Chapter 10_Measurement of Radiation

8/10/2019 Chapter 10_Measurement of Radiation

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NHA / FKPPT


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Describe methods used for measuring andsampling hazardous agents.

Conduct surveys in the workplace to assessthe risk of health hazards.

Analyze and present the results in a formuseful for health hazards assessmentpurposes to enable management to complywith relevant legislation.


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There are two types of radiation: ionizing andnon-ionizing.Ionizing radiation is defined as thespontaneous emission of ionizing particlesand/or ionizing photons (or gamma) from anucleus.Non-ionizing (or non-ionising ) radiation refers to any type of electromagnetic radiationthat does not carry enough energy perquantum to ionize atoms or molecules that is,to completely remove an electron from anatom or molecule.


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UV, visible, & IR radiation

RF & ELF extremely lowfrequency


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Although some radiation exposure is natural inour environment, it is desirable to keep

radiation exposure as low as reasonablyachievable (ALARA) in an occupationalsetting.This is accomplished by the techniques of

time , distance , and shielding . Time: The shorter the time in a radiation field, theless the radiation exposure you will receive.

Distance: The farther a person is from a source of

radiation, the lower the radiation dose. Shielding: Placing a radioactive source behind amassive object provides a barrier that can reduceradiation exposure.


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UV, visible, and IR radiation2 systems of quantities;- Radiometric = physical system that can be used to

describe the emission from, or exposure to, anyoptical radiation.

- Photometric = subset of the radiometric system butis based on the response of the human eye to opticalradiation

and is used only for visible radiation

Irradiance-illuminance, radiance-luminance, radiantintensity-luminous intensity,


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(1) sunlight;(2) lamps;

(3) incandescent (warmbody) sources;

(4) lasers.


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Radiometer= to measure UV in

effective irradiance(Eeff );

= W/cm,

Broad-band radiometers: A portableresearch radiometer with an opticalsampling system. The sampling probe

incorporates three elements:diffuser, filter, and detector;


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A hand-held radiometer and optical samplingprobe is shown with a small printer.


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Optical sampling system; input optics,band filters/ monochromators,detectors, & the electronics package.

Useful UV detectors for continuous- wave(CW) sources;

1. Photoelectric detectors (photodiodesand photomultiplier tubes)

2. Thermal detectors (thermopiles andpyroelectric detectors).

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Diffusers = uniform illumination of the detector,make the detector-source alignment less critical

Monochromators = to measure a narrow spectralregion without the use of filters.

Bandwidth or bandpass of a monochromator is the

width of the transmitted spectral distribution.


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Output = effective irradiance or radiance

Effective UV irradiance is calculated forinstruments that have their output in spectralirradiance ( E), which is a wavelength-dependentquantity, as:

E = measured spectral irradiance in a narrow bandwidth,S = relative spectral effectiveness at a given wavelength within

that band, and is the actual bandwidth in nanometers. TLVL = function of the instrument.


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Use of a hand-held radiometer. The optical sampling probe is directed toward

the source and the irradiance (or radiant exposure) is read from the display


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For welding arcs, the effective UV irradiance at agiven distance can be estimated - arc current is

known.

It has been found that values of measured effectiveirradiance do not exceed

I = the arc current in amperes,

r = distance from the source in centimeters.


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Monitoring = to detect and measure ELFelectric and magnetic fields.

The root mean-square (RMS) of the detectedsignal is computed.

The measurement is displayed on a directreadout meter.

Magnetic fields = magnetic flux density, in

units of milligauss (mG) or microtesla (mT).

Electric fields in units of volt/meter (V/m).


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Distances and heights relative to thesources of ELF electromagnetic fieldsmust be considered during monitoring.

Measurements are recorded at variousvertical and horizontal distances from thesource

The contribution of electric field andmagnetic field energies to the area thencan be attributed to the operatingsource.


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Tragedy: Chernobyl, 1986.

Main types = x-rays, gamma rays, alpha particles,beta particles, neutrons, and other high-energyparticles.

Alpha particles have the same structure as thenuclei of helium atoms: two protons and twoneutrons.

- little penetrating power- stopped by a piece of paper or the outer layer ofskin


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Beta particle = electron (negative charge) or positron(positive charge) separated from the nucleus of an atom.

- Smaller than alpha particles,- Travel at higher speeds and have enough penetrating

power to pass through nearly 1/4 in of tissue.

Gamma radiation = energy waves in the electromagneticspectrum.

- During radioactive decay, certain materials emit gammarays from the nucleus of decaying atoms.

- Greater penetrating power- Stopped by dense materials.


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X-rays = Energy waves generated from outside the nucleus

of an atom during decay or by impact from externalelectrons.- Penetrating powers similar to gamma rays.

Neutrons are particles that have high mass and no charge.- Produced by nuclear reactions.- Neutron energies are classified as slow, medium, and

fast.- High-density materials containing high levels of hydrogen

atoms are necessary to stop them.


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Natural and artificial

Natural radiation = cosmic and gamma radiation foundin certain soils.

- Building products ; create external exposures.- Some ingested food and water and some inhaled air;

internal exposures.- Estimates indicate that people in the US receive

approximately 125 mrem of natural radiation peryear: 100 mrem externally and 25mrem internally.


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Artificial sources = consumer products, medicalsources, occupational sources, and general

environment sources.

Products with ionizing radiation:- television sets, computer monitors, some smoke

detectors.- Medical sources are gamma rays, beta rays, and

x-rays for diagnostic and treatment procedures.- Occupational sources ; mining, production of

radioisotopes, nuclear fuel and weapons,transportation, waste handling and accidentalhandling.


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Different units of measure are used dependingon what aspect of radiation is being measured.For example, the amount of radiation beinggiven off, or emitted, by a radioactive materialis measured using : conventional unit curie (Ci),or the SI unit becquerel (Bq).The radiation dose absorbed by a person ismeasured using the conventional unit rad or theSI unit gray (Gy).The biological risk of exposure to radiation ismeasured using the conventional unit rem or theSI unit sievert (Sv).


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Survey devices or equipment consist ofportable, multiscaled radiation detectors toevaluate radiation dose over a relativelyshort period of time (usually dose perminute).

Survey instruments can operate on batteries,be light enough for an adult to carry in one

hand, and respond in multiple ways toradiation fields.


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Monitoring devices or equipment evaluates aradiation field over a relatively long period

of time (week or month).

Personnel monitors are generally evaluatedon a monthly schedule.

Personnel who require shorter timeevaluation wear special monitors.

Room monitoring equipment may be activecontinuously with threshold warning devices.


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Human exposure to ionizing radiation is part of coexistencewith the planet.

Background radiation includes exposure from long-livedradioactive nuclides in the earth, water, and air.

With the advent of modern medicine, exposure from dentaland medical X-rays, nuclear medicine studies, and radiationtherapy add to the accumulated exposure for both thepatient and the occupational worker.

Industrial and consumer products add to the body burden.

Radiation limitation levels are set for the occupationalworker, with more limited measures taken for the generalpublic.

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Chapter 10_Measurement of Radiation