An Aerial Radiological Survey of the California Bay Area · 2013. 3. 13. · Completing the Bay Area survey area required . 282 . flight lines needing about . 30 . hours of flight

An Aerial Radiological Survey of the California Bay Area

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the u.s.

Government. Neither the u.s. Government nor any agency thereof, nor any of their employees,

nor any of their contractors, subcontractors or their employees, makes any warranty or

representation, express or implied, or assumes any legal liability or responsibility for the

accuracy, 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 u.s. Government or any agency thereof. The views and

opinions of authors expressed herein do not necessarily state or reflect those of the u.s.

Government or any agency thereof.

TARD-ATD-ARES-0006v.1

December 2012

An Aerial Radiological Survey of the

California Bay Area

Survey Dates: August 27 - 31, 2012

This document is UNCLASSIFIED

This work was performed for the Department of Homeland Security's Domestic Nuclear

Detection Office by National Security Technologies, LLC, under IAA HSHQDC-ll-X-00376.

R[MOTE S NSING L .... BOR .... TORY


This page intentionally left blank.

ii


EXECUTIVE SUMMARY

In late August 2012, at the request of the Department of Homeland Security's Domestic Nuclear

Detection Office (DNDO), an aerial radiological survey of select portions of the California Bay

Area was conducted by the Department of Energy's Remote Sensing lab's Aerial Measuring

Systems (AMS). Data collected during the survey were used in the DI\lDO Airborne Radiological

Enhanced-sensor System (ARES) program to validate simulations of background radiation rates.

As this was a research mission, specific areas selected for the survey were chosen for their

suitability for that mission. Selection was not prejudiced by expectations of any particular

results.

The data were also analyzed by AMS using standard techniques to produce maps showing gross

count rates and exposure rates. Aside from a few signals consistent with radioisotopes used in

nuclear medicine, nothing other than the expected normal background was found. Finding

signals from medical isotopes is common in populated areas. However, because these data are

part of an effort to improve aerial radiological detection methods, future analyses may reveal

signals not found by standard AMS techniques.

At the request of the Department of Energy,Treasure Island, Verba Buena Island, and Hunter's

point were surveyed for the City of San Francisco and the California Department of Public

Health. AMS analysis of data collected in these areas showed only normal background

radiation, consistent with naturally-occurring radioisotopes. These data were not used by the

ARES program.

iii



iv


POINTS OF CONTACT

u.S. Department of Homeland Security

Domestic Nuclear Detection Office

DN DO Stop 0550

245 Murray lane

Washington, DC 20528-0215

E-mail: [email protected]

National Security Technologies, lLC

Remote Sensing laboratory

P.O. Box 98521

las Vegas, NV 89193-8518

v

mailto:[email protected]



vi


TABLE OF CONTENTS

EXECUTIVE SUMMARY ....................................................................................................................iii

POINTS OF CONTACT .......................................................................................................................v

LIST OF FIGURES ............................................................................................................................ viii

LIST OF TABLES .............................................................................................................................. viii

ACRONYMS ..................................................................................................................................... ix

1 Introduction ............................................... ..... ........................................................................ 1

2 Survey Methods 1............................................................................. . . . .. ................................ ....

2.1 Aerial Measurements 1................................................................................... . . ..................

2.2 Survey Equipment ............................................................................................................ 2

................................................................................................... .......... 3 Background Radiation 4

4 Description of Survey Areas 6....................................................................................................

5 Survey Operations ........................... : ....................................................................................... 8

5.1 Fixed Base Operator 8.........................................................................................................

5.2 Daily Operational Checks 8.................................................................. . ..............................

5.2.1 Pre-Flight Checks 8................................................................................ ... ....................

5.2.2 Ground Data, Test Line, and Water Line 8...................................................................

5.2.3 Post-flight Checks 9......................................................................................................

6 AMS Data Analysis 9......................................................... .........................................................

6.1 Gross Count Analysis . ........... . . . 10................................. . . . . . ........... ......................................

6.2 Exposure Rate Algorithm ............................................................................................... 10

7 Statistics ................................................ ........ . . . . . . . . . . . . . . .......................................................... 11

8 Aerial Survey Results ............................................................................................................. 13

9 Summary 15.................................................................................. . ....... ...... ... . ...........................

References 34.................................................................. . . . . ... . . ........................................................ .

Appendix 1. Survey Parameters 35................................ ..... . .. . . . . ..................................................

vii


LIST OF FIGURES

Figure 1. Schematic diagram of the aerial survey method 2. ............................................................

Figure 2. AMS Bell 412 helicopter used for aerial radiological surveys ............................ . .. 3. ..........

Figure 3. The AMS-configured RSI radiation detection system . . ...................................... . .......... 4 . ..

Figure 4. U.S. Geological Survey map of terrestrial gamma-ray exposure ..................................... 5

......................... . ........... Figure 5. Areas selected for data collection during the Bay Area Survey . 7

Figure 6. Average corrected gross count rates . ............................................................................ 12

Figure 7. Corrected gross count distributions for Oakland-Berkeley 1 and Pacifica . ................... 13

................................. . . . ................Figure 8. Oakland-Berkeley 1 gross count and exposure map . 16

Figure 9. Spectrum from the Oakland-Berkeley 1 survey area . 17.................................. .................

Figure 10. Spectrum from the Oakland-Berkeley 1 survey area . 18....................... ........ ..................

Figure 11. Spectrum from the Oakland-Berkeley 1 survey area 19. ........................... ... ...................

Figure 12. Spectrum from the Oakland-Berkeley 1 survey area . ........ . . . . . ....... .......... . . ................. 20

Figure 13. Oakland-Berkeley lA gross count and exposure map . ................... .................. . . ......... 21

Figure 14. Oakland-Berkeley 2 gross count and exposure map . 22..................................................

Figure 15. Presidio gross count and exposure map . ................ . .. .................... . .................. ........... 23

Figure 16. Pacifica gross count and exposure map . 24..................... . ................ ........... ....................

Figure 17. Alcatraz gross count and exposure map . ... ................................. . . .......................... ..... 25

Figure 18. Fisherman's Wharf gross count and exposure map . 26........ . . . . . .. . .. ............... ....... .... .......

