Resonant structure observed in the 3He(τ, γ)6Be capture reaction

The ³He(τ,γ)⁶Be capture reaction has been studied for ³He bombarding energies from 12 to 27, MeV. Transitions to the first excited state in ⁶Be(T = 1, 2⁺) are readily seen. Transitions to the ground state in ⁶Be (T = 1, 0⁺) are very weak and their presence could not be ascertained. The 90° excitation function for these transitions shows a broad maximum centered at E_τ = 23 ±1 MeV. This is interpreted as a resonance in the compound nucleus ⁶Be at E_x = 23.0±0.5 MeV with a configuration other than ³He+³He. These results are compared with other experimental work as well as with theoretical predictions.     

Trinucleon cluster structure at high-excitation energies in A=6 nuclei

Trinucleon molecular structures in ⁶He and ⁶Be were investigated by using the ⁶Li(⁷Li, ⁷Be)⁶He reaction at 455 MeV and ⁶Li(³He, t)⁶Be reaction at 450 MeV, respectively. Binary decays into t + t from a broad state at E _x =18.0±1.0 MeV in ⁶He and into ³He + ³He from one at E _x =18.0±1.2 MeV in ⁶Be, respectively, were observed by measuring trinucleon cluster decays in coincidence with reaction particles. The branching ratios for binary decay were estimated to be about 0.7 for ⁶He and ⁶Be. These large branching ratios show that a trinucleon cluster state exists as an isobaric partner around E _x =18 MeV in ⁶He and ⁶Be.     

Spectroscopy of excited states of 8He

The ¹⁰Be(¹²C,¹⁴O)⁸He-reaction has been used to study the levels of ⁸He. In addition to the known excited state of ⁸He at E_x = 3.6 MeV, with J^π = 2⁺, three additional states were found at excitation energies of 4.54(25) MeV, 6.03(10) MeV and 7.16(4) MeV.     

States in Be studied through the reaction B(p, α)Be with 40 MeV protons

Spectroscopy of the α- and τ-particles from 40 MeV proton bombardment of ¹¹B reveals transitions to ⁸Be states up to 19 MeV. The ratio of excitation of the 16.6 MeV state to the 16.9 MeV state is 2.3 ± 0.4. The ⁸Be(4⁺) state is found at 12.5 MeV with a width of 4.0 ± 0.5 MeV.     

High-lying excited states in <Superscript>10</Superscript>Be from the <Superscript>9</Superscript>Be(<Superscript>9</Superscript>Be,<Superscript>10</Superscript>Be)<Superscript>8</Superscript>Be reaction

A transfer-reaction experiment of ⁹Be(⁹Be, ¹⁰Be)⁸Be was performed at a beam energy of 45 MeV. Excited states in ¹⁰Be up to 18.80 MeV are produced using missing mass and invariant mass methods. Most of the observed high-lying resonant states, reconstructed from the α + ⁶He and t + ⁷Li decay channels, agree with the previously reported results. In addition, two new resonances at 15.6 and 18.8 MeV are identified from the present measurement. The 18.55 MeV state is found to decay into both the t + ⁷Li_g.s. and t + ⁷Li* (0.478 MeV) channels, with a relative branching ratio of 0.93 ± 0.33. Further theoretical investigations are encouraged to interpret this new information on cluster structure in neutron-rich light nuclei.     

High-spin states in123Te

The¹⁰Be(¹²C,¹⁴O)⁸He-reaction has been used to study the levels of⁸He. In addition to the known excited state of⁸He at E _x =3.6MeV, withJ ^π=2⁺, three additional states were found at excitation energies of 4.54(25)MeV, 6.03(10)MeV and 7.16(4)MeV.     

Die Breite des 4+(11,4 MeV)-Zustandes von8Be aus7Li(d,n) 2α

With the reaction⁷Li+“d→n+⁸Be→n+2α the location and width of the⁸Be(4,+) level is redetermined. While the location at 11.4±0.05 MeV is found in agreement with known values, the width is found to be onlyΓ=2.8±0.2 MeV thereby disagreeing with data fromα-α-scattering but being close to a recent determination from the reaction¹⁰B(d,α)⁸Be (Γ=2.6 MeV). — No indication for participation of an excited state of⁵He in the simultaneously possible reaction via⁵He is found.     

