(b)

()

@
©)

@®

If the pellet has been irradiated to a new dose, adjust the receiver gain. On a page
containing the chosen set of parameters (transferred from a previous recording or read from
a template file), make a trial spectrum acquisition (Acquisition (A), Signal Channel (C))
and, if necessary, change the gain using menu option Parameters (P) / Signal Channel
Parameters (C). The optimal receiver gain provides a signal that does not exceed the
receiver gain gauge and, at the same time, provides 5-digit readings of the derivative
minimum and maximum values. In some low-dose measurements, the 5-digit result is not

practical. In that case just get as much signal as possible without exceeding the
receiver gain gauge.

Select a page with appropriate parameters and start the automation routine using menu
option Acquisition (A) / Execute automation routine (E). It will automatically record the
spectra of both alanine and ruby, and then transfer the parameter of the alanine spectrum to
the next available page.

Rotate the sample tube by 90 degrees and start the routine again.

Measure the signal intensities on the last four pages using menu option Data Handling (D) /
Pick Picking (D) / Find Extremal Values (M). In each case, transfer the absolute values of
the readings “Min” and “Max” in the bottom of the screen to the spreadsheet.

Repeat this section until all samples are measured.

5.3.2.4 Data Processing

(a)

()

In the spreadsheet, calculate the alanine response (S) using the formula: S= averaged
alanine signal amplitude / averaged ruby signal amplitude / receiver gain / pellet mass.
Where appropriate, make response adjustments to the difference between the temperatures
during irradiation of calibration and test pellets. The response increases with temperature at
arate of 0.15%/deg C.

Dose interpretation of the response of each alanine dosimeter is by means of the calibration
response functions discussed in 5.2.2.1. The Low Dose range (10 Gy to 2 kGy) response
function is linear. The fitted Low Dose least squares curve for a typical alanine batch is
shown in Fig. 6. The fitted linear equation is y = a + bx; the fitted parameters in this case
are: a= 1.0448; and b = 0.17522. The High Dose range response function is nonlinear; a
fitted curve is shown in Fig. 7. The fitted equation is: {px }
S=all-exp \°

where S= the normalized EPR signal ; D = absorbed dose, in kGy;
and typical fitted parameters are: a = 10.3943; b = 72. 2446; ¢ = 0.243093.

15


Appendix 4
Fee schedule supplied to the customer:

February 21, 1997

From: James Puhl
NIST High-Dose Calibration Service
Building 245, Room C229
Gaithersburg, MD 20899

Dear Calibration Customer: New fees for high-dose calibration services are in effect.
Schedule No. Calibration of Dosimeters Cost
49010C_ | Irradiated with °Co Gamma Rays $589

Calibration irradiations are available for customer-supplied dosimeters (such as solid radiochromic or liquid
chemical types) or test samples that are sent to NIST, where they are packaged appropriately to provide electron
equilibrium conditions. They are irradiated in the NIST standard cobalt-60 calibration facility to specfic,
agreed-upon absorbed dose values in the nominal "high-dose" range of 10-10° Gy. The dosimeters are then sent
back to the customer for analysis and evaluation. Dosimeters should not exceed dimensions of 1 cm x 2 cm x 5
cm. A typical uncertainty value for irradiations of radiochromic film with the standard Gammacell 220-232 is +
1.8 at an approximate level of confidence of 95%.

Schedule No. Set of Three Transfer Reference Standard Dosimeters Cost
49020C Alanine Pellets or Radiochromic Film $1916
49030C Each Additional Dosimeter $391

NIST will provide transfer standards in the form of calibrated alanine or radiochromic film dosimeters packaged
in polystyrene. The sealed, packaged dosimeters are sent to the customer for irradiation to nominal agreed-upon
absorbed dose levels in a prescribed geometrical arrangement. The unopened, packaged dosimeters are then
returned to NIST to be read, evaluated and the results reported, thus providing calibration of the customer's
irradiator. The absorbed dose range that is suitable for use with the transfer dosimeters is 1 to 50 kGy in water.
The absorbed dose rate should be greater than 30 Gy/min. A typical uncertainty value for alanine transfer
standard calibrations is + 2.2% at an approximate level of confidence of 95%. A typical uncertainty value for
radiochromic film transfer standard calibrations is + 4.6% at an approximate level of confidence of 95%.

Schedule No. Additional Services Cost

49040S Spectrophotometric reading of dosimeters, optical density at one | $141
to five wavelengths (each dosimeter).

49041S Spectrophotometric reading of dosimeters, ultraviolet and visible | $367
spectrum scan (each dosimeter).

49050S Special measurement services. At cost

Please send requests and/or dosimeters to me at the above address. Be sure to specify the
name and phone number of a technical contact. Domestic orders require a purchase order and
foreign orders require pre-payment. If you have any questions, please contact me.

PHONE: 301-975-5581 FAX: 301-869-7682 E-MAIL: jpuhl@nist.gov

36


Appendix 2

thread.bas (DOS Basic) program:

10 COLOR 15,1:CLS:DIM DA(1000)

20 PRINT" THREAD.BAS - DOWNLOAD THICKNESS DATA FROM MULTIPLEXER
5/13/96 jmp"

30 XON$=CHR$(17) 'CTRL-Q

40 XOFF$=CHR$(19) 'CTRL-S

50 INPUT "ENTER STARTING FILM NUMBER: ",SNUM:LOCATE 3,1:PRINT "";
60 F$="THREAD.T":OPEN "0",2,F$:PRINT "DATA WILL BE WRITTEN TEMPORARILY
TO ";F$

70 LOCATE 4,1:J=0:L=4:C=1:INPUT"Press ENTER to start the transmission.",A$

80 LOCATE 23,1:PRINT"Press <SPACEWAR> to stop the transmission "

90 OPEN "COM1:1200,N,8,1" AS #1:

100 SNUM$=STR$(SNUM):SNUM$=SPACE$(4-LEN(SNUM$))+SNUM$

110 LOCATE L,C:PRINT" WAITING FOR ZERO READING... "

120 CO$="1":PRINT#1,CO$:INPUT#1,DA$:I=I+1

130 DA$=MID$(DA$,4,9):DA=VAL(DA$):CLOSE 1

140 IF DA> .001 THEN GOTO 90 ELSE SOUND 2000,1:SOUND 1000,1

150 DA(1)=1:DA(2)=2:1=2

160 WHILE DA(I)<>DA(-1):OPEN "COM1:1200,N,8,1" AS #1

170 LOCATE L,C:PRINT SPC(27):LOCATE L,C:PRINT"READING ";SNUM$;"..."
180 T1=TIMER :T2=T1+1: WHILE T2>=TIMER:PRINT "";:WEND:’ wait one second
190 A$=INKEY$:IF A$<>"" TIIEN CLOSE 1:GOTO 300

200 CO$="1":PRINT#1,CO$:INPUT#1,DA$:I=I+1

210 DA$=MID$(DA$,4,9):DA(I)=VAL(DA$): TH$=RIGHT$(DA$,6)

220 LOCATE L,C:PRINT SNUM$;"__";TH$:CLOSE 1:WEND

230 IF DA(I)< .01 THEN GOTO 150

240 IF L=19 THEN C=25 :L=4

250 IF L=37 THEN C=50 : L=4

260 O$=SNUM$+" = "+TH$+"mm "

270 SOUND 800,1:LOCATE L,C:PRINT O$:PRINT #2,SNUM$,TH$

280 LPRINT O$:L=L+1:SNUM=SNUM+1:GOTO 90

290'

300 'SPACEWAR ROUTINE

310 LOCATE 23,1:PRINT SPACE$(75):LOCATE 22,1:PRINT "1)";

320 INPUT " save file and quit 2) reset counter 3) continue 4) quit ";Q

330 LOCATE 22,1:PRINT SPACE$(75)

340 IF Q=3 THEN LOCATE 22,1:PRINT SPACE$(75):GOTO 80

350 IF Q=2 THEN LOCATE 22,1:INPUT "enter new counter number:";SNUM:GOTO 80
360 IF Q=1 THEN CLOSE:GOTO 380

32


The last page of this Report describes uncertainties and related factors in high-dose
calibrations, such as the one covered by this Report of Calibration. If there are further
questions, they should be directed to the first individual named below.

Measurements were made by

J. M. Puhl, Calibrations Technician
(301)975-5581

Approved by

Stephen M. Seltzer, Leader
Radiation Interactions and Dosimetry Group

For the Director
National Institute of Standards and Technology
by

Bert M. Coursey, Chief
lonizing Radiation Division
Physics Laboratory

REFERENCE TEST 846/256018-97 Sep. 25, 1997
NIST DB 932/018 HD9799
Page 2 of 3 Pages

42


FWT-60-00 radiochromic films. The parameters are shown in Table 2.

(d) Runa baseline to zero the instrument over the wavelength range 610 nm to 500 nm
with empty film holders in both reference (rear) and sample (front) light beams in the
sample compartment. The split holder shown in Fig. 3 is used to hold a FWT-60-00 film in
the sample light beam. A solid (non-split) version of the holder masks the reference beam
exactly the same as the split holder masks the sample beam.

(e) Handle films with tweezers at the corners to
avoid scratching near the center where the
light beam passes through. Number each
film in a corner with a small code number
using a fine permanent marker pen.

{—}-Film Plane (=) . .
---+#+----~ FH ---- (f) Place the film in the split holder and
Ss al ke place the holder in the sample holder in the
spectrophotometer sample compartment.
Figure 3 - Radiochromic Film Holder Read the absorbance values at 605 nm and
510 nm.

(g) The absorbance data is acquired by means of a software program called WLPG.ADL.
This program is listed in Appendix 1. To start this program, go to the Calculator page in the
Cary software. Start the WLPG program. This initiates Reports Display. As each film is
read out in turn a data set is generated on the monitor screen as shown in the example in
Table 3.

