Neutron Pulse Duration Research Articles

ИССЛЕДОВАНИЕ УСИЛИТЕЛЬНЫХ СВОЙСТВ ОБЛУЧАЕМОЙ НЕЙТРОНАМИ ДВИЖУЩЕЙСЯ ГАЗОВОЙ СРЕДЫ, СОДЕРЖАЩЕЙ НАНОЧАСТИЦЫ УРАНА

The search for promising ways of nuclear energy usage has led to the emergence of a whole line of research on the direct conversion of the nuclear reaction products energy into laser radiation. In the present work, the amplifying properties of a spatially inhomogeneous nuclear-excited containing uranium nanoparticles moving argon-xenon medium irradiated by an inhomogeneous neutron field were studied. This work purpose is to investigate the dependence of the laser active medium amplifying properties on the initial gas mixture velocity, neutron pulse duration, and the neutron flux space-time distribution. As a short result, we could present the radial dependence of the laser radiation intensity gain at different points in time showed on the picture below. Summarizing laser radiation intensity gain calculations results: an active laser- medium with a length of 1 m provides a significant amplification (10 or more times) of the laser radiation in one pass. And it seems to be reasonable to continue studying the amplifying properties of such laser-active medium, considering the laser radiation’s wave nature.

Enhanced photoneutron production by intense picoseconds laser interacting with gas-solid hybrid targets

Experiments to enhance photoneutron production from the Ta (γ,xn) reaction with 100 TW picosecond laser pulses irradiating on gas-solid hybrid targets have been performed on the XingGuangIII laser facility at the Laser Fusion Research Center (LFRC) in Mianyang. The so-called gas-solid hybrid target was composed of a 1 mm thick N2 gas jet and a 2 cm thick Ta block. Picosecond laser pulses with intensities up to 1019 W/cm2 first interact with the tenuous gas to enhance the yields of high energy electrons through the direct laser acceleration (DLA) mechanism, and then through bremsstrahlung and subsequent (γ, n) reactions in a Ta converter, photoneutrons were enhanced effectively and the total number of neutrons was optimized by changing the gas density. A maximum neutron yield of 4 × 107/shot over 4π was achieved which is 200 times higher than that in the direct laser-solid interaction shot in our experiment. The spectrum of photoneutrons was measured which is in agreement with Monte Carlo (MC) simulation. From the size of the reaction area and the neutron pulse duration inferred from simulation, the corresponding flux was calculated to be 1.2 × 1016 n/cm2/s.

Thermal and Epithermal Neutron Generation for Nuclear Medicine Using Electron Linear Accelerator

In this paper, to obtain streams of thermal and epithermal neutrons are used delayed neutrons emitted from the target with a fissile material. The target preliminarily activated with help of electron beam from linear accelerator with an energy of 20 MeV and a power of 9 Watts. At the same time to obtain a stream of thermal as well as epithermal neutron density 6 10^-5 n / (cm^2 s) The results of experiment are presented where half-decay curves have been measured of emitting delayed neutrons radioactive nuclei produced in the fission process. It has been shown that the activated target, which contains the fissile material, presents a compact small size source of delayed neutrons. It can be delivered to the formator where thermal and epithermal neutrons are formed during a certain time period with help of the moderator, absorber and collimator. Then this target is moved to the activator being replaced with another target. Thus, pulsed neutron flux is produced. The duration of neutron pulse corresponds to the presence time of the activated target in the formator, and time interval between pulses is determined by the delivery time of the target from the activator to the formator. Given that the yield of neutrons from the target is directly proportional to the power of the beam of accelerated electrons, shows that the beam power of 1.5 - 3 kW, the flux density of thermal and epithermal neutrons can reach the values of (2-3) 10^9 n / (cm^2 s). Such a neutron beam can be used in nuclear medicine, in particular, in neutron capture therapy of oncologic diseases.

Neutron beam tailoring by means of a novel pulsed spatial magnetic spin resonator

Since long neutron spin resonance in an arrangement of crossed homogeneous and spatially alternating transversal magnetic fields is known to allow for wavelength-selective polarisation manipulation. Combined with a pair of highly efficient polarising supermirrors it is an elegant method to single out a specific wavelength from an initially polychromatic polarised neutron beam, based upon the fact that in its rest frame each neutron creates its individual frequency. A spin flip process can then take place only if this individual frequency equals the neutron LARMOR frequency in the homogeneous field. Here, we present the first experimental results we have obtained with a conceptually novel type of such spatial spin resonator, consisting of a series of separate modules which can be controlled independently from each other. Thus it becomes possible to vary e.g. the amplitude distribution of the spatially alternating transversal field without any geometric modification of the setup. Moreover this device fulfils the requirements for fast electronic switching of each module, which will be an important asset for the possible decoupling of the minimal neutron pulse duration and the achievable wavelength resolution. We compare the actual performance of this prototype resonator system with the theoretically expected behaviour.

