Atomic Physics Flashcards
What was the set up for Rutherford’s gold foil experiment and what were the observations?
- A beam of α‑particles was directed at a thin gold foil.
- Most particles passed straight through, indicating that atoms are mostly empty space.
- A few were deflected at small angles (showing a concentrated positive charge) and a very few were deflected back, confirming a tiny, dense, positively charged nucleus.
What did Rutherford’s experiment reveal about the structure of the atom based on the deflection of α‑particles?
- Most α‑particles were undeflected, showing that the atom contains empty space
- A few were slightly deflected, indicating a positive charge that repels α‑particles
- A few were greatly deflected, proving that the atom contains a tiny, heavy particle—the nucleus.
How did Rutherford use his experimental conclusions to develop his atomic theory?
He proposed that an atom consists of a tiny, heavy, positively charged nucleus surrounded by electrons in a largely empty space.
What is the standard atomic notation and what does each part represent?
Atomic notation is (_Z^A)X, where A (the mass or nucleon number) is the total number of protons and neutrons, and Z (the atomic or proton number) is the number of protons (with electrons equal to protons in a neutral atom).
What are isotopes and how do the carbon isotopes C‑12, C‑14, and C‑15 illustrate this concept?
- Isotopes are elements with the same number of protons but different numbers of neutrons.
- For carbon, all isotopes have 6 protons, C‑12 has 6 neutrons, C‑14 has 8 neutrons, and C‑15 has 9 neutrons.
How do stable and unstable elements differ in terms of energy and nuclear radiation?
Stable elements have no excess energy, whereas unstable elements contain excess energy that is released as nuclear radiation.
What are the three types of nuclear radiations and their standard symbols?
The three types are:
1. Alpha particles: (2^4)α
2. Beta particles: (-1^0)β
3. Gamma rays: (_0^0)γ
Describe the structure and air penetration of alpha particles.
- Alpha particles consist of 2 protons and 2 neutrons (like a helium nucleus)
- They can penetrate only a few centimeters in air
- They can be stopped by a sheet of paper
What are the key properties of alpha particles regarding ionization, mass, charge, and deflection in electric and magnetic fields?
- They have the highest ionization
- They are heavy (4 amu)
- They carry a charge of +2e
- They deflect toward the negative plate in an electric field
- They deflect anticlockwise in a magnetic field (using Fleming’s left-hand rule).
What is the structure, penetration distance, and stopping material for beta particles?
- Beta particles are fast-moving electrons
- They can travel a few meters in air
- They are stopped by aluminium foil (>5mm)
Outline the ionization, mass, charge, and deflection properties of beta particles.
- Beta particles have intermediate ionization
- They are light (mass equal to an electron) They carry a charge of –1e
- Deflect toward the positive plate in an electric field
- Deflect clockwise in a magnetic field (using Fleming’s right-hand rule).
What are the characteristics of gamma rays regarding structure, penetration, and stopping material?
- Gamma rays are high-energy electromagnetic waves with high frequency and short wavelength
- They have no mass and no charge
- They have the lowest ionization
- They are nearly unstoppable in air
- They are significantly reduced by lead (>2cm)
Why are gamma rays not deflected by electric or magnetic fields?
Gamma rays are high‑energy electromagnetic waves that have no mass and no charge, so they remain undeflected in both electric and magnetic fields.
What does ionization mean in the context of atomic physics?
Ionization is the ability of radiation to make an atom lose an electron.
Write the general equation for alpha decay and give an example using uranium-236.
- The general alpha decay equation is (_Z^A)X → (_Z–2^(A–4))Y + (_2^4)α.
- For example: (_92^236)U → (_90^232)Kr + (_2^4)α
Write the general equation for beta decay and provide an example using uranium-236.
- The beta decay equation is (_Z^A)X → (Z+1^A)Y + (-1^0)β.
- For example: (_92^236)U → (93^236)Bl + (-1^0)β.
What is the equation for gamma decay and what does it indicate about the nucleus?
The gamma decay equation is (_Z^A)X → (_Z^A)X + (_0^0)γ, which indicates that the nucleus remains unchanged.
How do the atomic and mass numbers change in alpha, beta, and gamma decays?
- In alpha decay, the atomic number decreases by 2 and the mass number by 4
- In beta decay, the atomic number increases by 1 while the mass number remains unchanged
- In gamma decay, there is no change in either number
Define ‘activity’ and ‘half-life’ in radioactive decay.
- Activity is the number of decays per second
- Half-life (T₁/₂) is the time required for the activity to decrease to half its initial value OR the time for radioactive nuclei to decrease to half its initial value.
How is the half-life determined from a decay curve?
- First, take the maximum value (e.g., 600 counts) and divide it by 2 (giving 300).
- Draw a horizontal line at 300 counts until it meets the decay curve
- Then drop vertically to the time axis; that time is the half-life (e.g., 1.5 hours).
What is background radiation and what are its common sources?
Background radiation is the natural radiation present around us in absence of radioactive material. The main sources are:
* Outer space (Sun and stars)
* Radon gas (about 60% of BG radiation)
* Rocks
* Nuclear experiments
* Nuclear wastes
* Medical imaging
How is background radiation measured and what is its typical count rate?
It is measured using a GM (Geiger-Muller) counter and is usually around 10-30 counts, although it can vary significantly.
How is the total count rate measured using a GM (Geiger-Muller) counter calculated?
The total count rate equals the sum of the count rate from the radiation source and the background count rate.
Which rule is used to determine the deflection direction of positive particles like α‑particles in a magnetic field?
Fleming’s left-hand rule is used when a current or positive particle (such as an α‑particle or proton) moves in a magnetic field.
Which rule applies to negative particles like β‑particles when deflected in a magnetic field?
Fleming’s right-hand rule is used for induced current or β‑particles (electrons) moving in a magnetic field.
Why do α‑particles have a higher ionization effect compared to β‑particles?
- α‑particles are heavier
- They carry a higher charge
So, they interact more strongly with matter, resulting in greater ionization.
What safety measures can be taken to reduce exposure to ionizing radiation?
To lessen ionization risks:
* Reduce exposure time
* Work from a large distance
* Use a protective screen
What are some practical uses of the three types of nuclear radiations?
- Alpha particles are used in smoke detectors
- Gamma rays are used for sterilizing food and treating cancer
- Beta particles are used to measure the thickness of paper sheets.
Compare nuclear fission and fusion, including examples of reactions and methods to control a chain reaction.
Nuclear fission:
* Splits a large nucleus into smaller nuclei
* Releases energy
* Ex: (_0^1)n + (_92^235)U → (_56^141)Ba + (_36^92)Kr + 3(_0^1)n
* Its a chain reaction
Nuclear fusion:
* Combines two small nuclei at very high temperatures to form a larger nucleus
* Releases energy,
* Ex: (_1^2)H + (_1^3)H → (_2^4)He + (_0^1)n.
Contoling chain reactions:
* By moderators (to slow the reaction)
* By control rods (to absorb neutrons)
How does radiometric dating (carbon dating) utilize radioactive decay?
- Radiometric dating compares the measured activity of a radioactive isotope (e.g., Carbon‑14) in a sample with its expected decay rate.
- Using the known half-life, the age of the sample can be estimated.
Which conservation laws must be obeyed in radioactive decay processes?
Mass number: Total number of nucleons remains constant.
Atomic number: Total positive charge is conserved.
Charge: Overall electrical charge is conserved.
Energy: Energy (including the energy carried by radiation) is conserved.