(h) Upon exiting the WLPG.ADL program, it takes you to the DOS Editor. This pulls up
the current.rep file where the film absorbance data colected above is stored. Edit the data to
delete the column text headers to leave numerical data only. Save as new file name, e.g.,
test folder number (hd9616), with an extension of .A1 for pre-irradiation data, or an
extension of .A2 for post-irradiation data.

5.3.1.2 The thickness of each FWT-60-00 film is measured in order to be able to normalize the
absorbance data to unit thickness. The thickness is measured as follows:

(a) Power to the Mitutoyo electronic thickness gauge (bottom unit) should be left on at
all times to minimize warmup drift. If started from power-off mode, allow at least one hour
warmup time. Turn on power to Mitutuyo Multiplexer (top unit) and set all switches to up
position. The gauge unit data is routed through the Multiplexer unit into the serial port on
the Compac 386 control computer as an ASCII string. The gauge unit display should read in
“mm” with a resolution of 0.1 um (the resolution may be changed with a rotary switch on
the rear of the gauge unit).


(20) The customer’s dosimeters are ready to be shipped back;

(21) The dosimeters are packed appropriately;

(22) The dosimeters are shipped back to the customer by the requested method; this
information is recorded in the Control Log;

(23) The dosimeters are received by the customer;

1 Log &
}-¥ Calibration

Folder Closed}

(By) Ly
‘Complete |__| Documents
Test Folder Filed

ay

\

Irradiate
Page 2
B
Dosimeters
‘Customer Returned Report to
‘Customer
| Return |
\CP/OMS | | Test Folder
26)
Bs Division
Division Review &
Approval
Control ‘Q.C. Data
Log Logged |
za} x
|B CO cairaon Ea
Documents \_,J Prepare ‘Technician ‘Supervisor Calculate
Report | Review Review | Fee
30
Dosiineters; Dosimeters |
Dosimeters; | “Ready to. |
tions sh |
a——__ a —_ \
Shipping & | Dosimeters _
Receiving Pack i
Figure 8b - Procedures for Calibration Irradiations of Customer-Supplied Dosimeters

(24) The completed Calibration Report is reviewed by the Calibration Technician (i.e., the
person that did the calibrations);

(25) The Group Leader reviews the Calibration Report and if approved;

19



Appendix 5

Instructions to customer for handling of radiochromic film transfer dosimeters:

Guidelines for the use of NIST Transfer Dosimeters

1. Plcasc do not open the packages at any time; they provide a controlled environment for the
dosimeters.

2. Please provide average temperature for each dosimeter during the irradiation period.
3. Other irradiation data to include with the returning dosimeters

© Irradiation geometry (i.e., orientation, position, surrounding materials)

© Type of source (i.e., if gamma-ray source, identify the specific isotope)

© How you wish for us to identify your source in the Report of Calibration

© Date and time of irradiation

© Length of the irradiation period

© Nominal dose and dose rate

© Any other pertinent information

4. The nominal absorbed doses received should be within the range of 1 kGy to 30 kGy for
alanine and 5 kGy to 30 kGy for film.

5. Please irradiate and return the dosimeters to us within 60 days to minimize the uncertainty
in the final results. Please use the following address for return shipment:

NIST

ATTN: JAMES PUHL

BLDG. 245, ROOM C229
GAITHERSBURG, MD 20899

37


TABLE OF CONTENTS

TERMINOLOGY

SIGNIFICANCE AND USE .... 0.60 e cece cece nee nec e ene een ete e enn t tees 3

CALIBRATION PROCEDURES

MEASUREMENT UNCERTAINTY ...... 0.00 sce e eee eee cece ence ene ene 24

KEYWORDS

REFERENCES... 1.0.0.0 cece cece eee tte eee ene ete e teen nee enn ene 28

APPENDIXES



Appendix 1

WLPG.ADL program:

{This program can be actived from either the User_result line or the}
{Calculator page. It will measure the nominated number of samples at 510 }
{and 605 nm. These wavelengths can be easily changed. The user will then }
{ Author: Jim Puhl

{ Revised 4/10/97 }

dim A510[1000] A605[1000]

define readit
print("please wait, measuring sample",n,"...")
A510[N] = read(510)
A605[N] = read(605)
TABLEDATA(n,A605[N],A510[N])
n=n+1

enddef

define finchek
print ("Are you ready to end session and exit?")
q$=input
if (q$="y") or (qS="¥") then finis=1

enddef

define recount
print("What is the new film number? ")
n=input

enddef

define wipg

STARTPRINT
SET(AUTOP,1)

print("Enter user name ")

name$=input

Iprint("Operator: ",name$)

print("Enter your comment ")
comment$=input

Iprint("Comment: ",comment$)
Iprint("Date: ",recall_str(recall(5,35),0))

30


400

300-

200.

Alanine Response

100:

rh) 0s 1 1s 2
Dose (kGy)

Figure 6 - Alanine Batch 9b Low Dose Calibration Curve

10 —

0.

0 50 100 150
Dose (kGy)

Figure 7 - Alanine Batch 9b High Dose Calibration Curve

(c) A software program called TableCurve is used to fit the data sets for both the Low Dose
and High Dose ranges. Once the calibration plot is fitted, the doses for test pellets can be
determined by using the program option [Evaluate] , selecting[ X = Root at Y ], and
putting in the values of the normalized signals (Y).

(d) If doses in a material other than water is desired, multiply the determined doses by 4,
ratios (material/water) weighted over the calibration source energy spectrum.


Cavity for Pellets |

Figure 10 - Polystyrene Alanine Capsule
for Co” Gamma Irradiation

(6) Alanine pellets are
supplied in an appropriate
package depending on whether
intended for Co® gamma-ray
irradiation or electron-beam
irradiation. For Co” gammas, the
capsule shown in Fig. 10 is
supplied; for electron beams, the
flat holder shown in Fig. 11 is
supplied. For radiochromic films,
the slab holder shown in Fig. 2 is
supplied for either gamma or
electron beam irradiation.

(7) _ Packaged transfer dosimeters, including control dosimeters, are shipped to the
customer. Instructions are included on suggested dosimeter handling techniques and
information on irradiation conditions required for correct data interpretation (see an

example in Appendix 5).

Figure 11 - Polystyrene Alanine Pellet
Holder for Electron Beam Irradiations

(15) Data analysis is performed;

(8) to (9) Same as in 5.4.1;

(10) Irradiation of dosimeters by customer
with in-house source;

(11) Irradiated dosimeters, along with
unirradiated controls, are returned to NIST;

(12) Dosimeters are analyzed;
(13) Control Log is updated from both test
folder and data from irradiation of

dosimeters;

(14) Dosimeter readout data is collected;

(16) If data is not consistent, i.e., indicated dose values from dosimeters are different from
expected doses reported from the customer, than the results must be resolved. This may

22


(4) Upon receipt of the hard copy of the purchase order, it is logged in the Control Log

(5) Anda copy sent to the Calibration Program/Office of Measurement Services (CP/OMS)
for that office to generate a Test Folder (11);

(6) Customer’s dosimeters are received in the Division; note that no calibration work is
done past this step until a hard copy of the purchase order is in hand;

(7) The dosimeters are unpacked and appropriately tagged for identification throughout the
calibration process;

(8) The dosimeters are visually inspected for damage or flaws;

(9) Ifthe dosimeters are flawed in any way that would prevent proper calibration they are
returned to the customer with an explanation;

(10) The customer is requested to supply new dosimeters; if the customer complies, the
dosimeters are processed from step (6) on again;

(11) The Test Folder generated by the CP/OMS office is sent to the Division;
(12) The Test Folder is received by the Division;

(13) If the dosimeters are considered to be satisfactory in step (8), then they are irradiated to
the requested doses;

(14) The Control Log is updated with the Test Folder information and the irradiation data
(ie., irradiation source used, date and time of irradiation, dosimeter(s) ID, temperature during
irradiation, dose rate, etc.);

(15) The NIST quality control dosimeters irradiated along with the customer’s dosimeters are
analyzed and that data and the irradiation data are recorded;

(16) The QC and irradiation data are examined and analyzed;

(17) Ifthe QC data is not consistent with the irradiation data (i.e., the indicated dose is
different from the expected dose), then the problem must be resolved;

(18) Ifthe QC data is satisfactory (i.e., within control dose limits) then it is recorded in the
Control Log;

(19) The data is used to prepare the Calibration Report;

18


print("What is the starting film number? ")
bnum=input

n=bnum.

page=4

goto_page

TABLEFMT("DDZ","Z.DDDD","Z.DDDD")
TABLEHDR(" FILMID "," 605nm “," 510nm ")
finis=0
do while finis=0
statusstr("1=read 2=adjust counter 3=exit")
print ("ready for sample",n,", please choose 1-3 from the choices at the top:")
q=input
case q
L:readit
2:recount
3:finchek
end
end
SET(AUTOP,0)
prog$="c:\command.com /c edit c:\varian\cary13e\current.rep"
spawn_prog
enddef

31


The process is as follows: Put in a plastic sample tray and tare the balance. Go into the A160
program from the icon in the main Windows display. This is a DOS Basic program called
a160.bas; see the print out of the program in Appendix 3.

(c)
(a)

©

(09)

@)

(1) A prompt asks for the starting pellet number; then it generates a file name to store
the data and waits for the user to accept the name.

(2) _ The program looks for a “zero” reading. Ifa stable zero is indicated, then the
program begins reading the sample mass.

(3) | The program makes continuous mass measurements and increments a seconds
counter. If the mass value drifts, the counter is reset to zero. If the value remains
unchanged for ten seconds, the value is accepted. The program beeps twice.

(4) The program then waits for a stable zero reading to indicate the sample is being
changed and the zero has not drifted. If the balance goes to zero and remains for
two seconds, the program will beep once to indicate it ready to read the next
sample. If the balance settles somewhere beyond zero, the user must press tare.

(5) | When all pellets are measured, the program prompts the operator to hit any key.
Two choices are given: Q to quit or B to stay in basic. The usual choice is Q.

Log in in the EPR Logbook. This records details of the user. time of use, sample, etc.

