With a mass of just under 4 GeV (giga electron volts), for 10 points—name these nuclear particles composed of two protons and two neutrons, equivalent in composition to the helium nucleus.
Their "skin depth", or range of penetration, is only as large as four inches in air and they can be stopped with a sheet of paper, making them relatively harmless unless somehow ingested or inhaled. With a mass of just under 4 GeV (giga electron volts), for 10 points—name these nuclear particles composed of two protons and two neutrons, equivalent in composition to the helium nucleus.
Their "skin depth", or range of penetration, is only as large as four inches in air and they can be stopped with a sheet of paper, making them relatively harmless unless somehow ingested or inhaled.
{alpha} particle [accept {helium nucleus} before it is read]