The elastic scattering of polarized 3He by 3He and excitation in the 6Be system

Angular distributions of the polarization in the elastic scattering of ³He by ³He have been measured at eight energies between 18 and 33 MeV, corresponding to excitation of ⁶Be between 20.5 and 28 MeV. The measurements were made using the 33 MeV polarised ³He beam at the University of Birmingham Radial Ridge cyclotron and a small gas target. The data have been analysed in terms of real and complex phase shifts. The deduced phase shift energy dependence cannot be associated with a single isolated level in ⁶Be, however an application of the two-level R-matrix formula reveals some broad L = 3 structures around E_x = 25 MeV.     

Evidence for the constant-matrix-element mechanism in the breakup of the3He+7Li system and highly excited states in6Li

The inclusive alpha particle spectra from the breakup of the³He+⁷Li system atE ³He=42.9 MeV are analyzed in the frame of the nuclear reaction model whose matrix element does not depend on the relative energies of the outgoing particles and is therefore constant. The comparison with a recent analysis of thep+⁹Be interaction, leading to the same composite system, has shown the correlation of the final-state configuration on the entrance-channel cluster structure.the existence of broad excited states for⁶Li excitation energies between 19 and 28 MeV is confirmed.     

A study of excited states of5He by the7Li (d, α)5He-reaction

The interactions of deuterons with⁷Li, in which two α-particles and a neutron are produced in the final state are studied atE _d =1.2 MeV. The dual parameter α-α coincidence spectrum was analyzed with a search program. The results indicate two excited states of⁵He: One at excitation energy 2.9±0.1 MeV and with a reduced width of γ²=1.1±0.4 MeV, and the other at 4.8±0.4 MeV, with γ²=0.9±0.4 MeV. No contributions of sequential decay through the 4⁺ state in⁸Be or direct three body decay was observed.     

Cluster decay of the high-lying excited states in 14C

A cluster-transfer experiment of ⁹Be(⁹Be,¹⁴C→α+¹⁰Be)α at an incident energy of 45 MeV was carried out in order to investigate the molecular structure in high-lying resonant states in ¹⁴C. This reaction is of extremely large Q-value, making it an excellent case to select the reaction mechanism and the final states in outgoing nuclei. The high-lying resonances in ¹⁴C are reconstructed for three sets of well discriminated final states in ¹⁰Be. The results confirm the previous decay measurements with clearly improved decay-channel selections and also show a new state at 23.5(1) MeV. The resonant states at 22.4(3) and 24.0(3) MeV decay primarily into the typical molecular states at about 6 MeV in ¹⁰Be, indicating a well developed cluster structure in these high-lying states in ¹⁴C. Further measurements of more states of this kind are suggested.     

Experimental investigation of highly excited states of the 5,6He and 5,6Li nuclei in the (6Li, 7Be) and (6Li, 7Li) one-nucleon pickup reactions

The (⁶Li, ⁷Be) and (⁶Li, ⁷Li) reactions on ⁶Li and ⁷Li nuclei were investigated in the angular interval 0°–20° in the laboratory system at a ⁶Li energy of 93 MeV. In addition to low-lying states of the ^5,6He and ^5,6Li nuclei, broad structures were observed near the t(³He)+d and t(³He)+t thresholds at the excitation energies of 16.75 (3/2⁺) and ～20 MeV (for ⁵He), 16.66 (3/2⁺) and ～20 MeV (⁵Li), 14.0 and 25 MeV (⁶He), and ～20 MeV (⁶Li). The angular distributions measured in the ⁷Li(⁶Li, ⁷Be)⁶He reaction for transitions to the ground state (0⁺) and excited states at E _x=1.8 MeV (2⁺) and 14.0 MeV of the ⁶He nucleus were analyzed by the finite-range distorted-wave method assuming the 1p-and 1s-proton pickup mechanism. The (⁶Li, ⁷Be) and (⁶Li, ⁷Li) reactions were shown to proceed predominantly through the one-step pickup mechanism, and the broad structures observed at high excitation energies are considered as quasimolecular states of the t(³He)+d and t(³He)+t types.     

