Engineering topics

Swanberg, Erik L.

Publications and source records attributed to Swanberg, Erik L..

5 records

DOE OSTI2018

Transparent Ceramic Garnet Gamma-Ray Spectrometer With Directionality

We have developed a handheld γ -ray spectrometer based on 1024 pixels, 2.8mm×2.8mm×6 mm in size, of gadolinium–yttrium–gallium–aluminum garnet (GYGAG) ((Gd,Y,Ce) 3 (Ga,Al) 5 O 12 ) ceramic scintillator (total of 48-cm 3 detector volume) coupled to silicon photodiode (SiPD) arrays. The SiPD arrays and readout ASIC, originally developed for medical imaging applications, have been adapted for portability in a lightweight box with heatsink and thermoelectric cooling. Custom readout firmware for γ-ray spectroscopy has been implemented, and a system user interface was developed that runs on an Android tablet. Here, we have optimized the processing of the GYGAG(Ce), the pixel optical coupling, and electronics readout parameters to obtain single pixel energy resolution as good as R(662keV)=3.1 % full-width at half-maximum and full device resolution with singles events from all pixels summed of 4.5%. When Compton-summed events are included, full-energy peak efficiency increases by ~2× , and R(662keV)=4.7 % is obtained for the full device. The pixelated architecture is leveraged to locate point sources of radiological materials using Compton imaging and active masking techniques. Directional detection of a 1 mCi Cs-137 source at 10 m can be made to ±10° in ~2 s.

42 ENGINEERING↗

DOE OSTI2017

History and current status of strontium iodide scintillators

Eu-doped strontium iodide single crystal growth has reached maturity and prototype SrI 2 (Eu)-based gamma ray spectrometers provide detection performance advantages over standard detectors. SrI 2 (Eu) offers a high, proportional light yield of >80,000 photons/MeV. Energy resolution of <3% at 662 keV with 1.5” x 1.5” SrI2(Eu) crystals is routinely achieved, by employing either a small taper at the top of the crystal or a digital readout technique. These methods overcome light-trapping, in which scintillation light is re-absorbed and re-emitted in Eu 2+ -doped crystals. As a result, its excellent energy resolution, lack of intrinsic radioactivity or toxicity, and commercial availability make SrI 2 (Eu) the ideal scintillator for use in handheld radioisotope identification devices. A 6-lb SrI 2 (Eu) radioisotope identifier is described.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Nonproportionality of Scintillator Detectors. V. Comparing the Gamma and Electron Response

This paper is the fifth in a series of articles on the basic physics of light yield nonproportionality in scintillators. Here, we compare and contrast the nonproportionality as registered by gamma rays and high-energy electrons. As has been noted in the past, these two types of data have different curve shapes (for plots of the light yield against electron or gamma energy). Herein, we show how the experimental gamma nonproportionality curve can be calculated from the electron response by accounting for the distribution of high energy electrons created by the gamma photon via the photoelectric interaction. Similarly, we measure and model the gamma-induced resolution as a function of energy and compare this data to predictions from our model. The utility of the model is explored using data acquired with the scintillators SrI 2 (Eu), GYGAG(Ce) and CsI(Na).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2015

Bismuth- and lithium-loaded plastic scintillators for gamma and neutron detection

In this paper, transparent plastic scintillators based on polyvinyltoluene (PVT) have been fabricated with high loading of bismuth carboxylates for gamma spectroscopy, and with lithium carboxylates for neutron detection. When activated with a combination of standard fluors, 2,5-diphenyloxazole (PPO) and tetraphenylbutadiene (TPB), gamma light yields with 15 wt% bismuth tripivalate of 5000 Ph/MeV are measured. A PVT plastic formulation including 30 wt% lithium pivalate and 30 wt% PPO offers both pulse shape discrimination, and a neutron capture peak at ~400 keVee. Finally, in another configuration, a bismuth-loaded PVT plastic is coated with ZnS( 6 Li) paint, permitting simultaneous gamma and neutron detection via pulse shape discrimination with a figure-of-merit of 3.8, while offering gamma spectroscopy with energy resolution of R(662 keV)=15%.

36 MATERIALS SCIENCE↗

DOE OSTI2013

DHS HS-STEM Internship Summary Report

I had the opportunity to work at Lawrence Livermore National Laboratory within the MEMS, Electronics, and Photonics Technologies group. I worked under the direct supervision of Dr. Adam Conway and Dr. Erik Swanberg on a semiconductor based gamma ray detector. My work involved automating the experimental setup and data analysis portion of the project to alleviate the researcher’s busy schedules. A semiconductor is a material that has conductivity in between a metal and ceramic. In layman’s terms, if you provide it with just enough energy, charge can flow inside of the material. If we impose some form of ionizing radiation such as a gamma ray, we can detect the amount of energy imparted on the system by measuring the amount of charge produced in the material. Figure 1 outlines the process that a semiconductor undergoes to allow us to detect ionizing radiation. Certain materials properties make them ideal for gamma ray detection such as the average atomic number, carrier properties, resistivity, and bandgap energy. I was working with Thallium Bromide (TlBr) detectors for room temperature detection of gamma rays, specifically looking at how different metal electrodes affected the stability of our system. My work involved automating the stress and voltage tests applied to the TlBr detectors and allowing for easy analysis of the data to determine if the system was still functional.

36 MATERIALS SCIENCE↗