Correlation of hydrogen bond lengths and angles in liquid water based on Compton scattering

The temperature-dependent hydrogen-bond geometry in liquid water is studied by x-ray Compton scattering using synchrotron radiation combined with density functional theory analysis. Systematic changes, related to the weakening of hydrogen bonding, are observed in the shape of the Compton profile upon increasing the temperature. Using model calculations and published distribution functions of hydrogen-bond geometries obtained from a NMR study we find a significant correlation between the hydrogen-bond length and angle. This imposes a new constraint on the possible local structure distributions in liquid water. In particular, the angular distortions of the short hydrogen bonds are significantly restricted.     

Qualitative study of ethanol content in tequilas by Raman spectroscopy and principal component analysis

Using Raman spectroscopy, with an excitation radiation source of 514.5 nm, and principal component analysis (PCA) was elaborated a method to study qualitatively the ethanol content in tequila samples. This method is based in the OH region profile (water) of the Raman spectra. Also, this method, using the fluorescence background of the Raman spectra, can be used to distinguish silver tequila from aged tequilas. The first three PCs of the Raman spectra, that provide the 99% of the total variance of the data set, were used for the samples classification. The PCA1 and PCA2 are related with the water (or ethanol) content of the sample, whereas the PCA3 is related with the fluorescence background of the Raman spectra.     

Dose distribution of gamma radiation in a new geometric configuration of a standard carton date package and its experimental application for disinfestation of packed dates

A new geometrical configuration composed of three standard carton boxes (SCBs) full with polyethylene bags (PBs), where each bag contains 1 kg of date, was placed on a single turntable of Gammabeam-650 and irradiated with low doses. The mean “radiation absorbed dose” for disinfestation of this geometrical unit at 15 equally distributed positions (Fricke dosimeters) inside 3 SCBs put on a single turntable was calculated to be 0.46 ± 0.20 kGy and dose uniformity ratio (U) = 1.0019/0.2500 = 4.00. The development and genetic tests carried out on insects found in the PBs 1–2 days after irradiation resulted in that all insects were completely sterile and died within a short period of time. No sign of any reinfestation was recorded at all in the treated packages even after 30 days of storage in an insectory. Apparently the prevention of insects from invading and/or penetrating the date packages is due mainly to the new combination of standard carton boxes that are widely used for commercial purposes and hermetically heat-sealed polyethylene bags of dates in addition to the entire prevention of reproduction induced by the “low” doses of γ radiation. Therefore, by using similar geometrical configuration, 18 big standard carton date packages can be simultaneously disinfected, using the same range of doses or so, by utilizing all the 6 turntables inside the radiation chamber of the Gammabeam-650 irradiation facility.     

Molecular rectification through electric field induced conformational changes

A new approach for the design of a molecular rectifier is proposed. Using a simple model, we have shown that conformational changes induced by the electric field may lead to a rectifying junction. The simplest possible rectifier of this kind presents two almost isoenergetic conformations, with different conductances and dipole moments. A simple equation allows for the estimation of the range of molecular parameters and temperatures that lead to an effective rectification. Examples show that rectification based on this mechanism is also possible at room temperature.     

Application of a new standardization method in activation analysis with registration of soft gamma radiation

An application of a new standardization method for rapid activation mass analysis with registration of the strongly absorbed low-energy gamma radiation is described. This method makes it possible to avoid the use of the time-consuming and laborious method of Internal Standard.     

Evaluation of dose rate distribution in objects irradiated in large gamma sources

The codes DOSKMF2 and ISORADL makes it possible to describe numerically as well as graphically γ-irradiation facilities by means of dose rate values for a chosen set of points of interest in the radiation field or by means of dose rate isocurves for chosen crossections of the radiation field, respectively. The structure of DOSKMF2 is briefly described.The combination of this calculation procedure and experimental dose rate determination makes it possible to evaluate the radiation fields in existing γ-irradiators.A design procedure for γ-irradiators using the computer tools is briefly presented.     

