It might be better to say: "no known or theorised fusion".
Some physicists have suggested that a nuclear decay process via a large number of energy levels, each of only a few keV would not produce any detectable gamma.
That such a decay scheme has never been seen, nor is compatible with quantum mechanics, is an important caveat. However, to state "no gamma, no fusion" is, perhaps, opening oneself to criticism.
This very conveniently overlooks the postulated Rossi mechanism: Ni + H = Ni.
In the case of, for instance, 62Ni, the fusion produces 63Cu with some energy release, which is mysteriously not associated with the gamma radiation which is the hallmark of lesser, "conventional" fusion processes. Furthermore, the process can only produce a small amount of energy due to binding energy concerns, and may even be endothermic. The 63Cu is stable, so the process ends there and ends well. Of course, the two stable copper isotopes are produced from two nickel isotopes which have a abundance ratio of 3:1, Natural copper has the same two isotopes at a 7:3 ratio, And guess which ratio Rossi's "spent fuel" sample contained? (Hint: it wasn't 7:3)
So far, so good, and your statement stands. However, nickel has 5 stable isotopes, not 2, and the process does not end cleanly for the other 3. All 3 isotopes of copper (59Cu, 61Cu and 62Cu) undergo beta+ decay, producing a positron which immediately annihilates an electron and produces a pair of 511 kev gamma rays. Speculation that decay
can occur in small steps has only one drawback: it's not observed in nature.
Another problem with this process is obvious to anyone who bothers to do a little reading. The most common isotope of nickel is 58Ni, which makes up 68% of all naturally occurring nickel. 58Ni + H = 59Cu. 59Cu then decays to 59Ni with the usual gamma release. 59Ni, however, is not stable, and decays with a half-life of 7500 years to 59Co .
Rossi's patent application remarks that the nickel powder must contain only 62Ni, as this will produce stable copper. While this is praiseworthy, it misses the fact that 64Ni will also do. What is not mentioned is that these two isotopes make up 5% of naturally occurring nickel. A low-gamma process is indeed conceivable, but it can't possibly be a mystery to Rossi. He need "only" perform isotope separation on his nickel to eliminate the 95% of the material which causes problems. And I suggest that you look around to find out what that costs. I suggest you look real hard. Given the low energy release per atom of nickel, and the high cost of processing the fuel, even if the Rossi process isn't an outright scam I can't see it being economical - let alone revolutionary.