Engineering topics

Watts, J. W., Jr.

Publications and source records attributed to Watts, J. W., Jr..

At least 19 records

NASA NTRS1995

Linear Energy Transfer (LET) spectra of cosmic radiation in low Earth orbit

Integral linear energy transfer (LET) spectra of cosmic radiation (CR) particles were measured on five Cosmos series spacecraft in low Earth orbit (LEO). Particular emphasis is placed on results of the Cosmos 1887 biosatellite which carried a set of joint U.S.S.R.-U.S.A. radiation experiments involving passive detectors that included thermoluminescent detectors (TLD's), plastic nuclear track detectors (PNTD's), fission foils, nuclear photo-emulsions, etc. which were located both inside and outside the spacecraft. Measured LET spectra are compared with those theoretically calculated. Results show that there is some dependence of LET spectra on orbital parameters. The results are used to estimate the CR quality factor (QF) for the COSMOS 1887 mission.

Parnell, T. A.↗

NASA NTRS1995

Depth distribution of absorbed dose on the external surface of Cosmos 1887 biosatellite

Significant absorbed dose levels exceeding 1.0 Gy day(exp -1) have been measured on the external surface of the Cosmos 1887 biosatellite as functions of depth in stacks of thin thermoluminescent detectors (TLD's) made in U.S.S.R. and U.S.A. The dose was found to decrease rapidly with increasing absorber thickness, thereby indicating the presence of intensive fluxes of low-energy particles. Comparison between the U.S.S.R. and U.S.A. results and calculations based on the Vette Model environment are in satisfactory agreement. The major contribution to the dose under thin shielding thickness is shown to be from electrons. The fraction of the dose due to protons and heavier charged particles increases with shielding thickness.

Watts, J. W., Jr.↗

NASA NTRS1995

Experimental and calculated LET distributions in the Cosmos-2044 biosatellite orbit

During the flight of the Cosmos-2044 biosatellite, joint U.S.S.R.-U.S.A. investigations of different characteristics of cosmic radiation (CR) in the near-Earth environment were carried out. The U.S. dielectric track detectors CR-39 and Soviet BYa- and BR-type nuclear photo-emulsions were used as detectors. The present work shows some results of experimental measurements of linear energy transfer (LET) spectra of CR particles obtained with the use of these detectors, which were placed both inside and outside the satellite. The LET spectra measurements with plastic detectors is composed of two parts: the measurement of galactic cosmos rays (GCR) particles, and of short-range particles. The contributions of these components to the total LET distribution at various thicknesses of the shielding were analyzed and the results of these studies are presented. Calculated LET spectra in the Cosmos-2044 orbit were compared with experimental data. On the basis of experimental and calculated values of the LET spectra, absorbed and equivalent CR doses were calculated. In the shielding range of 1-1.5 g cm(exp -2), outside the spacecraft, the photo-emulsions yielded 10.3 mrad d(exp -1) and 13.4 mrem d(exp -1) (LET greater than or equal to 40 MeV cm(exp -1)). Inside the spacecraft (greater than or equal to 10 g cm(exp -2) the photo-emulsions yielded 8.9 mrad d(exp -1) and 14.5 mrem d(exp -1).

Watts, J. W., Jr.↗

NASA NTRS1995

Cosmic ray LET spectra and doses on board Cosmos-2044 biosatellite

Results of the experiments on board Cosmos-2044 (Biosatellite 9) are presented. Various nuclear track detectors (NTD) (dielectric, AgCl-based, nuclear emulsions) were used to obtain the Linear Energy Transfer (LET) spectra inside and outside the satellite. The spectra from the different NTDs have proved to be in general agreement. The results of LET spectra calculations using two different models are also presented. The resultant LET distributions are used to calculate the absorbed and equivalent doses and the orbit-averaged quality factors (QF) of the cosmic rays (CR). Absorbed dose rates inside (approximately 20 g cm (exp -2) shielding) and outside (1 g cm(exp -2) the spacecraft, omitting electrons, were found to be 4.8 and 8.6 mrad d (exp -1), respectively, while the corresponding equivalent doses were 8.8 and 19.7 mrem d(exp -1). The effects of the flight parameters on the total fluence of, and on the dose from the CR particles are analyzed. Integral dose distributions of the detected particles are also determined. The LET values which separate absorbed and equivalent doses into 50% intervals are estimated. The CR-39 dielectric NTD is shown to detect 20-30% of the absorbed dose and 60-70% of the equivalent dose in the Cosmos-2044 orbit. The influence of solar activity phase on the magnitude of CR flux is discussed.

