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Experiment Title: Linear Energy Transfer Spectrum Measurement Experiment

Original Principal Investigator(s): Benton, Dr. Eugene V. - Invest. Role: Original, Benton, Dr. Eugene V. - Invest. Role: Present, Parnell, Dr. Thomas - Invest. Role: Original, Parnell, Dr. Thomas - Invest. Role: Present,

In the past a series of cosmic ray radiation dosimetry measurements - including charged particle measurements - have been undertaken. These measurements are usually performed on short term flights and with changing orientations of the spacecraft and detectors during the flights. The unique features of the LDEF mission, such as the very long duration time in space and the fixed gravity orientation, provided excellent opportunities for dosimetric experiments on LDEF. For example plastic nuclear track detectors (PNTDs) can measure the high LET-tail of the LET (linear energy transfer)-spectra with superior statistical accuracy and can determine the directional dependence of cosmic ray particles as well as of their secondaries.

The linear energy transfer (LET) is the energy deposited per unit path length of a charged particle traversing matter. For estimating the rate of damage from single-hit phenomena, the quantity that best combines the radiation environment, orbital situation, and spacecraft shielding is the linear energy transfer (LET) spectrum at the device location. To date, LET spectra measurements have been severely limited by statistics due to the short nature of STS missions. The designers of future long-life spacecraft such as the Space Station need LET spectra measurements for exposures of one year or more to establish shielding requirements and to select materials and devices that will not be adversely affected in space during the required operation life.

The LDEF mission provided a unique and unprecedented opportunity to gather data on the space radiation environment in low Earth orbit. The collection of more comprehensive experimental data and its detailed analyses is invaluable in addressing the numerous issues concerning the ionizing radiation environment in space and its impact on manned and unmanned space missions. The remarkably detailed investigation of the charged particle radiation environment of the LDEF satellite will lead to a better understanding of the radiation environment of the Space Station Freedom. It will enable more accurate predication of single event upsets (SEUs) in microelectronics and, especially, more accurate assessment of the risk - contribution by different components of the radiation field (GCRs, trapped protons, secondaries and heavy recoils, etc.) - to the health and safety of crew members. Cosmic ray and trapped charged particles contribute to the health risk of crew members of manned space flight and produce SEUs in microelectronics in space. Risk estimations are usually based on measurements of the charged particle radiation environment external to the spacecraft in space and using transport codes to calculate the radiation environment internal to the spacecraft. Measurements of the spacecraft radiation environment are also essential to validate transport codes based on three-dimensional mass models, and in some cases to provide direct data for risk estimation. PNTDs have been widely used to measure both external (charge and energy spectra of GCRs and trapped particles) and internal (LET spectra, charge and energy spectra of secondary particles) charged particle radiation environments.

Photograph Classification: Postflight

Associated Photograph(s):
LaRC - L91-01572
KSC - KSC-390C-1460.02
JSC - None
LaRC - L91-01553
KSC - KSC-390C-1465.03
JSC - None
LaRC - L84-07150
KSC - KSC-384C-299.05
JSC - None
LaRC - L90-10497
KSC - None
JSC - S32-89-023

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