Investigating highly excited states of the 8Li isotope

Highly excited states of the ⁸Li isotope are sought in absorption reactions of π^? mesons stopped by ^10,11B isotopes. The ground and three excited states of the ⁸Li isotope are observed in inclusive measurements of reactions ¹⁰B(π^?, d)X and ¹¹B(π^?, t)X. The states with excitation energies E _x ≈ 8.7 and 10.1 MeV are observed for the first time in correlation measurements of reactions ¹⁰B(π^?, dt)X and ¹¹B(π^?, tt)X.     

Spectroscopy of the <Superscript>9</Superscript>Li isotope in stopped-pion absorption reactions

The origin of the ⁹Li isotope is sought in missing-mass spectra measured in ¹¹B(π⁻, d)X, ¹²C(π⁻, pd)X, and ¹⁴C(π⁻, dt)X stopped-pion absorption reactions. The parameters of the three observed low-lying excited states coincide with the literature data. A state with excitation energy E _x = 9.1 ± 0.1 MeV, lying above the threshold of ⁹Li decay into ⁶He + t, is observed for the first time.     

Searches for the superheavy hydrogen isotope 7H in the absorption of stopped π − mesons

Experimental searches for the superheavy hydrogen isotope ⁷H were performed in reactions involving the absorption of stopped π ^? mesons on ⁹Be and ¹¹B nuclei. In the reaction ⁹Be(π ^?, pp)X, the missing-mass spectrum shows evidence for the formation of ⁷H states, that of E _r = 16 ± 1 MeV and Γ ? 2 MeV and that of E _r = 21 ± 1 MeV and Γ ? 5 MeV (E _r is the resonance energy with respect to breakup into a trition and four neutrons, and Γ is the observed level width).     

Electroexcitation of isovector magnetic dipole and quadrupole transitions in 18O and their relation to radiative pion capture

In a high-resolution ¹⁸O(e, e′) experiment sharp states at E_X=16.38±0.01 MeV (J^π=2^?, ground state analogue of and at E_X=18.86±0.01 MeV (J^π=1⁺) and clustering of strength (possibly with J^π=1^?, 2^?) at E_X≈23.7 MeV have been observed and compared to theoretical predictions. The transition strengths for the narrow states are B(M2) ↑ = 58± 8 μ_K² fm² and B(M1) ↑ = 0.28± 0.04 μ_K², respectively. These results agree qualitatively with the resu lts from the analogous ¹⁸O(π^?, γ)¹⁸N reaction.     

The formation of the superheavy hydrogen isotope <Superscript>6</Superscript>H in the absorption of stopped π<Superscript>−</Superscript>-mesons by nuclei

An experimental search for the superheavy hydrogen isotope ⁶H was conducted through studying the absorption of stopped π^?-mesons by ⁹Be and ¹¹B nuclei. A structure in the missing mass spectrum caused by the resonance states of ⁶H was observed in three reaction channels, namely, ⁹Be(π^?, pd)X, ¹¹B(π^?, d³He)X, and ¹¹B(π^?, p⁴He)X. The parameters of the lowest state E_r=6.6±0.7 MeV and Γ=5.5±2.0 MeV (E_r is the resonance energy with respect to the disintegration into the triton and three neutrons) are evidence that ⁶H is a more weakly bound system than ⁴H and ⁵H. Three excited states of ⁶H were observed. Their resonance levels (E_1r=10.7±0.7 MeV, Γ_1r=4±2 MeV, E_2r=15.3±0.7 MeV, Γ _2r=3±2 MeV, and E_3r=21.3±0.4 MeV, Γ_3r=3.5±1.0 MeV) are energetically capable of disintegrating into six free nucleons.     

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.     

