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Radiation Meter FAQ

Radiation is energy that comes from a source and travels through space and may be able to penetrate various materials. Light, radio, and microwaves are types of radiation that are called nonionizing. The kind of radiation discussed in this document is called ionizing radiation because it can produce charged particles (ions) in matter.

Ionizing radiation is produced by unstable atoms. Unstable atoms differ from stable atoms because unstable atoms have an excess of energy or mass or both. Radiation can also be produced by high-voltage devices (e.g., x-ray machines).

Unstable atoms are said to be radioactive. In order to reach stability, these atoms give off, or emit, the excess energy or mass. These emissions are called radiation. The kinds of radiation are electromagnetic (like light) and particulate (i.e., mass given off with the energy of motion). Gamma radiation and x rays are examples of electromagnetic radiation. Gamma radiation originates in the nucleus while x rays come from the electronic part of the atom. Beta and alpha radiation are examples of particulate radiation.

Interestingly, there is a "background" of natural radiation everywhere in our environment. It comes from space (i.e., cosmic rays) and from naturally occurring radioactive materials contained in the earth and in living things.



External Background Radiation

0.60 mSv y-1, U.S. Average

Natural K-40 and Other Radioactivity in Body

0.4 mSv y-1

Air Travel Round Trip (NY-LA)

0.05 mSv

Chest X-Ray Effective Dose

0.10 mSv per view

Radon in the Home

2.00 mSv y-1 (variable)

Man-Made (medical x rays, etc.)

0.60 mSv y-1 (average)

  • Alpha Radiation
    • Alpha radiation is a heavy, very short-range particle and is actually an ejected helium nucleus. Some characteristics of alpha radiation are: 
      • Most alpha radiation is not able to penetrate human skin.
      • Alpha-emitting materials can be harmful to humans if the materials are inhaled, swallowed, or absorbed through open wounds.
      • A variety of instruments has been designed to measure alpha radiation. Special training in the use of these instruments is essential for making accurate measurements.
      • A thin-window Geiger-Mueller (GM) probe can detect the presence of alpha radiation.
      • Instruments cannot detect alpha radiation through even a thin layer of water, dust, paper, or other material, because alpha radiation is not penetrating.
      • Alpha radiation travels only a short distance (a few inches) in air, but is not an external hazard.
      • Alpha radiation is not able to penetrate clothing.
      • Examples of some alpha emitters: radium, radon, uranium, thorium.
  • Beta Radiation 
    • Beta radiation is a light, short-range particle and is actually an ejected electron. Some characteristics of beta radiation are: 
      • Beta radiation may travel several feet in air and is moderately penetrating.
      • Beta radiation can penetrate human skin to the "germinal layer," where new skin cells are produced. If high levels of beta-emitting contaminants are allowed to remain on the skin for a prolonged period of time, they may cause skin injury.
      • Beta-emitting contaminants may be harmful if deposited internally.
      • Most beta emitters can be detected with a survey instrument and a thin-window G-M probe (e.g., "pancake" type). Some beta emitters, however, produce very low-energy, poorly penetrating radiation that may be difficult or impossible to detect. Examples of these difficult-to-detect beta emitters are hydrogen-3 (tritium), carbon-14, and sulfur-35.
      • Clothing provides some protection against beta radiation.
      • Examples of some pure beta emitters: strontium-90, carbon-14, tritium, and sulfur-35.
  • Gamma and X  Radiation 
    • Gamma radiation and x rays are highly penetrating electromagnetic radiation. Some characteristics of these radiations are:
      • Gamma radiation or x rays are able to travel many feet in air and many inches in human tissue. They readily penetrate most materials and are sometimes called "penetrating" radiation.  
      • X rays are like gamma rays. X rays, too, are penetrating radiation. Sealed radioactive sources and machines that emit gamma radiation and x rays, respectively, constitute mainly an external hazard to humans.
      • Gamma radiation and x rays are electromagnetic radiation like visible light, radiowaves, and ultraviolet light. These electromagnetic radiations differ only in the amount of energy they have. Gamma rays and x rays are the most energetic of these.
      • Dense materials are needed for shielding from gamma radiation. Clothing provides little shielding from penetrating radiation, but will prevent contamination of the skin by gamma-emitting materials.
      • Gamma radiation is easily detected by survey meters with a sodium iodide detector probe.
      • Gamma radiation and/or characteristic x rays frequently accompany the emission of alpha and beta radiation during radioactive decay.
      • Examples of some gamma emitters: iodine-131, cesium-137, cobalt-60, radium-226, and technetium-99m.

The International System of Units (SI) for radiation measurement is now the official system of measurement and uses the "gray" (Gy) and "sievert" (Sv) for absorbed dose and equivalent dose, respectively.

