nuclear radiation

NUCLEAR RADIATION

Who Discovered Radioactivity?

Antoine Henri Becquerel

• Worked with uranium.• Noticed phosphorescence

caused film exposure after leaving uranium in the sun.

• Noticed same thing happened on cloudy days.

Pitchblende

Who’s the Famous “Madame” of Radiological Fame?

Marie Curie• With her husband

Pierre, discovered radium and coined the term “radioactive”

• First woman to win two Nobel Prizes

Pierre and Marie Curie

• Extracted two previously unknown and highly radioactive elements from pitchblende named:

• RADIUM• POLONIUM

Why Are Elements Radioactive?

Unstable nucleus:Unstable nucleus:

•Has excess energy.Has excess energy.

•Wants to go to “ground Wants to go to “ground state.”state.”

•Becomes stable by Becomes stable by emitting ionizing emitting ionizing radiation.radiation.

What does “ionizing” mean?What does “ionizing” mean?

Atomic Structure

Nucleus

• Contains positively-charged protons• Non-charged neutrons

Electrons

• Orbit nucleus• An atom can have as many electrons as it has

protons

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The Search for Stability An atom is stable based on it’s proton to

neutron ratio If there are too many or too few neutrons or

protons, the atom will give off excess energy as rays particles

This process is called radioactive decay

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What is Radiation?

• As either particles or rays• Two kinds: ionizing and non-

ionizing

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Ionizing Radiation• The energy given off by the nucleus is

called ionizing radiation• It is strong enough to detach an

electron from an atom– When an atom loses an electron, it has a

positive charge and is called an ion– The ion and its lost electron are called an

ion pair

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Radioactive Decay

• When an atom’s nucleus gives off excess energy, the process is called radioactive decay

• Radioactive half-life is the time it takes half the radioactive atoms present to decay

• Radioactive decay is a spontaneous process in which nucleons are emitted from or transformed within the nucleus, resulting in a change in the identity of the nucleus, and usually accompanied by the emission of one or more types of radiation from the nucleus and/or atom.

DECAY CHAINS

TYPES OF IONIZING RADIATION

Alpha Particle• Large mass• Consists of 2 protons and 2

neutrons • Electrical charge of +2• Range in air 1 to 2 inches

+1

+1

Alpha shielding• A sheet of paper• Outer layer of skin

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Biological Hazard Alpha radiation is not an external

hazard, because it can be stopped so easily

If inhaled or swallowed, the alphas emitted from an alpha emitter, can deposit large amount of energy in a small area of body tissue

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Sources of Alpha Radiation

• Plutonium 238 and 239• Uranium 238 and 235

Beta Particle - ß• Small mass• Electrical charge of -1• Emitted from nucleus• Range in air about 10 feet

Beta Shielding

• Beta has a limited penetrating ability because of its negative charge

• Most beta particles can be shielded by plastic, glass, metal foil, or safety glasses

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Biological Hazard

• If ingested or inhaled, a beta-emitter can be an internal hazard

• Externally, beta particles are potentially hazardous to the eyes and skin

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Beta Sources

• Uranium decay products• Decay of some radioactive substances

(Tritium)• Products of the fission process

Gamma and X-Rays

• An electromagnetic wave or photon, which has no electrical charge

• Great penetrating power

• Range in air easily several hundred feet

Gamma and X-Ray Shielding

• Concrete• Lead• Steel

• Half-life is the time required for half of the atoms of a radioactive material to decay to another nuclear form.

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Half life t1/2

• Describes how fast a particular nucleus transforms

• The time it takes for half the amount of a radioactive material to transform (often also referred to as decay)

Where:• t1⁄2 is the half-life of the decaying quantity,• τ is a positive number called the mean lifetime of

the decaying quantity,• λ is a positive number called the decay

constant of the decaying quantity.

Natural Background RadiationNatural Background Radiation

Man-Made RadiationMan-Made Radiation

Biological EffectsMechanisms of Injury

Ionizing Radiation

Cell Death

Cell Damage

Repair Transformation

Radiation Dose Dose or radiation dose is a generic term for a measure of radiation exposure. In radiation

protection, dose is expressed in millirem.

X-Ray MachineImage (film)

Subject is not radioactive but has been exposed to a radiation dose (single chest x ray = 5-10 mrem).

After

External Dose

Contamination Contamination is the presence of a radioactive

material in any place where it is not desired, and especially in any place where

its presence could be harmful.

Yuck!

Radiation Detection Instruments

Geiger Counter Liquid Scintillation Counter

Photo by Karen Sheehan Photo by Carl Tarantino

Lessons from the PastThe Radium Dial Painters

Photo by Carmelina Rattrovo from the Playwrights Theatre production of Radium Girls, by D.W. Gregory

Minimizing Radiation Exposure

Basic Concepts• Time• Distance• Shielding

Minimizing Exposure - Time

• Minimize the amount of time spent near sources of radiation.

Minimize Exposure by Maximizing Distance

As the distance from a radioactive source doubles, the exposure rate

decreases by a factor of four.

Minimizing Exposure By Using Shielding

Lead blanket shielding around letdown radiation monitors

Surry Power Station

Loss of Life ExpectancyActivity or Behavior LLE (DAYS)__________________

Recreational swimming 40 Being 15 percent overweight 900 Smoking 20 cigarettes per day 1,600 Using pesticides at home 12 Being exposed to radon in a home 35

Living within 10 miles of a nuclear power plant 0.4 Riding a bicycle 6 Driving a car 200

Skydiving 25 Consuming alcohol (U.S. average) 230

ADVANTAGES

Power Generation

Nuclear power Nuclear power supplies 20 percent supplies 20 percent of energy in the of energy in the United States. There United States. There are 104 nuclear are 104 nuclear power plants in the power plants in the United States.United States.

Photo by Karen Sheehan

Space Exploration

The fuel in:• Satellites• Jupiter Probe• Others

Jupiter Probe

Other Types of X-Ray Machines

Photos by Karen Sheehan

X-Ray Crystallography

Photo by Karen Sheehan

Nuclear MedicineDiagnostic Procedures

• Radioactive injection• Short half-life radionuclide • Pictures taken with special

gamma camera• Many different studies:

ThyroidLungCardiac White Blood Cell

Photo by Karen Sheehan

Bone Scans

Image courtesy of

Radiation TherapyUsed for treating cancer. Why does it work?

External Beam Brachytherapy (implants)

Image courtesy of

Photo by Karen Sheehan

Radioactive Consumer Products

Photo by Karen Sheehan

Suffering from thyroid cancer, Oleg, 54, and Dima, 13, receive care at a thyroid hospital in Minsk, where surgery is performed daily. As a liquidator, Oleg was exposed to extreme levels of radiation. This was his third thyroid operation. Dima’s mother claims that Chernobyl’s nuclear fallout is responsible for her son’s cancer, but Belarusian officials are often instructed to downplay the severity of the radiation. [Minsk, Belarus 2005]

For more information about radiation you may contact the

Health Physics Society.

http://www.HPS.orgHealth Physics Society

Specialists in Radiation Safety

HALF LIFE PROBLEM SOLVING

Where:

• N = the number of remaining nuclei• N0 = initial number of nuclei• k = the decay constant• t = time to reach the number of

remaining nuclei• T(1/2) = half life

Sample Problem

• A radioactive sample is sometimes used in thyroid scans. Suppose you originally store 50 mg of the radioactive isotope and it took 65 hrs until only 1.5 mg is left. What is the half life of the sample?

Boardwork

• How long will it take for a 64 g of a radioactive material to be reduced to 2 g if the half-life is ½ hours?