Kiwhan Chung

Large area neutron detector based on /sup 6/Li ionization chamber with integrated body-moderator of high density polyethylene

We describe the development of a large area neutron detector based on a pulse-mode ionization chamber lined with /sup 6/Li foil in a low-cost housing of HDPE (high density polyethylene) that serves as the moderator. The use of inexpensive materials, technology for mass production and simple construction, which integrates the basic components of the sensor together, results in a substantial cost reduction. For a given sensor size, detection efficiency, or counting time, the proposed detector is expected to provide an order-of magnitude cost reduction compared to current neutron detection technology. This paper describes the detection concept including the optimization of the design using neutron transport calculations. It also gives experimental results on some prototype units using neutron and gamma sources. The properties affecting long term counting stability are discussed. An approach to reduce the effect of outgassing from the HDPE body is suggested.

A range muon tomography performance study

Soft cosmic ray tomography has been shown to successfully discriminate materials with various density levels due to their ability to deeply penetrate matter, allowing sensitivity to atomic number, radiation length and density. Because the multiple muon scattering signal from high Z-materials is very strong, the technology is well suited to the detection of the illicit transportation of special and radiololgical nuclear materials. In addition, a recent detection technique based on measuring the lower energy particles that do not traverse the material (range radiography), allows to discriminate low and medium Z-materials. We have demonstrated it first using Monte Carlo simulations. More recently, using a Mini-Muon Tracker developed at Los Alamos National Laboratory, we performed various experiments to try out the radiation length technology. This paper presents the results from real experiments and evaluates the likelihood that soft cosmic ray tomography may be applied to detect high-explosives.