Tur on cooling water to the spectrometer magnet using the blue flat control valve on the
pipeline behind the magnet. No other controls of the water system should be touched.
Adjust the water pressure to about 40 psi, if required.

Turn on the magnet power. The switch is on the bottom front of the magnet. Turn on the
control console red power switch located on the top right of the electronics rack behind the
console glass door.

On the prompt of the control computer, put in User Profile name. This entails specifying the
directory where acquired data is stored or creating such a directory if it does not exist. For
example, the directory could be called “ho/alanine.” The User Profile should also include
the appropriate calibration file. If the operator does not specify a predefined user profile, the
spectrometer must be calibrated manually using Calibration (c) option in the main menu;
the name of the calibration file selected from the list must match the specification on the
front wall of the cavity.

If a sample tube is not in the microwave cavity, place it there. Make sure the correct size

Teflon collets (see Fig. 5) are used to mount the chosen sample tube (normally, a collet of a
smaller inner diameter is needed to support the tube from beneath). The tube must be held

13


Dimensions in mm and place it into the hole of the
five-hole cup normally occupied
by an ampoule. The
radiochromic thin film
dosimeters are normally
irradiated in polystyrene two-
piece square slab holders as

| films shown in Fig. 2. The slab

it oO assembly, with several
25.4 radiochromic films sealed in the

interior cavity, is held vertically
during irradiation. The
dosimeters are held in the
various holders or cups described in order to provide reproducible geometries as well as provide
approximate electron equilibrium conditions. Electron equilibrium is created when an
appropriate thickness of buildup material surrounds the dosimeter so that the incident photon
fluence generates a constant secondary electron spectrum. The exact thickness of the buildup
material is not very critical. For example, for “Co gamma rays, a thickness of 3 mm to 5 mm of
polystyrene is adequate. The Pool source and Gammacells provide nearly isotropic incident
photon fluences. This makes the ratio measurements discussed in Section 7.8 of SP250-44
necessary since the buildup material thickness can not be constant in all directions with
practically achievable geometries. The dose rates for all sources and configurations are given in
Table 1. The conversion of absorbed dose values in water to dose in silicon was done with the
use of ratios of mass energy absorption coefficients.

Luo | |
a
[254 |

Figure 2 - Holder for Radiochromic Thin Film Irradiation

5.1.2 The liquid-in-ampoules type dosimeters are not sensitive to external environmental
effects and require no special preparation before irradiation. The Red Perspex type dosimeters are
sealed in an aluminized pouch by the manufacturer to provide a constant relative humidity for the
dosimeters. These pouches must remain intact until after irradiation for the dosimeters to perform
properly. The FWT radiochromic thin film dosimeters are sensitive to humidity and must be
conditioned at a relative humidity of approximately 45% to 50% for at least 16 h then sealed in
aluminized trilaminate pouches before irradiation.

5.1.3. Nearly all dosimeters are sensitive to temperature during irradiation to some extent. It is
important to know that temperature so as to be able to apply a correction factor if necessary.
Even more desirable is to be able control the temperature during irradiation. The temperature in
GC-232 Gammacell can reach 50 °C if not controlled. A Turbo-Jet gas cooling system is used to
maintain the temperature of the dosimeters and holders at 23 °C during all irradiation.


As was the case for the alanine transfer dosimeters, the Type A uncertainty for the film block
dose rate is smaller than that shown in Table 6 for the same reason: the calibration was
performed in a fixed geometry in the GC-232 source only.

6.8 The uncertainty values provided may change. It shall be the responsibility of the calibration
laboratory to notify each affected client of any such changes, and the corrected values of all
affected quantities previously reported to that client.

7. Control Limits

7.1 The control limits referred to in Section 5 on quality control are derived from the
uncertainties associated with each type of dosimeter employed. For the alanine dosimeter system,
the combined relative standard uncertainty from Table 4 is 0.61%. For a safety factor of three, the
control limits would be 3 x 0.61 or +1.83%. Similarly, for the radiochromic film dosimeter
system, the combined relative standard uncertainty from Table 5 is 1.10% and the control limits
would be 3 x 1.10 or £3.30%.

7.2 Designate the target absorbed dose (discussed in Section 5), calculated from the irradiator
dose rate and irradiation time, as D,. Then the dose indicated by the alanine quality control
dosimeters should be within the control limits: D; +1.83%. Similarly, the dose indicated by the
tadiochromic film quality control dosimeters should be within D, +3.30%. If the doses indicated
by the quality control dosimeters are within the indicated limits than the quality control process is
said to be in a state of control. If the indicated doses are outside the control limits, then the
quality control process is “out of control” and the process must be investigated and appropriate
remedial action taken.

8. Keywords - Absorbed dose; calibration laboratory; dosimeter; dosimetry system; electron
beam; gamma ray; ionizing radiation; radiation processing; reference standard dosimeter.

9. References

1. Inn, K.G.W., Coursey, B.M., Eisenhower, E.H., Walker, M.D., Humphreys, J.C., Heaton,
H.T., Duvall, K.C., “The role of the Office of Radiation Measurement in quality assurance,” The
Science of the Total Environment, 130/131, Elsevier Science Publishers B.V., Amsterdam, 1993
pp. 497-507.

2. McLaughlin, W.L., “Reference dosimetry and measurement quality assurance,” Rad. Phys.
Chem. 40, 1989, pp. 945-951.

3. Nagy, V.Yu., Desrosiers,M.F., “Complex Time Dependence of the EPR Signal of Irradiated
L-a-Alanine,” Appl. Radiat. Isot. 47(8), 1996, pp. 789-793.

28


Table 4
Uncertainties of Alanine Absorbed Dose Measurements

Source of Uncertainty Type A(%) | Type B(%
Interspecimen scatter 0.71 -
Reproducibility and repeatability 0.08 -
System drift - 0.20
Pellet mass determination ~ 0.10
Combined separately 0.71 0.22
Combined relative standard uncertainty 0.75

Relative expanded uncertainty (combined x 2) 1.5

6.4 The uncertainties associated with measurement of absorbed dose with radiochromic film
dosimeters are shown in Table 5.

Uncertainties of Raidiochromle Fits: Absorbed Dose Measurements
Source of Uncertainty Type A (%) | Type B (%)
Interspecimen scatter | 1.00 --
Repeatability and reproducibility 0.10 -
Spectrophotometer zero drift - 0.20
Thickness measurement -- 0.40
Combined separately 1.00 0.45
Combined relative standard uncertainty 1.10
Relative expanded uncertainty (combined x2) {to 22

6.5 The relative uncertainties in absorbed dose values for irradiations of any type of dosimeters
in the standard geometries in both Gammacells and the Pool Source is shown in Table 6.

25


3.1.1 calibration - the process whereby the response of a dosimeter or measuring instrument is
characterized through comparison with an appropriate standard that is traceable to, and consistent
with, a national standard.

3.1.2 dosimetry system - a system used for determining absorbed dose, consisting of
dosimeters, measurement instruments and their associated reference standards, and procedures
for the system's use.
NOTE 1 - The types of dosimeters include reference standard dosimeters, transfer
standard dosimeters, and routine dosimeters. See Guide E 1261 for guidance on the
selection and calibration of the various dosimetry systems.

3.1.3 measurement assurance program - a documented program for the measurement process
that quantifies on a continuing basis the overall uncertainty of the measurements. This program
requires traceability to and consistency with national or international standards, and shall ensure
that the overall uncertainty meets the requirements of the specific application.

3.1.4 measurement traceability - the ability to demonstrate and document periodically that the
measurement results from a particular measurement system are in agreement with comparable
measurement results obtained with a national standard (or some identifiable and accepted
standard) to a specified uncertainty.

3.1.5 primary standard dosimeter - dosimeter, of the highest metrological quality, established
and maintained as an absorbed dose standard by a national or international standards
organization.

3.1.6 quality assurance - all systematic actions necessary to provide adequate confidence that a
calibration or measurement is performed to a predefined level of quality.

3.1.7 quality control - the operational techniques and procedures that are employed routinely to
achieve and sustain a predefined level of quality.

3.1.8 quality manual - document stating the quality policy, quality system, and quality practices
of an organization.

3.1.9 quality system - organizational structure, responsibilities, procedures, processes, and
resources for implementing quality management.

3.1.10 radiation processing - the intentional irradiation of products or materials to preserve,
modify, or improve their characteristics.

3.1.11 reference standard dosimeter - a dosimeter, of high metrological quality, used as a
standard to provide measurements traceable to, and consistent with, measurements made using
primary standard dosimeters.


1. Scope

1.1. This document contains detailed descriptions of the procedures used in the high-dose
radiation dosimetry calibration services at the National Institute of Standards and Technology
(NIST). These services are provided to the radiation processing industry by NIST staff or by
personnel employed by an industry trade organization, operating at NIST using NIST calibration
facilities, as part of a cooperative research and development agreement (CRADA). NIST staff
provide oversight and ensure the quality of the calibration services.

2. Referenced Documents
2.1 ASTM Standards:

E170 Terminology Relating to Radiation Measurements and Dosimetry

E1249 Practice for Minimizing Dosimetry Errors in Radiation Hardness Testing of Silicon
Electronic Devices using Co-60 Sources

E1250 Method for Application of Ionization Chambers to Assess the Low Energy Gamma
Component of Cobalt-60 Irradiators Used in Radiation-Hardness Testing of Silicon Electronic
Devices

E1261 Guide for Selection and Calibration of Dosimetry Systems for Radiation Processing
E1275 Practice for Use of a Radiochromic Film Dosimetry System

E1607 Practice for Use of the Alanine-EPR Dosimetry System

E1707 Guide for Estimating Uncertainties in Dosimetry for Radiation Processing

2.2 International Organization for Standards:

ISO/IEC Guide 25 (1990) General requirements for the competence of calibration and testing
laboratories

2.3. American National Standards Institute:

ANSI/NCSL Z540-1-1994 Calibration Laboratories and Measuring and Test Equipment -
General Requirements

2.4 National Institute of Standards and Technology:

NIST Special Publication 250-44 High-Dose Radiation Dosimetry Calibration Services and
Measurement Assurance Program

3. Terminology

3.1 Descriptions of Terms Specific to This Document:


Teflon —~Sample Tube:

Collet 7 495 mm ID
H |——-Cavity
q A ‘Alanine

Waveguide (h)
| Pellet
Locking — 1
Nut l| ~~Teflon Collet
50mm i

®

Figure 5 - Bruker Microwave Cavity

firmly enough to preclude any swinging, yet
allow its rotation. It must be in the lowest
attainable position in the cavity with its
horizontal surface in contact with the lower
collet.

