Gamma rays (also called gamma radiation), denoted by the lower-case Greek letter gamma (γ or formula_1 ), are penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei. It consists of photons in the highest observed range of photon energy. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900 while studying radiation emitted by radium. In 1903, Ernest Rutherford named this radiation "gamma rays". Rutherford had previously discovered two other types of radioactive decay, which he named alpha and beta rays. 

Gamma rays are able to ionize atoms (ionizing radiation), and are thus biologically hazardous. The decay of an atomic nucleus from a high energy state to a lower energy state, a process called "gamma decay", produces gamma radiation. 

Natural sources of gamma rays on Earth are observed in the gamma decay of radionuclides and secondary radiation from atmospheric interactions with cosmic ray particles. There are rare terrestrial natural sources, such as lightning strikes and terrestrial gamma-ray flashes, that produce gamma rays not of a nuclear origin. Additionally, gamma rays are produced by a number of astronomical processes in which very high-energy electrons are produced, that in turn cause secondary gamma rays via bremsstrahlung, inverse Compton scattering, and synchrotron radiation. However, a large fraction of such astronomical gamma rays are screened by Earth's atmosphere and can only be detected by spacecraft. Gamma rays are produced by nuclear fusion in stars including the Sun (such as the CNO cycle), but are absorbed or inelastically scattered by the stellar material, reducing their energy, before escaping and are not observable from Earth as gamma rays.
What is our main topic?
A.k.a?
What can they do to atoms?
A.k.a.?
Are they safe?
Name on place where can natural spots of gamma decay be found?
Name another.
What is those rays' origin?
What are Gamma rays?
Where is there a radioactive decay?
When did they get their name?
Who named them?
What else did he discover?
Gamma rays
Gamma rays (also called gamma radiation)
gamma radiation
also called gamma radiation
ionize them
Gamma rays are able to ionize atoms
ionizing radiation
ionize atoms (ionizing radiation)
no
and are thus biologically hazardous
lightning strikes
 There are rare terrestrial natural sources, such as lightning strikes and terrestrial gamma-ray flashes, that produce gamma rays not of a nuclear origin
terrestrial gamma-ray flashes
 lightning strikes and terrestrial gamma-ray flashes
natural, not nuclear
 that produce gamma rays not of a nuclear origin
penetrating electromagnetic radiation
are penetrating electromagnetic radiation
atomic nuclei
from the radioactive decay of atomic nuclei
In 1903
In 1903, Ernest Rutherford named this radiation "gamma rays". 
Ernest Rutherford
In 1903, Ernest Rutherford named
alpha and beta rays
Rutherford had previously discovered two other types of radioactive decay, which he named alpha and beta rays.