CALIFORNIA STATE UNIVERSITY, NORTHRiDGE
PHOTON SKYSHINE SURVEY OF A
\\
7.5 MEV FLASH X-RAY MACHINE
A
THESIS SUBMITTED
IN
PARTIAL
SATISFACTION
OF
THE
REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN
ENVIRONMENTAL HEALTH
BY
THOMAS JOSEPH FROELICH
AUGUST,
1975
THE THESIS OF THOMAS JOSEPH FROELICH IS APPROVED:
CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
AUGUST,
ll
1975
DEDICATION
TO MY WIFE,
MARTY, WHOSE
PATIENCE AND ENCOURAGEMENT
COMPLETED THIS WORK
Ill
TABLE OF CONTENTS
PAGE
DEDICATION
.................................................
lll
LIST OF TABLES
VI
LIST OF FIGURES
Vll
IX
ABSTRACT
CHAPTER
1.
INTRODUCTION ••.••...•.......•••••••••.•.••..• ~ •.••
1
PROBLEM STATEMENT •••••••• , • • • • • • • • • • • • • • • • • • • • • • • •
1
THE X-RAY MACHINE • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
2
·SHIELDING • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • ••
2
AREA SURROUNDING THE FACILITY • • • • • • • • • • • • • • • • • • • • • • •
3
REGULATING STANDARDS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
6
2. THE RADIATION FIELD • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
fO
THE PRJ MARY BEAM • • • • • . • • • • • • • • • • • • • • • • • • • • • • ·• • • • • • .
10
PHOTON SCATTERING ••••••••••••••••••••••••••••••••••
13
COMPTON SCATTER •••••••••••••••••••••••••••••••••••
17
PHOTON SKYSHINE .••••••••.••••••••••••••••• , , ••••••••
22
BLOCK WALL SCATTER •••••••••••••••••••••• ~ •••••••••
22
A 1R SeATTER • • • • • • • .. • • • • • • . • • • • • • • • • • . • • • • • • • • • • • . ..
23
3. THE ENVIRONMENTAL RADIATION SURVEY • • • • • • • • • • .
28
4.
THE INITIAL SURVEY ••••••••••••••••••••••••••••••••
28
DOS l METRY • • • • • . • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • .
32
MONITOR STATIONS •••••••••••• • •••••••••• • •••••••••
33
SURVEY RESULTS •••••••••••••••••••••••••••••••••••
BACKGROUND
DosE .•.••.....••.•.••.•..••..••••...
IV
e
••
36
36
CHAPTER
5.
PAGE
DOSIMETER ACCURACY
39
F I LMBADGE DOSIMETRY • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
39
PRIMARY BEAM DOSIMETRY • • • • • • • • • • • • • • • • • • • • • • • • • • • •
39
ANALYSIS AND CONCLUSIONS • • • • • • • • • • • • • • • • • • • • • • • • • • •
41
FOLLOW-UP SURVEY AND ADDITIONAL SHIELDING
43
PRIMARY BEAM SHAPE • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
43
INSIDE WALL DosE MAP • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
45
PRIMARY BEAM EFFECTIVE ENERGY . • • • • • • • • • • • • • • • • • • • •
45
SCATTERED DOSE MAPPING
48
AIR SCATTER VS. WALL SCATTER
52
ADDITIONAL LEAD SHIELDING • • • • • • • • • • • • • • • • • • • • • • • • • •
52
SCATTERED RADIATION FIELD RESURVEY • • • • • • • • • • • • • • • • •
52
BIBLIOGRAPHY • • . • • • • • • • • . • • • . . • . . • • . • • • • • • • • • • . • • • • • • • • • • .
59
APPENDIXES • • • • . • • • • . • . • • . . • . . . • . . . . • • • . • • • • . • • • • • • . • • • • • •
61
A.
TLD AND FILMBADGE READINGS SURVEY
1
61
B.
TLD AND FILMBADGE READINGS SURVEY
2
63
v
LIST OF TABLES
TABLE
PAGE
........... ..................... .
1-1.
.OCCUPANCY FACTORS
4-1.
NEAR FIELD ACCUMULATED DOSES FOR SURVEYS
4-2.
UNCONTROLLED AREAS EXPOSURE SUMMARY • • • • • • • • • • • • • •
42
5-1.
PRIMARY BEAM EFFECTIVE ENERGIES • • • • • • • • • • • • • • • • • • •
49
-
1
AND
2 ...
5-2.
PERCENTAGES OF SKYSHINE FROM BLOCK WALL SCATTER
5-3.
COMPARISON SUMMARY OF DOSE FIELD INSIDE TARGET
ROOM BEFORE AND AFTER LEAD SHIELD INSTALLATION. •
5-4.
40
49
56
COMPARISON OF FAR FIELD DOSE RATES BEFORE AND
AFTER LEAD SHIELD INSTALLATION • • • • • • • • • • • • • • • • • •
5-5.
8
57
UNCONTROLLED AREAS EXPOSURE SUMMARY AFTER
LEAD SHIELD INSTALLATION • • • • • • • • • • • • • • • • • • • • • • •
VI
58
LIST OF FIGURES
PAGE
FIGURE
1-1.
FLASH X-RAY MACHINE AND CUTAWAY OF SHIELDING. • • • • • • • •
4
1-2.
AREAS SURROUNDING FLASH X-RAY FACILITY • • • • • • • • • • • • • •
5
2-1.
TYPICAL BREMSSTRAHLUNG X-RAY SPECTRA FOR
TUNGSTEN TARGET. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
12
2-2.
ELECTRON ENERGY SPECTRUM
2-3.
ESTIMATED BREMSSTRAHLUNG ENERGY DISTRIBUTION
FOR PHOTONS FROM FLASH X-RAY MACHINE • • • • • • • • • • • • •
2-4.
11
14
ESTIMATED FLASH X-RAY BREMSSTRAHLUNG ANGULAR
MEV • • • • • • • • • • • • •
15
2-5.
PRIMARY BEAM INTENSITY HITTING PRIMARY SHIELD WALL...
16
2-6.
MASS ABSORPTION COEFFICIENTS FOR AIR AS A
DISTRIBUTION FOR PHOTONS OVER
0. 3
FUNCTION OF PHOTON ENERGY • • . • • • • • • • • • • • • • • • • • • • • •
;1..8
2-7.
COMPTON SCATTERING • • • • • • • • • • • • • • • • • • • • • • • • • • . • • • • • •
19
2-8.
FRACTION OF PHOTON ENERGY GIVEN TO SCATTERED
PHOTON BY SCATTERING ANGLE •••••••• , . . . . . . . . . . . . . .
19
DIFFERENTIAL KLEIN-NISHINA CROSS SECTIONS • • • • • • • • • • •
21
2-10.
PROBABLE SCATTERING CENTERS •••• , • • • • • • • • • • • • • • , • • •
25
2-11.
OPEN-TOP CELL DIAGRAM FOR CALCULATING AIR
2-9.
SCATTER DOSES , • • • • • • • • • • • • • • • • • • • • , • • • • • • • • • • • • •
27
3-1.
MONITOR STATION LOCATIONS • • • • • • • • • • • • • • • • • • • • , • • • • •
30
3-2.
DOSE RATE RESPONSE OF TLD (UF) AND FILM
34
3-3.
THEORETICAL SENSITIVITY OF LlF CALCULATED
AS THE RATIO OF THE ENERGY DEPOSITED IN THE
PHOSPHOR TO THE ENERGY DEPOSITED IN TISSUE
34
4-1.
SKYSHINE DOSE CURVES: SURVEY
1
37
4-2.
SKYSHINE DoSE CURVES: SURVEY
2
38
5-1.
BEAM SHAPE ONE METER FROM FACEPLATE • • • • • • • • • • • • • •
44
5-2.
BEAM SHAPE Two METERS FROM FACEPLATE • • • • • • • • • • • • •
44
\Ill
FIGURE
PAGE
5-3.
TLD MEASUREMENTS INSIDE NORTH SHIELD WALL • • • • • • • • • •
46
5-4.
TLD MEASUREMENTS INSIDE EAST SHIELD WALL • • • • • • • • • • •
47
5-5.
TLD MEASUREMENTS ABOVE ToP OF SHIELD WALL OUTSIDE..
50
5-6.
OUTSIDE CENTERLINE VERTICAL DOSIMETER ARRAY
51
5-7.
CENTERLINE SCATTER DOSE DIVIDED INTO AIR AND
• • • • • • • •
BLOCK WALL SCATTER COMPONENTS • • • • • • • • • • • • • • • • • • ,
5-8.
53
DOSIMETRY DIAGRAM FOR PRIMARY BEAM RESURVEY
AFTER LEAD SHIELD INSTALLATION • • • • • • • • • • • • • • • • • • • •
VIii
54
ABSTRACT
PHOTON SKYSHINE SURVEY OF A
7.5
MEV FLASH X-RAY MACHINE
BY
THOMAS JOSEPH FROELICH
MASTER OF SCIENCE IN ENVIRONMENTAL HEALTH
AUGUST,
1975
THE FLASH X-RAY MACHINE SURVEYED IS CAPABLE OF PRODUCING FIFTY
THOUSAND RAD-SILICON AT THE TARGET FACEPLATE WITH A
PHOTON ENERGY.
7. 5
MEV MAXIMUM
THE MACHINE IS SHIELDED BY AN OPEN-TOP CONFIGURATION.
SECONDARY SCATTER
FROM
BUILDING STRUCTURES AND THE AIR ABOVE THE MA-
CHINE ( 11 SKYSHINE 11) WAS CONSIDERED CAPABLE OF CAUSING NON-PERMISSIBLE
LEVELS OF RADIATION IN UNCONTROLLED AREAS OUTSIDE THE SITE BOUNDARIES.
THE MECHANISMS OF PHOTON SCATTER AND THE INTENSITY AND ANGULAR PARAMETERS OF THE RADIATIOH BEAM ARE DESCRIBED.
AN ENVIRONMENTAL RADIATION
SURVEY USING THERMOLUMINESCENT DOSIMETRY WAS DESIGNED AND COMPLETED.
DOSIMETER STATIONS WERE PLACED FOR MONTH LONG PERIODS IN A PATTERN
THAT USED THE ASSUMED SYMMETRY OF THE SCATTERED RADIATION FIELD TO
ESTIMATE THE DOSE IN INACCESSIBLE, UNCONTROLLED AREAS OUTSIDE OF THE
FACILITY BOUNDARIES.
UNACCEPTABLE DOSE RATES IN THE UNCONTROLLED AREAS
WERE DETERMINED WHICH WOULD CAUSE DOSE LEVELS APPROACHING FIVE TIMES
IX
THE LEGAL MAXIMUM PERMISSIBLE AT THE INTENDED FULL WORKLOAD OF THE MA-
CHINE.
FOR THE PURPOSE OF ADDITIONAL SHIELDING DESIGN. THE PRIMARY BEAM
WAS FURTHER CHARACTERIZED BY MEASUREMENTS TO DETERMINE THE ANGULAR
DISTRIBUTION OF DOSE AND THE BEAM EFFECTIVE ENERGY.
A
LIMITED RESURVEY
OF THE PRIMARY AND SCATTER RADIATION FIELDS AFTER ADDITIONAL LEAD SHIELDING CONFIRMED A DOSE RATE BELOW THE MAXIMUM PERMISSIBLE IN THE UNCONTROLLED AREAS.
X
CHAPTER
1
......
INTRODUCTION
THE FLASH X-RAY MACHINE IS A VERY SHORT DURATION, HIGH INTENSITY
X-RAY SOURCE.
TYPICALLY, THE FLASH X-RAY MACHINE CONSISTS OF AN ELEC-
TRICAL ENERGY STORAGE MODULE ON WHICH A POTENTIAL IS BUILT UP AND HELD
UNTIL IT IS TRIGGERED AS A SPRAY OF ELECTRONS UPON A TARGET TO PRODUCE
A PULSE OF X-RADIATION.
PASCHAL
(1970)
DESCRIBES THIS HIGH INTENSITY,
SHORT-DURATION RADIATION PULSE AS SIMILAR TO THE PROMPT-GAMMA RADI-
AT IONS FROM A NUCLEAR WEAPON.
THIS TYPE OF MACHINE IS USEFUL TO INVES-
TIGATE TRANSIENT RADIATION EFFECTS IN ELECTRONIC COMPONENTS, OR CAN BE
USED IN HIGH SPEED RADIOGRAPHY.
THE FLASH X-RAY MACHINE INVESTIGATED IS CAPABLE OF PRODUCING
A
50,000
RAD-SILICON DOSE PER PULSE AT THE TARGET FACEPLATE WITH A MAX-
IMUM PHOTON ENERGY OF APPROXIMATELY
7. 5
MEV.
THE MACHINE FACILITY HAS
AN OPEN-TOP SHIELDING CONFIGURATION WHICH, WHILE PROVIDING COMPLETELY
ADEQUATE PROTECTION FROM THE PRJ MARY BEAM, ALLOWS FOR A SMALL AMOUNT
OF SECONDARY SCATTER TO BE PRODUCED BY PHOTON SCATTER OFF THE AIR AND
BUILDING STRUCTURES ABOV£ THE MACHINE.
THE FACILITY SITE IS LOCATED IN.
AN INDUSTRIAL AREA BORDERED BY SEVERAL RESIDENTIAL DWELLINGS.
THE POS..,.
SIBILITY THAT THE MACHINF~ COI.:LD CAUSE UNACCEPTABLE LEVELS OF RADIATION
1
THROUGH SECONDARY SCATTERINGS IN AREAS OUTSIDE OF THE USER S CONTROL
REQUIRED THAT AN EXTENSIVE SURVEY OF THE SCATTERED RADIATION BE COMPLETED.
PROBLEM STATEMENT
THIS PAPER WILL DESCRIBE THE MACHINE FACILITY, THE RADIATION FIELD
PRODUCED SY THE MACHINE, THE APPLICABLE REGULATIONS, AND THE ENVIRON-
MENTAL SURVEY TAKEN TO CONFIRM COMPLIANCE TO THOSE REGULATIONS.
