nuclear reactions nuclei and nuclear...

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11Chemistry: OpenStax

Ch. 21: Nuclear Chemistry

Nuclear chemistry provides the basis for many useful diagnostic and therapeutic methods

in medicine, such as these positron emission tomography (PET) scans. The PET/computed

tomography scan on the left shows muscle activity. The brain scans in the center show

chemical differences in dopamine signaling in the brains of addicts and nonaddicts.

The images on the right show an oncological application of PET scans to identify

lymph node metastasis.

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Creative Commons License

� Images and tables in this file have been used from the following sources:

� OpenStax: Creative Commons Attribution License 4.0.

� ChemWiki (CC BY-NC-SA 3.0): Unless otherwise noted, the StatWiki is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Permissions beyond the scope of this license may be available at [email protected].

� Principles of General Chemistry (CC BY-NC-SA 3.0): http://2012books.lardbucket.org/pdfs/principles-of-general-chemistry-v1.0.pdf

� Nuclear (NOT Nucular) chemistry involves changes

in the nuclear composition (protons and neutrons) of

atoms that are radioactive.

� Nuclear chemistry can be used:

� to generate electricity

� 2 million kg of coal or 50 kg of uranium-235 can provide

electricity for a city of 1 million people

� for radiocarbon dating (e.g., determining the age of a

mummy or a meteorite)

� for medical diagnosis, treatment, and imaging (PET

scans, brain scans, x-rays)

� to create new elements 3

Nuclear Reactions

4

Spontaneous emission of particles or electromagnetic radiation is

known as radioactivity.

Atomic notation and terms:

Atomic number (Z) = number of protons

Mass number (A) = number of protons and neutrons in a

specific isotope (or nuclide) of an element

Protons and neutrons are collectively called nucleons.

Radioactive isotopes are often called nuclides.

How many neutrons are in each nuclide below?

Nuclei and Nuclear Reactions

5

How do we know whether an isotope is

stable? Which radioisotopes will

spontaneously decay?

1) Nuclei containing a magic number of

protons and/or neutrons are stable.

• The numbers 2, 8, 20, 50, 82, and 126

are called magic numbers.

2) Even numbers of protons and neutrons

tend to be stable.

3) All isotopes of the elements with

atomic numbers > 83 are radioactive.

4) All isotopes of technetium (Tc, Z = 43)

and promethium (Pm, Z = 61) are

radioactive.

21.1 Nuclear Structure and Stability

CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Prince_Georges_Community_College/General_Chemistry_for_Engineering/Unit_7%3A_Nuclear_Chemistry/Chapter_18%3A_Nuclear_Chemistry/Chapter_18.1%3A_The_Components_of_the_Nucleus

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Band of Stability


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The three general classes of radioactive nuclei are characterized by a different

decay process or set of processes:

N/Z too high. The nuclei on the upper left side of the band of stable nuclei in

Figure 18.1.2 have a neutron-to-proton ratio that is too high to give a stable

nucleus. These nuclei decay by a beta decay – converting a neutron to a proton,

thereby decreasing the neutron-to-proton ratio.

N/Z too low. Nuclei on the lower right side of the band of stable nuclei have a

neutron-to-proton ratio that is too low to give a stable nucleus. These nuclei

decay by positron emission or electron capture – converting a proton to a

neutron, thereby increasing the neutron-to-proton ratio.

Heavy nuclei. With very few exceptions, heavy nuclei (those with A ≥ 200) are

intrinsically unstable regardless of the neutron-to-proton ratio, and all nuclei

with Z > 83 are unstable. Such nuclei tend to decay by emitting an α particle

which decreases the number of protons and neutrons in the original nucleus by

2. The net result of alpha emission is an increase in the neutron-to-proton ratio.

Predicting Types of Decay

8

Figure 21.4: Symbols for subatomic particles

21.2 Nuclear Particles

Penetrating Ability of Particles

Figure 21.33

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• Radioactive decay/emission: an unstable nuclide emits a

particle or energy.

• Parent nuclide � daughter nuclide + radiation

• Fission: bombarding an isotope with a neutron to break it apart

into lighter isotopes.

