A Review of Aerial Radiological Surveys of Nevada Test Site Fallout Fields 1951 Through 1970

Page 1

A REVIEW OF AERIAL RADIOLOGICAL SURVEYS OF NEVADA TEST SITE FALLOUT FIELDS UNITED STATES DEPARTMENT OF ENERGY NEVADA OPERATIONS OFFICE

Page 2

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or' implied, or assumes any legal liability or responsibilityfortheaccuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Printed in the United States of America. National Technical. Information Service U.S. Department of Commerce 5285 Port Royal Road NTIS price codes

Page 3

A REVIEW OF AERIAL RADIOLOGICAL SURVEYS OF NEVADA TEST SITE FALLOUT FIELDS EG&G Energy Measurements, Inc. Las Vegas, Nevada This Document is UNCLASSIFIED This work was performed by EG&G Energy Measurements, Inc. for the United States Department of Energy under Contract Number DE-AC08-83NV1 0282.

Page 4

Aerial surveys of offsite fallout radiation fields from the Nevada Test Site began in the early 1950s and continued throughout the above-ground testing period. The results of the aerial surveys were used to support ground data in determining the extent of the fallout patterns. For the series of tests conducted in 1953 and 1955, the primary uncertainty of the results was knowing the location of the aircraft. Navigation was made from aeronautical charts of a scale 1:1,000,000, and errors in location of several miles were experienced. Another problem was that exposure rate readings made in the aircraft of 1 milliroentgen per hour or lower were not reliable. Exposure rate measurements above 1 milliroentgen per hour were more accurate, however, and are considered reliable to within a factor of two or three in predicting 3-foot exposure rate levels. For the 1957 series, the aircraft position data were quite accurate. Ground-level exposure rates predicted from aerial data obtained by the United States Geological Survey aircraft for the five-detector array were considered reliable to within ±40% or better for most of the surveys. When the single detector was used, the accuracy decreased to about a factor of two. Relative count rates obtained by the aircraft operated by the Atomic Energy Commission, Raw Materials Division, are probably valid, but quantitative determinations of 3-foot exposure rates are not. The Aerial Radiological Monitoring System performed all the aerial surveys in the 1960s. However, the air-to-ground conversion factors used were too low. Using a corrected conversion factor, the predicted 3-foot exposure rates should be valid to +40% in most fallout fields if all other parameters are considered.

Page 5

A review was made of the literature and records available at the United States Department of Energy's Coordination and Information Center in Las Vegas, Nevada, pertaining to aerial surveys of terrain radiation produced by the Nevada Test Site fallout fields during the period 1951 through 1970. Categories of reports reviewed were under the agency listings of: WT, NYO, USGS, EG&G, Inc. and UCRL. Approximately 100 documents were reviewed. Although extensive, this review was not comprehensive. Not all documents referring or relating to aerial surveys were reviewed and not all individual data points were examined. However, a sufficient review of documents and data was made to fulfill the purpose of this report, which is to evaluate the usefulness of the results in light of today's aerial survey technology. In addition, the review considered possible errors and uncertainties in the original data, as well as how the results were used in developing the fallout patterns. Finally, recommendations are given on how best to use the results today in evaluating or reassessing the original fallout patterns.

Page 6

2. DEVELOPMENT OF AERIAL MEASUREMENT SYSTEMS .........................3 3. UNCERTAINTIES IN AERIAL MEASUREMENTS .............................. . Locality of Source .......................................... 10 3.2.5 Air Temperature and Pressure .................................. . 3.2.6 Ground Roughness and Terrain Features .......................... . Crystal Sensitivity Ratios From USGS PLUMBBOB Measurements .......... . 5. REVIEW OF HISTORICAL DATA ......................................... 34

Page 7

5.3 Small Boy Event (1962) ............................................ 46 6. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS ......................... 49 6.4 1958- Operation HARDTACK II ....................................... 50