For practical purposes with gamma and x rays, these units of measure for exposure or dose are considered equal. Exposure can be from an external source irradiating the whole body, an extremity, or other organ or tissue resulting in an external radiation dose. Alternately, internally deposited radioactive material may cause an internal radiation dose to the whole body or other organ or tissue.

Smaller fractions of these measured quantities often have a prefix, e.g., milli (m) means 1/1,000. For example, 1 Sv = 1,000 mSv. Micro (μ) means 1/1,000,000. So, 1 Sv = 1,000,000 μSv.

With radiation counting systems, radioactive transformation events can be measured in units of "disintegrations per minute" (dpm) and, because instruments are not 100 percent efficient, "counts per minute" (cpm). Background radiation levels are typically less than 0.10 μSv per hour, but due to differences in detector size and efficiency, the cpm reading on fixed monitors and various handheld survey meters will vary considerably.


Radiation cannot be detected by human senses. A variety of handheld and laboratory instruments is available for detecting and measuring radiation. The most common handheld or portable instruments is:

Geiger Counter, with Geiger-Mueller (G-M) Tube or Probe. A G-M tube is a gas-filled device that, when a high voltage is applied, creates an electrical pulse when radiation interacts with the wall or gas in the tube. These pulses are converted to a reading on the instrument meter. If the instrument has a speaker, the pulses also give an audible click. Common readout units are roentgens per hour (R/hr), milliroentgens per hour (mR/hr), rem per hour (rem/hr), millirem per hour (mrem/hr), and counts per minute (cpm). G-M probes (e.g., "pancake" type) are most often used with handheld radiation survey instruments for contamination measurements. However, energy-compensated G-M tubes may be employed for exposure measurements. Further, often the meters used with a G-M probe will also accommodate other radiation-detection probes. For example, a zinc sulfide (ZnS) scintillator probe, which is sensitive to just alpha radiation, is often used for field measurements where alpha-emitting radioactive materials need to be measured.

It is an instrument that can detect Alpha, Beta, Gamma and X ray. These are primarily emitted by Radioactive materials present and for imaging in diagnostic centers or scanners.

It can detect Alpha, Beta, Gamma and X ray; it also can detect radiation pulse times. It measures the Radiation Dose rate, Impulse Dose rate, Radiation Dose Accumulation & Impulse Dose Accumulation 

The radiation meter DT-9501 was developed to detect α-, β-, γ- and x- radiation. The radiation meter DT-9501 provides many features including a large, high-resolution LCD display with background lights and many indicators. The radiation meter DT-9501 has an internal data storage for up to 2000 data sets, which are saved either manually or automatically. Furthermore the radiation meter DT-9501 is equipped with a Bluetooth interface meant to transfer the measured data with real-time speed to a computer. With the software that is included in delivery, these data can then be further processed and reviewed. The radiation meter DT-9501 stands out by its high accuracy and practical design. 

The radiation meter can be applied in the pharmacy industry, in laboratories, powerhouses, quarries, for ambulance corps, metal industries, petroleum reservoirs, environmental protection etc.

  • Groundwater, radium pollution  
  • Radioactivity of underground drill pipe and equipment  
  • Radon radiation, cesium pollution of the surround environment  
  • Radioactivity of construction materials
  • Radioactivity of porcelain, tableware and glass
  • Local radiation leak and nuclear radiation pollution  
  • The landfill and dump with risk of nuclear radiation  
  • Radioactive material detection of decoration material for houses and office buildings
  • Harmful radiation of personal property and valuable jewelry  
  • X-ray Intensity in Medical and Industrial usage and facilities

The radiation dose absorbed by a person (that is, the amount of energy deposited in human tissue by radiation) is measured using the conventional unit rad or the SI unit gray (Gy). The biological risk of exposure to radiation is measured using the conventional unit rem or the SI unit sievert (Sv)

DOSE : Dose is a general term used to express (quantify) how much radiation exposure something (a person or other material) has received. The exposure can subsequently be expressed in terms of the absorbed, equivalent, committed, and/or effective dose based on the amount of energy absorbed and in what tissues.

DOSE RATE : The quantity of radiation absorbed per unit time

RADIATION DOSE ACCUMULATION : ACCUMULATIVE DOSE is the total dose resulting from repeated exposures of ionizing radiation to an occupationally exposed worker to the same portion of the body, or to the whole body, over a period of time.

IMPULSE DOSE : Is a very short-term radioactive radiation exposure to the tune of 30mS.

IMPULSE DOSE ACCUMULATION : Is the total dose resulting from repeated exposures short time exposure of ionizing radiation to an occupationally exposed worker to the same portion of the body, or to the whole body, over a period of time.