Celeste Winant

Directional Neutron Detection Using a Time Projection Chamber

Measurement of the three dimensional trajectory and specific ionization of recoil protons using a hydrogen gas time projection chamber provides directional information about incident fast neutrons. Here we demonstrate directional fast neutron detection using such a device. The wide field of view and excellent gamma rejection that are obtained suggest that this device is well suited to searches for special nuclear materials, among other applications.

Analysis of dynamic SPECT/CT measurements of the arterial input function in human subjects

Measurement of the arterial input function (AIF) is essential to deriving quantitative estimates of regional myocardial blood flow using kinetic models. Accurate measurements have been possible with a wide range of radiotracers in both research and clinical PET/CT imaging. However, accurate measurements of the AIF with dynamic SPECT or SPECT/CT have posed various challenges; foremost being that imaging a rapidly evolving radiotracer distribution with a slowly-rotating single- or dual-head SPECT scanner yields temporally inconsistent projection data. A method is developed for quantifying the AIF in human subjects from dynamic SPECT/CT measurements of 99mTc-tetrofosmin concentration in the left atrium imaged with a Philips Precedence SPECT/CT scanner. A 2-minute infusion is imaged in a series of eight back-to-back 180-degree continuous-mode acquisitions (or rotations), with the dual camera heads. In each acquisition a set of 36 projections (128 × 128 pixels of dimension 3.19 mm × 3.19 mm) is acquired in each rotation each over a time span of 54 seconds yielding a total acquisition time of 432 seconds. The AIF is computed using both traditional image-based analysis and full spatiotemporal image reconstruction methods (referred to as 4D recon). The errors induced by data inconsistency are evaluated by two approaches. The first method derives SPECT-like dynamic (inconsistent) projection data from selected forward projections, chosen from modeled SPECT acquisitions, of existing dynamic 94Tc-MIBI PET images. The second validation method uses a database of SPECT measurements of an anthropomorphic phantom to generate SPECT-like projections. The first validation study using a two minute infusion showed very little bias in the time-activity curves estimated from the simulated dynamic cardiac SPECT patient study; whereas, the second validation study using a one minute infusion showed considerable more bias in the estimated time-activity curves and parametric parameters. We believe that this is the result of selecting non optimum basis functions.

Dual-phase argon ionization detector for measurement of coherent elastic neutrino scattering and medium-energy nuclear recoils

We propose to build and deploy a 10-kg dual-phase argon ionization detector for the detection of coherent neutrino- nucleus scattering, which is described by the reaction; nu + (Z,N) rarr nu + (Z,N), where v is the scattering neutrino, and (Z,N) is the target nucleus of atomic number Z and neutron number N. Its detection would validate central tenets of the standard model. We have built a gas-phase argon ionization detector to determine the feasibility of measuring the small recoil energies (~ 1 keV) predicted from coherent neutrino scattering, and to characterize the recoil spectrum of the argon nuclei induced by scattering from medium-energy neutrons. We present calibrations made with 55Fe, a low-energy X-ray source, and report on measurements to date of the recoil spectra from the 2-MeV LINAC Li-target neutron source at LLNL. A high signal-to-noise measurement of the recoil spectrum will not only serve as an important milestone in achieving the sensitivity necessary for measuring coherent neutrino-nucleus scattering, but will break new scientific ground on its own.