All roentgenium isotopes are extremely unstable and radioactive; in general, the heavier isotopes are more stable than the lighter. The most stable known roentgenium isotope, 282Rg, is also the heaviest known roentgenium isotope; it has a half-life of 2.1 minutes. (The unconfirmed 286Rg is even heavier and appears to have an even longer half-life of about 10.7 minutes, which would make it one of the longest-lived superheavy nuclides known; likewise, the unconfirmed 283Rg appears to have a long half-life of about 5.1 minutes.) The isotopes 280Rg and 281Rg have also been reported to have half-lives over a second. The remaining isotopes have half-lives in the millisecond range. The undiscovered isotope 287Rg has been predicted to be the most stable towards beta decay; however, no known roentgenium isotope has been observed to undergo beta decay. The unknown isotope 277Rg is also expected to have a long half-life of 1 second. Before their discovery, the isotopes 278Rg, 281Rg, and 282Rg were predicted to have long half-lives of 1 second, 1 minute, and 4 minutes respectively; however, they were discovered to have shorter half-lives of 4.2 milliseconds, 17 seconds, and 2.1 minutes respectively. Similarly, the measured half-life of the unconfirmed 283Rg of 5.1 minutes, while long, is less than the 10 minutes that had previously been predicted for it.
Of the isotopes 278Rg, 281Rg, and 282Rg, which have half-lives shorter than 2 minutes?
278Rg