Eur. Phys. J. A (2006) 27: 243-256
https://doi.org/10.1140/epja/i2005-10267-y

Interdisciplinary Topics

Precision measurement of the coherent neutron scattering length of ³He through neutron interferometry

¹ Institut für Physik, Staudinger Weg 7, D-55099, Mainz, Germany
² Atominstitut der österreichischen Universitäten, Stadionallee 2, A-1020, Wien, Austria

^* e-mail: Wolfgang.Ketter@de.bosch.com

Received: 20 April 2005
Accepted: 2 March 2006
Published online: 29 March 2006

Abstract

Improved knowledge of the real part of the neutron scattering length of ³He is important for further development of nuclear few-body theory, as well as for a thorough understanding of neutron scattering off quantum liquids. The real part of the bound incoherent neutron scattering length b _i' has recently been measured directly with an experimental uncertainty of better than 1% by means of spin echo spectrometry. The uncertainty of the more fundamental bound multiplet scattering lengths b _±' is thus limited by today's 1.2% uncertainty of the spin-independent coherent part b _c'. Employing the skew-symmetric perfect crystal Si-interferometer at the S18 experimental site at ILL, Grenoble, we have re-measured the real part of the bound coherent neutron scattering length b _c' of ³He. Our result b _c' = 6.010(21)fm exhibits a significant deviation compared to the latest accepted value b _c' = 5.74(7)fm (H. Kaiser, H. Rauch, G. Badurek, W. Bauspiess, U. Bonse, Z. Phys. A 291, 231 (1979)). Including the known value of the incoherent neutron scattering length, we obtain new values for the real parts of the free singlet and triplet scattering lengths, a _-' = 7.573(30)fm and a ₊' = 3.480(18)fm. Our result contravenes by more than 7 standard deviations the measurement of the same physical quantity that has recently been performed by a group at NIST in a very similar experiment (P.R. Huffman, D.L. Jacobson, K. Schoen, M. Arif, T.C. Black, W.M. Snow, S.A. Werner, Phys. Rev. C 70, 014004 (2004)) which yielded b _c' = 5.853(7)fm.