• Fusion: light isotopes collide to form heavier isotopes (only up

to Fe can be done naturally in the universe)

• Transmutation: atoms are bombarded by high energy particles

to create new elements/isotopes.

• 14N + 4He � 17O + 1H

+

Types of Nuclear Reactions

11

In balancing a nuclear reaction, we balance the total of all

atomic numbers and total of all mass numbers for the

products and reactants (conservation of protons and

neutrons).

Example 21.4

Mass number:

Atomic number:

+

212 208 + 4 = 212

84 82 + 2 = 84

21.3 Radioactive Decay

� Alpha decay - heavy radioisotopes tend to emit alpha particles (A dec. by 4, Z dec by 2)

� �� → ��

____

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Alpha Decay (or Emission)

http://underground.physics.berkeley.edu/SNO+.html

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� Beta decay - neutron is converted to a proton and an electron (A is same, Z inc. by 1)

� � �� → ��

� ____

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Beta Decay (or Emission)

http://www.ck12.org/user:chjpdgnoyxjkx3naagnkzs5vcmc./book/Chemical-Equations-and-Balancing-The-Equations/section/24.2/

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Gamma Decay (or Emission)

� Gamma – γ: energy with no mass or charge; the most

penetrating radiation (A and Z remain the same)

� This often occurs in conjunction with alpha or beta

decay.

� ��∗ � → ��

� �� _____

http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24-nuclear-chemistry.html

� Positron decay – proton is converted to a neutron and a positron (A is same, Z dec. by 1)

� A positron is the antiparticle of the electron

� ��

� → ��

� �� → ��

� _____

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Positron Decay (or Emission)


� Electron Capture – electron combines with a

proton to form a neutron (A is same, Z dec by 1)

� Same result as positron decay; opposite of beta decay

� ��

� → _____

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Electron Capture


� Write balanced equations for the following:

� Alpha decay of 214Bi

� Alpha decay of curium-242

� Beta decay of 239U

� Beta emission of magnesium-28

� Positron emission of 207Po

� Electron capture of 197Hg

� Electron capture of gallium-67

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Group Work - Practice

Answers:

� 210Tl

� 238Pu

� 239Np

� 28Al

� 207Bi

� 197Au

� 67Zn

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Uranium Series of Decay

CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity

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Natural radioactive decay:

Nuclear Transmutation:

Nuclear fission:

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Determining Products of Reactions

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Band of Stability


Four New Elements!

https://www.sciencenews.org/article/four-elements-earn-permanent-seats-periodic-table

110: Darmstadtium (Ds)111: Roentgenium (Rg)112: Copernicium (Cn)113: Nihonium (Nh)114: Flerovium (Fl)115: Moscovium (Mc)116: Livermorium (Lv)117: Tennesine (Ts) 118: Oganesson (Og)

Nuclide Type of Emission Half-life

Part of Body

Studied

Fluorine-18 Positron emission 1.83 hours PET studies of

heart, brain

Technetium-99m Gamma 6.01 hours Various organs,

bones

Thallium-201 Electron capture 3.05 days Heart

Iodine-131 Beta 8.0 days Thyroid

Phosphorus-32 Beta 14.3 days Tumors in various

organs

Iron-59 Beta 44.5 days Blood, spleen

Radioactivity in Medicine

Source Dose

5-hour plane ride 2.5 mrem/trip

Cosmic radiation 27 mrem/year

Natural radionuclides in body 35 mrem/year

Chest x-ray 8 mrem

Dental x-ray 30 – 80 mrem (pano vs bitewings)

Thallium heart scan 800 mrem

Building materials 3.5 mrem/year

Luminous watches 0.04 – 0.10 mrem/year

Tobacco products (30

cigarettes/day)

16,000 mrem/year

Exposure by Source – U.S.Dose (rem) Symptoms/Effects

< 5 No observable effect

5-20 Possible chromosomal damage

20-100 Decreased white blood cell count; possible increased cancer risk

50-100 Temporary sterility in men (up to a year)

100-200 Mild radiation sickness, vomiting, diarrhea, fatigue; immune system

suppressed; bone growth in children retarded

> 300 Permanent sterility in women

500 Fatal (often within 2 months) destruction of bone marrow and

intestine

1000 Fatal (often within 2 weeks)

2000 Fatal (often within hours)


Symptoms of Exposure

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� The rate of decay, as well as the type and energy

of the radiation, determines the damage caused by

radiation.

