# Experiment demonstrating interference patterns of neutrons

The question is about experiments (and references) that demonstrate interference patterns of neutral (chargless) particles (fermions), especially neutrons.

Like double-slit experiments for neutrons (or equivalent).

Searching around did not yield sth (or maybe i did not notice it).

My understading is that similar experiments have only been done for charged particles (i.e electrons, protons) or bosons (i.e photons).

Is this correct?

I would suggest 'Single- and double-slit diffraction of neutrons" by Zeilinger, Gahler, Shull, Treimer, and Mampe, Reviews of Modern Physics 60(4), 1067-1073 (1988). If I might quote the abstract:

The authors report detailed experiments and comparison with first-principle theoretical calculation of the diffraction of cold neutrons ($\lambda \approx$ 2 nm) at single- and double-slit assemblies of dimensions in the 20—100 $\mu$m range. Their experimental results show all predicted features of the diffraction patterns in great detail. Particularly, their double-slit diffraction experiment is its most precise realization hitherto for matter waves.

So, single and double slit experiments with neutrons have indeed been done, and indeed show just what would be expected.

Here's a brief description of how the experiment worked. They used neutrons from a reactor, which were brought down to room-temperature thermal energies using heavy water. They let those out through a collimator to make a beam. To make the beam monochromatic, they bent it through a quartz prism and selected one wavelength using a a slit. They verified the energies using time of flight (I think using a beam chopper). To produce diffraction, they used a tiny double slit with a spacing of 0.1 mm. At a distance of 5 m from the double slit, the spacing of the fringes was about 0.1 mm, and they had to make the graph by slowly moving the detector across the fringes and measuring a count rate at each position.

• i assume there is not free online version of the reference? – Nikos M. Aug 19 '14 at 22:57
• Nice. That must be a tour de force. – dmckee --- ex-moderator kitten Aug 19 '14 at 23:00
• i just realised is the same paper referenced by other answer, have already seen that, mostly intersted in double0slit interference exp – Nikos M. Aug 19 '14 at 23:03
• @NikosM. There is a "free" version here. – garyp Aug 19 '14 at 23:05
• While I get many journals through my institution, APS journals are pretty good about being readily available, particularly older ones. Go to aps.org, publications, Review of modern physics, search Zeiliner, and see if you have access. – Jon Custer Aug 19 '14 at 23:21

Neutron diffraction from crystals.

It's not an exact parallel, of course because it is more like a "many slit" experiment and it is reflective rather than transmissive, but the physics is the same.

It is worth noting that the best diffraction spectrometer tend to also be reflective rather than transmissive simple because that avoids chromatic aberration effects in the material of the diffraction grating.

It is also the case that neutral buckyballs (fullerenes) have been used in transmission diffraction experiments.

• thanks, mostly i am interested in double-slit (or equivalent) that demonstrate the "wave-particle duality" of neutrons in this sense – Nikos M. Aug 19 '14 at 22:44
• Diffraction does demonstrate the wave-particle duality. It only works (gets the diagnostic pattern as opposed to a out-of-focus blob) with waves, but the neutrons are still detected as particles. It's the same physics. – dmckee --- ex-moderator kitten Aug 19 '14 at 22:45
• Any idea why double-slit expriments not done with neutrons though? – Nikos M. Aug 19 '14 at 22:46
• Neutrons are much harder to scatter than electrons (the interaction cross-section is 5-7 orders of magnitude lower), so you want a lot of chances to bounce them---two just isn't practical. – dmckee --- ex-moderator kitten Aug 19 '14 at 22:47
• Protons interact strongly by electromagnetic means. Neutrons are neutral and interact mostly by the residual strong force which is reasonably modeled as a contact interaction. That makes the scattering cross-section proportional to the size of the area of the nucleus rather than the square of the distance between atoms. – dmckee --- ex-moderator kitten Aug 19 '14 at 22:54

I recall that there was a spate of neutron interferometer experiments some years ago.

Google helped me find this review paper from 1988. Search terms: Young's experiment with neutrons. (Rev. Mod. Phys. 60, 4, p. 1067, 4 October 1988.)

• Jon edged you out. Great minds or something. – dmckee --- ex-moderator kitten Aug 19 '14 at 23:01
• thanks already seen the paper, as i mentioned in other answer mostly interested in double-slit interfrerence experiments – Nikos M. Aug 19 '14 at 23:01
• Missed it by that much. Baseball is a game of inches. Etc. :) The RMP paper does mention double slit experiments. I haven't read it to know what's there in detail. – garyp Aug 19 '14 at 23:03
• @NikosM. Er...did you read the abstract? – dmckee --- ex-moderator kitten Aug 19 '14 at 23:04
• @NikosM. Ah. Diffraction is the go-to term that a pro would use to describe a n-slit type experiment. – dmckee --- ex-moderator kitten Aug 19 '14 at 23:13