George Gee

Radiation-induced charge collection in infrared detector arrays

A modeling approach is described for predicting charge collection in space-based infrared detector arrays due to ionizing particle radiation. The modeling uses a combination of analytical and Monte Carlo techniques to capture the essential features of energetic ion-induced charge collection to detector pixels in a two-dimensional array. The model addresses several aspects that are necessary for high-fidelity simulation of complex focal plane array structures including multiple layers, subregions within layers, variation of linear energy transfer with range, secondary electron scattering, free-field diffusion, and field-assisted diffusion. Example results are given and predictions are compared to experimental data.

First observation of proton induced power MOSFET burnout in space: the CRUX experiment on APEX

Ground testing has shown that power MOSFETs are susceptible to burnout when irradiated with heavy ions and protons. Satellite data from the Cosmic Ray Upset Experiment (CRUX) demonstrate that single event burnouts (SEBs) on 100-volt and 200-volt power MOSFETs can and do occur in space. Few SEBs occurred on the 100-volt devices, all at L/sup 1/>3. The 200-volt devices experienced many SEBs at L<3 when drain-to-source voltage (V/sub D-S/) was greater than 85% of maximum rated voltage. CRUX flight lot devices were ground tested with protons. The SEB rates calculated with the cross-sections from the ground tests show close agreement with the measured rates.

In-flight observations of long-term single-event effect (SEE) performance on Orbview-2 solid state recorders (SSR)

We present multi-layer single event upset (SEU) flight data on solid state recorder (SSR) memories for the NASA Orbview-2 mission. Actual SEU rates are compared to the predicted rates based on ground test data and environment models.

Proton-induced transients and charge collection measurements in a LWIR HgCdTe focal plane array

We compare measurements and modeling of 27 and 63 MeV proton-induced transients in a large-format HgCdTe long wavelength infrared (LWIR) focal plane assembly operating at 40 K. Charge collection measurements describe very limited diffusion of carriers to multiple pixels showing significantly reduced particle induced cross-talk for the lateral diffusion structure.

Radiation-induced transient effects in HgCdTe IR focal plane arrays

The operability requirements of NASAs James Webb Space Telescope (JWST) impose specific challenges on radiation effects mitigation and analysis. For example, the NIRSpec Instrument has the following requirements: •The percentage of pixels defined as operable for target acquisition shall not be less than 97% (TBR) (goal 99%) of the total number of pixels... An inoperable pixel is: ο A dead pixel: a pixel with no radiometric response o A noisy pixel: a pixel with a total noise greater than 21 e-, per Fowler 8 exposure •The percentage of pixels defined as operable for science observations shall not be less than 92% (TBR) (goal 98%) of the total number of pixels... An inoperable pixel is: ο A dead/low-DQE pixel: a pixel deviating by >30% from the DQE mean value ο A noisy pixel: a pixel with a total noise greater than 12 e- (goal 9e-). With these performance requirements and operation in space, the radiation environment from galactic cosmic rays (GCR), energetic solar particles, and activation of spacecraft materials can contribute significantly to the number of inoperable pixels. The two most important issues to date are radiation-induced transient effects and hot pixels. This paper focuses on the methods used to assess the impact of ionizing radiation induced transients on the HgCdTe SCA selected by JWST. Hot pixel effects in these detectors has been previously presented. Both effects are currently under investigation.

Characteristics of the Hubble Space Telescope's radiation environment inferred from charge-collection modeling of Near-Infrared Camera and Multi-Object Spectrometer dark frames

Dark frames from orbiting infrared detector arrays are analyzed using a charge-collection model to investigate the effects of secondary and primary particle environments in infrared detectors and related electronics. The effects of different components of the primary and secondary environments are assessed by examining trends with time and pixel-to-pixel charge correlations.

Proton-induced secondary particle environment for infrared sensor applications

We present measurements of the proton-induced secondary particle environment in the vicinity of an infrared focal plane array. Measurements were made of the energy depositions from secondary electrons and scattered protons from the interior of a cryogenic test dewar using an infrared detector array. The results are compared with model predictions and analyzed for implications to space-based infrared sensors.

In-flight observations of long-term single event effect (SEE) performance on X-ray Timing Explorer (XTE) solid-state recorders (SSRs) [SRAM]

We present multi-year single event upset (SEU) flight data on solid state recorder (SSR) memories for the X-ray Timing Explorer (XTE) NASA mission. Actual SEU rates are compared to the predicted rates, based on ground test data and environment models.