Figure 19. Treasure Island gross count and exposure map . ......................................................... 27

Figure 20. Spectrum from Treasure Island high count rate area 1. .............................................. 28

Figure 21. Spectrum from Treasure Island high count rate area 2 ............................................... 29

Figure 22. Spectrum from Treasure Island high count rate area 3 ............................................... 30

. ................ . . ................. ..Figure 23. Verba Buena Island gross count and exposure map . . ............ 31

Figure 24. Hunter's Point gross count and exposure map 32. ........ . . . . ......... ..... ............ . .......... ........ .

Figure 25. Spectrum from high count rate area of Hunter's Point . .............. . . . ....... . . . . ............... . .. 33

LIST OF TABLES

Table 1. Corrected gross count rate statistics for all survey areas . . . . ........... .. . . ...... . . . ... ... ........ ..... 12

viii


ADS

AGL

AMS

ARES

cps

DHS

DI\lDO

DOE

FBO

HPGe

Nal(TI)

PMT

RSI

RSL

USGS

R/hr

ACRONYMS

Advanced Digital Spectrometer

Above Ground Level

Aerial Measuring System

Airborne Radiological Enhanced-sensor System

Counts Per Second

Department of Homeland Security

Domestic Nuclear Detection Office

Department of Energy

Forward Base of Operations

High-Purity Germanium

Thallium-activated Sodium Iodide

Photomultiplier Tube

Radiation Solutions Inc.

Remote Sensing Laboratory

United States Geological Survey

Micro-Roentgen per hour

ix



x


1 INTRODUCTION

In late August 2012, at the request of the Department of Homeland Security's (DHS) Domestic

Nuclear Detection Office (DNDO), an aerial radiological survey of select portions of the

California Bay Area was conducted by the Department of Energy's (DOE) Remote Sensing Lab's

(RSL) Aerial Measuring Systems (AMS). Data collected during the survey were used in the DNDO

Airborne Radiological Enhanced-sensor System (ARES) program to validate simulations of

background radiation rates. The data were also analyzed by AMS using standard techniques to

produce maps showing gross count rates and terrestrial exposure rates. At the request of DOE

several additional areas were surveyed for the City of San Francisco and the California

Department of Public Health.

The ARES program is a DNDO-sponsored research and development effort that will result in

improved methods to detect and localize radiological sources from an airborne platform. It

incorporates improvements in radiation sensor technology and advanced processing algorithms

for data collected with the new sensors.

Section 2 of this report discusses aerial survey methods, and section 3 covers background

radiation. The surveyed areas are described in section 4. Section 5 outlines survey operations,

and section 6 gives some details about AMS analysis techniques. Results are presented in

sections 7 and 8, with the former focusing on the statistics of the entire survey, and the latter

giving details of results from each area.

2 SURVEY METHODS

2.1 Aerial Measurements

AMS has been conducting aerial surveys since 1967, including planned surveys over

metropolitan areas (AMS, 2011) and the Nevada National Security Site (Hendricks &

Reidhauser, 1994), as well as emergency response missions such as the Fukushima Daiichi

nuclear power plant accident (Lyons & Colton, 2012). General details of aerial radiological

surveys have been previously published (Proctor, 1997).

The California Bay Area survey was planned to provide one-hundred percent coverage of the

designated survey areas with the aerial detector footprint. This task was accomplished by flying

sets of parallel flight lines across the survey areas using one of AMS's helicopters carrying a

radiation detection system (see Figure 1). Normally, the distance between flight lines is twice

the altitude above ground level (AGL) of the aircraft, but for this survey a denser data set was

1


desired. Therefore, the flight altitude was 300 ft AGl and the flight lines were spaced 300 ft

apart. The areas were surveyed at a nominal ground speed of 70 knots (""118 ft/sec.)

Figure 1. Schematic diagram of the aerial survey method.

The helicopter, carrying the radiation detection equipment, flies a series of parallel lines over the survey area. The detector collects data from a circular area on the ground with a diameter that is roughly twice the

height of the detectors above the ground.

Completing the Bay Area survey area required 282 flight lines needing about 30 hours of flight

time to complete. As the helicopter's fuel capacity restricted the time for an individual flight to

approximately 2.5 hrs, a total of 14 flights were required to completely cover the survey area.

2.2 Survey Equipment

AMS utilized a Bell 412 helicopter (Figure 2) and a detection system acquired from Radiation

Solutions Inc. (RSI) for AMS applications. The Bell 412 is a twin-engine utility helicopter that has

been manufactured by Bell Helicopter since 1981. With a standard fuel capacity of 330 gallons,

it is capable of flying for up to 3.7 hours, with a maximum range of 356 nautical miles and a

cruising speed of 122 knots. However, with the AMS radiation survey configuration of 12

detectors, four crew members (two pilots, a mission scientist and an equipment operator), the

AMS Bell 412 was capable of 2.5 hours of flight time with a survey speed of 70 knots (120

feet/sec) at the survey altitude of 300 ft AGl.

2


Figure 2. AMS Bell 412 helicopter used for aerial radiological surveys.

Detector pods are seen on the right and left sides of the helicopter.

The RSI system, configured for AMS applications, employs a total of twelve thallium-activated

sodium iodide (Nal(TI)) crystals, fabricated as log-type detectors with dimensions of 2" x 4" X

16" (128 cu in :::: 2 liter). These detectors are packaged in four RSX-3 units. Each RSX-3 unit is a

carbon fiber box containing three Nal (TI) logs. Each Nal{TI) log is coupled to a photomultiplier

tube (PMT) that produces analog signals for analysis by an Advanced Digital Spectrometer (ADS)

module attached to each PMT.

Data from each of the three ADS modules is sent to one of four RS-701 consoles. An Edak case

houses an RS-S01 aggregator box and a power distribution unit. The RS-S01 receives and

consolidates the data from the RSX-3s for data display and storage. Four RSX-3 boxes and four

RS-701 consoles are fitted into the externally mounted aluminum pods (two RSX-3s and two RS-

701s per pod) on the left and right sides of the Bell 412 helicopter (see Figure 3). The Edak case

and a laptop computer with the data collection and display software are mounted inside the

helicopter. An operator uses the laptop to monitor data collection and system performance

during flight.

3

3


Figure 3. The AMS-configured RSI radiation detection system.

