i dont know if you mean lead instead of lean .
anyway i think gamma rays will penetrate further
this is because gamma rays are very penetrating , they have a shorter wave lenght than X-rays because the energy which produced them is greater .
Although both are similar but X-rays will become weaker and less penetrating when passing through a block of lead unlike the gamma rays eventhough it might reduse their intensity > but both will never stop ! .
This is a hard question!! 'cause both are similar but as i said i think gamma rays will penetrate further