Half-life

The amount of time it takes for half of the atoms in radioactive material to decay.

Common Radioactive Isotopes Produced During Nuclear Reactions
Isotope	Half-life	Isotope	Half-life	Isotope	Half-life

Relatively Short Half-Lives
Strontium-89	54 days	Zirconium-95	65 days	Niobium-95	39 days
Ruthenium-103	40 days	Rhodium-103	57 min.	Rhodium-106	30 seconds
Iodine-131	8 days	Xenon-133	8 days	Tellurium-134	42 minutes
Barium-140	13 days	Lanthanum-140	40 hours	Cerium-141	32 days

Year to Century-Scale Half-Lives
Hydrogen-3	12 years	Krypton-85	10 years	Strontium-90	29 years
Ruthenium-106	1 year	Cesium-137	30 years	Cerium-144	1.3 years
Promethium-147	2.3 years	Plutonium-238	85.3 years	Americium-241	440 years
Curium-224	17.4 years

Longer Half-Lives
Technecium-99	2 x 10⁶ y	Iodine-129	1.7 x 10⁷ y	Plutonium-239	24,000 y
Plutonium-240	6,500 y	Americium-243	7,300 y

Table can be found at Common Radioactive Isotopes Produced During Nuclear Reactions.

Haploid

A single set of chromosomes (half of the full compliment of a genome) which is found in the sex cells of sexually reproducing organisms.

Hemocyte

Blood cells.

Herbaceous

Term referring to any plant that does not have a woody stem.

Hermaphrodite

Having both male and female reproductive organs.

Heterosporous

A plant that produces both male and female spores, but does so separately.

Heterotroph

Literally means "other feeder." A term used to describe any organism that does not produce its own nutrients.

Hindgut

The portion of a vertebrate digestive tract that contains the colon and the rectum.

Homologous

Any anatomical structure or behavior that is shared by separate species because of common ancestry. Although an anatomical structure may be shared, it can have a different function. An example would be pentadactyly in terrestrial animals.

Hormone

A biochemical substance formed by one or more cells that can stimulate or inhibit other cells.

Host species

In a parasitic relationship, the species that is being parasitized.

Hybrid

The offspring between two separate species or subspecies.

Hydrocarbon

A molecule that contains only hydrogen and carbon.

Hydrolysis

A chemical reaction where water is used to break down a compound.

Hydroxyl group

A molecule comprised of one hydrogen atom to one oxygen atom, and has a free bond that can attach to another molecule. In chemical symbols, a hydroxyl group looks like ~OH. An organic compound that has a collection of hydroxyl groups is called alcohol.

Hymenium

In fungi, regularly arranged spore-producing bodies.

Hypha

The filament-like structures in multicellular fungi that form the mycelium. These structures promote nutrient distribution. Plural hyphae.

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