4He Reaction Research Articles

Measurement of the 236U(n,f) cross section at fast neutron energies with Micromegas Detectors

In the present work, the measurement of the 236U(n,f) cross section was performed, with reference to the 238U(n,f) reaction. The measurements took place at the neutron beam facility of the National Centre for Scientific Research "Demokritos" (Greece) and the quasi-monoenergetic neutron beams were produced via the 2H(d,n)3He reaction in the energy range 4–10 MeV. Five actinide targets (two 236U, two 238U and one 235U) and the corresponding Micromegas detectors for the detection of the fission fragments were used. Detailed Monte Carlo simulations were performed, on one hand for the study of the neutron flux and energy distribution at the position of each target, and on the other hand for the study of the energy deposition of the fission fragments in the active volume of the detector. The mass and homogeneity of the actinide targets were experimentally determined via alpha spectroscopy and the Rutherford Backscattering Spectrometry, respectively. The experimental procedure, the analysis, the methodology implemented to correct for the presence of parasitic neutrons and the cross section results will be presented and discussed.

Study of the 191Ir(n,2n)190Ir cross section

The 191Ir(n,2n)190Ir cross section was measured by using of the activation technique at four neutron energies in the range 10.0-11.3 MeV. The quasimonoenergetic neutron beam was produced via the 2H(d,n)3He reaction at the 5.5 MV Tandem Van de Graaff accelerator of NCSR ”Demokritos”. After the irradiations the induced activity of the samples was measured through a 56% relative efficiency HPGe detector. The cross section for the population of the second high spin (11−) isomeric state was measured along with the sum of the reaction cross section populating both the ground (4−) and the first isomeric state (1−). The experimental data will be combared to theoretical calculations in order to deduce information for the spin dependence of the level density parameters.

Statistical model calculations of 72,73Ge(n,p) and 72,74Ge(n,α) reactions on natural Ge

Systematic experimental and theoretical investigations of the 72,73Ge(n,p)72,73 Ga and 72,74Ge(n,α)69,71Znm reaction cross sections are presented in the energy range from thresh- old to about 17 MeV neutron energy. The above reaction cross sections were measured from 8.8 to 11.4 MeV by using the activation method, relative to the 27Al(n,α)24Na refer- ence reaction. The quasi-monoenergetic neutron beams were produced via the 2H(d,n)3He reaction at the 5 MV VdG Tandem T11/25 accelerator of NCSR “Demokritos”. Statisti- cal model calculations using the code EMPIRE-II (version 2.19) taking into consideration pre-equilibrium emission were performed on the data measured in this work as well as on data reported in literature.

A Large Volume (1m3) Spherical Proportional Counter for Atmospheric Neutron Measurements

A large volume (1m3) spherical proportional counter has been developed at CEA/Saclay, for low flux neutron measurements. Neutrons can be measured successfully, with high sensitivity, using 3He gas in the detector. The proton and tritium energy deposition in the drift gaseous volume, from the reaction 3He(n,p)3H, can provide the neutron spectra from thermal neutrons up to several MeV. The α resolution of the detector has been measured using 222Rn gas, in order to have the response of the total active volume of the detector. The three α peaks from 222Rn decay and 222Rn daughters decay have been measured with FWHM less then 2%, with gas mixture Ar 98% and CH4 2% at a pressure of 200 mbar. The neutron sensitivity has been tested inserting in the sphere 100mgr of 3He. The 0.765 MeV peak of p and 3H is well separated form the cosmic ray background after irradiation with 252Cf neutron source. The ground level atmospheric thermal neutrons have been also measured after several hours of exposure. The very low noise, the limited wall effect, the high resolution and the high sensitivity are some of the advantages of the detector.

