External Radiation Dose Calculator - HELP
(Virtual Geiger Counter)
(last updated 30 Oct 2006)
Contents:
The External Radiation Dose Calculator determines the radiation dose from a shielded gamma source. The source can be a point source, or a cylindrical volume source with an evenly distributed concentration of radionuclides.
For source and shield, a number of common materials and compositions of natural radionuclides can be selected, or a custom mix of elements and radionuclides can be entered.
The receptor location can be varied in two dimensions.
The Calculator does take into account:
- Nuclide-specific Gamma radiation for a selection of important natural and a few artificial radionuclides
- in case of a volume source, the Gamma radiation emitted from the top of the cylinder
- Self-shielding within a volume source, and within shield layers containing radioactive materials, depending on material properties
- Self-shielding can also be taken into account for sources otherwise treated as point sources, if sufficient material properties are known (density and attenuation coefficients); in this case, the effective radiation emitted from a cylinder top with height equaling diameter is used as the activity of the point source and the source is labeled "Effective Point Source"
- Attenuation of Gamma radiation through a selection of common shield materials; if no attenuation data is stored for the shield material, it is calculated from the shield's elemental composition, if given, and if attenuation data is stored for the relevant elements.
- Shielding of the gamma radiation in a selectable number of consecutive shield layers, according to the material properties of the shield(s); for volume sources, it is simplistically assumed that the radiation passes the shield perpendicularly, and the dose is calculated for the resulting circular area source at the top of the layer, while for point sources the direct radiation path is assumed between source and receptor.
- Dose contributions from the source, plus from radionuclides contained in the shield material(s)
- Gamma attenuation in air (from Point Source only, not from Volume Source nor radioactive shield layers)
The Calculator does not take into account:
- Alpha or Beta radiation, nor secondary X-Rays (Bremsstrahlung) from shielding of Beta radiation, nor neutron radiation
- in the case of a volume source, radiation from the side walls of the cylinder
- Build-up factors
- Gamma attenuation in air for Volume Sources or radioactive shields
- Radiation from radionuclides other than those for which decay energies are contained in its database
- Gamma attenuation from shield materials not contained in its database, nor composed of elements for which shielding properties are stored.
- Alteration of the given radionuclide compositions with time due to decay
With these properties, the calculator is suitable for a rough assessment of the following situations, for example:
- Gamma radiation on a bare or covered uranium mill tailings pile, also with multi-layer covers (Volume Source mode)
- Gamma radiation near transport containers carrying uranium ore, U3O8, UF6, or the like (Volume Source mode)
- Gamma radiation near transport containers containing heels after unloading UF6 (Point Source mode)
- Gamma radiation from DU penetrator lying on the ground, or buried in the ground (Point, or Volume Source mode)
Predefined sample parameter sets covering some of these cases can be used to obtain quick first results.
References to other calculators:
- For internal exposure from ingestion or inhalation of uranium and decay products, use the Uranium Individual Dose Calculator.
- For a residential exposure scenario, the radiation dose and risk for an individual living on soil contaminated from uranium and/or in a home built
from such contaminated material can be determined with the Uranium in Soil Individual Dose Calculator. It not only covers external exposure, but also the following pathways: ingestion of soil, inhalation of fugitive dusts, ingestion of produce grown in the soil, ingestion of contaminated
groundwater, and inhalation of radon.
- Determine the radon flux from a bare and/or water-covered uranium mill tailings pile: Uranium Mill Tailings Radon Flux Calculator
- Determine the radon flux through a multi-layer soil cover of an uranium mill tailings pile and/or optimize the cover for a given flux: Uranium Mill Tailings Cover Calculator
The geometry of the situation and the properties of the materials involved are defined in the Input Data table.
With Java enabled, a section of the geometry of the situation is shown in a Graph.
Upon execution of the calculation, the graph shows the Gamma dose rate at the selected receptor location. The receptor can easily be moved to other locations by mouse clicking.
In addition, the gamma dose can be visualized in a color map, if the Show color map box is checked.
Notes: Each square in the color map represents the dose value in its center, not the value averaged over the square.
Due to the sharp dose increase near point sources, the color scheme may change considerably with a decrease of the raster width.
In logarithmic mode, the color of the square with the highest dose value is red. The span given by the selected number of decades is represented by the rainbow colors red - yellow - green - cyan - blue - violet. If the range of values is not covered by the number of decades selected, the remaining (too low) values are displayed in a linear fade-out of violet.
