Development and Testing of New Tungsten Based Absorber Materials with Accordion Geometries for Nuclear Physics Applications

Electromagnetic and hadronic calorimeters are common tools used in high energy and nuclear physics to measure the energy of particles produced in high energy particle collisions. Scintillator based calorimeters are some of the most widely used today because of their relatively low cost and high performance. However, in order to fully absorb the energy of particles in the multi-GeV energy range, scintillators must be combined with absorber materials of much higher density. This is typically accomplished by interspersing the scintillator and absorber material in alternating layers to form what is called a sampling calorimeter, and using some form of optical readout to detect the light produced in the scintillator. For electromagnetic calorimeters, the most commonly used material is lead. One of the principle factors that determines the size of these calorimeters is the Moliere radius (OM) of the absorber material. The Moliere radius is defined as the radius of a cylinder that contains 90% of the energy of the electromagnetic shower of the incident particle. This is a critical parameter in that it determines the lateral spread of the shower, and therefore the ability to resolve nearby or overlapping showers in the calorimeter. Therefore, in order to separate multiple showers in the calorimeter, particularly in high multiplicity collisions, it is necessary to place the front face of the calorimeter far enough away from the interaction point that the produced particles spread out sufficiently that they can be resolved. If in addition, one wants to cover nearly the complete solid angle surrounding the interaction point, it requires a calorimeter of very large area. It is clear that if a higher density absorber material that had both a smaller Moliere radius and a shorter radiation length than lead could be used to construct a Compact Calorimeter with a much smaller volume, then one could potentially benefit from a significant cost savings without sacrificing performance. This is precisely the benefit of a tungsten scintillator sampling calorimeter. However, pure tungsten is an extremely difficult material to work. It is very brittle, expensive, and has the highest melting point of any metal (3422 C). Given its extreme hardness and high melting point, it is very difficult to bend or form pure tungsten plates into complex shapes. With the possibility of forming accordion shaped tungsten plates, it is now possible to consider using a so-called Optical Accordion calorimeter, where the absorber plates would consist of a tungsten alloy material with a density in the range of 15-17 g/cm3 that would be formed into an accordion shape, and active material would consist of extruded plastic scintillator read out with wavelength shifting fibers and silicon photomultipler photodetectors. A proposed research effort fabricating custom accordion shaped tungsten sheets. A few different options will be evaluated for these structures that might include the following: 1) plasma spray forming based on pre-agglomerated mixed elemental powders that deposit as alloy splats using preform mandrels 2) tape cast sheets with gradient particle sizes and alloys that would be draped over a ceramic preform mandrel with selectively induced one-directional shrinkage (into the plane 3) fabricated thin sheets with sufficient plasticity after sintering to deform into the desired shapes using mandrels designed for the anticipated elastic springback. Commercial and Scientific Potential: In the future, these preformed absorber plates will provide a simple and inexpensive material for the construction of large scale particle detectors in nuclear, high energy and space physics experiments, and for shielding purposes. It may also find commercial applications in x-ray instrumentation, medical imaging, baggage and container inspection, and material analysis.