Radioisotopes and Their Applications
RADIO ISOTOPES
A radioisotope is a type of isotope, which is an atom of a chemical element with the same number of protons but a different number of neutrons in its nucleus than the most abundant variety. The term "radioisotope" specifically refers to isotopes of an element that are unstable and undergo radioactive decay, emitting radiation in the process.
APPLICATIONS OF RADIO ISOTOPES
Radioisotopes have a wide range of applications across various fields.
Medicine: Radioisotopes are extensively used in medicine for diagnosis and treatment. Examples include Technetium-99m for imaging in nuclear medicine procedures like bone scans and thyroid scans, Iodine-131 for thyroid cancer treatment, and cobalt-60 for radiation therapy in cancer treatment.
Industry: Radioisotopes are used in industrial processes for thickness gauging, level gauging, and flow rate measurements. For instance, radioactive isotopes like Americium-241 and Cobalt-60 are used in industrial radiography for non-destructive testing of materials.
Agriculture: Radioisotopes play a crucial role in agricultural research, particularly in studies related to plant nutrition, soil erosion, and pest control. For example, Phosphorus-32 is used to study phosphorus metabolism in plants.
Food Preservation: Radioisotopes such as Cobalt-60 are used for food irradiation to extend the shelf life of certain food products by killing bacteria and pests and inhibiting sprouting.
Carbon Dating: Radioisotopes like Carbon-14 are used in archaeology and geology for carbon dating, which helps determine the age of organic materials and geological formations.
Smoke Detectors: Americium-241, a radioisotope, is used in smoke detectors to ionize air particles, which triggers an alarm when smoke enters the detector.
Environmental Studies: Radioisotopes are utilized in environmental studies to trace the movement of pollutants, study ocean currents, and monitor air and water quality. Examples include tritium for tracing water movement and Cesium-137 for studying soil erosion.
Power Generation: Radioisotopes are used in the generation of electricity in radioisotope thermoelectric generators (RTGs) commonly used in spacecraft and remote locations where traditional power sources are impractical.
Oil Exploration: Radioisotopes like Iodine-131 are used in oil well logging to measure the porosity and density of rock formations, aiding in the exploration and extraction of oil and gas reserves.
Biological Research: Radioisotopes are widely used in biological research for labeling and tracing biological molecules, studying metabolic pathways, and conducting molecular imaging studies. Examples include using tritiated thymidine to study DNA replication and Fluorine-18 in positron emission tomography (PET) scans for imaging biological processes in living organisms.
Radio Carbon Dating Notes - Ref: Introduction to Nuclear and Particle Physics By V.K. Mittal, R.C. Verma and S.C.Gupta
RADIO CARBON DATING
The principle of radioactive decay is applied in the technique of radioactive dating, a process widely used by scientists to determine the age of materials and artifacts.
Radioactive dating is defined as the method of determining the age of biological or geological samples by using the radioactive technique.
Radioactive C-14 atoms exist naturally in very minute quantities. C-14 is everywhere around us: in our clothes, in the food we eat, even in the air we breathe. The ratio of radioactive C-14 atoms to stable C-12 atoms in the atmosphere has remained constant over thousands of years. Although C-14 naturally decays, it is also continually being formed. C-14 atoms are formed when neutrons from the cosmic radiation collide with N-14 atoms in the atmosphere. Thus, the decay of C-14 is reasonably balanced with its production, resulting in a constant ratio of C-14 to C-12.
Carbon dioxide (CO2) molecules in the air contain both isotopes of carbon. This CO2
is continually used by plants to grow. Because the ratio of C-14 to C-12 in atmospheric CO2 is constant, the intake of CO2 by a plant results in a constant ratio of the two isotopes in the plant’s body while it is alive. However, when the plant dies it no longer takes in CO2. As a result, the C-14 decaying in the dead plant can not be replenished by CO2, resulting in the decrease in activity of C-14 with time. Because animals eat plants and inhale air, the activity of C-14 decreases once they die, since the C-14 cannot be replenished. In order to determine the radioactivity of C-14, a small portion of the sample is burnt, so that carbon present in it reacts with oxygen to form CO2. The CO2 that contains C-14 is radioactive, and the amount is measured using a radiation counter. Burning is done to facilitate measuring the level of C-14. C-14 has a half-life of about 5730 years. This means that in a given sample of a carbon-containing substance, (without the C-14 being replenished) the activity of C-14 decreases by half every 5730 years. Suppose someone discovers an ancient manuscript and finds that the activity of C-14 in the paper is half of that found in living trees. This would mean that the manuscripts would be about 5730 years old.
