alpha particles, two protons plus two neutrons (

There were composites of elementary particles—deuterons, a proton plus a neutron (the deuteron is a special part of the story told in this book because it is the nucleus of the heavy hydrogen atom, deuterium), and alpha particles, two protons plus two neutrons (the nucleus of the helium atom is an alpha particle).

a type of ionizing radiation ejected by the nuclei of some unstable atoms

Alpha particles (symbol α ) are a type of ionizing radiation ejected by the nuclei of some unstable atoms.

Positive helium nuclei

Positive helium nuclei are referred to as alpha particles.

a form of ionizing radiation

Alpha particles are a form of ionizing radiation, because they have the ability to steal electrons from their surroundings, and in doing so transforming the atoms they steal from into ions themselves.

a sub-microscopic, positively charged particle of matter

An alpha particle is a sub-microscopic, positively charged particle of matter.

helium nucleuses and neutrons

For instance, beta particles are electrons, alpha particles are helium nucleuses and neutrons are uncharged particles.

low-penetrating types of radiation

Alpha particles are low-penetrating types of radiation, and generally will not penetrate your skin and probably in all likelyhood, won’t penetrate your clothing.

low energy radioactive particles that consist of helium nuclei, with two protons and two neutrons

Alpha particles are low energy radioactive particles that consist of helium nuclei, with two protons and two neutrons.

The nucleus of a helium-4 atom

The nucleus of a helium-4 atom is known as an alpha-particle.

a helium nucleus - one of the products of a nuclear fission

The alpha particle is a helium nucleus - one of the products of a nuclear fission.

a helium atom without a helium atom's electrons

In 1907 British physicist Ernest Rutherford's research showed that the alpha particle is a helium atom without a helium atom's electrons.

a heat source in radioisotope thermoelectric generators, which are used to power some spacecraft

alpha particles is a heat source in radioisotope thermoelectric generators, which are used to power some spacecraft.

the same as the nucleus of a helium atom

An alpha particle is the nucleus of the helium atom and consists of two neutrons and two protons.

the first type of radiation one can observe in the natural world

Alpha particles are the first type of radiation one can observe in the natural world.

a type of ionizing radiation discovered by Ernest Rutherford in 1898

Alpha particles are a type of ionizing radiation discovered by Ernest Rutherford in 1898.

that is exerted from radioactive materials

An alpha particle is a type of ionizing radiation that is exerted from radioactive materials.

a helium nucleus i.e. a helium atom that has lost i.e. a helium atom's two orbital electrons

The alpha particle is a helium nucleus i.e. a helium atom that has lost i.e. a helium atom's two orbital electrons.

the most damaging type of ionizing radiation encountered in medical radiology

Alpha particles are the most damaging type of ionizing radiation encountered in medical radiology; however, medical radiology can be stopped with an ordinary sheet of paper.

a type of radiation that do not travel very far

Alpha particles are a type of radiation that do not travel very far, do not pass through anything very thick, and can generally be absorbed or stopped by an inch or less (1-2 centimeters) of air or a thin piece of tissue.