Basics of Radiation

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Topics

• Types of Radiation• How Radiation Interacts With You• Radiation Safety• Why Measure Radiation Today• Summary• Radiation Equivalents

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Two Types of Radiation

• Radiation can be non-ionizing or ionizing

• Non-ionizing radiation is generally a low energy electromagnetic wave– Sunlight– Radio waves– Microwaves– Infrared waves

• Mostly harmless

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Ionizing (Nuclear) Radiation

• Has enough energy to ionize (alter) atoms and molecules

• Because it can ionize, it can cause biological damage

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Ionizing Radiation

Ionizing radiation is all around us• Outer space, the earth, and medical treatments

• Low levels of naturally occurring radioactive material are in our environment, the food we eat, and in many consumer products

• Some consumer products also contain small amounts of man-made radioactive material

• Most of your annual dose of radiation comes from Radon gas in your house

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Types of Ionizing Radiation

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Topics

• Types of Radiation

• How Radiation Interacts With You

• Radiation Safety

• Why Measure Radiation Today

• Summary

• Radiation Equivalents

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What is a Dose of Radiation?

• When radiation hits your body, and its energy is transferred to your tissue, you have received a dose of radiation.

• The more energy deposited, the higher your dose.

• Measured in rem (R).

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What is the Dose Rate of Radiation?

• The amount of radiation given off by a source over time

• Measured in rem per hour (R/h)

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Gatling Gun Analogy

• The number of bullets released per hour is the dose rate

• The number of bullets that hit you is the dose

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Irradiated or Contaminated?

Irradiated

• You are irradiated when radiation hits you

• You do not become radioactive when you are irradiated

• Many foods are irradiated to kill molds and bacteria

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Irradiated or Contaminated?

Contaminated

• Contamination is radioactive dirt

• You can become contaminated by touching radioactive dirt

• Contamination can be washed off like any dirt

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Radioactive Contamination

Radiation cannot make you radioactive*

* Understanding Radiation: Bjorn Wahlstrom (overrides copyright below)

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Radioactive ContaminationRadioactive contamination can stick to clothes and skin. It can be washed away like any dirt*.

* Understanding Radiation: Bjorn Wahlstrom

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Common Doses in Everyday Life

100,000 Average annual chest x-ray exposure2,000,000 Annual exposure from radon gas in homes810,000 Annual exposure at high elevation

10,400,000 Gastro-intestinal Barium x-ray (GI series)

Cause of DoseDose (µR)

1R = 1,000,000 μR

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Acute Radiation Doses

μR R

25,000,000 – 50,000,000 25 - 50First sign of physical effects – drop in white blood cell count

100,000,000 100Vomiting within several hours of exposure

320,000,000 - 360,000,000 320 - 36050% die within 60 days with minimal supportive care

480,000,000 - 500,000,000 480 - 50050% die within 60 day with supportive care

1,000,000,000 1,000 100% die within 30 days

Dose Effects

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Topics

• Types of Radiation

• How Radiation Interacts With You

• Radiation Safety

• Why Measure Radiation Today

• Summary

• Radiation Equivalents

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Radiation Safety

• The fundamental principle of radiation safety is that radiation exposure should be As Low As Reasonably Achievable (ALARA).

• The three factors influencing radiation dose are:– Time– Distance– Shielding

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ALARA - Time

• The less time you’re exposed, the less exposure you get

• Dose = Dose Rate x Time

• Limit your time near the radiation source!

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ALARA - Distance

• The farther away from the source you are, the weaker the source is to you

• Exposure levels are based upon the inverse square law

• Increase the distance between you and the source!

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ALARA - Shielding

• Shielding can reduce or stop radiation from hitting you– α can be absorbed by a piece of paper– β can be absorbed by 1” of aluminum or glass– γ can be absorbed by thick lead shields– n can be absorbed by paraffin, water,

polyethylene• Increase the amount of shielding material

between you and the source!

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Shielding/Attenuating Radiation

Pap

er

Glass, th

in m

etal

Lead

, C

on

crete

W

ater, P

olyeth

ylene

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Topics

• Types of Radiation• How Radiation Interacts With You• Radiation Safety• Why Measure Radiation Today• Summary• Radiation Equivalents

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Radiological Terrorism

Radiological Terrorism is a real and possible threat

• High psychological/emotional impact

• High economic impact

• Many devices are easy to build

• Al Qaeda has threatened radiological terrorism

• It’s already being done

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Threat Comparison

Sev

erity

of

inci

dent

Probability of incident

Stolen nuclear weapon

Improvised nuclear device

RDD

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Radiological Terrorism

• Nuclear warheads use special nuclear materials– Plutonium– Uranium

• Medical and industrial radioactive materials cannot produce a nuclear warhead – they can only be used to contaminate

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Radiological Dispersion Devices

RDDs take two main forms

• A dirty bomb– Radiological material

wrapped in conventional explosives

• A simple radioactive source left discretely in a public place

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Making an RDD

• All you need is radiological material

• Orphan sources– Radiological materials are used everyday in a

variety of applications– Some sources are lost, forgotten, or disposed

of improperly – orphan sources– Over 200,000 available today

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Example of an RDD

• 1 pound of HE, two patient doses of liquid Technetium-99m (Tc-99m) near the HE

• Weather: 30 degrees F, sunny, light winds with gusts of 20 mph

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Example of an RDD

Contamination measured at 4 times background

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Commonly Available Isotopes Suitable For RDDs

Radioisotope Gamma Emission Neutron EmissionDetect with Gamma

Sensor*Cobalt-60 Yes No Yes

Cesium-137 Yes No Yes

Iridium-192 Yes No Yes

Stronium-90 No* No Yes

Americium-241 Yes No Yes

Californium-252 Yes Yes Yes

Plutonium-238 Yes Yes Yes

*Can be detected with a gamma sensor because daughter isotope emits gamma.

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Innocent Sources

• Radioactive sources seen in typical day to day operations– Cause innocent alarms– Could be used to disguise a real source

• Containers of tile & bricks containing uranium & thorium

• Containers of bananas & fertilizer containing potassium

• Patients who have received nuclear medicine treatments

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Topics

• Types of Radiation• How Radiation Interacts With You• Radiation Safety• Why Measure Radiation Today• Summary• Radiation Equivalents

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Summary

• Dose is measured in R– Cumulative effect on the

body

• Dose rate is measured R/h– Amount of radiation in your

vicinity

• Contamination is radioactive particles in or on the body

• Irradiation is exposure to a radioactive source

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Summary

• Time

• Distance

• Shielding

Three factors influenceradiation dose

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Questions?

RAE Systems3775 North First Street

San Jose, CA 5134

Voice: 408-952-8200

Fax: 408-952-8480

www.raesystems.com

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Topics

• Types of Radiation• How Radiation Interacts With You• Radiation Safety• Why Measure Radiation Today• Summary• Radiation Equivalents

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Radiation Equivalents

Rem Millirem (mrem)Microrem

(µrem)

1 1,000 1,000,000

0.1 100 100,000

0.01 10 10,000

0.001 1 1,000

0.0001 0.1 100

0.00001 0.01 10

0.000001 0.001 1

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Radiation Equivalents

Unit Measured Quantity

Rad, Grey (Gy) Absorbed Dose

Rem, Sievert (Sv) Biologically Equivalent Dose

Unit Equivalents

100 Rem 1 Sv

1 Rem 10 mSv (millisievert)

1 mrem (millirem) 10 Sv (microsievert)

1 rem (microrem) 0.01 Sv