Simulations of neutron emission in the irradiation of deuterated polyethylene by ultrahigh-intensity laser pulses

The neutron yield from deuterated polyethylene targets irradiated by ultrahigh-intensity laser pulses was calculated in a wide range of pulse energies. The resultant data are in better agreement with available experimental data than the data of the corresponding simulations performed by other authors earlier. The neutron pulse duration was shown to exceed the laser pulse duration by more than an order of magnitude. We also showed that the neutron yield accompanying the irradiation of a laminated target of deuterated polyethylene is, thanks to redistribution of deuteron fluxes in its volume, substantially higher in comparison with the irradiation of a continuous target

Transmission Bragg edge spectroscopy measurements at ORNL Spallation Neutron Source

Results of neutron transmission Bragg edge spectroscopic experiments performed at the SNAP beamline of the Spallation Neutron Source are presented. A high resolution neutron counting detector with a neutron sensitive microchannel plate and Timepix ASIC readout is capable of energy resolved two dimensional mapping of neutron transmission with spatial accuracy of ∼55 μm, limited by the readout pixel size, and energy resolution limited by the duration of the initial neutron pulse. A two dimensional map of the Fe 110 Bragg edge position was obtained for a bent steel screw sample. Although the neutron pulse duration corresponded to ∼30 mÅ energy resolution for 15.3 m flight path, the accuracy of the Bragg edge position in our measurements was improved by analytical fitting to a few mÅ level. A two dimensional strain map was calculated from measured Bragg edge values with an accuracy of ∼few hundreds μistrain for 300s of data acquisition time.

Design of a nanosecond beam bunching system

A nanosecond proton bunching system has been constructed at Korea Institute of Geoscience and Mineral Resources (KIGAM). This pulsed ion beam will be converted into corresponding duration of neutron pulse, which can reduce the scattered neutron background during neutron spectroscopy. The pulsed beam is obtained by deflection and double bunching by RF field. RF fields are applied to deflection and bunching electrodes as 2 kV p-p, 4 MHz and 2 kV p-p, 8 MHz, respectively. A push-pull RF amplifier has been designed and constructed with a maximum output power of 300 W continuous wave (CW) between 2 and 30 MHz. The main parameters of bunching beam were as follows: 8 MHz repetition rate, 2 ns FWHM, approximately 20% of duty factor and the maximum energy spread of 2 keV within a pulse.

New approaches in plasma neutron sources

Possibilities to improve yield parameters of compact neutron sources (∼1 m) based on ion acceleration in plasma systems, including laser-produced plasma bundles, are considered. Among such systems, generating d–d and d–t neutrons, are the same: (a) high voltage discharge with inertial confinement in laser plasma intrinsic electrical fields; (b) conical shock wave propagation in laser-produced plasma on a solid conical cavity target with a strong axial magnetic field; (c) non-stationary laser plasma, produced by interaction of intensive laser irradiation with solid targets. The laser-produced plasma is used as a neutron target or a medium for deuteron collective acceleration. Preliminary results have pointed that in the pulse operation mode of the (a) and (b) systems it is possible to reach a neutron yield of up to 108–109 n/pulse (d–t reaction) without using the traditional combination of a solid neutron target and ion acceleration by an external electrical field. The neutron pulse duration is more than 10 μs and the device power consumption is about a few kJ/pulse. Some schemes of the presented neutron sources are discussed. The neutron-emitting part of such a source may be a few cubic cm in size.

Neutron Production in a High-Power Pinch Apparatus

Neutrons produced in a pinched discharge in deuterium in the LASL device, the Columbus II, are reported on. This device is designed to operate above 60 kv, but the neutrons and the characteristic voltage or current fluctuations which identify the discharge disappear above 55 kv. The dependence of neutron yield on applied magnetic field, He contamination, gas pressure and voltage, as well as the long neutron pulse-duration, suggests a mechanism of neutron production different from the usual instability process. However, it is clear from the anistropy in the neutron energy spectrum at 200-gauss axial magnetic field that directed motion of the reacting deuteron system exists. (M.H.R.)