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This work presents a new technique for discriminating between alpha particles of different energy levels. In a first study, two groups of alpha particles emitted from radium-226 and americium-241 sources were successfully separated using a CR-39 microfilm of appropriate thickness. This thickness was adjusted by chemical etching before and after irradiation so that lower-energy particles were stopped within the detector, while higher-energy particles were revealed on the back side of the detector. The number of tracks on the front side of the microfilm represented all alpha particles incident on that side from the two sources. However, the number of tracks on the back side of the microfilm represented only the long-range alpha particles of higher energy that arrived at that side. Therefore, by subtracting the number of tracks on the back side from the number of tracks on the front side, one could easily determine the number of tracks for the short-range alpha particles of lower energy that remained embedded in the microfilm. Discrimination of the two energy levels is thus achieved in a simple, fast, and reliable process.

Alanine dosimeters in the form of pure alanine powder in PMMA plastic tubes were investigated for dosimetry in a clinical application. Electron paramagnetic resonance (EPR) spectroscopy was used to measure absorbed radiation doses by detection of signals from radicals generated in irradiated alanine. The measurements were performed for low-dose ranges typical for single-fraction doses often used in external photon beam radiotherapy. First, the dosimeters were irradiated in a solid water phantom to establish calibration curves in the dose range from 0.3 to 3 Gy for 6 and 18 MV X-ray beams from a clinical linear accelerator. Next, the dosimeters were placed at various locations in an anthropomorphic pelvic phantom to measure the dose delivery of a conventional four-field box technique treatment plan to the pelvis. Finally, the doses measured with alanine dosimeters were compared against the doses calculated with a commercial treatment planning system (TPS). The results showed that the alanine dosimeters have a highly sensitive dose response with good linearity and no energy dependence in the dose range and photon beams used in this work. Also, a fairly good agreement was found between the in-phantom dose measurements with alanine dosimeters and the TPS dose calculations. The mean value of the ratios of measured to calculated dose values was found to be near unity. The measured points in the in-field region passed dose-difference acceptance criterion of 3 % and those in the penumbral region passed distance-to-agreement acceptance criterion of 3 mm. These findings suggest that the pure alanine powder in PMMA tube dosimeter is a suitable option for dosimetry of radiotherapy photon beams.

This study attempts to overcome some of the reported discrepancies in alanine-EPR reproducibility that may be related to alanine dosimeter preparation and/or EPR spectrometer settings. The dosimeters were prepared by packing pure polycrystalline L - α - alanine directly as supplied by the manufacturer in glass tubes. This dosimeter production scheme avoids any possible contribution to the EPR signal from a binding material. The dosimeters were irradiated with gamma ray to low-dose ranges typical for medical therapy (0–20 Gy). Special attention has been paid to the study of minimum detectable dose, measurement repeatability and reproducibility, and post-irradiation stability. The dosimeter exhibited a linear dose response in the dose range from 0.1 to 20 Gy. These positive properties favor the polycrystalline alanine-in-glass tube as a radiation dosimeter.

Samples of the PM-355 polymeric solid state nuclear track detector were irradiated with gamma rays of various doses up to 10 6 Gy . AC impedance measurements in the frequency range from 100 Hz to 100 kHz were performed on irradiated and pristine samples at room temperature. The dielectric constant, dielectric loss, and dissipation factor were calculated from the AC impedance measurements and plotted as a function of frequency. An increase in the dielectric constant was observed when the irradiation dose increased. The intensity of the well-defined relaxation peaks, detected for all samples, increased upon irradiation. These changes were attributed to mobile charge carriers or dipolar molecules generated by structural changes in the irradiated samples.

