Why is uranium radioactive?

Answer 1

Positives repel each other. In an atom, the nucleas is full repelling protons with their positive charge. It is the nuclear force that holds them together in the nucleus. A Helium atom has only 2 protons which makes it more stable.

Uranium on the other hand, has 92 protons all squashed together. This makes it very unstable which allows it to undergo gamma radiation.

That is why Uranium is radioactive.
Unstable atoms as uranium are radioactive; the stability depends on the ratio between protons and neutrons.

Answer 2

Not all of the transition elements are radioactive. Many of them are, and some of them have common radioactive isotopes, but some of them have no naturally occurring radioactive isotopes. Please note that all elements have synthetic radioactive isotopes, at least.

Answer 3

Uranium itself is not very radioactive, as produced from newly mined ore it can be safely handled without radiation shielding. It is the fission products produced during operation in the reactor that make the spent fuel absolutely lethal and require the utmost care in shielding any human operators

Answer 4

The reason artificial elements are radioactive is primarily because they are artificial. All elements are naturally created by fusion in stars. However artificial elements are called thus because they do not remain in their elemental state for long. They are fundamentally unstable, and thus do not naturally occur on earth; thus they are artificial. Their instability is resolved through radioactive radiation when they degrade.

So all artificial elements are radioactive precisely because it is their instability that makes them artificial.

The difference between these elements and naturally occurring radioactive elements is that the half-life of naturally occurring radioactive elements is long enough that some of the elements still remain and can be found on earth, having not yet degraded.

Artificial elements are heavy; this causes a neutron/proton ratio which leads to instability.

Answer 5

Isotopes of the transuranium elements are radioactive because their large nuclei are unstable, and the transactinide, or superheavy, elements in particular have very short half-lives.

Answer 6

These elements are unstable because the ratio neutrons/protons is too high.