A Subnanosecond Time-Resolved Fluorescence Lifetime Spectrometer Applying Laser Diodes

 Since the first application of laser diodes (LD) for the determination of fluorescence lifetimes in our group in 1995, great technical improvements have been made to increase the time resolution of the apparatus. Using the phase fluorometric method, measurements down to 100 ps are now possible. Values can be measured in steps of 10 ps with good reproducibility using a high-frequency signal generator and a GHz digital storage oscilloscope. No additional optical equipment is necessary for this new method. Following an easy calibration procedure, results are available within one minute without any adjustments. The components of the new apparatus including light source, sample chamber for standard fluorescence cuvettes, and detection unit are situated in a 12 × 13 × 9 cm setup. The apparatus was tested with different fluorophores, and the results correlate very well with known values in the range of 0.1 to 1000 ns.     

Controlling bandgap energy and multivibronic modes of a poly(2,5-thiophene-1,4-dialkoxyphenylene) derivative by gamma photons

In this work, the influence of γ radiation on electronic, structural, and vibrational properties of a poly(2,5-thiophene-1,4-dialkoxyphenylene) derivative is studied by optical absorption and photoluminescence. A Gaussian fit of emission spectra within Franck-Condon vertical transitions formalism was carried out in order to understand how vibronic coupling is affected by the dose, because an unexpected luminescence behavior was observed. Aiming to understand the ionizing radiation-matter interaction processes, we employed a molecular modeling procedure, through the use of a semiempirical method (AM1) applied to conjugated oligomers' conformational structure and equilibrium geometries, to clarify the defects induction for the used doses. From AM1 optimized structures, electronic transitions were calculated by ZINDO/S-CI semiempirical method to measure the chain scission degree. Moreover, with the results presented in this work, it is possible to come up with a new physical-chemical route to treat and increase conjugated polymers' efficiency. Finally, we believe that the present paper contributes to the literature about defects on conjugated polymers.     

Mathematical efficiency calibration methods for high quality laboratory based gamma spectrometry systems

The efficiency calibration of laboratory based gamma spectrometry systems typically involves the purchase or construction of calibration samples that are supposed to represent the geometries of the unknown samples to be measured. For complete and correct calibrations, these sample containers must span the operational range of the system, which at times can include difficult configurations of size, density, matrix, and source distribution. The efficiency calibration of a system is dependent not only on the detector, but on the radiation attenuation factors in the detector–source configuration, and therefore is invalid unless all parameters of the sample assay condition are identical to the calibration condition. An alternative to source-based calibrations is to mathematically model the efficiency response of a given detector–sample configuration. In this approach, the measurement system is calibrated using physically accurate models whose parameters can generally be easily measured. Using modeled efficiencies, systems can be quickly adapted to changing sample containers and detector configurations. This paper explores the advantages of using mathematically computed efficiencies in place of traditional source-based measured efficiencies for laboratory samples, focusing specifically on the possibility of sample optimization for a given detector, uncertainty estimation, and cascade summing corrections.     

Inner radiation field modeling using multipole moments

In this work we extend the use of multipole moments expansion to the case of inner radiation fields. A series expansion of the photon flux was established. The main advantage of this approach is that it offers the opportunity to treat both inner and external radiation field cases. We determined the expression of the inner multipole moments in both spherical harmonics and in cartesian coordinates. As an application we applied the analytical model to a radiation facility used for small target irradiation. Theoretical, experimental and simulation studies were performed, in air and in a product, and good agreement was reached.     

Post-irradiation identification of papaya (Carica papaya L.) fruit

Impact of radiation processing on the volatile essential oil profile of papaya (Carica papaya) was investigated. Gamma-radiation processing resulted in the appearance of a new peak in the GLC profile that was identified as phenol. The observed dose dependent increase in phenol content suggested possible use of this compound as a marker for radiation processed papaya.     