Measurement of the differential cross sections and angle-integrated cross sections of the 6Li(n, t)4He reaction from 1.0 eV to 3.0 MeV at the CSNS Back-n white neutron source * * Supported by National Key R&D Program of China (2016YFA0401604), National Natural Science Foundation of China (11775006), Science and Technology on Nuclear Data Laboratory and China Nuclear Data Center

The 6Li(n, t)4He reaction was measured as the first experiment involving neutron-induced charged particle emission reactions at the CSNS (China Spallation Neutron Source) Back-n white neutron source. The differential cross-sections of the 6Li(n,t)4He reaction at 15 detection angles ranging from 19.2° to 160.8° are obtained from 1.0 eV to 3.0 MeV at 80 neutron energy points; for 50 energy points below 0.1 MeV they are reported for the first time. The results indicate that the anisotropy of the emitted tritium is noticeable above En = 100 eV. The angle-integrated cross-sections are also obtained. The present differential cross-sections agree in general with the previous evaluations, but there are some differences in the details. More importantly, the present results indicate that the cross-sections of the 6Li(n, t)4He reaction might be overestimated by most evaluations in the 0.5 − 3.0 MeV region, although they are recommended as standards below 1.0 MeV.

Monte Carlo calculation of the response of He-3 counter with Geant4

Monte Carlo calculations with Geant4 were performed to calculate the response of He-3 proportional counters for neutrons of the energy region of 230 keV – 7 MeV. The results are compared with experimental data obtained by irradiation of the detectors with monoenergetic neutron beams produced by 7Li(p,n)7Be and 2H(d,n)3He reactions in the Tandem accelerator, NSCR Demokritos Athens.

Cross Section Measurements on Isotopes of Ge and Hf Using the Activation Technique

Cross section measurements of neutron induced reactions on isotopes of Ge and Hf have been determined at energies 8.8, 9.6, 10.6, 11.1, 11.4 MeV using the activation technique. Neutrons produced by the 2H(d,n)3He reaction were used to irradiate pellets of natural Ge and Hf02- The neutron flux at the target position was determined using the 27Al(n,a)24Na, 93Nb(n,2n)92mNb and 197Au(n,2n)196Au reference reactions. HPGe detectors of relative efficiency εΓ=80% and 55% were used to determine the decay of the produced unstable nuclei. The cross section values were compared with those taken from the literature.

Experimental study of the 197Au(n,2n) reaction cross section

In the present work, the 197Au(n,2n) reaction cross section is experimentally determined relative to the 27Al(n,α)24Na reaction at incident neutron energies of 9.0 to 10.5 MeV by means of the activation technique. The quasi-monoenergetic fast neutron beam was produced via the 2H(d,n)3He reaction at the 5.5 MV Tandem Van de Graaff accelerator at the NCSR “Demokritos” and was studied to determine the contribution of background “parasitic” neutrons using the multiple foil activation technique and the SULSA unfolding code. The cross sections for the population of the second isomeric state (12−) of 196Au and the sum of the ground (2−) and first isomeric state (5−) population cross sections were independently determined. Auxiliary Monte Carlo simulations were performed with the MCNP code.

Underground Low Flux Neutron Background Measurements in LSM Using a Large Volume (1m3) Spherical Proportional Counter

A large volume (1m3) spherical proportional counter has been developed at CEA/Saclay, for low flux neutron measurements. The high voltage is applied to a small sphere 15mm in diameter, located in the center of the counter and the wall of the counter is grounded. Neutrons can be measured successfully, with high sensitivity, using 3He gas in the detector. The proton and tritium energy deposition in the drift gaseous volume, from the reaction 3He(n,p)3H, can provide the neutron spectra from thermal neutrons up to several MeV.The detector has been installed in the underground laboratory in Modane (LSM) to measure the neutron background. The sphere has been has been filled with gas mixture of Ar + 2% CH4 +3gr He-3, at 275 mbar. The thermal neutron peak is well separated from the cosmic ray and gamma background, permitting of neutron flux calculation. Other potential applications requiring large volume of about 10 m in radius are described in detail in reference

Measurements of the Cross-sections of Produced Short-Lived Nuclei Induced by Neutrons around 14MeV on Isotopes of Tungsten**Supported by the National Natural Science Foundation of China under Grant Nos 11605099 and 11575090.