1
THE
2
SURVEY OBJECTIVE WAS TO DESCRIBE THE RADIATION SUFFICIENTLY TO DETERMINE
WHETHER THE MACHINE AT FULL WORK LOAD WOULD CAUSE LEVELS OF RADIATION
IN THE UNCONTROLLED AREAS CAPABLE OF GIVING A WHOLE BODY DOSE IN EXCESS
OF THE MAXIMUM PERMISSIBLE DOSE.
THE X-RAY MACHINE
THE MACHINE ENERGY STORAGE MODULE IS A BANK OF
50
LARGE CAPACITORS.
DURING THE SEVERAL MINUTE LONG CHARGING CYCLE THE BANK OF PARALLEL
CAPACITORS IS CHARGED TO A MAXIMUM WORKING POTENTIAL OF APPROXIMATELY
90
KILOVOLTS.
THE MACHINE IS CAPABLE OF STORING
IN THIS FASHION.
100
KILOJOULES OF ENERGY
UPON TRIGGERING, THE CAPACITORS ARE SWITCHED TO A SERIES
CONFIGURATION RELEASING THE CHARGE TO A STAGE IN WHICH THE ENERGY IS
SHAPED TO A SMOOTH PULSE, TYPICALLY
LONG.
45
NANOSECONDS
THIS VOLTAGE PULSE PRODUCES A SMOOTH
11
(45x10-9
SECONDS)
SPRAY 11 OF HIGH ENERGY
EL.ECTRONS ACROSS A HIGH VACUUM FIELD EMISSION DIODE WHICH STRIKE THE ANODE
TARGET OF • 045 INCH THICK TANTALUM SHEET.
RADIATION WITH A DOSE IN EXCESS OF
50,000
FACEPLATE IN AN AREA OF APPROXIMATELY
7
A
BURST OF BREMSSTRAHLUNG
RAD-SILICON IS PRODUCED AT THE
CM.
IN DIAMETER.
THE ENERGY
SPECTRUM AND BEAM SHAPE OF THIS RADIATION PULSE ARE ESSENTIAL IN THE
CONSIDERATION OF PHOTON SCATTERING, AND WILL BE ELABORATE"D LATER IN THIS
REPORT.
SHIELDING
A
COMMON AND ACCEPTABLE METHOD OF SHIELDING HIGH INTENSITY
IONIZING PHOTON SOURCES, SUCH AS HIGHLY ACTIVE GAMMA-EMITTING RADIOISOTOPES, IS TO SURROUND THE SOURCE WITH A SUFFICIENT SHIEI..D WALL TO
PROTECT FROM DIRECT RAYS, BUT TO LEAVE THE TOP UNSHIELDED.
ACCESS TO A
ROOF OR POSITION DIRECTLY IN LINE WITH THE SOURCE IS FORBIDDEN. THIS METHOD
3
IS CHEAPER AND MORE FLEXIBLE THAN SURROUNDING THE SOURCE COMPLETELY.
PHOTON RADIATION EMERGING FROM THE OPEN TOP OF THE CELL, HOWEVER, WILL
BE SCATTERED BY AIR OR BY LIGHTS OR BY THE CEILING AND STRUCTURES OF THE
THIS SCATTERED RADIATION IS CALLED 11 SKYSHINE 11 AND THE DOSE
BUILDING.
LEVEL IN THE SHADOW OF THE PRIMARY SHIELD WALL FROM THE SKYSHINE MAY BE
THE LIMITING FACTOR IN THE USE OF THE SHIELDING METHOD (STEPHENSON,
FIGURE
1-1
SHOWS THE INVESTIGATED FLASH X-RAY MACHINE AND A
CUT-A-WAY OF THE PRIMARY SHIELD WALLS.
CONSTRUCTED OF
150
THE FLOOR LEVEL.
LINE, IS
6
1958).
THE PRIMARY SHIELD WALLS ARE
LB/CU-FT DENSITY CONCRETE TO A HEIGHT OF
18
FEET ABOVE
THE TARGET FACEPLATE, AND THEREFORE THE BEAM CENTER-
FEET ABOVE THE FLOOR RESULTING IN THE RADIATION SOURCE BEING
12
IN AN EFFECTIVELY
FOOT HIGH OPEN-TOP CELL.
ITSELF, WHICH IS FILLED WITH
27,000
THE MASS OF THE MACHINE
GALLONS OF TRANSFORMER OIL,
IS THE
SHIELDING 11 BEHIND 11 THE TARGET FACEPLATE IN THE OPPOSITE DIRECTION OF THE
ELECTRON SPRAY.
LINE AND IS
3
IS
3
5
THE NORTH SHIELD WALL IS DIRECTLY IN THE BEAM CENTER-
FEET THICK THROUGH ITS ENTIRE HEIGHT.
FEET WIDE CONCRETE TO ITS FULL HEIGHT.
THE EAST SHIELD WALL
THE WEST SHIELD WALL IS
FEET WIDE THROUGH ITS ENTIRE HEIGHT WITH AN ADDITIONAL
TO
10
2. 5
FEET THICKNESS
FEET ABOVE THE FLOOR AS PROTECTION FOR THE EQUIPMEN<r ROOM PERSON-
NEL DIRECTLY WEST OF THIS WALL.
To THE SOUTH, ADDITIONAL WALLS CLOSE IN
TO THE SIDES OF THE MACHINE TO ADD MASS TO THE BACKWARD DIRECTION OF THE
BEAM AND LIMIT BACKSCATTER.
AREA SURROUNDING THE FACILITY
FIGURE
1-2
OUTLINES THE AREA SURROUNDING THE FLASH X-RAY FACILITY.
IMMEDIATELY OUTSIDE THE SHIELD WALL IS THE FACILITY YARD.
THE YARD IS
SURROUNDED BY A SECURITY FENCE AND ACCESS IS CONTROLLED BY THE FACILITY.
4
FLASH X-RAY
TANTALUM TARGET
FACEPLATE
CONSOLE
N
;x:
FIGURE
1-1.
PRIMARY CONCRETE
SHIELD WALL
FLASH X-RAY MACHINE AND CUTAWAY OF SHIELDING
5
RESIDENTIAL
DWELLINGS
STREET
LIGHT
INDUSTRY
COMMERCIAL
VACANT LOT
DISTANCE IN FEET
FIGURE
1-2.
AREAS SURROUNDING FLASH X-RAY FACILITY
6
TO THE NORTH-WEST OF THE BUILDING IS THE COMPANY PARKING LOT.
ON THE NORTH PROPERTY LINE IS THE RAILROAD RIGHT-OF-WAY.
BORDERING
RAIL TRAFFIC
ON THE SINGLE SET OF TRACKS IS VERY LIGHT WITH AN AVERAGE OF TWO OR THREE
TRAINS PASSING DAILY DURING MACHINE USE HOURS. BEYOND THE RAILROAD RIGHTJ
OF-WAY ARE AREAS OF COMMERCIAL LIGHT INDUSTRY AND RESIDENTIAL DWELLINGS.
THE RESIDENTIAL PROPERTY CLOSEST TO THE MACHINE IS APPROXIMATELY
AWAY ON AN APPROXIMATELY
45°
375
FEET
ANGLE FROM BEAM CENTERLINE.
REGULATING STANDARDS
THE POSSESSION AND USE OF THIS FLASH X-RAY MACHINE IS REGULATEC BV
REGISTRATION
IN THE
STATE OF CALIFORNIA.
PROTECTION ARE SPECIFIED IN GROUP
REGULATIONS 11 •
3
THE STANDARDS FOR RADIATION
OF THE 11 CALIFORNIA RADIATION CONTROL
THE USER OF A RADIATION PRODUCING SOURCE MUST CONSIDER
ALL AREAS HE MAY IRRADIATE, AND DEFINE THEM AS 11 CONTROLLED 11 OR 11 UNCONTROLLED 11 ACCORDING TO THE DEGREE OF CONTROL OVER ACCESS THE USER HAS FOR
PURPOSES OF RADIATION SAFETY.
ALL AREAS SURROUNDING THIS FACILITY 1 EXCLUDING THE FENCED-IN YARD
AND THE BUILDING ITSELF
ARE 11 UNCONTROLLED AREAS 11 •
1,
THE REGULATION STATES
FOR UNCONTROLLED AREAS:
11
NO USE:R SHALL POSSESS SOURCES OF RADIATION IN SUCH
A MANNER AS TO CREATE IN ANY UNCONTROLLED AREA,
FROM SUCH SOURCES
1
RADIATION LEVELS WHICH COULD
CAUSE ANY INDIVIDUAL TO RECEIVE A DOSE TO THE WHOLE
BODY IN EXCESS OF;
(1.)
(2)
TWO MILLIREMS IN ANY ONE HOUR; OR
ONE HUNDRED MILLIREMS IN ANY
7
CONSECUTIVE DAYS;
OR
(3) 0. 5
REM IN ANY ONE YEAR. 11
(CALIFORNIA RADIATION CONTROL RE0ULATIONS,
THE MAXIMUM EXPOSURE OF
0. 5
REM PER YEAR IS CONSIDERED TO MAKE
UNCONTROLLED AREAS SAFE FOR THE POPULATION AT LARGE INCL.UDING
TIAL DWELLINGS.
THE
0.5
1973)
RESIDEN-
REM FIGURE AGREES WITH THE RECOMMENDATIONS OF
7
THE INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION (ICRP) FOR CONTRIBUTED DOSE FROM EXTERNAL SOURCES OF THE MAXIMUM PERMISSIBLE GENETIC
DOSE AN INDIVIDUAL (A NON-RADIATION WORKER) MAY RECEIVE IN ONE YEAR.
(I.C.R.P.,
1956)
IN SETTING GUIDELINES, THE ICRP HAS SET THE GENETIC
EFFECTS OF RADIATION EXPOSURE AS THE CRITERIA FOR ALLOWABLE POPULATION
DOSES.
GENETIC EFFECTS ARE ASSUMED TO BE RELATED LINEARLY TO GONADAL
(WHOLE BODY) DOSE WITH NO LOWER THRESHOLD.
THAT IS, ALL WHOLE BODY
DOSES WILL CAUSE SOME GENETIC DAMAGE TO AN INDIVIDUAL'S REPRODUCTIVE
CELLS.
THE LOWER THE DOSE, HOWEVER, THE LOWER THE PROBABILITY OF
PASSING THE EFFECTS OF THE GENETIC DAMAGE TO
PROGENY .
THEN, HAS DETERMINED A PERMISSIBLE GENETIC DOSE AS
11
THE ICRP,
THAT DOSE, WHICH IF
IT WERE RECEIVED BY EACH PERSON FROM CONCEPTION TO THE MEAN AGE OF CHILD
BEARING
(30
YEARS), WOULD RESULT IN AN ACCEPTABLE (GENETIC) BURDEN TO THE
WHOLE POPULATION.
(ICRP,
1966) 11
IN SPECIFYING A LEVEL OF RADIATION WHICH
11
MUST NOT CAUSE ANY
INDIVIDUAL 11 IN THE AREA TO RECEIVE A DOSE ABOVE THE PERMISSIBLE
CALIFORNIA REGULATION ALLOWS DOSE RATES GREATER THAN
0. 5
REM PER YEAR
TO BE IRRADIATED ON THE UNCONTROLLED AREAS AS LONG AS THEY COULD NOT
REASONABLY CAUSE AN INDIVIDUAL TO RECEIVE ABOVE THE PERMISSIBLE DOSE.
SINCE AN UNCONTROLLED AREA MAY OR MAY NOT BE POPULATED OR CONTINUALLY
POPULATED, THE ICRP HAS RECOMMENDED "OCCUPANCY FACTORS" TO ALLOW FOR
THE TIME AN AREA IS POPULATED IN FIGURING PROBABLE DOSE TO AN INDIVIDUAL.
INTERPERTING TABLE
1·-1
FROM THE ICRP PUBLICATION
#3,
(ICRP,
1960)
ONLY THE RAILROAD RIGHT-OF-WAY CAN BE GIVEN AN OCCUPANCY FACTOR LESS
THAN ONE.
THE FREQUENCY OR ACTUAL TIME IN THE IRRADIATED AREA OF AN
INDIVIDUAL ON A PASSING TRAIN, OR THE INFREQUENT RAILROAD WORKER OR CASUAL
8
OCCUPANCY FACTORS
FULL OCCUPANCY
(T-= 1)
CONTROL SPACE, OFFICES, CORRIDORS
AND WAITING SPACE LARGE ENOUGH TO
HOLD DESKS, DARKROOMS, WORKROOMS,
AND SHIPS, NURSE STATIONS, REST AND
LOUNGE ROOMS ROUTINELY USED BY
OCCUPATIONALLY EXPOSED PERSONNEL,
1
LIVING QUARTERS, CHILDREN S PLAY AREAS,
OCCUPIED SPACE IN ADJOINING BUILDINGS.
PARTIAL OCCUPANCY (T=1/ 4)
CORRIDORS TOO NARROW FOR DESKS,
UTILITY ROOMS, REST AND LOUNGE ROOMS
NOT USED ROUTINELY BY OCCUPATIONALLY
EXPOSED PERSONNEL, WARDS AND PATIENTS
ROOMS, ELEVATORS USING OPERATORS,
UNATTENDED PARKING LOTS.
OCCASIONAL OCCUPANCY (T=1/16)
CLOSETS TOO SMALL FOR FUTURE
OCCUPANCY, TOILETS NOT USED ROUTINELY
BY OCCUPATIONALLY EXPOSED PERSONNEL,
STAIRWAYS, AUTOMATIC ELEVATORS,
SIDEWALKS, STREETS.
TABLE
1-1.
OCCUPANCY FACTORS
(FROM lCRP PUBLICATION
3,
1960)
1
9
PEDESTRIAN IN THE IRRADIATED ZONE WOULD APPROXIMATE THE OCCUPANCY OF
"ELEVATORS USING OPERATORS" OR 11 UNATTENDED PARKING LOTS".
THIS WOULD
RESULT IN A 11 PARTIAL OCCUPANCY" DESIGNATION WITH A FACTOR OF
1/4.
