Question

How to convert Cu to Au(Gold) by nucleus bombardment

Answer 1

Atomic numbers Z of various metals are:
        Copper Cu= 29       Silver Ag = 47      Tin Sn = 50        Gold  Au = 79
        Mercury Hg = 80     Lead Pb = 82       Bismuth  Bi = 83

   Transmutation of metals into Gold was experimented by many.  It seems Lead, Mercury and Bismuth have been converted into Gold by bombarding the nucleus or radio active decay principles..  They are expensive and not economical perhaps.   Perhaps by fusing Copper and Tin into one nucleus could make  Gold nucleus..  The conditions and process may be difficult.

    Copper has atomic number 29.  To turn it into Gold the nuclear fusion has to take place.  Perhaps copper nucleus will grow by bombarding of alpha particles.  However, it will not be stable.

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       Copper cannot be turned into Gold metal by chemical reactions. So far conversion of one metal into  Gold  is not achieved in the laboratory, in spite of many efforts.   This is a chemistry trick that shows (silvery shine) gold color coating on copper.   It is actually brass layer that is formed on copper material.  It is not permanent either.

       Prepare the copper pieces or coins by cleaning them with salt water and vinegar to remove dirt on them.

      Take Zinc Chloride  (of 1 Molar) solution.  Then boil it with Zinc metal pieces.   Now add the copper coins or pieces.  Wait for 15 minutes.  Now remove the coins or pieces out.   Wash them cleanly.    Due to the layer of Zinc on the coins, we find the surface of the coin shines with silver color (but may not be so white).   Zinc gives its electrons to Copper and deposits on the surface.

      Now  take the coins and put them on a hot plate or directly on flame (perhaps 250 to 300 deg).  Need to be careful with the heat.   After a while they will turn to gold color due to diffusion of Zinc atoms into copper material.  The brass alloy is formed.   However, this color does not stay permanently.
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There are perhaps other methods like using Sodium Zincate also.  This is a chemistry experiment.

NOTE: It seems Transmutation of metals into Gold is Illegal..