Place one of the alanine pellets into the
sample tube in the cavity. Pellets are inserted
into and removed from the sample tube with
a vacuum pickup tool.

Press the F3 function key, then the right
cursor arrow in the lower row of the cursor
key panel to switch to the Tune mode. If
there is no dip observable in the display,
adjust the frequency to center the dip by
means of knob 1 on the knob control.

Gj) Press the Page-Up key to initiate the auto-tune procedure. After the systems returns to the
“Operate” mode, decrease the microwave attenuation to 7 dB by pressing the right of the
two ‘Home’ keys (the attenuation value is displayed in the second line of the right half of
the upper window). Then, press the (~||~) key to start the fine-tune procedure. Leave the

instrument working for at least 30 mins.

&)

Press F3 to activate the main menu and load an appropriate automation routine, such as

“replmeas.cmd” by using “Acquisition (A)” / “Automation Editor (L)” option.

(1) Load an appropriate parameter or spectrum file by pressing F (File) and then J (Directory of
Parameter Files) or I (Directory of Spectrum Files). Directory h0:/alanine/templates
contains a number of files with predefined parameters for Bruker and NIST pellets

irradiated to various doses.

(m) Create an Excel spreadsheet for the measurement data by copying and adjusting the file
“template.xls”. Copy the measured masses of pellets into it either manually or by opening
the file created by program “al60” as a new Excel worksheet (comma delimited).

5.3.2.3 Signal Measurements

(a) Puta pellet into the sample tube in the cavity by means of the vacuum pickup tool.

14


laboratory. These general criteria are completely consistent with ISO/IEC Guide 25 and its U.S.
equivalent ANSI/NCSL Z540-1. Laboratories that meet these general requirements comply, for
calibration activities, with Guide 25/Z540 and the relevant requirements of the ISO 9000 series of
standards, including those of the model described in ISO 9002 when they are acting as suppliers
producing calibration results.
4.5 In addition to the general requirements of ISO/IEC Guide 25/ANSI Z540, NIST SP250-44
contains specific criteria for particular types of ionizing radiation, that is, gamma rays, electron
beams and x-ray (bremsstrahlung) beams. It contains the theoretical basis for the traceability of

- dosimetry measurements used in the

i calibration services.
ann 4.6 This document contains the
procedures used in the handling of
customer’s calibration requests, for the
generation of calibration reports (with
13 mm dia. examples), and in the determination of
the uncertainties for the various
calibration services.

5. Calibration Procedures

5.1 Calibration Methods

5.1.1 The Pool source and Gammacell
Co gamma-ray irradiators?, described
in detail in NIST SP250-44, are used to
calibrate a variety of types of dosimeters
including liquid solutions sealed in glass

oan
4

L=-Suppor ampoules such as ceric cerous sulfate
kL] and dichromate, thin radiochromic solid
Figure 1 - Five-Hole Cup films, and thick solid slabs such as Red
for Ampoule Irradiation Perspex. Each type of dosimeter requires

a unique holder and geometry during

irradiation. For the liquid-in-ampoule
type, a polystyrene holder was used as shown in Fig. 1. This holder is referred to as the “five-hole
cup” since the five circumferential holes are normally used to hold the dosimeters being
calibrated and the center hole is used for quality control dosimetry. The hole size was chosen so
that a 2-mL ampoule would fit snugly. Red Perspex dosimeters are normally sealed in aluminum
pouches by the manufacturer and are not opened until after irradiation. The usual method for
handling these during calibration is to fold the pouch tightly around the slab of each dosimeter

?The mention of commercial products throughout this document does not imply
recommendation or endorsement by the National Institute of Standards and Technology, nor
does it imply that the products identified are necessarily the best available for the purpose.

4


(26) The Calibration Report is reviewed by the Division Chief and if approved;
(27) The Calibration Report is sent to the customer;

(28) The calibration fees are calculated by the Calibration Technician;

(29) The Test Folder is completed with the calibration fees;

(30) The Test Folder is returned to the CP/OMS office;

(31) The Control Log is updated with the QC data from step (16) and the date of completion
of the Test Folder;

(32) The CP/OMS office sends a bill to the customer;
(33) The customer makes payment to the CP/OMS office;

(34) All documents within the Division are filed; the calibration process is completed.

20


NIST Measurement Services:

NIST Special Publication 250-45

Radiation Processing Dosimetry Calibration
Services: Manual of Calibration Procedures

Jimmy C. Humphreys
James M. Puhl
Stephen M. Seltzer
William L. McLaughlin
Marc F. Desrosiers
Vitaly Y. Nagy

Debra L. Bensen
Marlon L. Walker

U.S. Department of Commerce
Technology Administration
National Institute of Standards and Technology


UNCERTAINTIES AND RELATED FACTORS IN HIGH-DOSE CALIBRATIONS

D luati B
Mailed Film Transfer Standard Dosimeters

(Relative expanded uncertainty: + 4.6% at a 95% confidence level)

The use of NIST transfer standard dosimeters to calibrate the dose rate of the
customer's in-house radiation source is subject to the limitations and precautions
described in the letter accompanying the dosimeters. The customer must follow the
prescribed procedures carefully in order to ensure that the results obtained from the
transfer dosimeters are valid.

In the case of absorbed dose in water evaluation based on NIST radiochromic film
dosimeters (nominal dose range 5 x 10° to 5 x 10* Gy) that are traceable to °Co
gamma-ray calibrations at NIST, the uncertainty value cited above (+ 4.6%) may be
assumed as long as suitable care is exercised.

A detailed list of the various sources of uncertainty and estimates of the magnitude of
those uncertainties that make up the overall uncertainty given above may be obtained
by requesting such information from NIST. The uncertainties are divided into two types:
A and B. Type A uncertainties are those evaluated by statistical methods, often
associated with random effects. Type B uncertainties are those evaluated by other
means, often associated with systematic effects.

Type A Uncertainties

The combined relative standard uncertainty evaluated by statistical methods is + 1.1%
at an approximate level of confidence of 68%.

Type B Uncertainties

The combined relative standard uncertainty based on scientific judgement is estimated
to be + 2.0% at an approximate level of confidence of 68%.

Expanded Uncertainty

The type A and type B uncertainties have been combined in quadrature (the square
root of the sum of the squares) and multiplied by a coverage factor of 2 to yield a
relative expanded uncertainty of + 4.6% at an approximate level of confidence of 95%.

REFERENCE TEST 846/256018-97 Sep. 25, 1997
NIST DB 932/018 HD9799
Page 3 of 3 Pages

43


5.2 Quality Control Procedures

5.2.1 Calibrated NIST radiochromic thin film dosimeters are used for quality control (QC)
during irradiation of customer-supplied radiochromic thin film dosimeters. The procedures are as
follows:

5.2.1.1 A new batch of radiochromic dosimeters is calibrated by irradiation to various absorbed
dose values over the dose range of interest. For example, for a range of 1 kGy to 50 kGy, 10 dose
points might be used, with 5 dosimeters irradiated at each dose value. Each dosimeter film is
marked with a code to maintain its identity through all subsequent operations. All dosimeters are
analyzed (read out) before irradiation as well as after irradiation. After the pre-irradiation
analysis, the dosimeters are stored under controlled humidity conditions of 45% to 50% R.H. for
at least 16 h to allow for equilibration of the water content of the films. Five films are stacked,
with a thin black polyethylene square on the top and bottom of the stack, and placed in the
polystyrene block assembly shown in Fig. 2. The black polyethylene squares are needed because
experimental evidence indicates an over response of the top and bottom films in the stack,
probably a result of fluorescence from the polystyrene during irradiation. The polystyrene block
assembly is then heat sealed in a trilaminate pouch (a polyethylene layer inside, then a thin
aluminum sheet, then a Mylar layer outside) in the controlled humidity environment. Each sealed
block assembly is irradiated to a specific dose value in one of the NIST “Co irradiators with the
block held in a reproducible position in the center of the source array geometry. After a storage
time of at least 16 h, the dosimeters are analyzed and the results provide a calibration of that
batch of radiochromic films (see 5.3 for details on the analysis and data reduction procedures).
The remainder of the unirradiated batch may be used for QC during irradiation of customer-
supplied dosimeters.

5.2.1.2 Unirradiated QC dosimeters are analyzed before irradiation and then stored, along with
the customer-supplied dosimeters, in the 45% to 50% R.H. environment for at least 16 h. A stack
of customer dosimeters ( a maximum of five) and three QC dosimeters are placed in the
polystyrene block assembly and sealed in the laminated pouch as described in 5.2.1.1.

5.2.1.3 The sealed block assembly is irradiated to the specified absorbed dose in one of the
NIST “Co irradiators and stored for at least 16 h (overnight) to allow for full development of the
film response. The pouch is opened, the films removed and the NIST QC films separated from
the customer’s films. The QC films are then analyzed and the indicated dose values are compared
with the target dose. If the results are within the specified control limits (discussed in Section 7)
then the irradiation is considered satisfactory. If the results are outside the control limits then the
irradiation must be investigated and appropriate corrective action taken. All QC results are
recorded as part of the calibration report and test folder.

5.2.2 Calibrated alanine pellets are used for QC for all irradiations that do not involve
radiochromic thin films. The procedures are as follows:


Tablel .

