Non-disturbing thermoacoustic dosimetry of electron and bremsstrahlung beams

The thermoacoustic response of thin targets (TTs) to pulsed electron/gamma irradiation is analyzed in the context of determination of the radiation characteristics. Basic equations of thermoacoustic dosimetry linking thermoacoustic stress amplitude to deposited energy density are presented. Using these equations, it is possible to restore the particle distribution in the pulsed beam from the thermoacoustic response of one-dimensional (wire, rod) or two-dimensional (film, plate) TTs. Generation coefficients for the TT-based dosimeters are presented. The construction and principles of operation of thermoacoustic TT-based dosimeters for determination of the characteristics of pulsed electron beams are considered. The availability of thermoacoustic gamma dosimetry is analyzed. Specific features and merits of the method of thermoacoustic dosimetry are discussed.     

Study on dosimetry of bremsstrahlung radiation processing

The dosimetry in high-power bremsstrahlung irradiation for the industrial processing has been studied. The dosimeter systems used are cylindrical ionization chamber to measure average exposure rate and CTA, clear PMMA and alanine dosimeters for routine dosimetry. The results gave some useful information on the measurement of average exposure rate using the ionization chamber. Clear PMMA and alanine dosimeters showed good characteristics for their usefulness as routine dosimeters for X-ray irradiation in the industrial processing.     

Sterilization of health care products by 5 MeV bremsstrahlung (X ray)

Radiation sensitivities of . pumilus and spores were examined to bremsstrahlung of 5 MeV EB and Cobalt -60 γ rays in order to confirm the effects of radiation and dose rate. Biological indicators (SPORTROL, NAmSA, USA) were irradiated with the X ray in the dose rate range of 4.7–47kGy/h. D-value of spores was 1.4–1.5 kGy, and that of was 1.1–1.3 kGy. The D-values of and have very small dose rate dependences to X ray, and the D-values are similar to those of γ ray. Dose distribution by X-ray and γ irradiation was measured for cartons containing 32 unit dialyzers. The D_max./D_min. of the X-ray irradiation (1.2) was smaller than that of γ ray (1.3).     

Nine MeV bremsstrahlung fission of 238U

The mass yield distribution of fission products produced in the photofission of ²³⁸U using 9 MeV bremsstrahlung have been radiochemically measured for 21 mass chains. The absolute activities of the nuclides measured were determined from gross β counting and total chain yields were measured relative to ⁹⁹Mo. The peak to valley ratio was found to be about 310, which is comparable with previous results measured at 10 MeV. Fine structure was found to be a prominent feature and occurred around mass number 133, although mass number 134 could not be measured in the present investigation. The fission yields measured in this work have been compared to all known existing values for work in photon energy range of 9 ± 1 MeV.     

Non-destructive photon-activation analysis of standard rocks with 30 MeV bremsstrahlung

Résumé On a appliqué l'activation aux photons à l'analyse non-destructive de roches étalons USGS. 16 éléments sont dosés. On a irradié simultanément l'échantillon de roche et les étalons multiéléments dans un bremsstrahlung de 30 MeV, et on a mesuré l'activité des adioisotopes produits par les réactions (λ,n)et (λ,p) avec un détecteur Ge(Li). La validité de la méthode est démontrée par les résultats obtenus pour ces roches. Les résultats concernent les éléments suivants: Na, Mg, Ca, Ti, Cr, Mn, Fe, Co, Ni, Rb, Sr, Y, Zr, Nb, Ba et Ce.      