Computing time increases considerably with number of shields, number of elements and radionuclides per layer, etc. The sample parameter sets take a few seconds to compute on current machines.
Output graph (with linear color map): Click image to view animation 
!
Also upon the calculation, the layer colors change according to the following color scheme, allowing for a simple overview and for easy detection of data problems:
| Layer Color Scheme |
|---|
Point
Source | Volume
Source | Shield | Meaning |
|---|
| red | red * | pink * | layer contains radionuclides |
| white * | yellow | yellow | attenuation data is defined for this layer |
| orange | orange | light orange | layer contains radionuclides, plus attenuation data is defined for this layer |
| white * | white * | white * | no, or insufficient information defined for this layer |
*) indicates problem
The Result field repeats some important input data, reports any warnings about missing input data, and shows the calculation results for the current receptor location. The contributions from the source and from each layer containing radionuclides are shown separately and in summary.
The contents of the Result field can be highlighted and copied for further use.
Note: The figures are for the current geometry - so, if the effect of a shield is to be compared to the open source, define a new geometry without the shield (set ds and/or rhosh to 0, for example) and compare the results manually.
The contents of the database of the calculator (decay energies of radionuclides, gamma attenuation and energy absorption coefficients) can be viewed with the Query Database button.
See instructions for offline use of this calculator.
Notes:
This selection must be made before any other entry, since it resets the complete calculator.
After a selection is made, the calculator can be bookmarked to obtain future direct access to the mode selected.
- Point / Volume Source
-
- Number of Shield layers
-
- Mass figure (Point Source only)
- Enter number
- Mass Unit (Point Source only)
- Select from pick list
- Source Material
- Material data for the radiation source
Select sample material from the pick list, or enter data in the table.
The pick list contains elemental compositions, as well as radionuclide compositions and radionuclide series. (The decay energy and attenuation data can be viewed with the "Query database" button.)
- rhoso - Source density [g/cm3]
Value must be larger than zero for Volume sources.
A value can also be entered for Point sources, to take self-shielding within the source into account: if attenuation coefficients are available for the source material, then the activity of the point source is taken as the activity at the top surface of an upright cylinder with diameter equalling height; in this case, the source is labeled "Effective Point Source". If self-shielding for point sources is not to be taken into account, then this field must be set to zero, or left open.
- Element / Nuclide [wt_% / * Bq/g]
- Enter short names of elements (e.g. U) or radionuclides (e.g. U-238) and associated abundance in weight-percent. For radionuclides, entry of activity in Bq per gram of source material is possible with an asterisk (*) preceding the number. When entering radionuclides, check the availability of the associated decay data with the "Query database" button.
In addition to elements and radionuclides, the short names of a number of pre-defined radionuclide compositions and radionuclide series can be entered. Please note, that an activity entered (with preceding *) for a radionuclide composition refers to the total activity of all uranium isotopes contained, while an activity entered for a radionuclide series refers to the activity of the nuclide given in the name of the series only.
Shield Parameters
- Shield Material
- Material data for each shield
Select sample material from the pick list, or enter data in the table.
The pick list contains some elements, as well as elemental compositions and radionuclide compositions. (The attenuation data and/or decay energy data can be viewed with the "Query database" button.)
- rhoshn - Shield density [g/cm3]
Value must be larger than zero, for the shield to be effective. If no value, or zero, is entered, this layer is treated as vacuum.
- Element / Nuclide [wt_% / * Bq/g]
- Enter short names of elements (e.g. U) or radionuclides (e.g. U-238) and associated abundance in weight-percent. For radionuclides, entry of activity in Bq per gram of shield material is possible with an asterisk (*) preceding the number. When entering radionuclides, check the availability of the associated decay data with the "Query database" button.
In addition to elements and radionuclides, the short names of a number of pre-defined radionuclide compositions and radionuclide series can be entered. Please note, that an activity entered (with preceding *) for a radionuclide composition refers to the total activity of all uranium isotopes contained, while an activity entered for a radionuclide series refers to the activity of the nuclide given in the name of the series only.
- Receptor Material
- Select from pick list
The absorbed gamma energy dose is usually calculated for air, and any further dose figures are derived from this value.
- Dose Rate Unit
- Select from pick list
The original unit calculated is Gy/h. All other units are derived from this one.
- Exposure for annual dose rates
- Select occupancy form pick list
- Gamma dose factor [Sv/Gy]
- Conversion factor from absorbed gamma energy in air to effective dose.