Dose Rates for “Co Sources for December 31, 1996
filename = B140 P5-90 c:\qpw\DR97c.WB1
Effective 3/1/97
Co-60 half-life value is adjusted from 1925.34 days to 1925.12 days
Domen Water Calorimeter Transfer Calibration
Source in B036 under 5 cm water at 100 cm source
for 14.5 cm by 14.5 cm field size

For 1/11/90 Dose rate =

1.8144 Gy/min

For 12/31/96 Elapsed time = 2546 days
Co-60 daily decay constant ( In2 / 1925.12 )= 3.60054e-04
Decay correction factor = 0.399837
Dose rate = 0.72546 Gy/min
or 0.012091 Gy/s

Absorbed Dose Rate in Water

GC232 Ratio Gy/s Gy/min kGy/h

3.5 mm Single-hole vial geometry 248.6 3.005 180.3 10.82

5.0 mm Polystyrene Film Block Geometry 0.9870 2.966 178.0 10.68

4.2 mm polystyrene 5-hole cup Perspex Geometry 0.9710 2.918 175.1 10.51

4.2 mm polystyrene 5-hole cup Ampoule Geom: 0.9560. 2.873 172.4 10.34
GC232 in Stainless Steel Dewar

3.5 mm Single-hole vial geometry 239.9 2.901 174.0 10.44

5.0 mm Polystyrene Film Block Geometry 0.9913 2.875 172.5 10.35

4.2 mm polystyrene 5-hole cup Perspex Geometry 0.9692 2811 168.7 10.12

4.2 mm polystyrene S-hole cup Ampoule Geometry 0.9599 2.784 167.1 10.02

GC45

3.5 mm Single-hole vial geometry 75.18 0.9090 54.54 3.272

5.0 mm Polystyrene Film Block Geometry 0.9889 0.8989 53.93 3.236

4.2 mm polystyrene 5-hole cup Perspex Geometry 0.9730 0.8844 53.07 3.184

4.2 mm polystyrene 5-hole cup Ampoule Geometry 0.9595 0.8722 52.33 3.140

F101 Pool Source

3.5 mm Single-hole vial geometry 26.85 0.3246 19.48 1.169

5.0 mm Polystyrene Film Block Geometry 0.9941 0.3227 19.36 1,162

4.2 mm polystyrene 5-hole cup Perspex Geometry 0.9883 0.3208 19.25 1.155

4.2 mm polystyrene 5-hole cup Ampoule Geometry, 0.9749 0.3164 18.99 1.139

for Gammacell and Pool, Combined Relative Expanded Uncertainty = 1.8%; dose rate (Silicon) = dose rate (Water) * 0.913

elapsed time = 366 days, decay correction factor = 0.876534

B036 Co-60 Vertical Beam Geometry Gy/s Gy/min Gy/h
BO036 s. 0.0 cm, coll=20 x 20 6 mm ps plate 2.676¢e-02 1.605e+00 96.32
B036 s. 1.6 cm, coll=20 x 20 6 mm ps plate 1,944e-02 1.167e+00 70.00
B036 s.d.=105 cm, coll=20 x 20 6mm ps plate 6.227e-03 3.736e-01 22.42

B034 Co-60 Vertical Beam
B034 s.d.=15.0 cm, coll.= 25 x 25 6 mm ps plate 5.306e-03 3.184e-01 19.10
B034 s. 00 cm, coll.= 25 x 25 6 mm ps plate 9.476e-04 5.685e-02 3.411
BO34 s. 30 cm, coll.= 25 x 25 6 mm ps plate 6.568e-04 3.941e-02 2.364

for vertical beams, Combined Relative Expanded Uncertainty = 2.2%; dose rate (Silicon) = dose rate (Water) * 0.896


The last page of this Report describes uncertainties and related factors in high-dose
calibrations, such as the one covered by this Report of Calibration. {f there are further
questions, they should be directed to the first individual named below.

Measurements were made by

J. M. Puhl, Calibrations Technician
(301)975-6581

Approved by

Stephen M. Seltzer, Leader
Radiation Interactions and Dosimetry Group

For the Director
National Institute of Standards and Technology
by

Bert M. Coursey, Chief
lonizing Radiation Division
Physics Laboratory

REFERENCE TEST 846/256018-97 Sep. 25, 1997
NIST DB 932/018 HD9799
Page 2 of 3 Pages

39


Table 7
Uncertainties in Absorbed Dose (in water) Values for Alanine Transfer Dosimeters

Source of Uncertainty Type A (%) | Type B (%)
Alanine single-hole cup dose rate 0.36 0.47
Alanine dose measurement (from Table 4) 0.71 0.22
Irradiation temperature correction - 0.10
Elapsed time between irradiation and analysis - 0.25
Dose value derived from calibration curve -- 0.50
Combined separately 0.80 0.77
Combined relative standard uncertainty 1

Relative expanded uncertainty (combined x 2) 2.2

The Type A relative uncertainty shown for the single-hole cup dose rate alanine response is
smaller than that shown in Table 6 because the dosimeters are calibrated in that fixed geometry
for GC-232 only.

6.7 The relative uncertainties associated with the use of radiochromic film transfer standard
dosimeters in shown in Table 8.

Table 8
Uncertainties in Absorbed Dose (in water) Values for
Radiochromic Film Transfer Dosimeters

Source of Uncertainty Type A (%) | Type B (%)
Film block dose rate 0.40 0.47
Film dose measurement (from Table 5) 1.0 0.45
Energy spectra correction . ~ 0.50
Elapsed time between irradiation and analysis - 0.50
Dose value derived from calibration curve ~ 1.80
Combined separately Ll 2.0
Combined relative standard uncertainty 2.3

Relative expanded uncertainty (combined x 2) 4.6

27


UNCERTAINTIES AND RELATED FACTORS IN HIGH-DOSE CALIBRATIONS

Absorbed Dose Evaluations Based on Use of
iled Alanine Transfer Dosimeters

(Relative expanded uncertainty: + 2.2% at a 95% confidence level)

The use of NIST transfer standard dosimeters to calibrate the dose rate of the
customer's in-house radiation source is subject to the limitations and precautions
described in the letter accompanying the dosimeters. The customer must follow the
prescribed procedures carefully in order to ensure that the results obtained from the
transfer dosimeters are valid.

In the case of absorbed dose in water evaluation based on NIST alanine pellet
dosimeters (nominal dose range 1 x 10° to 5 x 10* Gy) that are traceable to °Co
gamma-ray calibrations at NIST, the uncertainty value cited above (+ 1.8%) may be
assumed as long as suitable care is exercised.

A detailed list of the various sources of uncertainty and estimates of the magnitude of
those uncertainties that make up the overall uncertainty given above may be obtained
by requesting such information from NIST. The uncertainties are divided into two types:
A and B. Type A uncertainties are those evaluated by statistical methods, often
associated with random effects. Type B uncertainties are those evaluated by other
means, often associated with systematic effects.

Type AU, inties

The combined relative standard uncertainty evaluated by statistical methods is + 0.7%
at an approximate level of confidence of 68%.

Type B Uncertainties

The combined relative standard uncertainty based on scientific judgement is estimated
to be + 0.6% at an approximate level of confidence of 68%.
x in’

The type A and type B uncertainties have been combined in quadrature (the square
root of the sum of the squares) and multiplied by a coverage factor of 2 to yield a
relative expanded uncertainty of + 1.8% at an approximate level of confidence of 95%.

REFERENCE TEST 846/256018-97 Sep. 25, 1997
NIST DB 932/018 HD9799
Page 3 of 3 Pages

44


Table 6
Uncertainties in Absorbed Dose (in water) Values
for Irradiations in the Gammacells or the Pool Source

Source of Uncertain ‘Type A (%) | |
Cajorimeter measurement of Vertical Beam source 0.16 0.32
Scaling procedure - 0.35
Source ratio measurement data 0.35

Source decay, half life = 0.01
Irradiation timing 0.17 -
Geometry correction factor 0.61 -
Irradiation temperature correction - 0.02
Combined separately 0.74 0.47
Combined relative standard uncertainty 0.88
Relative expanded uncertainty (combined x 2) 1.8

To convert the dose values from dose in water to dose in silicon requires the use of ratios of mass
energy absorption coefficients and contributes an additional Type B component of 0.30% to
those in Table 6. Thus the combined separately Type B value increases to 0.55%, the total
combined value increases to 0.93%, and the total combined x 2 increases to 1.9%.

6.6 The relative uncertainties in the use of alanine transfer standard dosimeters in
measurements of absorbed dose is shown in Table 7.

26


3.1.12 routine dosimeter - dosimeter calibrated against a primary-, reference-, or transfer-
standard dosimeter and used for routine absorbed dose measurement.

3.1.13 transfer standard dosimeter - a dosimeter, often a reference standard dosimeter, suitable
for transport between different locations, used to compare absorbed dose measurements.

3.1.14 verification - confirmation by examination of objective evidence that specified
requirements have been met.
NOTE 2 - In the case of measuring equipment, the result of verification leads to a
decision either to restore to service or to perform adjustments, or to repair, or to
downgrade, or to declare obsolete. In all cases it is required that a written trace of the
verification performed be kept on the instrument's individual record.

3.1.15 working standard - a standard, usually calibrated against a reference standard, used
routinely to calibrate or check measuring instruments or devices.

3.2 Also see Terminology E 170.
4. Significance and Use

4.1 The radiation industry needs a source of reliable, prompt, dosimeter calibration services to
support accurate measurements of absorbed dose during radiation processing. Those
measurements, made routinely in industrial facilities, should be consistent with and traceable to
the physical measurement standards maintained by an appropriate national or international
standards laboratory.

4.2 To ensure the provision of adequate services, a calibration laboratory should be operating
with a full measurement assurance program (MAP). The fundamental requirements for such a
program include: (1) compliance with operational requirements of this document; (2)
documented procedures and in-house quality assurance (QA) program specific to the calibration
services provided; and (3) periodic performance evaluations, such as review by NIST staff and
measurement intercomparisons between national laboratories (1,2)'.