(Credits: http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/cardat.html)
The use of radioactive C-14 for dating was first done by William Libby, at the University of Chicago, USA, in 1947.
The age of a given sample can be determined using ,
A = A0 e–λt
In calculating the age of a sample, we make the following assumption:
The activity of C-14 in a living sample has remained same over thousands of years.
In the above equations A0 is the activity of the sample, when it is living. A is the activity of the sample whose age is to be determined. For example, if we wish to determine the age of a given piece of wood, A0 is the activity for a fresh wood piece taken from a presently living tree. A is the activity of the sample whose age is to be determined.
The relatively short half-life of C-14 (5730 years) means that the amount of C-14 remaining in materials and objects older than about 30,000 years is too small to be measured experimentally. Thus, carbon dating has following two limitations:
l It cannot measure the age of an object older than about 30,000 years.
l It cannot measure the age of non-living objects like rocks and minerals.
Mossbauer Effect and Its' Applications - Notes
Mossbauer Effect:
Before 1958, it was believed that gamma ray nuclear spectroscopy was
impossible due to high nucleus recoil, causing Doppler shifts in gamma ray
frequency and extremely narrow gamma ray lines. This recoil hindered
resonant absorption and emission of gamma rays by atomic nuclei. However, in
1958, Rudolf Mossbauer proved that recoil-free absorption or emission of
gamma rays is possible by embedding nuclei in crystal lattices. By embedding
experimental nuclei in crystal lattice, they can share recoil energy with
the entire lattice, effectively making their mass infinite compared to the
gamma ray photon. This allows for resonant emission and absorption of gamma
rays by the experimental nuclei.
The Mossbauer effect says that certain atoms in solid structures emit gamma rays without much recoil. This means the emitted gamma ray matches the energy needed for a nuclear transition. When this gamma ray hits another similar atom in a solid, absorption might happen because of the precise energy match. This process happens in tightly-packed crystals. A schematic is shown below:
Because nuclear energy states are very specific, even a tiny change in
photon energy can disrupt resonance. Mossbauer spectroscopy is highly
sensitive, allowing measurement of otherwise undetectable nuclear energy
differences. Small energy changes, nucleus magnetic fields, and lattice
distortions can alter absorption lines. These changes, called nuclear
hyperfine interactions, are observable effects caused by alterations in the
nuclear environment.
Mossbauer Measurements: The Hyperfine Interactions
The nuclear isomer shift – electric monopole interaction:
The isomer shift originates from the Coulomb interaction of the nuclear
charge distribution over the radius of the nucleus in its ground and excited
state, and, the electron charge density at the nucleus. It results in
a shift of the overall spectrum to higher and lower energies. The isomer
shift depends most strongly on the ionization state of the atom, as
shielding effects due to valence electrons will influence the s-electron
density at the nucleus.
The nuclear quadrupole splitting – electric quadrupole
interaction.
The quadrupole splitting results from the interaction between the Electron
Field Gradient (EFG) at the nucleus and the electric quadrupole moment eQ of
the nucleus itself. More specifically, the EFG at the nucleus will split the
Fe57 nuclear excited I = 3/2 state into a pair of doublets: Iz = ± 1/2 and ± 3/2.
The nuclear Zeeman effect – magnetic dipole interaction.
The nuclear magnetic dipole moment interacts with an applied magnetic field
B to produce this splitting of the energy levels at the nucleus.
Besides these three hyperfine interactions there are other measurable interactions called the relativistic effects. These are caused by a temperature or pressure changes, and acceleration and gravitational fields.
