R. Golub

The interaction of Ultra-Cold Neutrons (UCN) with liquid helium and a superthermal UCN source

Abstract We discuss the interaction of Ultra-Cold and Cold Neutrons with superfluid 4He and show that this interaction has all the characteristics which are necessary for the achievement of extremely high densities of UCN.

Super-thermal sources of ultra-cold neutrons

Abstract We discuss some systems in which the steady state UCN density corresponds to ‘temperatures’ much lower than the temperature of the moderator, contrary to the generally accepted view that this cannot occur.

Space-time description of neutron spin echo spectrometry

Abstract Neutron spin echo (NSE) [F. Mezei, ed., Neutron Spin Echo, Lecture Notes in Physics Vol. 128 (Springer, Berlin, 1980)] is a technique for neutron scattering in which the energy resolution can be much narrower than the spectral width of the incident beam and it allows the direct measurement of the Fourier transform of the energy transfer spectrum, i.e. the time dependence of the density—density correlation function of the scattering systems. It is normally discussed in terms of neutron Larmor precession in magnetic fields and the scattering process is described in terms of S( Q , ω) . We show how a quantum mechanical treatment of the NSE technique offers new insight into the scattering process and explains how NSE directly yields the intermediate scattering function S( Q , t) or pair distribution function G(r). In addition it gives a basic picture of the physics of ‘phonon focussing’ in NSE and reveals the link between the spin echo time τ, the resolution of the measurement and the details of the scattering process. In this paper we present three different approaches to understanding the system: (i) the usual classical Larmor precession, (ii) a semi-classical ray tracing model and (iii) a full quantum mechanical treatment. We apply these models to a spin echo spectrometer as used for various kinds of measurements.

Fluorescence efficiencies of thin scintillating films in the extreme ultraviolet spectral region

Abstract Fluorescence efficiencies of the organic scintillators tetraphenyl butadiene (TPB), p-terphenyl (TPH), and diphenyl stilbene (DPS) are measured relative to sodium salicylate at incident wavelengths of 58.4 and 74.0 nm. Optimum thickness and dopant concentration are determined for maximum fluorescence yield in evaporated, sprayed, and doped plastic films. Measurements made with alpha (α) particle induced scintillations in gaseous argon (a broad band vacuum ultraviolet light source) were in good agreement with those made using the line source. Transparent scintillator doped plastic films have been developed which yield fluorescence efficiencies comparable to that of sodium salicylate. Evaporated films show the highest fluorescent yields, reaching almost four times the efficiency of sprayed sodium salicylate. On the other hand, doped plastic films offer some advantages.

The Electric Dipole Moment of the Neutron

SUMMARY. There are seemingly compelling reasons for expecting the laws of physics to be unchanged under various symmetry transformations. However, during the last fifteen years it has been discovered that many of these symmetries are in fact broken. The search for the electric dipole moment of the neutron has already made, and will continue to make, an important contribution to the understanding of this fascinating and fundamental problem. The experimental limits of sensitivity can be understood in terms of the Heisenberg uncertainty principle and the achievable limits for such things as the electric field strengths and observation times in various systems. The two experimental methods used to date are neutron beam magnetic resonance and crystal diffraction. New methods which have been proposed, such as that using bottled neutrons and further work on existing methods, promise a considerable improvement in sensitivity in the next few years. 1. Introduction Physicists have been interested in the electric dipole moment (EDM) of the neutron since about 1950. Today, 22 years later, this interest has significantly increased even though nobody has succeeded in demonstrating the existence of an EDM for the neutron or any other particle. The reason for this interest is the role that the ideas of symmetry have played and are continuing to play in physics. An EDM, if it existed, would have rather special symmetry properties and would give us information about the forces acting on the neutron and other particles. Following the pioneering experiment of Smith, Purcell and Ramsey (1957) the results of a more recent generation of experiments to search for the EDM have now been available for about four years (Shull and Nathans 1967, Cohen et al. 1969 and Baird et al. 1969). Further descriptions of these experiments have been given by Cohen (1969) and Ramsey (1969). Plans are now being made in several laboratories for a new generation of experiments. We feel that this is an appropriate time to discuss at a non-specialist level the recent history of ideas on symmetry in physics in relation to the part played by the EDM, to review the past experiments in terms of what really limits their sensitivity and to speculate on the improvements which may be achieved in the future. Although this article is concerned solely with the neutron, attempts have been made and are currently in progress to search for the EDM’s of other particles (Player and Sandars 1970, Stein et al. 1969). The detection of an EDM for any elementary particle would have the same significance as it would for the neutron and much of what we will say about the interpretation of the neutron EDM experiments will apply to the EDM’s of other particles except for some quantitative differences.

Experimental searches for the neutron electric dipole moment

The possible existence of a neutron electric dipole (EDM) was put forward as an experimental question in 1949, 60 years ago, and still remains an outstanding question in modern physics. A review of the technical innovations that allowed for improving the experimental limit by nearly eight orders of magnitude (approximately a decade per decade) will be presented, along with a discussion of the prospects for further improvement.

Measurement of the ultra cold neutron production rate in an external liquid helium source

Abstract Ultra Cold Neutrons have been produced by down scattering of cold neutrons (λ = 10 A ) on liquid helium. The measured production rate is in agreement with the calculated value.

Magnetic trapping of ultracold neutrons

Three-dimensional magnetic confinement of neutrons is reported. Neutrons are loaded into an Ioffe-type superconducting magnetic trap through inelastic scattering of cold neutrons with

Production of UCN by downscattering in superfluid He4

{}^{4}\mathrm{He}.

Recent developments and results from the neutron resonance spin-echo spectrometer (NRSE) at BENSC Berlin

Scattered neutrons with sufficiently low energy and in the appropriate spin state are confined by the magnetic field until they decay. The electron resulting from neutron decay produces scintillations in the liquid helium bath that results in a pulse of extreme ultraviolet light. This light is frequency downconverted to the visible and detected. Results are presented in which