Henri Becquerel found that uranium salts caused fogging of an unexposed photographic plate through a covering paper in a manner similar to X-rays .
Marie Curie discovered that only certain elements gave off these rays of energy , soon discovering the intense radiation of radium .
Henri Becquerel found that uranium salts caused fogging of an unexposed photographic plate through a covering paper in a manner similar to X-rays , and Marie Curie discovered that only certain elements gave off these rays of energy , soon discovering the intense radiation of radium .