Of course one answer is that there have been 23 years of LENR experiments with no appreciable gamma emitted from the cells. But I know your question is deeper than that.
Let’s begin with what we know about the reaction sites.
Take a look at Larsen’s slides #32-34 from his “Nickel-seed LENR Networks” presentation from April 20 2011.
Note in particular page 34, there are photomicrographs of craters where reactions have taken place. They are tiny and have a non-uniform distribution.
Next, consider their size: a couple of nanometers to around 100 microns.
Next, take a look at the SPAWAR infrared video. You’ll see how the active sites come alive and die quite rapidly.
Now consider the beam and the target.
First, consider the nature of LENR reactions as the technology presently exists. You would have to have a lot of control – location, density, timing and other parameters – of the active sites. I don’t know anybody who has such control yet. I don’t even think Larsen does because if he did, we’d be buying his products already.
Second, you would have to be able to collimate your beam very tightly within the limitations of the best active LENR sites you can create.
Knowing all of this, and what you know of beam capabilities, what do think?