Measurement of the Coherent Neutron Scattering Length of (3) He.
By means of neutron interferometry the s-wave neutron scattering length of the (3)He nucleus was re-measured at the Institut Laue-Langevin (ILL). Using a skew symmetrical perfect crystal Si-interferometer and a linear twin chamber cell, false phase shifts due to sample misalignment were reduced to a negligible level. Simulation calculations suggest an asymmetrically alternating measuring sequence in order to compensate for systematic errors caused by thermal phase drifts. There is evidence in the experiment's data that this procedure is indeed effective. The neutron refractive index in terms of Sears' exact expression for the scattering amplitude has been analyzed in order to evaluate the measured phase shifts. The result of our measurement, b' c = (6.000 ± 0.009) fm, shows a deviation towards a greater value compared to the presently accepted value of b' c = (5.74 ± 0.07) fm, confirming the observation of the partner experiment at NIST. On the other hand, the results of both precision measurements at NIST and ILL exhibit a serious 12σ (12 standard uncertainties) deviation, the reason for which is not clear yet.
Institut für Physik, Universität Mainz, Germany.
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W
Ketter
Institut für Physik, Universität Mainz, Germany.
W
W
Heil
Atominstitut der Österreichischen Universitäten, Wien, Austria.
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G
Badurek
Atominstitut der Österreichischen Universitäten, Wien, Austria.
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M
Baron
Atominstitut der Österreichischen Universitäten, Wien, Austria.
R
R
Loidl
Atominstitut der Österreichischen Universitäten, Wien, Austria.
H
H
Rauch
elastic neutron scattering; few body systems; neutron interferometry; properties of the 3He nucleus; real part of the coherent scattering length