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PUMA vs. 3He
Comparison of PUMA Neutron Glass Versus 3He/BF3 Tubes


No single detector technology is ideal for all applications. However, specific detector technologies may out perform or provide inherent benefits to a given application. 

The PUMA fibers offer some unique features that are described here.


FEATURE Neutron Glass 3He/BF3
Solid State Technology Yes No
Spatial Resolution 0.1 mm 6.5 mm
Microphonic Susceptibility Low High
Thickness to capture 50% of neutrons 0.6 mm 12.1 mm
Gamma Sensitivity 1:1000 1:10000


There are several important advantages of scintillating glass fiber neutron sensors compared to conventional pressurized 3He gas tube detectors.  There are more moles of 6Li in the glass than 3He in a gas tube. In addition, the glass spatially distributes these atoms more efficiently.  This results in larger active areas of neutron detection with higher sensitivity at lower cost. The 6Li is difficult to separate from the glass matrix while 3He can be easily extracted from a gas tube and then purified to enhance the yield of a nuclear device in concentrated forms.  As a result, the glass fibers pose a low and acceptable nuclear proliferation risk.


The solid state nature of the glass fiber technology is inherently safer.  There are no explosive hazards with glass fiber, as there is with a pressurized tube of gas ranging from 3 to 20 atmospheres of pressure.  As there is no transport hazards, glass fiber systems can be shipped on commercial carriers as regular cargo.  Portable glass fiber systems can be transported as passenger luggage. Glass fibers are also less sensitive to vibration and other microphonic sources so it may be used while being moved in mobile and aerial measurement systems or when it is operated in industrial environments.

 

The glass fibers also have higher gamma sensitivity than a gas tube because of the higher effective atomic number of a silicate glass.  This feature can be viewed as either an advantage or disadvantage depending upon the application. Although the standard PUMA neutron sensitive glass fiber panel size is 2500 cm2, arrays of panels can be implemented with a single electronic pulse-processing box.  Currently, up to fifteen panels can be arrayed with a single processor, but larger arrays are possible. This aggregating of active detector areas is not possible with gas tube detectors.

 

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