The detector pods are shown with endcaps removed showing the RSI detectors inside. The Edak case in the center houses the RS-501 and power distribution panel. The laptop computer runs the system monitoring

and data collection software.

BACKGROUND RADIATION

Radiation is present everywhere in the environment from a variety of materials which include

naturally-occurring sources and sources due to human activity. The normal level of radiation is

known as background radiation and this varies from place to place, and to some extent from

one time to another. Radiation is produced when a radioactive nucleus emits particles and/or

gamma rays, a process known as radioactive decay. The total amount of particles and gamma

rays at a particular spot can be measured as exposure rate in units of micro-roentgen per hour

(J-lR/hr). The detectors used in the aerial survey are sensitive to gamma rays, and the number of

gamma rays detected in a given time is known as the count rate, typically expressed as counts

per second (cps). The detectors are calibrated to convert count rate to exposure rate.

The naturally-occurring sources include radioisotopes in the earth, radon in the atmosphere,

and cosmic rays. Most radiation exposure comes from these natural sources. The natural

radioisotopes in the earth produce what is called terrestrial radiation. These radioisotopes are

primordial and their measurement is the primary goal of an aerial background survey. Human

activities, such as construction and agriculture, can change the amount of natural radioisotopes

present in a particular area. Radon is a radioactive gas formed by the decay of natural isotopes

in the earth's crust. The amount of radon in the atmosphere at any given time depends largely

4

25


on the weather. Cosmic rays originate from the sun and outside the solar system. The

atmosphere and Earth's magnetic field provide shielding from cosmic rays, and so the number

of cosmic rays present depends on altitude and latitude, with the number of cosmic rays

increasing with increasing altitude and distance from the equator.

In the 1970s the governments of the United States and Canada conducted an aerial survey to

map potassium, uranium, and thorium deposits in North America. Essentially all naturally

occurring terrestrial radiation comes from these sources. Figure 4 shows terrestrial gamma-ray

exposure derived from this survey (Duval, Carson, Holman, & Darnley, 2005). The line spacing

varied from 1 to 25 km, with most of the western United States flown with 5 km spacing. The

United States Geological Survey (USGS) has made survey data available, and where there is

significant overlap between the USGS survey and the AMS survey this data was used to

calculate a terrestrial exposure rate for comparison (Grasty, Carson, Charbonneau, & Holman,

1984).

21

17

12 6

Dose

500 0 500 1500

(kilometers) Gamma -ray Absorbed Dose (nGy/hr)NAD271*DNAG

_f nGYlHrl

83 65

57 52

48

44

41

38

35 31

28

Figure 4. U.S. Geological Survey map of terrestrial gamma-ray exposure.

Dose rates are given in nanogray per hour (nGy/hr). To convert to microroentgen per hour (IlRlhr), divide the

value in nGy/hr by 10. (Figure from (Duval, Carson, Holman, & Darnley, 2005»

Human-created sources include medical isotopes, construction and industrial gauges,

sterilization units, power generators, consumer products, and fallout from nuclear tests and

accidents. The exposure rate from fallout from nuclear tests is very small, and is decreasing

5


with time due to radioactive decay. Unless one is in close proximity to a nuclear power plant

accident (e.g. Chernobyl or Fukushima), the exposure rate from these is also very small. The

remaining sources are confined and strictly regulated. For exampleJ radioactive sources used in

industrial gauges must be shielded to prevent harmful exposure to anyone nearby.

4 DESCRIPTION OF SURVEY AREAS

Several discrete areas in the Bay Area were chosen for the survey. Criteria for selection

included variability in terrainJ geologYJ topologYJ and development. Areas were chosen that had

been surveyed by a vehicle-mounted detection systemJ or could be surveyed by such a system.

Selection was done in collaboration with the ARES program. The areas selected had a range of

urbanJ suburbanJ and coastal environments.

For the purpose of the surveYJ each area was named for a prominent place name in the area. J

The areas were Oakland-Berkeley 1J Oakland-Berkeley 1AJ Oakland Berkeley 2J Fisherman s

WharfJ AlcatrazJ PresidioJ and Pacifica. In additionJ a two-line survey was flown along the coast

between Pacifica and Golden GateJ and is referred to as the Coastal survey. The survey areas

are shown in Figure 5.

• Oakland-Berkeley 1 covered the area from roughly Alameda north to Berkeley HillsJ and

from the bay east to the University of California Berkeley campus and Piedmont. This

area has dense residential and light industrial development.

• Oakland-Berkeley 1A covered the Outer Harbor. This area covers the port.

• Oakland-Berkeley 2 covered the area from Piedmont southeast to San LeandroJ and

consists of dense residential with some open space.

J

• Fisherman s Wharf covered the piers along the Embarcadero.

• Alcatraz covered Alcatraz IslandJ and was the only area completely surrounded by

water. • Presidio covered from Golden Gate on the north to Geary Boulevard on the southJ and

from Pacific Heights on the east to South Bay on the west. • Pacifica gave a good contrast to the other areas with light residential developmentJ

coastlineJ and hilly topography.

JAt the request of the Department of EnergYJ Treasure IslandJ Verba Buena IslandJ and Hunter s

point were surveyed for the City of San Francisco and the California Department of Public

Health. Data collected from these areas were not used by the ARES program. Because of the

Bay BridgeJ the helicopter could not fly at the required survey altitude over much of Verba

Buena Island; therefore only a few lines were flown over the southeastern tip of the island.

6

!I !I I I

10 I

!I

s;;

I" Pi

.... +' \ i , ;: ' I . Oil ,. •• 1"'£ I lOP'" ":I \'hl!\ Berk1 1ey r ':"i , " :' -, ':"' \.' j --, '24' , ' ,ck " ·\l' \ . , f".>r... _. " ,,1, I! I .; ) r'f I ... Xc. • C'\. ((\

;=P IAq\-·· JjIs'· _ I ' -=::..-, < , , ::an ;' [P i t· 0 \J.:.J'f ..

N' K " ' 1- " " . _ ' I , , I II ' ,'" ' , ' " I! I \� "( l.

", .; I I , I

-,I i \-lIt: I lUll"'" ..,""V ��\,,- ; { " -" 'P°o I I

�. Ji' .... ('"

X ;Q -rY ,, I •• .- .' \' ..r .., . . , \ )' r\: . , "AN"CI C

' r J \_ . " 1 P. lfl ' - )." , ,,_.

