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Ionizing and Non-ionizing Radiation Safety

Ionizing Radiation
Radioactive materials can be a solid, liquid or powder. Atoms in a radioactive material give off their extra energy and this is called a decay product.
Radioactive atoms that give up their extra energy emit radiation. The radiation emitted can be given off as:

Particles ­ alpha or beta
Photons - gamma and x rays

Radiation cannot be detected with our normal senses (seen, heard, felt, smelled or tasted) thus special instruments (detectors) are required to measure the type of radiation that is of interest.

Radiation travels at very high speeds. If radiation hits our bodies, it can transfer some of its energy to the cells that are hit. The amount of energy released at the cell is called a Radiation dose. If a large enough radiation dose is received, biological changes may occur.
Natural background radiation consists of:

Cosmic Radiation
Radioactivity in the earth due to naturally occurring elements including:
-Uranium and daughter products (e.g. radium, radon and bismuth)
-Thorium and daughter products (e.g. radium, radon and lead)
-Some Illuminated exit signs (tritium)

Man-made radioactivity and radiation applications include:

Medical sources such as X-rays, nuclear diagnostic equipment and cancer therapy drugs
Industrial sources such as radiography, oil and mineral exploration and food irradiation
Commercial applications including smoke detectors (americium 241) and lanterns
Nuclear power plants
Fallout due to nuclear weapons testing or power plant melt downs (Chernobyl)

Background radiation in the U.S. is reported to be about 360 millirem (mrem). The background levels are higher in Colorado due to its higher elevation (cosmic effect) and the abundance of uranium which is a source of radon exposure.

Types of Radiation
Alpha particles are large particles that contain 2 neutrons (n) + 2 protons (p). These particles are easy to shield against because of their size. This particle can only travel about 1-2 inches in air and thus a sheet or two of paper can stop the particle. Also, dead layers of skin can shield against this particle. Typical sources of alpha particles include radium-226, radon -222 and uranium 238.

Beta particles have a negative electrical charge that is small and relatively easy to shield against. This particle can travel several feet in air, but it can be shielded with 1/4" plywood or 1/4" Plexiglas. This particle can penetrate the dead skin layer.

X-Rays and Gamma Rays are pure energy without mass. Both are very penetrating electromagnetic radiations having wavelengths much shorter than that of visible light, but they are of different origin. X-rays originate in the extra nuclear part of the atom, whereas gamma rays are emitted from the nucleus in the process of nuclear transition or during particle annihilation. Usually X-rays are produced in an evacuated tube by accelerating electrons from a heated filament to a metal target with high voltages (50-500 KV). Gamma rays are emitted by the nucleus of certain radionuclides during their decay.

Radiation energy is measured in electron volt (eV), but it is usually referred to in Kev or Mev.

Exposure Limits
The ACGIH , has adopted the International Commission on Radiological Protection Guidelines for Exposure to Ionizing Radiation which has dose limits based on effective yearly and five year averages, and annual equivalent doses to specific target tissues including the lens of the eye, the skin, hands and feet.

The SEMI S2 emission limits exposure to X or Gamma rays is dependent upon whether the exposure is to the operator or the maintenance and service personnel. Operator exposure limit should not exceed 2 microsievert / hour (.2 millirem / hour). Maintenance and service workers exposure should not exceed 10 microsievert/ hour (1 millirem / hour).

Control Methods
The basic radiation controls methods consist of:

Time ­ Reducing exposure time
Distance ­ Radiation is reduced by the square of the distance from the source.
Shielding ­ If the radiation field is intense and source is small, shielding the source is generally the most practical.

Non-ionizing Radiation Hazards
The electromagnetic spectrum extends over a broad range of wavelengths, from less than 10-12 centimeters (cm) to greater than 10 ¹⁰cm. The shortest wavelengths are associated with cosmic or X-rays and the longer wavelengths are associated with microwave and electrical power generation. Ultra violet, visible and infrared radiations occupy an intermediate position.

The eye is the primary organ at risk to all non-ionizing radiation. Ultraviolet radiation at a wavelength ranging from 0.1 um to 0.4 um has the greatest effect on the eye.
Non-ionizing Radiation has insufficient energy to dislodge orbital electrons (<12 electron volts) like that of ionizing radiation. Common applications of this type of radiation for private industry includes: heat sealers, microwaves and plasma.

Electromagnetic Waves are characterization by the Intensity or strength of the wave which is expressed as:

Volts (V) / m for Electric field (E) or
Amperes (A) / m for Magnetic field (H)
Frequency (cycles per second = Hz)
Wavelength (meters> km / m / um / nm)

Non-ionizing Radiation Sources include:

LASERS
Static Magnetic
Radio-Frequency (RF - 30 kHz > 300 MHz) and wavelengths ranging from 3x10¹⁰ um to 3x10¹⁰ um.