Applications of Mossbauer Effect:
Material science: Studying crystal structures, phase transitions, and lattice
dynamics.
Chemistry: Analyzing chemical bonding, coordination environments, and reaction
mechanisms.
Physics: Investigating magnetic properties, quantum phenomena, and fundamental
atomic processes.
Geology: Examining mineral compositions, geological formations, and environmental
processes.
Astrophysics: Probing stellar nucleosynthesis, cosmic dust, and interstellar
matter.
Biology: Understanding metalloenzymes, biological mineralization, and protein
dynamics.
Archaeology: Identifying trace elements in ancient artifacts
Nanotechnology: Characterizing nanomaterials, surface properties, and molecular
interactions.
Pharmacology: Analyzing drug binding, molecular structures, and pharmaceutical
formulations.
Environmental science: Monitoring pollutants, studying soil composition, and tracing elemental
cycles.
Properties or Characteristics of Nuclear Radiation
Properties or Characteristics of Alpha Particles
1. Alpha particles are 24He nuclei with 2 units of positive charge and mass of 4 amu.
2. Because they are charged particles so they can be deflected by electric and magnetic fields.
3. They ionize the medium through which they pass. Their ionizing power is much higher than β- and γ-rays.
4. Because of the high-ionizing power, they can be easily absorbed by few centimeters of air or fraction of millimeter thick aluminum.
5. Naturally occurring a-emitters emit a-particles with energy in the range of 5 MeV to 10 MeV.
6. Alpha particles when fall on certain materials like ZnS, barium platinocyanide, etc. emit flashes of light called scintillations. This property of scintillation was initially used to detect a-particles.
7. Long exposures to a-emitters produce harmful effects on the human body.
Properties or Characteristics of Beta Particles
1. Beta particles are charged particles, either negatively charged (β-) or positively charged (β+), depending on whether they are electrons or positrons, respectively.
2. Beta particles have a much smaller mass compared to alpha particles. Electrons have a mass of approximately 9.11 × 10-31 kilograms, while positrons have the same mass but with a positive charge.
3. Beta particles can travel at high speeds, often close to the speed of light, especially in cases of beta particles emitted from highly radioactive isotopes.
4. Beta particles are moderately penetrating. They can penetrate through materials like paper or thin aluminum foil but can be stopped by thicker materials such as wood, plastic, or several millimeters of aluminum.
5. Beta particles ionize atoms they interact with by knocking off electrons. However, their ability to ionize is less than that of alpha particles due to their smaller mass.
6. Beta particles are deflected in a magnetic field, and the direction and degree of deflection depend on their charge and velocity, according to the Lorentz force law.
7. Beta particles interact with matter through electromagnetic interactions (Coulomb forces), which cause them to lose energy as they pass through material. This leads to a gradual decrease in their velocity and penetration power.
8. Beta particles are produced during the decay of certain radioactive isotopes, such as carbon-14 (14C), potassium-40 (40K), and strontium-90 (90Sr).
9. Beta particles can be detected using various methods, including Geiger-Müller counters, scintillation detectors, and cloud chambers, which exploit the ionizing properties of these particles to produce measurable signals.
Properties or Characteristics of Gamma Rays
1. Gamma rays are electromagnetic waves just like X-rays or visible light.
2. They always travel with velocity of light irrespective the energy of γ-rays.
3. They do not cause any appreciable ionization and are not deflected by electric or magnetic fields.
4. Gamma-rays have high penetrating power, much larger than that of α- or β-particles.
5. They have frequencies greater than 1019 Hz and wavelengths shorter than 10 picometers (pm).
6. They have no charge or mass.
7. Gamma rays can be detected using specialized instruments such as gamma-ray spectrometers and scintillation detectors.
Infinity Column - A Puzzle of Three Digits - Be the Kings Advisor !
The wisest men of the kingdom are called upon by the king to his court. One of them is to be chosen for the advisor rank and thus they should take part in a contest solving intelligence tests. After several days of competitions, only two winners emerged. The king called both of them to his palace and said, “Tomorrow morning I will write on a paper and hide three digits a, b, and c which you would need to identify. You will have to tell me any three numbers x, y, and z. I will calculate then the sum ax + by + cz and tell you the result. Knowing this number, whoever guesses the three digits a, b, and c which I have in hiding, will be the winner”. What is a possible strategy to win the competition and solve the king’s problem?
