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Radiation

Radiation:

The process of emitting energy in the form of waves or particles.

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Where does radiation come from?Radiation is generally produced when particles interact or decay.

A large contribution of the radiationon earth is from the sun (solar) or from radioactive isotopes of the

elements (terrestrial).

Radiation is going through you atthis very moment!

Discovery of Radioactivity• Antoine Henri Becquerel (1852-1908)

– Noticed the fogging of photographic plate by uranium crystals

• Pierre Curie (1859-1906), Marie Curie (1867-1934)– Further studies of uranium and discovery of

polonium and radium. Marie received two Nobel prizes. She died from the effects of radiation doses received during her experiments

Discovery

Discovery 2 Discovery 3

• Ernest Rutherford (1871-1937)– His understanding of atomic structure

helped us understand the role of the nucleus. He defined many of the terms used to discuss radioactivity today

Discovery of Radioactivity

Radioactivity is the spontaneous disintegration of atomic nuclei. The nucleus emits α particles, ß particles, or electromagnetic rays during this process.

Radioactivity is the spontaneous disintegration of atomic nuclei. The nucleus emits α particles, ß particles, or electromagnetic rays during this process.

After decaying, radioactive atoms “change” into other atoms

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• Why does the atom do this?– the nucleus of an atom attempts to become

more stable

• In some instances, a new element is formed and in other cases, a new form of the original element, called an isotope, appears. – this process of change is often referred to as

the decay of atoms.

• The rate of Radioactive decay is described in half-liveshalf-lives.

Energy is released during Energy is released during radioactive decayradioactive decay

Biological Effects of Radiation:Biological Effects of Radiation:Ionizing radiation causes

physical damage to cells and DNA.

Radiation can excite DNA and result in the destruction on the

DNA backbone.

At high doses of radiation (10,000 - 15,000 rads), death

occurs in a few hours because of neurological and cardiovascular

breakdown (Central Nervous Syndrome).

Biological Effects of Biological Effects of Radiation:Radiation:

Medium doses, 500 - 1200 rads, causes deathcauses death to occur in a

few days because of the destruction of the

gastrointestinal mucosa.

Lower doses, 250 - 500 rads, causes death to occur after

several weeks due to damage of the blood forming organs (hematopoietic syndrome).

Medicine•For example, radiation and radioactive radioactive tracerstracersare used to diagnose and treat medical problems.

•A radioactive tracer is a radioactive isotope that is added to a substance so that the substance can be detected later.

•Radioactive tracers are used to locate tumors, to study the functioning of a particular organ, or to monitor the flow of blood.

•For example, radioactive iodine-131 is used to diagnose thyroid problems.

•Radiation therapyRadiation therapy used to treat cancer may involve the use of implanted radioactive isotopes such as gold-198 or iridium-192.

Radiation is used positively in a variety of ways

Industry•Manufacturers can also use radiation

to check the thickness of metal containers by measuring the amount

of radiation that passes through. •Small amounts of radioactive

isotopes, like magnesium-28, can be introduced in a water source to

determine the flow of underground water or to determine

if an underground water system is leaking.

•Radioactive isotopes are even used in smoke alarms.smoke alarms.

Generate electrical powerGenerate electrical powerNuclear fission is used to Nuclear fission is used to generate electricity as an generate electricity as an alternative energy source.alternative energy source.

DatingDatingEven the age of fossils or Even the age of fossils or

rocks can be determined by rocks can be determined by using radioactive isotopes.using radioactive isotopes.

• Particles found in the nucleus of an atom – neutrons – protons

• Atomic Number (A) – number of protons in the nucleus

• Mass Number (Z) – sum of the number of protons and neutrons

A Review of Atomic Terms

Radioactive Decay • Radioactivity – the spontaneous

decomposition of a nucleus forming a different nucleus and producing one or more additional particles

• Nuclear Forces – strong nuclear force holds neutrons and protons together to form a nucleus (counters electromagnetic repulsion). Weak nuclear force operates within individual particles and gives rise to some kinds of radioactivity

Isotopes

What’s an isotope?Two or more varieties of an element having the same

number of protons but different number of

neutrons. Certain isotopes are “unstable” and decay to

lighter isotopes or elements.

A prime example is Uranium 238, or just

238U.

Radioactivity

By the end of the 1800s, it was known that certain isotopes emit penetrating rays.

Three types of radiation were known:

1)Alpha particles ()

2)Beta particles ()

3)Gamma-rays ()

By the end of the 1800s, it was known that certain isotopes emit penetrating rays.

Three types of radiation were known:

1)Alpha particles ()

2)Beta particles ()

3)Gamma-rays ()

Where do these particles come from ?

These particles generally come from the nuclei of atomic isotopes which are not stable.

The decay chain of Uranium produces all three of these forms of radiation.

Types of Nuclear Types of Nuclear RadiationRadiation

• When an unstable nucleus decays, particles and energy are given off from the decaying nucleus.

• α and β radiation is in the form of particles

• γ radiation is in the form of waves-kind of like light but higher frequency

Alpha Particles ()

Radium

R226

88 protons138 neutrons

Radon

Rn222

Note: This is theatomic weight, whichis the number ofprotons plus neutrons

86 protons136 neutrons

+ nnp

p

He)

2 protons2 neutrons

The alpha-particle is a Helium nucleus.