'\ _ . X . _ .�_ -.Lr I I aAl)ort f ,, .. " I , " ' '- ''

'-J . ,,'- "" . A l ti D ':: "'. I! I nu " 'J \At \ . . >;

-;d . \.: J " I l,\; . /> 1" \'.h" 7

OvelYiew Ma

I, l


BELVEDERE u ..

" CAN VON h/

fT

.

J;: "':;�' '\

s. ,

$.F. .. oo

.. " __ +

127373O'W 121-3C7trW I'U ,2,2 'Z'YJW 1221Q'tfW ,::7'XJW 1215'0"1'/

Figure 5. Areas selected for data collection during the Bay Area Survey.

BOUNDARIES OF SURVEYED AREAS

- Alcatraz

- Fisherman's Wharf

- Hunter's Point

- Oakland-Berkeley 1

- Oakland-Berkeley 1A

- Oakland-Berkeley 2 - Pacifica

- Presidio

- Treasure Island

- Verba Buena

- Coast Line Flight

oIK. P'S

. ""'" Scale: 1 :200,000

rms ""p "". pfodllC«! by t ...

.. ., ___ sy. __ d /JNSA:. _ s...v t."""""'y(R$l.j III ...... _ .. IIO!/N.-

7


5 SURVEY OPERATIONS

5.1 Fixed Base Operator

The survey was conducted out of the Hayward Executive Airport, which provided fuel and space

for ground operations. This fixed base operator (FBO) was chosen for proximity to the survey

areas and ease of access for the survey crew.

5.2 Daily Operational Checks

Every survey day, the radiation detection system and the data it collected were subjected to

multiple operational and data quality checks. These checks ensured the quality of data both

before and after collection.

5.2.1 Pre-Flight Checks

Prior to each day's flight, the detection system was turned on using ground power and its

operation checked using both background and a small Cs-137 source. This initial morning check

(known as a pre-flight) looked at detector response and calibration, as well as auxiliary system

data (GPS and altimeter). All systems had to pass these checks before the helicopter was

allowed to take off. On every survey day, the pre-flight checks showed the detector and

auxiliary systems to be working normally.

5.2.2 Ground Data, Test Line, and Water Line

After the helicopter engines were started, but prior to take-off, the detector system was started

and one minute of background data was taken on the ground. When the helicopter landed at

the FBO following a survey flight, another minute of background data was taken. These

background measurements were a check of detector consistency during the flight.

After take-off, the helicopter flew pre-determined lines at survey altitude over both land and

water. The line flown over land (known as the test line) was over a taxiway at Hayward

Executive Airport, and served as an additional consistency check on the data. Unlike the ground

data, which were taken at a fixed location, test line data were taken at survey altitude and

speed over an area of varying background. The test line data were examined for consistency

from flight to flight along the length of the line. Any variations outside of those expected from

normal fluctuations would be cause to examine the detector system for inconsistencies. No

such variations were found during the survey.

8


The line flown over water {known as the water line} was also flown at survey altitude and

speed. The location of the line was over San Francisco Bay. Because there is no terrestrial

radiation over the water line, data collected here has contributions from only cosmic rays,

radon, and the aircraft. These data are subtracted from data collected over the survey areas,

yielding an excellent measurement of count rates due to only terrestrial radiation. Aircraft and

cosmic ray backgrounds are essentially constant during the survey, but because of daily

fluctuations in atmospheric radon concentrations small variations were seen in the water line

count rates from day to day. However, because the water line was flown every flight, these

data provided an adequate subtraction of non-terrestrial radiation.

After the helicopter completed each survey flight, the water and test lines were flown again at

survey altitude and speed before it returned to the FBO. These lines provided an important

consistency check on the data. If the water line data showed an abnormal variation in the pre

survey and post-survey data this could generally be attributed to a changing level of radon in

the atmosphere. If this were the case, the water line rate subtracted from the survey data

would be found by linearly extrapolation between the pre-survey and post-survey water line

rates.

5.2.3 Post-Hight Checks

Following each survey flight, data were downloaded from the helicopter and analyzed for data

quality. Consistency in the data {count rate, spectral shape, etc.} was checked for the duration

of the flight. GPS and altimeter data were also checked for consistency and completeness.

6 AMS DATA ANALYSIS

Using AMS-developed techniques and software, data are analyzed and presented as contour

maps using commercial GIS software. Data can be viewed in several ways, each taking

advantage of and highlighting some specific aspect of the survey. A gross count map shows the

total count rate, corrected for non-terrestrial contributions {radon, cosmic, and aircraft} at

survey altitude. The exposure rate map takes the gross count map and converts into a map of

exposure rate at one meter above the ground using conversion coefficients derived from the

altitude spiral flown at Hayward Executive Airport and flights at the Lake Mohave, NV,

calibration range. Because the conversion from gross counts to exposure rate can be reduced to

a simple multiplicative factor, gross counts and exposure rates are shown on the same map.

9


6.1 Gross Count Analysis

The radiation detection system counts gamma rays that arrive at the detector, regardless of the

source of the gamma rays or their history. Gamma rays originate from the ground, radon (in the

air), cosmic rays, equipment surrounding the detector, and the flight crew. The count rate from

radon, cosmic rays, equipment, and crew is essentially constant during a survey flight, and must

be subtracted from the raw count rate. The remaining count rate is assumed to come from the

ground, and is the count rate of interest. Before they reach the detector, gamma rays from the

ground must travel though several hundred feet of air, which interacts with and attenuates the

gamma rays. Count rates are normalized to the nominal survey altitude with the following

equation:

where

GC =

RC =

BC =

SA =

GC = eRC - BC)e-(SA-MA)/1

corrected gross count rate

raw count rate

background count rate from radon and equipment

nominal survey altitude of 300 feet above ground level

MA = measured altitude

f.1 = attenuation factor

The nominal survey altitude is the desired flight altitude, which for this survey was 300 feet

above ground level. The measured altitude is determined from the on-board radar altimeter.

