Studied by 2 peopleWhat 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
⁰₋₁e
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₊₁e
Mass Number = 0
Charge = 1+
Gamma (γ) rays
Definition, symbol, charge, mass number
Pure energy
⁰₀γ
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
¹₀n
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
¹₁p → ¹₀n + ⁰₋₁e
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₊₁e
What type of nuclear reaction is this?
⁴⁹₂₄Cr
Positron Emission
What should be in place of the ?
⁴²₁₉K → ? + ⁰₋₁e
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 + ⁰₀γ
What type of nuclear reaction is this?
⁹⁹^m₄₃Tc (basically in the exponent position its 99m)
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 + ¹₀n
⁴₂He = bombarding particle
¹⁰₅B = stable nucleus
¹³₇N = new radioactive nucleus
¹₀n = 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₊₁e
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
¹₀n + ²³⁶₉₂U → ²³⁷₉₂U → ⁹¹₃₆Kr + ¹⁴³₅₆Ba + 3¹₀n
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 + ¹₀n + 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
Note
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