Tianjiao Liang

Hot electron generation via vacuum heating process in femtosecond laser–solid interactions

Hot electron generation by the vacuum heating process has been studied in the interaction of 150 fs, 5 mJ, 800 nm P-polarized laser pulses with solid targets. The measurements have suggested that the “vacuum heating” is the main heating process for the hot electrons with high energies. The energy of the vacuum-heated hot electrons has been found to be higher than the prediction from the scaling law of resonance absorption. Particle-in-cell simulations have confirmed that the hot electrons are mainly generated by the vacuum heating process under certain experimental conditions.

Z-dependence of hot electron generation in femtosecond laser interaction with solid targets

Hot electron emission is studied using 798 nm, 150 fs, p-polarized laser pulses at 1 × 1016 W cm−2, irradiating on plastic (CH), aluminium (Al), titanium (Ti) and copper (Cu) planar targets. The dependence of hot electron generation on atomic number Z is observed experimentally.

The production of residual radionuclides by a 250 MeV proton beam

Radionuclide production was studied by bombarding Cu, W and Pb targets with a 250 MeV proton beam. The data were obtained by using the off-line γ-spectroscopy method. Six nuclides in Cu, 28 nuclides in W and 34 nuclides in Pb targets were identified and their cross sections were determined. The measured results were compared to other experiments with isotopic Cu and W targets. Corresponding simulations using the MCNPX transport code were also performed to compare the measurements. In the simulations, eight different models or combinations of intranuclear cascade and de-excitation models were introduced. The comparison indicated that most cross sections were fairly reliably predicted for nuclides in the spallation mass region, but differ greatly for nuclides in the medium and fission mass regions.

Study of an unfolding algorithm for D-T neutron energy spectra measurement using a recoil proton method

A proton recoil method for measuring D-T neutron energy spectra using polyethylene film and a Si(Au) surface barrier detector is presented. An iteration algorithm for unfolding the recoil proton energy spectrum to the neutron energy spectrum is investigated. The response matrices R of the polyethylene film at angles of 0 degrees and 45 degrees were obtained by simulating the recoil proton energy spectra from mono-energetic neutrons using the MCNPX code. With an assumed D-T neutron spectrum, the recoil proton spectra from the polyethylene film at angles of 0 degrees and 45 degrees were also simulated using the MCNPX code. Based on the response matrices R and the simulated recoil proton spectra at 0 degrees and 45 degrees, the respective unfolded neutron spectra were obtained using the iteration algorithm, and compared with the assumed neutron spectrum. The results show that the iteration algorithm method can be applied to unfold the recoil proton energy spectrum to the neutron energy spectrum for D-T neutron energy spectra measurement using the recoil proton method.

Study of shielding design for SANS at CSNS

The small angle neutron scattering (SANS) instrument is presently being constructed at Chinese Spallation Neutron Source (CSNS) in China, and the biological shielding design is needed to prevent the instrument from causing excessive dose rates in accessible locations. In this paper, the study of shielding design for SANS that relies on Monte Carlo simulation is introduced. Beam line shielding calculations are performed considering both scenarios of closed versus open TO chopper. The basic design scheme of the beam stop is discussed. The size of the TO chopper rotor is also estimated.

The high-energy multi-group HEST1.0 library based on ENDF/B-VII.0: development, verification and preliminary application

ENDF/B-VII.0, which was released by the USA Cross Section Evaluation Working Group (CSEWG) in December 2006, was demonstrated to perform much better than previous ENDF evaluations over a broad range of benchmark experiments. A high-energy (up to 150 MeV) multi-group library set named HEST1.0 with 253-neutron and 48-photon groups has been developed based on ENDF/B-VII.0 using the NJOY code. This paper provides a summary of the procedure to produce the library set and a detailed description of the verification of the multi-group library set by several shielding benchmark devices, in particular for high-energy neutron data. In addition, the first application of HEST1.0 to the shielding design of the China Spallation Neutron Source (CSNS) is demonstrated.

