Measurement of background radiation , cosmic ray flux and their hazard parameter of Baghdad city districts

The aim of this work was directed to measure the cosmic ray (CR)flux and the background (BG) absorbed dose rate for districts ofBaghdad city. The maximum values of CR flux was 2.01(particle/cm2.s) registered for several Baghdad districts and theminimum was 0.403 (particle/cm2.s) belonging to Al-kadhimiyadistrict, whereas the overall average value was 1.24 (particle/cm2.s).The BG measurements showed that the maximum absorbed dose was25 nSv/h belonging to Noab AL-Dhbat district and the minimumabsorbed was 19.01 nSv/h observed in Al-Ghadeer district, whilethe overall average was 22.56 nSv/h, and this value is small than theIraqi permissible limit, which is restricted by Iraqi Center ofRadiation Protection.The hazard indices, radium equivalent activity (Raeq), absorbed dose(D), external annual effective dose (EAD), internal hazard index(Hin), and external hazard index (Hext), of TBG, were estimated andall the values of these indices are within the allowed internationallimits.


Introduction
Natural radioactivity on earth has been in existence ever since the planet was formed and there are about 60 radionuclides present in nature.About 82% of the environmental radiation is from natural sources.Some area of the world, called high background radiation areas (HBRAs), which have anomalously high levels of background radiations.The ionizing radiations are always present in the environment in which all of us are living [1].Exposure to ionizing radiation originates from two major sources; naturally occurring and manmade sources.Naturally occurring radioactivity present on the earth's crust can be further classified into two distinct source categories such as virgin and modified natural sources.Virgin sources of radiation are of cosmogenic or primordial (terrestrial) origin and have existed on the earth since primordial times.Modified natural sources are mainly from activities like mining, usage of fossil fuel, production of fertilizers or usage of natural materials for building constructions.The latter is known as Technologically Enhanced Natural Radiation (TENR).Natural radiation is the largest contributor to the collective radiation dose to the world population.Relatively constant exposure to the population at a location is the distinctive characteristics of this radiation.However, cosmic rays represents main part of the background radiation and, therefore, one must measure it to stand up about the hazards.Furthermore, the aim of this work is to measure the absorbed dose rate of background radiation (BG) and cosmic rays flux (CR) of Baghdad city districts and there health hazard indices.The study area; Baghdad city Baghdad is the capital of the republic of Iraq.The population of Baghdad, according to the statistical of the Iraqi Trade ministry, is approximately 7,216,040, which represents the largest city in Iraq [2], the second largest city in the Arab world (after Cairo, Egypt), and the second largest city in the Western Asia (after Tehran, Iran).On the other hand, Baghdad positioned in the central of Iraq and the Tigris River passes from the middle of it and divides it into two parts.The area of Baghdad is about 4555 km 2 .Baghdad is located at coordinates latitude 33°18'03.56"N,longitude 44°25'07.11"E,which is located between the coordinates latitude 33°31'53.29"N, longitude 44°20'14.12"Eat the entrance of the Tigris River from the north, and coordinate latitude 33°5'74.43"N,longitude 44°31'45.44"Eat the exit of the Tigris river from the south.The range of height above sea level of Baghdad is between 29 -44 m.However, Baghdad city includes fifty three districts as shown in Fig. 1.

The used dosimeter
The dosimeter that used in this work was developed in our laboratory by dependence the procedure of reference [3], which illustrated all the details of design.This developed dosimeter includes two sets of Geiger -Muller (GM) tubes in each set there are three GM tubes arranged in a way to separate between BG and CR.All the measurements have been done with one meter rising from the ground and in order to get accurate measurements, any reading was measured for five times and the overall average was dependent.an acceptable result for space travel as the cells affected end up with greater energy deposition and are more likely to die without proliferating into tumors with a probability of 10%.However, the health hazardous of CR can be estimated by the unshielded annual absorption dose of human phantom due to CR (AAD) which can be given by [9]:

The
where H ≈ 2 MeV/cm (200 MeV/m) is the stopping power of 1GeV cosmic rays in tissue (water), d ≈ 30 cm (0.3m) is the average thickness of human torso, S ≈ 7×10 3 cm 2 is the average cross-section of human body, M = 70 kg is the approximate mass of an adult astronaut [6].Further, the last column in table (1) showed the estimated results of AAD.The maximum value of AAD was 64.016 µSv/y and the minimum value was 12.802 µSv/y, while the overall average was 39.276 µSv/y.However, this value of AAD represents about 4% from the total maximum permissible allowed absorbed dose, which is 1 mSv/y [10].In order to show the contribution of CR relative to BG, the dose rate due to CR was measured for all study area.Fig. 2 illustrated the ratio between BG and CR dose rates.The maximum value of BG to CR ratio was 41 for Al-Kadhimiya district (which represents the minimum contribution of CR) and the minimum value was 7.8 for Saba Abkar district and AL-Husaniya district (which represents the maximum contribution of CR), while the overall average value was 14.12.

BG Radiation hazard indices
The terrestrial BG (TBG) was estimated by subtracted the CR absorbed dose rate contribution from the total BG measurements.The second column of 2 shows the results of TBG which indicate that the maximum value was 24.13 nSv/h in AL-Gadhra district and the minimum value was 17.19 nSv/h in Hor Rajab district, where as the overall average value was 20.96 nSv/h.Nevertheless, the researchers in reference [7] measured the activity concentrations of the NORM isotopes in soils (Natural Occurring Radioactive Materials which are 238 U, 232 Th, and 40 K) for some districts of Baghdad city using gamma spectroscopy, and calculated the hazard indices, which are radium equivalent activity (Ra eq ), absorbed dose rate (D), external annual effective dose (EAD), internal hazard index (H in ), and external hazard index (H ext ).However, in this work the results of the hazard indices of the above reference [7] were plotted against D and some useful fitting equations were obtained.These deduced fitting equations were used to estimate the hazard indices of our TBG results.The definition of these hazard indices and the explanation of the results can be showed as follow:-

Radium equivalent activity (Ra eq )
To represent the activity concentrations of 238 U, 232 Th and 40 K by a single quantity, which takes into account the radiation hazards associated with them, a common radiological index has been introduced.The index is called radium equivalent activity (Ra eq ) which is used to ensure the uniformity in the distribution of natural radionuclides 238 U, 232 Th and 40 K and is given by the expression [11]: Ra eq (Bq/kg) = A(U) + 1.43A(Th) + 0.077A(K) (2) [11] where, A(U), A(Th) and A(K) are the specific activities concentrations of 238 U, 232 Th and 40 K in (Bq/kg) respectively.However, Fig. 3a shows the Ra eq as a function of D and from it, the following fitting equation was deduced; 2.1371 1.0272 (3) [11] The third column of Table 2 gaves the estimated results of Ra eq of this work for TBG.The maximum value was 52.59 Bq/kg of AL-Gadhra district and the minimum value was 37.76 Bq/kg of Hor Rajab district, while the overall average was 45.82 Bq/kg.Furthermore, all the estimated values of Ra eq are within the allowed permissible limits of global limits [12], which is 370 Bq/kg.

External Annual Dose (EAD)
The external annual effective dose (EAD) was calculated using the following equation [11]: EAD (mSv/y)= {0.92 A(U) + 1.1 A(Th) + 0.08 A(K)} × (10 -9 Gy/h) × (0.7 Sv/Gy) × (24×365 h/y)× 0.8 (4) Fig. 3b shows the EAD as a function of D and from this figure the following linear fitting equation was deduced; EAD = 0.0157 D -0.0112 The fourth column of Table 2 illustrates the EAD values of the TBG of this work deduced by Eq. ( 5).The maximum value was 0.368 mSv/y for AL-Gadhra district and the minimum value was 0.259 mSv/y for Hor Rajab district, whereas the overall average value was 0.318 mSv/y.However, all the estimated values were within the global limits [13], which is 1.5 mSv/y.

Conclusions
According to this work, some important conclusions can be deduced;  The overall average of CR absorbed dose was 1.6 nSv/h, and the overall average of CR flux was 1.24 Particle/cm 2 .s.  To stand up about the health hazards of CR, the unshielded annual absorption dose of human phantom due to CR was estimated and the overall average value of it was 39.276 µSv/y. The overall average ratio of BG to CR was 14.12 and this reflects that the contribution of CR absorbed dose rate to BG is about 7 %, and the residual represents the terrestrial BG (TBG) absorbed dose rate.