The production rates of rare earth nuclides by 70 MeV bremsstrahlung for photon activation analysis

The combination of photon activation and solid state γ-ray detection provides a very effective method of analysis of rare earths. The present report describes the production rates of almost all of the product nuclides found in yttrium and 14 rare earths irradiated with 70 MeV bremsstrahlung photons from an electron synchrotron. A 20 cm³ lithium-drifted germanium diode was used as a detector. Sensitivities of this method have been summarized for photon activation analysis, and experimental reaction yields have been obtained in order to discuss the reactivity of high-energy photons with nuclei in the rare earth region. Work was performed at the Ames Laboratory of the U.S. Atomic Energy Commission. Contribution No. 2556     

X-ray treatment at 5 MeV and above

There is agreement in the scientific community that X-ray treatment of food at 7.5 MeV can be safe. Possible process improvements for treating at higher than 5 MeV X-rays have been re-visited. Monte Carlo methods have been applied to simulate the X-ray conversion process and to calculate dose distributions in homogeneous phantoms. Experimental data obtained using X-rays produced with a Rhodotron TT200 at 5 and 10 MeV verifies a representative set of data which is calculated with the presented method.

With this qualified Monte Carlo tool, calculations at 7.5 MeV incident electron energy were performed. The analysis gives special attention to higher photon yield, improved product penetration, as well as surface and edge effects.     

Application of bremsstrahlung activation analysis for the determination of carbon and nitrogen in sodium

Carbon and nitrogen are determined by means of the photonuclear reactions:¹²C(γ n)¹¹C and¹⁴N(γ, n)¹³N. This article presents a simultaneous chemical separation method for the isolation of¹¹C and¹³N. It is based mainly on combustion of the sample, after irradiation and etching, in a mixture of oxidising acid fused salts (B₂O₃ and Pb₃ O₄) containing a dispersing agent (NaCl and KCl) and the respective carriers. Each analysis takes about 40 min altogether. Minimum carbon and nitrogen contents of a few 10⁻² μg·g⁻¹ can be measured. The influence of the main competitive nuclear reactions on neighbouring elements, including the sodium itself, is examined.     

Fast determination of gold in large mass samples of gold ores by photoexcitation reactions using 10 MeV bremsstrahlung

The determination of gold is based on the photoexcitation reaction ¹⁹⁷Au(γ,γ’)^197mAu with the half-life of 7.73 seconds and energy of emitted gamma-rays of 279 keV. Three 100 ml aliquots of coarsely ground Au-ore (grains <2 mm) corresponding to ca. 150–180 g were irradiated for 20 seconds with bremsstrahlung of maximum energy 10 MeV produced by a microtron at the electron beam current of 30–40 μA, 1–10 times reactivation was applied. After 3 seconds of decay, samples were measured for 20 seconds using scintillation or semiconductor gamma-spectrometry with the detection limits for an ideal sample down to 0.5 μg·g⁻¹ and 0.1–0.2 μg·g⁻¹ of Au, respectively. Content of U and Th undergoing photo-fission increases the detection limits several times.     

Comparison of theory and experiment for polarizational bremsstrahlung

Portillo and Quarles have recently observed significant deviations from ordinary bremsstrahlung predictions for bremsstrahlung from gas targets, after not seeing such effects in solids. These deviations are interpreted as an observation of the polarizational bremsstrahlung component. We review previous discussion of this component. No adequate theory is presently available for the angular dependence of the bremsstrahlung cross section being measured in these new experiments. We examine the validity of the simple estimates which Portillo and Quarles have tried to use.     

Application of the 30 MeV microtron for gamma and neutron activation analysis

Based on studies of variable multiplicity electron acceleration, the power-current microtron, a cyclic electron accelerator up to energies of 30–35 MeV has been developed at the Institute on Physical Problems of the Academy of Sciences of the USSR. The 1–1.5 kW electron beam of the microtron is comparable to the power output of modern linear accelerators operating at similar energies. At the same time, the microtron has a number of significant advantages, due to the simplicity of design of both accelerator and ultrahigh-frequency tract, the high efficiency of ultrahigh-frequency power utilization, good operating characteristics, strictly monochromatic electron beams (variations not exceeding ±50 keV at 30 MeV) and the possibility of continuously changing particle energy as required by the given experimental task.     

