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Nuclear Science Merit Badge. Howard Matis Lawrence Berkeley National Laboratory. Radiation gives Superhuman Powers to Spiderman. Radiation gives Superhuman Powers to The Hulk. Chernobyl. Radiation is . Plot device for fiction Scary Deadly Life saving Misunderstood Useful. 60°. 60°.

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Nuclear science merit badge l.jpg

Nuclear Science Merit Badge

Howard Matis

Lawrence Berkeley National Laboratory

Howard Matis - [email protected]

Radiation gives superhuman powers to spiderman l.jpg
Radiation gives Superhuman Powers to Spiderman

Howard Matis - [email protected]

Radiation gives superhuman powers to the hulk l.jpg
Radiation gives Superhuman Powers to The Hulk

Howard Matis - [email protected]

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Howard Matis - [email protected]

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Radiation is

  • Plot device for fiction

  • Scary

  • Deadly

  • Life saving

  • Misunderstood

  • Useful

Howard Matis - [email protected]

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Radiation Hazard Symbol

  • The symbol is placed on a placard with the word CAUTION or DANGER or GRAVE DANGER centered about it. Under the symbol is the information addressing the types of hazards.

  • Examples are:

    • Radiation Area High Radiation Area Airborne Radioactivity Area Contaminated Area Radioactive Materials Area

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Radiation is Energy

  • The energy is given off by unstable (radioactive) atoms and some machines.

We will be focusing on ionizing radiation and its health effects.

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Atoms Building Blocks of Matter

  • All matter is made up of atoms

  • The nucleus is in center

    • almost all of the mass

  • Electrons go around

  • At this scale, electrons are at the edge of town

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What is a Nucleus?

  • Quarks determine if proton or neutron

  • Neutrons

  • Protons

  • Protons determine chemical properties

  • Ratio of neutrons to protons make a nucleus stable or unstable

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  • Many elements have nuclei with the same number of protons

    • same name

    • same chemistry

    • but different numbers of neutrons

    • different masses

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Examples - Isotopes

  • Hydrogen (1H)

    • 1 proton, 0 neutrons, mass 1

  • Deuterium (2D)

    • 1 proton, 1 neutron, mass 2

  • Tritium (31T)

    • 1 proton, 2 neutrons, mass 3

  • Helium (4He) (a-particle)

    • 2 protons, 2 neutrons, mass 4

  • Helium-3 (3He)

    • 2 protons, 1 neutron, mass 3

  • Uranium-238 (238U)

    • 92 protons, 146 neutrons, mass 238

  • Uranium-235 (235U)

    • 92 protons, 143 neutrons, mass 235

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Types of Radioactivity

Six Common Types

Alpha Decay

Beta Decay

Gamma Decay



Cosmic Rays

  • Each type of radiation is ionizing

  • But different properties

    • affect the hazards they pose

    • the detection mechanism

    • shielding

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How Does it Decay?

  • Alpha - lose an alpha particle ( - helium nucleus)

  • Beta - emit a beta particle ( - electron or anti-electron)

  • Gamma - emit a gamma ( or photon or light particle)

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Alpha decay l.jpg
Alpha Decay

  • Alpha particle or helium nucleus emitted

  • Nucleus changes mass by four units and charge by two units

  • Common for heavy elements

  • Changes chemical properties

  • Alpha particle easily stopped

    • 4 x nucleon mass

    • +2 Charge

    • Big

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Beta Decay

  • Beta minus - neutron converts to electron and anti-neutrino

  • Beta plus - proton converts to a anti-electron and neutrino

  • Nucleus changes charge but not mass number

  • Changes chemical properties

  • Radiation moderately penetrating

    • +1 charge

    • Small electron

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Gamma decay l.jpg
Gamma Decay

  • Nucleus changes energy level

    • Emits gamma ray or photon

  • Nucleus stays the same

    • No change in chemical properties

  • Very penetrating

    • Almost no size

    • Neutral

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Gamma and X-rays



Absorption of Radiation

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Sometimes a very heavy nucleus will fall apart before it can emit an alpha particle.

The heavy parent nucleus fissions …

… into two lighter (radioactive) fission fragment nuclei plus some left over neutrons

Fission can release an enormous amount of energy and is utilized in power plants and fission bombs (A-bomb).

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  • When two nuclei collide and stick together

  • Process that powers the sun and stars

  • All life arises from it

  • Not usually found in every day experience on Earth

  • Component of the H-bomb

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How Unstable Is It?

  • The “Half-life” describes how quickly Radioactive Material decays away with time.It is the time required for half of the unstable atoms to decay.

  • Some Examples:

    • Some natural isotopes (like uranium and thorium) have half-lives that are billions of years

    • Since Earth is about 5 billion years old, short lived naturally produced isotopes gone

    • Most medical isotopes (like 99mTc) last only a few days

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Half-Life Experiment

Guess the number I am thinking

from 1 to 4

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Some Isotopes & Their Half Lives

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How do we Measure the Amount of Radiation?

