Compulsory task in FYSKJM4710
Interaction theory and dosimetry
Task 1
Lithium formate monohydrate, LiHCO2·H2O, (Li-formate) is a promising EPR-dosimeter. It will
be used in our second laboratory practice. In the NIST Tables of X-Ray Mass Attenuation
Coefficients and Mass Energy-Absorption Coefficients Table 2 has listed the weight fractions of
compounds and mixtures of dosimetric interest and Table 4 have listed the Mass Attenuation
Coefficients and Mass Energy-Absorption Coefficients of the same materials. Li-formate is not
one of these. This task is to determent the Mass Attenuation Coefficients and Mass EnergyAbsorption Coefficients of Li-formate by use of Bragg-rule (Eq. 7.60-63 Attix).
a) Open the excel-file Bragg.xls. Save it.
b) Go to the NIST Tables of X-Ray Mass Attenuation Coefficients and Mass Energy-Absorption
Coefficients Table 1 and find the atom number, Z, and electron density, Z/A, of Hydrogen,
Lithium, Carbon and Oxygen and past them into Bragg.xls on the Sheet named “Table values”
(yellow) in the pink cells.
c) Go to the NIST Tables of X-Ray Mass Attenuation Coefficients and Mass Energy-Absorption
Coefficients Table 3 and find the Mass Attenuation Coefficients and Mass Energy-Absorption
Coefficients (Table 3) of Lithium, Carbon and Oxygen past them into Bragg.xls on the Sheet
named “Table values” (yellow) into the yellow cells in the same format as Hydrogen.
d) Do the same with “Water, Liquid” and past the missing values in sheet “H2O” (pink). Z, Z/A,
and the additional weight fractions, fH2 and f0 is found in Table 2 and the Mass Attenuation
Coefficients and Mass Energy-Absorption Coefficients are found in Table 4.
e) In the same sheet named “H20” (pink) are the calculated Mass Attenuation Coefficients and
Mass Energy-Absorption Coefficients based on the date found in the “Table values” sheet. The
calculation made of Mass Attenuation Coefficients is by Eq.7.60 and that of Mass EnergyAbsorption Coefficients is made by Eq.7.62 which is an approximation. In the graph seen in the
sheet named “Table.vs.calculation H20“(blue) is the deviation of our calculations from the
tabulated values seen.
Way is the there some deviations in the Mass Energy-Absorption Coefficients at the highest
energies?
In which range can it be assumed that our calculations of the Mass Energy-Absorption
Coefficients based on Eq.7.62 are valid, why?
f) In the green sheet named “Lithium format monohydrate calc.” is the calculated values of Liformate found copy these and those listed of Dry, air.
e) Save Bragg.xls.
Task 2
In the next task we are going to theoretically investigate the two X-ray spectra which are used in
the next laboratory practice. One 100 keV field filtered trough 1.5 mm Aluminum and the other
220 keV filtered trough 1.5 mm Aluminum and 0.5 mm Copper, both from the same Tungsten
target. The path of the photons trough tungsten is assumed to be 0.01 mm.
a) Open the excel-file HVL.xls. Save it!
b) Past the values copied in Task 1 f) into the sheet named “Lifo and Air”(yellow).
c) Go to the sheet named “100keV 0.01mm-W, 1.5mm-Al”(blue). In this sheet are the energy
fluence of the 100 keV X-ray spectrum with primary 1.5 mm Al-filter tabulated together with the
calculated relative dose to Air and Li-formate. CPE is assumed present. Explain the theory of
these calculations.
d) In the same sheet are two cells(pink) allowing for additional filtering of Copper and Aluminum.
seen. Fill the blue table by putting in the listed values of additional filtering, only one element,
copper or aluminum at one time.
e) Look at the two graph one the sheet and use the trend line function in excel to find the HVL in
Aluminum and Copper of this spectrum.
f) Go to the sheet named “220keV0.01mm-W,1.5-Al,0.5-Cu”(green). In this sheet are the energy
fluence of the 220 keV X-ray spectrum with primary 1.5 mm Al and 0.5 mm Cu-filtration
tabulated together with the calculated relative dose to Air and Li-formate. CPE is assumed
present. Reply point d) and e) in this X-ray spectrum.
g) Now look at the 100 keV X-ray spectrum without any additional filtering (just the 1.5mm
primary Al-filter).
An ionizing chamber has a kerma calibration factor NK defined by Dair = M·NK. In our ionizing
chamber NK = 43.4 mGy/nC. If the dose in air from the 100keV X-ray spectrum
Dair,100keV=4.69 Gy was measured by this chamber then according to the calculations in HVL.xls,
the dose in Li-format, DLifo,100keV=4.59 Gy will be measured in Li-format by EPR-dosimetry.
What will the calibration factor ND,Lifo, to transform the measurement done by the ionizing
chamber into dose to Li-formate be? The radiation quality calibration constant in the 100 keV Xray spectrum is then defined to be k100keV=1.
h) Whit this ND,Lifo found in g) what is the radiation quality calibration constant k220keV of the
220keV X-ray spectrum when the calculations give that a dose to air of Dair,220keV=6.83Gy equals
a dose to Li-format of DLifo,220keV=6.97Gy from this spectrum.
i) Save HVL.xls.
Task 3
Write a rapport with your answers and mail that together with the two xls-files to
audun@fys.uio.no before 6/3-2006.