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Radiation Detection

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ObjectivesIdentify sources of radiation Describe the basis of radiation Identify types of radiation Describe radiation dose and its impact on

humans Identify the common types of radiation

detection devices

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IntroductionMost responder are uncomfortable in dealing

with a radiation response

They lack in-depth understanding of radiation and its hazards.

With terrorism on the rise responders need to be comfortable with the detection and monitoring radiation.Nuclear detonation is very unlikely. 

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IntroductionRadiological dispersion device (RDD) is, using a

conventional explosive to distribute radioactive materials.

There is any number of potential sources of radiation that could be used.

Radiation detectors for responders are divided into two major groups.

One measures exposure to radiation.One measures the current amount of radiation

in the area.To be effective measure radiation you will need at

least two detectors. There is not one detector that measures all 5 types of radiation. 4

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Sources of Radiation We are subject to radiation every day

Our bodies have radioactive substances We eat foods containing radiation every day We breathe in radiation with out harm everyday

Our exposure to common radiation sources far exceeds those that would be found at a nuclear power plant Television, Medical test, Elevation

We are subjected to radiation that causes us no harm under normal circumstances

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How Can Radiation Hurt UsBasic atom (nucleus) Electrons, neutrons, and protons Protons and neutrons reside in nucleus Electrons are negatively charged and

orbit the nucleus Protons have a positive charge and

determine the element or type of atom Neutrons are same size as protons but

neutral

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How Can Radiation Hurt UsEach element, with a given number of

protons, can assume several forms, or isotopes.

Which are determined by the number of neutrons in the nucleus?

The chemical properties of each isotope of an element are the same.

If there are too few or too many neutrons the nucleus becomes unstable.

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RadioisotopesIsotopes, whose nuclei are unstable, are

radioactive and emit radiation to regain stability.

This emission of radiation, is known as radioactive decay

Usually takes form of Gamma radiation. May also be Alpha, Beta, or Neutron?

Unstable materials may become stable after one or two decays.

Others may take many decay cycles.

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RadioisotopesRadioisotope decays

by the emission of an alpha or beta particle.

The number of protons in the nucleus changes.

 The radioisotope becomes a different element

ExamplesUranium is the base

for the development of Radon

Common radioactive gas found in homes 

Radon decays into lead.

Cobalt-60 Beta and Gamma

energy emitted Decays to form

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Half-LifeAmount of time for half of a radioactive

source to decay

Activity of a source of radioactive material is a measure of the number of decays per second that occur within it.

Physical size of radioactive source is not an indicator of radioactive strength or activity.

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Radiation DoseAs confusing as understanding the makeup of a

radioactive material, so is the calculation of the radiation dose.

Three measurements can be used to describe radiation dose.

Absorbed dose

Equivalent dose

Effective dose

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$499

$595

Absorbed DoseMeasurement of energy transferred to a

material by radiationMeasured in units called

Gray (Gy) Radiation absorbed dose (rad)

I gray = 100 rad

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Absorbed DoseImpact on humans, we need to understand

the absorbed energy on the body and potential biological damage of radiation on humans. And convert the absorbed dose to equivalent dose.Basic unit of equivalent dose is roentgen.

  This value provides for the amount of ionization in

air caused by X-ray or Gamma radiation.

One roentgen equals 1 REM13

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Absorbed DoseRadiation monitors measure three scales.

REM (R) MilliRem (mR)MicroRem (µR)

The dose of radiation is expressed by a time factor, typically an hour.

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Radiation ProtectionRadiation dose should be kept

“as low as reasonably achievable” ALARA

Three factors that influence radiation dose.

TimeDistanceShielding

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Radiation ProtectionMinimize dose,

Stay near the radiation source for as little time as possible.

Stand as far away from the source and place as much shielding between people and the source as possible.

Time is important as in many cases a human can sustain a short exposure to radiation without being harmed.Example

Limit your exposure to 1 (mR/hr). Your source is 60 (mR/hr)

You could be at the source for 1 minute

 

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Radiation ProtectionDistance from the source also plays a factor.

Inverse square law

Source has a radiation level 20mR/hr at 2 feet

Moving back 4 feet provides an exposure level of 5 mR/hr.

Moving 6 feet would result in an exposure level of 1.25 mR/hr

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Action Levels1mR/hr Isolation zones

Public protection levels5 R Emergency response

All activities10 R Emergency response

Protecting valuable property25 R Emergency response

Lifesaving or protection of large populations˃ 25R Emergency response 

Lifesaving or protection of large population. Only on a voluntary basis for persons who are aware of the risk involved.

 

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Radiation MonitorsCurrent radiation monitors provide two

methods of measuring radiation.

REM and counts per minute

 REM being the most important to

responders.

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Radiation MonitorsThere are a variety of detection devices

out there, the important consideration is the probe attached to the unit.

Probe determines the what type of radiation can be detected Alpha, Beta, Gamma 

Most common probe are pancakes, this is useful for Alpha radiation.

Radiation MonitorsWhen the amount of

radiation becomes higher we need to switch to the internal probe.These are designed

for the higher level of radiation

When the monitor is turned on it will pick up background radiation.

This is naturally occurring radiation and it should read in micro/rem.

It is important that you go do some field testing in your area to determine normal background. 

Then responders know when they are being exposed to radiation at higher levels than background.

 

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Types of Radiation DetectorsThree type that are

common Geiger-Mueller

tubesScintillation

crystals Gamma

Spectroscopy

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Types of Radiation DetectorsGM tubes can detect Alpha, Beta, Gamma 

Uses electric current, a reaction takes place when radiation interacts with the walls of the tube.

Electrons are freed from the atom and flows to the anode which is in the center of the tube. 

This induces an electrical “pulse” which is used to determine when and how much radiation entered the GM tube.

These detectors are generally coupled with a proportional counter, which counts the electrical impulses. You have a choice to count in radiation dose or

counts per minute

Types of Radiation DetectorsScintillation CrystalsUses a crystal that emits

visible light when hit by radiation.Most common is sodium

iodideRadiation hits the

crystal, a pulse of light is produced which is detected by and amplified. 

This produces a electrical signal which is measured to determine the amount of radiation that hit the crystal. 

Scintillation detectors are best for Gamma.

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Types of Radiation DetectorsGamma

Spectroscopy

Radiation Isotope Identifier

Can identify the source of the radiation.

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Types of Radiation DetectorsRadiation Pagers/

DosimeterDetect X-ray and

Gamma radiation, but also will detect high levels of beta. 

When the pager is turned on it calibrates itself to the background.

They are designed to alert and provide reading of one-ten times above background.

 

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SummaryResponders need to become familiar with

radiation detection.Possibility exists for future events.Many radioactive substances exist and when

we deal with unidentified materials we need to check for radiation. 

Knowing how to monitor for it is as important as knowing the action levels.