The p-process in type-II supernovae

The nucleosynthesis of heavy proton-rich nuclei in a stellar photon bath at temperatures of the astrophysical $\gamma$-process was investigated where the photon bath was simulated by the superposition of bremsstrahlung spectra with different endpoint energies. The method was applied to derive ($\gamma$,n) cross sections and reaction rates for several platinum isotopes.

https://arxiv.org/pdf/nucl-ex/0007003.pdf

Experimental simulation of a stellar photon bath by bremsstrahlung: the astrophysical $\gamma$-process

The accelerator safety interlock system (ASIS) for XFEL/SPring-8 protects personnel from radiation hazards. The ASIS consists of three independent systems: central, emergency, and beam-route interlocks. If the ASIS detects an unsafe status, it turns off the permission signal for accelerator operation, thereby stopping the electron beams. The delay time for the permission signal propagation must be less than 16.6 ms. Furthermore, reliability and stability of the personnel protection system are indispensable. Therefore, we have used programmable logic controllers for stability and developed optical modules for fast signal transmission. In this paper, we describe the system design of the ASIS.

System design of accelerator safety interlock for the xfel/spring-8

Pair production was first observed in 1932, which led to two early Nobel prizes in physics, to Carl Anderson for the discovery of positrons (1936) and to Paul Dirac for the theory of anti particles (1933). Science textbooks state that the production of electron-positron pairs is possible at photon energies above 1.022 MeV, which is the sum of the rest masses of the particles involved. Measurements at the threshold require a selectable photon energy in the range above 1 MeV, high-energy resolution to scan the onset, and high intensities. Due to the need of simultaneous energy and momentum conservation, pair production needs a recoiling particle, and thus it can be observed most easily in solid matter. More exactly, the minimum energy required for pair production is given by the relation E γ ≥ 2 mec 2(1 + me /mr ), where mr is the mass of the recoiling particle [1]. With the particle rest energy of me = 511 keV/c2 , in heavy atoms we get mr >> me , and thus in a good approximation photon energies E γ ≥ 2·me...

The Miracle of the Electron-Positron Pair Production Threshold

We have re-engineered the data acquisition system for SPring-8 radiation monitors. The previous system consisted of dedicated digital indicator/controller modules (DICMs) optically linked with radiation monitors, embedded PCs for data acquisition, and programmable logic controllers (PLCs) for 1-h integrated dose surveillance. The embedded PCs periodically collected radiation data from the DICMs through GPIB. The DICMs and the dose surveillance PLCs were interfaced with an accelerator radiation safety interlock system (ARSIS). These components were dedicated, blackboxed, and complicated for operations. The GPIB interface was legacy and not reliable enough for the critical system. Therefore, we re-engineered the previous system by adopting PLCs and FL-net. Local PLCs were deployed as substitutes for all the previous embedded PCbased components. Another PLC was installed to enable centralized management of all 81 monitors. All the new PLCs and a VME computer for data acquisition were connected via FL-net networks. In this paper, the new system and a method for upgrading this system within the short shutdown interval of the accelerator operations are described.

Re-engineering of the spring-8 radiation monitor data acquisition system

An accelerator radiation safety system (accelerator safety interlock system) that protects users from radiation hazards induced by electron beams and synchrotron radiation has been operating for over a decade at SPring8. The working of the accelerator safety interlock system for SPring-8 is based on the operation mode control system. The working of the latter system became complicated because the number of “operation modes” increased over time in accordance with SPring-8 upgrades. Therefore, we are planning to construct a new accelerator safety interlock system. Here, we report the status of the current safety interlock system and the conceptual design of the new one. This upgrade is scheduled for the summer of 2010.

/pdf/upgrade-of-accelerator-radiation-safety-system-for-spring-8-4dvjuu15qa.pdf

Upgrade of accelerator radiation safety system for spring-8

The universe is filled with cosmic microwave background radiation at 2.73 K (Figure 1). It is a relic of the “fire-ball” that the universe once underwent shortly after its birth. This is the lowest-temperature black-body radiation that mankind has ever witnessed. Where can we expect highest-temperature black-body radiations? An answer may be found in the explosion of massive stars. Stars more massive than 10 solar masses that are destined to die as type II supernovae (Figure 2) evolve to form an onion-like pre-supernova structure consisting of multi-layers of hydrogen, helium, carbon, silicon, and the iron core as dominant elements. The gravitational collapse of the iron core triggers the explosion. Typically energy of about 1% (~1051 erg) of the gravitational energy is sufficient to explode massive stars, blowing off the outer layers and leaving neutron-stars (black-holes) as remnants. During the supernova explosion, the shock wave propagates the outer layers and heats material behind it, making, for exa...

10 Tesla Superconducting Wiggler at SPring-8: Source of Black-Body Radiations at Multi-Billions of Kelvin on Earth

The bunch purification of a singlet bunches for the SPring-8 storage ring is performed at the booster synchrotron, by clearing out electrons in neighbouring RF buckets by RF kick (RFKO). The injection period to the storage ring at top-up operation is tens seconds and is not fixed; however the booster is currently running at 1 Hz to stabilize the booster machine parameters. To save energy and the operation cost, we intend the on-demand operation of the booster at injection, however the large tune drift was observed in the on-demand operation and this drift drives the tune to off-resonance of the RFKO frequency. To overcome this tune drift, we are developing a tune tracking RFKO bunch cleaning system with transverse bunch-by-bunch feedback. In this system, the betatron oscillation of the main bunch is excited by positive feedback and the signal from the feedback excites the RFKO system, thus the frequency of the RFKO system is locked to the tune.

H. Yonehara

Papers

Upgrade of accelerator radiation safety system for spring-8

10 Tesla Superconducting Wiggler at SPring-8: Source of Black-Body Radiations at Multi-Billions of Kelvin on Earth

Tune tracking rfko bunch purification with bunch-by- bunch feedback at spring-8