4.3 In addition to standard calibration services such as irradiation of dosimeters and supplying
transfer dosimeters for customer in-house source calibration, the calibration laboratory MAP can
provide technical information, troubleshooting (at the customer's facility if necessary), and serve
as an independent group for resolution of disputes. The MAP can also conduct long term studies
of dosimetry system characteristics, such as environmental effects, and evaluate new, emerging
dosimetry systems to assist in technology transfer to industry.

4.4 NIST SP250-44 sets forth general criteria that shall be satisfied by the calibration

'The bold. numbers in parenthesis indicate references at the end of the text.

3


5.4 Handling of Calibration Requests

5.4.1

The process for calibration of customer-supplied dosimeters is shown schematically in

the flowcharts in Figs. 8a and 8b. These show the various administrative levels involved and the
documents and actions required to complete a calibration. The steps in the process (with step
numbers keyed to those in the flowchart) are as follows:

qd)
(2)

Irradiate
Page 1

Customer

CP/OMS

Division

Control
Log

Documents

Actions

Shipping &
Receiving

(3)

Dosimeters;

Figure 8a - Procedures for Calibration Irradiations of Customer-Supplied Dosimeters

The customer request a calibration or information;

A fee schedule is supplied to the customer (an example is shown in Appendix 4);

( Start )

equest New
Dosimeters

[n} |
Test Folder
[77 Prepared |

a
‘Customer | JP.

Request _| [ree

|
| |
| |
g—_ |
Fre tan| |
|_ Supplied Received

|. |
| _ & i

| [Return to |, Bad _-“Dosimeters OK J Irradiate
| | Customer ¥ Inspected.” Dosimeters
|

4

= m

T Pasimeters | + Dosimeters Uinpacked |
| Received | SID Assigned |

The customer prepares a purchase order and returns it;

17


Appendix 3

al160.bas (DOS Basic) program:

10 GOSUB 560:COLOR 15,1:CLS:ON ERROR GOTO 210

20 'COLOR 15,1:CLS:GOSUB 510:

30 PRINT "file A160READ.BAS _ last update 3/3/97"

40 INPUT "ENTER STARTING PELLET NUMBER: ";SPN

50 PRINT:PRINT " DATA WILL BE STORED TO FILE: ";F$

60 PRINT"Press ENTER to start the transmission or Q to quit."

70 A$=INKEY$:IF A$="" THEN GOTO 70

80 IF A$="Q" OR A$="q" THEN STOP

90 OPEN "COM1:4800,N,8,2,RS,CD,DS,CS" AS #1

100 PN=SPN: WAYT=10:OPEN "0",2,F$:CLOSE 2

110 PRINT"Press any key to stop the transmission "

120 LOCATE 24,1:GOSUB 290:TO=TIMER

130 IS=INKEY$:IF I$<>"" THEN CLOSE 1:GOTO 520

140 IF TIMER-TO > WAYT THEN GOSUB 230

150 LINE INPUT#1,A$:

160 NUM=VAL(MID$(A$,3,LEN(A$)))

170 IF NUMONUM THEN LOCATE 24,1:PRINT
PN,NUM,0;:ONUM=NUM:T0=TIMER:GOTO 200

180 LOCATE 24,1:PRINT PN,NUM,CINT(TIMER-TO);

190 OPEN "a",3,"a160all.dat": PRINT#3,PN,NUM,CINT(TIMER-T0), TIME$:CLOSE 3
200 GOTO 130

210 PRINT ERR:RESUME NEXT

220 GOTO 130

230 PN$=STRS(PN):PL=LEN(PNS)-1:NUM$=STR$(NUM):NUML=LEN(NUM$)-1
240 OL$=RIGHT$(PN$,PL)+CHR$(44)+RIGHTS(NUM$,NUML)
250 OPEN "A",2,F$:PRINT #2,OL$:CLOSE 2

260 OPEN "o",2,"A161.O0UT":PRINT #2,OL$:CLOSE 2

270 BEEP:'FOR I=100 TO 3200 STEP 100:SOUND I,.5:NEXT I
280 PN=PN+1:PRINT:PRINT "PRESS ANY KEY TO STOP":TO=TIMER
290 PRINT "WAITING FOR ZERO"

300 LINE INPUT#1,A$:

310 IS=INKEY$:IF I$<>"" THEN CLOSE 1:GOTO 510

320 NUM=VAL(MID$(A$,3,LEN(A$)))

330 TO=TIMER

340 IS=INKEY$:IF I$<>"" THEN GOTO 510

350 IF TIMER-T0 > 2 THEN GOTO 420

360 LINE INPUT#1,A8:

370 NUM=VAL(MID$(A$,3, LEN(A$)))

34


380 IF NUM<0 THEN LOCATE 24,1:PRINT,NUM,0;:TO-TIMER:GOTO 340
390 LOCATE 24,1:PRINT ,NUM,CINT(TIMER-TO0);

400 OPEN "a",3,"a160all.dat": PRINT#3,"zero",NUM,CINT(TIMER-TO0), TIME$:CLOSE 3
410 GOTO 340

420 IF NUM < 0 THEN GOTO 300

430 PRINT:'FOR I=2500 TO 100 STEP -100:SOUND I,.5:NEXT I

440 BEEP:BT=TIMER: WHILE TIMER<BT+.5:PRINT"";: WEND:BEEP

450 PRINT "WAITING FOR PELLET# ";PN

460 LINE INPUT#1,A$:

470 IS=INKEY$:IF I$<>"" THEN GOTO 510

480 NUM=VAL(MID$(A$,3,LEN(A$)))

490 IF NUM <.03 THEN GOTO 460

500 RETURN

510 PRINT:PRINT "PRESS Q TO QUIT OR B TO STAY IN BASIC"

520 A$=INKEY$:IF A$="" THEN GOTO 520

530 IF A$S="Q" OR A$="q" THEN SYSTEM

540 IF A$<>"B" AND A$>"b" THEN GOTO 520

550 STOP

560'

570' filename subroutine

580

DTE$=DATES$:M$=LEFTS$(DTE$,2):D$=MID$(DTE$,4,2): Y$=RIGHT$(DTES$,2):ANUM=0
590 DTES=Y$+M$+D$

600 F$=DTE$+CHR$(65+ANUM)+".DAT"

610 ON ERROR GOTO 640: NAME F$ AS F$

620'

630' ERROR TRAP

640 IF ERR=58 THEN EX$="y":RESUME 660

650 IF ERR=53 THEN EX$="N":RESUME 660

660 ON ERROR GOTO 0

670 IF EX$ <>"y" THEN GOTO 710

680 ANUM=ANUM+1:IF ANUM <=25 THEN GOTO 600

690 IF LEN(DTE$)=6 THEN DTES=DTE$+"A" :ANUM=0:GOTO 600

700 DTE$=LEFT$(DTE$,6)+CHR$(ASC(RIGHTS(DTES, 1))+1): ANUM=0:GOTO 600
710 RETURN

720 RETURN

35


Transfer

Page 2
ralibration
Customer Report to rT —
‘Customer —I
i Bj} 1,
Return | ‘Payment by
cP/OMS ‘Test Folder Customer
esaadahan
|
Division |
Division | Review & =———_!
Approval
t
me GG | —
Data | id
Control rife ed | Calibration |
og ened | Folder Closed
] )
| |

i ion |e Pte] ‘ 7
Oe ibraton | t Documents
repare |__[JSupervisor| | TCateulate ‘Complete "
Pocuments Report ‘Technician }——*) "Review Fee | Test Folder Filed
\
( Baa)

Dosimeters;
Actions

Shipping &
Receiving

Figure 9b - Procedures for NIST-Supplied Transfer Dosimeters for Customer Irradiation

require another set of dosimeters being irradiated by the customer;
(17) to (29) All subsequent steps are the same as in 5.4.1.
5.5 Calibration Reports
5.5.1 The requirements for content and format of calibration reports to be sent to customers

are covered in NIST SP250-44. Examples of both types, i.e., for NIST calibration irradiation of
customer-supplied dosimeters and NIST transfer dosimeters supplied for customer irradiation,

are shown in Appendix 6.

23


National Institute of Standards and Technology Special Publication 250-45
Nati. Inst. Stand. Technol. Spec. Publ. 250-45, 47 pages (Mar. 1998)
CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE
WASHINGTON: 1998

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325


United States Department of Commerce
National Institute of Standards and Technology
Gaithersburg, MD 20899 USA

REPORT OF CALIBRATION

OF: Ed's Sterilizers
©°Co Calibrator, s/n 10
by use of NIST
Transfer Dosimeters
FOR: Ed's Sterilizers
10 Gamma Avenue
Mega Rad, TX 99817
ATTN: Cobalt Jones
REF: PO# 232
Description: Transfer dosimetry packets, consisting of five calibrated FWT-
60-00 radiochromic dosimeters (NIST Batch #7f6a), held
between 5.0 mm thick blocks of polystyrene and sealed inside
a thin polymer-aluminum laminate pouch (R.H. = 45% at time
of sealing), were sent to Ed's Sterilizers for irradiation in their
®°Co calibrator. Upon their return to NIST, the dosimeters were
analyzed on 11/23/97, using a Cary 3 spectrophotometer( S/N
1101115, 4.0 nm S.B.W.). Absorbed dose interpretations were
made from a calibration of this batch of radiochromic
dosimeters performed in March 1997. The results are
summarized in the following table.
NIST Interpolated
Dosimeter ID Dose, kGy(H,O)
875-879 10.99
880-884 11.01
885-889 11.09
REFERENCE TEST 846/256018-97 Sep. 25, 1997
NIST DB 932/018 HD9799

Page 1 of 3 Pages

41


UNCERTAINTIES AND RELATED FACTORS IN HIGH-DOSE CALIBRATIONS

High-Dose Calibrations in St IK ie:
using the NIST Cobalt-60 Irradiators

(Relative expanded uncertainty: + 1.8% at a 95% confidence level)

The high-dose calibrations at NIST involve the administration of °Co gamma radiation
under environmentally controlled conditions. The dose values are based on standard
water calorimeter measurements and EPR/Alanine dosimetry, which are corrected by
certain modifying factors (such as the estimated photon spectrum, radiation energy
absorption and attenuation factors, and source decay factors).

