode rays, X-rays, and "radium rays." Villard's experiments in radioactivity led to the unexpected discovery of gamma rays in 1900.

French chemist and physicist Paul-Ulrich Villard 
discovered Gamma rays from radiation in 1900.

Villard recognized them as being different from X rays because Gamma rays had much bigger penetrating depth. He also had discovered that they were emitted from radioactive substances and were not affected by electric or magnetic fields.

Even tough Paul Villard had discovered gamma rays, Ernest Rutherford showed that they were a from of electromagnetic (EM) like light only wih a much shorted wavelength than X-rays. The name Gamma ray was given by Ernest Rutherford. Later on in history, Rutherford and his other friends received a Nobel Prize for this discovery... but Paul Villard never benefited from it.

Ernest Rutherford

Besides Villard and Rutherford, another French Physicist called Henri Becquerel was also given credit with teh discovery of Gamma rays. In 1986, he revealed that uranium minerals could expose a photographic plate though a heavy opaque paper. He then reasoned that Uranium emitted some hidden light comparable to X-rays. He called it "metallic phosphorescence." After all, Becquerel found gamma radiation being emitted by radium-226. Radium-226, according to the U.S. Environmental Protection Agency, is part of the uranium decay chain and commonly occurs with uranium.

Every radiation in the electromagnetic spectrum has its own properties. Gamma radiation is very high-energy ionizing radiation. Gamma photons have about 10,000 times as much energy as the photons in the visible range of the electromagnetic spectrum. They have no mass and no electrical charge. They are sometimes called pure electromagnetic energy. Because they have such high energy, gamma photons travel at the speed of light ( C = 3*10^8) and can cover hundreds to thousands of meters in air before using their energy. Gamma rays can pass through many kind of materials, including human tissue. They only exist as long as they have energy. Once their energy is used, whether in air or solid materials, they cease to live. The same condition applies also to X-rays.

To have a broad understading of Gamma radiation, it's also important to understand the phenomena called gamma ray emission. Gamma radiation emission happens when the nucleus of a radioactive atom has too much energy. Radioactive substances like Cobalt-60 and Cesium-137 emit gamma radiation. Most scientists believe taht a neutron changes to a proton and a beta particle. The additional proton changes the atom to barium-137. The nucleus then ejects the beta particle. Even tough the nucleus ejects the beta particle it still has too much energy and ejects a gamma photon to become more stable. Gamma emmitting radionuclide is the most widely used radiation sources. The penetrating power of gamma photons has many applications. So far, the most three radionuclides are Cobalt-60, Cesium-137 and Technetium- 99m. Cesium-137 is mostly used for cancer treatment, measure construction sites, measure and control flow of liquids in numerous industrial processes, and to ensure the proper fill level for packages of food, drugs and other products. Cobalt-60 is also used for some treatment of cancer. Technetium-99m is the moslty used radioactive isotope for diagnostic studies.

Usage of Gamma rays:

1. Medecine:

Mostly usend in killing and treat certain types cancers and tumors. It is also important to know that Gamma rays passing through tissue of the body produce ionization in tissue. they can also harm the cells in our body. Gamma rays can also detect brain and cardiovascular abnormalities.

Click this link to see how gama cameras are used to detect cancer:Gamma cameras

2. Industry:

Gamma rays can be used to examine metallic castings or welds in oil pipelines for weak points. The rays pass through the metal and darken a photographic film at places opposite the weak points. They are used to kill pesticides and bugs in food. They are also used in nuclear reactors and atomic bombs. For instance in the Hiroshima and Nagasaki tragedy, the initial reaction of the bomb was primarily composed of gamma rays and neutrons. The residual radiation is classified into 2 types: first, the nuclear fission products and the 235 Uranium that had not undergone nuclear fission dispered in mid-air and were converted into a radiation source consisting of gamma rays, beta rays and alpha rays. Second, the neutrons that bombarded the ground caused nuclear reactions, which led to induced radioactivity.

3. Consumer goods:

They are used in food industry. The radioisotopes preserve foods. This process is called food irradiation. Irradiation can eliminate harmful bacteria from our meat supply before it goes to the consumer. The gamma rays don't come in contact with goods, but beta radiationkills various organism, such as bacteria, yeast and insects.

It is difficult to detect or see gamma rays. You need specialized equipment to detect them. Gamma rays are considered the primary risk to the population during most radiological emergencies. Sometimes, when the term "radiation sickness" is used to describe the effects of large exposure in short time periods, the most common results from gamma radiation. High levels of gamma rays can produce dangerous ionization of the tissue and can cause skin cancer.

On the right, The Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory has detected gamma rays from the Moon as it passed through the instrument field of view severaltimes between 1991 and 1994. The average flux, and the energy spectrum of the lunar gamma radiation are consistent with a model of gamma ray production by cosmic ray interactions with the lunar surface, and the flux varies as expected with the solar cycle. Although the same processes may occur on the Sun, EGRET does not detect the quiet Sun.

In conclusion, Gamma rays are different from X-rays. They have no mass or electrical charges. Gamma rays originate in the nucleus, while X-rays originate in the electron fields surrounding the nucleus. Gamma rays have good affects and bad affects on nature. The dangers of gamma rays are not easy to deal with. With exposure to gamma rays, you can be easily affected with the risk of mutations or cancer in tissue. Even tough Gamma rays and X-rays can cause cancer, they can also be used to destroy cancer cells: radiotherapy.


1.EPA's Radiation Protection Program: Understanding Radiation.

2.National Aeraonautics and Space Administration


4.La decouverte des rayons gamma