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15. Determining dose rate

Gamman offers a feature that calculates the dose rate from collected gamma-ray data. It is taken from the full measured spectrum and represents the dose per second that the full body of an average person would receive if they were located at the spot where the detector collected the spectrum. So, for example, if a spectrum was measured at 5 meters above the ground, the dose rate is calculated for that height and not as if someone was standing on the ground. Gamman does not offer the possibility for height correction of the dose rate.

The dose rate for the average human body, known as the ambient dose equivalent H*(10), is calculated through the total counts of the measured spectrum per energy bin and a detector specific factor. This factor is constructed from two types of Monte Carlo simulations. One of them contains a sphere that is representing the human body (the ICRU sphere.) A point at 10 mm depth in this sphere is absorbing gamma-rays of certain energies. In the other simulation, those same gamma-rays are directed to and absorbed by a specific type of detector. In this way, the response of the detector can be linked to the dose received by the human body.
The contribution to the dose rate of the counts in all the energy bins for a data point are added by Gamman and this represents the dose rate for the specific data point.

The dose rate option can be accessed under the tab Tools|Ambient dose equivalent. The screen shown in the figure below will appear.

Here, the type of detector can be chosen, which holds the detector specific factor. After pressing “Calculate Dose”, the dose rate for every datapoint will be calculated and this will be added to the data as a separate column as “H*(10) in pSv/s.

A separate H*(10) column is added to the data

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