The uncertainty cited above is pertinent to absorbed dose in water in calibrated
geometries. A detailed list of the various sources of uncertainty and estimates of the
magnitude of those uncertainties that make up the overall uncertainty given above may
be obtained by requesting such information from NIST. The uncertainties are divided
into two types: A and B. Type A uncertainties are those evaluated by statistical
methods, often associated with random effects. Type B uncertainties are those
evaluated by other means, often associated with systematic effects.

Type A Uncertainti

The combined relative standard uncertainty evaluated by statistical methods is + 0.7%
at an approximate level of confidence of 68%.

Type B Uncertainties

The combined relative standard uncertainty based on scientific judgement is estimated
to be + 0.5% at an approximate level of confidence of 68%.

Expanded Uncertainty

The type A and type B uncertainties have been combined in quadrature (the square
root of the sum of the squares) and multiplied by a coverage factor of 2 to yield a
relative expanded uncertainty of + 1.8% at an approximate level of confidence of 95%.

REFERENCE TEST 846/256018-97 Sep. 25, 1997
NIST DB 932/018 HD9799
Page 3 of 3 Pages

40


the rear of the gauge unit).

(b) The film thickness is measured with a cartridge head connected to the electronic
gauge unit; the head is mounted on a rigid gauge stand. The cartridge plunger tip is raised
and lowered onto the stand anvil by a hand-operated vacuum plunger attached to the
cartridge. To check the “zero” of the unit initially, lift the tip, place a piece of clean lens
paper under it, lowering the tip onto the anvil, then pulling the lens paper out. This removes
any dirt on the tip or anvil. Raise and lower the tip several times and reset the zero if
necessary with the control knobs on the front of the gauge unit. Repeat this procedure until

a stable zero reading is obtained.

3eS

Table 2

Photometric Mode Absorbance
Ordinate (Y) Min. / Max. 0.0000 / 4.0000
Abscissa (X) Min. / Max. 500.00 / 610.00
Spectral Bandwidth (nm) 4.0
Signal Averaging Time (s) 1.000
Data Interval (s) 1,000
Wavelength Scan Rate (nm/min) 60.000
Lamps On Visible
Baseline Correction On
Auto Scaling Yes
Auto Store Data No
Auto Store Report Yes

Table 3

Sample Data from Film Readout

1 2.8137 0.4158
2 1.6882 0.2494
3 0.8441 0.1247

10



y=atbxtox’2+dx3
Eq#+2040 12=0.99968938

80

60 4

(A2-AL)/mm
&
r

20 4

0 pr T T 7 T 7
0 10 20 30 40 50 60 70
Dose, kGy

a YActual —s— ¥Predicted

5.3.2 Alanine Dosimeter Analysis

5.3.2.1 Analysis (read out) of the alanine dosimeter pellets is done with a Bruker model ESC 106
electron paramagnetic resonance (EPR) spectrometer. The spectrometer is used with a model
TM9222 microwave resonant cavity (Fig. 5). The procedure consists of three stages: preparation;
signal measurements; and data analysis.

5.3.2.2 Preparation

(a) Choose an optimal time for the measurements (3). This depends on the dose range:
10 Gy to 100 Gy 12 or more hours after irradiation
0.1 kGy to 25 kGy 48 h to 100 h after irradiation
25 kGy to 100 kGy 48 h to 72 h after irradiation
Calibration and test pellets must be irradiated approximately simultaneously.

(b) After irradiation, each alanine pellet is marked on top with an identification number with a
permanent ink pen. The mass of each pellet is measured before EPR analysis with a Denver
Instrument Company model 160 electronic balance to the nearest 0.1 mg. Program “al60”
on COMPAQ386/25e can be used for automatic input of the masses into the computer.

12


NIST Special Publication 250-45

NIST MEASUREMENT SERVICES:

Radiation Processing Dosimetry Calibration
Services: Manual of Calibration Procedures

Jimmy C. Humphreys, James M. Puhl, Stephen M. Seltzer,
William L. McLaughlin, Marc F. Desrosiers, Vitaly Y. Nagy,
Debra L. Bensen, and Marlon L. Walker

lonizing Radiation Division

Physics Laboratory

National Institute of Standards and Technology
Gaithersburg, MD 20899-0001

March 1998

U.S. Department of Commerce
William M. Daley, Secretary

Technology Administration
Gary R. Bachula, Acting Under Secretary for Technology

National Institute of Standards and Technology
Raymond G. Kammer, Director


370 IF Q> 4 THEN GOTO 300 ELSE STOP

380 ON ERROR GOTO 410:INPUT "Filename";N$ : NAME N$ AS N$

390'

400' ERROR TRAP

410 IF ERR=58 THEN EX$="y":RESUME 430

420 IF ERR=53 THEN EX$="N":RESUME 430

430 ON ERROR GOTO 0:IF EX$ >"y" THEN T$="0":GOTO 460

440 INPUT "FILE ALREADY EXISTS - A to append ,O to overwrite or R to rename";T$
450 ON ERROR GOTO 0

460 IF T$="R" OR T$="r" THEN GOTO 380

470 IF T$="0" OR T$="0" THEN SHELL "DEL "+N$:SHELL "REN "+F$+" "+N$
480 IF T$="A" OR T$="a" THEN SHELL "COPY "+N$+" + "+F$

490 INPUT "WOULD YOU LIKE TO CHECK IT? (Y OR N)";Z$:

500 IF Z$="y" OR Z$="Y" THEN GOTO 510 ELSE GOTO 520

510 SHELL "edit "+N$:

520 STOP

33


5.4.2 The process for the supply of NIST transfer dosimeters to a customer for irradiation in
the customer’s in-house radiation facility is shown schematically in Fig. 9a and 9b. The steps in
generating the paper work (i.e., P.O., Test Folder, Control Log updates, etc.) are essentially the
same as for the process when customer-supplied dosimeters are calibrated. The real difference is
that NIST-supplied transfer standard dosimeters are sent to the customer. These dosimeters may

Hiei (Start ) -
ico nee ae
vustomer 0.
customer «| Irradiation of |
Request | ["|Prepared Dosimeters
w

cPiOMs — Test Folder

| ] Prepared

7 |
Divi Fee Schedule P.O.
wision Supplied | Received
3 | |
Controt i P.O.
Log Logged rT
| |

i | |
Documents | Division

| —

16
Dosimeters; Fee
‘Actions _
—— Ope toe
Shipping & Srrranster—] Transfer irradiated |
F Dosimeters +} Dosimeters Dosimeters | ——!

Receiving Packed _| L Shipped |_Returned_|

Figure 9a - Procedures for NIST-Supplied Transfer Dosimeters for Customer Irradiation

be alanine pellets or radiochromic films, as requested by the customer. However, it is generally
recommended that alanine pellets be used because of the wider dose range, lack of known dose
rate effect, and better precision and stability of that dosimetry system. The steps in the process of
using transfer dosimeters will not be listed in the detail given in 5.4.1 for the irradiation of
customer dosimeters because of the redundancy in many steps. Only those areas where the
procedures are different will be discussed.

(1) to (5) Steps are the same as in 5.4.1;

21


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“assist industry in


SP 250-1

SP 250-2

SP 250-3

SP 250-4

SP 250-5

SP 250-6

SP 250-7

SP 250-8

SP 250-9

SP 250-10

SP 250-11

SP 250-12

SP 250-13

SP 260-14

SP 250-15

SP 250-16

SP 250-17

SP 250-18

SP 250-19

THE SP 250 SERIES ON NIST MEASUREMENT SERVICES*

Spectral Radiance Calibrations
PB87 179883

Far Ultraviolet Detector Standards
PB87227609

Radiometric Standards in the Vacuum
Ultraviolet
PB87227625

Fricke Dosimetry in High-Energy Electron Beams
PB8BI10374

Alpha-Particle Calibrations
PB88168620

Regular Spectral Transmittance
PB88108550

Radiance Temperature Calibrations
PBEB123674

Spectral Reflectance
PB88109905

Calibration of Beta-Particle-Emitting
Ophthalmic Applicators
PB8108535

Radioactivity Calibrations with the “
Gamma lonization Chamber and Other
Radioactivity Calibration Capabilities
PB88123708

Dosimetry for High Dose Applications
PB88201587,

Neutron Personnel Dosimetry
PB87227617

Activation Foil Irradiation with Californium
Fission Sources
PB88217443

Activation Foil Irradiation by Reactor Cavity
Fission Sources
PB88217435

Photometric Calibrations
PB88153747

Calibration of X-Ray and Gamma-Ray
Measuring Instruments
PB8821 1826

The NBS Photodetector Spectral Response
Calibration Transfer Program
PB88201595

Neutron Source Strength Calibrations
PB88211818

Calibration of Gamma-Ray-Emitting
Brachytherapy Sources
P 889193858

SP 250-20

SP 250-21

SP 250-22

SP 250-23

SP 250-24

SP 250-25

SP 259-26

SP 250-27

SP 250-28

SP 250-29

SP 250-30

SP 250-31

SP 250-32

SP 250 33

SP 250-34

SP 250-35

SP 250-36

SP 250-38
SP 250-40

Spectral irradiance Calibrations
PB88123781

Calibration ot Beta-Panicle
Radiation Instrumentation
PB88201579

Platinum Resistance Thermometer
Calibrations
PB88138367

Liquid-in-Glass Thermometer
Calibration Service
PB89128888

Standard Cell Calibrations
PB8B123690

Calibration Service for Inductive
Voltage Dividers

NBS Phase Angle Calibration Services
PB88225636

AC-DC Difference Calibrations
PB892222616

Solid-State DC Voltage Standard Catibrations
PB88168703

Traceable Frequency Calibrations
PBGB 168364

GOES Satellite Time Code Dissemination
Description and Operation
PB88 168760

Mass Calibrations
PB89153894

A Calibration Service for 30 MHz
Attenuation and Phase Shift
PB88238324

A Calibration Service for Voltage Transformers
and High-Voltage Capacitors
PB882252903

High Vacuum Standard and Its Use
PB89193841

The Calibration of Thermocouples
and Thermocouple Materials
PBg9209340

A Calibration Service for
Current Transformers

NIST Leak Calibration Service

Absorbed-Dose Calibration of
fonization Chambers in a
"Co Gamma-Ray Beam
$N003-003-03034-1 $2.00

* Entries Entries containing a stock number (SNO03-003-) and price can be purchased from the Superintendent of Documents, U.S.
Government Printing Office, Washington, DC 20402. GPO will accept checks, money orders, VISA, and MasterCard. For more infomation,
oF to place an order, call (202) 783-3238, Be sure to cite the stock number on all orders.

