New intensity and visibility aspects of a double loop neutron interferometer

Various phase shifters and absorbers can be put into the arms of a double loop neutron interferometer. The mean intensity levels of the forward and diffracted beams behind an empty four plate interferometer of this type have been calculated. It is shown that the intensities in the forward and diffracted direction can be made equal using certain absorbers. In this case the interferometer can be regarded as a 50/50 beam splitter. Furthermore the visibilities of single and double loop interferometers are compared to each other by varying the transmission in the first loop using different absorbers. It can be shown that the visibility becomes exactly 1 using a phase shifter in the second loop. In this case the phase shifter in the second loop must be strongly correlated to the transmission coefficient of the absorber in the first loop. Using such a device homodyne-like measurements of very weak signals should become possible.Comment: 12 pages, 9 figures, accepted for publication in the Journal of Optics B - Quantum and Semiclassical Optic

Neutron Interferometry constrains dark energy chameleon fields

We present phase shift measurements for neutron matter waves in vacuum and in low pressure Helium using a method originally developed for neutron scattering length measurements in neutron interferometry. We search for phase shifts associated with a coupling to scalar fields. We set stringent limits for a scalar chameleon field, a prominent quintessence dark energy candidate. We find that the coupling constant $\beta$ is less than 1.9 $\times10^7$~for $n=1$ at 95\% confidence level, where $n$ is an input parameter of the self--interaction of the chameleon field $\varphi$ inversely proportional to $\varphi^n$.Comment: 7 pages, 4 figure

Testing of quantum phase in matter wave optics

Various phase concepts may be treated as special cases of the maximum likelihood estimation. For example the discrete Fourier estimation that actually coincides with the operational phase of Noh, Fouge`res and Mandel is obtained for continuous Gaussian signals with phase modulated mean.Since signals in quantum theory are discrete, a prediction different from that given by the Gaussian hypothesis should be obtained as the best fit assuming a discrete Poissonian statistics of the signal. Although the Gaussian estimation gives a satisfactory approximation for fitting the phase distribution of almost any state the optimal phase estimation offers in certain cases a measurable better performance. This has been demonstrated in neutron--optical experiment.Comment: 8 pages, 4 figure

Maximum-likelihood absorption tomography

Maximum-likelihood methods are applied to the problem of absorption tomography. The reconstruction is done with the help of an iterative algorithm. We show how the statistics of the illuminating beam can be incorporated into the reconstruction. The proposed reconstruction method can be considered as a useful alternative in the extreme cases where the standard ill-posed direct-inversion methods fail.Comment: 7 pages, 5 figure

On Quantum Jumps, Events and Spontaneous Localization Models

We propose a definite meaning to the concepts of "experiment", "measurement" and "event" in the event-enhanced formalism of quantum theory. A minimal piecewise deterministic process is given that can be used for a computer simulation of real time series of experiments on single quantum objects. As an example a generalized cloud chamber is described, including multiparticle case. Relation to the GRW spontaneous localization model is discussed. The second revised version of the paper contains references to papers by other authors that are are aiming in the same direction: to enhance quantum theory in such a way that it will provide stochastic description of events triggered by individual quantum systems.Comment: 20 page

Monte Carlo simulation of neutron transmission of boron alloyed steel

For material characterization, it is of specific importance to define the homogeneity distribution of strong absorbing elements within shielding materials quantitatively. Boron is the important absorber used for the production of boron alloyed steel to serve in long term storage of spent nuclear fuel or nuclear waste disposals. Due to the high neutron absorption of boron compared to steel, the neutron radiography is a powerful tool for the nondestructive investigation. This paper concerns quantitative estimations of secondary effects on the neutron transmission measurements through thermal neutron shielding materials such as beam hardening, background, and inhomogeneous absorber distribution within the samples, which decrease the neutron attenuation in absorber materials. Neutron transmission measurements have been performed for boron alloyed steel plates having different thickness using thermal neutrons. The investigated samples are from the Austrian Steel Production Company Bohler Bleche GmbH, which uses natural boron in the form of boron carbide within the steel matrix. The attenuation coefficients of boron alloyed steels were measured with neutron radiography and the special neutron transmission set up JEN 3, which is used for routine test measurements of shielding materials by the Austrian Steel Production Company Bohler Bleche GmbH. In addition to the transmission measurements, Monte Carlo Neutron Particle MCNP simulations were performed for better understanding and interpretation of the obtained experimental results. This is the first step of our study covering the estimation of some secondary effects on the neutron transmission. Further experiments will be continued using different absorber materials and homogeneity distribution in order to verify afore said factors in the transmission experiments of neutron shielding material

Testing of operational phase concepts

Various phase concepts may be treated as special cases of the maximum likelihood estimation. For example, the discrete the operational phase of Noh, Fougeres and Mandel is obtained for continuous Gaussian signals with phase modulated mean. Although the Gaussian estimation gives a satisfactory approximation for fitting the phase distribution of almost any state the optimal phase estimation offers in certain cases a measurably better performance. This has been demonstrated in a neutron-optical experiment

Neutron phase contrast tomography on isotope mixtures

Perfect crystal neutron interferometry is an extreme sensitive instrument for the detection of phase shifts induced in materials or magnetic fields. The utilisation of neutron beams and phase signals in tomography permits the investigation of weakly absorbing substances and isotope mixtures. Due to the larger fluctuation of count numbers and phases, an optimised maximum-likelihood algorithm has to be engaged. We present the analysis of isotope mixtures, which are nearly transparent to thermal neutrons, with a sensitivity of about 1% in the detection of isotopic density differences

Analysis of neutron attenuation in boron alloyed stainless steel with neutron radiography and JEN 3 gauge

This paper concerns the neutron attenuation behavior of boron alloyed stainless steels, and quantitative estimations of secondary effects on the neutron transmission measurements, such as beam hardening, background and micro structure of neutron absorber causing a decrease in the total macroscopic cross sections. Systematic thermal neutron transmission measurements of boron alloyed steel plates have been performed at different neutron radiography facilities and at a portable gauge called JEN 3, which is a practical neutron transmission setup for industrial demands in non destruclive material inspection. In addition, MCNP Monte Carlo Neutron Particle transport simulations were performed for a better understanding of the experimental results, the secondary factors affecting the total macroscopic cross sections, and the characteristics of the JEN 3 gauge. The detectable thickness limit for 1.88 wt natural boron alloyed steel plates was determined as 1 1.5 cm depending on the contributions of the secondary factors in each facilit