External Radiation Dose Calculator - HELP
(Virtual Geiger Counter)
(last updated 6 Jun 2011)
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 (for point sources and shields without radioactive elements), or one dimension otherwise.
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. The calculator uses the point-kernel method with buildup factors. In case the shield material consists of more than one element and buildup factors for the material are not available, buildup factors are used for the major component only.
- Shielding of the gamma radiation in a selectable number of consecutive shield layers, according to the material properties of the shield(s). Buildup factors are calculated for the top shield layer only - a simplification that produces reasonable results only for a layer with a thickness of several mean-free paths.
For point sources, this relaxation length R can be checked for the relevant radiations in the top shield layer with Result Detail selection "by Radiations".
- Dose contributions from the source, plus from radionuclides contained in the shield material(s)
- Gamma attenuation in air
- Cosmic ionizing radiation, if required (calculated according to UNSCEAR 2000)
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
- 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
- Cosmic neutron radiation
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 example 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 and Building Material 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 case of a volume source and/or of shield layers containing radioactive elements, the receptor can be moved in one dimension only.
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, and in particular with color map enabled. The example 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, disable the shield (select Layer OFF) 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.
Mode ·
Point/Volume Source Material ·
Shield #n Material ·
Cosmic Radiation ·
Geometry ·
Output ·
Element and Radionuclide Compositions and Series
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.
- Number of Shield layers
-
- Point / Volume Source
-
- Example data sets
- These data sets preset the whole calculator for certain typical cases of interest. A first calculation result can then be obtained by just clicking the Calculate button. After selection, the example data can also be modified as required, to study the effect of parameter variations.
Note: set Number of Shield layers=1 and select appropriate source mode first, before choosing an example data set!
- Ex. 1: Shielding in free air (for Point Source Mode)
- Study the impacts of distance, shield thickness, and shield material. With the highest Result Detail setting, the factors affecting attenuation can be checked for each single energy emitted by the radiation source.
Note: when entering individual source radionuclides, make sure that the calculator's database actually contains the gamma energy data for these nuclides (Query Database button): for space considerations, the calculator contains energy data for a few selected nuclides only.
- Ex. 2: 48Y Cylinder with Heels (for Point Source Mode)
- After unloading of an uranium hexafluoride (UF6) cylinder by heating in an autoclave, the decay products of the uranium remain in the cylinder as so-called Heels. See, how an "empty" cylinder emits much more gamma radiation than a full one.
- Ex. 3: DU bullet buried in soil (for Point Source Mode)
- Depleted uranium bullets buried in soil are difficult to locate by their gamma radiation emission. To see the dose variation for the situation without bullet, set the Source layer to "RAD. OFF".
- Ex. 4: Uranium mill tailings cover (for Volume Source Mode)
- Gamma radiation from uranium mill tailings can be reduced by soil covers, often applied in several layers. Check the effects of cover thickness and of residual radioactivity contained in the cover material.
- Ex. 5: 48Y Cylinder with UF6 nat (for Volume Source Mode)
- Determine the gamma dose outside the top of a typical transport cylinder for natural uranium hexafluoride.
Note: In addition, the cylinder emits neutron radiation which is not covered by this calculator.
- Layer usage selector
- This drop down list allows to easily disable parts or all of the properties of the source layer:
| NORMAL |
the layer is fully operational |
| ATTEN. OFF |
the attenuation properties of the layer are disabled |
| RAD. OFF |
any radiation emission from the layer is disabled |
| Layer EMPTY |
attenuation and radiation properties are disabled; the layer is filled with air |
| Layer OFF |
the layer is completely removed |
- 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 #n Material Composition
- Layer usage selector
- This drop down list allows to easily disable parts or all of the properties of each shield layer:
| NORMAL |
the layer is fully operational |
| ATTEN. OFF |
the attenuation properties of the layer are disabled |
| RAD. OFF |
any radiation emission from the layer is disabled |
| Layer EMPTY |
attenuation and radiation properties are disabled; the layer is filled with air |
| Layer OFF |
the layer is completely removed |
- 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.
- Layer usage selector
- This drop down list allows to enable/disable the inclusion of cosmic radiation to the dose calculations:
| NORMAL |
cosmic radiation is considered |
| Layer OFF |
cosmic radiation is neglected |
- Altitude [m above sea level]
- Cosmic radiation increases with altitude.
(Note: for terrestrial use only)
- Latitude [°]
- Cosmic radiation is slightly lower at latitudes below 30°.
- Outdoor/Indoor
- The ceiling of a building provides some shielding from cosmic radiation.
- Indoor: Shielding factor
- Dimensionless ratio of indoor to outdoor radiation level from ionizing cosmic radiation.
Point Source Geometry: (2 shield layers)
Volume Source Geometry: (2 shield layers)
The geometry parameters can be initialized with 5 predefined data set examples, corresponding to the example buttons in the Mode section.
Note: While the buttons in the Mode section initialize all parameters, here only the geometry is affected.
- Ex. 1: Shielding in free air (for Point Source Mode)
- Ex. 2: 48Y Cylinder (for Point Source Mode)
- Ex. 3: Source buried in soil (for Point Source Mode)
- Ex. 4: Tailings cover (for Volume Source Mode)
- Ex. 5: 48Y Cylinder (for Volume Source Mode)
- 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] (Point Source only)
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.
- 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)
- integration step width [cm]
- maximum horizontal size of the volume elements used for the point-kernel method.
Note: smaller sizes improve the precision, but increase computing times considerably
(In the case of a point source, this parameter is only required if the shield contains radionuclides)
- integration step height [cm]
- maximum vertical size of the volume elements used for the point-kernel method.
