Nuclear Chemistry Flashcards
What are the 4 rules for significant figures?
All non zero digits are significant
Zeroes appearing between any two non - zero digits are significant
Leading zeroes aren’t significant (i.e. 0.024 is still 2 sf but 0.345 is 3 sf)
Trailing zeroes in a number containing a dp are significant
What are the two important things to remember when giving an answer to a calculation?
Units and a number
What are units? Examples?
It provides measure to the numerical quantity associated with it. Adds a magnitude to the quantity which it is associated with.
For example, kilogram and seconds are all units because they give a measure to the numerical quantity
How is force measured
In newtons (N)
What is the formula for force (N)
Mass (kg) x Acceleration (ms^-2)
What is the formula for energy / joules (J)
Energy (J) = Force (kg ms^-2) x distance (m)
What are subatomic particles?
These make up the atom. This includes electrons, neutrons and protons
What are nucleons?
These are the subatomic particles found within the nucleus. This includes the protons and neutrons
What are the charges of protons and neutrons and electrons respectively
1+, 0, 1-
What are positrons?
These are another subatomic particles which has a charge of 1+ and mass of 0.000549. It is the opposite of an electron. These aren’t present in a stable atom
How is the nuclear notation arranged?
Atomic number (z) on the bottom left, and mass number (m) on the top left, followed by the element in big writing in the middle right.
What is atomic number (z)
This refers to the number of protons in an atomic nucleus. It also assists in defining the chemical nature (element) of the atom. It is also equal to the total charge in the atomic nucleus
What is the mass number
It describes the total number of nucleons (protons and neutrons) in the atomic nucleus
What are nuclides?
A distinct atom with a particular mass number and atomic number
What are isotopes?
A nuclide with the same atomic number but different mass numbers
What is atomic mass?
It is the total mass of the particles in an atom
How do you calculate the atomic mass of an element (relative atomic mass)
achieved by multiplying the atomic masses of the different naturally occurring isotopes with their natural abundance and summing it all.W
What is nucleogenesis?
It is the formation of new nuclei from existing nucleons
Explain the basis/process of nucleogenesis.
All atoms are generated from the simplest nuclide; hydrogen by nuclear reactions. The hydrogen nucleus is simply a proton
In the star formation, clouds of atomic hydrogen are pulled together by gravity and heat as they are compressed. When the temp reaches high enough, the cloud ignites as a star and this continues to react to form certain atoms from the basic building block of a hydrogen atom
From here, it follows the proton-proton chain (look in book), which allows for nucleogenesis, allowing for more complex atoms to be formed such as helium from just hydrogen. The proton proton chain provides energy for the sun
From helium, 3 heliums can be reacted to form C-12. This process continues to replicate further, as the star continues to burn hydrogen until it exhausts all the H atoms. From there, it begins to form increasingly larger atoms. These new element forming reactions are exothermic until iron. All elements up to iron are produced in stars.
When a star only has iron to burn it consumes energy and implodes, forming a supernova
Is the process of hydrogen fusion / proton proton chain exothermic or endothermic?
It releases energy due to bonds being broken and re made.
Here, energy comes from a change n mass, according to E = mc^2 (look in book)
What is radioactivity?
the emission of ionizing radiation or particles caused by the spontaneous disintegration of atomic nuclei.
It occurs, as nuclei undergo decay to attempt to become a stable nucleus
What is the highest mass for a stable isotope?
Lead - 206 has the highest mass for a stable isotope
What are the two options a nuclei can be divided into (nuclear wise)
Stable and radioactive
What are the unique characteristics to each radioactive nuclide?
A characteristic mode of decay and half life
What is half life? GIve an example
It is the time required for half of the nuclei in a sample to undergo a decay event
For example, I - 131 has a half life of 8 days, so if we start with 160 nuclei, after 8 days, only 80 original I-131 nuclei will remain
What is the exponential decay curve equation?
N = N0 x e ^-kt
N = number of nuclei
N0 = initial number of nuclei
k = decay constant
t = time
What is the decay constant?
The decay constant (k) is characteristic of the particular radioactive nuclide
Does the decay constant or the rate of decay depend on number of nuclei present
It depends on the number of the original nuclei present
What is Activity (A)?
The activity (A) of a radioactive isotope is a specific measure of the rate of decay, defined as the number of nuclei that disintegrates per second
What is nuclear decay / disintegration?
It is defined when the atom is unstable and spontaneously emits energy in the form of radiation
What is the unit of Activity (A)
It is the becquerel (Bq).
1 becquerel = 1 disintegration per second
WHat is the formula for Activity (A)
A = kN (where N is the no. of nuclei in sample), and k is the decay constant
How are final and initial activity related by exponential decay? (formula)
A = A0 x e^ -kt
What are the two different types of activity?
Specific Activity and Molar activity
What is specific activity?
Is the activity per gram of radioactive nuclide
What is molar activity?