The air attenuation factor f.1 is derived from the altitude spiral flown over the test line at

Hayward Executive Airport. During flight, the helicopter's altitude above ground will vary by

about ten percent from the desired survey altitude. This technique effectively normalizes the

count rate from terrestrial sources to the count rate measured at the nominal survey altitude of

300 feet above ground level.

The resulting corrected gross count rates are then displayed as a contour plot superimposed

over a map or image of the survey area. Doing this analysis allows the display of count rate due

to only terrestrial sources and removes changes in the count rate due to variations in helicopter

altitude.

6.2 Exposure Rate Algorithm

Once the corrected gross count rate is determined, it can be converted into a terrestrial

exposure rate with the use of a conversion factor. The conversion factor takes the count rate at

300 feet above ground level from the survey and converts it to an exposure rate in micro

Roentgen per hour ( lR/h) at three feet above ground level. The conversion factor was

determined from calibration flights made at the Lake Mohave Calibration Range in Clark

10


County, NV, and the air attenuation factor from the altitude spiral flown at Hayward Executive

Airport.

The Lake Mohave calibration flights give the conversion from count rate at 300 feet AGL to

exposure rate at three feet AGL at the calibration range. Because of the elevation difference

between the calibration range and the Bay Area there is also an atmospheric pressure

difference that needs to be accounted for. This pressure difference changes the amount of

attenuation gamma rays experience between the ground and the air-borne detector. Since the

air attenuation factor was measured at Hayward Executive Airport, it can be used to modify the

Lake Mohave calibration factor to make it appropriate for use in the Bay Area.

The conversion from corrected gross count rate to exposure rate is simply the following

equation:

GC ER =

CF

where

ER = exposure rate at three feet AGL in JlR/h

GC = corrected gross count rate in counts per second (cps)

CF = conversion factor

For the Bay Area Survey the conversion factor was the following: cps

CF = 1808 IlR/h

Because of the linear relationship between corrected gross counts and exposure rate, both

quantities can be displayed on the same contour plot using the same color levels.

7 STATISTICS

An overview of all the data collected can be had by looking at average corrected gross count

rates for each survey area. This can give some guidance on what to expect when looking at the

contoured data. Table 1 lists the number of data points, the minimum and maximum corrected

gross count rates, the average corrected gross count rate, and the standard deviation of the

corrected gross count rates for all survey areas. Only data pOints which were over land areas

were included in the table.

Figure 6 displays the average count rates of all surveyed areas. The average of the average rates

for all areas is 4150 ± 650 cps. The frequency of average count rates is shown in a bar chart on

the right side of the figure. Pacifica shows the largest standard deviation in count rate,

reflecting the large range of count rates measured. Oakland-Berkeley 1 has a larger count rate

11


range, but its exposure rate distribution is concentrated symmetrically around the average,

compared to the much broader and asymmetric Pacifica distribution. The corrected count rate

distributions from Oakland-Berkeley 1 and Pacifica are shown in Figure 7, illustrating the

difference in the shapes of the distributions that lead to the difference in standard deviations.

Table 1. Corrected gross count rate statistics for all survey areas.

Area

Alcatraz

Hunter's Point

Oakland-

Berkeley 1

Oakland-

Berkeley 1A

Oakland-

Berkeley 2

Pacifica

Presidio

Treasure Island

Fisherman's

Wharf

Verba Buena

Island

7000Ii)fr 6000

5000nI

4000 s::: 5 3000 u 2000

o 1000

QJ 0 ...

QJ> « ..::;cJ

Number of

Data Points

24

828

23526

2075

13085

2017

2970

434

51

32

..... "y . q;.Q.0 Q} q;.

, eo, Q}

Minimum Rate Maximum Rate

[cps] [cps]

2105 4180

2200 6992

512 13912

1693 6011

1359 8968

933 11430

3149 9690

2774 5947

1078 4244

3234 6321

'V q;.

Q}

'71 .,f> b b ...... . ,f ,fv cz/ $ Q.'71 ct- COil; COil;"V COil;;:,t:::

Q.' ,Il; ,eo,

,f ;:,Il; -

�-----------------------------------------------

+---� �---------------------------------------


Oakland-Berkeley 1

4500

4000

3500

3000

2500

2000

1500

1000

500

0

0 2000 4000 6000 8000 10000 12000 14000

Corrected Gross Count Rate [cps]

Pacifica

120

100

80

60

40

20

o

o 2000 4000 6000 8000 10000 12000 14000

Corrected Gross Count Rate [cps]

Figure 7. Corrected gross count distributions for Oakland-Berkeley 1 and Pacifica.

The Oakland-Berkeley 1 distribution, although having the larger range, is more concentrated around its average than the Pacifica distribution.

8 AERIAL SURVEY RESULTS

Results are presented here as contour maps of corrected gross counts and exposure rates. The

radiation level scales on the maps of different areas use the same break points, but only levels

present in a given map are shown in its legend.

The gross count and exposure rate contour maps are presented below. As discussed above, the

conversion from gross counts to exposure rate is a simple multiplicative constant, so both can

13


be shown on a single map by simply renaming the contours. When this was done, exposure rate

levels were rounded to the nearest tenth of a J.!R/hr. The USGS exposure rate map in Figure 4

indicates terrestrial exposure in the Bay Area is expected to be in the range of about 2.5 - 5

J.!R/hr. Data collected during the AMS survey compare favorably with that span.

The Oakland-Berkeley 1 area is shown in Figure 8. Exposure rate values over land are, in

general, in the range 1.4 - 4.3 J.lR/hr. A relevant feature to note is the very low count and

exposure rates over areas of water. This is because it is the terrestrial radiation being mapped,

after correction for cosmic, radon, and aircraft rates. This is a feature typical to all surveys. Also

of note are the relatively high rates toward the northeast of this area, going up to 12.2 J.!R/hr.

This difference between this section and other sections of lower count rate is primarily due to

the geology of the hills in that area and is well within normal background radiation fluctuations.

Certain roads stand out having a higher or lower count rate than adjacent areas. This is also a

common occurrence caused by materials used to construct the roads having been trucked in

from another area.

The average terrestrial exposure rate for this area is 2.50 ± 0.48 J.!R/hr. Two lines from the

USGS survey (Section 3) crossed this area, and the exposure rate calculated from those lines is

2.23 ± 0.44 J.!R/hr.

