New transitions and feeding of the J\u3csup\u3eπ\u3c/sup\u3e=(8\u3csup\u3e+\u3c/sup\u3e) isomer in \u3csup\u3e186\u3c/sup\u3eRe

The spallation neutron source at the Los Alamos Neutron Science Center Weapons Neutron Research facility was used to populate excited states in 186Re via (n,2nγ) reactions on an enriched 187Re target. Gamma rays were detected with the GErmanium Array for Neutron Induced Excitations spectrometer, a Compton-suppressed array of 18 HPGe detectors. Incident neutron energies were determined by the time-of-flight technique and used to obtain γ-ray excitation functions for the purpose of identifying γ rays by reaction channel. Analysis of the singles γ-ray spectrum gated on the neutron energy range 10≤En≤25MeV resulted in five transitions and one level added to the 186Re level scheme. The additions include the placement of three γ rays at 266.7, 381.2, and 647.7 keV which have been identified as feeding the 2.0×105yr, Jπ=(8+) isomer and yield an improved value of 148.2(5)keV for the isomer energy. These transitions may have astrophysical implications related to the use of the Re-Os cosmochronometer. Abstract © APS

Topological and measurable issues of the dynamics of interval maps

In this thesis we study one-dimensional dynamics. That is we study the iterations of interval maps. We prove that every piecewise monotone interval map which is expanding and satisfies a Markov condition is topologically conjugate with one piecewise linear interval map. Furthermore if the map is continuous we calculate the topological entropy. Finally we give a complete description of the dynamics of a piecewise linear map with two brances: one expanding and one contracting.Στην παρούσα διδακτορική διατριβή μελετάμε θέματα μονοδιάστατης δυναμικής. Με τον όρο μονοδιάστατη δυναμική εννοούμε τη δυναμική που προκύπτει από τις επαναλήψεις μιας συνάρτησης που απεικονίζει ένα διάστημα των πραγματικών αριθμών στον εαυτό του. Αποδεικνύουμε ότι μια κατά τμήματα μονότονη, επεκτατική συνάρτηση που πληροί τη συνθήκη Markov είναι τοπολογικά ισοδύναμη με μια κατά τμήματα γραμμική συνάρτηση. Αν επιπλέον η συνάρτηση είναι συνεχής τότε δίνουμε μια μέθοδο υπολογισμού της τοπολογικής εντροπίας. Ακόμη δίνουμε μια πλήρη περιγραφή της δυναμικής που προκύπτει από τις επαναλήψεις μιας συνάρτησης που είναι κατά τμήματα γραμμική και αποτελείται από δύο κλάδους: έναν επεκτατικό και ένα συσταλτικό

The total kinetic energy release in the fast neutron-induced fission of

The post-emission total kinetic energy release (TKE) in the neutron-induced fission of 232Th was measured (using white spectrum neutrons from LANSCE) for neutron energies from $E_{n} = 3$ to 91MeV. In this energy range the average post-neutron total kinetic energy release decreases from $162.3 \pm 0.3$ at $E_n = 3$ MeV to $154.9 \pm 0.3$ MeV at $E_n = 91$ MeV. Analysis of the fission mass distributions indicates that the decrease in TKE with increasing neutron energy is a combination of increasing yields of symmetric fission (which has a lower associated TKE) and a decrease in the TKE release in asymmetric fission

Applications of (CLYC)-L-7 scintillators in fast neutron spectroscopy

The capabilities of Li-enriched Cs LiYCl (CLYC) scintillation detectors for fast neutron spectroscopy are explored in benchmark experiments that exploit its excellent pulse-shape discrimination between neutrons and rays, and its unprecedented 10% energy resolution for fast neutrons in the few MeV range, obtained through the 35Cl(n,p) reaction. Energy- and angle-resolved elastic and inelastic neutron scattering cross-section measurements of 56Fe(n,n') were performed at Los Alamos National Laboratory with a pulsed white neutron source and an array of CLYC crystals. The results convincingly establish the utility of this dual n/ scintillator for fast neutron spectroscopy. Intrinsic efficiency measurements of both and the first ever CLYC crystal have been initiated, using mono-energetic fast neutron beams at UMass Lowell generated via the Li(p,n) reaction. The spectroscopic capabilities and potential of CLYC are discussed in the context of developing this emerging scintillator for targeted science applications.The work was supported by the U.S. Department of Energy (DOE) NNSA Stewardship Science Academic Alliance program Grants DE- NA0001988 and DE-NA0002932, and Office of Science Grant DE-FG02-94ER40848. Portions of this work benefited from use of the LANSCE accelerator facility supported under DOE Contract No. DE- AC52-06NA2539

