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Transmutations • The changing of one element to another is called transmutation • This occurs whenever there is an alpha decay or a beta decay • Remember, that for a gamma decay, the nucleus just changes internal energy levels, but doesn’t change the identity of nucleons

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Page 1: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Transmutations

• The changing of one element to another is called transmutation

• This occurs whenever there is an alpha decay or a beta decay

• Remember, that for a gamma decay, the nucleus just changes internal energy levels, but doesn’t change the identity of nucleons

Page 2: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Transmutations

• Consider an alpha decay

• 238U -> 234Th + alpha (4He)

• Have to count the number of protons and neutrons

• Protons [U-92, Th-90, He-2] Balance!!

• Neutrons [U-146, Th-144, He-2] Balance!!

• Mass No. [U-238, Th-234, He-4] Balance!!

Page 3: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Transmutations

• Consider a beta decay

• 234Th -> 234Pa + beta

• This means a neutron changed into a proton

• So mass number stays the same

• Proton number increases by one and the thorium changes into protactinium

• Actually an anti-neutrino appears also

Page 4: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Transmutations

Page 5: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Artificial Transmutation

• First example was Rutherford bombarding nitrogen with alpha particles

• 4He + 14N -> 17O + 1H

• He viewed the reaction with a cloud chamber

• The particles left a vapor trail in the mist

Page 6: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

H H H

http://education.jlab.org/glossary/isotope.html

Page 7: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Isotopes of Carbon

Page 8: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Emission of alpha particles :

• helium nuclei • two protons and two neutrons • charge +2e  • can travel a few inches through air• can be stopped by a sheet of paper,

clothing.

Alpha Decay

Page 9: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Alpha Decay

Uranium Thorium

Page 10: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Beta Decay

Page 11: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Beta Decay

Thorium Protactinium

Page 12: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Types of Radioactive Decay Positron Emission

Loss of a positron (a particle that has the same mass as but opposite charge than an electron)

e01

C116

B115 + e0

1

Page 13: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Types of Radioactive Decay Electron Capture (K-Capture)

Addition of an electron to a proton in the nucleus– As a result, a proton is transformed into a neutron.

p11 + e0

−1 n1

0

Page 14: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

• Gamma radiation electromagnetic energy that is released. 

• Gamma rays are electromagnetic waves.

• They have no mass.• Gamma radiation has no charge.

– Most Penetrating, can be stopped by 1m thick concrete or a several cm thick sheet of lead.

Gamma Decay

Page 15: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that
Page 16: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Which is more penetrating? Why?

Page 17: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that
Page 18: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear Stability

• Depends on the neutron to proton ratio.

Page 19: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Neutron-Proton Ratios• Any element with more than

one proton (i.e., anything but hydrogen) will have repulsions between the protons in the nucleus.

• A strong nuclear force helps keep the nucleus from flying apart.

• Neutrons play a key role stabilizing the nucleus.

• Therefore, the ratio of neutrons to protons is an important factor.

Page 20: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Neutron-Proton Ratios

For smaller nuclei (Z 20) stable nuclei have a neutron-to-proton ratio close to 1:1.

Page 21: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Neutron-Proton Ratios

For smaller nuclei (Z 20) stable nuclei have a neutron-to-proton ratio close to 1:1.

Page 22: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Neutron-Proton Ratios

For smaller nuclei (Z 20) stable nuclei have a neutron-to-proton ratio close to 1:1.

Page 23: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Stable Nuclei

• Nuclei below the belt have too many protons.

• They tend to become more stable by positron emission or electron capture.

Page 24: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Some Trends

Nuclei with 2, 8, 20, 28, 50, or 82 protons or 2, 8, 20, 28, 50, 82, or 126 neutrons tend to

be more stable than nuclides with a different number of nucleons.

Nuclei with an even number of protons and neutrons tend to be more stable than nuclides that have odd numbers of these nucleons.

Page 25: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Measuring Radioactivity

• One can use a device like this Geiger counter to measure the amount of activity present in a radioactive sample.

• The ionizing radiation creates ions, which conduct a current that is detected by the instrument.

Page 26: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Objectives

• Explain the relationship between number of nucleons and stability of nuclei.

• Describe the different types of radioactive decay and their effects o the nucleus.

• Define nuclear fission, chain reaction, and nuclear fusion, and distinguish between them.

• Discuss the possible benefits and the current difficulty of controlling fusion reations.

Page 27: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Energy in Nuclear Reactions• There is a tremendous amount of energy

stored in nuclei.

• Einstein’s famous equation, E = mc2, relates directly to the calculation of this energy.

• In chemical reactions the amount of mass converted to energy is minimal.

• However, these energies are many thousands of times greater in nuclear reactions.

Page 28: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Einstein• "The intuitive mind

is a sacred gift and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift." 

Page 29: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Man-Made Radioactive Decay on Earth

• Fission

• Fusion– Occurs naturally in space– Powers the sun– Supernovas allow atoms to fuse into heavier

elements, this is how the other elements came into existence

Page 30: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

• "Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius -- and a lot of courage -- to move in the opposite direction."

Page 31: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that
Page 32: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Fission

• Nuclear fission occurs when scientists bombard a large isotope with a neutron.

• This collision causes the larger isotope to break apart into two or more elements.

• These reactions release a lot of energy.

• You can calculate the amount of energy produced during a nuclear reaction using an equation developed by Einstein: E=mc2

Page 33: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear Fission

1n + 235U -> 91Kr + 142Ba + 31n

Page 34: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear Fission• How does one tap all that energy?• Nuclear fission is the type of reaction carried out

in nuclear reactors.

