Chapter 5: Nuclear Chemistry

What does natural radioactivity comes from?

Unstable nuclei

What are unstable nuclei found in?

Carbon, hydrogen, and elements with atomic numbers 20 or higher

Unstable Nuclei

Nuclei in which the nuclear forces cannot offset the repulsions between the protons

* Radioactive

Radiation

Small particles of energy emitted by unstable nuclei to become more stable

What are the forms of radiation?

* alpha (*α*) particle
* beta (*β⁻*) particle
* positrons (*β⁺*)
* gamma (*γ*) rays

Radioisotope

An isotope of an element that emits radiation

Are radioisotopes one isotope of an element?

No, they can be one or more

How are radioisotopes named?

With the mass number

* For example, iodine-131

Alpha (*α*) particles

* Definition, symbol, charge, mass number

Identical to helium nucleus

* ⁴₂He
* Mass Number = 4
* Charge = 2+

Beta (*β⁻*) particles

* Definition, symbol, charge, mass number

High energy electrons

* ⁰₋₁*e*
* Mass Number = 0
* Charge = 1-

Positrons (*β⁺*)

* Definition, symbol, charge, mass number

A positron is a particle with the same mass as an electron but with a positive charge

* ⁰₊₁*e*
* Mass Number = 0
* Charge = 1+

Gamma (*γ*) rays

* Definition, symbol, charge, mass number

Pure energy

* ⁰₀*γ*
* Mass Number = 0
* Charge = 0

Proton (*p*)

* Symbol, charge, mass number

Positively charged subatomic particle

* ¹₁H
* Mass Number = 1
* Charge = 1+

Neutron (*n*)

* Symbol, charge, mass number

Neutrally charged subatomic particle

* ¹₀*n*
* Mass Number = 1
* Charge = 0

Biological Effects of Radiation

Ionizing radiation strikes molecules in its path and…

* knocks away the electrons in molecules, forming unstable ions such as H₂O⁺
* causes undesirable chemical reactions

What happens to the cells when a biological species is hit with radiation?

It damages cells most sensitive to radiation, rapidly dividing cell in bone marrow, skin and reproductive organs, thus causing cancer

Alpha (*α*) particle

* Travel distance in air, tissue depth(penetration), shielding, typical source

**Travel distance in air:** 2-4 cm

**Tissue depth(penetration):** 0.05 mm

**Shielding**: Paper, clothing

**Typical Source:** Radium-226

Beta (β⁻) particle

* Travel distance in air, tissue depth(penetration), shielding, typical source

**Travel distance in air:** 200-300 cm

**Tissue depth(penetration):** 4-5 mm

**Shielding**: Heavy clothing, lab coats, gloves

**Typical Source:** Carbon-14

Gamma (*γ*) rays

* Travel distance in air, tissue depth(penetration), shielding, typical source

**Travel distance in air:** 500mm

**Tissue depth(penetration):** 50 cm or more

**Shielding**: Lead, thick concrete

**Typical Source:** Technetium-99m

For those working in an environment where radioactive materials are present, how do you limit exposure?

* Minimizing the time spent near a radioactive source
* Increase distance from the source

Radioactive Decay

A process in which the nucleus breaks down

* represented by a nuclear equation

Nuclear Equation (what it’s like)

The mass number and atomic number may change

* The sum of the mass numbers are equal and the atomic numbers are equal for products and reactants

Alpha Decay

* Relate to nuclear equation

Occurs when a radioactive nucleus emits an alpha particle, forming a new nucleus with a mass number that is decreased by 4 and an atomic number that is decreased by 2

Beta Decay

* Relate to nuclear equation

In the nuclear equation, the mass number of the new nucleus remains the same, and its atomic number increases by 1

Positron Emission

* Relate to nuclear equation

A proton is converted to a neutron and a positron

¹₁*p* → ¹₀*n* + ⁰₋₁*e*

* The mass number of the new nucleus is the same, but the atomic number decreases by 1

Gamma Radiation

* Relate to nuclear equation

Energy emitted from an unstable nucleus, indicated by *m* following the mass number

* The mass number and the atomic number of the nucleus are the same

What should be in place of the *?*

* ⁴⁹₂₅Mn → *?* + ⁰₊₁*e*
* What type of nuclear reaction is this?

⁴⁹₂₄Cr

* Positron Emission

What should be in place of the *?*

* ⁴²₁₉K → *?* + ⁰₋₁*e*
* What type of nuclear reaction is this?

⁴²₂₀Ca

* Beta Decay

What should be in place of the *?*

* ²⁵¹Cf₉₈ → *?* + ⁴₂He
* What type of nuclear reaction is this?

²⁴⁷₉₆Cm

* Alpha Decay

What should be in place of the *?*

* *?* → ⁹⁹₄₃Tc + ⁰₀*γ*
* *What type of nuclear reaction is this?*

⁹⁹^*m*₄₃Tc (basically in the exponent position its 99*m*)

* Gamma Radiation

How are radioactive isotopes produced?

* What is the process called?

When a stable nucleus is converted to a radioactive nucleus by bombarding it with a small particle

* Transmutation (nuclear)

Label the parts in this transmutation process:

* ⁴₂He + ¹⁰₅B → ¹³₇N + ¹₀*n*

⁴₂He = bombarding particle

¹⁰₅B = stable nucleus

¹³₇N = new radioactive nucleus

¹₀*n* = neutron

* It can be any particle though

Geiger Counter

* How does it work?

A common instrument that detects alpha particle, beta particles, and gamma rays

* It uses ions produced by radiation to create an electrical current

Units for measuring radiation (list)

* Which is a common unit and which are SI units?
* What are the pairs?