UNSCEAR (2000) recommends 0.7 Sv/Gy for adults, 0.8 for children, and 0.9 for infants. (Note: this factor is used energy-independently.)
Point Source Geometry: (2 shield layers)
Volume Source Geometry: (2 shield layers)
The geometry parameters can be initialized with 5 predefined data set examples (not to be confused with the sample buttons at the top of the page, which preset all parameters, not only the geometry):
- Ex. 1: Shielding in free air (for Point Source Mode)
- Ex. 2: Tailings cover (for Volume Source Mode)
- Ex. 3: 48Y Cylinder (for Volume Source Mode and 1 shield layer)
- Ex. 4: 48Y Cylinder (for Point Source Mode and 1 shield layer)
- Ex. 5: Source buried in soil (for Point Source Mode, at least 1 shield layer)
- a - Distance of source from shield front surface [cm] (Point Source only)
If no value is entered, zero is assumed.
If a negative value is entered, the point source is located inside the shield (Shield #1 only).
- x - Displacement of receptor [cm]
If no value is entered, zero is assumed.
- y - Distance of receptor from x-axis [cm] - or -
b - Distance of receptor from shield rear surface [cm]
Enter either y or b. The value must be larger than zero.
Upon entry of y, b is erased, and vice versa.
- d - Source depth [cm] (Volume Source only)
Value must be larger than zero.
- dsn - Shield #n thickness [cm]
If no value is entered, zero is assumed.
Setting this value to zero allows for an easy temporary removal of a shield layer.
- r - Source radius [cm] - or -
sa - Source surface area [m2] (Volume Source only)
Enter either r or sa. The value must be larger than zero.
Upon entry of r, sa is calculated automatically, and vice versa.
- rs - Shield radius [cm] - or -
sas - Shield surface area [m2]
Enter either rs or sas. The value must be equal or larger than the source radius.
Upon entry of rs, sas is calculated automatically, and vice versa.
(In the case of a point source, this parameter is only required if the shield contains radionuclides)
- Show color map
- Calculate dose values for the following raster of x and y positions and show result as coloured map.
Note: If this checkbox is checked, computing time increases considerably!
- Raster width [pixel]
- Raster width in pixels for calculation of dose values in color map
Min. value: 10 pixel
If no value, or zero, is entered, the minimum raster width is used.
Note: Reduction of the number increases computing time considerably!
- Logarithmic color scale
- Check for logarithmic color scale, otherwise a linear scale is used
- Decades
- Number of decades to be covered by color map in logarithmic mode.
If no value, or zero, is entered, an appropriate scale is selected automatically.
If, for logarithmic scale, the range of values is not covered by the number of decades selected, the remaining (too low) values are displayed in a linear fade-out of violet.
| Element Compositions |
|---|
| Name | Description | Notes |
|---|
| Air | Air, Dry (Near Sea Level) | |
| Water | Water, Liquid | |
| Concr_od | Concrete, Ordinary | |
| Glass_Pb | Glass, Lead | |
| Glass_BS | Glass, Borosilicate ("Pyrex") | |
| Tiss_sft | Tissue, Soft (ICRU-44) | |
| St_304 | Type 304 Stainless Steel | |
| Soil_US | U.S. Soil | |
| Soil_05 | U.S. Soil with Ra-226 @ 5 pCi/g = 0.185 Bq/g (U-series in equil.) | 1) |
| Soil_15 | U.S. Soil with Ra-226 @ 15 pCi/g = 0.555 Bq/g (U-series in equil.) | 1) |
| Rock_cru | Rock, Crustal | |
| Uorenor | Uranium ore, Nordic Lake, Elliot Lake, Ontario, Canada | 2) |
| Uore01 | Uranium ore 0.1% U | 2) |
| Utail01 | Uranium mill tailings from 0.1% U ore, extraction = 90% | 2) |
| Utaildgo | Uranium mill tailings, Durango, Colorado, USA | |
| Utailnor | Uranium mill tailings, Nordic Lake, Elliot Lake, Ontario, Canada | |