The highest gross count rate in this area occurs at about latitude 37 ° 51.866', longitude

-122° 14.273 (circle 1 in Figure 8). A spectrum was extracted from this area is displayed in

Figure 9 along with a spectrum (corrected for collection time) from a nearby area with low

gross count rate. The shapes of the spectra are nearly identical, indicating the high count rate is

due to elevated natural background. The reason for this elevated rate could be difference in

geology of this region, or it could be because this region is relatively undeveloped compared to

the rest of the survey area, and the ground is unshielded by construction materials.

Several anomalous signals were detected in this area (circles 2 - 4 in Figure 8), which were all

determined to be consistent with radioisotopes used in nuclear medicine. Detections of this

type are common in populated areas. Spectra from these anomalies are displayed in Figure 10

through Figure 12.

Oakland-Berkeley 1A is shown in Figure 13. Normal fluctuations are seen in this area, with

perhaps some indication of slightly elevated rates over the railroad yard in the southeast

corner. This is also common occurrence, caused by the rock used in the rail bed.

Oakland-Berkeley 2 is shown in Figure 14. This area also shows normal variations, with the

largest count rates probably caused by changes in geology.

14


Survey results from Presidio are shown in Figure 15. Exposure rates measured in these areas,

1.4 - 4.3 J.lR/hr, also compare we" with those reported by USGS.

The gross count contour map from Pacifica is shown in Figure 16. Exposure rates measured in

this area are within the normal range. The map shows typical variations due to geology and

differences in development. The average exposure rate for this area is 2.25 ± 1.18 J.lR/hr. A

single line from the USGS survey (Section 3) crossed this area, and the exposure rate calculated

from that line is 1.67 ± 0.83 J.lR/hr.

Alcatraz is shown on Figure 17. Results are as expected for a sma" island. Because the detection

footprint (the area measured in one second by the helicopter) is a significant fraction of the size

of the island, the water-land boundary is not clearly seen. This is a typical effect, and can be

seen along other coastal areas.

Results from Fisherman's Wharf are shown in Figure 18. Interesting things to note here include

the elevated count rate shown by the Bay Bridge, a result of the construction materials used

standing out against the very low background rate of the water. Exposure rates are we" within

the normal range and these show nothing unusual.

Treasure Island is shown in Figure 19. As with Alcatraz, because of the size of the effective

detection area, there is no sharp demarcation of the shoreline. Spectra from the highest count

rate area (3.0 - 4.3 lR/hr) are displayed in Figure 20 to Figure 22. These spectra are consistent

with higher natural background due to normal variations.

Verba Buena Island is shown in Figure 23. Because of the Bay Bridge, only a few lines were

flown here.

Hunter's Point is shown in Figure 24. This sma" peninsula shows the same shoreline effect as

Alcatraz and Treasure Island. The spectrum from the highest count rate region (3.0 - 4.3 J.lR/hr)

is shown in Figure 25. The high count rate here is due to more potassium-40 (a natura"y

occurring radioisotope) here than other places on the peninsula.

9 SUMMARY

The data collected during the aerial radiological survey of the Bay Area are of good quality and

pass all validation tests. Analysis of this data shows expected variations in normal background

count rates. Several medical isotopes were identified, which is a common occurrence in a

survey such as this.

15

OnnI_ -IP

I l I ". t \--,. ,

\, ,


GROSS COUNTS hr cps < 0.3 < 500

500 . 1500 1500 . 2500 2SOO 3500•

3500 ." 4500 2.5· 30 4500· 5

3.0· 4.3 5500 . 7700 4.3·66 noo . 12000

12000 . 22000

N..SA ...

Figure 8. Oakland-Berkeley 1 gross count and exposure map.

The high gross count rate at about latitude 37° 51.866', longitude -122° 14.273 (circle 1) is elevated natural background. Anomalous signals found in areas marked by circles 2 - 4 were determined to be medical isotopes.

16

-+I--�--- ---- ----------�

+_- - r_---+_--+-- r_------- M -----�

-1----- --- ------

+_-----+----+---+---r------- I- ---�

10000

1000

Vi' a.

100 OJ ..... ro cc ..... c

10 0 u

1

0.1

6

5

Vi' 4 a.

OJ..... ro

3cc ..... c

0 u

2

1

0


Oakland-Berkeley 1, Circle 1

- Signal -Background

q- q- q-M MN --

0 - NM I q- I co iii iii

N

«;J

o 500 1000 1500 Energy [keV]

2000


.c I-

2500 3000

- Signal/Background q- q- q-M M -- 0 - M

«;J «;J q- «;J N iii iii iii

.c

0 500 1000 1500 2000 Energy [keV]

2500

Figure 9. Spectrum from the Oakland-Berkeley 1 survey area.

3000

The upper plot shows the spectrum taken at circle 1 in Figure 8 (blue trace) and a spectrum taken from a nearby area (green trace), corrected for collection time. The spectra have essentially the same shape,

indicating the higher count rate is due to an elevated level of natural radiation. The ratio is shown in the lower plot, and is essentially constant below 1500 keV, indicating the difference in count rates is due to

differing levels of background radiation. Marked peaks are from naturally-occurring radioisotopes.

17

--- ----- ------ ----1

.... c-----------------------l \ +---...... - ___ ------- ___ -I

""'" '" -


1000

100

Vi' 0.

OJ ro

a::: 10 C :::s0U

1

0.1

Oakland-Berkeley I, Circle 2

-Signal C -Background C

.q.....viN .q .q N ..... 0 ..... gJo ..!.Q..co .q .r. co co .....

2000 2500 3000o 500 1000 1500 Energy [keV]

Oakland-Berkeley I, Circle 2 100 -Signal - Background

80

60

OJ ro

a::: 40

C :::s oU

20

o

-20 2500 3000

O ..!. . .!. 0 N N Q.. co co __ '1 - ..!. .r. '" '" I-

o 500 1000 1500 2000 Energy [keV]


The spectrum was taken at circle 2 in Figure 8. The blue trace in the upper plot is the spectrum of the anomaly and the green trace is a background spectrum collected nearby. Spectra are real time normalized.

The excess counts below about 1500 keV are consistent with a medical facility. The peak at 511 keV is likely due to positron emission from fluorine-18, a commonly used medical isotope.