Target station status of China Spallation Neutron Source

For information and subscription rates, please email subscriptions@tandf.co.uk or see www. tandfonline.com/pricing/journal/gnnw. This journal is available via a traditional institutional subscription (either print with online access, or online only at a discount) or as part of our libraries, subject collections, or archives. For more information on our sales packages, please visit www.tandf online.com/page/librarians. All current institutional subscriptions include online access for any number of concurrent users across a local area network to the selected backfi le and articles posted online ahead of publication. Subscriptions purchased at the personal rate may not include online access and are strictly for personal, noncommercial use only. The reselling of personal subscriptions is prohibited. Personal subscriptions must be purchased with a personal check or credit card. Proof of personal status may be requested. Neutron News

Investigation of ortho↔para hydrogen conversion by collisions with neutrons

ABSTRACT Liquid hydrogen (LH) is constituted by para hydrogen (pH) and ortho hydrogen (oH) molecules. We analyzed the neutron scattering cross sections for pH→oH, pH→pH, oH→pH, and oH→oH reactions in LH. Results show that incident neutron energy lower than 14.7 meV is not sufficient to achieve pH→oH conversion. As energy increases, the cross section of pH→oH reaction increases sharply. If incident neutron energy is larger than 30 meV, branching fraction of pH molecules being converted into oH molecules upon inelastic scattering with the neutrons approaches 100%. As for the opposite process, branching fraction of oH→pH conversion is 10%–20% when incident neutron energy is lower than 30 meV. This conversion fraction oscillates with increasing incident neutron energy, eventually stabilizing at 30%. Based on the cross sections of the four reaction channels, we calculated the corresponding conversion rates based on a reactor cold neutron source model. There is 0.12% pH molecules of LH moderator would be converted to oH for one month operation . If neutron flux increased by 2 orders of magnitude, more than 10% pH would be transformed into oH, which means relative conversion rate of pH→oH induced by neutron inelastic scattering is not negligible.

Application of the first collision source method to CSNS target station shielding calculation

Ray effects are an inherent problem of the discrete ordinates method. RAY3 D, a functional module of ARES, which is a discrete ordinates code system, employs a semi-analytic first collision source method to mitigate ray effects. This method decomposes the flux into uncollided and collided components, and then calculates them with an analytical method and discrete ordinates method respectively. In this article, RAY3 D is validated by the Kobayashi benchmarks and applied to the neutron beamline shielding problem of China Spallation Neutron Source(CSNS)target station. The numerical results of the Kobayashi benchmarks indicate that the solutions of DONTRAN3 D with RAY3 D agree well with the Monte Carlo solutions. The dose rate at the end of the neutron beamline is less than10.83 μSv/h in the CSNS target station neutron beamline shutter model. RAY3 D can effectively mitigate the ray effects and obtain relatively reasonable results.Ray effects are an inherent problem of the discrete ordinates method. RAY3 D, a functional module of ARES, which is a discrete ordinates code system, employs a semi-analytic first collision source method to mitigate ray effects. This method decomposes the flux into uncollided and collided components, and then calculates them with an analytical method and discrete ordinates method respectively. In this article, RAY3 D is validated by the Kobayashi benchmarks and applied to the neutron beamline shielding problem of China Spallation Neutron Source(CSNS)target station. The numerical results of the Kobayashi benchmarks indicate that the solutions of DONTRAN3 D with RAY3 D agree well with the Monte Carlo solutions. The dose rate at the end of the neutron beamline is less than10.83 μSv/h in the CSNS target station neutron beamline shutter model. RAY3 D can effectively mitigate the ray effects and obtain relatively reasonable results.

Validation of source biasing method for its use in CSNS beamline shielding calculation

The Chinese spallation neutron source (CSNS) is a high-performance pulsed neutron source, having 20 neutron beamlines for neutron scattering instruments. The shielding design of these beamlines is usually needed for Monte Carlo (MC) calculation, and the use of variance reduction methods is critical to carrying out an efficient, reliable MC shielding calculation. This paper discusses the source biasing method based on actual source term and geometry model of a CSNS neutron beamline. Dose distribution throughout the geometry model was calculated with the FLUKA MC code. Full analogue calculation and biased calculation were compared, and it was validated that the source biasing method can effectively promote the calculation efficiency.