IS A CONSERVATIVE EVALUATION WHICH WOULD PERMIT A DOSE LEVEL OF
THIS
2.0
REM
PER YEAR TO THE RAILROAD RIGHT-OF-WAY WITH A RESULTING MAXIMUM DOSE TO
ANY INDIVIDUAL OF
0. 5
REM PER YEAR.
CHAPTER
2
THE RADIATION FIELD
THE PRIMARY BEAM
MACHINE X-RADIATION IS PRODUCED BY ACCELERATING A BEAM OF ELEC-
TRONS ONTO A TARGET.
WHEN THE ELECTRONS ARE STOPPED BY THE TARGET
MATERIAL A PORTION OF THE ELECTRON ENERGY IS GIVEN OFF AS ELECTROMAGNETIC
RADIATION.
THIS IS THE SO-CALLED BREMSSTRAHLUNG OR 11 BRAKING 11 RADIATION
WHICH IS THE RESULT OF DECELERATIONS OF THE ELECTRONS BY COULOMB INTERACTIONS WITH THE TARGET MATERIAL NUCLEI.
FOR A GIVEN ELECTRON BEAM ENERGY THE SPECTRUM OF PHOTON
ENERGIES PRODUCED IS A CONTINUUM WITH A MAXIMUM PHOTON ENERGY EQUAL
TO THE ENTIRE ELECTRON ENERGY.
FIGURE 2-1 SHOWS A TYPICAL SPECTRAL
DISTRIBUTION OF PHOTON ENERGIES OF BREMSSTRAHLUNG RADIATION.
A
SPECTRUM OF DIFFERENT ENERGY X-RAYS ARE EMITTED AT VARIOUS
ANGLES TO THE BEAM OF ELECTRONS.
WITH THIN TARGETS AND HIGH ELECTRON
ENERGIES, THE X-RAYS ARE PRODUCED PREDOMINANTLY IN THE FORWARD DIRECTION
OF THE ELECTRON WITH THIS EFFECT BEING INCREASED WITH EVEN HIGHER ELECTRON
ENERGIES,
(NATIONAL BUREAU OF STANDARDS, 1964B).
THE ELECTRONS PRODUCED BY THE FJELD EMISSION DIODE OF THE FLASH
X-RAY SYSTEM ARE NOT ALL THE SAME ENERGY AS THEY STRIKE THE TARGET.
FIGURE 2-2 DISPLAYS THE EXPECTED SPECTRUM OF ELECTRON ENERGIES FROM
THE SURVEYED FLASH X-RAY MACHINE.
EACH RANGE OF ELECTRON ENERGY IS
GOING TO PRODUCE A SPECTRAL FIELD EMITTED AT AN ANGULAR DISTRIBUTION
CHARACTERISTIC OF ITS ENERGY.
THE HIGHER ENERGY ELECTRONS WILL EMIT A
HIGHER Ef'lERGY PHOTON SPECTRUM IN AN INCREASINGLY FORWARD DIRECTION.
RESULTANT BEAM ENERGY SPECTRUM IS A SUMMATION OF ALL THE DIFFERENT
10
THE
11
I I)
1-
z
:I
>
a:
~
1-
m
a:
~
>
III)
z
Ill
1-
z
200 KV
150 KV
FIGURE
0.2
0.1
0
2-1.
• 0.3
~(A)
TYPICAL BREMSSTRAHLUNG X-RAY SPECTRA FOR TUNGSTEN
TARGET (FROM BLATZ,
1964
AS FOUND IN ARENA,
1971)
1.0
0.8
w
(,)
z
IJ.I
:J
..1
l.L.
a:::
IJ.I
Q]
::E
0.6
:J
z
..1
<C
I-
z
IJ.I
a:::
IJ.I
1.1.
I!.
0.4
r5
IJ.I
>
5
11.1
0::
0.2
0
0
1.0
2.0
FIGURE
3.0
2-2.
4.0
5.0
ELECTRON ENERGY SPECTRUM
6.0
MEV
( COMPUTER SIMULATION)
~
~
13
PHOTON SPECTRA AND IS
CALCULATED FOR THIS MACHINE AS DISPLAYED IN
FIGURE 2-3.
THE RESULTANT INTENSITY SHAPE OF THE PHOTON BEAM IS DIRECTED WITH
A MAXIMUM INTENSITY AND HIGHEST ENERGY ALONG THE ELECTRON BEAM CENTERLINE.
THE CALCULATED ANGULAR DISTRIBUTION OF BEAM INTENSITY IS DISPLAYED
IN FIGURE 2-4.
THE INTENSITY AND ENERGY CHARACTERISTICS OF THE X-RAY PHOTONS
WHICH ARE TO BE SHIELDED OR SCATTERED DEPEND, THEN, ON THE ANGLE FROM
THE ELECTRON BEAM CENTERLINE.
FIGURE 2-5 SHOWS THE SURVEYED MACHINE
AND THE BEAM INTENSITY RELATION TO THE PRIMARY SHIELDING.
THE HIGHEST
INTENSITY AND PHOTON ENERGIES ARE ATTENUATED BY THE PRIMARY CONCRETE
SHIELD WALL.
INTENSITY AND PHOTON ENERGIES DECREASE AT ANGLES ABOVE
THE BEAM CENTERLINE AND APPROACHING THE TARGET PLANE NORMAL TO THE
CENTERLINE.
NATIONAL BUREAU OF STANDARDS (NBS) RECOMMENDS THAT FOR
SHIELDING AND SCATTERING ESTIMATES OF BREMSTRAHLUNG SPECTRUM PHOTONS,
A GOOD APPROXIMATION IS TO ASSUME THE TOTAL BEAM INTENSITY IS CONCENTRATED AT AN ENERGY CORRESPONDING TO ONE-THIRD OF THE INITIAL ELECTRONS'
KINETIC ENERGY (NBS, 1964B).
AN APPROXIMATION OF A
2. 5
IF THE ENTIRE ELECTRON BEAM WERE
7. 5
MEV PHOTON BEAM WOULD BE APPROPRIATE.
MEV,
HOW-
EVER, AS SEEN IN THIS MACiiiNE, A LARGE PORTION OF THE ELECTRONS ARE OF
LOWER ENERGIES, AND THUS, USING FIGURE 2-3 AS A GUIDE, A BEAM OF AROUND
2 MEV EFFECTIVE ENERGY WILL BE USED.
PHOTON SCATTERING
WHEN AN X-RAY PHOTON PASSES THROUGH MATTER, SUCH AS THE GASES
THAT MAKE UP AIR OR THE MATERIAL OF CONCRETE, SEVERAL DIFFERENT PROCESSES
ACT TO ABSORB THE: PHOTON ENERGY AND/OR DEFLECT IT FROM ITS ORIGINAL
14
10
°
z
0
0::
I0
\11
.
..1
w
2
.......... 10-
>
\11
~
..........
Ul
z
0
I0
:r:
D.
10- 3
1
0
2
3
PHOTON ENERGY (MEV)
FIGURE
2-3.
ESTIMATED BREMSSTRAHLUNG ENERGY DISTRIBUTION
FOR PHOTONS FROM FLASH X-RAY MACHINE
(COMPUTER SIMULATION)
_.
15
,\
DEGREES FROM CENTERLINE
FIGURE
2-4.
ESTIMATED FLASH X-RAY BREMSSTRAHLUNG
ANGULAR DISTRIBUTION FOR PHOTONS OVER
(COMPUTER SIMULATiON)
0.3
MEV
•
16
BLOCK WALL
~--
-- ----
~---E"--
<-----~--~-,_..
----j ---fill--
- - --
.
,...
I
y
I
FLASH X-RAY
MACHINE
FIGURE
2-5.
PRIMARY BEAM INTENSITY
HITTING PRIMARY SHIELD WALL
17
PATH (SCATTER}.
THE PROBABILITY THAT A PHOTON WILL INTERACT DEPENDS ON
THE MEDIUM THROUGH WHICH IT IS PASSING AND THE ENERGY OF THE PHOTON.
FIGURE
2-6
DISPLAYS THE MASS ABSORPTION COEFFICIENTS FOR PHOTONS
THROUGH AIR AS A FUNCTION OF PHOTON ENERGY.
THESE COEFFICIENTS GIVE A
MEASURE OF THE PROBABILITY OF AN INTERACTION OCCURING BETWEEN
A PHOTON
AND THE MATERIAL THROUGH WHICH IT IS PASSING.
FoR THIS MACHINE, THE ENERGY RANGE OF THE PHOTONS FROM THE TARGET
IS
0. 2
TO
7. 5
MEV.
PHOTONS LESS THAN
0. 2
MEV ARE COMPLETELY ABSORBED
IN THE ALUMINUM STRUCTURE OF THE VACUUM CHAMBER AND THE TARGET ROOM
WALL WHICH TOTALS .
825
INCHES OF ALUMINUM.
FIGURE
2-6
SHOWS THAT
COMPTON AND PAIR PRODUCTION INTERACTIONS OCCUR IN THE ENERGY RANGE OF
INTEREST.
PAIR PRODUCTION INTERACTIONS OCCUR ABOVE
PROBABILITY AT HIGHER PHOTON ENERGIES.
PRODUCTION OF TWO PHOTONS OF
FIGURE
2-2
0.51
1. 02
MEV WITH INCREASING
THE INTERACTION RESULTS IN THE
MEV ENERGY.
HOWEVER, AS SEEN IN
THE GREAT MAJORITY OF PHOTONS PRODUCED BY THIS MACHINE ARE IN
THE ENERGY REGION WHERE COMPTON INTERACTION IS THE MAJORITY PROCESS.
AT
6
MEV, PAIR PRODUCTION ACCOUNTS FOR ONLY
INTERACTION, THE REMAINDER BEING COMPTON,
15
PERCENT·OF THE TOTAL
(HINE AND BROWNELL,
1956).
COMPTON SCATTER
COMPTON INTERACTIONS OCCUR BETWEEN THE PHOTON AND THE ELECTRONS
OF THE SCATTERING MATERIAL.
WHEN THE PHOTON COLLIDES WITH THE ELECTRON,
THE ELECTRON IS SCATTERED AND THE PHOTON IS SCATTERED THROUGH AN ANGLE,
(SEE FIGURE
2-7),
HOWEVER, THE SCATTERED PHOTON ENERGY .lS LESS THAN THE
ORIGINAL PHOTON BY THE AMOUNT OF ENERGY IMPARTED TO THE ELECTRON.
RATIO OF THE SCATTERED PHOTON ENERGY,
E,
THE
TO THE ORIGINAL PHOTON ENERGY,
e
18
10
5
0::
<(
~
\
2
1-
z
1
u
0.5
'~
1.11
11.
11.
1.11
0
(.)
z
0
1Q.
0::
0
(/)
m
<(
(/)
(/)
~
~
:2
l!)
u
0.2
\
0.1
\
0.05
--- r-- """" r......
(j.h
i'...
\
0.02
\
0.01
\
0.005
0.002
1'
"~ ""' ~
?f /
\~
\
0.001
0.01
'(
0.1
1
I
/
.,.. ..-
'
10
~
100
PHOTON ENERGY (MEV)
FIGURE
2-6.
MASS ABSORPTION COEFFICIENTS FOR AIR AS A FUNCTION
OF PHOTON ENERGY (FROM HINE AND BROWNELL,
~ = COMPTON
MASS ABSORPTION COEFFICIENT
f
1> = PHOTOELECTRIC
}LJ
f
~=PAIR
1956)
MASS ABSORPTION COEFFICIENT
PRODUCTION MASS ABSORPTION COEFFICIENT
19
SCATTERED PHOTON
INCIDENT
PHOTON
SCATTERED ELECTRON
FIGURE
2-7.
COMPTON SCATTERING
0
v ""'
.1
.2
v I/
I vI 1/
11 v
/4/2
'/
/
•3
FRACTION OF
t:::
vv
1/
ENERGY GIVEN TO
I
SCATTERED PHOTON. 4
0 ME\
.5
.6
I I/ .2 .........
v; v ) v
V/ 1// / v y
~/ v/ / v
/
I
.7
I !J
h 1/ -~7
j
.8
v
.9
'~
1
2
/
II'
./
~ ~v ~~
4
6
10
20
40
100
180
ANGLE OF PHOTON
SCATTERING
FIGURE
2-8.
FRACTION OF PHOTON ENERGY GIVEN TO SCATTERED
PHOTON BY SCATTERING ANGLE (FROM HINE AND BROWNELL,
1956)
20
E0
,
IS GIVEN BY THE EQUATION
E/E0
= -1-
(2-1)
(1- cos 9)
1 + E0
0.51
THE RATIO OF THE ENERGIES FOR A GIVEN ANGLE IS DEPENDENT ON THE ORIGINAL
PHOTON. ENERGY.
FIGURE
2-8
GIVES THE FRACTION OF ENERGY GIVEN TO THE
SCATTERED PHOTON FOR SEVERAL PHOTON ENERGIES.
FOR MOST SCATTERING
MATERIALS ALL THE ELECTRONS IN THE SUBSTANCE ARE CAPABLE OF COMPTON
INTERACTIONS.
THE PROBABILITY THAT A PHOTON WILL SCATTER FROM AN ELECTRON OR
THE
11
CROSS SECTION 11 IS GIVEN BY THE KLEIN-NISHINA FORMULA (STEPHENSON,
1958).
THE CROSS SECTION IS DEPENDENT ON THE INITIAL PHOTON ENERGY.
THE
PROBABILITY THAT THE PHOTON WILL SCATTER INTO SOME UNIT OF SOLID ANGLEd.!\.,
AT AN ANGLE
FROM FIGURE
9
IS GIVEN BY THE
2-9,
11
DIFFERENTIAL CROSS SECTION 11
•
AS IS SEEN
HIGHER ENERGY PHOTONS HAVE LESS PROBABILITY OF SCATTERING
INTO LARGE ANGLES.
LOWER ENERGY PHOTONS HAVE A HIGHER PROBABILITY OF
SCATTERING INTO ALL ANGLES.
