Deuterated Polyethylene Targets Research Articles

Optimisation of neutron yield under ultra-intense laser impact on deuterated polyethylene targets

The modelling of interaction of ultra-intense femtosecond laser pulses with deuterated polyethylene targets is carried out with the processes of multiple field ionisation of the target atoms and theemission of neutrons produced in the course of the fusion reaction at high-energy deuteron collisions taken into account. The possibility of essential increase in the neutron yield (by tens of times) when using layered deuterated polyethylene targets with optimal dimensions of the layers and interlayer separations ∼1 μm is demonstrated.

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

A new measurement of the astrophysical 8Li(d, t)7Li reaction

The excitation function of the 8Li(d, t)7Li reaction was directly measured using 8Li beam irradiating a deuterated polyethylene target at center-of-mass system beam energies (Ecm) between 0.3 and 1.2 MeV. This is the first cross section measurement of the above reaction below Ecm=1.5 MeV, covering Gamow peaks for 1–3×109 K of astrophysical interest. A broad resonance-like structure was observed at around Ecm=0.8 MeV. The astrophysical reaction rate deduced from the present result is far larger than the previously reported values estimated from extrapolation of data observed at higher energies, roughly by one order of magnitude at about 1×109 K.

Neutron production from interactions of high-intensity ultrashort pulse laser with a planar deuterated polyethylene target

The deuteron acceleration from a planar uniform deuterated polyethylene (CD2) target was studied with a two-dimensional electromagnetic particle-in-cell method in the ultrarelativistic regime for peak laser intensities between 1023 and 1025W∕m2. Under identical conditions the deuteron energy and angular distributions are very different when compared to that produced from a double-layer target. The neutron production from D(d,n)–He3 nuclear fusion reactions was also investigated with a three-dimensional Monte Carlo ion beam-target deposition model. The neutron yield and its angular distribution were studied as a function of peak laser intensity and laser pulse duration. A neutron yield of 104–106neutronsperJoule laser energy is inferred from simulations of a 4 μm thick planar uniform CD2 target. The angular scattering of neutrons is found to be nonisotropic and has a significant component in the forward (laser propagation) direction.

A new measurement of the astrophysical 8Li(α,n)11B reaction

Abstract The excitation function of the 8 Li(d, t) 7 Li reaction was directly measured using 8 Li beam irradiating a deuterated polyethylene target at center-of-mass system beam energies ( E cm ) between 0.3 and 1.2 MeV. This is the first cross section measurement of the above reaction below E cm = 1.5 MeV , covering Gamow peaks for 1 – 3 × 10 9 K of astrophysical interest. A broad resonance-like structure was observed at around E cm = 0.8 MeV . The astrophysical reaction rate deduced from the present result is far larger than the previously reported values estimated from extrapolation of data observed at higher energies, roughly by one order of magnitude at about 1 × 10 9 K .

Fast Neutron Emission from a High-Energy Ion Beam Produced by a High-Intensity Subpicosecond Laser Pulse

Neutron emission as high as ${10}^{7}$ is observed when a high intensity (a few ${10}^{19}\mathrm{W}/{\mathrm{cm}}^{2}$) subpicosecond laser pulse at 529 nm wavelength is focused on a deuterated polyethylene target. Neutron emission is also measured in different directions. The emission of neutrons along the laser axis is higher than in the transverse direction. Nonisotropic emission is consistent with neutrons generated by $\mathrm{D}(d,n){\ensuremath{-}}^{3}\mathrm{He}$ reaction for 0.3--1 MeV deuterons accelerated in the direction of the laser beam. The energy transferred to the ions is roughly estimated and compared with the energy carried out by the electrons.

Neutron production by 200 mJ ultrashort laser pulses

We report the observation of neutrons released from ${d(d,n)}^{3}\mathrm{He}$ fusion reactions in the focus of 200 mJ, 160 fs Ti:sapphire laser pulses on a deuterated polyethylene target. Optimizing the fast electron and ion generation by applying a well-defined prepulse led to an average rate of 140 neutrons per shot. Furthermore, the production of a substantial number of MeV \ensuremath{\gamma} rays could be observed. The occurrence of neutrons and \ensuremath{\gamma} rays is attributed to the formation and explosion of a relativistic plasma channel in the laser focus, which is confirmed by numerical calculations.

No evidence for enhanced (d,d) fusion under (CD4)n+ cluster impact.

Possible enhancement of (d,d) nuclear fusion rate under clusters impact has been investigated. (${\mathrm{CD}}_{4}$${)}_{\mathit{n}}^{+}$ cluster were sent onto deuterated polyethylene targets and protons resulting from fusion were detected. Using light clusters (n from 1 to 5) of constant velocity we measured essentially constant proton yields per incident deuteron, i.e., observed no deviation from binary (d,d) fusion cross sections. With heavier clusters (n=110,145) we could only determine upper limits of proton yields which seem to be entirely accounted for by beam contamination.

