BAEN/625
Fall/2010
RGM
Homework # 3
Biological and Agricultural Engineering
Texas A&M University
Due date: February 15, 2010
1) Finding the hotspot and the beam calibration number with the information provide by Table
1 below
(a) Plot the kGy/Average Counts in cartesian coordinates
(b) Average the 5 points (including the hotspot) and supply the "Beam Calibration
Number" (kGy/Counts)
(c) What is your hotspot coordinate? Justify it!
Table 1: Experimental data to determine the hotspots and bean calibration number
Point/Repetition
Coordinates
A1
A2
A3
B1
B2
B3
C1
C2
C3
D1
D2
D3
E1
E2
E3
F1
F2
F3
G1
G2
G3
H1
H2
H3
X
-1
-1
-1
-1
-1
-1
-1
-1
-1
0
0
0
-2
-2
-2
-3
-3
-3
-2
-2
-2
-2
-2
-2
Y
TIC
Counts
IC
Exposure [kR]
-2
-2
-2
-3
-3
-3
-1
-1
-1
-2
-2
-2
-2
-2
-2
-2
-2
-2
-1
-1
-1
-3
-3
-3
21660
21720
21675
23626
23757
23746
23510
23440
23256
25151
24915
24889
20724
20531
20600
21307
21660
21821
22289
22034
21108
21583
21606
21537
5.05
5.08
5.12
5.08
5.09
5.07
5.1
5.11
5.08
5.12
5.05
5.05
5.06
5.06
5.05
5.03
5.07
5.11
5.13
5.09
5
5.09
5.08
5.06
Dose
[Gy]
?
?
?
kGy/counts
?
?
?
Average
kGy/Counts
?
BAEN/625
Fall/2010
RGM
2) Finding the calibration constants for the Radiochromic Films (RF) from the data provided in
Table 2 below.
A set of RF were irradiated at the exact hotspot previously found (#1 question). The
Transmission counts and the optical density of each and every RF (pre and post irradiated) were
recorded.
(a) Plot the Dose (kGy) and the specific abosorbance (k) for every individual
radiochromic film and find its calibration constants. Check the ppt slides!
(b) Once you have found the calibration constants, find the Actual Dose (kGy) absorbed
by each RF based on its OD readings.
Table 2: Experimental data to determine the RF constants.
Sample #
3_A_1
3_A_2
3_B_1
3_B_2
3_C_1
3_C_2
2_A_1
2_A_2
2_B_1
2_B_2
2_C_1
2_C_2
1_A_1
1_A_2
1_B_1
1_B_2
1_C_1
1_C_2
Transmission
counts
1452159
1452159
1452425
1452425
1452992
1452992
968879
968879
968361
968361
968607
968607
483816
483816
483923
483923
483850
483850
Dose
[kGy]
?
?
?
?
?
?
Initial OD
(Ao)
Final OD (Af)
k
[OD/mm]
Actual Dose
[kGy]
0.0897
0.397
0.0897
0.399
0.0897
0.366
0.0897
0.379
0.0897
0.374
0.0897
0.393
?
?
?
?
?
?
?
?
?
?
?
?
0.0897
0.281
0.0897
0.292
0.0897
0.294
0.0897
0.285
0.0897
0.293
0.0897
0.281
0.0897
0.186
0.0897
0.182
0.0897
0.187
0.0897
0.194
0.0897
0.194
0.0897
0.191
BAEN/625
Fall/2010
RGM
3) Assessing the absorbed dose of spinach bags through RF readings.
Bags of spinach (2 x 2 inches) were placed in front of the e-beam at the hotspot area. Behind
the bags (opposite side of the beam entrance), RF were placed to verify the dose absorbed by
the spinach leaves. Look at the schematic below! Transmission counts and OD readings were
recorded after the irradiation test. Two levels of target dose were considered (0.4 kGy and 1.0
kGy).
(a) What were the doses applied according to the transmission counts and according to
the RF readings?
(b) Are there any significant discrepancies between the TIC and the RF readings as far as
the target dose is concerned? Justify your answer using your knowledge of Radiation
Theory!
Bags
1-a
1-b
1-c
2-a
2-b
2-c
OD readings
Counts
482669
482670
482666
193068
193075
193076
Ao
0.087
0.087
0.087
0.087
0.087
0.087
OD readings
Af
Ao
0.199
0.087
0.2
0.087
0.209
0.087
0.129
0.087
0.138
0.087
0.146
0.087
Af
0.201
0.202
0.206
0.136
0.142
0.141
Figure 1: Schematic of the experimental setup to irradiate a bag of baby leaves spinach
using a 1.35 MeV van de Graaff accelerator.