CRISTIAN SALAZARNEW YORK (AP) â¿¿ It was a decade when tens of millions of people in the U.S. experienced mass unemployment and social upheaval as the nation clawed its way out of the Great Depression and rumblings of global war were heard from abroad. Now, intimate details of 132 million people who lived through the 1930s will be disclosed as the U.S. government releases the 1940 census on April 2 to the public for the first time after 72 years of privacy protection lapses. Access to the records will be free and open to anyone on the Internet â¿¿ but they will not be immediately name searchable. For genealogists and family historians, the 1940 census release is the most important disclosure of ancestral secrets in a decade and could shake the branches of many family trees. Scholars expect the records to help draw a more pointillistic portrait of a transformative decade in American life. Researchers might be able to follow the movement of refugees from war-torn Europe in the latter half of the 1930s; sketch out in more detail where 100,000 Japanese Americans interned during World War II were living before they were removed; and more fully trace the decades-long migration of blacks from the rural South to cities. Henry Louis Gates Jr., a Harvard University professor and scholar of black history who has promoted the tracing of family ancestry through popular television shows, said the release of the records will be a "great contribution to American society." Gates, whose PBS series "Finding Your Roots" begins March 25, said the "goldmine" of 1940 records would add important layers of detail to an existing collection of opened census records dating to 1790. "It's such a rare gift," he said of the public's access to census records, "especially for people who believe that establishing their family trees is important for understanding their relationship to American democracy, the history of our country, and to a larger sense of themselves."