| UF6_nat+ | Uranium hexafluoride, natural, solid, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| UF6_enr+ | Uranium hexafluoride, enriched to 3.5% U-235, solid, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| UF6_ere+ | Uranium hexafluoride, enriched to 3.5% U-235 equiv., solid, from recycled U (3.5% init.enr. 39 GWd/tHM, 5 y), with short-lived progeny (Th-228, Ra-224, Pb-212, Bi-212, Tl-208, Th-231, Th-234, Pa-234m) | |
| UF6_dep+ | Uranium hexafluoride, depleted to 0.2% U-235, solid, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| UF6_dre+ | Uranium hexafluoride, depleted to 0.2% U-235, solid, from recycled U (3.5% init.enr. 39 GWd/tHM, 5 y), with short-lived progeny (Th-231, Th-234, Pa-234m) | |
| U3O8_nat+ | U3O8, natural, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| U3O8_dep+ | U3O8, depleted to 0.2% U-235, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| UO2_enr+ | UO2, enriched to 3.5% U-235, with short-lived progeny (Th-231, Th-234, Pa-234m) | |
| UO2_ere+ | UO2, enriched to 3.5% U-235 equiv., from recycled U (3.5% init.enr. 39 GWd/tHM, 5 y), with short-lived progeny (Th-228, Ra-224, Pb-212, Bi-212, Tl-208, Th-231, Th-234, Pa-234m) | |
| Heels_nat | Heels from sublimation of natural uranium hexafluoride, radionuclides only (Th-234, Pa-234m, Th-231) | |
Notes:
1) based on Soil_US, density and/or radionuclides modified
2) based on Utailnor, density and/or radionuclides modified
| Radionuclide Compositions |
|---|
| Name | Description | Notes |
|---|
| U_nat | Natural Uranium, without progeny | |
| U_nat+ | Natural Uranium, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| U_nat++ | Natural Uranium, with all major progeny in sec. equilibrium | |
| U_rec | Recycled Uranium, init. enr. 3.5%, burnup 39 GWd/tHM, 5 y delay | |
| U_rec+ | Recycled Uranium, init. enr. 3.5%, burnup 39 GWd/tHM, 5 y delay, with progeny | |
| U_dep | Depleted Uranium, 0.2 wt-% U-235, without progeny | |
| U_dep+ | Depleted Uranium, 0.2 wt-% U-235, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| U_dre | Depleted Recycled Uranium, 0.2% U-235, init. enr. 3.5%, burnup 39 GWd/tHM, 5 y delay | |
| U_dre+ | Depleted Recycled Uranium, 0.2% U-235, init. enr. 3.5%, burnup 39 GWd/tHM, 5 y delay, with short-lived progeny (Th-231, Th-234, Pa-234m) | |
| U_enr | Enriched Uranium, 3.5 wt-% U-235, without progeny | |
| U_enr+ | Enriched Uranium, 3.5 wt-% U-235, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| U_ere | Enriched Recycled Uranium, 3.5% U-235 equiv., init. enr. 3.5%, burnup 39 GWd/tHM, 5 y delay, without progeny | |
| U_ere+ | Enriched Recycled Uranium, 3.5% U-235 equiv., init. enr. 3.5%, burnup 39 GWd/tHM, 5 y delay, with short-lived progeny (Th-228, Ra-224, Pb-212, Bi-212, Tl-208, Th-231, Th-234, Pa-234m) | |
| Radionuclide Series |
|---|
| Name | Description | Notes |
|---|
| Th-232++ | Thorium-232, with all major progeny in sec. equilibrium | |
| U-238+ | Uranium-238, with short-lived progeny (Th-234, Pa-234m) | |
| U-238++ | Uranium-238, with all major progeny in sec. equilibrium | |
| Th-230++ | Thorium-230, with all major progeny in sec. equilibrium | |
| Ra-226+ | Radium-226, with short-lived progeny (Pb-214, Bi-214) | |
| Ra-226++ | Radium-226, with all major progeny in sec. equilibrium | |
| Pb-210++ | Lead-210, with all major progeny in sec. equilibrium | |
| U-235+ | Uranium-235, with short-lived progeny (Th-231) | |
| U-235++ | Uranium-235, with all major progeny in sec. equilibrium | |
| Pa-231++ | Protactinium-231, with all major progeny in sec. equilibrium | |
| U-232++ | Uranium-232, with all major progeny in sec. equilibrium | |
| Np-237+ | Neptunium-237, with short-lived progeny (Pa-233) | |
| Cs-137+ | Cesium-137, with progeny | |
With these Radionuclide Series, the uranium decay series can be composed as follows, for example:
| Name | Complete Series |
|---|
| U-238 |
U-238++
U-238+ U-234 Th-230++
U-238+ U-234 Th-230 Ra-226++
U-238+ U-234 Th-230 Ra-226+ Pb-210++ |
|---|
| U-235 |
U-235++
U-235+ Pa-231++
|
|---|
