Whenever a nuclear transmutation happens, do we get a new element or do we have the same element with chemical properties of a different element? Isn't it very much against the intuition?
By definition, a nuclear transmutation involves transformation of one element into another. This means the element has undergone some sort of change in the nucleus (either by nuclear reaction or nuclear decay), hence a change in atomic weight and/or number.
Whether or not this goes against intuition depends upon what experiences one's intuition is based on.