When trans-1, 2-bispyrazylethylene in benzene solution is subjected to $^{60}Co$ $\gamma$-ray irradiation, an efficient $\mbox{\underline{trans}}$-cis isomerization is observed along with radiochemical reduction product, 1, 2-bispyrazylethane. Extended irradiation produced more unknown products, especially from $\underline{cis}$ - isomer and the major product is suggested to be dehydrocyclization product which is supposed to occur via excited singlet state of $\underline{cis}$ - isomer like in stilbene solution.
$G_{t-c}$ values for both 1, 2-bispyrazylethylene and 2-styrylpyrazine is obtained along with $underline{cis}/\underline{trans}$ ratio at radiostationary states and the results are compared to photochemical data, the photostationary states and $\underline{trans}-\underline{cis}$ quantum yield measurements. The radiostationary state of 1,2-bispyrazylethylene showed 89% of cis isomer and the value agreed well with the cis isomerportion at the photostationary state indicating the same mechanism in radio-and photochemical $underline{cis}-\underline{trans}$ isomerization of 1, 2-bispyrazylethylene in benzene. The $\underline{cis}-\underline{trans}$ isomerization of the olefin is determined to go through excited triplet state after energy transfer from benzene to BPE.