Watts, J. W., Jr.↗

NASA NTRS1994

Comparison of model predictions with LDEF satellite radiation measurements

Some early results are summarized from a program under way to utilize Long Duration Exposure Facility (LDEF) satellite data for evaluating and improving current models of the space radiation environment in low Earth orbit. Reported here are predictions and comparisons with some of the LDEF dose and induced radioactivity data, which are used to check the accuracy of current models describing the magnitude and directionality of the trapped proton environment. Preliminary findings are that the environment models underestimate both dose and activation from trapped protons by a factor of about two, and the observed anisotropy is higher than predicted.

Armstrong, T. W.↗

NASA NTRS1993

LET spectra measurements of charged particles in the P0006 experiment on LDEF

Measurements are under way of the charged particle radiation environment of the Long Duration Exposure Facility (LDEF) satellite using stacks of plastic nuclear track detectors (PNTD's) placed in different locations of the satellite. In the initial work the charge, energy, and linear energy transfer (LET) spectra of charged particles were measured with CR-39 double layer PNTD's located on the west side of the satellite (Experiment P0006). Primary and secondary stopping heavy ions were measured separately from the more energetic particles. Both trapped and galactic cosmic ray (GCR) particles are included, with the latter component being dominated by relativistic iron particles. The results from the P0006 experiment will be compared with similar measurements in other locations on LDEF with different orientation and shielding conditions. 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 prediction of single event upsets (SEU's) in microelectronics and, especially, more accurate assessment of the risk - contributed by different components of the radiation field (GCR's, trapped protons, secondaries and heavy recoils, etc.) - to the health and safety of crew members.

Benton, E. V.↗

NASA NTRS1993

Three-dimensional shielding effects on charged particle fluences measured in the P0006 experiment of LDEF

Three-dimensional shielding effects on cosmic ray charged particle fluences were measured with plastic nuclear track detectors in the P0006 experiment on Long Duration Exposure Facility (LDEF). The azimuthal and polar angle distributions of the galactic cosmic ray particles (mostly relativistic iron) were measured in the main stack and in four side stacks of the P0006 experiment, located on the west end of the LDEF satellite. A shadowing effect of the shielding of the LDEF satellite is found. Total fluence of stopping protons was measured as a function of the position in the main and side stacks of the P0006 experiment. Location dependence of total track density is explained by the three-dimensional shielding model of the P0006 stack. These results can be used to validate 3D mass model and transport code calculations and also for predictions of the outer radiation environment for the Space Station Freedom.

Csige, I.↗

NASA NTRS1992

Revised predictions of LDEF exposure to trapped protons

Initial estimates of LDEF exposure to the trapped proton environment were reported previously to aid in the interpretation dosimetry data and in conjunction with dosimetry response predictions. These previous estimates were made using the standard NASA AP8 trapped proton models for two sets of assumed conditions: (1) the omnidirectional flux spectra were calculated with the LDEF altitude and solar activity variations taken into account; and (2) the NASA Marshall anisotropy model was applied to obtain directional spectra, but only for solar minimum conditions and at a single altitude. Herein, the directional trapped proton fluence spectra is calculated considering both the altitude variation and solar activity during the LDEF mission. These additional results represent an extension of previous calculations to provide a more definitive description of the LDEF trapped proton exposure.