Spin-alignment and g-factor measurement of the I^{\pi} = 12+ isomer in 192Pb produced in the relativistic-energy fragmentation of a 238U beam

Reactions of a 16.8 MeV ⁶He beam with a ⁹Be target have been investigated using highly segmented detector setup covering a large solid angle. Data on elastic and quasi-free scattering, as well as two-neutron transfer, are reported. The results for elastic scattering are fairly well reproduced by a CDCC calculation, in agreement with the interpretation of a breakup effect already observed for the scattering of ⁶He on other light targets. Exotic quasi-free scattering of ⁶He on $ \alpha$ -cluster in ⁹Be is clearly observed. Inclusive and coincident events were used to extract information on the two-neutron transfer reaction ⁹Be(⁶He, $ \alpha$ )¹¹Be . Sequential decay of the ¹¹Be state at the excitation energy $\ensuremath E_x = 10.6$ MeV through different channels is discussed.     

Proton total cross sections on 1H, 2H, 4He, 9Be,C and O in the energy range 180 to 560 MeV

Proton total cross sections have been measured for the nuclei ¹H, ²H, ⁴He, ⁹Be, C and O from 180 to 560 MeV (610 to 1170 MeV/c). The standard transmission technique was used with a resulting total error of 1 % to 2 %. Statistical errors were small (< 1 %) and the major contribution to the final error comes from uncertainties in applying the correction for Coulomb-nuclear interference in elastic scattering at small angles. For ⁴He, ⁹Be, ¹²C. and ¹⁶O this experiment also gives new information on the real part of the spin-independent forward scattering amplitude for proton-nucleus elastic scattering. Total cross sections have been calculated using a Glauber model approach and poor agreement with the data is obtained, even for deuterium.     

The breakup of24Mg into16O and8Be

The breakup of²⁴Mg into¹⁶O and⁸Be fragments has been studied using the reactions¹²C(²⁴Mg,¹⁶O⁸Be)¹²C and¹²C(²⁰Ne,¹⁶O⁸Be)⁸Be. In the latter case, discrete states are observed near 24–28 MeV of excitation in²⁴Mg and the yield from this reaction is an order of magnitude greater than that of the former. This implies the excited configuration populated in²⁴Mg is favoured by the transfer of an alpha-particle and would therefore suggest an association with a 4-particle 4-hole configuration. This suggests a link with the octupole stabilised deformed minimum which appears in Nilsson-Strutinsky calculations of the potential energy surface in²⁴Mg, and also with theα —¹⁶O —α structure predicted in cranked cluster model calculations. In the excitation spectrum no states appear above 31 MeV indicating a possible band termination in disagreement with recent results using the¹⁶O+¹²C reaction. These results are discussed in terms of the Harvey model.     

Identification of gamma transitions from He and Be ternary fission fragments

He and Be ternary fission processes of ²⁵²Cf have been studied in two experiments with the Gammasphere detector array with light charged particle detectors surrounding the source. From α-γ double gated spectra, neutron multiplicity distributions were determined for related α ternary fission pairs. In going from binary to α ternary SF for approximately the same mass splittings (A ≈ 104–146) the average neutron multiplicity decreases about 0.7 AMU. In the first light charged particle (LCP) γ-γ experiment, the ¹⁰Be spectrum was cutoff below 27 MeV and in the recent experiment, below 18 MeV. For high energy (E > 27 MeV) ¹⁰Be ternary fission, the data indicate that the largest yields go via the cold process (zero neutron evaporation). In the recent experiment with E cutoff of 18 MeV, the ¹⁰Be ternary SF was observed for zero to 4n emissions. It seems that in some cases like ¹³⁶Te, the On channel is the strongest and in the other cases like ¹⁰⁰Zr the 1n or 2n channel dominates. Clearly, there is a shift to lower average number of neutrons emitted for ¹⁰Be compared to α ternary SF. The ¹⁰⁴Zr and ¹³⁶Te cases where zero neutron emission occurs may be related to the fact that these nuclei are near the limits of the more neutron rich Zr and Te nuclei observed. The ¹³⁶Te is more spherical than the heavy partners in the other pairs and this may influence the 0n channel. Finally, the 0n channel may be more enhanced in the first data with the higher ¹⁰Be energy cutoff, leading to lower excitation energy. Also, we confirmed the 3368 keV peak with the FWHM of 60 keV emitted from the moving Be particles in the Doppler effect corrected spectrum.     