� Nuclear decay follows first-order kinetics, which

gives a constant t1/2 over the course of the decay.

� Typically we are given half-life (t1/2) values. We

can use these to calculate rate constants (or decay

constants) for radioactive nuclides.

Nuclear Decay – Half-Lives

25 26

All radioactive decays obey first-order kinetics.

No = amount at beginning (if %, No = 100%)

Nt = amount (mass or %) remaining after time

k = rate or decay constant, with units (1st order: time-1)

t = time

Half-life is the time it takes for the amount of a substance to

decrease by 50%.

Nuclear Radioactivity

First Order Decay


� Can use kinetics equations, just like in Chapter 12, to perform calculations:

� How much nuclide (mass or %) is left after ___ time?

� How long does it take for ___% to decay (or remain)?

� The half-life for sodium-24, a radioisotope used

medically in blood studies, is 906 minutes. What is

the rate constant for 24Na (in hr-1)?

� 4.59 x 10-2 hr -1

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Nuclear Decay - Kinetics

� If you ingest a 75.0 mg sample of 131I with a rate

constant of 0.0861 d-1, how long would it take to decay

to 12.5 mg?� t = 20.8 days

� Gold-128 undergoes beta decay to give mercury-128

with a half-life of 2.7 days. If you start with 5.6 mg of 128Au, what mass of gold-128 is left after 9.5 days?� Nt = 0.49 mg

� 214Bi decays by alpha emission with a half-life of 19.7 min. How long does it take for 75.0% of 214Bi to decay?� k = 0.035178 min-1; t = 39.4 min

� Examples 21.5 – 21.729

Group Work

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Video about fallout from Chernobyl(46 min.):

http://www.youtube.com/watch?v=GezeZlu70oI

10 Interesting Facts about Chernobyl:

http://imgur.com/gallery/AfbNLQ9

Fermi and the “Atomic Pile”: http://www.fi.edu/learn/case-

files/fermi/pile.html

Distribution and history of energy sources: http://www.world-

nuclear.org/info/Current-and-Future-Generation/Nuclear-Power-in-

the-World-Today/#.Uebm_ZyETLc

How geological dating on rocks is done:

http://www.youtube.com/watch?v=1920gi3swe4

Informative/Interesting Links

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http://www.world-nuclear.org/info/inf01.html

http://www.nucleartourist.com/basics/why.htm� List of advantages/disadvantages

of each energy source.

Global Energy Sources World Energy Consumption

https://en.wikipedia.org/wiki/Renewable_energy#/media/File:Total_World_Energy_Consumption_by_Source_2013.png

� Energy released from 200 g U = 2x1013 J

� Energy released from 1 ton coal = 5x107 J

� It would take 1 million tons of coal to create the

same amount of energy.

� Nuclear power plants don’t explode (like TNT)

unless an uncontrolled nuclear chain reaction occurs.

When nuclear power plants have meltdowns, the

threat is from leakage of radioactive material (water,

airborne, soil contamination, etc.)

Nuclear Energy

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Schematic of a cyclotron particle accelerator.

21.4 Nuclear Transmutation

http://www.physbot.co.uk/magnetic-fields-and-induction.html

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Nuclear transmutation differs from radioactive decay in

that transmutation is brought about by the collision of two

particles.

Particle accelerators made it possible to synthesize the so-

called transuranium elements, elements with atomic

numbers greater than 92.

Transmutation

+ +

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A Linear Particle Accelerator. (a) An aerial view of the SLAC, the longest linear

particle accelerator in the world; the overall length of the tunnel is 2 miles. (b)

Rapidly reversing the polarity of the electrodes in the tube causes the charged

particles to be alternately attracted as they enter one section of the tube and repelled

as they leave that section. As a result, the particles are continuously accelerated

along the length of the tube.

