The natural plants which are used for the treatment of living beings are known as medicinal plant. More than five hundred types of medicinal plants are being used as raw materials of drugs. Medicinal plants are unique type of natural product requiring special consideration due to their potential impact on human health. The pharmacological properties of the medicinal plants have been attributed to the presence of active chemical constituents which are responsible for important physiological function in living organisms [1] .

Naturally occurring radioactive materials (NORM) are found in every constituent of the environment: air, water, soil, food and in humans. According to the International Food Safety Authorities Network [2] [3] , plants used as food commonly have ⁴⁰K, ²³²Th and ²³⁸U and their progenies. It is expected that likewise would be found in plants used for medicinal purpose since plants are the primary pathway of natural radionuclides entering into the human body through the food chain. Radionuclides and their decay products from ²³⁸U and ²³²Th series together with ⁴⁰K are terrestrial primordial radionuclides, which originated from the earth’s crust and are the sources of natural radioactivity in the environment [4] .

Human exposure to radiation in the environment is from sources that are widely used in industry, agriculture, as well as for scientific and medical purpose. Traditional medicine involving use of grasses and herbs is the most ancient method of curing diseases [5] .

In Nigeria, there is shift of interest to the use herbal medicine for the cure of diverse diseases. Apart from the high cost of procuring available allopathic medicines for treating even common health disorders, other reasons for this shift are inaccessibility of health institutions in the rural or remote locations in the country and the growing awareness of adverse reaction to some allopathic drugs [6] .

Herbal or medicinal plant products, in various forms, have been used to treat illness for many hundreds of years on all continents and within cultures across the world. About 70% - 80% of the world populations, especially in the developing countries, rely on nonconventional medicine in their primary health care [7] . An emerging problem in many developing countries is industrial pollution that causes contamination of vegetation with heavy metals, pesticides, or radioactivity [8] . Therefore the medical properties and effectiveness of medicinal plants depend on environmental conditions, which also have a direct influence on their growth in the place of their occurrence and cultivation [9] . Moreover, medicinal plants are not included in the past, possibly because the ingestion of radioactive material through their consumption had been recognized or was considered insignificant. As mankind uses traditional herbal medicine for the treatment of various diseases and aliments, the study of radionuclide concentration in such plants has great significance [10] . The objective of this study is to determine the natural radioactivity presented in some selected medicinal plants commonly used in Iraq and to assess the radiological risk associated with the use of these medicinal plants.

Gross alpha, beta and gamma spectrometry (Proportional counter + NaI detector) type (XLB5) and gamma-ray spectroscopy with (HPGe) techniques were used to determine the concentrations of the radioactive isotopes ⁴⁰K, ²²⁶Ra and ²³²Th.

Samples of medical herbs imported to Iraq were collected from the local markets of Iraq, nine types of herbs shown in Table 1, each sample was dried and blended until it became powder.

The gross alpha, beta and gamma spectrometry includes gas-flow proportional counters for alpha and beta counting and sodium iodide NaI(Tl) scintillation detector for gamma ray in the same system, using software package type ECLIPS [11] . (100 g) weight of the powdered sample placed in a bowl blanchet made of stainless steel material and into custom place to counting the total alpha, beta and gamma.

The gamma-ray spectroscopy system consists of high purity germanium (HpGe) detector with a relative efficiency of (40%), 1.95 keV energy resolution (FWHM) at energy peak of 1332 KeV of ⁶⁰Co isotope. A multichannel analyzer (MCA) with 4096 channel was used. A detector shield had a cavity adequate to accommodate large samples. The shield had lead walls with 10 cm thickness lined inside with graded absorber of Cd ~1.6 mm Cu ~0.4 mm.

Calibration and efficiency of the system were carried out using multi-gamma ray standard source (MGS-5, Canberra) of Marinelli beaker geometry. A library of radionuclide’s which contained the energy of the characteristic gamma emissions of each nuclide was analyzed and their corresponding emission probabilities were built from the data supplied in the software.

Samples were placed in Marinelli beaker sealed off and kept for one month to achieve radioactive secular equilibrium between ²²⁶Ra and ²²²Rn and daughter nuclei.

In order to determine the background distribution due to naturally occurring radionuclide’s in the environment around the detector, an empty Marinelli beaker container was counted in the same manner as the samples.

After measurement and subtraction of the background, the activity concentrations were calculated.

Each sample was ground into a fine powder with a particle size <1 mm, 500 gm of each samples were put into standard Marinelli beaker and the activity concentrations for the natural radionuclide’s in the measured samples were computed using the following relation [12] :

where N(E, i) is the net counts for the radionuclide i at energy E, εγ(E) is the photopeak efficiency at energy E, Tc is the counting live-time (s), Pγ(E, i) is the gamma emission probability of the radionuclide i for a transition at energy E, M is the dry-weight of samples (kg).

The average annual committed effective dose, Eave, for ingestion of NORMS in the medicinal plants was calculated using the expression in equation [13] :

where DCF_ing is the dose convection factor for ingestion, for each radionuclide (i.e., 4.5 × 10⁻⁵ mSv/Bq, 2.3 × 10⁻⁴ mSv/Bq and 6.2 × 10⁻⁶ mSv/Bq for ²³⁸U, ²³²Th and ⁴⁰K respectively for an adult) (UNSCEAR, 2000), I_p is the consumption rate from intake of NORMS in medicinal plants and is the activity concentration in the plant sample.

Results of gross alpha, beta, gamma and gamma spectroscopy analysis of medical herbals are shown in Table 2.

The average activity concentration obtained for ⁴⁰K obtained in this study (431.35 Bq/kg) is less than other values of ⁴⁰K in other studies [3] [14] . Results of gross alpha, beta and gamma are slightly low.

The corresponding average annual effective dose determined in this study to any individual’s organ or tissue in the population group due to the ingestion of natural radionuclides in the medicinal plants is far below the average radiation dose of 0.3 mSv/y received per head worldwide due to the ingestion of natural radionuclide (UNSCEAR, 2000).