As with all man made radioactive elements, there is not just one form of radioactive Curium, but many. This is why there are thousands of toxic radioactive elements coming out of all nuclear reactors, not just the short lived radioactive elements that are talked about on the mass media. Curium is the most toxic and most dangerous, but it is very hard to detect and measure, so it does not show up on Geiger Counters for example, much like Tritium. Other radioactive elements are released in much larger amounts and are easier to detect, such as strontium and cesium for example.
Wikipedia; "About 20 radioisotopes and 7 nuclear isomers between 233Cm and 252Cm are known for curium, and no stable isotopes. The longest half-lives have been reported for 247Cm (15.6 million years) and 248Cm (348,000 years).
Other long-lived isotopes are 245Cm (half-life 8500 years),250Cm (8,300 years) and 246Cm (4,760 years). Curium-250 is unusual in that it predominantly (about 86%) decays via spontaneous fission. The most commonly used curium isotopes are 242Cm and 244Cm with the half-lives of 162.8 days and 18.1 years, respectively.[11]