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Radiation Absorbed Dose

Qty: Dose

Unit: rad (Gray)

1 rad = 1000 mrad

1 rad = 100 erg/gram

1 Gy =100 rad


Qty: Activity

Unit: Curie (Bequerel)

1 Ci = 1000 mCi

1 Bq = 1 disintegration/sec

1 Ci = 3.7  1010 Bq




Radiation Risk

Qty: Dose Equivalent

Unit: rem (Sievert)

1 rem = 1000 mrem

1 Sv=100 rem

Radiation Quantities and Units

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Convert from Curies to Rad

  • Curie is the number of decays/s

    • 1 Curie = 3.7  1010 decays/s (exactly)

  • Rad is the absorbed dose or physical dose

    • Amount of energy deposited in unit mass

      • human tissue or other media

    • 1 Rad = 100 erg/g

      • Often use gray

        • 1 J/kg

        • 1 gray = 100 rad

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Need Biological Dose – REM

  • To convert from rad to rem multiply by appropriate value of Q

  • Q is the Quality Factor

  • Q reflects the damage

rad  Q = rem

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Radiation and Health

Does radiation affect you?

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Ionizing Radiation can Damage DNA

Ionizing radiation has the ability to ionize* atoms and molecules, possibly altering structure and function.

* ionize = produce

positive and negative

electrical charge

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Alpha Radiation Is Only a Hazard When Inside Your Body (Internal Hazard)

Your skin will stop it

can’t penetrate skin

internal hazard

stopped by paper

found in soil, radon and other radioactive materials

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Beta Radiation Is a Skin, Eye and Internal Hazard (Internal Hazard)

skin, eye and internal hazard

stopped by plastic

found in natural food, air and water

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X ray and gamma radiation are penetrating radiation and an external hazard l.jpg

found in medical uses (Internal Hazard)

stopped by lead

naturally present in soil and cosmic radiation

X-ray and Gamma Radiation Are Penetrating Radiation and an External Hazard

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- (Internal Hazard)


How does Radiation Injure Cells?

  • High energy radiation breaks chemical bonds.

  • This creates free radicals, like those produced by other insults as well as by normal cellular processes in the body.

  • The free radicals can change chemicals in the body.

  • These changes can disrupt cell function and may killcells.

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Types of Exposure & Health Effects (Internal Hazard)

  • Acute Dose - Deterministic

    • Large radiation dose in a short period of time

    • Large doses may result in observable health effects

      • Early: Nausea & vomiting

      • Hair loss, fatigue, & medical complications

      • Burns and wounds heal slowly

    • Examples: medical exposures andaccidental exposure to sealed sources

  • Chronic Dose - Stochastic

    • Radiation dose received over a long period of time

    • Body more easily repairs damage from chronic doses

    • Does not usually result in observable effects

    • Examples: Background Radiation andInternal Deposition


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At HIGH Doses, We KNOW Radiation Causes Harm (Internal Hazard)

  • High Dose effects seen in

    • Radium dial painters

    • Early radiologists

    • Atomic bomb survivors

    • Populations near Chernobyl

    • Medical treatments

    • Criticality Accidents

  • Cancer

    • Leukemia (A-bomb data)

    • Thyroid (Chernobyl data)

    • Bone and other solid cancers (A-bomb data)

  • Birth defects (A-bomb data)

  • Genetic effects (only animal data)


  • Howard Matis - [email protected]

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    Effects of ACUTE (Deterministic) Exposures (Internal Hazard)

    * For common external exposures 1 rad ~ 1 rem = 1,000 mrem

    Howard Matis - [email protected]

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    At LOW Doses, We (Internal Hazard)PRESUME Radiation Causes Harm

    • No physical effects have been observed

      The Bad News: Radiation is a carcinogen and a mutagen

      The Good News: Radiation is a very weak carcinogen and mutagen!

    Very Small DOSE = Very Small RISK

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    Sources of Radiation (Internal Hazard)

    • Average radiation exposure in the United States

      • 360 mrem or

      • 0.360 rem

    • Very location dependent

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    Manufactured Sources of Radiation Contribute an Average of 60 mrem/year

    cigarette smoking - 1300 mrem

    lung dose

    medical - 53 mrem

    building materials - 3.6 mrem

    smoke detectors - 0.0001 mrem

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    Risks in Perspective 60 mrem/year

    1 in 1 million chance of fatality

    • 40 tablespoon peanut butter (aflotoxin)

    • 2 days in New York City (air quality)

    • 3 mrem radiation (cancer)

    • 1 mile on motorcycle (collision)

    • 300 miles in car (collision)

    • 10 charbroiled steaks

    • Smoking 1 cigarette

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    ALARA 60 mrem/year

    ALARA stands for As Low As Reasonably Achievable

    Reduce radiation dose by using:

    • Time

    • Distance

    • Shielding

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    Reduce Time 60 mrem/year

    Spend as short as time as necessary to complete the task

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    Activity 60 mrem/year

    Demonstrate Time – (t)

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    Increase Distance 60 mrem/year

    Twice the distance = ¼ of the dose

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    Activity 60 mrem/year

    Demonstrate Distance – (d)

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    Use Shielding 60 mrem/year

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    Activity 60 mrem/year

    Demonstrate Shielding – (s)

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    Reactors Glow in the Dark 60 mrem/year

    • Reactor core emits electrons

    • Electrons move faster than the speed of light in water

    • At that speed they emit blue light

      • Cherenkov Radiation

    • Similar to sonic boom or wake of a boat

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    Can You Glow in the Dark? 60 mrem/year

    • Ingest a very hot radiation source

      • Beta needed

      • Short half life

    • Do not swallow

      • Unless your midriff is exposed

    • Or inject source into your blood

    • Don’t be in direct light

      • Usually too faint for sunlight

    • Try it for Halloween?

    Howard Matis - [email protected]

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    Summary 60 mrem/year

    • Radiation is part

      • Our natural environment

      • Technology

    • Health effects

      • Known for high doses

      • Unknown for low

    • You deal with it regularly

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    The End 60 mrem/year

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