Watts, J. W., Jr.↗

NASA NTRS1992

Charge, energy, and LET spectra measurements of charged particles in P0006 experiment of LDEF

Measurements are under way of the charged particle radiation environment of the LDEF satellite using stacks of plastic nuclear track detectors (PNTDs) placed in different locations of the satellite. In the initial work, the charge, energy, and linear energy transfer (LET) spectra of charged particles were measured with CR-39 double layer PNTDs located on the west end of the satellite. Primary and secondary stopping heavy ions as well as relativistic galactic cosmic rays (mostly iron particles) were measured separately. The results will be compared with similar measurements in other locations on LDEF with different orientation and shielding conditions. The remarkably detailed study 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 prediction of single event upsets (SEUs) in microelectronics and, especially, more accurate assessment of the risk, contributed by the different components of the radiation field to the health and safety of crew members.

Benton, E. V.↗

NASA NTRS1992

Three-dimensional shielding effects on charged particle fluences measured in the P0006 experiment in LDEF

The azimuthal and polar angle distribution of the galactic cosmic ray particles (mostly relativistic iron) was measured in the main stack and four side stacks of the P0006 experiment located on the west end of the LDEF satellite. A clear shadowing effect of the radiation shielding of the LDEF satellite is found. The total fluence of stopping protons (mostly primary, trapped particles) was measured as a function of the position in the main and side stacks of the P0006 experiment. Experimental results are compared with theoretical calculations and the effect of the strong location dependence of particle fluences is explained by the three dimensional shielding model of the P0006 stack. Through comparisons between experimental results and calculations, this work will lead to the refinement of the radiation environment computational models.

Csige, I.↗

NASA NTRS1992

Radiation exposure of LDEF: Initial results

Initial results from LDEF include radiation detector measurements from four experiments, P0006, P0004, M0004, and A0015. The detectors were located on both the leading and trailing edges of the orbiter and also on the Earthside end. This allowed the directional dependence of the incoming radiation to be measured. Total absorbed doses from thermoluminescent detectors (TLDs) verified the predicted spatial east-west dose ratio dependence of a factor approx. 2.5, due to trapped proton anisotropy in the South Atlantic Anomaly. On the trailing edge of the orbiter a range of doses from 6.64 to 2.91 Gy were measured under Al equivalent shielding of 0.42 to 1.11 g/sq cm. A second set of detectors near this location yielded doses of 6.48 to 2.66 Gy under Al equivalent shielding of 0.48 to 15.4 g/sq cm. On the leading edge, doses of 2.58 to 2.10 Gy were found under Al equivalent shielding of 1.37 to 2.90 g/sq cm. Initial charged particle LET (linear energy transfer) spectra, fluxes, doses and dose equivalents, for LET in H2O greater than or = 8 keV/micron, were measured with plastic nuclear track detectors (PNTDs) located in two experiments. Also preliminary data on low energy neutrons were obtained from detectors containing (6)LiF foils.

Benton, E. V.↗

NASA NTRS1992

Charged particle LET-spectra measurements aboard LDEF

The linear energy transfer (LET) spectra of charged particles was measured in the 5 to 250 keV/micron (water) interval with CR-39 and in the 500 to 1500 keV/micron (water) interval with polycarbonate plastic nuclear track detectors (PNTDs) under different shielding depths in the P0006 experiment. The optimal processing conditions were determined for both PNTDs in relation to the relatively high track densities due to the long term exposure in space. The total track density was measured over the selected samples, and tracks in coincidence on the facing surfaces of two detector sheets were selected for measuring at the same position on each sheet. The short range (SR) and Galactic Cosmic Ray (GCR) components were measured separately with CR-39 PNTDs and the integral dose and dose rate spectra of charged particles were also determined. The high LET portion of the LET spectra was measured with polycarbonate PNTDs with high statistical accuracy. This is a unique result of this exposure due to the low flux of these types of particles for typical spaceflight durations. The directional dependence of the charged particles at the position of the P0006 experiment was also studied by four small side stacks which surrounded the main stack and by analyzing the dip angle and polar angle distributions of the measured SR and GCR particle tracks in the main stack.