Transmutation


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Nuclear fission: heavy nuclei (mass number > 200) are

bombarded by neutrons to form smaller nuclei and one or more

neutrons. Used in nuclear power plants.

Nuclear Fission


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235U is capable of a self-sustaining sequence of nuclear fission

known as a nuclear chain reaction. The minimum mass of

material required to generate a self-sustaining chain reaction is the

critical mass.

Nuclear Fission


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Nuclear Fissionyoutube video


(a)The Diablo Canyon Nuclear Power Plant near San Luis Obispo is the only nuclear power

plant currently in operation in California. The domes are the containment structures for the

nuclear reactors, and the brown building houses the turbine where electricity is generated.

Ocean water is used for cooling. (b) The Diablo Canyon uses a pressurized water reactor, one

of a few different fission reactor designs in use around the world, to produce electricity.

Energy from the nuclear fission reactions in the core heats water in a closed, pressurized

system. Heat from this system produces steam that drives a turbine, which in turn produces

electricity. (credit a: modification of work by “Mike” Michael L. Baird; credit b: modification

of work by the Nuclear Regulatory Commission)

� The decay of radioactive isotopes allows for the relative age of once-living things to be calculated.

� Radiocarbon dating uses 14C

� Living things have a dynamic equilibrium of 14C in their system (ex: inhaling/exhaling)

� When a plant or animal dies, it no longer incorporates new 14C, and the 14C begins to decay, causing the 14C content to become less than that in the atmosphere.

� 146C � 14

7N + 0-1e-

C -14 Dating: http://www.youtube.com/watch?v=81dWTeregEA&feature=related

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21.5 Archeological Dating

� Geological dating is similar to archeological dating, but uses longer-lived nuclides

� Measure ratio of 40K to 40Ar in rocks

� 4019K + 0-1e � 40

18Ar

� 4019K � 40

20Ca + 0-1e

� 40K has a half-life of 1.28x109 years

� Rocks are crushed, 40Ar escapes, and the ratio of 40K to 40Ar is measured.

� This allowed the age of the earth to be calculated to be 4.5 billion years.

Radiometric Dating: http://www.youtube.com/watch?v=1920gi3swe4

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Geological Dating

� Three-Mile Island (Pennsylvania, 1979): Caused by

mechanical failures; small radiation leak (not linked to a

cancer fatality, no observable long term health effects).

� Chernobyl (Ukraine, 1986): No containment, 31 deaths

attributed to accident, radiation leak caused health issues

(50,000 excess cancer cases).

� Fukushima, Japan (March 2011): Not caused by

earthquake – low-lying generators flooded from tsunami;

seawater to cool down reactors used too late. Single-

replacement reaction produced hydrogen gas causing

several chemical explosions. Radioactivity release about

1/10 of Chernobyl.

Well-Known Incidents

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Nuclear fusion is the process of combining small nuclei

into larger ones (up to 59Fe). Because fusion reactions take

place at very high temperatures, they are often called

thermonuclear reactions.

Nuclear Fusion


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ITER: France – building the Tokamak, a device that uses

magnetic fields to contain and control hot plasma needed

for fusion.

Due to the high temperature

requirements, containment

is an issue.

Nuclear Fusion

https://en.wikipedia.org/wiki/Tokamak_Fusion_Test_Reactor

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Radioactive and stable isotopes have

applications in science and medicine.

Radioactive isotopes are used as

tracers.

Use of tracers for diagnosis include:

�Sodium-24 – blood flow

� Iodine-131 – thyroid conditions

� Iodine-123 – brain imaging

21.5 Uses of Isotopes

45https://en.wikipedia.org/wiki/Brain_positron_emission_tomography

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The fundamental unit of radioactivity is the curie (Ci)

1 Ci = 3.70 x 1010 disintegrations per second.

21.6 Biological Effects of Radiation

https://en.wikipedia.org/wiki/Geiger_counter

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A common unit for the absorbed dose of radiation is the

rad (radiation absorbed dose).

1 rad = 1 x 10−5 J/g of tissue irradiated

The rem (roentgen equivalent for man) is determined from

the number of rads:

Number of rems = number of rads x 1 RBE

RBE = the relative biological effectivness.

Biological Effects of Radiation

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