THE GENERAL METHOD OF SOLVING A PHOTON SCATTERING PROBLEM IS TO
TREAT EACH ELECTRON AS A POINT SOURCE OF SCATTERED RADIATION.
THE TOTAL
SCATTERING MAY THEN BE FOUND BY INTEGRATING OVER THE ENTIRE VOLUME OF THE
SCATTERING MATERIAL EACH iNTENSITY WHICH IS SEEN BY A DETECTOR FROM EACH
UNIT VOLUME OF THE SCATTERER.
THE SCATTERED INTENSITY,
Is
FROM THE
SCATTERER UNIT VOLUME IS THE PRODUCT OF THE ORIGINAL INTENSITY
THE NUMBER OF PHOTONS IN THE SCATTERER,
SECTION FOR THE ANGLE OF SCATTER
...A£.
N,
5
=
I N
0
J..a-
ct.n.
TIMES
TIMES THE DIFFERENTIAL CROSS
(HINE AND BROWNELL,
ol.n.
L
10
(2-2)
1956).
21
10
8
Lt'
\
6
1\\' l\.
' 1\' l'\~\ f\'
1
4
~-..~
~
'~\ 1\
\
3
2
!'-... L/
~\ \.._
~
v
L
v
_, 1--"
E=.051
...._
.204
-
.51 MEV
~
~ ~ ~"- -
1--'
dcr
1
_xlo-26
o{Jl.
\
.8
1\
"'"
"'
..........
\
1\
\
.4
•3
MEV
r-. ...
3.06
MEV
t-....... r--
6.12
MEV
~
'~
'
.2
f'...
~~
"' '
.1
0
20
60
100
140
180
SCATTERING ANGLE (DEGREES)
FIGURE
2-9.
MEV
1.02
\ 1\
.6
MEV
V'
DIFFERENTIAL KLEIN-NISHINA
CROSS SECTIONS (FROM STEPHENSON,
1958)
22
PHOTON 5KYSHINE
THE X-RAY PHOTONS WHICH ARE NOT ATTENUATED BY THE PRIMARY SHIELD
WALLS ARE SUBJECT TO BEING SCATTERED INTO THE SHADOW OF THE SHIELD WALLS
BY MATERIALS OF THE AIR AND BUILDING STRUCTURES ABOVE THE SHIELD WALL.
FIGURE
2-10
SHOWS THE TWO MOST PROBABLE CENTERS OF SIGNIFICANT SCATTER
FROM THE PRIMARY BEAM;
(1)
SUPPORTS THE CEILING, AND
THE BLOCK WALL ABOVE THE SHIELD WALL WHICH
(2)
THE AIR ABOVE THE FACILITY.
BLOCK WALL SCATTER
THE BLOCK WALL OVER THE SHIELD WALL IS CONSTRUCTED OF UNFILLED
CONCRETE BLOCKS WHICH GIVE AN APPROXIMATE EFFECTIVE THICKNESS OF
(5
CM.) OF CONCRETE.
1969)
THE WALL GIVES
SCATTER PHOTONS.
PHOTONS
(87%
OF
6
2
INCHES
USING COMPONENTS OF ORDINARY CONCRETE (CEMBER,
3. 52Xl0 24
ELECTRONS PER SQUARE CENTIMETER TO
THE WALL IS PRACTICALLY TRANSPARENT TO HIGHER ENERGY
MEV PHOTONS PASS UNEFFECTED).
THE INTERACTIONS
OCCURRING TO HIGH ENERGY PHOTONS WILL CAUSE SCATTER THROUGH SMALL ANGLES
WITH A SMALL LOSS IN PHOTON' ENERGY.
THE LOWER ENERGY COMPONENTS OF THE
PRIMARY BEAM WILL BE SCATTERED THROUGH GREATER ANGLES, AND WILL RETAIN
A GREATER FRACTION OF THEIR INITIAL ENERGY THAN THE HIGHER ENERGY PHOTONS.
THE EFFECT OF THI.3 BLOCK WALL SCATTER, THEN,
IS THAT THE NEAR
FIELD AREAS 11 SEE 11 A LARGE SOURCE OF LOWER ENERGY SCATTER PHOTONS AND THE
FAR FIELD AREAS 11 SEE11 THE HIGHER ENERGY PHOTONS.
CALCULATING A SCATTERED
DOSE FROM THE BLOCK WALL SURFACE AT A DETECTOR POINT IN THE SHIELD WALL
SHADOW WOULD REQUIRE AN INTEGRATION OF ALL DOSES FROM UNIT AREAS OF THE
WALL.
EACH UNIT AREA OF THE WALL WOULD RECEIVE A DIFFERENT ENERGY AND
INTENSITY COMPONENT OF THE PRIMARY BEAM CORRESPONDING TO ITS POSITION
RELATIVE TO THE BEAM CENTER LINE.
THE CALCULATION OF THIS EXPECTED DOSE
23
IS BEYOND THE SCOPE OF THIS PAPER.
AIR SCATTER
MANY TEXTS ADDRESS THE PROBLEM OF PHOTON AIR SCATTER BY DESCRIBING METHODS FOR ESTIMATING THE AIR SGATTER DOSE IN THE SHIELD SHADOW
OF AN OPEN TOP CELL CONTAINING A GAMMA EMITTING RADIOISOTOPE
(STEPHENSON,
1958;
HARRISON,
1957;
BIRCHALL,
1967;
GLOYNA,
1969).
AGAIN, THE AIR ABOVE THE SOURCE IS DIVIDED INTO SMALL SCATTERING VOLUMES
AND THE DOSE TO A DETECTOR IN THE SHADOW OF THE SHIELD IS CALCULATED AND
SUMMED.
THE PHOTONS ARE ASSUMED TO BE ISOTROPICALLY EMITTED AND ARE ALL
OF THE SAME ENERGY.
USING FIGURE
2-11
TO DESCRIBE THE GEOMETRY, THE
GENERAL EQUATION FOR AIR SCATTERED GAMMA PHOTONS IS;
DosE= SN
B...;;;;..:..4,;,..1r.,....-r-
S
=
(2-3)
THE ISOTROPICALLY IRRADIATED NUMBER OF PHOTONS EMITTED FROM
THE POINT SOURCE AT A GIVEN ENERGY
N
=
THE NUMBER OF ELECTRONS IN THE SCATTERED MEDIA PER CUBIC
CENTIMETER
B
=
A
PHOTON FLUX TO DOSE CONSTANT DEPENDENT ON THE EMITTED
PHOTON ENERGY
J.qo- = KLEIN-NISHINA CROSS
M
V'
SECTION CONSTANT (USUALLY ESTIMATED AS
AN AVERAGE VALUE FOR SCATTERING GREATER THAN
=
90°)
.
DISTANCE FROM SOURCE TO RECEPTOR
THIS APPROACH HAS ASSUMED ONLY SINGLE SCATTER INCIDENTS, NEGLECTS
AIR ABSORPTION IN BOTH THE PRIMARY AND SCATTER PHOTONS, AND NEGLECTS DOSE
BUILDUP.
BIRCHALL
(1968)
POINTS OUT THAT THE DOUBLE SCATTER INCIDENTS "AND
AIR ABSORPTION EFFECTS CAN BE NEGLECTED WITH SOURCE-TO-RECEPTOR DISTANCES
SMALL COMPARED TO THE PHOTON-MEAN-FREE PATH IN AIR.
HOWEVER THE
MACHINE
PRIMARY SOURCE IS NEITHER ISOTROPIC IN PHOTON ENERGY NOR PHOTON INTENSITY.
THIS GENERAL EQUATION ALSO ASSUMES THAT THE BEAM IS DIRECTED UPWARD IN
24
SUCH A WAY THAT SCATTERING ANGLES ARE 90° OR GREATER IN WHICH CASE THE
KLEIN-NISHINA CROSS SECTION IS APPROXIMATELY CONSTANT.
AS SEEN IN
FIGURE 2-10, THE INTENSE PORTION OF THE BEAM DIRECTLY OVER THE SHIELD.
WALL (AND BLOCK WALL) ALLOWS SCATTER ANG,LES LESS THAN 90° TO REACH THE
NEAR FIELD.
THE GENERAL EQUATION DOES SUGGEST THAT AT LARGER DISTANCES
A DOSE TO DISTANCE DEPENDENCE OF R-
1
DUE TO THE GREATEST PORTION OF THE
BEAM INTENSITY PROPAGATING UPWARDS CAUSING SECONDARY SCATTERS AT 90°
AND GREATER . DOES OCCUR.
AGAIN, AN ACCURATE CALCULATION OF THE AIR SCATTER DOSE
EXTREMELY COMPLICATED AND BEYOND THE SCOPE OF THIS PAPER.
IS
A SEARCH
OF THE CURRENT LITERATURE REVEALS ONLY GROSS GENERAL STATEMENTS
CHARACTERIZING SPECTRAL, PHOTON AIR SCATTER.
1.
THEY INCLUDE;
FoR AN ACCELERATOR OPERATING WITH NO ROOF, THE RADIATION
FROM AIR SCATTER WILL BE OF THE ORDER OF 1/50 OF THE DIRECT
RADIATION (NBS, 1964B).
2.
FoR X-RAYS GENERATED AT POTENTIALS LESS THAN 500KV,
COMPTON SCATTERING DOES NOT GREATLY DEGRADE ENERGY
(NBS, 1964A).
3.
FOR X-RAYS ·3ENERATED AT POTENTIALS ABOVE 500KV THE 90°
SCATTERED RADIATION IS, TO A FIRST APPROXIMATION, EQUAL IN
ENERGY DISTRIBUTION TO X-RAYS GENERATED BY POTENTIALS OF
500 KV REGARDLESS OF THE KILOVOLT AGE (NBS, 1964A).
4.
FoR A 90° SCAl'TERING ANGLE, THE SCATTERED-TO-INCIDENT
RADIATION EXPOSURE IS
0.1
PERCENT.
FOR LARGER SCATTERING
ANGLES, THE AMOUNT OF SCATTER IS SLIGHTLY LESS THAN 0.1
PERCENT AND FOR SMALLER ANGLES OF SCATTER THE PERCENT
,{
(
'
"SOFT" LARGE '
ANGLE SCATTER '
FROM AIR
'
''
----
'
'
"HARD" SMALL
ANGLE SCATTER
~ ~FF BLOCK WALL
'
~
~
"SOFT" LARGE ANGLE
SCATTER OFF BLOCK WALL
FIGURE
2-10.
PROBABLE SCATTERING CENTERS
~
c.n
26
INCREASES
(NBS, 1964A).
FROM THESE GENERAL STATEMENTS THE AIR-SCATTER-FIELD MAY BE
CHARACTERIZED WITH AN ENERGY LESS THAN
IN THE FAR-FIELD LESS THAN
DISTANCE.
OF
350
FoR A POINT
200
0.1
500
KEV PHOTONS AND AN INTENSITY
PERCENT OF THE PRIMARY BEAM AT THAT
FEET FROM THE TARGET AND A PRIMARY BEAM DOSE
REM AT ONE METER, A DOSE OF
.1
REM PER SHOT COULD BE EXPECTED.
27
(RECEPTOR)
CELL SIDE VIEW
FIGURE
2-11.
CELL FRONT VIEW
OPEN- TOP CELL DIAGRAM FOR CALCULATING
AIR SCATTER DOSES (FROM STEPHENSON,
1958)
CHAPTER
3
. THE ENVIRONMENTAL RADIATION SURVEY
THE SURVEY WAS DESIGNED TO ACCOMPLISH TWO OBJECTIVES:
1.
DETERMINE THE DOSE PRODUCED BY THE MACHINE IN UNCONTROLLED
AREAS OUTSIDE THE FACILITY BOUNDARIES
2.
CHARACTERIZE THE SCATTERED RADIATION FIELD.
THE INITIAL PART OF THE SURVEY CHARACTERIZED THE SCATTER FIELD
IN THE FACILITY YARD AND OUT INTO THE UNCONTROLLED AREA.
THIS FIRST PART
DETERMINED THAT THE DOSE IN THE UNCONTROLLED AREAS WAS ABOVE THE PERMISSIBLE LEVELS AND THEREFORE NECESSITATED A SERIES OF MEASUREMENTS TO
DETERMINE THE RELATIVE IMPORTANCE OF DIFFERENT SCATTERING CENTERS AND
THE EFFECTIVE ENERGY OF THE INITIAL AND SCATTERED BEAMS.
THE INITIAL SURVEYS
THE X-RAY MACHINE FACEPLATE IS POSITIONED NORMAL TO THE NORTH-
SOUTH CENTERLINE OF THE SHIELDED TARGET ROOM.
THE PRIMARY SHIELD WALL IS
THE SAME HEIGHT AROUND THE FACEPLATE AND THE PRIMARY BEAM IS THEORETICALLY
SYMMETRICAL AROUND THE CENTERLINE OF THE ELECTRON SPRAY.
FROM THESE
CONSIDERATIONS IT WAS ASSUMED THE AIR SCATTER IN THE FAR FIELD WOULD BE
SYMMETRICAL ACROSS THE BEAM CENTERLINE.
THE CLOSEST UNCONTROLLED AREAS TO THE TARGET FACIZPLATE WERE THE
RAILROAD RIGHT-OF-WAY, THE LIGHT INDUSTRY AND THE RESIDENTIAL AREA
APPRIXIMATELY
FIGURE
AREAS.
1-2).
45°
OFF BEAM CENTERLINE TO THE NORTH-EAS1"
(SEE
LONG TERM DOSIMETERS COULD NOT SECURELY BE PLACED IN THESE
GIVEN THE SYMMETRY OF THE AIR SCATTERED RADIATION FIELD, THE DOSE
RATE PROFILES OF THE UNCONTROLLED AREAS TO THE
DETERMINING THE DOSE PROFILES TO THE
NW
28
NE
COULD BE DEDUCED BY
IN THE RELATIVELY SECURE AREA OF
29
OF THE COMPANY PARKING LOT.