Neutron-induced charged-particle reactions in 6Li and 9Be

Angular distributions of tritons from the ⁶Li(n, t)⁴He reaction were measured at E_n = 7.25, 6.77, 6.57, 5.24 and 4.71 MeV. Angular distributions of douterons from respectively, the ⁶Li(n, d)⁵He two-body breakup reaction were measured at E_n = 6.77 and 6.57 MeV, and of protons from the ⁶Li(n, p)⁶He reaction at E_n = 6.77, 5.24 and 4.71 MeV. All these reactions in ⁶Li were analyzed as direct interaction in the formalism of the distorted wave Born approximation. The optical model for the nuclear interaction was found to apply reasonably well to nuclei as light as ⁴He, ⁵He, ⁶He and ⁶Li. In addition, ⁶Li as an alpha-deuteron cluster gives the best bound-state wave function to describe the experimental angular distribution of tritons. The excitation functions at forward angles of the ⁶Li(n, t)⁴He, ⁶Li(n, d)⁵He and ⁶Li(n, p)⁶He reactions were measured for incident neutron energies between 4.4 and 7.3 MeV. It is found that the ⁶Li(n, d)⁵He two-body breakup reaction has a threshold at about E_n = 5.3 MeV. Angular distributions at E_n = 18.3 MeV for tritons and protons from the ⁹Be(n, t)⁷Li and ⁹Be(n, p)⁹Li, respectively, were also measured.     

Observation of abnormally large radii of nuclei in excited states in the vicinity of neutron thresholds

Differential cross sections for inelastic scattering leading to the excitation of some nuclear states situated near neutron-emission thresholds were analyzed. With the aid of a modified diffraction model, abnormally large radii were found for the 1/2₁⁺ state of the ¹³C nucleus at 3.09 MeV, for the first levels of positive-parity rotational bands in the ⁹Be (1/2⁺ level at 1.68 MeV and 5/2⁺ level at 3.05 MeV) and ¹¹Be (5/2⁺ level at 1.78 MeV and 3/2⁺ level at 3.41 MeV) nuclei, and for the 2₁⁺ state of the ¹⁴Be nucleus at 1.54 MeV and 1₁⁻ state of the ¹²Be nucleus at 2.7 MeV. All of these states possess signatures typical of neutron halos.     

Investigation of the near-threshold cluster resonance in ~(14)C

An experiment for p(~(14)C,~(14)C~*→~(10)Be+α)p inelastic excitation and decay was performed in inverse kinematics at a beam energy of 25.3 Me V/u.A series of~(14)C excited states,including a new one at 18.3(1)Me V,were observed which decay to various states of the final nucleus of~(10)Be.A specially designed telescope system,installed around zero degrees,played an essential role in detecting the resonant states near theα-separation threshold.A state at 14.1(1)Me V is clearly identified,being consistent with the predicted band-head of the molecular rotational band characterized by theπ-bond linear chain configuration.Further clarification of the properties of this exotic state is suggested by using appropriate reaction tools.     

Structure studies of 11Be and 12Be: Observation of molecular rotational bands

Excited states of ¹¹Be have been studied with several transfer reactions. Nine states between 3.96 and 25.0 MeV excitation energy show the characteristic energy dependence of a rotational band. The deduced large moment of inertia is consistent with a 2α structure with large deformation. In ¹²Be four high-lying states observed at 7.3, 10.7, 14.6, and 21.7 MeV in the reaction ⁹Be(¹⁵N,¹²N)¹²Be, also form a rotational band with almost the same moment of inertia; tentative spin assignments of 2⁺–8⁺ are used.