It’s the same as the element Helium, with the electrons stripped off !

• Alpha particles consist of two protonstwo protons and two neutronstwo neutrons, identical to the nucleus of a helium atom.

• A sheet of paper or a person’s surface layer of skin will stop them.

• Alpha particles are only considered hazardous to a person’s health if they are ingested or inhaled and thus come into contact with sensitive cells such as in the lungs, liver and bones.

Beta Particles ()

CarbonC14

6 protons8 neutrons

NitrogenN14

7 protons7 neutrons

+e-

electron(beta-particle)

We see that one of the neutrons from the C14 nucleus “converted” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus.

• Beta particlesBeta particles are electrons emitted from the are electrons emitted from the nuclei of many fission products.nuclei of many fission products.

•They can travel a few feet in air but can usually be stopped by clothing or a few centimeters of wood.

•They are considered hazardous mainly if ingested or inhaled, but can cause radiation damage to the skin if the exposure is large enough.

•Unstable Neutron decays into a proton.

Gamma particles ()In much the same way that electrons in atoms can be in an excited state, so can a nucleus.

NeonNe20

10 protons10 neutrons

(in excited state)

10 protons10 neutrons

(lowest energy state)

+

gamma

NeonNe20

A gamma is a high energy light particle.

It is NOT visible by your naked eye.

A gamma is a high energy light particle.

It is NOT visible by your naked eye.

• Gamma rays are a form of electromagnetic radiation (like light, radio, and television) that come from the nucleus of a radioactive atom.– Occurs when an unstable nucleus emits

electromagnetic radiation. The radiation has no mass, and so its emission does not change the element.

– They penetrate matter easily and are best stopped by water or thick layers of lead or concrete.

– Gamma radiation is hazardous to people inside and outside of the body.

•However, gamma radiation often accompanies alpha and beta emission, which do change the element's identity.

•Gamma rays have the lowest ionizing power, but the highest penetrating power.

How do these particles differ ?

ParticleMass*(AMU)

Charge

Gamma () 0 0

Beta () ~1/1836 -1

Alpha () ~4 +2

Nuclear Decay

Neutron decays into a proton

2 protons & 2 neutrons

Rate of DecayBeyond knowing the types of particles which are emittedwhen an isotope decays, we also are interested in how frequentlyone of the atoms emits this radiation.

A very important point here is that we cannot predict when aparticular entity will decay.

We do know though, that if we had a large sample of a radioactive substance, some number will decay after a given amount of time.

Some radioactive substances have a very high “rate of decay”,while others have a very low decay rate.

To differentiate different radioactive substances, we look toquantify this idea of “decay rate”

Half-Life The “half-life” (h) is the time it takes for half the atoms of a radioactive substance to decay.

For example, suppose we had 20,000 atoms of a radioactive substance. If the half-life is 1 hour, how many atoms of that substance would be left after:

10,000 (50%)

5,000 (25%)

2,500 (12.5%)

1 hour (one lifetime) ?

2 hours (two lifetimes) ?

3 hours (three lifetimes) ?

Time #atoms

remaining% of atomsremaining

Half Life is the amount of time it takes for half of the nuclei in a sample to decay

Mass

(kg)

Decay of a Radioactive Element

Half of the radioactive parent atoms decay after one half-life. Half of the remainder decay after another half-life and so on……..

Half-life activity

25g

• The half life of 14C is 5,730 years.

• If a sample originally contained 100 g, how much would be left

after 11,460 years?

50g

Older Dating MethodsOlder Dating MethodsThe isotopes 235U and 238U can be used to date objects billions of years old.•235U has a half life of 704 million years.•238U has a half life of 4.5 billion years.•Mainly used for rocks.

Geiger Counter

• Used to measure radiation.

• The more intense the radiation the more “clicks”.

Fission and FusionFission Fusion

Splitting a nucleus Combining of two nuclei.

•Nuclear power can come from the fissionfission of uranium, plutonium or thorium or the fusion of hydrogen into helium.

•Today it is almost all uranium.

•The fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal.

Issues for Fission Power PlantsIssues for Fission Power Plants

•Need for a spent fuel disposaldisposal facility and a decommissioning plan •Use of large amounts of water for

cooling purposes (if wet cooling towers are used) –thermal pollution

•Biological impactsBiological impacts on the ocean due to thermal discharge (if seawater

cooling is used) •Public safety safety concerns

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FUSIONFUSION•A fusion reaction occurs when nuclei of light

elements, specifically hydrogen and its isotopes (deuterium, or "heavy water," and tritium), are

forced together at extremely high high temperaturestemperatures and densities until they fuse into nuclei of heavier elements and release enormous

amounts of energy.

If fusion is to yield net energy, the fuel

must be heatedheated in the form of plasma (a

highly ionized gas) to a very high

temperaturetemperature and the plasma must then

be held together for a sufficiently long time

such that the number of fusion reactions

occurring releases more energy than was

required to heat the fuel.