A
11
PICTURE 11 OF THE SCATTER DOSE FIELD EXTENSIVE ENOUGH TO SHOW
THE MAXIMUM AREAS OF SCATTER DOSE AND THE DROP OFF RATE IN THE DOSE WITH
INCREASING DISTANCE FROM THE TARGET WAS SOUGHT.
DOSE PROFILES ALONG
LINES EXTENDING FROM THE TARGET ALONG;
1.
THE BEAM CENTERLINE
2.
45°
WEST OF BEAM CENTERLINE
3.
90°
WEST OF BEAM CENTERLINE
{SEE FIGURE
3-1)
WERE NEEDED TO ESTABLISH THE PICTURE OF THE SCATTER FIELD.
THE DOSE
PROFILE ALONG THE BEAM CENTERLINE CURVE WOULD INDICATE THE AREA OF HIGHEST
DOSE RATES.
THE
45°
THE
90°
LEG WOULD SHOW THE WEAKEST DOSE RATES, AND, FINALLY,
LEG WOULD DEMONSTRATE THE DOSE RATE AT THE ANGLE CLOSEST TO THE
UNCONTROLLED AREA.
AT EACH ANGLE,
CURVE.
AT THE
45°
AND
ENOUGH POINTS WERE SOUGHT TO CONSTRUCT A SMOOTH
90°
ANGLES THE DOSES MEASURED IN THE PARKING LOT
COULD BE TRANSFERRED TO POINTS IN THE UNCONTROLLED AREAS.
ON THE EAST SIDE OF THE CENTERLINE AT
AT
90°
(POINT
#19)
45°
(POINTS
#18
AND
MONITOR POINTS
#20)
AND A POINT
WERE SET UP TO CONFIRM THE SYMMETRY ASSUMPTION.
IN
ADDITION, TWO POINTS INSIDE THE TARGET ROOM AND ON THE TARGET ROOM ROOF
WERE PLACED TO DETERMINE THE INITIAL DOSE AT THE TARGET WHICH INITIATED
THE SCATTER.
FINALLY, THE LOW DOSE RATE EXPECTED, THE LARGE AREA AND THE MANY
POINTS NEEDED TO DETERMINE THE DOSE IN A FEW MONTHS PROHIBITED POINTS
BEING TAKEN INDIVIDUALLY, ONE PER SHOT.
MANY INEXPENSIVE DOSIMETERS,
SUITABL.E TO BE PLACED IN THE FIELD FOR AT LEAST ONE MONTH WERE INDICATED.
ALTHOUGH A MEASURE OF SECURITY (THE COMPANY SECURITY CHECKS OF THE
30
200
100
0
~
Wtjlll?ZZZZZ;i
DISTANCE IN FEET
12*
11*
)t
FLASH
.
2. 1
....4 3• •
/
""
/
"+"-;
..
-
7
•
9
lOA
t/
'
•
9A
+
~/
X-RAY
•
•
13
•
14
"
•
15
llA
10
•
•
12
•
11
•
16
•
, .. ,
I e' INDICATES TRANSPOSED
...,./
FIGUHE
3-1.
•
LOCATIONS
MONITOR STATION LOCAT10NS
17
•
)t
31
PARKING) WAS HELD FOR ALL POINTS, ONLY THE BEAM CENTERLINE POINTS AND
THOSE INSIDE THE FACILITY FENCE COULD BE ASSURED.
IN PLANNING HOW THE LOW DOSES EXPECTED WERE TO BE MEASURED SEVERAL
PROBLEMS WERE APPARENT.
FIRST, THE EXTREMELY FAST PULSE
(45
NANO-
SECONDS) COULD NOT BE MONITORED BY A CONVENTIONAL SURVEY RATE-METER.
A
PRACTICALLY DOSE RATE INDEPENDENT DOSIMETER WAS INDICATED.
SECOND, THE DOSE PRODUCED IS A FUNCTION OF THE NUMBER OF PULSES.
BOTH BECAUSE OF THE BREAK-IN OPERATIONAL MODE, AND TO AVOID PRODUClNG
STILL UNCONFIRMED LEVELS OF RADIATION ON THE UNCONTROLLED AREAS, THE
MACHINE AT THE TIME OF THE SURVEY WAS RUNNING AT ONLY ABOUT TWENTY-FIVE
PERCENT OF THE NORMAL WORKLOAD.
IMUM PERMISSIBLE DOSE OF
500
THIS MEANT THAT TO CONFIRM THE MAX-
MREM PER YEAR
(42
MREM PER MONTH) THE
DOSIMETRY HAD TO HAVE THE CAPABILITY TO MEASURE ONE FOURTH OF THIS OR
APPROXIMATELY
10
MREM PER MONTH.
THIS BROUGHT THE EXPECTED DOSES TO BE
MEASURED TO ROUGHLY THE SAME MAGNITUDE AS THE NATURAL BACKGROUND
RADIATION.
BACKGROUND GAMMA RADIATION IS PRODUCED BY COSMIC RADIATION,
RADIONUCLIDES IN THE SOIL, THE NATURAL DECAY PRODUCTS OF URANIUM AND
THORIUM (RADON AND THORON), WHICH ARE IN THE ATMOSPHERE AS WELL AS FALLOUT FROM NUCLEAR WEAPONS TESTING {BURKE,
ON THE LATITUDE, ALTITUDE
OF THE SOIL.
(0 1 BRIEN
1975).
AND BURKE,
THE DOSE IS DEPENDENT
1973),
AND THE COMPOSITION
WEATHER CONDITIONS MAY TEND TO CAUSE INVERSION LAYERS
WHICH CONCENTRATE THE AIRBORNE RADIONUCLIDES NEAR THE GROUND.
THE
PRESENCE OF STANDING WATER ON THE GROUND CAN ABSORB SOME OF THE
RADIATIONS FROM THE GROUND {GEIGER AND SANCHEZ,
THEN CAN VARY FROM PLACE TO PLACE AND WITH TIME.
1973).
THE BACKGROUND,
IN THE UNITED STATES
THE AVERAGE ANNUAL WHOLE BODY DOSE DUE TO EXTERNAL NATURAL RADIATION
32
IS ABOUT 130 MREM PER YEAR (EPA, 1972).
OF THIS DOSE IT IS ESTIMATED
THAT A DETECTOR MEASURING ONLY EXTERNAL IONIZING RADIATION WILL DETECT
ABOUT 100 MREMS PER YEAR {JENKINS, 1972).
HOWEVER, THE BACKGROUND
DOSES CAN HAVE MONTHLY VARIATIONS AS HIGH AS TWENTY-FIVE PERCENT
(EPA, 1972).
SINCE THERE IS NO PREVIOUS DATA ON THE FACILITY BACKGROUND
DOSE, IT IS ESTIMATED THAT AN APPROXIMATELY 10 MREM PER MONTH BACKGROUND EXISTS IN THE AREA.
DOSIMETRY
To MEASURE THE LONG TERM, LOW DOSE PHOTON RADIATION WHICH COULD
BE EXPECTED FROM THE MACHING SKYSHINE, A COMBINATION OF FILMBADGES AND
THERMOLUMINESCENT DOSIMETERS (TL0 1s) WAS CHOSEN.
BOTH DETECTORS WERE
INEXPENSIVE AND READILY AVAILABLE FROM ESTABLISHED COMMERCIAL SERVICES
WHO WOULD PROVIDE THE DOSIMETERS AND ACCURATELY READ AND REPORT THE
DOSE MEASUREMENTS.
TLD SERVICE WAS FROM EBERLINE INSTRUMENT CORPORATION OF
SANTA FE, NEW MEXICO.
THEIR STANDARD AREA MONITOR PACKET CONSISTS OF
FIVE 1/8"x1/811 x.035" LITHIUM FLOURIDE (TLD-100) EXTRUDED CHIPS.
TLD MATERIAL MEASURES RADIATION DOSE IN THE FOLLOWING MANNER.
EXPOSURE OF THE TL MATERIAL TO IONIZING RADIATION CAUSES ELECTRONS IN THE
MATERIAL TO BE RAISED TO HIGHER ENERGY LEVELS AND HELD BY 11 ELECTRON TRAPS 11
IN NUMBERS PROPORTIONAL TO THE RADIATION EXPOSURE.
UPON HEATING THE
MATERIAL, THE ELECTRONS ARE RELEASED WITH A PRODUCTION OF LIGHT.
THIS
THERMOLUMINESCENCE CAN BE MEASURED AND CALIBRATED TO A KNOWN DOSE THUS
GIVING A MEASURE OF THE ORIGINAL RADIATION EXPOSURE (CAMERON, 1966).
THE USEFUL DOSE RANGE OF TLD-100 IS A FEW MILLIREMS TO 10,000
REM (CAMERON, 1968).
FIGURE 3-2 SHOWS THAT THERE IS ESSENTIALLY NO DOSE
33
RATE EFFECT IN LIF.
FIGURE 3-3 SHOWS THAT THE SENSITIVITY OF LIF IS
STABLE OVER A LARGE ENERGY RANGE AS THE RATIO OF THE ENERGY DEPOSITED IN
THE PHOSPHOR TO THE ENERGY (oR DOSE) DEPOSITED IN TISSUE (CHUCHET AND
JOFFRE, 1967).
THIS DOSIMETER IS USEFUL IN THE LOW MREM RANGE NEEDED,
IS INDEPENDENT OF DOSE-RATE AND PHOTON ENERGY, AND HAS BEEN SHOWN
(GEIGER AND SANCHEZ, EBERLINE, 1971) TO SHOW NO FADING IN ENVIRONMENTAL
MONITORING OVER PERIODS UP TO ONE YEAR.
WITH THEIR DOSIMETER SERVICE,
EBERLINE PROMISES MEASUREMENT PRECISION OF 20% STANDARD DEVIATION WITH
A
5
A
5%
MREM EXPOSURE, 10% STANDARD DEVIATION WITH A 10 MREM EXPOSURE, AND
STANDARD DEVIATION ON DOSES UP TO 30 REM.
A STANDARD PERSONNEL FILM BADGE SUPPLIED BY RADIATION DETECTION
OF SUNNYVALE, CALIFORNIA WAS ALSO INCLUDED IN EACH MONITORING STATION.
FILM DOSE MEASUREMENTS ARE AFFECTED BY ENVIRONMENTAL CONDITIONS SUCH
AS HEAT, HUMIDITY, LIGHT AND ORGANIC VAPORS CAUSING DARKENING OF THE FILM
WHICH CAN BE ERRONEOUSLY READ AS EXPOSURE.
THE PROPERTIES MAKE THEM
UNACCEPTABLE FOR ENVIRONMENTAL DOSE MEASUREMENTS, HOWEVER, A SERIES OF
PL.ASTIC, ALUMINUM, CADMIUM PLUS ALUMINUM, AND LEAD PLUS ALUMINUM
FILTERS MAKE POSSIBLE ROUGH ESTIMATIONS OF EFFECTIVE PHOTON ENERGY.
THIS QUALITATIVE INFORMATION COULD HELP IDENTIFY OR CONFIRM THE SOURCE
OF THE RADIATION MEASURED.
MONITOR STATIONS
EACH MONITOR STATION CONSISTED OF A SMALL ALUMINUM !!CHASSIS" BOX
ON A 3FT HIGH STAND. THE CHASSIS BOX WAS MADE OF .040 INCH THICK
ALUMINUM SHEET.
THE DOSE SEEN IS REPRESENTATIVE OF THE WHOLE BODY DOSE
SPECIFIED IN THE CALIFORNIA REGULATIONS.
THE ADVANTAGES OF THIS BOX
INCLUDED ITS DURABILITY AND INEXPENSIVE AVAILABILITY IN THE COMPANY STORES.
34
DOSE RATE (RAD/SEC)
1.2
1.0
0.8
.
.
10
•
RESPONSE
•••
.
1.0
0.8
0.6
0.4
6
10 7
• •• •
• ••
.
. ..
t•
10 8
•
10 9
.·
.
•
•
.
•
I
10- 3
10- 2
10-1
10°
•
••
...
l
•
2
RAD/PULSE
FIGURE
3-2.
DOSE RATE RESPONSE OF TLD (LJF) AND FILM
10
RESPONSE
1.0
~-----------------------
0.1
10 c
PHOTON ENERGY (KEV)
FIGURE
3-3.
THEORETICAL SENSITIVITY OF LJF CALCULATED AS
THE RATIO OF THE ENERGY DEPOSITED IN THE PHOSPHOR TO THE
ENERGY DEPOSITED IN TISSUE
35
AN ATTEMPT TO MOISTURE PROOF THE FILM BADGES WAS MADE BY WRAPPING THE:M
IN THIN PLASTIC BAGS AND SEALING WITH TAPE.
THIS WAS FOUND TO BE
INEFFECTIVE AS MANY OF THE BADGES WERE FOUND TO BE WATER DAMAGED.
CHAPTER
4
SURVEY RESULTS
FIGURES
4-1
AND
4-2
DISPLAY THE DOSE PROFILES FOR THE FIRST AND
SECOND MONTH LONG SURVEYS RESPECTIVELY.
POINTS DISPLAYED ARE THE DOSE
PER SHOT OR THE TOTAL DOSE MEASURED (MINUS BACKGROUND) DIVIDED BY THE
NUMBER OF SHOTS DURING THE TIME PERIOD THE MONITORS WERE IN POSITION.
ToTAL DOSE IS THE AVERAGE READING OF THE FIVE TLD CHIPS IN THE
EBERLINE AREA MONITOR BADGE • .APPENDIXES A AND B TABULATE MONITOR DOSES
FOR THE TLD AND FILMBADGE DOSIMETERS.
BACKGROUND DOSE
THE BACKGROUND DOSE REMOVED FROM THE TOTAL DOSE WAS CALCULATED
FROM GENERAL RATES OBTAINED IN REFERENCE TEXTS.
EACH SHIPMENT OF DOS-
IMETER BADGES WERE STORED IN AN OFFICE DESK ON RECEIPT AT THE COMPANY
UNTIL PLACED IN THE MONITOR STATIONS.
THE OFFICE WAS LOCATED IN THE
GROUND FLOOR OF A TWO STORY CONCRETE AND STEEL BUILDING.
