Apoorva G Wagh
Articles written in Pramana – Journal of Physics
Volume 63 Issue 1 July 2004 pp 51-56
Interfering with the neutron spin
Apoorva G Wagh Veer Chand Rakhecha
Charge neutrality, a spin 1/2 and an associated magnetic moment of the neutron make it an ideal probe of quantal spinor evolutions. Polarized neutron interferometry in magnetic field Hamiltonians has thus scored several firsts such as direct verification of Pauli anticommutation, experimental separation of geometric and dynamical phases and observation of non-cyclic amplitudes and phases. This paper provides a flavour of the physics learnt from such experiments.
Volume 63 Issue 2 August 2004 pp 369-373
A polarised SUSANS facility to study magnetic systems
Apoorva G Wagh Veer Chand Rakhecha Markus Strobl Wolfgang Treimer
Using a right-angled magnetic air prism, we have achieved a separation of ∼10 arcsec between ∼2 arcsec wide up and down-spin peaks of 5.4 Å neutrons. The polarised neutron option has thus been introduced into the SUSANS instrument. Strongly spindependent SUSANS spectra have been observed over ±1.3 × 10^{−4} Å^{−1} range for several magnetic alloy samples. Spatial pair-distribution functions for the up and down-spins as well as the nuclear and magnetic scattering length density distributions in the micrometer domain, have been deduced from these spectra.
Volume 63 Issue 2 August 2004 pp 375-379
On measuring the neutron coherent scattering length with ultrahigh precision
We propose an order of magnitude improvement in the present five parts in 10^{5} precision of a nondispersive interferometric measurement of the neutron coherent scattering length
Volume 63 Issue 2 August 2004 pp 381-385
Geometric formula for prism deflection
Apoorva G Wagh Veer Chand Rakhecha
While studying neutron deflections produced by a magnetic prism, we have stumbled upon a simple ‘geometric’ formula. For a prism of refractive index
Volume 71 Issue 5 November 2008 pp 1109-1114 Neutron Optics and Reflectometry
Neutron forward diffraction by single crystal prisms
Sohrab Abbas Apoorva G Wagh Markus Strobl Wolfgang Treimer
We have derived analytic expressions for the deflection as well as transmitted fraction of monochromatic neutrons forward diffracted by a single crystal prism. In the vicinity of a Bragg reflection, the neutron deflection deviates sharply from that for an amorphous prism, exhibiting three orders of magnitude greater sensitivity to the incidence angle. We have measured the variation of neutron deflection and transmission across a Bragg reflection, for several single crystal prisms. The results agree well with theory.
Volume 71 Issue 5 November 2008 pp 1115-1122 Neutron Optics and Reflectometry
Pancharatnam geometric phase originating from successive partial projections
The spin of a polarized neutron beam subjected to a partial projection in another direction, traces a geodesic arc in the 2-sphere ray space. We delineate the geometric phase resulting from two successive partial projections on a general quantal state and derive the direction and strength of the third partial projection that would close the geodesic triangle. The constraint for the three successive partial projections to be identically equivalent to a net spin rotation regardless of the initial state, is derived.
Volume 71 Issue 5 November 2008 pp 1171-1175 Neutron Instrumentation
Bragg prism monochromator and analyser for super ultra-small angle neutron scattering studies
Apoorva G Wagh Sohrab Abbas Markus Strobl Wolfgang Treimer
We have designed, fabricated and operated a novel Bragg prism monochromator–analyser combination. With a judicious choice of the Bragg reflection, its asymmetry and the apex angle of the silicon single crystal prism, the monochromator has produced a neutron beam with sub-arcsec collimation. A Bragg prism analyser with the opposite asymmetry has been tailored to accept a still sharper angular profile. With this optimized monochromator–analyser pair, we have attained the narrowest and sharpest neutron angular profile to date. At this facility, we have recorded the first SUSANS spectra spanning wave vector transfers $Q \sim 10^{−6}$ Å^{-1} to characterize samples containing agglomerates up to tens of micrometres in size.
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