Visible light spectrum ranges from 0.7 um to 0.4 um
Ultraviolet (UV) Light (100 > 400nm)
Infra-red (IR) Light (760 nm > 1mm)

Static Magnetic Fields
The static magnetic field strength is dependent on the process application. Measurements must be taken during normal operation and during maintenance and servicing. Exposure levels will vary with the exposure site i.e. whole body versus limb. (Note: Units: 10 milliTesla = 100 Gauss)

Radio Frequency
Radio-Frequency (RF) Equipment Application wavelengths for microwaves, industrial applications, induction heaters and cellular phones operate at a RF range from 30 KHz ­ 300 MHz.

Instrumentation such as the Tri-axis - E / H / Integrated probe (frequency specific) can be used to make the following measurements:

E field = Volts / meter
H field = Amperes / meter
Equivalent plane wave density (S) = mW/cm2
S = E2 / 3770 or S = 37.7 H2

Measurement should be made at a distance of 2 cm up to 20 cm during a 6 minute averaging period.

RF Exposure Guidelines
OSHA PEL (10 mW/cm2) mW/cm2

ACGIH TLV Frequency Dependant

For example at 13.56 MHz
    S = 4.89 mW/cm2 for E field
    S = 54.3 mW/cm2 for H field

RF Biological Effects
Energy transfer occurs by passing heat to the system or tissue. Attenuation of the energy field can be attenuated by affecting the exposure factors such as the RF intensity, frequency, size or shape.

Ultraviolet Light
Ultraviolet (UV) Light Wavelength 100 nm - 400 nm
There are a number of industrial applications and consumer products that operate at this broad wavelength including: Plasma environment, Curing, Germicidal (220 - 280nm), Solar (>290nm), Fluorescent lamps, Welding,
Suntan (Vitamin D3), Production of Ozone (O³) (170 -220nm), Process point detection.
Measurements of UV light operating at this wavelength can be made using a light meter with a spectral range unique to this light source. It is important to consider any process variables which might affect the power level and specific wavelength. It is important to perform background light adjustment and to zero the instrument. The units of measurement are microWatts (uW)/cm2 or microJoules (uJ)/cm2. Note: 1 Watt = 1 Joule / sec
Exposure to light in this wavelength can cause acute and chronic eye irritation. Symptoms of exposure may not be felt for 4 to 6 hours. The symptoms of exposure include photokeratitis and /or conjunctivitis (UV-B & UV-C) or development of cataracts. It is important to remember that exposure factors are related to the wavelength and energy of the source and time of exposure.
Acute and/or chronic exposure to the skin can produce any of the following symptoms including erythema (reddening of the skin much like a sunburn), melanin production and migration (360 ­ 400 nm), aging and cancer.

UV Exposure Guidelines
ACGIH TLV

0.1 uW/cm2 exposure limit for broadband UV source in the Actinic region = 180 - 315 nm
Measurements must use probe which has weighting based upon for relative hazard per ACGIH table
Sources of specific wavelength have wavelength dependant criteria based upon relative hazard
UV-A (315 -400nm) = 1.0 J/cm2 <1000s

Near Infrared (IR) Radiation
Typical wavelength ranges are 760 nm to 3 um. Tools or operations operating at this wavelength include:

Drying ovens or baking of paint, varnishes, adhesives,
Heating of metal parts
Conditioning surfaces
Brazing
Dehydrating textiles, paper, leather, food, pottery ware
Spot heating of any material

Measurements of IR operating at this wavelength can be made using a light meter with a spectral range unique to this IR light source. It is important to consider any process variables which might affect the power level and specific wavelength and to zero the instrument. The instrument units of measurement are milliWatts per cm2 .

Exposure to light at this wavelength can cause acute and/or chronic eye irritation. Symptoms of exposure may not be felt for 4 to 6 hours. The symptoms of exposure include photokeratitis and /or conjunctivitis (UV-B & UV-C) or development of cataracts. It is important to remember that exposure factors are related to the wavelength and energy of the source and time of exposure.

Acute and/ or chronic exposure to the skin can produce any of the following symptoms including erythema (reddening of the skin much like a sunburn), melanin production and migration (360 ­ 400 nm), aging and cancer.

It is important to remember that Near IR exposure factors are related to the wavelength and energy of the source and time of exposure. Exposure hazard to the eye can be acute and/or chronic. Glass blower¹s can develop cataracts (heat cataract). The cornea, iris, lens and retina are more affected by shorter wavelengths.

Skin exposure hazards can be acute and/ or chronic depending on the wavelength and symptoms can include:

Complete absorption by skin for far wavelength (5,000nm - 0.3 cm)
Skin burn / increased persistent skin pigmentation (750 - 1,500 nm)
Short wavelengths (760- 3 um) capable of eye injury

IR Exposure Guidelines
ACGIH TLV (Periods greater than1000 seconds)

10 mW/cm2

Infra-red (IR) Light
The application of this light source is found in a plasma environment where the signal is pulsed. It is important to consider any process variables (recipe dependent) which might affect the instrument readings. It is important to zero the instrument. The instrument units of measurement are Watts per cm2.