Dose Rate from a Radioactive Line Source Calculator

Technical background for radioactive line sources

The Ionactive website already features some excellent resource on this : try this if you want to delve into the physics and maths behind this calculator: When 1/d² breaks down - part 1: line source. 

Release notes

Version 1.0  The Dose Rate from a Radioactive Line Source Calculator has two operational modes:

• Forward (Linear activity → Dose Rate): This mode allows you to calculate the dose rate from a line source at a specified linear activity.
• Reverse (Dose Rate → Linear activity): Here you may enter known, measured or assumed dose rate data and infer the potential activity of the line source (assuming linear activity per unit length). 

The parameters, choices and inputs will vary slightly between the two modes selected. In almost all cases, if you make a change to the variables then you need to click calculate to see the changes. 

We first consider input choices for the forward calculation. 

• Radionuclide: Select from a popular list of beta / gamma radionuclides covering medicine, industry and of historical significance.  
• Unit system: Choose SI or Non Si units (you cannot mix between the two).
• Mode: Here you select Linear activity → Dose Rate (forward) or Dose Rate → Linear activity (reverse).
• Linear activity (λ): Enter activity per unit length, also selecting the units of activity and length.
• Line Length (L): Enter the length of the line source and it's units.
• Position: Use this to choose between calculating from the midpoint of the source, or an offset. If you choose offset you can enter a negative or positive value of length to move the calculation point left or right (as if you were facing the source).
• Perp distance (p): This is the perpendicular distance between the mid point of the source and the calculation point (unit selectable). Use this, in conjunction with the offset (if required) to define the actual desired calculation point.
• Add shielding: choose to add either lead, steel, concrete (several densities given) and water. If this setting is used then the shielding thickness input fields will appear where the thickness and desired units can be entered.
• Dose scaling output: Choose base for Gy / Sv / R etc, or micro, milli, kilo etc as desired. 

At the bottom of the calculator is the calculate and reset buttons. Use the calculate button each time you make a change to the desired inputs. The reset button will revert the calculator to standard settings as if the page has been reloaded. 

The outputs in the forward (Linear activity → Dose Rate) direction are as follows.

• A summary of the calculation case.
• Line source absorbed dose rate in air.
• Line source effective dose rate.
• A geometry factor (essentially the angle in radians subtended by the active length of the radioactive line source at the calculation point).
• A point source equivalent absorbed and effective dose rate (for comparison with the line source calculation).
• The ratio of the line to point source calculation for effective dose rate. This is useful  for investigating how the inverse square law may apply, and if linear source calculations are actually needed.   

We now consider the input choices for reverse calculations. Only those different from the forward calculation will be featured below. 

• Linear activity (λ) - calculated: this is now an output field, but the unit, and over what length the calculation is performed, can be specified (remember to click calculate if you change these parameters).
• Measured dose rate: This is the dose rate that has been measured (or determined in some other way) which you wish to use in the calculation of linear activity. You can choose to specify this as effective dose rate or absorbed dose rate in air. 

The outputs in the reverse calculation (Dose Rate → Linear activity) are as follows:

• A summary of the calculation case.
• Calculated linear activity (λ).
• Line source dose rate chosen.
• The geometry factor (as noted above). 

Have a play with the calculator and see what you come up with.