It is the activity per mole of radioactive nuclide
What is the general value of the decay constant and half life for a low activity
Small decay number and long half life
What is the general value of the decay constant and half life for a high activity
High decay number and short half life
What is the general formula for duration of half life?
t(1/2) = ln2 / k
What is the process of carbon dating? (3 steps)
- Measure the C-14 activity of the archaeological sample (this is ‘At’)
- Measure the C-14 activity of an equivalent modern day sample (this is ‘A0’)
- Substitute these values into the equation for C-14 age:
t = 8033 x ln(A0 / At)
- note C-14 dating is only appropriate from objects less than 60000 years old
Note: m0 is initial sample and mt is how much is left after t amount of time
yes
What are the two types of atomic nuclei?
Stable and radioactive
What forces does the stability of a nucleus depend on?
Involves the competition between two main forces:
Electrostatic (coulomb) repulsion between protons act to push the nucleons apart over a long range
The strong nuclear force, which is a short range attraction between all nucleus
How does electrostatic and strong nuclear forces influence decay?
Decay occurs when the electrostatic repulsion by the protons overwhelms the strong nuclear attraction by nucleons.
In nuclides with too few neutrons, the electrostatic repulsion overwhelms the strong nuclear attraction. This causes it to be radioactive.
As the nucleus gets larger, the long range electrostatic repulsion between protons accumulate and overwhelms the strong nuclear attraction. This causes the nucleus to become too big (because all the nucleons are repelled from each other). This causes radiation.
When there are too many neutrons, the nucleus is unstable as well.
What are the 6 forms of radioactive decay?
Alpha decay (Helium atom)
Beta decay (B- / electron)
Positron decay (B+)
Electron Capture
Neutron emission
Gamma emission
What is alpha decay? Why does it occur?
Alpha decay involves the emission of an alpha particle, which is a helium nucleus with a mass number of 4 and charge 2+.
Alpha decay occurs because the nucleus becomes too heavy with protons and neutrons. It is too heavy to keep itself together. There are too many protons as well so it starts decaying
This decreases both neutrons and protons
What is beta decay (B-)? Why does it occur?
This is when an electron is ejected from the nucleus. One neutron is changed into a proton and an electron. The proton is added to the nucleus and electron is ejected.
Beta decay occurs because there are too many neutrons to protons. the n/z ratio is too high. This helps decrease it
This decreases neutrons and increases protons
n/z increases
What is positron decay (B+)? Why does it occur?
B+ (positron) is the antimatter of an electron, and is emitted from the nucleus. One proton is changed into a neutron in this nuclear reaction to balance the charge. The ejected positron will collide with the electron in the surrounding environment, producing 2 gamma rays
This occurs because there are too many protons to neutrons. n/z ratio is too low. This helps increase it whilst emitting a positron
This decreases the number of protons and increases neutrons
What is electron capture? Why does it occur?
This is when an electron from the outer cloud is captured by the nucleus and combines with a proton to form a neutron
This is typically followed by emissions of x rays and electrons fall into lower energy states to fill vacancy left by the captured electron
This increases the number of neutrons and decreases the number of protons
I.e. Iron - 55 + electron –> Manganese - 55
n/z increases
What is neutron emission? Why does it occur?
This involves a simple emission of a neutron, which changes mass but leaves no of protons unchanged
This reduces the number of neutrons
Example:
Helium - 7 –> helium 6 + neutron
What is gamma emission? Why does it occur?
This is the high frequency radiation that often acompanies other forms of decay. It is essentially energy.
I.e. Tc - 99m –> Tc - 99 + gamma
What is n/z
neutron to proton ratio
So what are the two main parameters to determine nuclear stability?
Size of nucleus (too many protons or neutrons)
Composition of nucleus (n/z ratio)
WHat is the heaviest stable nuclei?
Lead - 208
What is the zone of stability?
It is where all known stable nuclides fall inside the ‘zone of stability’. The zone has a n/z ratio near to one for light electrons, but as the nucleus gets larger, the n/z ratio increases until 1.5 for heavier elements.
Unstable isotopes must decay towards the zone of stability
How does an unstable isotope decay towards the zone of stability?
It can only go diagonally for decaying in the zone of stability.
It can go either up or down the zone of stability to become stable.
What are the negative effects of radiation
It has a harmful interaction with biological tissue. This can cause effects such as radiation sickness, cancers and nuclear weapons
What are the positive effects of radiation
The radiation is probably responsible for saving many more lives than it takes through forms such as cancer therapy and medical imaging
What is ionising radiation
It is produced by radioactive decay and has high energy, and can eject electrons from the orbit of an atom
how many eV does it take to ionise a single molecule?
10eV, so each unit of radiation can ionise a large number of molecules
What is the approx energy of Alpha particles?
5MeV = 5000000 eV = 5 x 10^5 ionised molecules
What is the approx energy of Beta particles?