Fusion yields for carbon-cluster impact on CD2 targets.

Nuclear fusion yields for the secondary reaction D+D have been measured for carbon-atom anions and carbon-cluster anions incident on a deuterated polyethylene target for atom and cluster energies up to 324 keV. Comparison of the cluster- and atom-anion fusion yields per carbon at the same bombarding energy per carbon show no evidence of a collective enhancement for clusters as large as ${\mathrm{C}}_{19}$. The absolute yields can be reproduced by a knock-on model. An upper limit to the fusion yield for ${\mathrm{C}}_{7}$${\mathrm{D}}_{7}$${\mathrm{SO}}_{3}^{\mathrm{\ensuremath{-}}}$ bombardment has also been determined.

Experimental confirmation of cluster-impact fusion.

We have investigated deuteron-deuteron fusion induced by impact of (${\mathrm{D}}_{2}$O${)}_{\mathit{n}}^{+}$ and (${\mathrm{H}}_{2}$O${)}_{\mathit{n}}^{+}$ clusters with n=1\char21{}150 on deuterated polyethylene targets at energies of 135\char21{}225 keV. Both the energy dependence and magnitude of the fusion yield measured with (${\mathrm{D}}_{2}$O${)}_{115}^{+}$ clusters confirm the results of Beuhler et al. [J. Phys. Chem. 94, 7665 (1990)]. Furthermore, we have observed that the size dependence of the (${\mathrm{D}}_{2}$O${)}_{\mathit{n}}^{+}$ fusion yields measured at the impact energy of 225 keV for small (n10) clusters follow the ``thermonuclear'' model proposed by Carraro et al. [Phys. Rev. A 42, 1379 (1990)] rather than the thick-target model. For ${\mathrm{H}}_{2}$${\mathrm{O}}^{+}$ and (${\mathrm{H}}_{2}$O${)}_{2}^{+}$ at 225 keV, the yields roughly agree with the ``knock-on'' model by Carraro et al. No fusion event was observed for (${\mathrm{H}}_{2}$O${)}_{\mathit{n}}^{+}$ clusters with n=4\char21{}50; however, n=115 clusters produced an observable fusion rate. The ratio between fusion rates of (${\mathrm{H}}_{2}$O${)}_{115}^{+}$ and (${\mathrm{D}}_{2}$O${)}_{115}^{+}$ is 5%\ifmmode\pm\else\textpm\fi{}2%, in close agreement with the result, \ensuremath{\sim}5%, measured by Beuhler et al. at 300 keV.

Absolute neutron detection efficiency calibration of a stilbene organic scintillator in the energy range 2 to 20 MeV with the associated particle technique

The associated particle technique (APT) has been used with neutrons from D(d, n) 3He and T(d, n) 4He reactions to measure the absolute neutron detection efficiency of a stilbene detector (3.81 cm diameter, 1.27 cm thick) in the energy range 2–20 MeV as a function of the light collection threshold. The measurements have been carried out using thin TiT and home made self-supporting deuterated polyethylene targets. The APT facility of the INFN-Laboratori Nazionali di Legnaro, the efficiency measurements and their comparison with both analytical and Monte Carlo (SANREMO code) calculations are described. The good agreement between the experimental data and the SANREMO code predictions allows extension of the efficiency evaluation throughout the whole energy range 2–20 MeV with an uncertainty of 5–10%. The experimental uncertainty in efficiency values is about 2%.

The reaction d(p, pp)n measured with bol at Ep = 50 MeV

We measured proton-deuteron breakup with the multi-detector system BOL for protons with an energy of 50 MeV hitting a deuterated polyethylene target. Proton-proton coincidences were registered with 40 position-sensitive detector telescopes. We present data covering ~ 85 % of the four-dimensional kinematical phase space. The data are compared with Faddeev calculations using two local S-wave Malfliet-Tjon potentials. Regions of discrepancy between data and theory in two-dimensional (2D) subspaces (cuts) are shown to be connected in 4D. The cross section structure (experimental and theoretical) is studied in a 4D representation consisting of a 2D matrix of 2D matrices. Prominent patterns are observed in the 4D differential cross section which can be traced back to quasi-two-body reaction mechanisms. Observed symmetries can be understood in terms of the simple impulse approximation.

A high flux associated particle neutron source

An associated particle system for neutron production using the 2H(d, n) 3He reaction is described. The system employs a thin-walled scattering chamber, an assembly to rotate a deuterated polyethylene target and a magnetic analyzer for recoil particle separation in high flux applications. Neutron beam intensities of up to 1000 s −1 are routinely obtainable.

