upgrading processor mac pro 8 core 2.8GHz to mac pro 12 core processor

hello and thanks ahead of time for your help. I WOULD LIKE TO KNOW IF MY PROCESSORS COULD BE UPGRADED TO 12 CORE PROCESSORS 2.93 OR 3.06

I have a Mac Pro 8 MODEL #(MA970LL/A) Quad core Intel xeon processors 2.8GHz.

Standard Configuration

5400 Serries 800MHz DDR2 ECC FULLY BUFFERED / Dimm (FB-Dimm) THERMAL

memory 18gbRAM L2 Cache per processor 12MB

MAC PRO 3.1 MEMORY 4X4GB KIT= (MB193G/A). // 2X1SINGLE GB

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again thank you for your help