0.05 to 1 MeV = 5 x 10^3 to 1 x 10^5 ionised molecules
What is the approx energy of Gamma particles
1 MeV = 1000000eV = 1 x 10^5 ionised molecules
Why is radiation damaging?
This is because the body is 50-70% water by weight, so large proportions of reactions will be with water.
When exposed to radiation, water is ionised to a cation and electron:
H2O + ionising radiation –> H2O (+) + e(-)
The H2O(+) then reacts with water to form:
H2O(+) +H2O –> H3O (+) + OH *
Meanwhile, the e- reacts with water to form:
e(-) + H2O –> OH (-) + H *
Both OH * and H * are free radicals. Free radicals are very reactive, and can damage:
DNA strands –> genetic damage, cancer
Cell membranes –> cells break apart
Proteins –> enzymes lose function
What are the factors that the effects of radiation damage depends on?
Type of radiation
Length of exposure
Source of exposure
What are the 3 main types of radiation
alpha, beta and gamma (need to remember their properties such as energy and pentration)
What is the approx energy, penetration (air), penetration (biological tissue) and relative biological effectiveness (Q) of alpha radiation?
energy = 5 MeV
penetration (air) = 40 mm
Penetration (biological) = 0.05mm
relative biological effectiveness = 20
What is the approx energy, penetration (air), penetration (biological tissue) and relative biological effectiveness (Q) of beta radiation?
energy = 0.05 - 1 MeV
penetration (air) = 6-300 mm
Penetration (biological) = 0.06 - 4mm
relative biological effectiveness = 1-1.7
What is the approx energy, penetration (air), penetration (biological tissue) and relative biological effectiveness (Q) of gamma radiation?
energy = 1 MeV
penetration (air) = 400 mm
Penetration (biological) = 50cm
relative biological effectiveness = 1
What is relative biological effectiveness?
RBE (relative biological effectiveness) is a relative measure of the damage done by a given type of radiation per unit of energy deposited in biological tissues.
How does length of exposure impact extent of radiation damage?
Short term (acute): called radiation poisoning. Involves high doses for a short period of time, causing acute cell damage and often death
Long term (chronic): Radiation induced cancer. Anything that interrupts DNA can lead to cancer
How does source of exposure impact extent of radiation damage?
Internal exposure: Ingestion or inhalation. Here, alpha and beta radiation are the most dangerous as although they have bad pentration they have high ionising power, and once they’re in its easier to suffer radiation damage
External exposure: alpha cant pentrate through air and skin. Beta might be able to cause some damage, Gamma radiation can pentrate skin, and is likely more dangerous
What unit is used to measure the biological effect of radiation?
The Sievert (Sv)
What are 3 forms of natural radiation that we are exposed to?
Radon - It is part of decay of Uranium 238. COlourless and odourless gas which damages lungs. Contributes to 55% of natural radiation dose
Potassium - 40 - This is naturally occurring, such as through bananas, kidney beans and sunflower seeds. It provides a low form of radiation
Cosmic rays - high kinetic energy particles. This is usually absorbed in the upper atmosphere, but some still goes through and provides radiation
How can ionising radiation be used to kill cancerous cells?
Focusing ionising radiation onto tumour
Internal admission of a radiopharmaceutical
How does focusing ionising radiation onto tumour work?
It uses gamma radiation as it must penetrate air and skin, and this is tuned into the cancerous cells to cause the cancer cells to be destroyed
How does internal admission of a radiopharmaceutical work to kill cancer cells?
The radiopharmaceutical must be targeted to the tumour. It uses alpha or beta emitters, which have short range effect.
For example, iodine naturally accumulates in the thyroid, so I-131 (beta emission, with half life of 8 days) is used to treat thyroid cancer
Current focus / research is attempting to attach radionuclides to antibodies which guide radiopharmaceuticals to other cells or organs
How is radiation used for imaging?
Radioimaging uses radiation emitted from within the body to map the body.
The radiation used must be highly penetrating so that it can be detected and isn’t harmful to the patient –> uses gamma radiation
Distribution of radioisotope is imaged by scintilallation counting ( no need to know this)
Computer tomography can give a 3d reconstruction of the body
Radiation can come from a number of sources such as technetium - 99m and positron emitters
Why is technetium - 99m ideal?
Because it is easily incorporated into drugs. It is also easily prepared from Mo - 99.
It also doesn’t change chemistry when it decays, and emits only high penetrating gamma rays, not any harmful alpha and beta particles
Explain the process of PET imaging
It uses a radionuclide that emits positrons. Inside the body, the positron reacts with electrons, producing two high energy gamma rays, which are detected outside the body
The most common PET imaging agent is fludeoxyglucose (FDG), in which an oxygen atom of glucose is replaced by a fluorine - 18
FDG is used to observe parts of the body that use high levels of glucose, such as tumours, and the brain
What is the unit of the decay constant?
s^-1
per second