Page 8

1 1:1,000,000 Scale Aeronautical Chart 9 2 Sensitivity of Equipment as a Function of Energy ............................. 13 3 Variation of Radiation From a Broad Source vs Height .......................... 13 4 Relative Air-to-Ground Correlation vs Fission Fallout Age for Sodium Iodide Crystal Detectors ............................................. 13 7 Section of Strip Chart for the Smoky Test .................................. 15 8 Altitude Curves with Various Discriminator Settings Taken Above a Flat Mesa Containing Natural Ground Radioactivity .............................. 17 9 Relationship of Theoretical and Observed Count Rates ......................... 18 10 Strip Chart Results for the Five-Crystal Array for Operation PLUMBBOB 20 11 Correlation Curve for Readings Taken Over Ground Zero 17 Days After 12 Altitude Correlation Factors (1955) for Interpreting Aerial Survey Radiation Rates as Ground-Level Radiation Rates for Light Aircraft Flying at Minimum 13 Strip Chart Results for the Single Crystal for the Smoky Test ..................... 25 14 Normalized Exposure Rates Above Infinite Smooth Planes of Fission Products 15 Illustration of Limitations in Detecting Surface Contamination Due to 17 Aerial Survey Data Overlaid on Fallout Pattern-Badger D+1 Day ................... 35 18 Aerial Survey Data Overlaid on Fallout Pattern-Simon D Day ..................... 37 19 Aerial Survey Data Overlaid on Fallout Pattern-Simon D+1 Day ................... 37 20 Aerial Survey Data Overlaid on Fallout Pattern-Annie .......................... 38 22 Aerial Survey Data Overlaid on Fallout Pattern-Nancy .......................... 39

Page 9

23 Aerial Survey Data Overlaid on Original Fallout Pattern-Harry D Day 24 Aerial Survey Data Overlaid on Original Fallout Pattern-Harry D+1 Day 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 40 25 Aerial Survey Data, D+1, Shot Boltzmann, Arc Ill 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 42 26 Aerial Survey Data, D+1, Shot Boltzmann, Arc IV 44 27 Aerial Survey Data, D+3 and D+4, Shot Smoky, Northern Utah and Colorado 0 0 0 0 0 0 0 0 0 0 0 0 45 28 Aerial Survey Data, D+4, Shot Smoky, Southern Wyoming 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 47 29 Fallout Pattern in Fruitland Area, Small Boy Test 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 48 30 Revised Fallout Pattern in Fruitland Area, Small Boy Test (Revised 1984) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 48 1 Aerial Radiological Surveys of Fallout Fields 2 Uncertainties Associated with Aerial Survey Results 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 3 Coordinate System Used in Rad-Safe Operations 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 10 5 Comparison of Nai(T.£) Detector Sensitivities and Predicted Conversion Factors for Fission Products 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 30 6 ARMS II Conversion Factor Considerations 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 33

Page 10

Aerial radiological surveys were performed as early as 1948 in the United States when the United States Geological Survey (USGS) began using this technique to search for uranium deposits.1 At about this same time, the Canadians also began developing an aerial prospecting technique, and the United States Air Force began testing radiological instruments in aircraft for The first functional detector system used for prospecting contained an array of 19 Geiger tubes. Later, sodium iodide crystals replaced the Geiger tubes in the detector systems.1 During the 1950s and early 1960s, development efforts were directed toward four separate 1. Prospecting-development of very sensitive detectors and survey techniques for searching for uranium deposits. 2. Civil Defense-development of detectors and survey techniques for quickly assessing the extent of fallout distribution in the event of nuclear war. 3. Military application-development of aerial survey techniques generally confined to locations very close-in to a nuclear detonation. 4. Background monitoring-development of the Aerial Radiological Measuring System (ARMS) for background radiation surveys as part of an emergency response capability. No separate effort appears to have been made to develop aerial techniques for assessing the fallout radiation generated by nuclear tests at the Nevada Test Site (NTS). Techniques developed for the four missions listed above were simply applied, as appropriate, to the fallout assessment A brief history of the development of aerial measurement systems is presented in Section 2. In the early 1950s, all the aerial survey results were reported with essentially no interpretation, explanation, or discussion. Three main sources of error and uncertainties were recognized. Aircraft altitude and position were the first problems to be addressed. These are discussed in Section 3. Air-to-ground correlations remained the primary uncertainty in aerial survey assessment of fallout fields throughout the 1960s. This problem is discussed in Section 4. Data obtained from aerial surveys were used extensively from 1953 through 1970 to assist in quickly estimating the fallout radiation patterns. Both air and ground measurements were used, as applicable, to develop the original contours. Aerial survey results were used to support ground data, not vice versa, because aerial survey techniques were still under development and many uncertainties existed in the application of these techniques. However, ground measurements were not made extensively, and scientists relied on the aerial survey results to extend the fallout patterns. This occurred particularly during 1957 and in the 1960s when aerial survey results were more reliable. Historical data for selected tests are reviewed in Section 5. The review effort is summarized in Section 6, which also presents conclusions regarding use of conversion factors. During the early days of nuclear testing at the NTS, a series of tests was assigned an "operation" name. Individuals thoroughly familiar with the nuclear testing program customarily refer to all tests in a given year by the assigned operation. Because this procedure could confuse ,__ less familiar individuals, the following table provides a summary of the operations referenced in this report. Few of the individual tests are referenced by name.