RATE DURING THIS PERIOD WAS
5
MICRORADS PER HOUR,
(YEATES,
ESTIMATED DOSE
1972).
DURING
THE SURVEY, THE SHIPMENT CONTROL BADGE REMAINED IN THE OFFICE AND WAS
RETURNED WITH THE SURVEY BADGES, TO EBERLINE IN NEW MEXICO, FOR READING.
THE DOSE FROM THE EXPOSURE IN THE OFFICE WAS SUBTRACTED FROM THE TOTAL
REPORTED DOSE ON THE CONTROL BADGE.
THE REMAINING DOSE WAS ATTRIBUTED
TO IRRADIATION OF THE SHIPMENT DURING AIRCRAFT FLIGHTS FROM THE SUPPLIER
TO THE COMPANY AND TI-lE RE:TURN TRIP.
THE BACKGROUND SUBTRACTED FROM EACH DOSIMETER TOTAL DOSE WAS
THE SUM OF:
1)
THE DOSE DURING SHiPMENT
2)
THE DOSE DURING STORAGE BEFORE SURVEY PLACEMENT
36
3.0
2.5
2.0
DOSE/ SHOT
1. 5
'M
I
BEAM CENTERLINE
X
(MREM)
"
1.0
0.5
0
2.0
1.5
55
1.0
0
OFF BEAM CENTERLINE (WEST)
0.5
0
1.0
90
0.5
0
X
0
OFF BEAM CENTERLINE (WEST)
7(
40
DISTANCE FROM FACEPLATE
(FEET)
FIGURE
4-1.
SKYSHINE DOSE CURVES; SURVEY
1
Cl-'
~
3.0
2.5f
,r
2.0
)C'
BEAM CENTERLINE
DOSE/SHOT
I
(MREM)
1.0
)(
I
X
~
49°
.1.0
OFF BEAM CENTERLINE (WEST)
)(
~. 0
I
I
I
I
I
I
I
I
I
I
I
90°
I
I
,X
I
,
I
,
I
,.
I
OFF BEAM CENTERLINE (WEST)
)(
)(
0
40
DISTANCE FROM FACEPLATE
(FEET)
FIGURE
4-2.
SKYSHINE DoSE CURVES; SURVEY
2
t.:)
(X)
39
3)
THE FRACTION OF THE ESTIMATED 10 MREM MONTHLY NATURAL BACKGROUND DURING THE SURVEY PERIOD CALCULATED ON A THIRTY DAY
MONTH.
CALCULATED BACKGROUND DOSE TO THE FIRST SURVEY WAS 18.5 MREM;
FOR THE SECOND SURVEY • 19.8 MREM.
DOSIMETER ACCURACY
THE VENDOR SPECIFIED ACCURACY OF THE TLD CHIPS IN THE FIVE CHIP
PACKETS FOR THE RANGE OF THE TOTAL DOSE WAS A STANDARD DEVIATION OF 5%.
FoR THE FIRST SURVEY THE AVERAGE DEVIATION OF THE SCATTER MONITOR STATION
WAS
3. 8%.
8. 5%.
FOR THE SECOND SURVEY
1
THE AVERAGE STANDARD DEVIATION WAS
THIS IS CONSIDERED STILL WITHIN THE ACCURACY RANGE DESIRED.
FILMBADGE DOSIMETRY
THE FAILURE TO PROPERLY KEEP THE FILMBADGES FROM ENVIRONMENTAL
MOISTURE DURING THE ONE MONTH EXPOSURES RESULTED IN REJECTING THE
READINGS.
RADIATION DETECTION COMPANY INDICATED MANY OF THE FILMS
APPEARED TO BE WATER DAMAGED AND WOULD READ LOW.
THE FILMBADGE SERVICE INDICATED THE FILTER RATIO ON MOST OF THE
FILMS WAS TYPICAL OF TECHNETJUM-99 WHICH EMITS A BETA PARTICLE.
THE
BETA ENERGY SPECTRUM HAS A .295 MEV MAXIMUM ENERGY AND .085 AVERAGE
ENERGY.
THIS WOULD INDICATE A LOW ENERGY SKYSHINE SPECTRUM.
WOULD RULE OUT DIRECT LEAKAGE OF THE PRIMARY BEAM
1
THIS
BUT BE OTHERWISE OF
LITTLE AND/OR QUESTIONABLE VALUE IN SKYSHINE ENERGY DETERMINATION.
PRIMARY BEAM DOSIMETRY
1
TABLE 4-1 LISTS THE DOSE MEASUREMENTS OF TLD S PLACED IN THE
PRIMARY BEAM INSIDE OR. ON THE TARGET ROOM ROOF.
40
LOCATION
DISTANCE
LOCATION
SURVEY
1
SURVEY
2
FROM
FACEPLATE
FEET
23
INSIDE TARGET
ROOM;
90
8.0
TOTAL
DOSE/
TOTAL
DOSE/
DosE
PULSE
DosE
PULSE
MREM
MREM
MREM
MREM
276.4
2.3
416
2.4
DEGREES
OFF CENTERLINE
24
INSIDE TARGET
ROOM;
45
11.3
2379
19.9
2377 13.9
DEGREES
OFF CENTERLINE
25
TARGET ROOM
ROOF;
90
19.5
16.0
.1
21
.1
132.8
1.1
134
.8
DEGREES
OFF CENTERLINE
26
TARGET ROOM
ROOF;
55
28
DEGREES
OFF CENTERLINE
TABLE
4-1.
NEAR FIELD ACCUMULATED DOSES FOR SURVEYS
1
AND
2
41
ANALYSIS AND CONCLUSIONS
THE PROMINENT PEAK IN THE DOSE CURVES OF ALL THREE PROFILES
INDICATE5THE5CATTER PHENOMENA PRODUCES ONE SINGLE RING OF HIGH DOSE
RATE IN THE SHADOW OF THE SHIELD WALL.
THE DOSE RATE PER SHOT DROPS
OFF SMOOTHLY FROM THE PEAKWITH OBVIOUS INCURSION INTO THE UNCONTROLLED
AREAS.
THE SYMMETRY OF THE SCATTER Fl ELD WHICH ENABLES THE MEASUREMENTS IN THE PARKING AREA WEST OF THE CENTERLINE TO BE TRANSPOSED TO THE
UNCONTROLLED AREAS EAST OF THE CENTERLINE 15 VERIFIED IN THE 90° FROM
CENTERLINE AREAS BY LOCATIONS #19 AND #15 WITH 290 SHOT DOSE PER 51-lOT
MEASUREMENTS OF • 28 AND • 27 MREM RESPECTIVELY.
IN THE 45° PROFILES THE TRANSPOSED LOCATION #9A IS ONLY 10 FEET
FARTHER OUT FROM THE FACEPLATE THAN LOCATION #18.
USING AN INVERSE
DISTANCE (1/R) RELATIONSHIP TO ACCOUNT FOR THE 10 FOOT DIFFERENCE, THE
DIRECT READING 15 32% HIGHER (#18=. 88, #9A=. 67 MREM PER SHOT).
THIS DISCREPANCY IS MOST LIKELY CAUSED BY THE SHADOW EFFECT ON THE
LOW ANGLE BLOCK WALL SCATTER BY THE FACILITY BUILDING TO THE WEST PARKING LOT.
TABLE 4-2 LISTS THE SUMMARY OF THE EXPOSURE DATA WITH ALL
TRANSPOSED PARKING LOT IV:EASUREMENTS INCREASED BY 32%.
THIS IS A
CONSERVATIVE APPROACH ATTEMPTING TO INCLUDE THE WORST POSSIBLE CASE.
FROM TABLE 4-2, IT CAN BE SEEN THAT THE MAXIMUM PERMISSIBLE
DosE (MPD) IN THE UNCONYROLLED AREAS 15 EXCEEDED AT THE DESIRED WORK
LOAD OF 120 SHOTS PER WEEK.
EXCEED THE
MPD BY ALMO!:iT
5
THE EDGE OF THE INDUSTRIAL AREA WOULD
TIMES.
THE SURVEY CONCLUDES THAT ADDITIONAL SHIELDING OR A WORKLOAD
REDUCED BY
80%
15 INDICATED.
LOCATION
NUMBER
AREA
DosE/
PERCENT MAXIMUM
OCCUPANCY
PULSE
PERMISSIBLE DOSE
FACTOR
i
(FOR ONE YEAR
DOSE HISTORY
@
120 PULSES/WEEK)
MREM
PERCENT
10
INDUSTRIAL
.21
262
1
lOA
INDUSTRIAL/
• 39
487
1
TRANSPOSED FROM PARKING LOT;
119 PULSES; 2/5-3/1; TIMES 1.32
11
TRANSPOSED FROM PARKING LOT;
171 PULSES; 3/4-3/29; TIMES 1.32
RR RIGHT-OF-WAY
RESIDENTIAL
262
.21
1
TRANSPOSED FROM PARKING LOT;
119 PULSES; 2/5-3/1; TIMES 1.32
llA
250
.20
INDUSTRIAL
1
TRANSPOSED FROM PARKING LOT;
171 PULSES; 3/ L,i:-3/29; TIMES 1.32
12
RESIDENTIAL
.15
187
1
TRANSPOSED FROM PARKING LOT;
17
INDUSTRIAL
.20
250
1
TRANSPOSED FROM PARKING LOT;
290 PULSES; 2/5-3/29; TIMES 1.32
i
290 PULSES; 2/5-3/29; TIMES 1.32
21
254
• 20
INDUSTRIAL/
1
9
DIRECT MEASUREMENT; 150 PULSES;
3/6-3/29
RR RIGHT-OF- WAY
RR RIGHT-OF-WAY
228
.73
1/4
TRANSPOSED FROM PARKING LOT;
119 PULSES; 2/5-3/1; TIMES 1.32
9A
RR RIGHT-OF-WAY/
278
• 89
1/4
FACILITY YARD
18
RR RIGHT-OF-WAY/
.99
309
1/4
.28
88
1/4
RR RIGHT-OF- WAY/
FACIL.ITY YARD
DIRECT MEASUREMENT; .
290 PULSES; 2/5-3/29
FACILITY YARD
19
TRANSPOSED FROM PARKING LOT;
171 PULSES; 3/4-3/29; TIMES 1. 32
I
TABLE 4-2.
DIRECT MEASUREMENT; 290 PULSES
2/5-3/29
-----
----
UNCONTROLLED AREAS EXPOSURE SUMMARY
.p.
~
CHAPTER
5
FOLLOW-UP SURVEY AND ADDITIONAL SHIELDING
THE INITIAL ENVIRONMENTAL SURVEY INDICATED THAT SCATTERED RADIA~
TION WAS CAUSING EXPOSURES ABOVE THE PERMISSIBLE FOR UNCONTROLLED AREAS.
SEVERAL PROCEDURES WERE THEN UNDERTAKEN TO IDENTIFY THE EXTENT OF EACH
SCATTER SOURCE AND CHARACTER! ZE THE PRl MARY AND SCATTERED BEAM FOR
DETERMINING THE REQUIRED ADDITIONAL SHIELDING.
THE PRIMARY BEAM WAS DOSE-MAPPED CLOSE TO THE TARGET PLATE TO
DETERMINE BEAM SHAPE.
WAS MEASURED.
THE DOSE AT THE BLOCK WALL ABOVE THE SHIELD WALL
THE EFFECTIVE ENERGY OF THE PRIMARY BEAM WAS MEASURED.
THE SCATTERED RADIATION FIELD WAS CHARACTERIZED BY DETERMINING
THE PORTION OF THE GROUND LEVEL DOSE DUE TO AIR SCATTER BY SHIELDING OUT
THE BLOCK WALL SCATTER.
THE EFFECTIVE ENERGY OF THE SCATTERED
RADIATION WAS ALSO DETERMINED.
FINALLY, AN ADDITIONAL SHIELD WAS PLACED OVER THE TARGET ROOM
AND THE X-RAY FIELD INSIDE THE TARGET ROOM AND IN THE FAR FIELD WAS
RESURVEYED TO CONFIRM SHIELD EFFECTIVENESS.
PRIMARY BEAM SHAPE
EBERLINE TLD BADGES CONTAINING FIVE CHIPS EACH WERE PLACED ON
A CARDBOARD PATTERN SUSPENDED FROM THE CEILING BY STRING AND TAPE TO
LIMIT BACK SCATTER.
BADGES WERE ~LACED AT
10 0
INTERVALS FROM
0 0 -900
OFF BEAM CENTERLINE ON A HORIZONTAL PLANE ON THE EAST SIDE OF BEAM
CENTERLINE.
THE HALF-RINGS OF DOSIMETERS WERE PLACED AT
FROM THE FACEPLATE,
FIGURES
5-1
AND
5-2
1
AND
2
METERS
SYMMETRY ACROSS THE BEAM CENTERLINE IS ASSUMED.
INDICATE THE AVERAGE OF THE FIVE CHIPS AS THE DOSE
PER SHOT,
43
44
ELECTRON
BEAM
FIGURE
5-l,
BEAM SHAPE ONE
METER FROM FACEPLATE
FIGURE
5-2.
BEAM SHAPE TWO
METERS FROM FACEPLATE
45
THE MEASURED BEAM SHAPE IS SIMILAR TO THE PREDICTED SHAPE OF
FIGURE
2-4,
HOWEVER, A WIDER FRONTAL DOSE INDICATES THAT A LARGER THAN
EXPECTED PORTION OF THE DOSE WOULD IRRADIATE THE BLOCK WALL ABOVE. THE
SHIELD WALL AND BE CAPABLE OF PRODUCING SMALL ANGLE, ENERGETIC SCATTER.
THE MEASURED
OVER THE
470
618
REM AT ONE METER IS AN INCREASE OF ABOUT
REM ORIGINALLY ESTIMATED
1
30%
METER, CENTERLINE DOSE.
INSIDE WALL DOSE MAP
TLD BADGES WERE SUSPENDED FROM THE CEILING INSIDE THE MACHINE
TARGET ROOM TO MAP THE IMPINGING DOSE INTENSITY OF THE BEAM ON THE WALL
ABOVE THE PRIMARY SHIELD.