Deuterated polyethylene microspheres of variable density for laser-fusion targets

This paper describes the experimental procedure we have developed for producing spherical deuterated polyethylene targets with a continuum of densities in the range 20–60% that of solid (ρsolid?1.0 g/cm3). These spheres (termed ’’microsponges’’) are typically 80–300 μm in diameter and are highly porous networks with average pore sizes of a few microns or smaller. The technique consists of (i) forming solid (i.e., normal density) microspheres by pulverizing and spheroidizing the (CD2)n starting material, (ii) cross linking the polyethylene chains in a γ-ray flux, (iii) swelling the cross-linked network in an appropriate hot solvent such as p-xylene, and (iv) rapidly extracting the solvent to ’’freeze-in’’ the expanded structure in the final target. A quantitative model based upon the theory of swollen networks has been employed to correlate the measured densities with the experimental parameters, such as radiation dosage, solvent type, and swelling temperature.

The production of a 2–20 MeV collimated monoenergetic neutron beam of known flux using the associated particle technique

An associated particle system employing the 2H(d, 3He)n reaction has been developed to produce a neutron beam with accurately known properties in the 2–20 MeV range. In these experiments a deuterated polyethylene target is bombarded with 4–26 MeV deuterons from the ANU cyclograaff facility. The 3He ions emitted within a small solid angle are detected with a solid state detector telescope using particle identification. The neutron beam associated with these detected ions has typically a fwhm energy width of 5–10% and a corresponding spatial width of 3–4°. Counting the 3He ions determines the neutron flux absolutely. Procedures have been developed at the higher incident deuteron energies to exclude counting 3He events from the 12C(d, 3He) 11B reaction where the recoils from the 2H(d, 3He)n reaction are of similar energy. The neutron flux obtained within the experimental beam is typically 3 neutrons/nA·s from a 3 mg/cm 2 thick deuterated polyethylene target depending on the kinematic scheme chosen. The facility has been used to obtain spectra and measure cross sections for the 6Li(n, α) 3H reaction using a 6LiI(Eu) scintillator as the 6Li target.

Improved technique for the preparation of deuterated-polyethylene targets

Self-supporting uniform deuterated polyethylene foils with thickness in the range 1–5 mg/cm 2 and an area of 5 cm 2 have been prepared. The foils are built up in a series of layers using a saturated solution of polyethylene in boiling xylene.

The production of a 2–10 MeV collimated monoenergetic neutron beam of known flux using the associated particle technique

The associated particle technique is used with neutrons from the 2H(d, n) 3He reaction to provide a monoenergetic neutron beam in the range 2–10 MeV. The neutron energy range achieved with this system requires a corresponding range in deuteron energy of 2–12 MeV. The collimation of the neutron beam is accomplished electronically. To produce neutron beams with energies in the 2–5 MeV range the associated 3He ions are counted with unambiguous resolution in a solid state detector. Above 5 MeV the 3He ions are counted with similar accuracy by comparing the yield from the primary deuterated-polyethylene target with the yield from a carbon target of comparable areal density. For a 0.5 μA deuteron beam in the MeV range the flux at the centre of the neutron beam produced with a 0.5 μm thick deuterated-polyethylene target is typically 100 s −1 msr −1. Neutron cross sections and nuclear lifetimes are measured using an appropriate scintillator which serves simultaneously both as target and detector. The timing resolution between associated events in the 3He-ion and neutron detectors is 1–2 ns depending on the neutron detector used.

A rotating target assembly for thin targets

The design of a rotating target system is described which is both simple and readily compatible with most types of scattering chambers. The performance of deuterated polyethylene targets enclosed between carbon layers is reported.

11B(n,α)8Li(β−)8Be*(2α) Reaction for 25 and 38 MeV Neutrons

Boron-loaded K-2 emulsions were exposed to the neutrons produced by 41 MeV protons incident upon a deuterated polyethylene target. The developed emulsions were scanned for the resulting "hammer tracks" produced from the 11B(n,α)8Li(β−)8Be*(2α) reaction. Measurements were made of the range and space angles of these events. The neutron cross section for this reaction was found to be 0.098 ± 0.057 mb for 37.7 ± 3.3 MeV neutrons and 1.87 ± 0.75 mb for 25.0 ± 3.0 MeV neutrons.

Gamma-ray yields from the reaction D(p, γ)3He at low energies

Total cross sections and measurements of the small isotropic component of the γ-ray yield from the reaction D(p, γ)3He have been determined in the energy range from 57 to 1100 KeV using gas and deuterated polyethylene targets. The results are compared with some theoretical predictions.