By: Amal

Detecting Radiation

Radiation can not be detected by sight, hearing, feeling, or smelling. Radiation can only be detected by radiation devices that warn people of the presence of radiation and to keep watch of their level of r effected radiation. The most common radiation detectors are Geiger counters, scintillation counters, and film badges. These devices function because of the effects of radiation when it strikes atoms. Ions are created when the radiation knocks electrons off the atoms. These ions can then be detected by radiation devices and can also be seen through a photographic plate that shows the areas exposed to radiation with color. This radiation that has sufficient energy to knock off electrons of atoms of the attacked substance to produce ions is called ionizing radiation. Ionizing radiation is radiation emitted by radioisotopes.

Geiger Counter

Geiger counters can detect gama, alpha and beta radiation. A geiger counter has a Geiger- Mueller tube, a visual readout, and an audio readout. The Geiger- Mueller tube is a metal tube filled with gas that detects the radiation. This metal tube has a central wire electrode that is connected to a power supply. At one end of the tube, there is a thin window which is made from a material that can be penetrated by alpha, beta, and gamma rays. When ionizing radiation penetrates the thin window at that end of the metal tube, the gas inside the tube becomes ionized creating electrons and ions. This ionized gas becomes an electrical conductor because of the ions and the free electrons produced. The flow of electrons produces an electrical current flowing between the tube and the inside wire. Current flows every time the gas-filled metal tube is exposed to radiation. The bursts of current are detected by the Geiger counter which records the amount of radiation detected by these bursts. The Geiger counter beeps when it detects a burst of current and calculated the amount of radiation.

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Scintillation Counter

Detecting radiation can also be accomplished with the use of a scintillator. A scintillator is a substance which emits light when struck by an ionizing particle. Scintillation counters have been functioned to detect all types of ionizing radiation, and is therefore the most useful.
A scintillation counter detects radiation by using a transparent crystal coat, usually phosphor, that emits bright flashes of light when ionizing radiation strikes the crystal. Electrons from the ionizing radiation effect are trapped into an excited state and emit a photon when they decay to the ground state. The emition of a photon causes a bright flash of light to appear called scintillations. The number of flashes, and each of their energies are detected electronically with the scintillation counter. The information is then converted into electronic pulses, which are measured and recorded.

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Scintillation counter
Scintillation counter

Film Badge

A film badge consists of various layers of photographic film covered with black lightproof paper. These many layers of photographic film covered with black lightproof paper are all encased in a plastic or metal holder. This film badge is an important and useful radiation detector, epecially for people who work near any type of radiation source, such as technicians and radiologists. These people who work near a radiation source wear the film badge the whole time that they are at work. At specific intervals, the film is removed and developed depending on the frequency with the type of work being involved. The darkening of the film determines the strength and type of radiation that was exposed. These results are then recorded. Film badges can only monitor the degree of radiation exposure. Film badges can not protect a person from radiation exposure. Keeping a safe distance from the radiation source and using appropriate shielding is the only way to protect oneself from radiation.

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What exactly are gamma, alpha, and beta rays in a brief definition, and why are they significant in Geiger Counter? In other words, does the Geiger Counter differentiate these types of rays? -Thanh

Ben Fallis:
Alpha particles are fast-moving, high energy helium atoms, able to be stopped by a few inches of air or a piece of paper.
Beta particles are fast-moving, high energy electrons, able to be stopped by a few feet of air or a few millimeters of paper or plastic.
Gamma particles are fast-moving, high energy photons, able to be stopped by a few inches of lead.
I'm not sure about your last question, but I am almost certain that the geiger counter can't differentiate between these types of radiation.

Thanh, like Ben said, Geiger counters can not differentiate between the different types of radiation. It can only detect the amount of radiation. -Amal
Prentice Hall: Chemistry