This data set measures the radioactive decay of nuclear material from Northern and Southern hemisphere nuclear testing. Firn cores were taken from three locations on Roosevelt Island, an ice dome within the Ross Ice Shelf, and were measured at increasing depth for density in kilograms per cubic meter, and for beta counts per hour per kilogram. The data were collected between November and December of 1997. Measurements were taken incrementally down to approximately 17 meters for each of the three cores. Data are available in text format via ftp.