Entries containing PB numbers can be purchased from the National Technical Information Service, Springfield, VA 22161. NTIS will
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call (800) 336-4700. Be sure to cite the PB number on all orders.

Entries without stock or PB numbers are in preparation.


4. Taylor, B.N. and Kuyatt, C.E., “Guidelines for Evaluating and Expressing the Uncertainty of
NIST Measurement Results,” NIST Technical Note 1297, Natl. Inst. Stand.Tech., Gaithersburg,
MD, 1994,

5. “Guide to the Expression of Uncertainty in Measurement,” International Organization for
Standardization, 1993, ISBN 92-67-10188-9°.

Available from ISO Central Secretariat, Case Postale 56, CH-1211 Geneva 20,
Switzerland.

29


Appendix 6

Examples of calibration reports:

NIST

REPORT OF CALIBRATION

OF:
FOR:

DESCRIPTION:

United States Department of Commerce
National Institute of Standards and Technology
Gaithersburg, MD 20899 USA

FWT-60 Batch 6F5 Radiochromic Film Dosimeters

Ed's Sterilizers
10 Gamma Avenue

Mega Rad, TX 99817

ATTN: Cobalt Jones
REF: PO# 232

Batch 6F5 film dosimeters were supplied by Ed's Sterilizers in
pre-sealed foil pouches. The dosimeters were irradiated under
controlled conditions using gamma radiation from a calibrated

Co irradiator, the NIST Gammacell 220-232. During

irradiation the pouches were held between two polystyrene
blocks with a wall thickness of 5 mm. The dates of irradiation,
values of dose rate, absorbed dose, and mean irradiation
temperature were as follows:

For December 31, 1996, film block, in Gammacell 220-232, Dy o7 10.68 kGy/h
hs

Dio Absorbed
Dosimeter ‘ Irradiation Dose

Identification Date of Irradiation (kGy/h) Temp. °C | kGy(H,O)
Pouch 1 Nov 21, 1997 9.210 24.0 10.00
Pouch 2 Nov 20, 1997 9.211 24.0 20.00
Pouch 3 Nov 20, 1997 9.211 24.0 30.00
Pouch 4 Nov 21, 1997 9.210 24.0 40.00
Pouch 5 Nov 21, 1997, 9.210 24.0 50.00

REFERENCE TEST 846/256018-97 Sep. 25, 1997
NIST DB 932/018 HD9799

38



6. Measurement Uncertainty

6.1 To be meaningful, a measurement shall be accompanied by an estimate of uncertainty.
Components of uncertainty shall be identified as belonging to one of two groups:

a) components based on the statistical analysis of a series of observations or

b) components based on other methods of analyses.
Additional information is given in ASTM Guide E 1707 and references 4 and 5, where these
components are referred to as Type A and Type B, respectively. In reporting uncertainty, other
classifications such as precision and bias may be useful.

NOTE 3 - The identification of Type A and Type B uncertainties in this document uses the
methodology adopted in 1993 by the International Organization for Standardization (ISO)
for estimating uncertainty. This is different from the way that uncertainty has been
traditionally expressed in terms of "precision" and "bias," where precision is a measure of
the extent to which replicate measurements made under specific conditions are in
agreement, and bias is a systematic error. The purpose of using the method of expressing
uncertainties as Type A and Type B recommended in the ISO Guide to the Expression of
Uncertainty in Measurement (5) is to promote an understanding of how uncertainty
statements are arrived at and to provide a basis for the international comparison of
measurement results.

NOTE 4 - ASTM Guide E 1707 defines possible sources of error in dosimetry performed in
radiation processing facilities and offers procedures for estimating the resulting magnitude
of the uncertainties in the measurement results. Basic concepts of measurement, estimate of
the measured value of a quantity, “true” value, error and uncertainty are defined and
discussed. Components of uncertainty are discussed and methods are given for evaluating
and estimating their values. Their contributions to the standard uncertainty in the reported
values of absorbed dose are considered and methods are given for calculating the combined
standard uncertainty and an estimate of overall (expanded) uncertainty.

6.2. The components of uncertainty involved in a measurement shall be estimated or
determined. The overall uncertainty in the measurement may be estimated from a combination of
these components, and the procedure for combining these components shall be specifically stated
or referenced in all results.

6.3 The relative standard uncertainties associated with measurement of absorbed dose with
alanine dosimeters from any radiation source are shown in Table 4. The components are assumed
to be uncorrelated and are combined in quadrature, i.e., by taking the square root of the sum of
the squares. The combined relative standard uncertainty is multiplied by a coverage factor of two
which corresponds approximately to a 95% confidence level.

24


5.2.2.1 A batch of NIST-fabricated alanine dosimeter pellets is produced as described in detail
in section 7.8 of NIST SP 250-44. The dosimeters are sorted by height and those in the range of
2.5 mm to 2.7 mm are used for subsequent dosimetry measurements. The variation in mass of
these pellets is about 2.2 %. Bruker-fabricated pellets may also be employed; these have a mass
variation of about 1.7 %. The new alanine batch is calibrated in a manner similar to that used for
radiochromic films discussed in 5.2.1. The differences in the procedures are that the alanine
dosimeters do not require humidity equilibration (after the initial conditioning during fabrication)
or sealing, and the alanine dosimeters are calibration over two dose ranges. The Low Dose range
extends from 10 Gy to 2 kGy; the High Dose range extends from 1 kGy to 100 kGy (or higher).
The alanine pellets are irradiated in the single-hole cup shown in Fig. 9 of NIST SP 250-44
during calibration. Five pellets are placed in the hole and irradiated for each dose value required.
Five dose points are used per decade of dose. The dosimeters are analyzed and the calibration
response functions are determined as described in 5.3.

5.2.2.2 Unirradiated alanine dosimeters from the calibrated batch are used to monitor the dose
received by customer’s dosimeters of various types such as Red Perspex, ceric cerous ampoules,
and dichromate ampoules. Three alanine pellets are placed in a polystyrene cylinder the same
size as the liquid dosimeter ampoule; the cylinder is placed in the center hole of the five-hole cup
shown in Fig. 1 and the customer’s dosimeter ampoules are placed the outer five holes. The
assembly is irradiated to the required dose and the QC alanine dosimeters are analyzed according
to the procedures given in 5.3. The indicated dose values are compared with the target dose. If
the results are within the specified control limits (discussed in Section 7) then the irradiation is
considered satisfactory. If the results are outside the control limits then the irradiation must be
investigated and appropriate corrective action taken. All QC results are recorded as part of the
calibration report and test folder.

5.3. Dosimeter Analysis Procedures
5.3.1 Radiochromic Film Analysis
5.3.1.1 Analysis (read out) of the radiochromic thin film dosimeters is done with a Cary model
3e spectrophotometer. Read out of each film is performed both before and after irradiation. The
read out procedures is as follows:
(a) | Turn on power to control computer (Compac 386), go to Windows, run the Cary
software program (indicated by the Cary 13e icon) ina DOS window so that the DOS
Editor can be used in another window.
(b) | Turn on power to Cary 3e spectrophotometer; let it warm up for at least one hour.
The Cary software starts diagnostic checks of the instrument by turning on the UV lamp

and scanning for the emission line 656.1 nm to calibrate the wavelength scale.

(c) The computer program boots up with operating parameters set up to read


oes 9s

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Go into the Film Thickness program from the icon in the main Windows display.

This is a DOS Basic program called thread.bas; see the print out of the program in
Appendix 2. This program provides prompts on the monitor to step the operator through
the thickness measurement process to ensure reliable data. The process is as follows:

a)
Q)

G)

(4)

(5)

A prompt asks for the starting film number;

Take a “zero” reading with no film. Ifa stable zero is indicated, then a film
reading is requested;

Raise the cartridge tip and place the first film on the anvil under the tip. The
program reads the thickness once a second. If the same reading is recorded on
consecutive reading, the program accepts the data, beeps to alert the operator, and
outputs the data to the printer. The program then advances the film number
counter and waits to read zero again. ‘lhe program runs in background while the
absorbance measurements are being made with the spectrophotometer. Thus, the
thickness of a given film can be measured immediately after the absorbance is
measured.

When all films thicknesses are measured, the program prompts the operator to hit
the space bar and four options are given:

Save file and quit;

Reset film counter;

Continue;

Quit.
The usual choice is to save the file and quit. The file is saved temporarily In
“thread.t”. The program asks for another file name (e.g., test.t). After saving the
file, the program checks to see if it is a duplicate. Then the program asks if the
operator wants to check the file; if “Yes,” then it goes to the DOS Editor.

After exiting the Film Thickness program, the computer returns to DOS Basic.

5.3.1.3. The radiochromic film analysis data is reduced by importing the absorbance and
thicknesses data into a Quattro Pro spreadsheet. The response is calculated by the formula (A2-
ADT. A software program called TableCurve is used to calculate dose. Once the calibration
plot is fitted, the doses for can be determined by using the program option [Evaluate] , selecting
[ X = Root at Y ], and putting in the values of the response (Y). An example of that calibration
data and the fitted response curve is shown in Fig. 4. The fitted polynomial equation is y = a+
bx + cx? + dx’; the fitted parameters are: a= 0.6290; b= 1.7013; c= -0.0100; d= 2.6729.