Theory of Radioactivity

Question 1

What is the rest mass of a proton?

Answer 1

1.00727 u

Question 2

What is the rest mass of a neutron?

Answer 2

1.00866 u

Question 3

Graph the stability of a nucleus.

Answer 3

Question 4

Graph the Binding Energy per Nucleon (MeV) vs. the Mass Number (A).

Answer 4

Question 5

State the general equation for alpha (α) decay and give one example (Ra-226).

Answer 5

Most alpha emitters have between 4 - 6 MeV of energy.

Question 6

State the general equation for beta (β^-) decay and give one example (H-3).

Answer 6

Question 7

State the general equation for beta (β⁺) decay and give one example (Na-22).

Answer 7

Question 8

Compare the energy spectra for both alpha and beta decays.

Answer 8

• Alpha decays are monoenergetic and produce one energy of alpha particle.
• Beta decay produces a spectrum of beta energies up to a maximum energy (E_max) with the average energy (E_avg) equal to 1/3 of the E_max.

Question 9

State the general equation for gamma-ray (γ) emission (decay) and give one example (Ba-137*).

Answer 9

Question 10

Most radioactive nuclides with Z < 82 decay by either __________ or ___________ decay.

Answer 10

Most radioactive nuclides with Z < 82 decay by either Beta or Positron decay.

Question 11

What are the three types of fission decay?

Answer 11

1. Thermal neutron absorption
2. Fast fission
3. Spontaneous fission

Question 12

What happens during fast fission?

Answer 12

A nuclide captures a high energy or fast neutron. The resultant nuclide is unstable and decays by separating into two pieces called fission fragments.

Question 13

Nuclides able to undergo fast fission by capturing a high energy or fast neutron are referred to as _______________.

Answer 13

Nuclides able to undergo fast fission by capturing a high energy or fast neutron are referred to as fissionable.

Question 14

What happens during spontaneous fission?

What is a common nuclide capable of undergoing spontaneous fission?

Answer 14

A nuclide is able to decay by fissioning without capturing a neutron.

Californium-252 (Cf-252), with a half-life of 2.6 years, is commonly used in calibrating neutron survey meters and personnel radiation dosimeters, as well as treating solid tumors.

Question 15

State the general equation for electron (e^-) capture and give one example (Cr-51).

Answer 15

Occurs in neutron deficient nuclei.

Nuclides deficient in neutrons like to convert one of their protons into a neutron (by capturing a K-shell electron) to become “less deficient.”

Question 16

State the general equation for internal conversion and give one example (Hg-198*).

Answer 16

Instead of the excited nucleus using its extra energy to produce and release a gamma-ray, it transfers the decay energy to an orbtial electron (usually a K-shell electron).

Since this electron is bound to the nucleus by the Coulomb force, it “uses up” an amount of energy called the electron binding energy to escape the atom.

Question 17

Define the situation that creates Transient Equilibrium (case 2).

Answer 17

The parent has a slightly larger half-life than the daughter (usually the same order of magnitude).

λ_D > λ_P

Question 18

Define

Isotope

Answer 18

Atoms with the same number of protons.

Question 19

Define

Isotone

Answer 19

Atoms with the same number of neutrons.

Question 20

Graph

Activity vs. Time for secular equilibrium (case 1).

Answer 20

Question 21

Graph

Activity vs. Time for transient equilibrium (case 2).

Answer 21

Question 22

Why do heavy nuclei have an N-value approximately 1.5 times the Z-value?

Answer 22

• Protons all carry a positive charge and will strongly repel each other according to Coulomb’s Law (when forced together in the nucleus).
• This highly disruptive force is overcome in stable nuclei by the presence of a force even strong than the Coulomb Force called the Nuclear Force.
• By adding relatively more neutrons than protons, additional “glue” is added to heavy nuclei without causing more instability by adding more positive charge.

Question 23

List

Fundamental forces of nature

Answer 23

• Gravitational ⇒ Long range
• Electromagnetic ⇒ Long range
• Strong nuclear ⇒ Short range
• Weak nuclear ⇒ Short range