Nuclear Physics Test. 4

In the gold foil experiment, the unexpected deflection of some alpha particles led Rutherford to conclude that the atom's positive charge and mass are concentrated in a small, dense nucleus.

According to E=mc², any energy released (or absorbed) during a reaction is directly proportional to the change (decrease or increase) in the total mass of the particles.

The decay constant represents the probability of decay. A higher probability (large constant) means the substance decays quickly, resulting in a short half-life.

From the activity formula A = λN, the number of atoms is N = A / λ. So, N = (1.2 x 10⁶ Bq) / (3.0 x 10⁻⁹ s⁻¹) = 0.4 x 10¹⁵ = 4.0 x 10¹⁴ atoms.

A short half-life ensures it decays quickly and doesn't remain in the body. Gamma rays are used because they can easily exit the body to be detected by external cameras.

The photon, the quantum of light, has no charge or other quantum numbers that would distinguish it from its antiparticle. Therefore, it is its own antiparticle.

Reactants mass = 2(2.0141) = 4.0282 amu. Products mass = 3.0160 + 1.0087 = 4.0247 amu. Δm = 4.0282 - 4.0247 = 0.0035 amu. Energy = 0.0035 × 931.5 ≈ 3.26 MeV.

Particle accelerators are used in research to study particles, but are not part of a commercial nuclear reactor, which relies on a self-sustaining chain reaction.

In negative beta decay, a neutron (n) turns into a proton (p). This decreases the number of neutrons and increases the number of protons, thus decreasing the n/p ratio.

The time elapsed is 9 years, which is 3 half-lives (9/3 = 3). The fraction remaining is (1/2)³ = 1/8.

Ionizing power is the ability to knock electrons off atoms. Large, highly charged alpha particles are the most ionizing, while uncharged gamma rays are the least.

Nuclei are positively charged and repel each other. High temperature gives them enough kinetic energy to overcome this electrostatic repulsion and get close enough for the strong force to fuse them.

Breeder reactors are designed to convert fertile material (like U-238) into fissile material (like Pu-239) at a rate faster than they consume their own fissile fuel.

Thermal neutrons are in thermal equilibrium with their surroundings. These slow-moving neutrons have a much higher probability of being captured by a U-235 nucleus.

An inert gas like Argon is used because it is easily ionized. A quenching agent (like alcohol vapor) is added to stop the discharge after each detection.

The mean life (τ) is related to the half-life (T₁/₂) by τ ≈ 1.44 × T₁/₂. So, τ ≈ 1.44 × 200 s = 288.6 s.

Quenching absorbs excess energy and positive ions, preventing the tube from firing continuously after a single radiation event, thus resetting it for the next detection.

When a particle (like an electron) and its antiparticle (a positron) meet, they annihilate each other, converting their entire mass into energy, typically in the form of two gamma-ray photons.

Uranium-235 is the primary fissile isotope used in most commercial nuclear reactors. Natural uranium is enriched to increase the concentration of U-235.

Whether a single particle of radiation interacts with matter is a matter of probability. We can predict the behavior of large numbers of particles but not a single one.