Pulse-mode measurement of electron beam halo using diamond-based detector

Using a diamond-based detector, the electron beam halo in a high-energy accelerator can be measured with a lower detection limit than that using other instruments, such as a core monitor, a dose meter, or an optical fiber. We have successfully measured an electron beam halo using diamond-based detectors operating in the ionization mode, which were installed in the beam duct to measure the intensity of the beam halo directly. Pulse-by-pulse measurements were adopted to suppress the background noise efficiently. Feasibility tests on the diamond-based detector and beam halo monitor were performed in the beam dump area of the 8 GeV SPring-8 synchrotron booster and at the 250 MeV SPring-8 Compact SASE Source test accelerator for the SPring-8 Angstrom Compact free electron LAser (SACLA), respectively. We achieved a lower detection limit of 2×10^{3}  electrons/pulse for single-shot measurement, which corresponds to a ratio of about 10^{-6} relative to the typical charge of the beam core of 0.3 pC. We also confirmed the feasibility of the electron beam halo monitor for use as an interlock sensor to protect undulator permanent magnets used in SACLA from radiation damage

Measurement of neutron energy spectra for Eg=23.1 and 26.6 MeV mono-energetic photon induced reaction on natC using laser electron photon beam at NewSUBARU

Photo-neutron energy spectra for Eg=23.1 and 26.6 MeV mono-energetic photons on natC were measured using laser Compton scattering facility at NewSUBARU BL01. The photon energy spectra were evaluated through measurements and simulations with collimator sizes and arrangements for the laser electron photon. The neutron energy spectra for the natC(g,xn) reaction were measured at 60 degrees in horizontal and 90 degrees in horizontal and vertical with respect to incident photon. The spectra show almost isotropic angular distribution and flat energy distribution from detection threshold to upper limit defined by reaction Q-value

Measurement of neutron spectra for photonuclear reaction with linearly polarized photons

Spectra of neutrons produced by a photonuclear reaction from a 197Au target were measured using 16.95 MeV linearly and circularly polarized photon beams at NewSUBARU-BL01 using a time-of-flight method. The difference in the neutron spectra between the cases of a linearly and circularly polarized photon was measured. The difference in the neutron yield increased with the neutron energy and was approximately threefold at the maximum neutron energy. In a direction perpendicular to that of the linear polarization, the neutron yields decreased as the neutron energy increased

Measurement of neutron spectra for photonuclear reaction with linearly polarized photons

Spectra of neutrons produced by a photonuclear reaction from a 197Au target were measured using 16.95 MeV linearly and circularly polarized photon beams at NewSUBARU-BL01 using a time-of-flight method. The difference in the neutron spectra between the cases of a linearly and circularly polarized photon was measured. The difference in the neutron yield increased with the neutron energy and was approximately threefold at the maximum neutron energy. In a direction perpendicular to that of the linear polarization, the neutron yields decreased as the neutron energy increased

Measurement of neutron energy spectra for E

Photo-neutron energy spectra for Eg=23.1 and 26.6 MeV mono-energetic photons on natC were measured using laser Compton scattering facility at NewSUBARU BL01. The photon energy spectra were evaluated through measurements and simulations with collimator sizes and arrangements for the laser electron photon. The neutron energy spectra for the natC(g,xn) reaction were measured at 60 degrees in horizontal and 90 degrees in horizontal and vertical with respect to incident photon. The spectra show almost isotropic angular distribution and flat energy distribution from detection threshold to upper limit defined by reaction Q-value

Comparison of double-differential cross-section between nuclear data library and experimental data for photoneutron production

In this study, we compared double differential cross-sections (DDXs) between the experimental data obtained by 16.6 MeV of polarized photons and the DDXs from JENDL2004 and JENDL/PD-2016.1 for 197Au, natPb, natCu, and natTi targets. Using Python-based software, we extracted the DDXs from the nuclear data libraries (NDLs), which were subsequently deduced considering the abundances of each target’s isotopes, the width of the photon beam, and the energy resolution of the neutron detectors. For the Ti target, the experimental DDX data were consistent with that of the NDLs. For Pb, Au, and Cu targets, the experimental DDX data at neutron energies higher than 4 MeV were larger than the DDX values obtained from the NDLs. The inconsistency between the DDXs of the experimental data and those of the NDLs indicates the need to improve the physical models to generate the spectrum of photoneutrons

Target mass dependence of photoneutron spectrum for 16.6 MeV photons on medium-heavy mass targets

We measured neutron energy spectra for the photonuclear reactions of 16.6 MeV linearly polarized photons on Pb, Au, Sn, Cu, Fe and Ti. The spectra for each target show dependence on the target mass, as well as on the angle between the directions of neutron emission and polarization. The components show angular dependence were extracted from the spectra for each target and compare with the excited levels of residual nuclei. Based on the data, we discuss a plan for further experiments to clearly observe the features of the spectra

Visualization of light-emitting diode lighting damage process in radiation environment by an in situ measurement

We investigated the radiation damage process of commercially available light-emitting diode (LED) lightings in an X-ray radiation environment such as the electron storage ring SPring-8. It was found that metal-oxide-semiconductor field-effect transistors (MOSFETs) in the LED power supplies were damaged by X-ray irradiation by the total dose effect greater than several hundred Gy (air kerma). To visualize the whole damage process, we performed in situ measurement of the MOSFET under an irradiation from an X-ray tube. The result clearly showed a sudden increase of the off-state drain current accompanying with a sharp increase of MOSFET temperature as a function of radiation dose, which eventually caused the device failure. We supposed from the result a significant increase of device lifetime by switching off the LED power supply and experimentally verified it by observing the increase of lifetime by an order of magnitude or more under the same irradiation condition. The revealed X-ray radiation damage process is expected to provide useful tips for employing LED lightings in X-ray radiation environments

Electron beam halo monitor for a compact x-ray free-electron laser

An electron beam halo monitor using diamond-based detectors, which are operated in the ionization mode, has been developed for the SPring-8 Angstrom compact free-electron laser (SACLA) to protect its undulator magnets from radiation damage. Diamond-based detectors are inserted in a beam duct to measure the intensity of the beam halo directly. To suppress the degradation of the electron beam due to the installation of the beam halo monitor, rf fingers with aluminum windows are newly employed. We evaluated the effect of radiation from the Al windows on the output signal both experimentally and by simulation. The operational results of the beam halo monitor employed in SACLA are presented