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Characterization of a novel, short pulse laser-driven neutron sourcea)
a)Paper YI2 4, Bull. Am. Phys. Soc. , 369 (2012).
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) Experimental setup inside the target chamber. The laser is hitting a CH or CD foil and generates the driving proton or deuteron beam. This beam is deposited in a Be-converter on the laser propagation axis behind the target. (b) Global experimental setup. Around the target chamber, a variety of diagnostics for laser pulse and neutron beam characterization are placed. For the latter nTOF, spectrometers consisting of a plastic scintillator coupled to PMT, bubble detectors, and a neutron-imager are used. Not shown is the iWASP that has been used to analyze the driving ion right beam behind the target prior to the actual experiment.

Image of FIG. 2.
FIG. 2.

Angularly resolved deuteron spectrum from −0.5° to 16.5°, measured in a plane parallel to the laser polarization axes. 0° is laser and target normal. The flux is color coded in PSL/MeV/msr.

Image of FIG. 3.
FIG. 3.

Schematic depiction of the nuclear activation-based imaging spectroscopy. The black squares show auto-radiography scans of different layers of the copper stack. Each layer corresponds to small energy window, depending on the position of the layer on the stack and its thickness. The center energy is noted in the top of each square. Brighter colors correspond to higher signal.

Image of FIG. 4.
FIG. 4.

Sensitivity of BTI-BND bubble detector units (1 bubble/mrem calibration) for different neutron energies. Experimental data are derived from Refs. . The sensitivity is reduced by more than a factor of three for neutron energies exceeding 30 MeV.

Image of FIG. 5.
FIG. 5.

Typical nTOF signal recorded with a fast digital oscilloscope. The blue solid line is the raw scope trace. The red solid line shows the raw neutron spectrum, accounting for the gamma flash, which serves as time reference (the green solid line).

Image of FIG. 6.
FIG. 6.

Spectral response of the nTOF detectors as a function of the neutron energy for different thicknesses of lead shielding.

Image of FIG. 7.
FIG. 7.

Neutron image of an arrangement of 3 tungsten blocks of different dimensions as measured with the scintillator in the neutron imager. The imager started to record 31 ns after the x-ray/gamma flash. The gate time of 80 ns made the detector sensitive to neutron energies between 2.5 MeV and 15 MeV. Brighter grey scales correspond to higher neutron signal.

Image of FIG. 8.
FIG. 8.

Typical deuteron spectrum from a 400 nm CD foil target. The spectrum is an average from 6° to 8° of an angularly resolved measurement such as shown in Fig. 2 . Numbers are approximated based on image plate calibrations published in Refs. .

Image of FIG. 9.
FIG. 9.

Neutron spectra from a 400 nm CH foil (red) and a 480 nm CD foil (blue), measured with an nTOF detector. Peak flux is around 4 MeV with maximum neutron energies of 15 MeV for the CH neutron spectrum. For the CD target, neutron flux peaks between 10 MeV and 20 MeV with maximum neutron energies of close to 100 MeV.

Image of FIG. 10.
FIG. 10.

Left side: Polar plot of the neutron distribution measured with bubble detectors using a 3.2 m CD driver target. The distribution is nearly isotropic. At this thickness, where TNSA is dominant, acceleration of deuterons is very inefficient and hence there is no forward component in the distribution. Right side: Polar plot of the neutron distribution from a 400 nm CD driver target. Two components are visible, an isotropic one from (d,n) and (p,(2)n) reactions and a strong forward directed one from deuteron break-up reactions. Far right side: Neutron spectra from nTOF-detectors at different positions around the target chamber for the 400 nm CD shot. The neutron spectrum in forward direction (upper plot) shows the highest neutron energies, with peak flux at 15 MeV and extending up to 60 MeV. The other detectors, middle and lower spectrum, show peak flux at a few MeV with maximum energies extending up to about 15 MeV, consistent with the results from CH shots.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Characterization of a novel, short pulse laser-driven neutron sourcea)