yukiさん
ご質問どうもありがとうございます。
下記の言い方ではいかがでしょうか。
34 years have passed since the bombing of Hiroshima on August 6th and while a memorial service was recently held, the number of surviving witnesses who had experienced the bombing first-hand and could give us their personal account of what happened is getting less and less every year. Thus, the "real memory" fades away by the second.
ご参考にしていただければ幸いです。