Triton Beam Research Articles

Generation of a controllable TNSA deuteron beam using deuterated metal targets

This study investigated the feasibility of using deuterated titanium targets for the generation of a target normal sheath acceleration (TNSA) deuteron beam. Commercial 25-μm-thick titanium foil was cut into 500 × 500-μm2 squares and subsequently deuterated using different approaches. The spectra and total yields of all emitted ions were measured using a Thomson parabola ion spectrometer. It was found that a 24-h exposure to 1 atm of D2 gas at 400 °C is the most-efficient deuteration method, producing yields in the mid-1011 deuterons per shot. The deuteron energy spectra changed from an exponential shape at low ion yields to exponentially modified Gaussians at higher yields. Simulations suggest that this effect is due to increased Coulomb interactions between the ions, which suppress the low energies. Separate campaigns will utilize the presented approach to produce a TNSA triton beam. Two such targets will be used in a pitcher/catcher configuration to study the tritium–tritium reaction T(t, 2n)α.

First demonstration of a triton beam using target normal sheath acceleration

Tritiated titanium targets were irradiated by the short-pulse OMEGA EP laser (1.25 kJ, 10 ps) to generate a laser-accelerated pulsed beam of tritons by target normal sheath acceleration. Using a Thomson parabola, the beam was found to contain 1012 tritons per pulse, with a mean energy of 2.2 MeV and an exponential tail reaching up to 10 MeV. In a separate experiment, the triton beam was directed onto a secondary deuterated polyethylene (CD) target to induce deuterium–tritium (D–T) nuclear reactions. Using neutron time-of-flight spectrometers, approximately 108 D–T fusion neutrons were observed per laser pulse. This triton beam presents new research opportunities for the study of the 3H(t, 2n)4He reaction and di-neutron transfers to lithium and beryllium that may produce exotic neutron-rich nuclei of interest to basic nuclear science, astrophysics, and inertial confinement fusion technology.

Isovector excitations in 100Nb and their decays by neutron emission studied via the [formula omitted] reaction at 115 MeV/u

Spin–isospin excitations in Nb100 were studied via the Mo100(t,He3) charge-exchange reaction at 115 MeV/u with the goal to constrain theoretical models used to describe the isovector spin response of nuclei. The experiment was performed with a secondary beam of tritons, and 3He particles were analyzed in the S800 magnetic spectrometer. Decay by neutron emission from excited states in Nb100 was observed by using plastic and liquid scintillator arrays. Differential cross sections were analyzed and monopole excitations were revealed by using a multipole decomposition analysis. The Gamow–Teller transition strength observed at low excitation energies, which is important for estimating the electron-capture rate in astrophysical scenarios, was strongly fragmented and reduced compared to single-particle and spherical mean-field models. The consideration of deformation in the theoretical estimates was found to be important to better describe the fragmentation and strengths. A strong excitation of the isovector spin giant monopole resonance was observed, and well reproduced by the mean-field models. Its presence makes the extraction of Gamow–Teller strengths at high excitation energies difficult. The branches for statistical and direct decay by neutron emission were identified in the spectra. The upper limit for the branching ratio by direct decay (integrated over all observed excitations) was determined to be 20±6%. Even though the statistical uncertainties in the neutron-coincident data were too large to perform detailed studies of the decay by neutron emission from individual states and resonances, the experiment demonstrates the feasibility of the method.

Estimation of Double-Differential Angle-Dependent Neutron Production Cross Sections from Tritons on 197Au at Energies from 5.97 to 19.14 MeV

Estimated cross sections for neutron production from triton bombardment of gold are deduced from measurements of triton interactions with gas targets that used gold as a triton beam stop material. Differential cross sections for production of neutrons from 5.97-, 7.47-, 10.45-, 16.41- and 19.14-MeV tritons on 197Au were evaluated. Corrections for the neutron interaction in gold, in the target structure, and in the air of the flight path were obtained by means of a Monte Carlo technique. Uncorrelated scale uncertainties range from 24% to 41% whereas those of double-differential cross sections range from 0.2% to 5%. Based on these cross-section data, calculation of neutron yield at 0 deg from fully stopped tritons at 20.22 MeV agrees with an independent measurement. Least-squares fits with a gamma distribution model indicate an anisotropy in the high-energy portion of the neutron spectra. Legendre polynomial fits of differential cross sections are reported. All neutron cross-section data are made available through the Experimental Nuclear Reaction Data (EXFOR) library at international data centers.