18

-Signal Background

+.-. .... - ---- --------------�-�----�--- q- -------- ------�

........ U....... ::::-=--=-:-=--=-:-=-_=_-=--=--=--=--=--=-_=_-=--=-: .I ..

.-.. .. - -

1;

Vi' a. Q)...... ro

0::: ...... C ::::I 0

u

Vi' a. Q)...... ro

0::: ...... C ::::I o

U


Oakland-Berkeley 1, Circle 3 1000 - Signal - Background

q-100 .-I - .-I m

1 as

10

1

0.1 o 500

40

q-.-I as

1000

q-0

.-I

q- as

1500 2000 Energy [keV]


N m N 1;I-

2500 3000

35 30 25 20

-

q- q-.-1 .-1 .-I

- ..!.. 0) co q-

15 0 .-1 N-- as I-10

5 o

-5 -10

o 500 1000 1500 2000 Energy [keV]

2500


3000

The spectrum was taken at circle 3 in Figure 8. The blue trace in the upper plot is the spectrum of the anomaly and the green trace is a background spectrum collected nearby and corrected for collection time. The lower plot is the difference between the spectra. The background has been normalized by total counts

above 1364 keV. The peak at about 364 keV is consistent with gamma emission from iodine-131, a commonly used medical isotope. The excess counts below this peak are caused by gammas originally at the peak

energy that have lost part of their energy through interactions in material between the source and the detector.

19

II ,

____ ------- ----\

o�� - -

Vi' c..

Q)

ro a::

c :J 0 u


1000

100

10

1

0.1

50

40

30

o

E en

u

E en

u t-

20

10


- Signal

- Background

500 1000 1500 2000

Energy [keV]


2500 3000

- Signal - Background

q- q- q-.-i 0 Nt;J ..!.. _- "t -- I J:.ii5 co ii5

-10

o 500 1000 1500 2000

Energy [keV] 2500


3000

The spectrum was taken at circle 4 in Figure 8. The blue trace in the upper plot is the spectrum of the anomaly and the green trace is a background spectrum collected nearby and corrected for collection time. The lower plot is the difference between the spectra. The background has been normalized by total counts

above 1364 keV. The peak at about 141 keV is consistent with gamma emission from technicium-99m, a commonly used medical isotope. The excess counts below this peak are caused by gammas originally at the

peak energy that have lost part of their energy through interactions in material between the source and the detector.

20

=-

_-== ___ '


Oakland-Berkeley 1A

GROSS COUNTS IJRlhr cps

< 500

500 - 1500

2.5 - 3.0 4500 - 5500

3.0 - 4.3 5500 - 7700

Q'15 05 KtQIll4:NA

1.1".

Scale: 1 :30,000

•

Figure 13. Oakland-Berkeley 1A gross count and exposure map.

21

I :;;:

--==---'

•


Oakland-Berkeley 2

f;:,

GROSS COUNTS IJRlhr cps < 03 < 500

_ 0.3-0.8 _ 500 - 1500 1500 - 2500 2500 - 3500

_ 3500 - 4500 2.5 - 3.0 4500 - 5500 3.0 - 4.3 I 5500 - 7700 4.3 - 6.6 7700 - 12000

I

S kll:rn •• n

_-=:i::ioiio_-",05.-.J

< 0.3


Presidio


< 500

_ 0.3-0.8 _ 500 - 1500 1500 - 2500

2500 - 3500

3500 - 4500

2.5 - 3.0 4500 - 5500

3.0 - 4.3 5500 - 7700

4.3 - 6.6 7700 - 12000

Scale: 1 :35,000

•

Figure 15. Presidio gross count and exposure map.

23

=-


Pacifica

GROSS COUNTS

",Rlhr cps

< 0.3 < 500

500 - 1500

1500 - 2500

2500 - 3500

3500 - 4500

2.5 - 3.0 4500 - 5500

3.0 - 4.3 5500 - 7700

4.3 - 6.6 7700 - 12000

C D ..... 1kWM .. ·""

'l'l

Scale: 1 :25,000

•

Figure 16. Pacifica gross count and exposure map.

24

!;; i

_-=::::.o. __ O J


Figure 17. Alcatraz gross count and exposure map.

GROSS COUNTS RJhr cps

< 0.3 < 500

0.3 - 0.8 _ 500 - 1500 1500 - 2500

2500 - 3500

1.9 - 2.5 _ 3500 - 4500

�l +\li:m•• Ml,

Scale: 115,000

25

" =-

0,


Fisherman's Wharf

GROSS COUNTS

IJRlhr cps

< 0,3 < 500

_ 0.3-0.8 _ 500 - 1500 1500 - 2500

Dt'l 01

Scale: 120.000

•

Figure 18. Fisherman's Wharf gross count and exposure map.

26

__ -===-___ ..;;00 •.

53 ...... · 1 \ ' "


Figure 19. Treasure Island gross count and exposure map.

Treasu re Island


< 0.3

0.3 - 0.8

< SOO

500 - 1500

0.8 -1.4 1500 - 2500

1.4 -1.9 _ 2500 - 3500 1.9 - 2.5 _ 3500 - 4S00 2.5 - 3.0 4S00 - 5500

3.0 - 4.3 5S00 - 7700

Scale 1 :20,000

N.."SA

The circles indicate areas of highest corrected gross count rate. The spectra from these areas are shown in following figures.

27

..

IMl .. IJ .... .a.. .... _ .-. ... I

.. '"'W - -

1000

100

Vi' 0.

OJ ..... co

0::: 10 ..... C ::J 0

u

1

0.1

120

100

80 Vi' 0.

OJ 60 ..... co

0::: ..... c 40::J 0

u

20

0

-20


o

o

Treasure Island High Count Rate Area 1

500 1000 1500 2000

Energy [keV]

-Signal

- Background

N M N

1:. r-

2500 3000


oo::t'

+-JIIk------- ----

+---��-r----�--�-- ._l ------------ _____

•

M A I.. Y'V'V

.A.a .. - --

10000

1000



.q .q._l r:j -- 0 , .q

iii iii

- Signal - Background

.q N 100 m

Q) ..-

It)0::: ..--

§ 10 o

u

Vi' a.

Q)..--It)

0::: ..--C ::)0

u

1

0.1

120

100

80

60

40

20

0

-20 o

o 500 1000

iii t=.