A Subnanosecond Time-Resolved Fluorescence Lifetime Spectrometer Applying Laser Diodes

Summary.  Since the first application of laser diodes (LD) for the determination of fluorescence lifetimes in our group in 1995, great technical improvements have been made to increase the time resolution of the apparatus. Using the phase fluorometric method, measurements down to 100 ps are now possible. Values can be measured in steps of 10 ps with good reproducibility using a high-frequency signal generator and a GHz digital storage oscilloscope. No additional optical equipment is necessary for this new method. Following an easy calibration procedure, results are available within one minute without any adjustments. The components of the new apparatus including light source, sample chamber for standard fluorescence cuvettes, and detection unit are situated in a 12 × 13 × 9 cm setup. The apparatus was tested with different fluorophores, and the results correlate very well with known values in the range of 0.1 to 1000 ns. Received February 16, 2000. Accepted March 13, 2000     

On-line analysis of coal by neutron induced gamma spectrometry

Thermal neutron prompt gamma activation analysis (PGNAA) has proven to be a useful tool for the multi-elemental characterization of coal. The use of isotopic neutron sources allows the construction of relatively small irradiation facilities for the on-line analysis of large volume samples. As a first step to an on-line analysis system for process control in a coal blending plant we have developed a facility using a Cf-252 neutron source with an actual strength of 1 mg. This source, which is shielded by layers of high purity lead and paraffin, can be moved to the center of cylindrical sample holders containing up to 150 kg of coal. To avoid background radiation the sample holders are made from polyethylene. The prompt gamma rays emitted from the sample are measured with a 22% high purity germanium detector housed in a special horizontally extended cryostate assembly. The detector is positioned on top of the sample; it is surrounded by a multi-layer decreasing Z-absorber to reduce low energy gamma background. Paraffin loaded with 95% enriched lithium-6-carbonate is used between sample and detector as a gamma window with high absorption for thermal neutrons. Moreover the detector is shielded against background radiation by lead and natural lithiumcarbonate. The data processing system consists of high count-rate analogue electronics including pileup-suppression and a fast data acquisition system, which permits on-line analysis of the collected data. Analysis of several samples of simulated coals as well as Western Germany coals shows a good spectral response of our system for the elements H, C, Al, Si, S, Cl, Ca, Ti and Fe, whereas the sensitivity for N, K and Na is somewhat lower. This means, that the quantitative determination of the above elements will be possible within 20 minutes. Optimization of the system is continued with a stress on analysis time and detection sensitivity. Supported by Bundesministerium für Forschung und Technologie D-5300 Bonn 1, Fed. Rep. of Germany.     

Influence of gamma radiation onto polymeric matrix with papain

Papain is a proteolytic enzyme that has been widely used as debridement agent for scars and wound healing treatment. However, papain presents low stability, which limits its use to extemporaneous or short shelf-life formulations. The purpose of this study was to entrap papain into a polymeric matrix in order to obtain a drug delivery system that could be used as medical device. Since these systems must be sterile, gamma radiation is an interesting option and presents advantages in relation to conventional agents: no radioactive residues are formed; the product can be sterilized inside the final packaging and has an excellent reliability. The normative reference for the establishment of the sterilizing dose determines 25 kGy as the inactivation dose for viable microorganisms. A silicone dispersion was selected to prepare membranes containing 2% (w/w) papain. Irradiated and non-irradiated membranes were simultaneously assessed in order to verify whether gamma radiation interferes with the drug-releasing profile. Results showed that irradiation does not affect significantly papain release and its activity. Therefore papain shows radioresistance in the irradiation conditions applied. In conclusion, gamma radiation can be easily used as sterilizing agent without affecting the papain release profile and its activity onto the biocompatible device is studied.     

