A) Ni
B) C-14
C) C-12
D) Rd
Correct Answer: B
Solution :
Radioactive carbon dating method is used for determining the ages of the archeological objects (wood, dead plants and animals). Due to the bombardment of cosmic rays \[{{\text{N}}_{\text{2}}}\]present in upper atmosphere gets converted into radioactive \[{{\text{C}}^{14}}\]isotope. \[_{7}{{N}^{14}}{{+}_{0}}{{n}^{1}}{{\xrightarrow{{}}}_{6}}{{C}^{14}}{{+}_{1}}{{H}^{1}}\] It forms \[^{\text{14}}\text{C}{{\text{O}}_{\text{2}}}\] which is assimilated by plants. Living plarfts and animals have definite proportion of \[{{\text{C}}^{12}}\]and \[{{\text{C}}^{14}}\]when plant dies, no fresh \[{{\text{C}}^{14}}\]are received by it. The \[{{\text{C}}^{14}}\]present decays according to following reaction. \[_{6}{{C}^{14}}{{\xrightarrow{{}}}_{7}}{{N}^{14}}{{+}_{-1}}{{e}^{o}},{{t}_{1/2}}=5770\,\]years By knowing \[{{C}^{14}}\]content {i.e., by counting number of \[\beta \]particles emitted per minute by 1 g of sample) and its \[{{t}_{1/2}},\]age of sample can be determined. \[t=\frac{2.303}{\lambda }=\log \frac{{{N}_{0}}}{{{N}_{t}}}\] \[{{N}_{0}}=\]counrs per minute of living wood \[{{N}_{t}}=\]counts per minute of dead wood
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