Csige, I.↗

NASA NTRS1992

Ionizing radiation calculations and comparisons with LDEF data

In conjunction with the analysis of LDEF ionizing radiation dosimetry data, a calculational program is in progress to aid in data interpretation and to assess the accuracy of current radiation models for future mission applications. To estimate the ionizing radiation environment at the LDEF dosimeter locations, scoping calculations for a simplified (one dimensional) LDEF mass model were made of the primary and secondary radiations produced as a function of shielding thickness due to trapped proton, galactic proton, and atmospheric (neutron and proton cosmic ray albedo) exposures. Preliminary comparisons of predictions with LDEF induced radioactivity and dose measurements were made to test a recently developed model of trapped proton anisotropy.

Armstrong, T. W.↗

NASA NTRS1986

The measured radiation environment within Spacelabs 1 and 2 and comparison with predictions

A set of passive and active radiation detectors was flown as part of the verification flight instrumentation (VFI) in an attempt to measure the radiation environment in the Spacelab (SL) module and on the pallet. SL 1 carried 4 passive and 2 active detector packages which were used to evaluate the radiation environment within the spacecraft and SL 2 carried 2 passive VFI units on the pallet. Dose equivalents of 330 + or - 70 mrem and 537 + or - 37 mrem were measured in the SL 1 module and SL 2 pallet, respectively.

Parnell, T. A.↗

NASA NTRS1985

Radiation environment of Spacelab-1

The results of passive and active radiation measurements on Spacelab-1 are reported. Spacelab-1 was flown on the STS-9 mission, orbited at an altitude of 241 km, with an inclination of 57 deg and 240 hours of flight time. Approximately thirty passive detectors deployed inside the module, in the access tunnel, and outside on the pallet made possible the radiation measurements. The various forms of radiation measured were a low linear energy transfer component ranging from 94 to 133 mrads inside the module (average dose rate of 10.0 mrads/day; about twice the rate of earlier shuttle flights), an average mission dose-equivalent rate of about 18.5 mrem/day (six times higher than earlier flights), accumulated doses of 125 and 128 mrads and a yield of 17 and 12 mrads for passages through the South Atlantic Anomaly. Spacelab-1, because of its low altitude and short duration, was relatively benign in terms of total radiation dose. Some of the measurements such as high-LET particles and neutrons have biological significance and potential effects on future experiments.

Benton, E. V.↗

NASA NTRS1984

Effect of the Mott cross section on charge identification in the HEAO-3 Heavy Cosmic Ray Experiment

Corrections to the Z-squared dependence of ion chamber and Cherenkov response due to the Mott cross section are calculated for the HEAO-3 Heavy Cosmic Ray Experiment. The effect of the production and escape of high energy secondary electrons on detector response is accounted for by numerical calculations. These secondary electron effects are shown to influence the size of the non Z-squared effects and thus affect the charge assignments and detector resolution. The Bloch and relativistic Bloch corrections are not included in the results presented here but may be combined with the Mott corrections when the Bloch corrections are properly evaluated.

Derrickson, J. H.↗

NASA NTRS1978

New limits on gamma-ray bursts

Two balloon flights of large-area scintillation crystal detector arrays indicate that the rate of weak gamma-ray bursts is significantly below that expected from a uniform distribution of burst sources. This result, combined with the data from stronger bursts, gives strong evidence for a galactic confinement of burst sources. Reasonable models of confinement limit the intrinsic radiated energy per burst to the order of 10 to the (39th to 41st power) ergs.

Fishman, G. J.↗

NASA NTRS1977

The hard X-ray pulse profile of the transient source A0535+26

Measurements of the 104 sec pulse profile of A0535+26 at energies near 50 keV are reported. The data were obtained with a balloon-borne detector system which was launched on May 22, 1975 with the objective to observe transient or periodic emissions from X-ray or gamma-ray sources. The presence of the source was detected by a superposed epoch analysis. The pulse profile of A0535+26 in two energy channels is presented in a graph.

Fishman, G. J.↗