VARIATION OF GAMMA RADIATION DOSE RATE DUE TO COSMIC
RADIATION AS A FUNCTION OF ALTITUDE
I. Sarrou a, A. Ophanou a, E. Sotirioua
a
AN.O. Applied Technologies, Dasoupoleos 25, 2015, Nicosia ,Cyprus
Abstract
The aim of this paper is to determine the relationship between Gamma Radiation Dose Rate (GRDR)
from cosmic radiation and altitude for altitude < 2 km. In order for this to be achievable two
instruments have been used. The one was Gamma Monitor Model DKS-96K whose task was to
measure the terrestrial GRDR and the Gamma tracer whose task was to measure the total GRDR. The
cosmic GRDR was found when terrestrial GRDR was subtracted from total GRDR. The cosmic GRDR
seems to follow an exponential relationship with altitude for altitude < 2 km.
Keywards: GRDR; altitude; exponential relationship; terrestrial ; cosmic;
1.Introduction
Cosmic Radiation
The cosmic radiation at sea level is consisted of 80 % Muons, 18 % Electrons and 1-2
% protons and neutrons. Thus the Cosmic Gamma Radiation Dose Rate at sea level
is, 25 nSv/h due to muons, 6 nSv/h due to electrons, 0.4 nSv/h due to protons and 0.4
nSv/h due to neutrons.
Thus the total GRDR at sea level due to cosmic radiation is therefore equal to 31.8
nSv/h.
Cosmic ray variations tend to be small and result first from changes in barometric
pressure, with a high pressure system, there is a large mass of air to provide a
shielding effect, as compared to a low pressure system, which has less air mass and
less shielding. Second from the Height of the main muon production level. Last from
Extraterrestrial factors (11 years period of solar sunspots)
The GRDR due to cosmic radiation increases with altitude. (See table 1).
Table 1: Variation of Cosmic GRDR with altitude.
Position
Cosmic GRDR [μSv/h] Altitude[km]
Sea level
30
0
Himalayas
1
6.7
Airplane flight
5
10
Concorde flight
10
15
Terrestrial Radiation
Cyprus lithology consists of two rock types, namely the igneous and sedimentary
formations .The sedimentary rock types (e.g. limestone and gypsum) contain
relatively high amounts of uranium (10-50 parts per million (ppm)) because
uranium enrichment has taken place in certain rock horizons by gradual
evaporation of enclosed seawater. On the other hand, the igneous ophiolithic
rocks, which form the underlying lithology of the mountain Troodos, are generally
characterized by relatively low uranium content (< 6 ppm).
2. Materials and Methods
Measurements of the terrestrial GRDR were carried out using the Gamma Monitor
Model DKS-96K, supplied by Doza company. Τhe measuring range of this
instrument is 50 nSv/h – 100 μSv/h. The calibration error is no more than 10%.
The instrinsic relative error is  30% and the uncertainty of measurement at 2
sigma and 95% confidence limits is  6%. In order to calculate the terrestrial
GRDR the sodium Iodine detector was placed on the ground where all
measurements were taken. Τhe collected data was transfer to the computer via
USB cable for further analysis.
Measurements of total GRDR were carried out using the gamma dose
measurement probe Gamma Tracer. The measurement range of the instrument is
20 nSv/h – 10 mSv/h. The one sigma error at 100 nSv/h and 60 min measuring
cycle is  3 % and the calibration error is 5%. The total GRDR was continually
registered in 60 min measuring cycle and the data were transferred to the
computer for further analysis by infrared transmission. Note that the probe was
hanging on a tripod with the lower end being one meter above the ground, where
the observations were taken.
The exact position of the altitude measurements points were taken via GPS
monitor.
3. Results and discussion
In order to see if the two different rock types are different the GRDR was
measured using the Gamma Monitor Model DKS-96K for 20 locations of
sedimentary and igneous rock. The values were compared to the ones that were
calculated indirect (from concentration of K–40, Th-232, and U-238).
Table 2 : Terrestrial GRDR from direct and indirect measurements.
Rock Type
Mean Value direct measurement
Mean Value indirect
[nSv/h]
measurement [nSv/h]
Igneous
13  5
11.0  5.4
Sedimentary
30  10
29.0  6.2
Ιn order to see the variation of cosmic GRDR with altitude,
6 points of
measurements were chosen. The cosmic GRDR was calculated if terrestrial
GRDR was subtracted from total GRDR (see table 3).
Τable 3: Τοtal Terrestrial and cosmic GRDR for various altitudes.
Location
Altitude
Total
Terrestrial GRDR
Cosmic
[km]
GRDR
[nSv/h]
GRDR
[nSv/h]
Paralimni
0
50
20
30
Nicosia (Sedimentary)
0.2
65
30
35
Kalopanagiotis(igneous)
0.575
56
10
46
Kakopetria (igneous)
0.667
61
10
51
P. Amiantos (igneous)
1.33
93
10
83
Olympos (igneous)
1.9
125
10
115
(Sedimentary)
Variation of Cosmic GRDR with Altitude
140
Cosmic GRDR [nSv/h]
120
100
80
60
40
20
0
0.5
1
1.5
2
Altitude [km]
1. Conclusions
The results obtained from this study lead to the following conclusion:
The variation of cosmic GRDR with altitude follows an exponential relationship and
more specific the equation is: cosmic GRDR [nSv/h] =30,6.e
0,72.Altitude[km],
with a
Regression factor of 0.997 for altitude < 2 km.
References
1. M. Tzortzis , H. Tsertos, C.Christofides, G. Christodoulides, Gamma – ray
measurements of naturally occurring radioactive samples from Cyprus
characteristic geological rocks, Radiation Measurements 37 (2003) 221 – 229.
2. Fokianos, K., Sarrou, I., Paschalidis I., 2005 A two sample model for the
comparison of radiation doses. Chemometrics Intell.Lab.Syst.79, 1-9.