Note: smaller sizes improve the precision, but increase computing times considerably
(In the case of a point source, this parameter is only required if the shield contains radionuclides)
- Dose: Dose Rate Unit
- Select from pick list
The primary unit calculated is Gy/h. All other units are derived from this one.
- Dose: Exposure for annual dose rates
- Select occupancy form pick list
- Dose: Receptor Material
- Select from pick list
The absorbed gamma energy dose usually is calculated for air, and any further dose figures are derived from this value.
- Dose: Terrestrial gamma dose coeff. in air [Sv/Gy]
- Conversion coefficient from absorbed dose in air to effective dose equivalent for terrestrial gamma rays.
UNSCEAR (2000) recommends 0.7 Sv/Gy for adults, 0.8 for children, and 0.9 for infants.
(Note 1: this coefficient is used energy-independently)
(Note 2: this coefficient is only used for receptor air, otherwise unity is used)
(Note 3: the coefficient used for the contribution from cosmic ionizing radiation is unity)
- Dose: Use buildup factors for:
- check to enable computing of buildup factors for the top shield layer. The material to be used for the buildup factor calculations can be selected manually from the drop-down list, or auto select can be chosen. For auto select, the buildup data for the shield material is used; if this is unavailable, the buildup data for the element with the highest weight percentage in the layer is used.
Note: the use of buildup factors increases computing time.
- Color Map: Show color map
- Calculate dose values for the following raster of x and y positions and show result as coloured map.
Note: a two-dimensional color map is only available in Point Source mode and if no radionuclides are contained in any shields.
Note: If this checkbox is checked, computing time increases considerably!
- Color Map: 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!
- Color Map: Logarithmic color scale
- Check for logarithmic color scale, otherwise a linear scale is used
- Color Map: 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.
- Result Detail: Dose from each layer
- Select desired level of detail for the dose summary in the Result field.
(The selection "by Radiations" is available in Point Source mode only and affects the contributions from the point source itself only)
Element Compositions ·
Radionuclide Compositions ·
Radionuclide Series
| 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 | Stainless Steel (Type 304) | |
| 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 | |
| Uore_nor | Uranium ore, Nordic Lake, Elliot Lake, Ontario, Canada | 2) |
| Uore_01 | Uranium ore 0.1 wt-% U | 2) |
| Utail_01 | Uranium mill tailings from 0.1 wt-% U ore, extraction = 90% | 2) |
| Utail_dgo | Uranium mill tailings, Durango, Colorado, USA | |
| Utail_nor | 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_rec+ | Uranium hexafluoride, recycled uranium, solid, init. enr. 3.5 wt-%, burnup 39 GWd/tHM, 5 y delay, with progeny | |
| UF6_enr+ | Uranium hexafluoride, enriched to 3.5 wt-% U-235, solid, from natural uranium, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| UF6_ere+ | Uranium hexafluoride, enriched to 3.5 wt-% U-235 equiv., solid, from recycled U (3.5 wt-% 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 wt-% U-235, solid, from natural uranium, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| UF6_dre+ | Uranium hexafluoride, depleted to 0.2 wt-% U-235, solid, from recycled U (3.5 wt-% 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_rec+ | U3O8, recycled uranium, init. enr. 3.5 wt-%, burnup 39 GWd/tHM, 5 y delay, with progeny | |
| U3O8_dep+ | U3O8, depleted to 0.2 wt-% U-235, from natural uranium, with short-lived progeny (Th-234, Pa-234m, Th-231) | |
| UO2_enr+ | UO2, enriched to 3.5 wt-% U-235, from natural uranium, with short-lived progeny (Th-231, Th-234, Pa-234m) | |
| UO2_ere+ | UO2, enriched to 3.5 wt-% U-235 equiv., from recycled U (3.5 wt-% 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_tailx90++ | Uranium in mill tailings, extraction = 90%, with all major progeny | |
| U_rec | Recycled Uranium, init. enr. 3.5 wt-% U-235, burnup 39 GWd/tHM, 5 y delay | |
| U_rec+ | Recycled Uranium, init. enr. 3.5 wt-% U-235, 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 wt-% U-235, init. enr. 3.5 wt-% U-235, burnup 39 GWd/tHM, 5 y delay | |
| U_dre+ | Depleted Recycled Uranium, 0.2 wt-% U-235, init. enr. 3.5 wt-% U-235, 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 wt-% U-235 equiv., init. enr. 3.5 wt-% U-235, burnup 39 GWd/tHM, 5 y delay, without progeny | |
| U_ere+ | Enriched Recycled Uranium, 3.5 wt-% U-235 equiv., init. enr. 3.5 wt-% U-235, 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++
|
|---|
- [Parks 1988] Assessment of shielding analysis methods, codes, and data for spent fuel transport/storage applications
, by C. V. Parks, B. L. Broadhead, O. W. Hermann, et al., Oak Ridge National Laboratory, ORNL/CSD/TM-246, July 1988
- [Trubey 1988] New gamma-ray buildup factor data for point kernel calculations: ANS-6.4.3 standard reference data , by D. K. Trubey, NUREG/CR-5740, U.S. Nuclear Regulatory Commission, ORNL/RSIC-49, Oak Ridge National Laboratory, September 1988 (3.1MB PDF)
- [UNSCEAR 2000] Sources and Effects of Ionizing Radiation, UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes, United Nations Scientific Committee on the Effects of Atomic Radiation, United Nations, New York, 2000
> Download full text: Vol. I: Sources · Vol. II: Effects