BADGES WERE PLACED AT
1. 3
FOOT INTERVALS
INSIDE THE NORTH WALL EAST OF THE CENTERLINE AND BACK ALONG THE EAST
WALL TO INCLUDE THE MAJOR PART OF THE PRIMARY BEAM.
5-4
FIGURES
5-3
AND
GRAPH THE MEASURED DOSE PER SHOT ALONG THE INSIDE OF THE BLOCK WALL
ABOVE THE SHIELD.
TWO INSIDE VERTICAL ARRAYS ARE ALSO DISPLAYED.
BACK-
SCATTER WITHIN THE TARGET CHAMBER I S ASSUMED TO HAVE PRODUCED THE
DISCONTINUITIES IN THE DOSE PATTERNS OF THE VERTICAL ARRAYS.
PRIMARY BEAM EFFECTIVE ENERGY
AS WAS DISCUSSED EARLIER, THE SPECTRAL ENERGY DISTRIBUTION OF
THE PRIMARY BEAM CHANGES WITH THE ANGLE TO THE ELECTRON BEAM OR BEAM
CENTERLINE.
EACH POINT IN THE PRIMARY BEAM 11 SEES 11 PHOTONS OF MANY
DIFFERENT ENERGIES.
A
METHOD OF DETERMINING AN 11 EFFEC'TIVE ENERGY 11 OF
THE BEAM FOR SHIELDING PURPOSE, IS BY UTILIZING THE THICKNESS OF A
MATERIAL THAT WILL REDUCE A SEAM DOSE RATE BY
50%
AND GIVING THE BEAM
THE EFFECTIVE ENERGY OF A HOMOGENEOUS PHOTON BEAM WITH THE SAME
THICKNESS FOR
50%
REDUCTION OR 11 HALF-VALUE LAYER".
THE EFFECTIVE ENERGY WAS DETERMINED BY COMPARING DOSES
46
Xx
~
3
)(
-,()(
•')(
"1-
)( )(
2
)(
REM/SHOT
)(
1
0
10
5
10
5
0
15
DISTANCE FROM CENTERLINE
(FEET)
HORIZONTAL. ARRAY
(40
INCHES FROM SHIELD WAL.L.}
20
X
)(
VERTICAL. ARRAY
15
(40
DISTANCE
')(
INCHES FROM
SHIELD WAL.L.}
ABOVE
CENTERL.I NE
)(
10
X
)(
)(
5.
X
..,+l---~.1_---~.1_
0
0
1
2
3
__.~,_ _,.__~-'-'_
4
5
REM/SHOT
FIGURE
5-3.
TLD MEASUREMENTS INSIDE
NORTH SHIELD WAL.L.
6
__._,--.xi*'-'_
7
8
47
3.0
X
2.0
X
REM/SHOT
X
X
1.0
0
10
20
15
25
DISTANCE FROM TARGET FACEPLATE PLANE (FEET)
HORIZONTAL ARRAY
(32
INCHES FROM SHIELD WALL)
20
DISTANCE ABOVE
15
CENTERLINE (FEET)
10
0
1.0
2.0
REM/SHOT
VERTICAL ARRAY
15
FIGURE
(32
INCHES FROM SHIELD WALL.
FEET IN FRONT OF FACEPLATE PLANE)
5-4.
TLD MEASUREMENTS INSIDE EAST SHIELD WALL
48
MEASURED THROUGH THREE DIFFERENT THICKNESSES OF LEAD SHEETS TO THE
UNSHIELDED DOSE AT THAT POINT AND BY USING THE LINE DETERMINED BY THE
THREE POINTS, EXTRAPOLATED TOTHE HALF-VALUE THICKNESS.
FoR THE PRIMARY BEAM, FOUR OF THE FIVE CHIP EBERLINE TLD BADGES
WERE PLACED ON A
SURROUNDED BY
OF
1/16,
AND
6
INCH SQUARE CARDBOARD.
1/8, 1/4,
1/4
AND
1/2
THREE BADGES WERE COMPLETELY
INCHES OF LEAD RESPECTIVELY COMPOSED
INCH COMMERCIAL LEAD SHEET.
THE FOURTH BADGE WAS
UNSHIELDED.
TABLE
5-1
DISPLAYS HALF-VALUE THICKNESSES WHICH WERE DETERMINED
BY EXTRAPOLATING UP THE 11 BEST FIT LINE 11 •
BOTH VALUES REPRESENT ONE
SHOT AT THE DISTANCE AND ANGLE-OFF-CENTERLINE INDICATED.
THE CENTER-
LINE BADGES WERE AFFIXED TO THE TARGET ROOM WALL; THE ANGLE BADGES WERE
AFFIXED TO A WOODEN LADDER.
THE DETERMINED EFFECTIVE ENERGY ON BEAM CENTERLINE IS THE SAME
AS THAT ESTIMATED IN CHAPTER
2.
AS EXPECTED, THE ENERGY DECREASES AS
THE ANGLE OFF CENTERLINE INCREASES.
SCATTERED DOSE MAPPING
A
MAPPING OF THE DOSE JUST OUTSIDE THE BLOCK WALL AND ABOVE THE
SHIELD WALL WAS COMPLE'T'ED ON THE EAST, NORTH AND WEST WALLS.
5-5
DISPLAYS THE HORIZONTAL DOSE PATTERN APPROXIMATELY
3
FIGURE
FEET ABOVE
THE SHIELD WALL AND TWO FEET OUT FROM THE BLOCK WALL.
A VERTICAL ARRAY DESCENDING IN THE SHIELD SHADOW AT THE CENTERLINE WAS CONSTRUCTED TO CONFIRM THAT THE SCATTERED BEAM DECREASED IN
THE SHADOW OF THE SHIELD WALL.
FIGURE
5-6
DOSES AND VERIFIES THE EXPECTED REDUCTION.
DISPLAYS THESE MEASURED
49
ANGLE OFF OF
DISTANCE FROM
HALF-VALUE
CENTERLINE
TARGET FACEPLATE
LAYER OF LEAD
EFFECTIVE
ENERGY OF
BEAM
FEET
INCHES
MEV
CENTERLINE
28
0.53
2.0
26
15
·0.48
1.7
DEGREES
TABLE
5-1.
POSITION DESCRIPTION
17. 5
CENTERLINE;
PRIMARY BEAM EFFECTIVE ENERGIES
NUMBER
TOTAL
DosE/
PERCENT
OF SHOTS
DOSE
PULSE
SHADOWED
MREM
MREM
14.6
4.6
3.8
1.2
70
FT.
FROM SHIELD WALL
NOT SHADOWED
SHADOWED
CENTERLINE;
60
4
4
FT.
FROM SHIELD WALL
NOT SHADOWED
SHADOWED
CENTERLINE;
111
59
59
109
44
1.8
.8
60
59
59
62
28
1.1
.5
55
59
59
70
32
1.2
FT.
FROM SHIELD WALL
NOT SHADOWED
SHADOWED
55
DEGREES OFF
CENTERLINE;
60
FT.
FROM SHIELD WALL
NoT SHAD OWED
SHADOWED
TABLE
5-2.
. 54
54
PERCENTAGES OF SKYSHINE FROM BLOCK WALL SCATTER
50
1000
900
800
X
700
600
X
X
500
'i..
400
I.
300
X
200
100
0
20
10
0
10
20
DISTANCE FROM CENTERLINE (FEET)
(36
OUTSIDE HORIZONTAL DOSIMETER ARRAY
30
48
FROM BLOCK WALL;
INCHES
INCHES ABOVE TOP OF SHIELD WALL)
~
30
)(
DISTANCE
FROM FACEPLATE
20
PLANE
(FEET)
10
0
0
0
100
0
200
OUTSIDE HORIZONTAL ARRAY
FROM BLOCK WALL;
48
(36
INCHES
INCHES ABOVE
TOP OF WEST SHIELD WALL)
FIGURE
100
200
DosE/SHOT (MREM)
DosE/SHOT (MREM)
5-5.
(36
48
OUTSIDE HORIZONTAL ARRAY
INCHES FROM BLOCK WALL;
INCHES ABOVE TOP OF EAST SHIELD)
TLD MEASUREMENTS ABOVE
TOP OF SHIELD WALL OUTSIDE
51
D21
D22
D23
D2
D25
D26A-~----------~
Dll
D5
400
300
200
100
0
DosE/SHOT (MREM)
(AVERAGE OF
16
NORTH SHIELD
WALL
SHOTS)
(CENTERLINE
CROSS ECTION)
• D5
FIGURE
5-6.
OUTSIDE CENTERLINE VERTICAL
DOSIMETER ARRAY
52
AIR SCATTER VS. WALL SCATTER
To DETERMINE THE PROPORTION OF THE SCATTER THAT WAS FROM THE
BLOCK-WALL ABOVE THE SHIELD WALL, AT FOUR POSITIONS IN THE Y.ARD
BADGES WERE PLACED BEHIND A
2
INCH THICK LEAD BRICK TO SHADOW OUT THE
BLOCK WALL ABOVE THE SHIELD WALL.
THE PLACEMENT WAS OPTICALLY VERIFIED.
A SECOND BADGE WAS PLACED UNSHADOWED WITHIN
SCATTER DOSE.
TABLE
LEAD BRICK, FIGURE
5-2
5-7
TLD
1
FOOT TO MEASURE ALL THE
DISPLAYS THE PERCENT OF DOSE SHADOWED BY THE
DISPLAYS THE CENTERLINE CURVES PRODUCED BY
ASSUMING ALL DOSE SHADOWED WAS FROM SCATTER OFF OF THE BLOCK WALL
AND THE REMAINDER OF THE MEASURED DOSE WAS FROM AIR SCATTER.
ADDITIONAL LEAD SHIELDING
IN ORDER TO REDUCE THE SCATTER IN THE FAR FIELD A
SHEET WAS PLACED ABOVE THE TARGET PLATE.
1
INCH LEAD
THIS WAS TO REDUCE THE PRIMARY
BEAM INTENSITY IMPINGING ON THE BLOCK WALL ABOVE THE SHIELD WALLS AND
THE BEAM STREAMING THROUGH THE CEILING.
AS INDICATED IN FIGURE
5-8,
THE WIDTH OF THE LEAD PLATE SHADOWED THE NORTH BLOCK WALL AND THE
AIR SPACE ABOVE.
SIMILARLY, THE SHEET SHADOWED THE EAST AND WEST
BLOCK WALLS {NOT SHOWN).
THE LEAD THICKNESS REPRESENTS
2
HALF-VALUE THICKNESSES
(THICKNESS OF LEAD WHICH WOULD REDUCE INTENSITY OF A GIVEN BEAM BY A
FACTOR OF TWO) FOR AN EFFECTIVE ENERGY OF
MEASURED AT
26°
1. 7
MEV, THt: EFFECTIVE ENERGY
OFF BEAM CENTERLINE IN THE PRIMARY BEAM.
SCATTERED RADIATION FIELD RESURVEY
A LIMITED RESURVEY TO CONFIRM THE EFFECTIVENESS OF THE LEAD
SHIELD WAS COMPLETED.
lN-COMPANYTLD DOSIMETERS WERE USED TO REMEASURE THE DOSE
4.0
'/.
3.0
TOTAL DOSE/SHOT
.,.
~
I
DosE/SHOT
(MREM)
2.0
- )(
-
DOSE/SHOT FROM
BLOCK WALL SCATTER
1.0
'"
L
--...)(
>t-
DOsE/SHOT FROM
AIR SCATTER
0
I
0
I
10
I
20
I
30
40
50
60
70
80
90
100
110
DISTANCE FROM SHIELD WALL (FEET)
FIGURE
5:-7.
CENTERLINE SCATTER DOSE
DIVIDED
INTO AIR AND BLOCK WALL SCATTER COMPONENTS
OJ
~
54
• D4
D5 •
..
• D3
......
..... ....
• D2 - ......
•Dl
...
-
ADDITIONAL LEAD SHIELD
-•- --
-~-~------------DO
FLASH
X-RAY
MACHINE
DOSIMETER LOCATIONS IN PLANE OF BEAM CENTERLINE
FIGURE
5-8.
DoSIMETRY DIAGRAM FOR PRIMARY BEAM
RESURVEY AFTER LEAD SHIELD INSTALLATION
55
INSIDE THE TARGET ROOM AND IN THE NEAR-FIELD FACILITY YARD.
DOSIMETER PACKETS CONSISTED OF THREE 1/8"x1/8"X. 35 11
EXTRUDED CHIPS IDENTICAL TO THE EBERLINE AREA BADGES.
LJF
THE CHIPS WERE
READ ON AN EBERLINE TLR 5 DOSIMETER READER USING A CESUIM-137 SOURCE
FOR READER CALIBRATION.
THE CHIPS WERE WRAPPED IN BLACK TAPE AND READ-
INGS INDICATED WERE THE ARITHMETIC MEAN OF THE THREE CHIPS STATED IN
MREM.
TABLE 5-3 INDICATES THE MEASURED DOSES INSIDE THE TARGET ROOM
AND COMPARES THESE DOSES WITH THOSE TAKEN.PRIOR TO THE LEAD INSTALLATION.
AT SEVERAL LOCATIONS IN THE FACILITY YARD, IDENTICAL TO THE
ORIGINAL SURVEY, THREE CHIP TLD DOSIMETER PACKETS WERE PLACED IN THE
ALUMINUM CHASSIS BOXES USED IN THE ORIGINAL SURVEY AND REMAINED IN THE
FIELD FOR 3 MONTHS ACCUMULATING 541 SHOTS.
WAS 10 MREM/ MONTH.
THE BACKGROUND ESTIMATED
TABLE 5-4 LISTS AND COMPARES THE RESURVEY
MEASUREMENTS WITH THE MEASUREMENTS OF THE IDENTICAL LOCATIONS DURING
THE ORIGINAL TWO MONTH SURVEY.
