Chapter 21 - Nuclear Chemistry

Radioactivity:

the spontaneous emission of particles or electromagnetic radiation

All elements with Z __ are radioactive

> 83

What is Z?

atomic number — the number of protons in the nucleus of an atom

In nuclear reactions, elements are:

converted to other elements or isotopes

In nuclear reactions, what subatomic particles are involved?

protons, neutrons, and α particles

What are α particles?

a type of radiation emitted during alpha decay, a process by which unstable atoms release excess energy

In nuclear reactions, reactions are accompanied by:

the absorption or release of tremendous amounts of energyr

In nuclear reactions, rates of reaction are:

normally not affected by temperature, pressure, or catalysts

What is a positron?

a type of subatomic particle that is the antiparticle of an electron

What does antiparticle mean?

a particle that has the same mass as a corresponding particle but has opposite charge and other quantum properties

How do you balance a nuclear reaction?

simply balance the total of all atomic numbers and total of all mass numbers for the products and reactants

Principle factor for nuclear stability is:

neutron - to - proton ratio (n/p)

There are more stable nuclei with 2:

8, 20, 50, 82, or 126 protons or neutrons (Magic Numbers)

All with atomic number > 83 are:

radioactive

All isotopes of _ and _ are radioactive

Tc and Pm

The conversion of one nuclide into another is called:

nuclear transmutation

What are the 5 types of radioactivity?

• alpha decay

• beta decay

• gamma decay

• positron emission (β + decay)

• electron capture

Alpha particles can be stopped by:

a piece of paper

Alpha decay:

occurs when an unstable nucleus emits a particle composed of two protons and two neutrons (called an α particle)

• nucleus loses protons and neutrons

Beta decay/emission:

occurs when an unstable nucleus emits an electron (called an β particle )

• nucleus loses neutron and electron, gains proton

Beta particles are stopped by:

few millimeters of Al

Gamma radiation:

• significantly different from alpha/beta decays, gamma ray emission is the emission of gamma radiation, a form of electromagnetic radiation

• excited nuclei lose this extra energy in the form of light

• high energy nuclei lower their energy by emitting gamma rays

Gamma rays easily pass through:

1cm of Pb

Positron emission ( β + decay):

the emission of a positron from the nucleus

• nucleus loses proton; gains neutron and emits positron

Electron capture:

• occurs when an inner electron in an atom is captured by the atom’s nucleus

• generally occurs when the inner electron combines with a proton to make a neutron

• nucleus loses a proton and electron, gains a neutron

What type is this?

alpha decay

What type is this?

beta decay/emission

What type is this?

Gamma ray emission

What type is this?

Positron emission

What type is this?

Electron capture

EC processes produce:

x-rays

In a nuclear stability graph, stable nuclei are in an area of the graph known as:

belt of stability

In a nuclear stability graph, the most radioactive nuclei lie:

outside the belt

In a nuclear stability graph, above the belt the nuclei have:

higher neutron - to - proton ratio

In a nuclear stability graph, below the belt:

isotopes mostly decay by beta emission

In a nuclear stability graph, above the belt isotopes mostly decay by:

positron emission or electron capture

Nuclear Binding Energy:

A quantitative measure of nuclear stability — the energy required to break up a nucleus into its component protons and neutrons

Proton mass =

1.0073 amu

Electron mass =

5.4858x10^-4 amu

Neutron mass =

1.0087 amu

The difference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons is called the:

mass defect

The disintegration of a radioactive nucleus often is the beginning of a:

radioactive decay series

Radioactive decay series:

a sequence of nuclear reactions that ultimately result in the formation of a stable isotope

The beginning radioactive isotope is called the:

parent

The product isotope is called the:

daughter

All radioactive decays obey:

first - order kinetics

What is k in radioactive decay?

decay constant

High k =

faster decay

Low k =

slower decay

Common dating methods:

• Radiocarbon

• Uranium – lead

• Rubidium – strontium

• Potassium – argon

Nuclear transmutation differs from radioactive decay in that transmutation is brought about by:

the collision of two particles

What make is possible to synthesize the so called transuranium elements?

particle accelerators

What are transuranium elements?

elements with atomic numbers greater than 92

Nuclear fission:

the process in which a heavy nucleus (mass number > 200) divides to form smaller nuclei and one or more neutrons

Critical Mass =

The minimum mass of fissionable material required to generate a self - sustaining nuclear chain reaction

Nuclear fusion =

the process of combining small nuclei into larger ones

Because fusion reactions take place at very high temperatures, they are often called

thermonuclear reactions

In medicine, radioactive isotopes are used as:

tracers

Sodium - 24 –

blood flow

Iodine - 131 —

thyroid conditions

Iodine - 123 —

brain imaging

Fluorine - 18 as [ 18 F]fluorodeoxyglucose –

PET scans

What is Internal therapy/Brachytherapy:

“radioactive seeds” Implant Ti capsules containing iodine - 125 can be implanted next to a tumor to kill the cancer cells

The fundamental unit of radioactivity is the:

curie (Ci)

1 Cu =

3.70 x 10^10 disintegrations per second

A common unit for the absorbed dose of radiation is the:

rad ( radiation absorbed dose)

1 rad =

1 x 10^-5 J/g of tissue irradiated

The rem ( roentgen equivalent for man) is:

determined from the number of rads

Number of rems =

number of rads x 1 RBE

• RBE = the relative biological effectivness