New experimental cross-section data for the 180W(n,2n)179mW, 186W(n,2n)185mW and 186W(n,p)186Ta reactions at the neutron energies of 13.5 and 14.4 MeV are obtained by the activation technique. The neutron beams are produced by means of the 3H(d,n)4He reaction. The gamma activities of the product nuclei are measured by a high-resolution gamma-ray spectrometer with a coaxial high-purity germanium detector. The neutron fluence is determined using the monitor reaction 93Nb(n,2n)92mNb. The results in the current work are discussed and compared with the measurement results found in the literature. It is shown that these higher accuracy experimental cross-section data around the neutron energy of 14 MeV agree with some previous experimental values from the literature within experimental uncertainties.

Positron-electron annihilation momentum transfer to trapped deuterons

The probability of positron annihilation momentum transfer to a trapped deuteron is calculated based on neutron measurements from 2H(d,n)3He reactions in deuterated palladium thin films. Deuterium gas loading in Pd thin films creates a high D/Pd fraction at point defects in the metal lattice. Unmoderated positrons from a Na-22 source thermalize and are trapped in the same point defects as deuterium in the Pd thin films. Similar to the Mössbauer effect, an interaction with the surrounding crystal lattice allows for conservation of momentum during electron-positron annihilation energy transfer to the trapped deuteron.

Measurement of 67Zn(n,p)67Cu, 64Zn(n,2n)63Zn, 89Y(n,γ)90mY and 89Y(n,2n)88Y reaction cross sections at the neutron energy of 14.54 MeV with covariance analysis

The 67Zn(n,p)67Cu, 64Zn(n,2n)63Zn, 89Y(n,γ)90mY and 89Y(n,2n)88Y reaction cross sections relative to the 197Au(n,2n)196Au monitor reaction have been determined at the neutron energy of 14.54 ± 0.002 MeV by using the method of activation and off-line γ-ray spectrometry. The neutron energy used was obtained from the 3H(d,n)4He reaction. The covariance analysis was performed by taking the uncertainties arising in various attributes and the correlations between those attributes. The analyzed results from the present measurement were compared with the literature data and evaluated data of various libraries like ENDF/B-VIII, JEFF-3.3, JENDL-4.0 and ROSFOND-2010 libraries as well as with the calculated values based on TALYS-1.9 code.

Diffusion of helium in radiation-damaged zircon

Diffusion of helium was characterized in natural zircon that had been implanted with Kr at a range of energies to simulate the effects of alpha recoil in natural radiation damage. Polished slabs of zircon, oriented either normal or parallel to c, were implanted with Kr+ ions at a series of energies to produce a damaged region ∼ 1μm in thickness, then implanted with 100keV 3He at a dose of 1×1015 3He/cm2, which placed the 3He within the region damaged by the Kr ion implantation. The implanted zircons were annealed isothermally in Pt capsules in 1-atm furnaces at temperatures ranging from 51 to 252°C and times ranging from 15min to 3 weeks. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. For diffusion in zircon normal to c, we obtain the following Arrhenius relation:D=1.7×10−8 exp(−71±2kJ mol−1/RT) m2sec−1.This activation energy for diffusion is about half of the value for He diffusion in zircon from the same sample locality but without Kr implantation, measured with an otherwise similar experimental and analytical approach (Cherniak et al., 2009). He diffusivities in the Kr-implanted material are also significantly faster. Further, He diffusivities normal and parallel to c in the Kr-implanted zircon are similar, in contrast to the marked diffusional anisotropy (with differences of two orders of magnitude for diffusion normal and parallel to c) observed for He diffusion in this zircon in samples not implanted with Kr.These data indicate that heavily damaged zircon will have very limited retentivity of helium. Only those zircons larger than a few hundred μm will have mean closure temperatures exceeding typical earth surface temperatures; mean closure temperatures for He in highly damaged zircon will be about ∼200°C lower than those for relatively undamaged zircon. At 200°C, equivalent amounts of He will be lost from severely damaged zircon at a rate about a million times faster than from relatively undamaged zircon. For retentivity of He comparable to that for low-damage zircon at 200°C, the severely damaged zircon would require residence temperatures of ∼ -10°C.