TABLE 5-5 INDICATES THE EFFECTIVENESS OF THE Lf.:AD SHIELD IN
REDUCING THE PROJECTED DOSE IRRADIATED ON THE UNCONTROLLED AREAS FOR
A FULL MACHINE WORK LOPD OF 120 SHOTS PER WEEKe
ALL UNCONTROLLED AREAS NOW RECEIVE DOSES BELOW THE REQUIRED
MAXIMUM PERMISSIBLE DoSE.
56
DOSIMETER
LOCATIONS
(KEYED TO FIGURE
5-8)
AFTER LEAD SHIELD
BEFORE LEAD SHIELD
INSTALLATION
INSTALLATION
DosE/
RATIO:
DosE/
RATIO:
PULSE
ON
PULSE
ON
REM
DO
REM
00
72
BEAM CENTERLINE;
2
no
1.0
125
1.0
METERS FROM FACE-
PLATE
01
9.43
.13
7.75
.062
CENTERLINE
1.52
.021
2.50
.020
CENTERLINE
.36
.0050
2.25
.018
CENTERLINE
.25
.0034
2.25
.018
.043
.00060
. 76
.0061
.014
.00019
.11
.00091
BEAM CENTERLINE
PLANE
02 BEAM
PLANE
03 BEAM
PLANE
04 BEAM
PLANE
05 BEAM
CENTERLINE
PLANE
NOT SHOWN IN FIGURE
APPROX.
45°
CENTERLINE, N.
4
5-8
OFF
E.,
FEET ABOVE SHIELD
WALL OUTSIDE
TABLE
5-3.
COMPARISON SUMMARY OF DOSE FIELD
INSIDE TARGET ROOM BEFORE AND AFTER LEAD
SHIELD INSTALLATION
LOCATION NUMBER
3
BEFORE LEAD
AFTER LEAD SHIELD
RATIO;
SHIELD
INSTALLATION
AFTER LEAD
290
541
PULSES
PULSES
BEFORE LEAD
LOCATION
MEASURED
MEASURED
MEASURED
DESCRIPTION
DOSE/PULSE
TOTAL DOSE
DosE/PULSE
BEAM CENTERLINE;
95
FEET
MREM
MREM
2.62
214
.39
.15
MREM
FROM FACEPLATE
.4
BEAM CENTERLINE;
116
FEET
2.03
172
.32
.16
148
FEET
1.33
124
.23
.17
.99
108
.20
.20
1.66
194
.36
.22
FROM FACEPLATE
5
BEAM CENTERLINE;
FROM FACEPLATE
18
45°
20
45°
OFF CENTERLINE;
140
I
FEET FROM FACE PLATE
OFF CENTERLINE;
85
FEET FROM F ACEPL.ATE
TABLE
5-4.
COMPARISON OF FAR-FIELD DoSE RATES BEFOREANDAFTER LEAD SHIELD INSTALLATION
I
Cl1
-.:,
LOCATION
AREA
NUMBER
EXPECTED YEARLY
AFTER LEAD SHIELD INSTALLATION
EXPOSURE BEFORE
EXPECTED YEARLY
LEAD SHIELD
'EXPOSURE
INSTALLATION
(Do)
MREM
lOA
INDUSTRIAL/
RR
I
EXPECTED YEARLY
FACTOR
EXPOSURE
% MP D
0, 2)
MREM
PERCENT
2434
486
1
97
RIGHT-OF-WAY
11
RESIDENTIAL
1310
262
1
52
12
RESIDENTIAL
936
187
1
37
17
INDUSTRIAL
1248
249
1
50
INDUSTRIAl)
1248
249
1
50
6177
1235
1/4
62
t
i
(DO X
MAXIMUM PERMISSIBLE DOSE
OCCUPANCY
RR RIGHT-OF-WAY
RR RIGHT-OF-WAY/
FACILITY YARD
----L..
TABLE
5-5.
UNCONTROLLED AREAS EXPOSURE
SUMMARY AFTER LEAD SHIELD INSTALLATION
en
00
BIBLIOGRAPHY
1•.
BIRCHALL,
1969.
GAMMA SCATTER FROM OPEN-TOP CELLS.
HEALTH PHYSICS
16:47-56.
BURKE, G.
DE P.
1975.
VARIATIONS IN NATURAL ENVIRONMENTAL GAMMA RADI-
ATION AND ITS EFFECT ON THE INTERPRETABILITY OF TLD MEASUREMENTS
MADE NEAR NUCLEAR FACILITIES.
HASL-289.
NEW YoRK: USERDA HEALTH
AND SAFETY LABORATORY.
CALIFORNIA.
1973.
CAMERON, J. R.
ADMINISTRATIVE CODE.
ET AL.
1968.
THERMOLUMINESCENT DOSIMETRY.
MADISON:
UNIVERSITY OF WISCONSIN PRESS.
CEMBER,
H.
1969.
INTRODUCTION TO HEALTH PHYSICS.
LONDON; PERGAMON
PRESS.
CLUCHET, J. AND JOFFRE, H.
1967.
DOSIMETRY IN HEALTH PHYSICS.
APPLICATIONS OF THERMOLUMINESCENCE
LUMINESCENCE DOSIMETRY.
OF INTERNATIONAL CONFERENCE, STANFORD 1965.
VoL. 8.
CONF-650637.
GEIGER, E. AND SANCHEZ,
E.
DIV. OF TECHNICAL INFORMATION, USAEC.
1973.
ENVIRONMENTAL RADIATION MONITORING
WITH THERMOLUMINESCENT DOSIMETERS.
CORP.
GEIGER,
PROCEEDINGS
AEC SYMPOSIUM SERIES.
SANTA FE: EBERLINE INSTRUMENT
MIMEOGRAPHED.
E.
1971.
TLD VS. FILM.
PAPER READ AT SYMPOSIUM ON RECENT
DEVELOPMENTS IN. PRACTICAL DOSIMETRY AND STANDARDS, WASHINGTON, D.C.
Ml MEOGRAPHED.
GLOYNA, E. F. AND LEDBETTER, J.
HEALTH.
0.
1969.
NEW YORK; MARCEL DEKKER,
HARRISON, J. R.
1958.
PRINCIPLES OF RADIOLOGICAL
INC.
GENERAL METHODS FOR GAMMA-RAY SHIELDING.
GLOVE BOXES AND SHIELDED CELLS FOR HANDLING RADIOACTIVE MATERIALS.
PROCEEDINGS OF THE SYMPOSIUM ON GLOVE BOX DESIGN AND OPERATION
IN COCKCROFT HALL, AERE HARWELL ON FEB.
19-20, 1957;
HELD
NEW YORK:
ACADEMIC PRESS INC.
HINE, G. J. AND BROWNELL, G.
L.
1956.
RADIATION DOSIMETRY.
NEW YORK!
ACADEMIC PRESS INC.
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION.
1960.
REPORT OF
COMMITTEE Ill ON PROTECTION AGAINST X-RAYS UP TO ENERGIES OF 3 MEV
AND BETA-AND GAMMA- RAYS FROM SEALED SOURCES.
PUBLICATION 3.
RECOMMENDATIONS OF THE INTERNATIONAL COMMISSION ON RADIOLOGICAL
PROTECTION.
GLASGOW: PERMAGON PRESS.
59
60
INTERNATIONALCOMMISSIONON RADI.OLOGICAL PROTECTION.1966.
PROTECTION.
PUBLICATION 9.
RADIATION
RECOMMENDATIONS OF THE INTERNATIONAL
COMMISSION ON RADIOLOGICAL PROTECTION.
ADOPTED SEPT. 17, 1965.
GLASGOW; PERGAMON PRESS.
JENKINS, T.
PHYSICS.
O'BRIEN,
M.
1974.
ACCELERATOR BOUNDARY DOSES AND SKYSHINE. HEALTH
27:251-257.
K. AND BURKE, G. DE P.
1973.
JOURNAL GEOPHYSICAL RESEARCH.
78:3013.
PASCHAL, F. L.
JR.
1970.
FLASH X-RAY MACHINES.
HYGIENE ASSOCIATION JOURNAL.
PRICE, B. T. ET AL,
STEPHENSON, R.
1957.
1958.
AMERICAN INDUSTRIAL
JAN. -FEB.
RADIATION SHIELDING.
LONDON;PERGAMON PRESS.
INTRODUCTION TO NUCLEAR ENGINEERING.
NEW YORK;
MCGRAW-HILL BOOK Co.
STEYN, J. ET AL.
1974.
REACTOR SITE 16N SKYSHINE DOSE RATE.
TRANS-
ACTIONS OF THE AMERICAN NUCLEAR SOCIETY 1974 ANNUAL MEETING.
PENNSYLVANIA; AMERICAN NUCLEAR SOCIETY.
U.S.
DEPT. OF COMMERCE,
NATIONAL BUREAU OF STANDARDS.
1964. SAFETY
STANDARD FOR NON-MEDICAL X-RAY AND SEALED GAMMA-RAY SOURCES.
PART 1.
GENERAL NATIONAL BUREAU OF STANDARDS HANDBOOK 93.
WASH-
INGTON; GOVERNMENT PRINTING OFFICE.
U. S. DEPT. OF COMMERCE,
NATIONAL BUREAU OF STANDARDS.
ING FOR HIGH-ENERGY ELECTRON ACCELERATOR INSTALLATIONS.
NATIONAL BUREAU OF STANDARDS HANDBOOK 97.
1964. SHIELDGENERAL
WASHINGTON; GOVERNMENT
PRINTING OFFICE.
U. S.
ENVIRONMENTAL PROTECTION AGENCY.
YEATES,
D. B. ET AL.
NUCLEAR SAFETY.
1972.
1972.
REPORT ORP/SID 72-2.
NATURAL RADIATION IN THE URBAN ENVIRONMENT.
13:4:275-286.
APPENDIX A
TLD AND FILMBADGE READINGS
SURVEY 1
DOS IMETERS: PLACED; 2-5-74 REMOVED; 3-1-74 PULSES; 119
LOCATION
FILMBADGE
TLD
BADGE
NUMBER
TOTAL
DOSE
MREM
TOTAL
DOSE MINUS
BACKGROUND
MREM
DosE/
PULSE
BADGE
NUMBER
TOTAL
DOSE
MREM
MREM
A060
0
2.35
A061
280
214
1.80
A062
520
355
337
2.83
A063
300
0004
275
257
2.16
A064
260
5
0005
172
154
1.29
A065
140
6
0006
LOST
A066
LOST
7
0007
206
188
1.58
A067
150
8
0008
228
210
1.76
A068
170
9
0009
83.0
65.0
.55
A069
70
10
0010
37.4
19.4
.16
A070
35
11
0011
37.2
19.2
.16
A071
25
12
0012
28.8
10.8
.09
A072
15
13
0013
49.0
31.0
.26
A073
45
14
0014
66.2.
48.2
.40
A074
55
15
0015
55.8
37.8
.32
A075
35
16
0016
3'Z.4
19.4
.16
A076
25
17
0017
39.8
21.8
.18
A077
25
18
0018
143
125
1.05
A078
110
CONTROL
0000
13.4
1
0001
298
280
2
0002
232
3
0003
4
61
62
APPENDIX A
TLD AND FILMBADGE READINGS
SURVEY 1
DOSIMETERS:
LOCATION
PLACES; 2-5-74 REMOVED; 3-1-74 PULSES; 119
FILMBADGE
TLD
BADGE
NUMBER
TOTAL
DOSE
MREM
TOTAL
DOSE MINUS
BACKGROUND
MREM
19
0019
53.6
35.6
20
0020
232
214
21
0021
22
DosE/
PULSE
BADGE
NUMBER
MREM
TOTAL
DOSE
MREM
.30
A079
45
1.80
A080
170
NOT USED
A081
NOT USED
0022
NOT USED
A082
NOT USED
23
0023
276.4
X 1000
2322
24
0024
2379
X 1000
19991
25
0025
16.0
X 1000
134
26
0026
132.8
X 1000
1116
APPENDIX B
TLD AND FILMBADGE READINGS
SURVEY 2
DOSIMETERS: PLACED; 3-4-74 REMOVED; 3-29-74 PULSES; 171
(*150)
(*3-6-74)
LOCATION
FILM BADGE
TLD
BADGE
NUMBER
TOTAL
DOSE
MREM
TOTAL
DOSE MINUS
BACKGROUND
MREM
DosE/
PULSE
BADGE
NUMBER
MREM
TOTAL
DOSE
MREM
A060
NOT USED
2.60
A061
190
466
2.92
A062
240
443
423
2.47
A063
250
0004
353
333
1.95
A064
160
5
0005
252
232
1.36
A065
120
6
0006
156
136
.80
A066
70
7
0007
301
281
1.64
A067
130
8
0008
321
301
1. 76
A068
130
9A
0009
135
115
.67
A069
50
lOA
0010
70.8
50.8
.30
A0'70
30
11A
0011
45.8
25.8
.15
AO'll
15
12
0012
40.4
20.4
.12
A072
5
13
0013
80.4
60.4
.35
A0'73
35
14
0014
79.4
59.4
.35
A0'74
30
15
0015
59.8
39.8
.23
A075
20
16
0016
54~0
34.0
.20
A076
10
17
0017
41.2
21.2
.12
A077
10
18
0018
182.4
162.4
.95
A078
75
CONTROL
0000
14.0
1
0001
464
444
2
0002
486
3
0003
4
63
64
APPENDIX 8
TLD AND FILMBADGE READINGS
SURVEY 2
DOSIMETERS: PLACED; 3-4-74 REMOVED; 3-29-74 PULSES; 171
(*3-6-74)
(*150)
LOCATION
FILMBADGE
TLD
BADGE
NUMBER
TOTAL
DosE
MREM
TOTAL
DOSE MINUS
BACKGROUND
MREM
DOSE/
PULSE
BADGE
NUMBER
MREM
TOTAL
DosE
MREM
.27
A079
40
1.56
A080
160
.20*
A081
0
.62*
A082
5
19
0019
66.6
46.6
20
0020
288.4
268.4
21
0021
49.6*
30.6*
22
0022
112.4*
93.4*
23
0023
416 X 10 3
2432
24
0024
2377.5 X 10 3
13903
25
0025
21.3 X 10 3
124.1
26
0026
134 X 103
784