The electrical behavior of die drawn isotactic polypropylene was investigated at room temperature in the frequency range 10 Hz to 10 6 Hz. The electric permittivity and electric modulus were determined from ac impedance measurements. In the low frequency range a dramatic increase in the imaginary and real components of dielectric permittivity was observed both parallel and normal to the chains alignment. This change is associated with a well defined relaxation peak in the plot of the imaginary component of electric modulus versus frequency. A high degree of anisotropy was observed in dielectric permittivity and electric modulus. This anisotropy is a result of chains alignment and the decrease in the mobility of molecules in the amorphous region due to the high constrains imposed on this region as a result of the drawing process. The Cole-Cole plot of the real component versus the imaginary component of electric modulus for both normal and parallel to the direction of chains alignment yields nearly perfect circles indicating that a certain polarization mechanism is dominant in die drawn isotactic polypropylene copolymer.

Therapeutic ultrasound is used to enhance the repair of soft tissue, muscle, etc., and because many of the cellular reactions involved in these processes are dependent on the intracellular availability of free calcium ions, it becomes important to study the effects of ultrasound in the presence and the absence of calcium ions. Using frog skin as a biological model, the effect of therapeutic ultrasound (300 mW/cm2 1 MHz CW) was investigated. Sonication for two minutes caused a significantly larger increase in total ionic conductance (Gt) in the presence of calcium ions (140% vs. 27%). However, the time constant for Gt to return to steady state was significantly longer in calcium-free solutions (122 vs. 18 min.). This study demonstrates that the biological effects of ultrasound are influenced by calcium ions. Furthermore, the recovery time constants confirm recent findings regarding the function of calcium ions in the formation of tight junctions. The role of free radicals produced by cavitation and calcium potentiated lipid and protein peroxidation is discussed.

Previous work in our laboratories has shown that, amongst other effects, irradiation of frog skin with low intensity ultrasound causes reductions in the chemical driving force of the short-circuit current. This indicated that either the Na/K dependent ATPase or ATP availability were being reduced. We measured the effect of ultrasound irradiation on ATP and NA/K-dependent ATPase from inverted erythrocyte ghosts and on firefly luciferin and luciferase activity. Our findings demonstrate that ultrasonic cavitation-induced sonochemical reactions were responsible for irreversible inactivation of luciferase and ATPase but had little or no effect on ATP and luciferin. We measured the levels of hydrogen peroxide generated by ultrasound under the conditions of our experiments and found that it could account for only part of the enzyme inactivation observed. Free radical scavengers/antioxidants were capable of fully protecting the enzymes from ultrasound-induced inactivation. These findings demonstrate that, in addition to hydrogen peroxide, free radicals generated by ultrasound are responsible for the effects.

This study examines the feasibility of utilizing pure polycrystalline alanine-in-glass tubes as commercial dosimeters. The design of the dosimeters avoids preparation complications such as mortaring, sieving, and/or binder addition. It also reduces several fabrication techniques of alanine dosimeters and hence it allows other laboratories to conduct similar electron paramagnetic resonance (EPR) measurements. The dosimeters were irradiated with gamma rays ranging from 0 to 20 Gy. The dosimeters were found to be more sensitive to low radiation doses than other types of alaninewith- binder dosimeters. They exhibited a linear response in the dose range from 0.1 to 20 Gy. These positive properties favor the pure polycrystalline alanine-in-glass tube as a radiation dosimeter for low gamma irradiation doses.

Purpose: The objective of this study was evaluation of accuracy of pure alanine dosimeters measuring intensity-modulated radiation therapy (IMRT) dose distributions in a thorax phantom. Methods: Alanine dosimeters were prepared in the form of 110 mg pure L-α-alanine powder filled into clear tissue-equivalent polymethylmethacrylate (PMMA) plastic tubes with the dimensions 25 mm length, 3 mm inner diameter, and 1 mm wall thickness. A dose-response calibration curve was established for the alanine by placing the dosimeters at 1.5 cm depth in a 30×30×30 cm3 solid water phantom and then irradiating on a linac with 6 MV photon beam at 10×10 cm2 field size to doses ranging from 1 to 5 Gy. Electron paramagnetic resonance (EPR) spectroscopy was used to determine the absorbed dose in alanine. An IMRT treatment plan was designed for a commercial heterogeneous CIRS thorax phantom and the dose values were calculated at three different points located in tissue, lung, and bone equivalent materials. A set of dose measurements was carried out to compare measured and calculated dose values by placing the alanine dosimeters at those selected locations inside the thorax phantom and delivering the IMRT to the phantom. Results: The alanine dose measurements and the IMRT plan dose calculations were found to be in agreement within ±2%. Specifically, the deviations were −0.5%, 1.3%, and −1.7% for tissue, lung, and bone; respectively. The slightly large deviations observed for lung and bone may be attributed to tissue inhomogeneity, steep dose gradients in these regions, and uncontrollable changes in spectrometer conditions. Conclusion: The results described herein confirmed that pure alanine dosimeter was suitable for in-phantom dosimetry of IMRT beams because of its high sensitivity and acceptable accuracy. This makes the dosimeter a promising option for quality control of the therapeutic beams, complementing the commonly used ionization chambers, TLDs, and films.