2500


3000

- Signal- Background

.q._l

iii

500

.q .q--._lN O N .!.. "1 . !.. co co


N m

..c I-

2000 2500

Figure 21. Spectrum from Treasure Island high count rate area 2.

3000

The upper plot shows the spectrum from the area marked by circle 2 in Figure 19 (blue trace) and a background taken from the northern part of the island normalized by total counts above 2500 keV (green trace). The lower plot shows the difference between the signal and background from the upper plot. The

result is consistent with no excess radioisotopes. Marked peaks are from naturally-occurring radioisotopes.

29

._l --

--- ------- ----i

1000

100

Vi' a.

Q) ......

10co a: ...... c :J 0 u

1

0.1

o

140

120

100

Vi' 80a.

Q)......

60co a: ...... c :J

400 u

20

0

-20

0



500 1000 1500

Energy [keV) 2000

-Signal

Background

2500 3000


500

-Signal - Background

""" """ M

__ 0 -- M N """ £

1000

I-

1500 2000

Energy [keV) 2500 3000

Figure 22. Spectrum from Treasure Island high count rate area 3.

The upper plot shows the spectrum from the area marked by circle 3 in Figure 19 (blue trace) and a background taken from the northern part of the island normalized by total counts above 2500 keV (green trace). The lower plot shows the difference between the signal and background from the upper plot. The

result is consistent with no excess radioisotopes. Marked peaks are from naturally-occurring radioisotopes.

30

1"'6., Bu ..

't\ ""'

---==:::::.;,--_...::." ��.


'1fd

Figure 23. Verba Buena Island gross count and exposure map.

Verba Buena

GROSS COUNTS

IJRlhr cps

< 0.3 < 500

_ 0.3-0.8 _ 500 - 1500 0.6 - 1.4 1500 - 2500

_ 1 4 - 1.9 _ 2500 - 3500

_ 1.9·2.5 _ 3500 . 4500

2.5·3.0 4500 . 5500

3.0·4.3 5500 . 7700

U.

Scale: 1 :8,000

•

31

_..::::::::=-_ ...

[S3


Figure 24. Hunter's Point gross count and exposure map.

The high count rate area is show as orange in the figure.

32

Hunter's Point

GROSS COUNTS RIhr cps < 0.3 < 500

0.3 - 0.8 _ 500 - 1500 0.8 - 1,4 1500 - 2500

1.4 - 1.9 _ 2500 - 3500 1.9-2,5 _ 3500 - 4500 2.5 - 3.0 4500 - 5500

3 0 - 4.3 5500 . 7700

"'0':1-..

Scale: 125,000

9

N SJ14

+-------""I�- --- ------------1

+--------r--- _* -_1-------- ---�

+----------- --- ------ ----I

10000

1000

Vi' c.. 100 Q) .j...J

ro 0:::

.j...J

c 10:J 0 u

1

0.1

140

120

100

Vi' c..

80 Q) .j...J

ro 0:::

.j...J 60

C :J 0

40u

20

a

-20


Hunter's Point High Count Rate Area

-::t -::t

- Signal

Background i:i5 c6 -- -

t;J in N

m N

1:.

a 500 1000 1500 2000 Energy [keV]

2500 3000

Hunter's Point High Count Rate Area

- Signal- Background

-::t -::t t;J -- - t;J in c6

a 500 1000 1500 2000 Energy [keV]

2500

Figure 25. Spectrum from high count rate area of Hunter's Point.

3000

The upper plot shows the spectrum from the high count rate area in Figure 24 (blue) and a background spectrum taken from the northwest portion of the survey area (green). The lower plot shows the difference in

these two spectra and reveal an excess of K-40, a naturally-occurring radioisotope, in the high count rate area of Hunter's Point. Marked peaks are from naturally-occurring radioisotopes.

33

34


References

AMS. (2011). An Aerial Radiological Survey for King and Pierce Counties. Retrieved December

2012, from Washington State Department of Health:

http://www.doh.wa.gov/CommunityandEnvironment!Radiation/RadiologicalEmergencyPrepar

edness/AeriaIRadiologicaISurveyforKingandPierceCou.aspx

Duval, J., Carson, J., Holman, P., & Darnley, A. (2005). Terrestrial radioactivity and gamma-ray

exposure in the United States and Canada: U.S. Geological Survey Open-File Report 2005-1413.

Retrieved January 2013, from http://pubs.usgs.gov/of/2005/1413/index.htm

Grasty, R., Carson, J., Charbonneau, B., & Holman, P. (1984). Natural background radiation in

Canada. Geological Survey of Canada Bulletin 360 .

Hendricks, T. J., & Reidhauser, S. R. (1994). An Aerial Radiological Survey of the Nevada Test Site

DOE/NV/11718-324. Washington DC: U. S. Department of Energy.

Lyons, c., & Colton, D. (2012). Aerial Measuring System in Japan. Health Physics, 102 (5), 509-

515.

Proctor, A. E. (1997). Aerial Radiological Surveys DOE/NV/11718-127. Washington DC: U. S.

Department of Energy.

http://pubs.usgs.gov/of/2005/1413/index.htmhttp://www.doh.wa.gov/CommunityandEnvironment!Radiation/RadiologicalEmergencyPrepar

35


Appendix 1. Survey Parameters

Survey Site:

Survey Coverage:

Survey Date:

Survey Altitude:

Aircraft Speed:

Line Spacing:

Navigation System:

Line Direction:

Detector Configuration:

Acquisition System:

Conversion Factor:

Air Attenuation Coefficient:

Aircraft:

California Bay Area, CA

68 square miles ("'176 square kilometers)

August 27 - 31, 2012

300'feet ("'91 meters)

70 knots ("'36 meters per second)

300 feet ("'91 meters) (Alcatraz 100 feet)

Trimble DGPS (WAAS corrections)

Varied with survey area

Twelve 2" x 4" x 16" Nal(TI) detectors

RSI RS-501

1808 cps per IlR/h @ 300 feet

0.00191 feerl (0.00627 meters-l)

Bell-412 Helicopter

An Aerial Radiological Survey of the California Bay Area · 2013. 3. 13. · Completing the Bay Area survey area required . 282 . flight lines needing about . 30 . hours of flight

Documents