Cross sections of proton capture reactions of Sr isotopes

Cross section measurements of the proton capture reactions of the 86Sr, 87Sr and 88Sr isotopes were carried out at energies Ep=1.4-5 MeV. At Ep <3.5 MeV an array of 4 HPGe detectors with 100% relative efficiency shielded with BGO scintillators for Compton background suppression was used, whereas at Ep >3.5 MeV, the measurements were performed by means of one HPGe detector of 80% relative efficiency. For the 87Sr(p,7)88Y and 88Sr(p,7)89Y reactions total cross sections ranging from 0.5 μο-5 mb were found. The data analysis of the 86Sr(p,7)87Y reaction is in progress. Cross sections have also been calculated by means of the statistical model code MOST. A very good agreement between the experimental data and the theoretical predictions has been found.

Cross section measurements of the 7 8Se(p,7)7 9Br and 8 0Se(p,7)8 1Br reactions

In beam cross section measurements of the 78Se(p,7)79Br and 80Se(p,7)81Br reactions have been carried out at Ep=1.4-3.5 MeV, by using high efficiency HPGe detectors with BGO shields for Compton background suppression. A preliminary analysis yielded total cross sections ranging from 10 μb to 3 mb. By means of the statistical compound nucleus theory of Hauser-Feshbach cross sections have also been calculated. A comparison between experimental data and theoretical predictions is presented.

A Library of Potential Nanoparticle Contrast Agents for X-Ray Fluorescence Tomography Bioimaging

Nanoparticles (NPs) have been used as contrast agents for several bioimaging modalities. X-ray fluorescence (XRF) tomography can provide sensitive and quantitative 3D detection of NPs. With spectrally matched NPs as contrast agents, we demonstrated earlier in a laboratory system that XRF tomography could achieve high-spatial-resolution tumor imaging in mice. Here, we present the synthesis, characterization, and evaluation of a library of NPs containing Y, Zr, Nb, Rh, and Ru that have spectrally matched K-shell absorption for the laboratory scale X-ray source. The K-shell emissions of these NPs are spectrally well separated from the X-ray probe and the Compton background, making them suitable for the lab-scale XRF tomography system. Their potential as XRF contrast agents is demonstrated successfully in a small-animal equivalent phantom, confirming the simulation results. The diversity in the NP composition provides a flexible platform for a better design and biological optimization of XRF tomography nanoprobes.

The γ-γ fast-timing technique and the EXILL&FATIMA campaign

At the Institut Laue-Langevin in Grenoble, germanium-gated γ-γ fast-timing lifetime measurements of nuclear excited states in neutron-rich nuclei have been performed within a prompt γ-ray spectroscopy experimental campaign. We report on results obtained from the cold-neutron induced fission of 235U. The excited secondary fission products were stopped almost instantaneously within the thick target and the γ rays emitted were collected triggerlessly using the EXILL&FATIMA mixed array of HPGe and LaBr3(Ce) detectors. Precise lifetimes could be determined by analysing the γ-γ time difference spectra using the generalized centroid difference method. This picosecondsensitive method provides many advantages and is briefly explained. Still, the major source of systematic errors is related to the contribution of time-correlated Compton background. The EXILL&FATIMA results are discussed with respect to the typical energy-dependent timing behaviour of the background. According to the time response of the background, appropriate methods and a time correction for the sub-nanosecond regime are proposed.

Borehole field calibration and measurement of low‐concentration manganese by decay gamma rays

The manganese concentration in the Arundel clay formation, Prince Georges County, Maryland, was determined from a borehole by using delayed neutron activation. The neutrons were produced by a [Formula: see text] source. The 847 keV gamma ray of manganese was detected continuously, and its counting rate was measured at intervals of 15 s as the measuring sonde was moved at a rate of 0.5 cm/s. The technique measured the concentration ratio of manganese to aluminum. This ratio, when combined with an estimate of the aluminum concentration of the clay, made it possible to determine the percentage concentration of manganese without using a test‐pit calibration facility. The measurements were made by using an NaI(Tl) scintillation detector and a Ge(HP) solid‐state detector cooled by solid propane. A two‐pass technique had to be used with the scintillation detector because Compton background from the 1 779 keV photopeak of aluminum masked the manganese line. The Compton background did not interfere when the solid‐state detector was used. The borehole measurements compared favorably with a chemical core analysis and were unaffected by water in the borehole.

A Theoretical and Laboratory Evaluation of Carbon Logging - Laboratory Evaluation

Results we presented from a laboratory experimental evaluation of a carbon well-logging tool based on the detection of the 4.43-MeV gamma rays produced by the inelastic scattering of 14-MeV neutrons. The success of a carbon logging tool is dependent primarily upon the gamma-ray detection scheme used, which in this investigation is a two-crystal pair spectrometer. Using such a device in a simulated reservoir with and without casing and a cement annulus, semiquantitative detection of carbon was accomplished for a fluid-filled packed sand of 35-percent porosity. Analysis of the spectral results show that the log would be sensitive to lithology, saturation and porosity as well as carbon. With the resolution of this particular gamma-ray detector scheme, the presence of the casing using seen, but did not interfere with the carbon signal. Likewise the 1-in. annulus of concrete had no effect on the carbon detection. Comparison of our results with those previously published show that the oxygen and silicon interference encountered i, other proposed logging schemes is eliminated by the two-crystal pair spectrometer. As presently envisaged, between 5 to 10 minutes per pay zone to be evaluated is required to per pay zone to be evaluated is required to accumulate raw data. However, the growth potential offered by the new Ge(Li) gamma-ray counters may well remove this restriction. Introduction Theoretical results presented in Ref. 1 have indicated that liquid hydrocarbons should be detectable in noncarbonaceous reservoirs. Although the interference problem posed by energy degraded gamma rays from omnipresent oxygen is severe, it is not severe enough to prohibit detection of hydrocarbons by nuclear means. The theoretical data also showed thermal neutron effects caused by energy degradation of gamma rays from thermal capture in silicon, chlorine and iron could be eliminated by proper choice of a neutron source gamma detector gating scheme. Indeed, this has been demonstrated experimentally. The crux of the hydrocarbon detection problem lies with finding a gamma detector system with sufficient resolution to pick out 4.43-MeV gamma rays (carbon) from the background provided by oxygen. Previous investigations have shown that single NaI(T1) crystal detectors did not have sufficient energy resolution to accomplish the task. However, energy resolution is not the whole answer when it comes to extracting a monoenergetic signal from a continuum background. In addition to the interfering gamma rays produced through Compton collisions external to the detector system, there is an in-crystal Compton background in single-crystal spectrometry. The second source of interference arises because gamma rays entering the crystal at energies higher than the discrete energy of interest will produce Compton collisions within the crystal generating electrons that have precisely the same energy as that of the "desired signal". This second source of interference significantly reduces the carbon sensitivity of a single-crystal detector. Hence, elimination of the in-crystal background from oxygen produced gamma rays would go far in improving the in-situ carbon detection picture. In searching for an acceptable detector system, this point was kept foremost in mind. It was known a three-crystal pair spectrometer would virtually eliminate the in-crystal Compton background, but limitations imposed by borehole tool size ruled out its use. However, from studying the working principle of this device the concept of the principle of this device the concept of the two-crystal pair spectrometer emerged. A description of such a device was later found in Ref. 4 although no evidence has been found that such a device has been used to record spectra in a borehole or simulated borehole environment. This report presents experimental results obtained with such a presents experimental results obtained with such a two-crystal spectrometer in various simulated reservoir conditions. SPEJ P. 129