SNL Marleau

Peter Marleau

Peter is a physicist with a degree from the University of California, Davis in experimental high energy particle physics (Ph.D., 2007).  He has been with the Radiation and Nuclear Detection Systems department at Sandia National Laboratories for over 8 years where he has been actively involved with the several fast neutron imaging projects where he has led data analysis, development of image processing tools, Monte Carlo detector modeling, and performance characterization.  More recently he has been the Principle Investigator leading R&D on projects ranging from fast neutron and gamma imaging using time modulation to the characterization of fissile material using fast neutron/ gamma-ray time-energy correlations to high energy (10-500 MeV) neutron spectrometers for underground background characterization.

Possible Projects:

  1. Zero Knowledge Protocol and/or information transparent techniques applied to passive fast neutron imaging: I would like to explore the implementation of a template matching scheme in the same vein as those illustrated in the recent Nature paper on the Zero Knowledge Protocol as applied to passive neutron/gamma-ray imaging.  There are several Sandia led advancements that may lend themselves well to this investigation:
    1. The jointly developed ORNL/SNL neutron coded aperture imager could be used to make real world measurements. The scintillator based detection plane still retains a digital acquisition system which does not provide information transparency, but practical issues such as the effect of room return, cross-talk, imprecision in dwell time, and object/detector misalignment can be evaluated.  The neutron coded aperture imaging project is currently funded which could be used to augment an internship.
    2. Sandia has developed a method of two dimensional passive imaging that works by modulating the signal in a single detector pixel as a function of time. Time-encoded imaging provides a greatly simplified context to explore zero knowledge scenarios.  For instance, the timing and/or angular orientations could be scrambled or removed while leaving enough information to achieve confirmation.
    3. Exploration of analog techniques toward image recording. Because coded aperture (and radiographic) imaging relies on the gross integral of a measurement rather than event by event processing, it could lend itself to analog integration techniques that maintain the advantage of remaining free of digital computation and thus information transparent while relying on well understood and reliable techniques.
  2. Electronic Collimation: Sandia National Laboratories has extensive experience in directional and imaging detector systems.  One of the central advantages of directionality is the ability to estimate and reject backgrounds without a reference measurement.  In this research, we would model, design, and evaluate a simple directional system based on kinematic reconstruction of coincident events in two scintillator volumes.  This “electronic collimation” could be used as a simple directional item monitor.  Because the simplicity of design, most if not all of the hardware components already exist in our laboratory.  Design, implementation, and evaluation are remaining tasks.
  3. Capture gated fast neutron spectrometry: In this instrument focused project, I propose to use an existing detector, The Multiplicity and Recoil Spectrometer (MARS), in an innovative new way.  MARS has been designed to measure the neutron energy spectrum from ~50-500 MeV by multiplying neutrons using (n, kn) reactions in a large mass of lead.  In this mode, the number of low energy neutrons that spill out of the lead are proportional to the incident neutron energy.  These neutrons are detected by two large (100cm x 70cm x 22cm) plastic scintillator detectors that are infused with layers of gadolinium. 
    In the proposed work, these same detectors will be used as a capture gated spectrometer.  In this mode incident fast neutrons with lower energies (>4 MeV) will recoil in the detectors until all of their energy is lost and then capture on the gadolinium.  A large deposition of energy followed by the Gd capture energy after a characteristic thermalization time is an indication that full energy has been deposited. 
    MARS has been constructed and deployed to the Kimballton Underground Research Facility (KURF) near Virginia Tech in Blacksburg Virginia where it has measured the neutron background at three different depths (380 m.w.e, 600 m.w.e, and 1450 m.w.e) over the last 18 months.  The multiplicity signature is currently being unfolded to reconstruct the flux >50 MeV.  I propose that it would be a great project to unfold the capture gated events to reconstruct energies greater than 4-8 MeV with overlap to the first measurement.  This will make a very nice compliment to the existing work and will help to estimate systematic uncertainties.