MCAT Chemical and Physical Foundations of Biological Systems Flashcards: 4e Nuclear Decay Radioactivity

What this deck covers

This deck focuses on 4e Nuclear Decay Radioactivity, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Chemical and Physical Foundations of Biological Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What is the relationship between half-life $t_{1/2}$ and decay constant $\lambda$?

Answer: $t_{1/2}=\frac{\ln 2}{\lambda}$. Half-life inversely relates to the decay constant, where $ln 2$ arises from solving for half remaining nuclei.

Flashcard 2: What particle is emitted in  a decay, written in nuclide notation?

Answer: $^{4}_{2}\text{He}$ (alpha particle). Alpha particles are helium nuclei with 2 protons and 2 neutrons, ejected from heavy unstable nuclei.

Flashcard 3: Identify the daughter nuclide after  beta^- decay: $^{14}_{6}\text{C} \to \ ?$

Answer: $^{14}_{7}\text{N}$. Beta-minus decay of carbon-14 yields nitrogen-14 by converting a neutron to a proton.

Flashcard 4: What particles are emitted in  beta^+ decay in a standard nuclear equation?

Answer: $e^+ + \nu_e$. Beta-plus decay emits a positron and neutrino to balance the conversion of a proton to a neutron.

Flashcard 5: What is the definition of radioactive (nuclear) decay in terms of nucleus stability and emissions?

Answer: Spontaneous transformation of an unstable nucleus with particle and/or  gamma emission. Radioactive decay stabilizes an unstable nucleus by spontaneously emitting alpha, beta, or gamma radiation to release excess energy.

Flashcard 6: Which radiation type has the highest ionizing power:  a,  beta, or  gamma?

Answer: $\alpha$ (highest ionizing power). Alpha particles, with high charge and mass, deposit energy densely, causing greatest ionization per path length.

Flashcard 7: What shielding is typically sufficient to stop most  a radiation?

Answer: A sheet of paper or outer dead skin layer. Alpha particles lose energy rapidly in matter due to strong interactions, stopped by minimal barriers.

Flashcard 8: What is the emitted particle in electron capture, and what lepton is typically produced?

Answer: An inner $e^-$ is captured; typically emits $\nu_e$. Electron capture involves absorbing an inner electron to convert a proton to a neutron, typically producing a neutrino.

Flashcard 9: What is the activity formula $A(t)$ in terms of $\lambda$ and $N(t)$?

Answer: $A(t)=\lambda N(t)$. Activity equals the product of decay constant and remaining nuclei, representing the decay rate.

Flashcard 10: What shielding is typically sufficient to stop most  beta radiation?

Answer: Thin metal or plastic (e.g., aluminum). Beta particles, being lighter electrons, require denser materials to absorb their kinetic energy.

Flashcard 11: What changes in $A$ and $Z$ occur in  beta^- decay of $^{A}_{Z}X$?

Answer: $A$ unchanged; $Z \to Z+1$. Beta-minus decay converts a neutron to a proton, increasing atomic number by 1 without changing mass.

Flashcard 12: What changes in $A$ and $Z$ occur in  beta^+ (positron) emission of $^{A}_{Z}X$?

Answer: $A$ unchanged; $Z \to Z-1$. Positron emission converts a proton to a neutron, decreasing atomic number by 1 while mass remains constant.

Flashcard 13: What changes in $A$ and $Z$ occur in  gamma emission from an excited nucleus?

Answer: No change: $A$ and $Z$ unchanged. Gamma emission releases excess energy from an excited nucleus without altering proton or neutron count.

Flashcard 14: What particles are emitted in  beta^- decay in a standard nuclear equation?

Answer: $e^- + \bar{\nu}_e$. Beta-minus decay emits an electron and antineutrino to conserve charge, energy, and lepton number.

Flashcard 15: What shielding is typically required to significantly attenuate  gamma radiation?

Answer: Thick lead or concrete. Gamma rays demand high-density shielding to increase interaction probability and attenuate intensity.

Flashcard 16: What is the exponential decay law for remaining nuclei $N(t)$ using decay constant $\lambda$?

Answer: $N(t)=N_0 e^{-\lambda t}$. The exponential law describes the statistical decrease in undecayed nuclei over time due to constant decay probability.

Flashcard 17: What is the activity as a function of time if initial activity is $A_0$?

Answer: $A(t)=A_0 e^{-\lambda t}$. Activity follows exponential decay as it is proportional to the number of undecayed nuclei.

Flashcard 18: Identify the daughter nuclide after  a decay: $^{238}_{92}\text{U} \to \ ?$

Answer: $^{234}_{90}\text{Th}$. Alpha decay of uranium-238 produces thorium-234 by ejecting a helium-4 nucleus.

Flashcard 19: What is the relationship between mass number $A$, protons $Z$, and neutrons $N$?

Answer: $A = Z + N$. The mass number $A$ equals the sum of protons $Z$ and neutrons $N$ in the nucleus.

Flashcard 20: What changes in $A$ and $Z$ occur in  a decay of $^{A}_{Z}X$?

Answer: $A \to A-4$ and $Z \to Z-2$. Alpha decay ejects a helium nucleus, reducing mass by 4 and protons by 2.

Flashcard 21: Which radiation type has the highest penetration through matter:  a,  beta, or  gamma?

Answer: $\gamma$ (highest penetration). Gamma rays, being high-energy photons, interact least with matter, allowing deepest penetration.

Flashcard 22: What is the unit of activity in SI, and what does it measure physically?

Answer: Becquerel (Bq) = $1$ decay per second. The becquerel quantifies radioactive decay rate in disintegrations per second for precise measurement.

Flashcard 23: What do the symbols $A$ and $Z$ represent in nuclide notation $^{A}_{Z}X$?

Answer: $A$ = mass number; $Z$ = atomic number (protons). In nuclide notation, $A$ represents the total nucleons while $Z$ indicates the number of protons defining the element.

Flashcard 24: What changes in $A$ and $Z$ occur in electron capture by a nucleus $^{A}_{Z}X$?

Answer: $A$ unchanged; $Z \to Z-1$. Electron capture transforms a proton into a neutron by absorbing an orbital electron, reducing atomic number by 1 with unchanged mass.

Flashcard 25: What is the half-life definition in terms of number of undecayed nuclei?

Answer: Time for $N$ to decrease to  frac{1}{2}N_0. Half-life measures the time required for half the radioactive nuclei to decay, reflecting probabilistic decay.