Neutron Emission Spectra of Triton Beams of 20.22-MeV Fully Stopped in Targets of H2O, D2O, LiF, Si, Ni, Mo, Ta, W, Pt, and Au

The Ion Beam Facility of Los Alamos National Laboratory could routinely provide accelerated bunched triton beams to be used in neutron time-of-flight experiments. Exploratory measurements at 0 deg were done to determine the neutron yield with target materials throughout the periodic system yielding absolute specific double-differential neutron yields. Only a few of these measurements were made public previously. The results of these measurements having a mainly demonstrative purpose are presented here because of their uniqueness. For lithium and beryllium, double-differential neutron emission cross sections are given at 17.2 and 15.2 MeV, respectively.

Accelerator-based neutron source using a cold deuterium target with degenerate electrons

A neutron generator is considered in which a beam of tritons is incident on a hypothetical cold deuterium target with degenerate electrons. The energy efficiency of neutron generation is found to increase substantially with electron density. Recent reports of potential targets are discussed.

NUCLEAR STRUCTURE OF 99Mo FROM THE (t,p) REACTION

The 97 Mo (t,p)99 Mo reaction has been studied with the triton beam energy of 12 MeV obtained from tandem Van de Graaff accelerator at the Atomic Weapon Research Establishment, Aldermaston. Proton spectra were obtained at 12 different angles from 5° to 87.5° at an interval of 7.5° and were detected in nuclear emulsion plates. Angular distributions for transitions to 46 levels in the energy range from 0 to 2.054 MeV have been measured. Absolute differential cross-sections for the levels have been measured. The experimental angular distributions are compared with the distorted-wave Born approximation calculations (DWBA) to determine L and Jπ values. The present results are compared with the previous experimental results and model predictions.

Gamow-Teller transitions toCu64measured with theZn64(t,He3) reaction

The $^{64}\mathrm{Zn}$($t$,$^{3}\mathrm{He}$) reaction has been studied by using a secondary triton beam of 115 MeV/nucleon to extract the Gamow-Teller transition-strength distribution to $^{64}\mathrm{Cu}$. The results were compared with shell-model calculations with the $\mathit{pf}$-shell effective interactions KB3G and GXPF1A and with existing data from the $^{64}\mathrm{Zn}$($d$,$^{2}\mathrm{He}$) reaction. Whereas the experimental results exhibited good consistency, neither of the theoretical predictions managed to reproduce the data. The implications for electron-capture rates during late stellar evolution were investigated. The rates based on the theoretical strength distributions are lower by factors of 3.5--5 compared to the rates based on experimental strength distributions.

Gamow-Teller strengths inNa24using the24Mg(t,3He)reaction at115AMeV

Gamow-Teller transitions from $^{24}\mathrm{Mg}$ to $^{24}\mathrm{Na}$ were studied via the ($t,{}^{3}\mathrm{He}$) reaction at $115A$ MeV using a secondary triton beam produced via fast fragmentation of $150A$ MeV $^{16}\mathrm{O}$ ions. Compared to previous ($t,{}^{3}\mathrm{He}$) experiments at this energy that employed a primary $\ensuremath{\alpha}$ beam, the secondary beam intensity is improved by about a factor of five. Despite the large emittance of the secondary beam, an excitation-energy resolution of $~200$ keV is achieved. A good correspondence is found between the extracted Gamow-Teller strength distribution and those available from other charge-exchange probes. Theoretical calculations using the newly developed USDA and USDB $\mathit{sd}$-shell model interactions reproduce the data well.

A STUDY OF 97Mo FROM THE (t, p) REACTION

The 97 Mo nucleus has been studied with the reaction 95 Mo (t, p) 97 Mo using a multichannel magnetic spectrograph. The isotopically enriched thin target 95 Mo was bombarded with the 12 MeV triton beam obtained from the tandem Van de Graaff accelerator at the Atomic Weapon Research Establishment, Aldermaston. Proton spectra are obtained at 12 different angles from 5° to 87.5° at an interval of 7.5° and are detected in nuclear emulsion plates. Forty-eight levels in the energy range from 0.000 to 3.189 MeV have been observed. Absolute differential cross-sections for these levels have been measured. The angular distributions are compared with the theoretical distorted-wave Born approximation calculations to determine L and Jπ values. The nuclear properties of 97 Mo are compared with previous experimental results and model predictions.

