I am calculating the free neutron decay energy completely outside the Standard Model and obtained a possible analytical photon peak located at 511 keV+27.2 eV. This peak is so easy to be mixed with the positron annihilation gamma rays, which is currently interpreted as the contamination of positron background. But this possible 511 keV+27.2 eV photon is solo, it doesn't have the characteristic back-to-back gamma ray pair feature, so it should be very easy to experimentally distinguished from the positron annihilation.
I am bring this up because the possible free neutron decay mode, if experimentally verified to be true, will affect the solar neutrino deficit. As we know the solar neutrino detection relies on the capture of free neutrons by nuclei as a definitive confirmation of neutrino interaction with the detector. If some free neutrons decay and emit 511 keV+27.2 eV photons, then the detector will definitely miss some of the neutrino interactions, resulting in the so-called solar neutrino deficit.
Your expertise in the free neutron decay is of very high importance. I am looking for an experimental support for the puzzle I am faced with.
Best Regards,
Hong Du
As Hong Du says, 511 keV single photon emission can be distinguished from back-to-back annihilation radiation by using coincidence measurements.
As another proof, I would recommend to use a pure Ge semiconductor detector to examine the width of photoelectric peak in the energy spectrum. Positrons/positronium have large kinetic velocities even at room temperature because of their light mass. Waves emitted from a source with a large velocity possess a longer/shorter wavelength, namely Doppler effect. For this reason, 511 keV photoelectric peak of the annihilation radiation is significantly wider than 512 keV photoelectric peak of gamma-rays from Ru-106/Rh-106 source. If the gamma-rays are really emitted from neutrons, there is almost no Doppler effect as the latter source.
You can read about Doppler effects in the annihilation radiation and gamma-rays in the following paper (see Eq.5 and Fig.2). There is significant difference between them.
Article Annihilation photon acollinearity in PET: Volunteer and phan...
Thanks Kengo Shibuya .
The PET -like detectors can not only provide time coincidence, but also spatial information. Even a gamma ray camera can partially verify the location of these gamma rays. If the annihilation 511 keV gamma rays are not located in the path of neutron beam, they can be excluded from the total 511 keV gamma counts. It can help identify the the 511 keV gamma rays born in the neutron beam as the decay product.
The verification of the source of 511 keV gamma rays is of fundamental physics importance. If it shows that 511 keV does come from neutron decay, then it can be used to explain the free neutron lifetime puzzle where existing neutron lifetime measurements have discrepancies between the beam decay method and bottle method because the beam decay method might have missed the 511 keV gamma rays and thought the lifetime was longer.
If the missed count is significant, it can even help explain the solar neutron deficit.
Hi Hong Du, I am talking about Ge semiconductor detector and its spectroscopy, not about PET.
As you know, the Doppler effect is a phenomenon in which the pitch of an ambulance sounds like it is dropping as it passes by. This phenomenon occurs not only with sound, but also with electromagnetic waves. The strength of the Doppler effect tells us the speed of motion of the wave source. If the wave source is a particle, the difference due to the mass of the particle will be reflected. Since the mass of an electron differs from the mass of a neutron by a factor of about 1,800, this measurement method is expected to be sensitive to which is the true wave source.
Hi Kengo Shibuya , thank you for pointing out the spectroscopic information.
I briefly read you paper, and realized that you used Ge spectroscopic detector which can offer gamma ray peak width measurement. I am not particularly familiar with Ge detector, but I believe its good for differentiating the source of the 511 keV gamma rays, for example e+e- annihilation tends to have wider peak due to the small mass of e+e-. It sure is a fast way to preliminary distinguish the source of gamma rays without making changes to existing neutron decay experiment.
But still, time-correlation and location information of the 511 keV gamma rays is the best information to definitively determine if the 511 keV gamma rays are really from free neutron decays.
Hi Hong Du, thank you for your reply.
I agree with you that the first choice is time-correlation in your situation. If the data is inadequate, or if the reviewers fumbles with the interpretation of the data, then please remember my comments.
The Ge or any other imaginable detectors would be certainly way too crude to distinguish energy delay of 27eV over 511KeV. One can see what Ge detector can see (they improved a bit since 1978 but not dramatically) :
An experiment to demonstrate the energy broadening of annihilation gamma rays American Journal of Physics 46, 740 (1978); https://doi.org/10.1119/1.11113
However, as it was mentioned filtering out coincident events will provide some degree of rejection of annihilation gammas (which are omnipresent e.g.) : Article A very long-term HPGe-background gamma spectrum
However the efficiency of detecting 511keV cannot be practically any close to 100% therefore it is not very efficient rejection method.
I wonder if the expected gamma directivity correlates with neutron's spin - that would open the possibility to modulate it by somehow modulating the spin of the neutrons - this way separating it from the background.
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