Computer-aided acquisition and processing of data for caloric measurements with isoperibol calorimeters

The undisturbed temperature equilibration of the vessel in an isoperibol calorimeter must follow an exponential time function. Any caloric effect within this vessel must cause a deviation of this function. A mathematical relation has been derived for linking the extent of this caloric effect and the integral of the temperature-time function.This algorithm has been utilized for a computer program capable for an automatic acquisition of the data of an appropriate digital temperature meter and for the automatic calculation of the calorimetric results.In two different calorimetric units these arrangements have been applied for the following determinations: -specific heat capacities of liquid samples -heats of chemical reactions -reaction rates -heats of vaporization of liquid samples.     

Dynamic range and response speed of heat-flux differential calorimeters

A technique for the linearization of calorimeter cell (CC) thermal feedback in differential calorimeters was investigated. The technique was shown to ensure the linearity of the tract of rapid compensation measurements of thermokinetics (W _in(t)) in a dynamic range of heat-fluxes limited in principle only by the linearity of the CCs themselves, while their original identity is not required. The technique was employed in prototype models of updated DAK calorimeters, in which W _in(t)_max reached 0.5 W while the duration of the transition process associated with the insertion of the test specimen was reduced by a factor of 2.3. This was shown to reduce calorimeter inertia, extend the possibilities of thermokinetic measurements, and record earlier stages of the initial thermokinetics.     

Thermal hazard evaluation of complex reactive substance using calorimeters and Dewar Vessel

In this paper, several small-scale screening test methods were discussed on evaluating the thermal hazard of reactive substances. Generally the sensitivities of DSC and ARC are not high enough to evaluate the thermal hazards for all reactive substance, especially, for those of complex reactions containing a phase and/or chemical reaction mechanism change in the lower temperature range. Using the C80, however, the reaction can easily be detected in the lower temperature range due to its high sensitivity. Therefore, the C80 gives generally more accurate results than DSC and ARC. Data from C80 and Dewar vessel were compared and it indicates that the Dewar vessel has also high enough sensitivity to evaluate the thermal hazard and determine the heat flux in lower temperature range of reactive substances. This revised version was published online in July 2006 with corrections to the Cover Date.     

Explosion evaluation and safety storage analyses of cumene hydroperoxide using various calorimeters

Plenty of thermal explosions and runaway reactions of cumene hydroperoxide (CHP) were described from 1981 to 2010 in Taiwan. Therefore, a thermal explosion accident of CHP in oxidation tower in 2010 in Taiwan was investigated because of piping breakage. In general, high concentration of CHP for thermal analysis using the calorimeter is dangerous. Therefore, a simulation method and a kinetic parameter were used to simulate thermal hazard of high concentrations of CHP only by the researcher. This study was applied to evaluate thermal hazard and to analyze storage parameters of 80 and 88 mass% CHP using three calorimeters for the oxidation tower, transportation, and 50-gallon drum. Differential scanning calorimetry (DSC) (a non-isothermal calorimeter), thermal activity monitor III (TAM III) (an isothermal calorimeter), and vent sizing package 2 (VSP2) (an adiabatic calorimeter) were employed to detect the exothermic behavior and runaway reaction model of 80 and 88 mass% CHP. Exothermic onset temperature (T ₀), heat of decomposition (ΔH _d), maximum temperature (T _max), time to maximum rate under isothermal condition (TMR_iso) (as an emergency response time), maximum pressure (P _max), maximum of self-heating rate ((dT/dt)_max), maximum of pressure rise rate ((dP/dt)_max), half-life time (t _1/2), reaction order (n), activation energy (E _a), frequency factor (A), etc., of 80 and 88 mass% CHP were applied to prevent thermal explosion and runaway reaction accident and to calculate the critical temperature (T _c). Experimental results displayed that the n of 80 and 88 mass% CHP was determined to be 0.5 and the E _a of 80 and 88 mass% CHP were evaluated to be 132 and 134 kJ mol^?1, respectively.     

