Half-Life Quiz: Master Radioactive Decay Concepts

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Questions and Answers

What causes beta rays to bend toward the positive plate?

Their positive charge

Their negative charge (correct)

Their neutral charge

Their lack of charge

Which type of radiation has about 1000 times the penetrating power of alpha rays?

Electrons

Gamma rays (correct)

Protons

Neutrons

What is the stopping material needed for beta rays?

Aluminum sheet

Lead block

Wood or heavy clothing (correct)

A few sheets of paper or top skin layer

What unit is used to express masses conveniently?

Unified mass units (u) Signup and view all the answers

What keeps nuclei stable despite the large repulsive electrostatic forces between protons?

Strong nuclear force Signup and view all the answers

How does Rutherford's formula contribute to determining the size of the nucleus?

Setting an upper limit based on Coulomb force and particle KE Signup and view all the answers

What is the charge of a neutron?

No charge Signup and view all the answers

Which of the following is a property of gamma radiation?

It has the highest frequency of all types of electromagnetic radiation Signup and view all the answers

Which of the following describes the decay rate of a radioactive substance?

The decay constant Signup and view all the answers

Which type of nuclear reaction involves the capture of an electron by the nucleus?

Electron capture Signup and view all the answers

What is the relationship between the decay constant and the half-life of a radioactive substance?

The decay constant is inversely proportional to the half-life Signup and view all the answers

What is the primary difference between alpha and gamma radiation?

Alpha radiation is made up of helium nuclei, while gamma radiation is a form of electromagnetic radiation Signup and view all the answers

What is the definition of the decay constant, ?

The rate at which the material will decay Signup and view all the answers

Which of the following is the correct formula for the decay rate or activity, R, of a radioactive sample?

R = N Signup and view all the answers

What is the unit of activity, R, in the Curie (Ci) system?

1 Ci = 3.7 10^10 decays/second Signup and view all the answers

What is the purpose of the Q-value in a nuclear reaction?

To represent the energy released or required in the nuclear reaction Signup and view all the answers

What is the threshold energy, KEmin, required for a nuclear reaction to occur?

$\frac{m}{M+m}Q$ Signup and view all the answers

What is the relationship between the mass numbers (A) and atomic numbers (Z) in an alpha decay process?

A decreases by 4 and Z decreases by 2 Signup and view all the answers

What is the main difference between beta decay and gamma decay?

Beta decay results in the conversion of a neutron to a proton, while gamma decay involves the transition of a nucleus from an excited state to a lower energy state. Signup and view all the answers

What is the purpose of the neutrino in the beta decay process?

To conserve energy and momentum in the decay process Signup and view all the answers

Which of the following is the correct equation for a beta decay process?

$A_Z X \to A_{Z+1} Y + e^-$ Signup and view all the answers

What is the relationship between the decay constant, , and the half-life, T1/2, of a radioactive material?

$\lambda = \frac{\ln 2}{T_{1/2}}$ Signup and view all the answers

Study Notes

Radioactive Decay

The number of particles that decay in a given time is proportional to the total number of particles in a radioactive sample: ΔN = -λNΔt
λ is called the decay constant and determines the rate at which the material will decay
Decay rate or activity, R, is defined as the number of decays per second: R = ΔN / Δt = λN

Decay Curve

The decay curve follows the equation: N = No e^(-λt)
Half-life is defined as the time it takes for half of any given number of radioactive nuclei to decay: T1/2 = ln2 / λ ≈ 0.693 / λ

Units of Activity

The unit of activity, R, is the Curie (Ci): 1 Ci = 3.7 x 10^10 decays/second
The SI unit of activity is the Becquerel (Bq): 1 Bq = 1 decay/second
1 Ci = 3.7 x 10^10 Bq
The most commonly used units of activity are the mCi and the µCi

Nuclear Reactions

Structure of nuclei can be changed by bombarding them with energetic particles
The atomic numbers and mass numbers must balance on both sides of the equation
Example: Alpha particle colliding with nitrogen: 4He + 14N → X + 1H

Decay Series

A decay series starts with a radioactive nucleus and ends with a stable isotope
Example: 232Th → ... → 208Pb

Alpha Decay

When a nucleus emits an alpha particle, it loses 2 protons and 2 neutrons: A - 4, Z - 2
A parent nucleus (X) becomes a daughter nucleus (Y) and an alpha particle (4He)
Example: 226Ra → 222Rn + 4He

Beta Decay

Beta decay occurs when a neutron in the nucleus is transformed into a proton and an electron
The emission of the electron is from the nucleus
Energy must be conserved
Example: A Z X → A Z+1 Y + e- + ν (electron and antineutrino emitted)

Gamma Decay

Gamma rays are given off when an excited nucleus "falls" to a lower energy state
Similar to the process of electron "jumps" to lower energy states and giving off photons
Example: 12B → 12C* → 12C + γ

Mass

A convenient unit of mass is the unified mass unit (u): 1 u = 1.660 559 x 10^-27 kg
Mass can also be expressed in MeV/c^2: 1 u = 931.494 MeV/c^2

Size of the Nucleus

First investigated by Rutherford in scattering experiments
The size of the nucleus is typically measured in femtometers (fm): 1 fm = 10^-15 m
The average radius of a nucleus is r = ro A^(1/3), where ro = 1.2 x 10^-15 m

Nuclear Stability

The nuclear attractive force is stronger than the Coulomb repulsive force at short ranges within the nucleus
Nuclei are stable due to the presence of the nuclear force, which acts between all nuclear particles

Stable and Unstable Isotopes

Every element in the periodic table has at least one radioactive isotope
Over 3300 radioisotopes are known
Stable isotopes do not decay, while unstable isotopes do

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Test your knowledge about radioactive decay, decay constant, decay rate, and half-life with this quiz. Learn about the equations and concepts related to the decay of radioactive materials.

Radioactive Decay and Half-Life Quiz

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