TOSCA - Istituto Nazionale di Fisica Nucleare
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Transcript TOSCA - Istituto Nazionale di Fisica Nucleare
THE NEUTRON SPECTROMETER
TOSCA
M.
1
Celli ,
D.
1
Colognesi ,
2
Parker ,
3
Rossi-Albertini ,
S. F.
V.
J. Tomkinson2, and M. Zoppi1
F.
4
Sacchetti ,
([email protected])
1IFAC-CNR
(IT); 2ISIS - R.A.L. (UK); 3ISM-CNR (IT);
4Dip.to di Fisica and INFM, Univ. di Perugia (IT)
Science with TOSCA:
The principles of molecular transitions
Virtual level
Excited molecular levels
Ground level
E0=p02/2m=incoming neutron energy
E1=p12/2m=scattered neutron energy
= E0- E1 =energy transfer
View of TOSCA-II showing detector banks for forward and backward scattering.
Q= p0-p1 = momentum transfer
The TOSCA project
(http://www.ifac.cnr.it/tosca/tosca-main.htm)
The final version of the high-resolution crystal analyser spectrometer, TOSCA, has been built, installed and operated at the ISIS pulsed neutron
source (Rutherford Appleton Laboratory, Chilton, Didcot, UK) as a joint project of Consiglio Nazionale delle Ricerche (Italy) and Rutherford
Appleton Laboratory (UK). TOSCA is mainly intended for molecular vibrational spectroscopy but will have also some general diffraction capability
with elastic detectors in forward and backward scattering (0.02-2 nm in d-plane spacing).
The instrument, placed 17 m apart from the neutron water moderator, makes possible to measure inelastic neutron scattering in a large energy
transfer range ω=(5-1000) meV, with a relative energy-resolution of about Δω/ω=1-2% in the whole interval of ω. It has replaced both the old
TFXA, removed in spring 1998, and subsequently, a prototypical version of TOSCA (TOSCA-I) which was incorporated into the final version of
TOSCA (TOSCA-II) in spring 2000. The advantage over its two predecessors is both in detected flux and energy resolution. TFXA and TOSCA-I,
which were placed 12 m apart from the neutron moderator, included two and ten back-scattering detector modules, respectively and showed a
Δω/ω of 3-4% and 2-2.5%, respectively.
In addition, dowstream of the TOSCA spectrometer, the INES (Italian Neutron Experimental Station) experimental and test facility will be built.
This experimental station will be initially equipped with a multi-purpose time-of-flight neutron diffractometer whose construction should be
completed during the current year (2004). The modular instrument design, the large blockhouse, and the ample sample space will allow INES to
be used for a large variety of different applications ranging from powder diffraction, to archaeometric measurements, to neutron detector testing.
TOSCA-II detection geometry: the
yellow arrow represents all the
scattered neutrons, the black plate
is the graphite analyser, the yellow
block is the Be filter and the white
arrow stands for the monocromatic
neutrons detected by the 3He
tubes.
TOSCA-II inelastic spectra from potassium hydrogen phtalate at 20 K.
The fully protonated sample is reported as blue line, while the red line
represents a selectively deuterated one. Missing peaks clearly indicate
two hydrogen bond modes.