Sun Nuclear Corporation 1136 Manuel D’Utilisation
Calculations
79
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A Zip-Loc (or equivalent) sandwich bag. (7x8”)
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Adhesive tape
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Water
Mount the thermometer to the buildup with tape, and mount the detectors face-down to the
buildup. For maximum of 8 detectors, place the detectors and the thermometer uniformly along a
5 cm circle in a 20x20 cm
buildup. For maximum of 8 detectors, place the detectors and the thermometer uniformly along a
5 cm circle in a 20x20 cm
2
field at 100 cm SSD.
Fill the bag with 400mL of cold tap water, enough water that the bag is roughly 2 cm thick when
sealed and laid flat. Try to avoid sealing in any large bubbles.
sealed and laid flat. Try to avoid sealing in any large bubbles.
The first step on the IVD display after choosing the experimental route is “Apply cold bag to
diodes.”
diodes.”
Lay the bag flat over the diodes, and then press ENTER. The display will begin a 7-minute count-
down. This delay is to allow the system to reach thermal equilibrium. The countdown can be
stopped early by pressing both the left arrow and the right arrow at the same time, but this is not
recommended unless the bag really has been applied for at least 7 minutes.
down. This delay is to allow the system to reach thermal equilibrium. The countdown can be
stopped early by pressing both the left arrow and the right arrow at the same time, but this is not
recommended unless the bag really has been applied for at least 7 minutes.
After the delay, the system beeps and asks you for a temperature in degrees (from the thermom-
eter). Immediately after the temperature is entered, the diodes’ junction voltages are read and
stored along with the entered temperature. These numbers will be used to find the V primes.
eter). Immediately after the temperature is entered, the diodes’ junction voltages are read and
stored along with the entered temperature. These numbers will be used to find the V primes.
Then, A 15-second background measurement is made, a beep is sounded, and you are presented
with a dose-counting screen, with dosages in counts and an alternate message asking you to turn
on the beam. Deliver a dose of 100 monitor units at any energy. When this is done, the dose is
stored, along with the final junction voltage measurement after the dose measurement. These
numbers will be used to find the Tc’s.
with a dose-counting screen, with dosages in counts and an alternate message asking you to turn
on the beam. Deliver a dose of 100 monitor units at any energy. When this is done, the dose is
stored, along with the final junction voltage measurement after the dose measurement. These
numbers will be used to find the Tc’s.
The next step on the IVD display is to “Apply hot bag to diodes,” and press Enter. The steps are
the same as above except that now the bag is to be heated for 45 seconds in the microwave
before application.
the same as above except that now the bag is to be heated for 45 seconds in the microwave
before application.
After the dose is delivered, you can use the hot and cold data sets to calculate all of your coeffi-
cients for each channel:
cients for each channel:
V’ = (ThotCts – TcoldCts) * 0.2265 / (ThotDeg – TcoldDeg)
Where ThotCts is the second junction voltage in counts measured after you enter the tempera-
ture, TcoldCts is the first junction voltage in counts, ThotDeg is the second temperature you enter,
and TcoldDeg is the first temperature you enter. The 0.2265 is the factor to convert junction volt-
age counts into milliVolts.
ture, TcoldCts is the first junction voltage in counts, ThotDeg is the second temperature you enter,
and TcoldDeg is the first temperature you enter. The 0.2265 is the factor to convert junction volt-
age counts into milliVolts.
Tc = 100.0 * (DoseHot – DoseCold) / (DoseCold * (Thot – Tcold) * 0.2265/V’)
Where DoseHot is the second measured dose for a channel in background-compensated counts,
DoseCold is the first measured dose, Thot is the junction voltage (in counts) following the second
dose measurement, Tcold is the first junction voltage. V’ is the V’ described above.
DoseCold is the first measured dose, Thot is the junction voltage (in counts) following the second
dose measurement, Tcold is the first junction voltage. V’ is the V’ described above.
Internally, these numbers are stored as unsigned short integers. For this reason, V’ is kept multi-
plied by –100 (i.e. –2.0 would be stored as 200) and Tc is kept multiplied by 100. (0.6 would be
stored as 60.)
plied by –100 (i.e. –2.0 would be stored as 200) and Tc is kept multiplied by 100. (0.6 would be
stored as 60.)
To apply these coefficients to correct a dose measurement, the formula is as follows:
DoseCorrect=DoseMeasured / (1+(Tc / 100) * (Tmeas – Tcal) * 0.2265/V’)
Where DoseMeasured is a background compensated and calibrated dose reading in Gy, cGy, etc.,
Tc is the Tc from above, Tmeas is the junction voltage following the dose measurement (counts),
Tcal is the junction voltage following calibration, and V’ is the V’ from above.
Tc is the Tc from above, Tmeas is the junction voltage following the dose measurement (counts),
Tcal is the junction voltage following calibration, and V’ is the V’ from above.
Keep in mind that because Tc and V’ are stored as positive integers they will need to be divided
by 100 and –100 respectively, before inserting them into the above equation.
by 100 and –100 respectively, before inserting them into the above equation.
Computing dose calibration factor for energy button ‘btn’
Calculate CF as follows: