4 K Cryocoolers — Mössbauer Spectroscopy
The proven Janis cryostat design for Mössbauer spectroscopy is extended to lower temperatures with the introduction of the SHI-850-5 cryostat system. With a base temperature of less than 5 K, the SHI-850-5 cryostat combines liquid helium temperatures with the convenience of a closed-cycle system. The exchange gas environment ensures even cooling and offers fast sample exchange.
The Janis design features the following advantages:
- Proven design for Mössbauer spectroscopy with very low line broadening.
- Suitable for samples of any shape or constitution (including powders and liquids) because the system does not rely on the thermal conductivity of samples for cooling.
- Fast sample exchange since the cryostat does not need to be warmed up to change samples.
- Hassle-free integration into the laboratory: a vibration isolation stand is included with every system, so no independent stands or mounts need to be constructed in the laboratory.
- No permanent installation in the laboratory required, easily transported/moved.
- Flexible design may be used for other applications.
The refrigerator cools a column of static helium exchange gas, into which the sample is inserted. This indirect cooling mechanism means that the sample is surrounded by the cooling medium, and samples are cooled uniformly regardless of their shape. Samples may be removed from the system while it is still running, saving valuable time during experiments if multiple samples need to be studied.
Samples are isolated from the refrigerator vibrations by the use of flexible bellows between the sample support flange and the refrigerator. This sample support flange is mounted on an independent, pneumatically isolated, mounting stand. This stand requires no drilling or permanent construction in the laboratory, and can easily be disassembled and moved if the need arises.
The SHI-850-5 system uses a powerful Sumitomo 4 K refrigerator to provide the required cooling. The refrigerator is mounted below the sample chamber in a compact configuration that simply sits on the floor. The sample chamber extends up through the mounting stand, and a shelf may easily be added to the stand for mounting the source and detector.
- Vibration isolation mounting stand
- Vibration isolation bellows
- Isothermal static helium gas sample chamber
- Optical vacuum jacket and radiation shield with two Mylar windows
- Gold-plated OFHC copper sample holder
- 10-pin electrical feedthrough for customer wiring into the sample area
- Two spare electrical access ports
- Evacuation valve and safety pressure relief
- 4 K closed-cycle system components
- Additional electrical feedthroughs (BNC, SMA, multipin, and others)
- High temperature (500 K, 800 K)
- Additional optical window ports for UV/VIS measurements
- Larger or smaller diameter sample chamber
- Custom configurations.
- Complete turnkey systems, including temperature controller and pumping station, are available.
SHI-850 Series Specifications
(excluding radiational and experimental heat loads)
|Temperature range||<5 K to 300 K|
|Initial cooldown time||2.5 h to 5 K|
|Sample change time||5 min|
Shown to the right are Fe57 Mössbauer spectra (dots) of a 25 µm iron metal foil at 298 K with the CCR off and on. The velocity scan of ±2 mm/s covers only the innermost lines of the iron metal sextet. Also shown are least squares fits (lines) of a symmetric quadrupole pair with Lorentzian line shapes to each spectrum. The results of the fits were linewidth estimates of 0.234 mm/s with the CCR off and 0.241 mm/s with the CCR on. The uncertainty in the line width estimates due to the counting statistics is ±0.002 mm/s.
NOTE: Data provided by Science Engineering & Education Co. (SEE Co. — formerly Web Research Co.), http://www.seeco.us. Special thanks to Professor Darby Dyar, Mount Holyoke College.