CHE 2C - Ch. 20: The Nucleus

Thermodynamic Stability

refers to the potential energy of a particular nucleus in comparison to the sum of protons and neutrons

Kinetic Stability

refers to the probability that a nucleus will undergo decomposition to form a different nucleus

• radioactive decay

Radioactive Nuclei

particle that decomposes and forms another nucleus and other particles

Types of RD

1. Alpha Particle Production

2. Beta Particle Production

3. Positron Production

4. Gamma Ray Production

The number of _____ are related to a nuclei’s stability

neutrons and protons

Zone of Stability

area that encompasses the stable nuclides on a plot of their positions as a function of the number of protons and neutrons in the nucleus

Nuclides with 84 or more protons are _______ with respect to radioactive decay

unstable

Light nuclides are stable when ______

• neutron/proton ratio is 1:1

• heavier elements have rations greater than 1 and increase with atomic number

Combination of the number of protons and neutrons given _____

different stabilities

____ number of protons and neutrons are more often stable than _____ numbered

Even, Odd

Magic Numbers

reminiscent of noble gas electrons

• 2, 8, 20, 28, 50, 82, 126

Types of Radioactive Decay

1. changes in the mass number of the decaying nucleus

2. those that do not

Alpha Particle

a helium nucleus

• change in mass

Spontaneous Fission

splitting of a heavier nuclide into two lighter nuclides

• occurs at extremely slow rates

Beta Particle Production

• electron particle with a negative charge

• mass remains constant but atomic number changes

  • neutron changes to a proton

Nuclides with high n/p rations lie above the zone of stability; they are _____ producers

beta particle

The electron given off during beta particle production doesn’t come from a nucleus, it comes from unstable nuclides creating one as_______

energy is released in the decay process

Gamma Rays

a high-energy photon

The emission of a gamma ray is a way the nucleus with excess energy ________

relaxes to ground state

Positron Production

a particle formed having the same mass as the electron but opposing charge

• proton changes to a neutron

Positron production occurs for nuclides _______ the zone of stability; n/p ration less than 1

below

• the product nuclide has a higher ratio than the original nuclide

The collision of a positron and a beta particle results in _________

the production of a gamma ray

Annihilation

matter-antimatter collisions that interchange of forms of matter

Electron Capture

process in which one of the inner-orbital electrons is captured by the nucleus

Decay Series

radioactive nucleus undergoes a series of decay processes to produce a stable nuclide

Rate of Decay

the change in number of radioactive nuclides in a sample per unit of time

The order of radioactive processes is ________

first order

Nuclear Transformation

the conversion of one element to another is achieved using particle acceleration

Particle Acceleration

device used to speed up nuclear particles to very high velocities that overcomes particle repulsion and penetrates the nucleus

Transuranium Elements

artificially made elements beyond uranium by particle bombardment

What is the relationship that displays how energy is a form of matter

E = mc²

When a system loses or gains energy, it also gains or loses ______

mass

Mass Defect (delta m)

change in mass occurring when a nucleus is formed from its component nucleons

Thermodynamic stability of a given nucleus is represented as _____________

energy released per nucleon

Binding Energy

smallest amount of energy required to remove a particle from a system of particles or to disassemble a system of particles into individual parts

Energy is ________ when a process goes from a less stable to a more stable state

released

2 Types of Exothermic Processes

1. Fusion

2. Fission

Fusion

combining 2 light nuclei to form a heavier, more stable nucleus

Fission

splitting a heavy nucleus to 2 nuclei with smaller mass numbers

• requires high binding energy

Nuclear Fissions

the rxns products are nuclides and neutrons

Chain Reaction

a self-sustaining fission process caused by the production of neutrons that proceed to split other nuclei

Subcritical

when less than one neutron from each fission event cause another fission event

• the process stops

Critical

when exactly neutron from each fission event causes another fission event, the process sustains itself at the same level

• require critical mass: the mass of fissionable material required to produce a self-sustaining chain rxn

Supercritical

when more than one neutron from each fission event causes another fission event, the process rapidly escalates, and the heat buildup causes a violent explosion

Critical Mass

the mass of fissionable material required to produce a self-sustaining chain reaction

• if the sample is too small, neutrons escape, and the rxn stops

Nuclear Reactor Components

1. reactor core

2. moderator

3. control rods

Breeder Reactors

developed due to the depletion of Uranium 235

• fissionable fuel is produced during rxn

What do breeder reactors require?

absorption of a neutron and the production of 2 beta particles

_____ of energy are produced by the fusion of 2 light nuclei

large quantities

How are high temps required to initiate fusion?

the charge of the nucleus due to the protons due repulsion, the particles obtain high velocities and are shot at each other

The repulsion forces between hydrogen atom nuclei need ________ to overcome binding force and particle collide

4 × 10^7 K

Effects of Radiation

en

Nuclear particles produced by radioactive nuclei have _________ bonding and ionization energies of biological molecules

energy greater than

Nuclear radiation breaks and ionizes molecules, which produce _____ that cause further damage

free radicals

Radiation Damage

1. Somatic

2. Genetic

Somatic Damage

damage to the organism itself resulting in its sickness or death

Genetic Damage

damage to genetic machinery: produces malfunctions in the offspring

Biolo

Energy of Radiation

• higher energy=more damage from free radicals

• SI unit Gray 1 J/kg

Penetrating Ability

produced particles and rays have varying abilities to penetrate

1. gamma rays highest

2. beta particles 1cm

3. alpha particles stopped at the skin

Chemical Properties

damage depends on its residence time

• chemically similar elements can collect in the body and cause damage

______ particles have high RBE

alpha

rem (roentgen equivalent for man)

= # rads x RBE

Radioactive decay is ________

1. a process whose rate is pressure and temperature independent

2. a process with a low activation energy

3. a process whose rate is not affected by a change in temperature.