Not new and almost forgotten… https://www.newscientist.com/article/dn20049-atomic-disguise-makes-helium-look-like-hydrogen http://science.sciencemag.org/content/331/6016/448
This is interesting in the context of Holmlid’s muons. “The neutral muonic helium atom may be regarded as the heaviest isotope of the hydrogen atom, with a mass of ~4.1 atomic mass units (4.1H), because the negative muon almost perfectly screens one proton charge. We report the reaction rate of 4.1H with 1H2 to produce 4.1H1H + 1H at 295 to 500 kelvin. The experimental rate constants are compared with the predictions of accurate quantum-mechanical dynamics calculations carried out on an accurate Born-Huang potential energy surface….” One thought which comes to mind for an immediate use of this finding - is that a tank of compressed helium could be modified to become a muon detector, based on the decay of muonic helium. This would depend on the characteristic decay energy which should be unique (but I do not know the exact details). If this characteristic emission were to be a soft x-ray (as suspected) then the design should be based on a carbon fiber tank which is more transparent to x-rays than steel. Air Venturi makes a Carbon Fiber Tank, approved to 4500 psi, DOT-approved - Carbon fiber filament wound over aluminum bladder. This should work fine for helium, allowing one to detect muons with a simple x-ray detector (or – even easier – use film).
