Well I've only learned about it this morning from Google, but here is one quote:

Threnody to the Victims of Hiroshima for 52 strings was composed at the turn of 1959 and it won the 3rd prize at the G. Fitelberg Composers' Competition in Katowice in 1960 . . . . The piece, which immediately aroused a tremendous interest around the world, and which won the composer a widespread popularity, was originally called 8'37" and at times also 8'26" ; the time of the performance on the stage was thus elevated to the rank of title. The piece represented an attempt to apply the sonoristic technique and rigors of specific counterpoint to an ensemble of strings treated unconventionally as to the manner in which the tone was obtained. "While reading the score" - Zielinski wrote in 1961 - "one may admire Penderecki's inventiveness and coloristic ingeniousness. Yet one cannot rightly evaluate the Threnody until it has been listened to, for only then does one face the amazing fact: all these effects have turned out to serve as a pretext to conceive a profound and dramatic work of art!" The expression of this music was received by the audience in terms of solemnity and luridness, thus making its later classification as "threnody" fully justified. On the 12th of October, 1964, Penderecki wrote: "Let the Threnody express my firm belief that the sacrifice of Hiroshima will never be forgotten and lost."