Study on gamma and electron beam sterilization of third generation cephalosporins cefdinir and cefixime in solid state

The effect of gamma radiation from ⁶⁰Co source and 2 MeV e-beam was studied on two thermolabile cephalosporin antibiotics viz cefdinir and cefixime in solid state. The parameters studied to assess radiolytic degradation were loss of chemical and microbiological potency, change in optical rotation, electronic and vibrational absorption characteristics, thermal behavior and color modification. ESR spectroscopic study, HPLC related impurity profile, thermogram and Raman spectrum are applied in deducing the nature of radiolytic impurities and their formation hypotheses. Cefixime is radiation sensitive, whereas cefdinir has acceptable radiation resistance at 25 kGy dose. The nature of radiolytic related impurities and their concentrations indicates that the lactam ring is not highly susceptible to direct radiation attack, which otherwise is considered very sensitive to stress (thermal, chemical and photochemical).     

A novel shielding material prepared from solid waste containing lead for gamma ray

Human beings are continuously exposed to cosmogenic radiation and its products in the atmosphere from naturally occurring radioactive materials (NORM) within Earth, their bodies, houses and foods. Especially, for the radiation protection environments where high ionizing radiation levels appear should be shielded. Generally, different materials are used for the radiation shielding in different areas and for different situations. In this study, a novel shielding material produced by a metallurgical solid waste containing lead was analyzed as shielding material for gamma radiation. The photon total mass attenuation coefficients (μ/ρ) were measured and calculated using WinXCom computer code for the novel shielding material, concrete and lead. Theoretical and experimental values of total mass attenuation coefficient of the each studied sample were compared. Consequently, a new shielding material prepared from the solid waste containing lead could be preferred for buildings as shielding materials against gamma radiation.     

Use of synchrotron-radiation-based FTIR imaging for characterizing changes in cell contents

FTIR imaging of individual cells is still limited by the low signal-to-noise ratio obtained from analysis of such weakly absorbing organic matter when using a Globar IR source. In this study, we used FTIR imaging with a synchrotron radiation source and a focal plane array detector to determine changes in the cellular contents of cryofixed cells after culture for 48 h on Si(3)N(4) substrate. Several spectral differences were observed for cells deprived of glucose compared with control cells: a lower amide I-to-amide II ratio (P < 0.01); a different secondary structure profile of proteins (obtained from amide I spectral region curve fitting), with a significant increase in non-ordered structure components (P < 0.01); and a higher ν(C = C-H)/ν(as)(CH(3)) absorption ratio (P < 0.01), suggesting increased unsaturation of fatty acyl chains. Therefore, our study has shown that FTIR imaging with a synchrotron radiation source enables determination of several spectral changes of individual cells between two experimental conditions, which thus opens the way to cell biology studies with this vibrational spectroscopy technique.     

New design of Co-60 source for wet gamma irradiators

Co-60 sources represent one of the key factors in industrial radiation processing and applications such as sterilization of disposable products and food preservation. Design of the sources being currently used in wet gamma irradiators can be improved with the purpose of increasing the source corrosion stability and mechanical integrity during use. This paper describes the proposed new design of Co-60 source for wet gamma irradiators. As a result of changes in capsule material and some dimensions, product quality and reliability can be improved with no additional cost for end user.     

Imaging Therapeutic Proteins in Gelatin for Controlled Drug Release

Preliminary results from this study show that x-ray microcomputed tomography can be used to image model proteins for bone inducing growth factors. Small quantities (<1 μg protein/mg gelatin) of soybean trypsin inhibitor labeled with either gold nanoparticles or nonradioactive iodine were detected using synchrotron radiation. These results could lead to a new method of measuring the release profile of therapeutic proteins.     

Directional dependence of the mean excitation energy and spectral moments of the dipole oscillator strength distribution of glycine and its zwitterion

In this contribution, we consider the interaction of glycine, a small, model biomolecule, and its zwitterion with fast ion radiation. The object of the study is to determine the differences in properties among various conformers and orientations of the neutral molecule and the zwitterion and to determine if these differences will have implications in terms of radiation protection and radiation therapy. To this end, quantum mechanical calculations were carried out on three conformers of the neutral molecule and two of the zwitterion to determine both the isotropic and directional components of the moments of the dipole oscillator strength distribution in each case. It is these moments that determine the interaction of swift radiation with a molecule.