Binding Energy Vs Mass Number Curve
Binding Energy and Mass Number Curve
The Binding Energy per Nucleon vs. Mass Number curve is a graph that illustrates the relationship between the binding energy per nucleon (BE/A) and the mass number (A) for atomic nuclei. This curve is a crucial concept in nuclear physics and provides insights into the stability and energy characteristics of atomic nuclei.
The key components of the plot are as follows:
Binding Energy per Nucleon (BE/A): The binding energy of a nucleus is the energy required to completely separate all the nucleons (protons and neutrons) in that nucleus. The binding energy per nucleon is obtained by dividing the total binding energy by the number of nucleons in the nucleus. Mathematically, it is expressed as
The binding energy per nucleon is a measure of the average energy required to remove one nucleon from the nucleus.
Mass Number (A): The mass number (A) of a nucleus is the total number of nucleons (protons and neutrons) in the nucleus.
Now, when we plot the binding energy per nucleon against the mass number for a range of atomic nuclei, we get the Binding Energy per Nucleon vs. Mass Number curve. The curve typically exhibits the following features:
Peak Stability: There is a region where the binding energy per nucleon is at its maximum. This indicates the most stable nuclei. Iron-56 is often used as an example of a nucleus near this peak, and it is considered a particularly stable nucleus.
Trend Towards Iron: As we move away from the peak (either to the left or right along the x-axis), the binding energy per nucleon generally decreases. This means that nuclei on both the lighter and heavier sides of the peak are less stable. Heavier nuclei tend to undergo nuclear reactions, such as fission, to move towards more stable configurations, while lighter nuclei tend to fuse together, when provided with enough energy and yield more energy in the process.
Energy Release in Nuclear Reactions: Nuclear reactions, such as nuclear fusion (combining lighter nuclei) or nuclear fission (splitting heavier nuclei), often result in a release of energy. This energy release is related to the difference in binding energy per nucleon between the initial and final nuclei.
In summary, the Binding Energy per Nucleon vs. Mass Number curve provides valuable information about the stability of atomic nuclei and helps explain phenomena such as nuclear fusion, fission, and the energy release in nuclear reactions. The trend of decreasing binding energy per nucleon away from the peak indicates the tendency of nuclei to move towards more stable configurations.
General Properties of Atomic Nuclei
Mass Number (A): The total number of protons and neutrons in the nucleus is called the mass number. It is denoted by the symbol 'A.'
Atomic Number (Z): The number of protons in the nucleus is the atomic number, denoted by the symbol 'Z.' It determines the element to which the nucleus belongs.
Nucleons: Protons and neutrons are collectively referred to as nucleons. They are the subatomic particles found in the nucleus.
Size: The size of the nucleus is much smaller than the overall size of the atom. The vast majority of an atom's mass is concentrated in the nucleus.
Density: Nuclei are incredibly dense. The density of nuclear matter is on the order of 1017 to 1018 kg/m3.
Binding Energy: The energy required to disassemble a nucleus into its individual protons and neutrons is the binding energy. It's a measure of the stability of the nucleus. Usually measured in the units of eV.
Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons are called isotopes. Isotopes have similar chemical properties but different atomic masses.
Nuclear Stability: Nuclei with a specific ratio of neutrons to protons tend to be more stable. The stability is influenced by the nuclear forces between nucleons.
Radioactivity: Some nuclei are unstable and undergo spontaneous transformations, emitting particles or electromagnetic radiation. This process is known as radioactivity.
Half-life: The time it takes for half of a sample of radioactive material to decay is the half-life. It is a characteristic property of each radioactive isotope.
Charge: The nucleus carries a positive charge due to the presence of protons. The number of protons determines the overall charge of the nucleus.
Nuclear Forces: The forces that bind protons and neutrons in the nucleus are called nuclear forces. These forces are short-range and overcome the electrostatic repulsion between positively charged protons.
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