Superconducting High Energy Resolution Gamma-ray Spectrometers
We have demonstrated that a bulk absorber coupled to a TES can serve as a good gamma-ray spectrometer. Our measured energy resolution of 70 eV at 60 keV is among the best measurements in this field. We have also shown excellent agreement between the noise predictions and measured noise. Despite this good result, we noted that our detector design has shortcomings with a low count rate and vulnerabilities with the linearity of energy response. We addressed these issues by implementation of an active negative feedback bias. We demonstrated the effects of active bias such as additional pulse shortening, reduction of TES change in temperature during a pulse, and linearization of energy response at low energy. Linearization at higher energy is possible with optimized heat capacities and thermal conductivities of the microcalorimeter. However, the current fabrication process has low control and repeatability over the thermal properties. Thus, optimization of the detector performance is difficult until the fabrication process is improved. Currently, several efforts are underway to better control the fabrication of our gamma-ray spectrometers. We are developing a full-wafer process to produce TES films. We are investigating the thermal conductivity and surface roughness of thicker SiN membranes. We are exploring alternative methods to couple the absorber to the TES film for reproducibility. We are also optimizing the thermal conductivities within the detector to minimize two-element phonon noise. We are experimenting with different absorber materials to optimize absorption efficiency and heat capacity. We are also working on minimizing Johnson noise from the E S shunt and SQUID amplifier noise. We have shown that our performance, noise, and active bias models agree very well with measured data from several microcalorimeters. Once the fabrication improvements have been implemented, we have no doubt that our gamma-ray spectrometer will achieve even more spectacular results.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15007522
- Report Number(s):
- UCRL-LR-147515; TRN: US0402090
- Resource Relation:
- Other Information: Ph.D. thesis submitted to the Univ. of California, Davis, CA (US); PBD: 22 Feb 2002
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION
AMPLIFIERS
BYPASSES
EFFICIENCY
ENERGY RESOLUTION
FABRICATION
IMPLEMENTATION
MEMBRANES
OPTIMIZATION
PHONONS
ROUGHNESS
SPECIFIC HEAT
SPECTROMETERS
THERMAL CONDUCTIVITY
THERMODYNAMIC PROPERTIES