Radiation Physics and Chemistry 71 (2004) 795–796

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*Correspond

E-mail addr

0969-806X/$ - s

doi:10.1016/j.ra

Environmental radioactivity in South Africa

James Larkina,*, Henk Coetzeeb, Shaun Guyc, John Wattersona

aThe Schonland Research Institute for Nuclear Sciences, the University of Witwatersrand, Johannesburg, South AfricabThe Council for Geosciences, Silverton, Pretoria, South Africa

cALARA Consultants c.c. PO Box 6297 Pretoria, Gauteng, South Africa 0001

1. Introduction

Data were accumulated from a number of sources and

combined into a comprehensive geographical informa-

tion system for the National Nuclear Regulator of South

Africa (NNR).

Sources include:

* Public Hazard Assessments submitted by nuclear

licence holders to the NNR.* Agricultural Research Council.* Water Research Commission.* Nuclear Energy Corporation of South Africa (NEC-

SA) Council for Geosciences.

Data include:

* Geology; lithography, chronological age, distribu-

tion.* Soil; depth distribution, type, class.* Topography.* Commodities; mines, distribution and deposits.* Political maps.* Hydrology.

Total Count Calibration

050

100150200250300

Dos

e (n

Gy/

h)

2. Experiment

Cosmic background radiation is calculated from

altitude and the dose rate is reported in nanogreys/hour

(nGy.h�1). Using the following relationship:

EI ðZÞ ¼ EI ð0Þ½0:21e�1:694Z þ 0:79e0:4528Z�;

ing author.

ess: larkin@src.wits.ac.za (J. Larkin).

ee front matter r 2004 Elsevier Ltd. All rights reserv

dphyschem.2004.04.096

where EI(0) is the dose rate at sea level and Z is the

altitude in kilometres.

Terrestrial background radiation is calculated from a

calibrated total count map of South Africa. This

calibration (Fig. 1) was carried out using some 839 in

situ measurements of potassium, equivalent uranium

and equivalent thorium concentrations as measured

using a Geofyzika-Brno GS256 MCA with a 3 in Na (I)

detector. These concentrations were then turned into

dose rates using default dose coefficients taken from

UNSCEAR (2000) and plotted against recorded total

counts as measured by airborne radiometric survey.

3. Results & discussion

One of several concerns is the following: is it possible

to extend airborne radiometric data reported in units of

equivalent uranium, to in situ measurements of radio-

isotope concentrations?

The following graph (Fig. 2) shows the unprocessed

airborne spectrum, an in situ spectrum and its corre-

sponding soil sample from the same location.

0 20 40 60 80 100Total Counts (as equivalent U3O8)

Fig. 1. Total count calibration.

ed.

ARTICLE IN PRESS

Comparison of soil sample, airborne measurement & insitu measurements taken at SS 1

1

10

100

1000

10000

0 500 1000 1500 2000 2500keV

Cou

nts

Fig. 2. Various spectra accumulated in different manners from

the same location. Dotted line—in situ spectrum; Solid line

below dotted line—airborne spectrum; Solid line (bottom of

graph) soil sample.

J. Larkin et al. / Radiation Physics and Chemistry 71 (2004) 795–796796

4. Conclusions

It is interesting to note the correlation between the

various measurement techniques used for determining

the activity present within the environment, even prior

to the additional signal processing that is usually carried

out on the airborne spectra, using the windows indicated

above and a set of stripping ratios that are determined

for each set of detection apparatus. It gives a degree of

confidence that the various dose rate maps that have

been developed from the airborne surveys do reflect the

prevailing radiological conditions.

Acknowledgements

The National Nuclear Regulator of South Africa and

the Council for Geoscience in making much of this data

available.

References

UNSCEAR, 2000. Report of the United Nations Scientific

Committee on the Effects of Atomic Radiation to the

General Assembly, ANNEX B Exposures from natural

radiation sources. Table 6 External exposure rates calcu-

lated from various concentrations of terrestrial radio-

nuclides in soil, p. 116.