Introduction

Man has always been subjected to natural radiation. He is exposed to radiation fromj the sun and outer space, naturally occuring radioactive materials are present in the earth, in the structures we inhabit, and in the food and water we consume.

There are radioactive gases in the air we breathe and our bodies are them selves radioactive. The levels of this natural (or background) radiation vary greatly from location to location.

The U²³⁸ , Th²³² and U²³⁵ series present naturally inh the earth=s crust and thereforealso present in our drinking waater may be divided into groups each with along-lived main nuclide and its short lived daughters.

In the context of drinking water Ashort lived@ are those radionuclides that develo0p during under ground transport or during processing and storage prior to consumption. @Long lived@ are those radionuclides that went into solution are the rock-water interface and are still detectable at the point of sampling (well, spring or drain out put) (Surbeck,1994)

According to our literature survey only a few studies have been made to measure the natural radioactivity in the north part of Jordan, especially in the Wadi Al_Arab area. The quality of water, the concentration and distribution of heavy elements and other studies were the main subjects of on the wadi Al_Arab dam, and in the neighbouring area. All of these studies concerned the concentration and distribution of heavy elements in the study area and they found that heavy metal concentrations nearly reflect the natural background value given gby Turekian and wedepole (1961). Therefore, this study is a comprehensive one, which takes into account the measurement of natural radiation in the Wadi Al_Arab area.

Experimental Method

A 1.00L samples of surface and ground water were taken from different locations and depths on the dam reservoir, using a water sampler.

These samples after were immediately transferred to Merineelli(polyethylene) beakers; the sampled water washed the beakers before they were used. The beakers must to be immediately closed to reduce the amount of volatile radon, which may effect on the results.

In the laboratory, the water samples were analysed by Gamma spectrometer. Gamma spectroscopy measurements were carried out using a germinaium detector gamma-ray spectra (EG&G ORTEC=s GammaVision). Theactivities of a lot of elementscan thus be determined with the restrictions that some elements do not have a significant gamma ray and also of possible enterference.

a) ²²²Rn concentration was determined by measuring the 295.1 (19.2%) and 352 (37.1%) keV γ-rays from Pb²¹⁴ and the 609.3 (46.1%) and 1120.3 (15%) keV γSrays from Bi²¹⁴.

The Ra²²⁶ concentration was calculated by averaging over the measured concentrations for Pb²¹⁴ and Bi²¹⁴.

b) Ra²²⁶ concentration was determined by measuring the 186 (5.4%) keV γSray.