By Sunil Bhardwaj

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In 1934, Curie family found that when Al, B and Mg are bombarded with (alpha) -particles, in addition to neutrons, positrons are also emitted. It is similar to atomic transmutation reaction. They found that Recoil target in this case is unstable and acquire the stability after the emission of positron (({ eta }^{ + })) or electron (({ eta }^{ - })). Examples are given below: $$ underset { Target }{ _{ 12 }^{ 24 }{ Mg } } + underset { Projectile }{ _{ 2 }^{ 4 }{ He } } longrightarrow underset { Recoil target }{ _{ 14 }^{ 27 }Si } + underset { Ejected particles }{ _{ 0 }^{ 1 }{ n } } qquad ...(Transmutation) $$ $$ underset { Unstable }{ _{ 14 }^{ 27 }Si } longrightarrow _{ 13 }^{ 27 }Al + _{ 1 }^{ 0 }{ e }qquad ...(Induced Radioactivity) $$ Similarly, $$ underset { Target }{ _{ 13 }^{ 27 }Al } + underset { Projectile }{ _{ 2 }^{ 4 }{ He } } longrightarrow underset { Recoil target }{ _{ 15 }^{ 30 }P } + underset { Ejected particles }{ _{ 0 }^{ 1 }{ n } } qquad ...(Transmutation) $$ $$ underset { Unstable }{ _{ 15 }^{ 30 }P } longrightarrow _{ 14 }^{ 30 }Si + _{ 1 }^{ 0 }{ e }qquad ...(Induced Radioactivity) $$ In atomic transmutation reaction, when the recoil target is unstable, it becomes radio active and the phenomenon is called Induced (ar) Artificial radio activity. In this type of radio activity the emission may be ({ eta }^{ + }) (OR) ({ eta }^{ - }).

The example of ({ eta }^{ - }) is as follow: $$ underset { Target }{ _{ 13 }^{ 27 }Al } + underset { Projectile }{ _{ 0 }^{ 1 }{ n } } longrightarrow underset { Recoil target }{ _{ 11 }^{ 24 }Na } + underset { Ejected particles }{ _{ 2 }^{ 4 }{ He } } qquad ...(Transmutation) $$ $$ underset { Unstable }{ _{ 11 }^{ 24 }Na } longrightarrow _{ 12 }^{ 24 }Mg + _{ -1 }^{ 0 }{ e }qquad ...(Induced Radioactivity) $$ When the unstable recoil target has mass no. greater than the stable in that case the emission is ({ eta }^{ - } (_{ -1 }^{ 0 }{ e })) and when the mass no. of recoil target is less than corresponding stable in that case emission is ({ eta }^{ + } (_{ 1 }^{ 0 }{ e })).