What is Alpha particle?
{{no sources|date=April 2021}} [[File:Alpha Decay.svg|right|200px|thumb|A diagram of alpha decay]] An '''alpha particle''' is a [[radioactive]] particle that is made up of two [[protons]] and two [[neutrons]]. It is a [[helium]] [[Atomic nucleus|nucleus]]: that is a helium atom without [[electron]]s. Radioactive elements give out alpha particles when they go through a kind of [[radioactive decay]], known as [[radioactive decay#Alpha decay|alpha decay]]. During alpha decay, the [[atomic nucleus]] releases an alpha particle. The nucleus will lose two protons and two neutrons when this happens. After the decay, the atom will change to another element, because the atom loses two protons. For example, when [[americium]] goes through alpha decay it changes into [[neptunium]] because neptunium is defined to have two protons less than [[americium]]. Alpha decay usually happens in heavy elements, those containing more neutrons and protons, such as [[uranium]], [[thorium]], [[plutonium]], and [[radium]]. Alpha particles cannot even go through a few centimetres of air. Alpha [[radiation]] cannot hurt humans when the alpha source is outside the [[human body]], because human skin does not let the alpha particles go through, it cannot ''penetrate'' it. Alpha [[radiation]] can be very harmful if the source is inside the body, such as when people breathe dust or [[gas]] containing materials which decay by emitting alpha particles. To look at americium again, the [[isotope]] [[americium]]-241 gives off alpha radiation. This radiation can be very harmful if it is inside someone's body because it can change the [[DNA]] in the [[cells]]. But it is not harmful when it is outside of the body because alpha radiation does not travel through the outside layers of the skin very well. When scientists write equations about [[nuclear reaction]]s they use the Greek letter [[Alpha (letter)|Alpha]]. [[Ernest Rutherford]] started this when he discovered and named three kinds of [[Ionization|ionizing]] radiation. {{physics-stub}} [[C