Radioactivity to Dose Rate Calculator (with shielding and dose rate ratio options)
Published: Jul 30, 2025
Source: Ionactive Radiation Protection Resource
Ionactive Radioactivity to Dose Rate Calculator
Version 1.1 - release 06 January 2026
Looking for a different calculation - try Dose Rate to Radioactivity Calculator (with optional shielding). If you need to consider neutrons, then try the Ionactive Neutron Source Dose Rate Calculator.
Radioactivity to Dose Rate
Formal advice
If you require formal advice on calculating dose rates based on radioactivity or the shielding required then head over to our Radiation Protection Adviser (RPA) services , or try our online radiation protection training courses for in-depth study of gamma emissions from radioactive materials and shielding.
Release notes
Version 1:0. The Radioactivity to Dose Rate Calculator is fully working with a limited range of radionuclides - more to be added over the coming weeks. Each data set has been analysed using the latest version of MicroShield, and spot checked using Monte Carlo simulation via openMC. Buildup is included as standard in the calculation process, but is not equally applied across all gamma radionuclides. Buildup is applied less aggressively where low density / low Z number shielding materials are selected. This current version of the calculator supports point source geometry. No beta dose rate contribution is considered (this will feature in a separate calculator).
Version 1:1 (current version). Ra-226 (sealed source) has been added. Assuming a sealed source means that the decay series below Ra-226 (i.e. Rn-222 → Pb-206) will be in secular equilibrium with the parent (i.e. current activity of Ra-226) for aged sources (>> one month), which will be relevant for almost all likely sources. Therefore the photon contributions from Pb-214 / Bi-214 will be significant, which would not be the case for unsealed Ra-226 (e.g. a salt) where the Rn-222 would not be contained.
Calculator use notes
Most functions and settings are self-explanatory but we will highlight some key points below. If you make a change to any parameter or input, please ensure you use the calculate button to use the most recent settings.
- Calculator mode - two modes are available. The default mode is Activity → Dose Rate , the alternative mode is Dose Rate →Thickness. With the alternative mode you can enter a known / measured dose rate and a desired dose rate (i.e. < measured dose rate). Once other parameters (described below) are set, the calculator will output the required shielding thickness to achieve the desired dose rate. When in the Dose Rate → Thickness mode certain parameters not needed (e.g. activity) are inhibited.
- Radionuclide selection - drop down menu, select what you need.
- Input unit system - specify activity and distance in SI or Non-SI units.
- Activity - enter activity in the desired units, and apply a multiplication factor (e.g kBq, MBq, microCi, mCi etc).
- Distance (from source) - enter distance and set desired multiplication factor (e.g mm, cm, m, inches, feet etc).
- Output dose unit system - choose the Gy / SV (SI) or Rad/Rem (Non-SI) system for dose rate output.
- Output multiplier - apply micro, milli, base, kilo, mega etc to the output dose rate.
- Output format - choose from standard notation or scientific notation (i.e. 0.1347 µGy/h or 1.347e-1 µGy/h).
- Shielding - choose if the calculation should consider shielding.
Output
The output of the calculator is specified as follows.
- Absorbed Dose in Air: XXX µGy/h
- Effective Dose Equivalent: YYY µSv/h
If the shielding option is picked then the following additional parameters are included below the unshielded dose rate results area
- Material - choose the shielding material.
- Thickness - choose the shielding thickness (units will be based on the unit system selected).
The output post shielding is in Effective Dose Equivalent rate as this is more meaningful (the differences between absorbed dose and effective dose equivalent become less important for practical radiation purposes after shielding).
Dose Rate →Thickness
This option is selected by using the mode drop down menu at the top of the calculator. Additional inputs and parameters will appear below the calculate button.
- Dose Rate Before Shielding (arbitrary units)
- Dose Rate After Shielding (arbitrary units)
Arbitrary units are used since the two dose rates entered create a ratio and are technically dimensionless once the ratio is created. Ensure that Dose Rate Before Shielding > Dose Rate After Shielding (an error message will be displayed if this is not so). A unit multiplier (e.g. micro, milli, kilo etc) can be applied to either dose rate entered.
- Material - select the shielding material and desired units (mm, cm, inches).
Output
Obtain the thickness from the dose rate ratio by clicking on the calculate button - the result will appear at the bottom of the calculator.
Note that although some of the selections at the top of the calculator are inhibited when using the Dose Rate →Thickness mode, the radionuclide selector remains available.
Why use this Ionactive calculator?
This calculator is offered as a radiation protection tool, it is not formal radiation safety advice. If you need such advice then seek assistance from a Radiation Protection Adviser (RPA).
This calculator is complementary to our 'Dose Rate to Radioactivity Calculator (with optional shielding)'. A particular feature of all the Ionactive calculators in this section, and also the educational radiation protection interactive widgets, is they are designed to work on all platforms and devices using modern style sheet techniques - try these calculators on a mobile phone in portrait orientation.
Don't necessarily expect all similar calculators to output the same calculation result given the same inputs. In theory the output should be the same, in practice it depends on the methodology used. For example, elsewhere on this site you will see we state that the TVT for Cs-137 with lead is 22mm. This is a viable approximation that works pretty well (we use it).
We have provided a good technical discussion of TVT in this article: 'How reliable is TVT (10th Value Thickness) in radiation shielding calculations?'.
In the above referenced article we look at the attenuation of gamma (or x-ray) photons in lead. Take a look at the following slider.
Note that the attenuation of medium energy (662 keV) photons in lead shows a fairly consistent 22mm of lead for the geometric sequence of attenuation / transmission (i.e 10th value). For the much lower energy photons (which happen to be from an x-ray source in our example) you will note that the first two TVT are less than those which then follow.
Conversely, if you consider something like Co-60 (gamma ray photons at approximately 1.2 & 1.3 MeV) with a lower density shielding material such as 2.35 g/m3 concrete, you will note the opposite effect - i.e. the first TVT, often denoted TVT1 is more than the second TVT, often denoted as TVTe, where e means equilibrium. This is even more pronounced at much higher energies (>> 1MeV photons in concrete).
This very brief explanation is often the reason why you will find that specific gamma ray constants (of the form X mSv/h per MBq at 1m etc), and TVT shielding data varies across the internet depending on which resource you choose. Sometimes these factors make little difference (i.e. 22mm of lead as a TVT for Cs-137 is pretty well recognised everywhere), but other times the choices made will lead to differences which may or may not be significant (may over or underestimate). Professional codes such as MicroShield and RANKERN (point kernel integration), and codes based on Monte Carlo (MC) such as MCBEND & MCNP et al, will often be the choice when undertaking elaborate shielding design for sophisticated plant. However, our own calculators and other similar resources found online are likely to be adequate for simpler radiation protection challenges (as long as you combine this with professional Radiation Protection Adviser consultation).