X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) have been used to examine the chemical composition of GaAs(100) surfaces after different standard cleaning sequences, using aqueous H2 SO4 :H2 O2/ HCl and H3 PO4 :H2 O2/ HCl solutions. XPS measurements show that the oxides, Ga2 O3 and As2 O3 , which remain at a relative concentration of 1.7:1 after H3 PO4 :H2 O2 :H2 O etch, are totally removed by the subsequent aqueous HCl solution. These same oxides, which have a relative concentration of 2.5:1 after H2 SO4 :H2 O2 : H2 O etch, are then not totally removed by HCl. Elemental arsenic was found to increase in concentration as the surface oxides decreased. The surface, initially gallium rich (Ga/As ratio 1.11), became arsenic rich (Ga/As ratio 0.93) after cleaning in HCl. The excess elemental As can be removed by subsequent treatment in NH4 OH. LEED patterns could be obtained only for H3 PO4 :H2 O2 /HCl cleaned surfaces. Au/Ti/GaAs Schottky diodes were made on both types of samples after cleaning. I–V measurements show that the diodes on the H3 PO4 :H2 O2/HCl cleaned surfaces have a better ideality factor (ranging from 1.15 to 1.20), than those on H2SO4 :H2 O2/HCl cleaned surfaces (ranging from 1.20 to 1.25), while the barrier heights are about the same for both (∼0.74 eV).

Patients administered with a therapeutic dose of I for thyroid cancer treatment are potential sources of unacceptably high radiation exposure to other individuals, particularly the patient's immediate family members. Generally, patients are hospitalized until such time that the retained radioactivity in the body or the measured dose rate at 1 m from the patient's body surface fall to within acceptable levels. Patient release criteria are set to ensure that no individual shall be liable to receive exposures above the regulatory dose limit for the public or dose constraints for the patient's relatives or caregivers.

Routine monitoring of occupational radiation exposure is done primarily to demonstrate compliance with dose limits. Statistical analysis of past and present dose records provides a useful tool in the management of institutional radiation safety programs. In this study, a statistical analysis of annual dose records from 1985-1999 from a large tertiary care medical center with a cyclotron and radiopharmaceutical production facility is performed. A total of 6,089 annual dose records, categorized into ten occupational groups, were included in the analysis. Dose distribution is skewed, with 85% of workers receiving an annual dose of less than 1.0 mSv, while 1.3% have doses > or =10 mSv. The mean annual dose of all monitored workers during this 15-y period ranged from 0.5 to 1.2 mSv. Large variation in the mean annual dose exists among the different occupational groups. Four occupational groups were identified as relatively highly exposed, namely cyclotron and radiopharmaceutical production, cardiac catheterization, nuclear medicine, and diagnostic radiology. These four occupational groups also showed different trends in the mean annual dose. A correlation study showed that total annual collective dose has no linear association with the number of monitored workers, the number of measurably exposed workers, or the number of workers with annual dose between 0.1 to <10 mSv. Moderate correlation (r = 0.64) was observed between the annual collective dose and the collective dose of workers with an annual dose between 0.1 to <10 mSv. A strong and significant correlation (r = 0.95) exists between the total annual collective dose and both the number of workers with annual dose of > or =10 mSv and the corresponding collective dose due to these highly exposed workers. Although the fraction of these highly exposed workers is small (about 1%), they have a significant impact on the total collective dose and their contribution can be as high as 50%. Workers with annual dose of > or =10 mSv tend to concentrate in a few identified occupational groups and not across all occupational groupings. The cyclotron and radiopharmaceutical production department is of particular concern due to its high individual dose levels and increasing mean annual dose trend for the last 5 y. Radiochemists and cyclotron engineers tend to receive an annual dose exceeding the dose limit. A plot of the collective dose of highly exposed workers vs. the total collective dose shows that if a dose constraint of 10 mSv is imposed on highly exposed occupational groups, the total collective dose is expected to be about 200 person-mSv.

The administration of intravenous contrast media by hand or power injection in paediatric computed tomography (CT) procedures is carried out at King Faisal Specialist Hospital and Research Centre for chest, abdomen and torso diagnostic examinations. Some procedures require the CT unit to commence patient scanning during the injection of the last volume of the contrast medium. During the injection, even if the nurse is wearing a 0.5 mm lead equivalent protective apron, the head region and the hand are likely to receive high doses. This study was therefore made to assess the head and extremity doses to the nurses during CT procedures where typical exposure parameters of 200 to 220 mA s and 120 kVp were used. Thermoluminescence dosemeters were deployed for three consecutive months in two CT rooms. A total of 96 procedures were performed during this period and they were included in this study. Scattered radiation measurements were done at different locations where the nurse may be positioned. Results showed that the average dose to the head region and the hands per paediatric case were 50 microSv and 80 microSv respectively. This study investigated the factors that affect the dose and found them to be the length of stay inside the room, type of CT examination. exposure parameters and location of the nurse.