# Relating the Gamma Constant to the absorbed dose

• khary23
In summary, Turner's Atoms, Radiation and radiation protection suggests that one can use a gamma constant, Γ, to calculate exposure rate dX/dt and exposure, X, and subsequently dose rate, dD/dt and dose, D.
khary23
It is unclear from my text. Can you use the gamma constant to find the absorbed dose for a point source of photons?

khary23 said:
It is unclear from my text. Can you use the gamma constant to find the absorbed dose for a point source of photons?
What text is one using? What is the context?

According to this document - https://www.nrc.gov/docs/ML1122/ML11229A688.pdf (see slides 15-33) - one can use a gamma constant, Γ, to calculate exposure rate dX/dt and exposure, X, and subsequently dose rate, dD/dt and dose, D.

I want to calculate the dose per activity (Gy/Bq/hr) of a point source of photons to theoretically check an MCNP result. The only way I could see to do it so that the units work, with the exception of the m^2, is with the gamma constant.

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Are you referring to the mass attenuation coefficient?

no,
with H/phi factor,
with mass attenuation it is :
K (mGy/h)=5.74e-4*(mu/rho)*phi*E
same reference

I have not heard of the dose factor, but will look it up. What are its units?

Also edited my original post to clarify what I am doing.

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the conversion fluence dose factor is in pSv.cm2
I Don't know "
gamma constant " but the "
conversion fluence dose factor" is defined in the ICRP

Yes, Use ICRP PUBLICATION 119.
For extra safety you can use another software like RadMap (radmap.tech) to cross check your result. It has a nice gui with a Geant4 backend and you can get a time limited free license.

I assume that you want to calculate the dose in tissue due to a source within the tissue.
khary23 said:
I want to calculate the dose per activity (Gy/Bq/hr) of a point source of photons to theoretically check an MCNP result.
What MCNP result do you want to check. Your own simulation or another? Can you be more specific?

KlasM said:
Yes, Use ICRP PUBLICATION 119.
For extra safety you can use another software like RadMap (radmap.tech) to cross check your result. It has a nice gui with a Geant4 backend and you can get a time limited free license.

Thank you for the suggestion. I will check it out!

gleem said:
I assume that you want to calculate the dose in tissue due to a source within the tissue.

What MCNP result do you want to check. Your own simulation or another? Can you be more specific?

My own simulation. I am calculating the dose to water for a brachytherapy source to validate that it conforms to the TG-43 protocol.

For your information the TG-43 report has been updated to the AAPM Report #84. I recommend you check it out.

## 1. What is the Gamma Constant and how is it related to absorbed dose?

The Gamma Constant, also known as the Gamma Factor, is a constant used in radiation dosimetry to relate the absorbed dose to the energy deposited by gamma rays in a material. It is a measure of the efficiency of a material in absorbing radiation.

## 2. How is the Gamma Constant calculated?

The Gamma Constant is calculated by dividing the absorbed dose by the energy deposited by gamma rays in a material. It is typically expressed in units of Gray per Joule (Gy/J).

## 3. What is the significance of the Gamma Constant in radiation dosimetry?

The Gamma Constant is an important parameter in radiation dosimetry as it allows for the conversion of absorbed dose to energy deposited, which is necessary for accurately measuring the radiation exposure of a material or organism.

## 4. How does the Gamma Constant vary for different materials?

The Gamma Constant can vary significantly for different materials, as it is dependent on the physical and chemical properties of the material. For example, materials with high atomic number or density tend to have higher Gamma Constants.

## 5. Can the Gamma Constant be used for all types of radiation?

No, the Gamma Constant is specific to gamma rays and cannot be used for other types of radiation, such as alpha or beta particles. Each type of radiation has its own unique constant that is used for dosimetry calculations.

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