Yields of photonuclear reactions for photon-activation analysis with high-energy bremsstrahlung

Experimental reaction yields have been determined for various types of photonuclear reactions, induced in 52 elements by means of Bremsstrahlung irradiation with maximum energies ranging from 30 to 72 MeV, and of detection of the resultant activities with a lithium-drifted germanium detector. From the results obtained, sensitivities in photon-activation analysis were evaluated and the reactivity of high-energy photons with nuclei in a wide range of atomic number is discussed. Some nuclear considerations in photon-activation analysis, involving the relative probability of forming each product as a result of the (gamma,xnyp) reactions are also given.     

Interest of thick-target bremsstrahlung for an innovative compact X-ray source

A compact X-ray source (1 dm³) has been built, the basis of X-ray production being that of bremsstrahlung (Br) of the hot electrons generated in situ in the core of a hot magnetized plasma. Among the advantages of this device are that it can be pulsed or operated in a stable continuous mode and that there is no requirement for any filament nor high-voltage power supply. Thick-target Br (from a solid material) is involved, first in view of investigating runaway electrons leaking to the lateral walls. Second and more importantly, the features of thick-target Br are exploited in order to make the X-ray source point-like and more intense, a small target being inserted in the way of the hot electrons. The brightness obtained at 20 keV is 3.5×10¹¹ photons s⁻¹ mm⁻² sr⁻¹ keV⁻¹, which for example allows the obtaining of mammographic images in exposure times of a few seconds.     

Electrical calibration and testing of calorimeters with simulated, time-variable reaction power

For calorimetric investigations where the reconstruction of the real heat-flow rate during the experiment is required, the usual electrical calibration with constant power is often not sufficient. However, the use of a chemical calibration is limited by the number of suitable and certified reactions showing a known dynamics of the heat-flow rate. Therefore, a computer controlled electrical calibration unit was developed capable of duplicating any simulated reaction power-time curve in the calorimetric cell. The calibration unit consists of a universal simulation software with an interface to a programmable precision current supply connected to the calibration heater inside the calorimetric vessel. The reliability of the electrical calibration was proved with a continuous titration calorimeter using different recommended test reactions (TRIS+HCl, dilution of aqueous KCl, NaCl and urea solutions).

In order to test the electrical calibration procedure in the dynamic mode the heat-flow rate of a first-order equilibrium reaction during a continuous titration experiment was simulated. It is demonstrated that the combination of simulation software and electrical calibration hardware provides a very close adaptation of calibration and experiment, allows a more reliable estimation of experimental uncertainties, simplifies the verification of complex data analysis procedures and opens up new possibilities for the optimization of experimental parameters.     

Radiation dosimetry using clear PMMA and PVC in the range of 5–45 kGy

Some plastic sheets manufactured or commercially available in Pakistan have been tested as radiation dosimeters for cobalt-60 -rays. Radiation induced colouration in the plastics have been measured spectrophotometrically. The results show that 2 mm thick clear poly(methyl methacrylate) (PMMA) can be used as radiation dosimeter up to 45 kGy when absorption measurements are made at 305 nm and 314 nm; whereas 1 mm thick clear poly(vinylchloride) (PVC) is useful up to 30 kGy when measured at 396 nm. The response of PMMA dosimeter is stable for at least 15 days and that for PVC for 30 days, when stored under ambient conditions after irradiation. Post-irradiation stability at various temperatures (–10 to 55°C) has also been studied.     

New reference materials for the calibration (temperature and energy) of differential thermal analysers and scanning calorimeters

Several organic compounds like phenanthrene, benzanilide, anisic acid, triphenylene, 2-chloroanthraquinone, hexachlorobenzene, carbazole, 4-iodobenzoic acid, perylene, anthraquinone, as new reference materials for temperature and energy calibration of DTA and DSC apparatuses were studied in the range 300—600 K.

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Zusammenfassung Als neue Referenzsubstanzen für Temperatur- und Energiekalibrierung von DTA- und DSC-Geräten wurden im Temperaturbereich 300–600 K einige organische Verbindungen, wie z.B. Phenanthren, Benzanilid, Anissäure, Triphenylen, 2-Chloranthrachinon, Hexachlorbenzol, Karbazol, 4-Jodbenzoesäure, Perylen und Anthrachinon untersucht.