Study of radioactivity built-up and decay with singles time-stamped data

Time-stamped data have been used to estimate the decay half-lives of radioactive 118mSb and 64,66,68Ga nuclei. These nuclei are populated through the reaction 4He (Elab = 32 MeV) + natIn and p (E0lab = 1 MeV) + natZn, respectively. The γ-rays emitted by the excited daughter nuclei are detected by a single high purity germanium (HPGe) detector and the data are acquired using a CAEN 5780M desktop digitizer. Half-lives of different orders of magnitudes for the above mentioned nuclei are obtained from both the decay of parent and the growth of daughter nuclei. It is observed that the half-lives obtained from both these techniques match fairly well and also are consistent with the reported values. It is demonstrated that the time-stamped data can be useful while studying certain half-lives which are too long for measurement using in-beam electronic technique and too short for decay studies in off-beam methods. The data also have a special relevance for constant monitoring of beam current and beam-tuning.

Detection of alpha particles from 7Li(p,α)4He and 19F(p,α)16O reactions induced by laser-accelerated protons using CR-39 with potassium hydroxide-ethanol-water etching solution.

Alpha particles generated by 7Li(p,α)4He and 19F(p,α)16O reactions are selectively detected in the presence of abundant primary protons by reducing the proton sensitivity of CR-39 using a potassium hydroxide-ethanol-water (PEW) etching solution. These nuclear reactions are induced in a LiF crystal using the laser-accelerated protons (4 × 1011 protons/pulse with a maximum energy of 3.3 MeV) generated and accelerated by the interaction of a 40-fs laser pulse with a polyethylene thin film target at a peak intensity of 5 × 1019 W/cm2. Subsequent etching of the CR-39 in the PEW solution (KOH: 17 wt. %; C2H5OH: 25 wt. %; H2O: 58 wt. %) permits the selective detection of 4.0 MeV alpha particles, which is independently confirmed by an experiment using alpha particles from an 241Am source. The described method is expected to be useful for research into nuclear reactions in laser plasma.

Experimental cross section and angular distribution of the 2H(p,$\gamma$)3He reaction at Big-Bang nucleosynthesis energies

The cross section for the 2H(p,$\gamma$)3He reaction was measured in the energy range E = 47–210 keV, relevant for primordial nucleosynthesis. A proton beam was incident on two deuterated titanium targets. The angular distribution of emitted $ \gamma$-rays was determined using two HPGe detectors, placed at $ 90^{\circ}$ and $ 135^{\circ}$ with respect to the incident beam direction. Results were compared with the latest ab initio theoretical calculation, including one- and many-body contributions. The predicted cross section and astrophysical S-factor are found to be in a very good agreement with measured values.

Activation cross-sections of titanium isotopes at neutron energies of 13.5–14.8 MeV * * Supported by the National Natural Science Foundation of China (11575090, 11605099)

The cross-sections for 46Ti(n,2n)45Ti, 46Ti(n,p)46m+gSc+47Ti(n,d*)46m+gSc, 46Ti(n,p)46m+gSc, 47Ti(n,p)47Sc+48Ti(n,d*)47Sc, 47Ti(n,p)47Sc, 48Ti(n,p)48Sc+49Ti(n,d*)48Sc,48Ti(n,p)48Sc, and 50Ti(n,α)47Ca reactions were investigated around neutron energies of 13.5–14.8 MeV by means of the activation technique. Fast neutrons were produced by the 3H(d,n)4He reaction. Neutron energies from different directions in the measurements were obtained in advance using the method of cross-section ratios for 90Zr(n,2n)89m+gZr and 93Nb(n,2n)92mNb reactions. The results obtained are analyzed and compared with the experimental data provided by the literature and verified nuclear data in the JEFF-3.3, CENDL-3.1, ENDF/B-VIII.0 libraries, as well as results calculated by Talys-1.9 code.