Page 11

Operation Name Period of Testing Number of Tests Several tests conducted during the 1960s are referenced without including the operation name. However, in each case, the year of the test is provided.

Page 12

2. DEVELOPMENT OF AERIAL MEASUREMENT SYSTEMS The Military first tested a "radiac" instrument system in an aircraft during 1951 to develop the techniques for conducting rapid aerial radiological surveys. The system consisted of a simple radiac instrument, de amplifier, and recorder. Extrapolating the results to ground level produced sufficient agreement with ground-level readings to warrant further testing.2 Some simple additions and modifications to the detection and recording system were made in 1952.2 Close-in onsite aerial surveys were emphasized during 1951 and 1952, although some offsite surveys were conducted.3 The aerial survey techniques continued to be used during 1953 to determine the extent of the fallout patterns onsite or close-in to a nuclear detonation. For extended surveys offsite, longer-range aircraft and a wider variety of aerial survey instruments were used. Initially, it was not certain whether aerial survey data would be useful. Fallout patterns for the Badger and Simon tests (sixth and seventh in the 1953 series) were plotted from the aerial survey data alone, then compared to the ground data. Reference 4 indicates that the correlation was excellent; however, by today's standards the correlation was poor. The aircraft utilized for the 1953 surveys consisted of one C-47 and two L-20s. Most of the surveys were flown at an altitude of 500ft. Fallout patterns were determined from the combined results of both aerial and ground data. Three radiation detector systems were used during this time period: the MX-5, the T1 B, and the Scintelog. All the instruments were calibrated using cobalt-60 sources. The MX-5 was a Geiger counter, the energy response of which changed slightly in mixed radiation fields since the energy spectrum of fission products changes with time. The spectrum of radiation fields also changes with height above the ground. The T1 B was an ion chamber with an energy response reasonably flat with energy. In 1953 it was considered the primary instrument for both aerial and ground measurements. The T1 B had a slow response time, however, and measurements below 1 milliroentgen per hour (mR/h) were not The Scintelog was a new, experimental scintillation detector developed by the Atomic Energy Commission's New York Operations Office. Both sodium iodide and plastic scintillators were tested. The output was recorded in mR/h on a recorder. The plastic scintillator was essentially energy-independent for detecting gamma rays having energies above 80,000 electron volts (80 keV),5 while the sodium iodide scintillator was not. Both detectors had a fast response time. Agreement among the three detector systems was generally within a factor of two or three, although in some cases a factor of 10 was observed.* In high radiation fields, the MX-5 and Scintelog were unreliable. In low radiation fields (below 1 mR/h), the T1 B readings tended to be too high. A study was made (by the author of this report) of the ratio of T1 B readings to the Scintelog readings above 1 mR/h. The average ratio was 2.0, but the spread was from 0.1 to 6.2. Aerial measurement techniques were not highly developed by 1953. Reference 4 states that "the T1 B ion chamber instrument was found to be the most suitable survey meter for this type work." However, in a recent analysis of historical data collected after the Nancy test (second test in *An error of a factor of two means the measured value probably lies within the range defined as a result of dividing or multiplying by two. For example, if the measured value is 80, a factor of two error means that the real value lies between 40 and 160.

Page 13

1953), Steadman 6 indicated that a much better correlation between air and ground results was found with the Scintelog readings than with either the MX-5 or T1 B results. It was determined empirically that a 1-mR/h Scintelog reading at 500ft above ground corresponded …