Experimental Prompt Fission Neutron Spectra Comparisons for the

The Chi-Nu project to measure prompt fission neutron energy spectra for the major actinides has now completed two measurements, for neutron-induced fission of 239Pu and 235U for incident neutron energies from 1 to 20 MeV, and has almost completed the prompt fission neutron spectrum measurement for 238U. In addition, similar data have been taken for spontaneous fission in some other isotopes, and a measurement of fission neutron spectra from 240Pu(n, f ) is in progress. These measurements are done at the same facility, with the same equipment and analyzed in a similar way. A useful way to look at such data is to examine ratios of the prompt fission neutron spectra among actinides, as some of the experimental uncertainties involved in these data are the same from isotope to isotope, making the ratios of fission neutron spectra less dependent on the experimental and analysis details. We discuss here the ratios of prompt fission neutron spectra between 239Pu(n, f ) and 235U(n, f ) , as well as the evolution of the mean fission neutron energy for 239Pu(n, f ) and 235,238U(n, f ) with increasing incident neutron energy

Prompt Fission Neutron Spectra for Neutron-Induced Fission of 239Pu and 235U

We report the current results of a large effort to accurately measure the Prompt Fission Neutron Spectra (PFNS) for neutron-induced fission of 235U and 239Pu for incident neutrons with energies from 1 to 20 MeV. The Chi-Nu experiment at the Los Alamos Neutron Science Center used an unmoderated, white spectrum of neutrons to induce fission in actinide samples that were placed inside a parallel plate avalanche counter to provide a fast fission signal. A double time-of-flight technique was used to determine the incoming and outgoing neutron energies. Two neutron detector arrays, one with 54 liquid scintillators and another with 22 lithium glass detectors, were used to detect the outgoing neutrons and measure the PFNS distributions over a wide range in outgoing neutron energy, from below 100 keV to 10 MeV. Extensive Monte Carlo modeling was used to understand the experiment response and extract the PFNS. Systematic errors and uncertainties in the method have been examined and quantified. A summary of these results for incoming energies from 1 to 5 MeV is presented here

Prompt Fission Neutron Spectra for Neutron-Induced Fission of

We report the current results of a large effort to accurately measure the Prompt Fission Neutron Spectra (PFNS) for neutron-induced fission of 235U and 239Pu for incident neutrons with energies from 1 to 20 MeV. The Chi-Nu experiment at the Los Alamos Neutron Science Center used an unmoderated, white spectrum of neutrons to induce fission in actinide samples that were placed inside a parallel plate avalanche counter to provide a fast fission signal. A double time-of-flight technique was used to determine the incoming and outgoing neutron energies. Two neutron detector arrays, one with 54 liquid scintillators and another with 22 lithium glass detectors, were used to detect the outgoing neutrons and measure the PFNS distributions over a wide range in outgoing neutron energy, from below 100 keV to 10 MeV. Extensive Monte Carlo modeling was used to understand the experiment response and extract the PFNS. Systematic errors and uncertainties in the method have been examined and quantified. A summary of these results for incoming energies from 1 to 5 MeV is presented here

Measurements of the Prompt Fission Neutron Spectrum at LANSCE: The Chi-Nu Experiment

The goal of the Chi-Nu experiment at the Los Alamos Neutron Science Center is to measure the prompt fission neutron spectra from major actinides using a double time-of-flight method with a pulsed, white incoming neutron source. Fission events are detected with a parallel-plate avalanche counter and outgoing neutrons are detected with either a 6Li-glass or liquid scintillator detector array for low- or high-energy neutrons, respectively. A detector response matrix for the interaction of neutrons with the experimental environment for neutrons measured with the Chi-Nu 6Li-glass detector array has been calculated to obtain a full understanding of the measured Chi-Nu data and also to allow for nearly instantaneous production of simulated Chi-Nu data spectra. Prompt fission neutron spectra corresponding to 19 incoming neutron energy ranges from 0.7-20 MeV have been extracted using the ratio-of-ratios method with Chi-Nu 6Li-glass data on the neutron-induced fission of 235U

Measurements of the Prompt Fission Neutron Spectrum at LANSCE: The Chi-Nu Experiment

The goal of the Chi-Nu experiment at the Los Alamos Neutron Science Center is to measure the prompt fission neutron spectra from major actinides using a double time-of-flight method with a pulsed, white incoming neutron source. Fission events are detected with a parallel-plate avalanche counter and outgoing neutrons are detected with either a 6Li-glass or liquid scintillator detector array for low- or high-energy neutrons, respectively. A detector response matrix for the interaction of neutrons with the experimental environment for neutrons measured with the Chi-Nu 6Li-glass detector array has been calculated to obtain a full understanding of the measured Chi-Nu data and also to allow for nearly instantaneous production of simulated Chi-Nu data spectra. Prompt fission neutron spectra corresponding to 19 incoming neutron energy ranges from 0.7-20 MeV have been extracted using the ratio-of-ratios method with Chi-Nu 6Li-glass data on the neutron-induced fission of 235U