Activation of Mn, Li2O and LiF in the JSI TRIGA reactor to study potential tritium production monitors for fusion applications

Two series of measurements were performed in the JSI TRIGA research reactor in 2014 and 2017 to validate the 55Mn(n,γ)56Mn cross-sections and experimentally investigate the relationship between the 55Mn(n,γ)56Mn reaction and the rate of tritium production through the 6Li(n,t)4He reaction. Indeed, previously observed similarities between the sensitivity profiles of the neutron reaction of tritium production on lithium, 6Li(n,t)4He, and those of the 55Mn(n,γ)56Mn reaction in tritium breeder modules indicated that the latter reaction could be used as an effective monitor of tritium production, at least for short-term monitoring (the half-life of 56Mn being 2.579 h). However, experimental verification, improvements and validation of the 55Mn(n,γ)56Mn cross-sections are needed in order to meet the required accuracy. Foils of certified reference material Al–1%Mn, as well as LiF thermoluminescent detectors and Li2O samples were irradiated, both bare and under cadmium, to study the potential use of the 55Mn(n,γ)56Mn reaction for monitoring tritium production in fusion devices. Additionally, Al–0.1%Au was also irradiated for comparison, the 197Au(n,γ)198Au reaction cross-section being a standard. In order to obtain complementary information for data validation purposes, the irradiations were performed in positions within the JSI TRIGA reactor with different neutron spectra, i.e. in the central channel, the pneumatic tube and the F19 position, both in the outer ‘F’ ring of the reactor core and in the IC-40 irradiation channel located in the graphite reflector surrounding the reactor core. Bare and cadmium-covered irradiations were needed to subtract the contribution of epithermal neutrons to the 55Mn(n,γ)56Mn reaction. Calculations of the reaction rates were performed using the Monte Carlo code MCNP6.1 with a detailed model of the JSI TRIGA reactor, with the samples, the irradiation capsules and covers being modelled explicitly. The uncertainties involved in the measurements and the calculations were carefully evaluated. The principal objective was to study the energy response and correlations between the 55Mn(n,γ)56Mn reaction in irradiated Al–1%Mn and the 6Li(n,t)4He reaction in irradiated LiF and Li2O. Good consistency between the measured and calculated 55Mn(n,γ)56Mn and 197Au(n,γ)198Au reaction rates, in most cases within the uncertainty bars, was observed.

Investigation of the D(3He, p)4He reaction on ZrD targets in the energy region of 16–34 keV

The article is devoted to study of the D(3He, p)4He reaction in the 3He+ ion energy range EHe = 16÷34 keV (E= 6.41÷13.61 keV in the center-of-mass system) with a step of 2 keV. The goal of this paper was to determine experimentally the electron screening potential Ue and the enhancement factor of the D(3He, p)4He reaction using the deuterated metal targets ZrD with different crystal textures. In this work we present results of measuring the D(3He, p)4He reaction enhancement factor using the targets ZrD with Miller indices [111] and [100]. The ZrD targets was deposited on the stainless steel foil 50 μm thick. The protons of energy 14.7 MeV from the D(3He, p)4He reaction were detected by a scintillation detector based on the BC-404 scintillator 115 mm in diameter and 4 mm thick, which was placed in optical contact with the XP-2040 PMT. The measured enhancement factors of the D(3He, p)4He reaction much higher than for gas targets and energy behavior is not described by the classical exponential formula. The effect of the crystal structure of the targets is evident. The measured enhancement factors of the D(3He, p)4He reaction are higher for the ZrD target with a crystal structure characterized by the Miller index [100] than for the target with index [111], which probably indicates the contribution of channeling. A non-proportional increase of the enhancement factors for the D(3He, p)4He reaction in energy range 16÷22 keV probably indicates a low-lying resonance effect in 5Li.

A platform for nuclear physics experiments with laser-accelerated light ions

A novel platform for nuclear physics experiments has been developed on the high-energy, short-pulse OMEGA EP Laser System. Planar foil targets are irradiated with a 10-ps, 1-kJ infrared beam focused to an intensity of the order of 1018 W/cm2. Relativistic electrons generated in the laser–target interaction escape the target, generating a very large electrostatic field, which extracts ions from the target’s back surface and accelerates them to MeV energies. The energetic ion flow from the back side of this primary target creates neutrons and charged particles through nuclear reactions in a secondary target placed in the ion flow. Charged-particle detectors were used to measure the energy spectra of the ions. The energy spectrum of the neutrons generated in the secondary target was measured using scintillator-based neutron time-of-flight detectors. First experiments to validate the performance of this setup studied d(d,n)3He and 9Be(d,n)10B reactions. This experimental platform is suitable especially for survey-type studies of nuclear reactions and for reactions that involve rare or radioactive ions like tritium.