Purpose: The first medical physics Master's program in the Arabian Gulf region was started in 2002 at King Fahd University of Petroleum & Minerals (KFUPM), Dhahran, Saudi Arabia. Methods: After consulting with national and international representatives from the AAPM, IOMP, the University of Wisconsin‐Madison and King Faisal Specialist Hospital and Research Center (KFSHRC) we constructed a versatile and rigorous curriculum. The program requires the completion of 7 core courses, 7 required labs, a minimum of 3 elective courses, a research project, a four‐month clinical rotation and passing and a comprehensive examination. The success of the program required very close collaboration with national hospitals such as King Fahad Specialist Hospital in Dammam (KFSH‐D), KFSHRC, and Riyadh Military Hospital. We cemented the collaboration with a formal agreement between KFUPM and KFSH‐D, whereby the clinical medical physicists are actively involved in teaching lectures and labs, evaluating students’ performance and co‐supervising their clinical rotation and research projects. In order to prepare our graduates for their medical physics careers, we emphasize innovative learning methods such as students centered learning, execution of course projects, experiential learning and acquiring research skills and tools such as Monte Carlo simulations.Results: Our graduates have succeeded in securing clinical positions in some of the best hospitals in the region and achieved high employer satisfaction. Some students have gone to pursue their PhD's in North America and Europe. Many of our students succeeded in publishing their projects in international journals and international conferences. One of our students was instrumental in obtaining a USpatent(USPatent # 785298) for an innovative x‐ray tube design. Conclusions: We have achieved national recognition through the excellence of our graduates. In order to maintain high education quality standards and achieve international recognition, we are presently working to acquire IAEA approval and CAMPEP accreditation.

Ultrasound has been used in physical therapy for > 4 decades. Recent studies indicate that non-thermal mechanisms such as cavitation are involved in the observed effects. Free radicals and other highly reactive compounds are known to form during sonochemical reactions associated with acoustic cavitation. Using frog skin as a biological model, the possibility that the increase in ionic conductance (Gt) upon exposure to therapeutic ultrasound is due to the effect of free radicals generated by sonochemical reactions, was investigated. It was found that the presence of cystamine, cysteamine and sodium ascorbate significantly reduced the increase in conductance caused by the exposure to 300 mW/cm2 (1 MHz CW) therapeutic ultrasound. The attenuation in the effects was dependent on the concentration of the radical scavengers/antioxidants used, the incubation time, and the intensity of ultrasound. The effects were also dependent on the lipid solubility of free radical scavengers/antioxidants. The time constant for the recovery process of Gt in the presence of free radical scavengers and antioxidants after exposure to ultrasound was found to be not significantly different from control. These results suggest that the increase in Gt due to ultrasound is induced by free radicals and other reactive species generated from acoustic cavitation. This study provides an indirect evidence to the contingent that free radicals are generated and act inside the cells. Furthermore, the radical scavengers and antioxidants used provide protection from oxidative damage without being involved in the recovery of Gt towards steady state values after sonication.

Temperature profiles were measured in large sections of bovine muscle and bovine liver exposed to single pulses from a clinical Nd:YAG laser. The data were analyzed with a photothermal model applicable to an incident gaussian beam including the effects of beam spread and heat flow. Closed form expressions for the radial average initial temperatures and thermal relaxation were derived and compared with the measurements.