The (t, 3He) and ( 3He,t) reactions as complementary probes of the spin-isospin response of nuclei

The ( t , 3 He) reaction at 115 MeV/nucleon has been developed as a tool to extract Gamow-Teller strengths. A secondary triton beam was used, initially produced from a primary α -beam, but since recently from a primary 16 O beam. An important advantage of the ( t , 3 He) probe is that the data can be combined with results from the ( 3 He, t ) reaction, so that studies in the Δ T z = − 1 and Δ T z = + 1 direction can be performed with similar probes and good resolutions. This is important for improving the understanding of the reaction mechanism and associated errors in the extraction of transition strengths.

Measurement of weak rates for stellar evolution via the ( t, 3He) reaction

The (t,3He) charge-exchange reaction has been developed as a tool to extract Gamow-Teller strengths on nuclei of importance for stellar evolution. A secondary triton beam of 115 MeV/nucleon is used, either produced from a primary α beam, or, since recently, from a primary 16O beam. Here, the (t,3He) reaction is used to study the Gamow-Teller strength distribution in 58Co via the 58Ni(t,3He) reaction. The experimental results are compared with calculations in large-scale shell models using the kb3g and gxpf1 interactions, as well as existing data from 58Ni(n, p) and 58Ni(d,2He) experiments. The differences between the data and theoretical models are studied in terms of electron-capture rates in the pre-collapse stages of core-collapse supernovae.

Measurement of the Gamow-Teller strength distribution inCo58via theNi58(t,He3) reaction at 115 MeV/nucleon

Electron capture and \ensuremath{\beta} decay play important roles in the evolution of presupernovae stars and their eventual core collapse. These rates are normally predicted through shell-model calculations. Experimentally determined strength distributions from charge-exchange reactions are needed to test modern shell-model calculations. We report on the measurement of the Gamow-Teller strength distribution in $^{58}\mathrm{Co}$ from the $^{58}\mathrm{Ni}$($t$,$^{3}\mathrm{He}$) reaction with a secondary triton beam of an intensity of $~{10}^{6}$ pps at 115 MeV/nucleon and a resolution of $~250$ keV. Previous measurements with the $^{58}\mathrm{Ni}$$(n,p)$ and the $^{58}\mathrm{Ni}$($d$,$^{2}\mathrm{He}$) reactions were inconsistent with each other. Our results support the latter. We also compare the results to predictions of large-scale shell-model calculations using the KB3G and GXPF1 interactions and investigate the impact of differences between the various experiments and theories in terms of the weak rates in the stellar environment. Finally, the systematic uncertainties in the normalization of the strength distribution extracted from $^{58}\mathrm{Ni}$($^{3}\mathrm{He}$, $t$) are described and turn out to be nonnegligible due to large interferences between the $\ensuremath{\Delta}L=0,\ensuremath{\Delta}S=1$ Gamow-Teller amplitude and the $\ensuremath{\Delta}L=2,\ensuremath{\Delta}S=1$ amplitude.

Development of a secondary triton beam from primary 16,18O beams for (t, 3He) experiments at intermediate energies

The in-flight heavy-ion fragmentation technique has been used to produce a secondary beam of tritons ( 3H) at intermediate energies ( E t > 100 MeV / nucleon ) from primary 16,18O beams of 150 and 120 MeV/nucleon, respectively. The best results are obtained with a 16O beam of 150 MeV/nucleon, producing a 115 MeV/nucleon triton beam. The triton beam will be used in (t, 3He) charge-exchange experiments at the S800 spectrometer at the NSCL. At the target of the S800, a triton rate of 5 × 10 6 particles per second is achieved, for a primary 16O beam of 100 pnA. The (t, 3He) reaction using this beam was tested with a 24Mg target. An excitation-energy resolution of 190 ± 15 keV is achieved.

