what are its type?
Three of the most common types of decay are alpha decay, beta decay, and gamma decay
Radioactive decay
 alpha, beta, and gamma, in increasing order of their ability to penetrate matter.
where can helium be found in the world Most helium on Earth is a result of radioactive decay. Helium is found in large amounts in minerals of uranium and thorium, including uraninite and its varieties cleveite and pitchblende, carnotite and monazite. what are some of its uses? The largest use is in cryogenic applications, most of which involves cooling the superconducting magnets in medical MRI scanners and NMR spectrometers. who discovered it? Astronomer Jules Janssen when was it discovered? August 18, 1868 is this element hazardous? Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood. When a person speaks after inhaling helium gas, it  causes a change in timbre of the amplified sound, resulting in a reedy, duck-like vocal quality. what exactly is the decay that you mentioned earlier? It  is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
wiki:13605803
Radioactive decay [SEP] Types of decay
Early researchers found that an electric or magnetic field could split radioactive emissions into three types of beams. The rays were given the names alpha, beta, and gamma, in increasing order of their ability to penetrate matter. Alpha decay is observed only in heavier elements of atomic number 52 (tellurium) and greater, with the exception of beryllium-8 (which decays to two alpha particles). The other two types of decay are observed in all the elements. Lead, atomic number 82, is the heaviest element to have any isotopes stable (to the limit of measurement) to radioactive decay. Radioactive decay is seen in all isotopes of all elements of atomic number 83 (bismuth) or greater.