Page 35: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Chain Reaction

Page 36: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear Fission

• Bombardment of the radioactive nuclide with a neutron starts the process.

• Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons.

• This process continues in what we call a nuclear chain reaction.

Page 37: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear Fission

• If there are not enough radioactive nuclides in the path of the ejected neutrons, the chain reaction will die out.

• Therefore, there must be a certain minimum amount of fissionable material present for the chain reaction to be sustained: Critical Mass.

Page 38: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Critical Mass

Page 39: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Atomic Bombs• Because of the tremendous amount of energy released in

a fission chain reaction, the military implications of nuclear reactions were immediately realized.– The first atomic bomb was dropped on Hiroshima, Japan, on

August 6, 1945.

• In an atomic bomb, two pieces of a fissionable isotope are kept apart. Each piece by itself is subcritical.

• When it’s time for the bomb to explode, conventional explosives force the two pieces together to cause a critical mass.

• The chain reaction is uncontrolled, releasing a tremendous amount of energy almost instantaneously.

Page 40: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Mushroom Cloud

Page 41: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Atom Bomb

Page 42: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear Power Plants• If the neutrons can be controlled, then the

energy can be released in a controlled way. Nuclear power plants produce heat through controlled nuclear fission chain reactions.

• The fissionable isotope is contained in fuel rods in the reactor core. All the fuel rods together comprise the critical mass.

• Control rods, commonly made of boron and cadmium, are in the core, and they act like neutron sponges to control the rate of radioactive decay.

Page 43: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear Power Plants (cont)• In the U.S., there are approximately 100 nuclear

reactors, producing a little more than 20% of the country’s electricity.

• Advantages– No fossil fuels are burned.

– No combustion products (CO2, SO2, etc) to pollute the air and water.

• Disadvantages– Cost - expensive to build and operate.

– Limited supply of fissionable Uranium-235.

– Accidents (Three Mile Island & Chernobyl)

– Disposal of nuclear wastes

Page 44: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear ReactorsIn nuclear reactors the heat generated by the reaction is used to produce steam that turns a turbine connected to a generator.

Page 45: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear Reactors

• The reaction is kept in check by the use of control rods.

• These block the paths of some neutrons, keeping the system from reaching a dangerous supercritical mass.

Page 46: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Three Mile Island

Page 47: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Chernobyl

Page 48: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that
Page 49: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear Fusion

• Fusion is when lighter nuclei are fused into a heavier nucleus.

• Fusion powers the sun. Four isotopes of hydrogen-1 are fused into a helium-4 with the release of a tremendous amount of energy.

• On Earth, H-2 (deuterium) & H-3 (tritium) are used.

Page 50: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that
Page 51: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Fusion Reactions

Page 52: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that
Page 53: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Nuclear Fusion

• Fusion would be a superior

method of generating power.– The good news is that the

products of the reaction are

not radioactive.

– The bad news is that in order to achieve fusion, the material must be in the plasma state at several million kelvins.

– Tokamak apparati like the one shown at the right show promise for carrying out these reactions.

– They use magnetic fields to heat the material.

Page 54: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Positron emission tomography, also called PET imaging or a PET scan, is a diagnostic examination that involves the acquisition of physiologic images based on the detection of radiation from the emission of positrons. Positrons are tiny particles emitted from a radioactive substance administered to the patient.

Page 55: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Isotopic Dating

• Cosmic rays (mostly high energy protons) strike upper atmosphere and cause transmutations that result in many protons and neutrons being sprayed out

• Protons tend to grab electrons from other atoms and become simple hydrogen

• Neutrons keep going and smash into other atoms

Page 56: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Isotopic Dating

• When a neutron strikes nitrogen

• 1n + 14N -> 14C + 1H

• In the atmosphere, 14C is about 1 part in 1011

• Reacts with plants just like 12C

• 14C decays via beta emission

• 14C -> 14N + beta half life of 5730 years

Page 57: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Half-Life

Page 58: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Half-Life

• There are a large range of half-lives seen in nature

• Half-lives are unaffected by the nuclei’s surroundings and only depend on what goes on inside the nucleus

• 238U has a half-life of 4.5 billion years

Page 59: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Half-Life

• To summarize, one-half of the sample will decay in one half-fife

• One-half of that one-half will decay in the next half life

• One-half of that one-fourth will decay in the next half life

Page 60: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Carbon Dating

• When a plant dies, it stops the intake of carbon

• Since the 14C decays, after 5730 years, half of it will be gone

• We can just weigh a piece of dead wood, calculate how much 14C it originally had and measure to how much it has now to get the age

Page 61: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Uranium Dating

• We know the half -life of 238U and 235U• They have series that end in 206Pb and 207Pb• Compare how much U vs. special lead and

calculate the age of the rock!!• Carbon dating only good for about 50,000

years• Uranium rock dating good for millions of

years

Page 62: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

ExampleYou have 100 g of radioactive C-14. The half-

life of C-14 is 5730 years.

• How many grams are left after one half-life? Answer:50 g

• How many grams are left after two half-lives?

Page 63: Transmutations The changing of one element to another is called transmutation This occurs whenever there is an alpha decay or a beta decay Remember, that

Problem

A sample of 3x107 Radon atoms are trapped

in a basement that is sealed. The half-life of

Radon is 3.83 days. How many radon atoms

are left after 31 days?

answer:1.2x105 atoms