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Register a new userGEANT4 simulation of the neutron background of the C$_6$D$_6$ set-up for capture studies at n_TOF
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The neutron sensitivity of the C$_6$D$_6$ detector setup used at n_TOF for capture measurements has been studied by means of detailed GEANT4 simulations. A realistic software replica of the entire n_TOF experimental hall, including the neutron beam line, sample, detector supports and the walls of the experimental area has been implemented in the simulations. The simulations have been analyzed in the same manner as experimental data, in particular by applying the Pulse Height Weighting Technique. The simulations have been validated against a measurement of the neutron background performed with a $^mathrm{nat}$C sample, showing an excellent agreement above 1 keV. At lower energies, an additional component in the measured $^mathrm{nat}$C yield has been discovered, which prevents the use of $^mathrm{nat}$C data for neutron background estimates at neutron energies below a few hundred eV. The origin and time structure of the neutron background have been derived from the simulations. Examples of the neutron background for two different samples are demonstrating the important role of accurate simulations of the neutron background in capture cross section measurements.
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Electronic spectra of C$_6$H are measured in the $18,950-21,100$ cm$^{-1}$ domain using cavity ring-down spectroscopy of a supersonically expanding hydrocarbon plasma. In total, 19 (sub)bands of C$_6$H are presented, all probing the vibrational manifold of the B$^2Pi$ electronically excited state. The assignments are guided by electronic spectra available from matrix isolation work, isotopic substitution experiments (yielding also spectra for $^{13}$C$_6$H and C$_6$D), predictions from ab initio calculations as well as rotational fitting and vibrational contour simulations using the available ground state parameters as obtained from microwave experiments. Besides the $0_0^0$ origin band, three non-degenerate stretching vibrations along the linear backbone of the C$_6$H molecule are assigned: the $ u_6$ mode associated with the C-C bond vibration and the $ u_4$ and $ u_3$ modes associated with C$equiv$C triple bonds. For the two lowest $ u_{11}$ and $ u_{10}$ bending modes, a Renner-Teller analysis is performed identifying the $mu^2Sigma$($ u_{11}$) and both $mu^2Sigma$($ u_{10}$) and $kappa^2Sigma$($ u_{10}$) components. In addition, two higher lying bending modes are observed, which are tentatively assigned as $mu^2Sigma$($ u_9$) and $mu^2Sigma$($ u_8$) levels. In the excitation region below the first non-degenerate vibration ($ u_6$), some $^2Pi-^{2}Pi$ transitions are observed that are assigned as even combination modes of low-lying bending vibrations. The same holds for a $^2Pi-^{2}Pi$ transition found above the $ u_6$ level. From these spectroscopic data and the vibronic analysis a comprehensive energy level diagram for the B$^2Pi$ state of C$_6$H is derived and presented.
SF$_{6}$ is an inert and electronegative gas that has a long history of use in high voltage insulation and numerous other industrial applications. Although SF$_{6}$ is used as a trace component to introduce stability in tracking chambers, its highly electronegative properties have limited its use in tracking detectors. In this work we present a series of measurements with SF$_{6}$ as the primary gas in a low pressure Time Projection Chamber (TPC), with a thick GEM used as the avalanche and readout device. The first results of an $^{55}$Fe energy spectrum in SF$_{6}$ are presented. Measurements of the mobility and longitudinal diffusion confirm the negative ion drift of SF$_{6}$. However, the observed waveforms have a peculiar but interesting structure that indicates multiple drift species and a dependence on the reduced field ($E/p$), as well as on the level of water vapor contamination. The discovery of a distinct secondary peak in the waveform, together with its identification and use for fiducializing events in the TPC, are also presented. Our measurements demonstrate that SF$_{6}$ is an ideal gas for directional dark matter detection. In particular, the high fluorine content is desirable for spin-dependent sensitivity, negative ion drift ensures low diffusion over large drift distances, and the multiple species of charge carriers allow for full detector fiducialization.
The MUGAST-AGATA-VAMOS set-up at GANIL combines the MUGAST highly-segmented silicon array with the state-of-the-art AGATA array and the large acceptance VAMOS spectrometer. The mechanical and electronics integration copes with the constraints of maximum efficiency for each device, in particular {gamma}-ray transparency for the silicon array. This complete set-up offers a unique opportunity to perform exclusive measurements of direct reactions with the radioactive beams from the SPIRAL1 facility. The performance of the set-up is described through its commissioning and two examples of transfer reactions measured during the campaign. High accuracy spectroscopy of the nuclei of interest, including cross-sections and angular distributions, is achieved through the triple-coincidence measurement. In addition, the correction from Doppler effect of the {gamma}-ray energies is improved by the detection of the light particles and the use of two-body kinematics and a full rejection of the background contributions is obtained through the identification of heavy residues. Moreover, the system can handle high intensity beams (up to 108 pps). The particle identification based on the measurement of the time-of-flight between MUGAST and VAMOS and the reconstruction of the trajectories is investigated.
At the n_TOF experiment at CERN a dedicated single-crystal chemical vapor deposition (sCVD) Diamond Mosaic-Detector has been developed for (n,$alpha$) cross-section measurements. The detector, characterized by an excellent time and energy resolution, consists of an array of 9 sCVD diamond diodes. The detector has been characterized and a cross-section measurement has been performed for the $^{59}$Ni(n,$alpha$)$^{56}$Fe reaction in 2012. The characteristics of the detector, its performance and the promising preliminary results of the experiment are presented.
We describe the Monte Carlo (MC) simulation package of the `2K-CAPTURE setup and discuss the agreement of its output with data. The `2K-CAPTURE MC simulates the energy loss of particles in detector and components of the passive shield and generates the resulting response in working volume large proportional counter (LPC). The simulation accounts for absorption, reemission, and scattering of both photons and neutrons and tracks them until they either are absorbed. The algorithm proceeds with a detailed simulation of the electronics chain. The MC is tuned using data collected with radioactive calibration source deployed in the internal channel of the installation. The simulation reproduces the energy response of the detector corresponding to distribution of the generated pointwise clusters of a charge of primary ionization in LPC.
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