* Curie = common unit
* Becquerel = SI unit
* Rad = common unit
* Gray = SI unit
* Rem = common unit
* Sievert = SI unit

\
Common + SI Unit Pairs:

* Curie and Becquerel
* Rad and Gray
* Rem and Sievert

Curie

* Definition, abbreviation, equivalent

The number of disintegrations that occurs in 1g of radium

* Ci
* 3.7 x 10¹⁰ disintegrations per second
* 3.7 x 10¹⁰ disintegrations/s = 1 Ci

Becquerel

* Definition, abbreviation, equivalent

The SI unit of radiation activity

* Bq
* 1 disintegration per second
* 1 disintegration/s = 1 Bq

Relation between Ci and Bq

1 Ci = 3.7 x 10¹⁰ Bq

Rad

* Definition, abbreviation

Radiation absorbed dose--measures the amount of radiation absorbed by a gram of material such as body tissue

* rad is the abbreviation

Gray

* Abbreviation, equivalent

Gy

* 1 Gy = 1 (J/Kg) of tissue

Relation between rad and gy

1 Gy = 100 rad

Rem

* Definition, abbreviation

The radiation equivalent in humans--measures biological effects(damage) of different kinds of radiation

* Rem is the abbreviation

Sievert

* Abbreviation

Sv

Relation between Rem and Sv

1 Sv = 100 rem

Match each(radiation) with it’s unit of measurement:

* Activity
* Absorbed Dose
* Biological Damage

Activity = Ci or Bq

Absorbed Dose = Rad or Gy

Biological Damage = Rem or Sv

Dosimeters

Detect them amount of radiation exposure from

* X-rays
* Gamma rays
* Beta particles

\
Usually worn as a tag-like device on clothing

What are some every day things that expose us to low levels of radiation?

* Buildings where we live and work
* Food and water
* The air we breathe

What is an LD₅₀?

Lethal dose

* The amount of something it takes to kill half of an observed population

LD₅₀ of radiation in Sv for

* Insects
* Bacterium
* Rats
* Humans
* Dogs

Insects = 1000 Sv

Bacterium = 500 Sv

Rats = 8 Sv

Humans = 5 Sv

Dogs = 3 Sv

Half-life

The time it takes for the radiation of a radioisotope to decrease(decay) to half the original value

What radioisotope is used to date really old biological things due to its long half-life?

Carbon-14

* It has a half-life of 5730 years

Decay Curves

Illustrate the amount of time that is required for half of the substance to be converted into a different element

If the radioisotope of strontium-90 has a half-life of 35.1 years, how many mg of a 36.0mg sample will remain after 152.4 years?

152\.4 yr(1 half-life/35.1 yr) = 4 half-lives

\
36 → 18 → 9 → 4.5 → 2.25 ***2.25mg remains***

* Each arrow is a half-life

What types of radioisotopes are used in medical applications?

* Why?

Radioisotopes with short half-lives because…

* the cells in the body do not differentiate between nonradioactive atoms and radioactive atoms
* they decay within a few months of use
* To avoid any bad damage to healthy cells

How is a radioisotope used in medical applications?

Once the radioisotope is incorporated into cells, the radioactive atoms can be detected as they emit radiation, giving an image of an organ

Scans with radioisotopes

* After the radioisotope is ingested by the patient

* The scanner moves slowly over the organ where the radioisotope is absorbed
* The radiologist determines the level and location of the radioactivity emitted by the radioisotope
* The gamma rays emitted from the radioisotope can be used to expose a photographic plate, producing a scan of the organ

Positron Emission Tomography (PET)

Positron emitters with short half-lives

* can be used to study brain function, metabolism, and blood flow
* combine with electrons after emission to produce gamma rays, which are then detected by computers, creating 3D image of the organ

What are some examples of positron emitters with short half-lives

carbon-11, oxygen-15, nitrogen-13, flourine-18

\
¹⁸₉F → ¹⁸₈O + ⁰₊₁*e*

Computed Tomography (CT)

An imaging method used to scan organs such as the brain, lungs, and heart

* A computer monitors the absorption of 30000 x-ray beams directed at the brain in successive layers
* Differences in absorption based on tissue densities and fluids provide images of the brain

Magnetic Resonance Imaging (MRI)

An imaging technique that doesn’t require nuclear radiation

* Is the least invasive imagine method available
* Based on the absorption of energy when protons in hydrogen atoms are excited by a strong magnetic field

Why does an MRI work?

It works because the energy absorbed is converted to color images of the body

Nuclear Fission Reaction

A large nucleus is bombarded with a neutron, making an unstable isotope

* The large nucleus then splits into two smaller nuclei and three neutrons

\
¹₀*n* + ²³⁶₉₂U → ²³⁷₉₂U → ⁹¹₃₆Kr + ¹⁴³₅₆Ba + 3¹₀*n*

Atomic energy

Large amount of energy generated by the splitting of a large nuclei in a nuclear fission reaction

OR

The leftover mass that comes from the fusing of nuclei in a nuclear fusion reaction

How is nuclear fission used in power plants?

It is used to keep the systems cool so the reaction doesn’t get out of hand

What is a nuclear chain reaction?

In nuclear fission, the resulting neutrons of one reaction bombard and cause fission in other nuclei

Nuclear Fusion Reaction

Atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy

\
Ex. Hydrogen isotopes combine in a fusion reaction to produce helium, a neutron, and energy

* ³₁H + ²₁H → ⁴₂He + ¹₀*n* + energy

What temperatures are necessary for fusion reactions?

Very high

Radioactive Decay vs Nuclear Fission

**Nuclear fission:** The splitting of one large atomic nucleus into smaller fragments

**Radioactive decay:** The change of a less stable nucleus to a more stable nucleus