Maximum pressure achieved on SNAP increases again!

In collaboration with the instrument staff, members of the Carnegie IDT team (Guthrie, Boehler, Li, Machida) have increased the maximum pressure for measuring structural refinement-quality data to 57 GPa. At this (unofficial) record-breaking pressure Bragg intensities were clearly visible down to ~0.75 Å and full structural refinements have conducted.

On increasing the pressure further, there was a failure of the carbide seat (at an estimated 60 GPa). In ongoing developments, these seats will be replaced with a sintered diamond variant, with the aim of extending the maximum pressure further into the 100 GPa range.  

The figure shows a Rietveld fit to a typical data set from a test sample of D2O at around 3 GPa measured on SNAP.

Zr gasket provides new window at high d

For crystalline systems with structure at high d-spacings 7-10 Å, including many magnetic systems, it has been so far necessary to use detectors in a low-angle geometry, with concurrent loss in resolution. Another possibility has been to use the bandwidth choppers to use very long wavelength neutrons to probe this structure with increased resolution. However, the substantial attenuation of the gasket and pressure vessel has made this unfeasible.

Xiaojia Chen has used IDT time to successfully test a pure Zr gasket in place of the more conventional TiZr alloys. The low absorption cross-section of Zr (0.185 barn at 2200m/s) versus Ti (6.09 barn at 2200m/s) means that a much stronger sample signal is accessible with the new gaskets. These measurements use a vertical geometry with the beam entering and exiting through the gasket and both detectors at 90 degrees. Testing has shown that the resulting data shows sharp strong Bragg peaks on very low backgrounds.

Pellet mass calculator

Jamie has released a mass calculator for typical pellets used with the PE toroidal anvils...you may find this useful:

http://neutrons.ornl.gov/instruments/SNS/SNAP/calc.shtml

IDT time allocated for 2012-A

The IDT allocation committee have met and decided on the beamtime allocations. We received requests for 62 days of beamtime with a total of 24 days available this cycle. In making the allocations, the committee followed the core priorities of the IDT. Here's looking forwards to a successful cycle!

Magnetic order in new polymorph of Mn3O4

As part of the ongoing development of low-temperature capabilities on 
SNAP, IDT member Shigeto Hirai has determined the magnetic structure of 
the orthorhombic Mn3O4 measured at ambient pressure 
and below the Neel temperature. As part of an IDT focus on 
low-temperature capabilities for SNAP, Shigeto aims to extend these 
measurements combining high pressure and lower temperature.

Figure shows Shigeto's Rietveld fit to the new magnetically ordered low temperature phase.

IDT Proposal deadline today!

Today is the deadline for submitting proposals for IDT beamtime. There are 24 days available in the upcoming cycle from Feb-June 2012.

IDT team reaches 44 GPa on SNAP!

An IDT team including Malcolm Guthrie, Reini Boehler and Kuo Li (all Geophysical Laboratory) has achieved a new pressure record for SNAP. Using specially designed anvils inside a panoramic cell driven by a PE press, a sample of ice VII (D2O) was compressed to 44 GPa at room temperature.  The panoramic cell can be gas loaded, adding and adds this important capability to the instrument. Also, optical access facilitates in-situ measurement of pressure via ruby fluorescence.