Nuclear structure ofMo102

Nuclear structure of the $^{102}\mathrm{Mo}$ nucleus has been studied using the $^{100}\mathrm{Mo}$($t,p$)$^{102}\mathrm{Mo}$ reaction with the triton beam energy of 12 MeV obtained from the tandem Van de Graaff accelerator and a multichannel magnetic spectrograph. Proton spectra are obtained at 12 different angles from 5\ifmmode^\circ\else\textdegree\fi{} to 87.5\ifmmode^\circ\else\textdegree\fi{}, at an interval of 7.5\ifmmode^\circ\else\textdegree\fi{} and are detected in nuclear emulsion plates. Thirty-five levels in the energy range from 0.000 to 3.248 MeV have been observed. The results yield a number of new levels with spin assignments. Absolute differential cross sections for the levels have been measured. The experimental angular distributions are compared with the theoretical distorted-wave Born approximation calculations to determine $L$ and ${J}^{\ensuremath{\pi}}$ values. The present results are compared with the previous results.

Gas Feeding System Supplying the U-400M Cyclotron Ion Source with Hydrogen Isotopes

Automated system feeding into ion source hydrogen isotopes as molecules with preset ratio of the fluxes is described. The control system automatically maintained the working parameters and provided graphic and digital representation of the controlled processes. The radiofrequency (RF) ion source installed at the axial injection line of the cyclotron produced ion beams of HD+, HT+, DT+, D2H+, etc. At a several months DT+ beam acceleration the tritium consumption was less than 108 Bq/hr. The intensity of a 58.2 MeV triton beam (T+ ions) extracted from the cyclotron chamber was about 10 nA.

Experimental study of 4H in the reactions 2H(t, p) and 3H(t, d)

The 4H resonance was investigated in the transfer reactions 2H(t,p)4H and 3H(t,d)4H using cryogenic liquid targets of deuterium and tritium and 58 MeV triton beam. The multidetector system with a large angular acceptance was used to measure the recoil protons and deuterons in coincidences with tritons or neutrons from the decay of 4H. Data analysis involved careful considerations made for the competing processes of final state interaction and quasifree scattering. The experimental data show a peak with resonance parameters Eres=3.05±0.19 MeV and Γobs=4.18±1.02 MeV. The pole of S-matrix corresponding to the physical values of energy and width, E0=1.99±0.37 MeV and Γ0=2.85±0.3 MeV, has been extracted.

Tritium target for research in exotic neutron-excess nuclei

A cryogenic tritium target and computer-controlled equipment providing for feeding/recovering tritium into/from the target cell and radiation monitoring in technological lines and in workrooms is described. The tritium target set-up showed reliable operation in experiments done with a 58.3 MeV triton beam focused on a 5 mm spot at intensity approaching 3×10 7 s −1. The t+t elastic scattering cross-section was obtained in a wide angular range.

Resonance states of hydrogen nuclei 4H and 5H obtained in transfer reactions with exotic beams

To investigate 5H resonance states with a better instrumental resolution, we utilized the two-neutron transfer reaction 3H(t, p)5H accomplished with the use of a cryogenic liquid-tritium target and 57.5-MeV triton beam. As a result of this study, a valuable fraction of protons detected at θlab = 18°-32° in ptn coincidence events was attributed to the states of the 5H nucleus. Two resonance states situated at 1.8 plusmn; 0.1 and 2.7 ± 0.1 MeV above the t + n + n decay threshold were obtained in the missing mass energy spectrum of the 5H nucleus. The peak located close to E5H = 1.8 MeV was clearly seen in the H spectrum obtained from the energy distributions of 3H nuclei emitted in the reaction 2H(6He, 5H)3He at θ lab = 17°-32°. The width (Γobs ≤ 0.5 MeV) obtained for the two 5H resonance states is surprisingly small. A state of 4H with Eres = 3.3 MeV and γ2 = 2.3 MeV was obtained in the reaction 2H(t, p)4H from the spectra of protons leaving the target at θlab = 18°-32° and detected in coincidence with neutrons emitted in the decay of 4H nuclei. © 2003 MAIK "Nauka/Interperiodica".

Evidences for resonance states in 5H

Resonance states of 5H were investigated through the two-neutron transfer reaction t(t,p)5H. A triton beam at 57.5 MeV and a cryogenic liquid tritium target were used. The 5H missing mass spectrum in triple coincidence, proton+triton+neutron, shows a resonance at 1.8±0.1 MeV above the t+2n decay threshold. This energy is in good agreement with the result reported in Phys. Rev. Lett. 87 (2001) 092501. The resonance width, Γintr⩽0.5 MeV, is surprisingly small and difficult to reconcile with theory predictions.