Spectroscopy of the <Superscript>5</Superscript>H superheavy hydrogen isotope

The formation of the ⁵H superheavy hydrogen isotope was experimentally sought in the reactions induced by stopped π^? mesons absorbed by ⁹Be nuclei. Peaks in missing-mass spectra were observed in two reaction channels, ⁹Be(π^?, pt)X and ⁹Be(π^?, dd)X, and were attributed to the ⁵H resonance states. The lowest state has parameters Er=5.5±0.2 MeV and Г=5.4±0.5 MeV [E_r is the resonance energy measured from the (triton + two neutrons) threshold]. Therefore, ⁵H is bound more weakly than ⁴H. Excited states of ⁵H were also observed. All three resonance levels (E_1r=10.6±0.3 MeV, Г_1r=6.8±0.5 MeV; E_2r=18.5±0.4 MeV, Г_2r=4.8±1.3 MeV; E_3r=26.7±0.4 MeV, Г_3r=3.6±1.3 MeV) can decay into five free nucleons.     

Production of Heavy Helium <Superscript>5</Superscript>Hе in the Absorption of Stopped Pions by <Superscript>10,11</Superscript>B Nuclei

Helium ⁵Hе states are sought in missing-mass (MM) spectra from reactions of the absorption of stopped pions: ¹⁰В(π^?, dt)Х and ¹¹В(π^?, tt)Х. The experiment is conducted using the LANL accelerator equipped with a two-arm semiconductor charged-particle spectrometer. The parameters of the ground state agree with the literature data. The best fit for the first excited level is obtained at E_r = 1.8(5) MeV and Γ = 4.7(7) MeV. Neither of the two reactions produce statistically significant evidence for the presence of highly excited (E_x ≥ 20 MeV) states of ⁵Hе.     

Λ, Λ production in e+e− annihilation at 33 GeV centre of mass energy

Performing a PWA of the π^?π^?π⁺ system over the ^?tp/p range 0.2 to 0.4 GeV² we find evidence for a J^P = 0^? ,J^G=1^? meson of mass 1342 ± 20 MeV and width 220 ±70 MeV decaying into ?π. This state is produced by natural parity exchange with a slope similar to that of elastic scattering. It can be interpreted as a radial excitation of the π meson (π′).     

High-resolution (e,e') study of isovector M1 and M2 transitions in the oxygen isotopes: (I). 16O

The M1 and M2 transition strength distribution for ¹⁶O in the excitation energy range from 16 to 20 MeV has been measured in a high-resolution electron scattering experiment. The M1 strength is concentrated in three sharp states at E_x = 16.22, 17.14 and 18.79 MeV (± 0.01 MeV) with B(M1, k)↑ = 0.20 ± 0.02, 0.32 ± 0.03 and 0.13 ± 0.03 μ_N², respectively. An additional strength of 0.35 ± 0.09 μ_N², distributed over eight weakly excited states with excitation energies E_x = 17.4 to 18.0 MeV, brings the total measured M1 strength to B(M1, k)↑ = 1.0 ± 0.1 μ_N². The experimental M2 strength is distributed over states at E_x = 16.82, 17.78, 18.50 and 19.0 MeV (± 0.01 MeV) with B(M2, k)↑ = 19 ± 2, 13 ± 2, 59 ± 7 and 341 ± 51 μ_N² · fm², respectively. Electric transitions were also measured to states at E_x = 16.45 MeV (2⁺, E2), 17.30 MeV (1⁺, E1) and 18.20 MeV (2⁺, E2). Calculations were performed using the modified surface delta interaction in a 2p-2h shell model for the M1 transitions and the random phase approximation for the M2 transitions. The results show the sensitivity of the M1 strength as a measure of ground-state correlations and compare well with results from the ¹⁵N($\text{p}$, γ) reaction.     

Search for superheavy hydrogen isotopes <Superscript>4,5</Superscript>H in reactions of pion absorption by <Superscript>10,11</Superscript>B nuclei

The results of searching for production of superheavy hydrogen isotopes ^4,5H in reactions of absorption of stopped π^? mesons by ^10,11B nuclei are reported. A peak near 3 MeV was observed in the missing mass spectra measured in the reactions ^10,11B(π^?, t⁴He)X, ¹⁰B(π^?, d⁴He)X, and ¹⁰B(π^?, t³He)X. A structure caused by two ⁵H states with the resonance energies E _R = 5.2 and 10.4 MeV was observed in the missing mass spectra measured in the reactions ¹¹B(π^?, d⁴He)X, ¹¹B(π^?, t³He)X, and ¹⁰B(π^?, d³He)X.     

Triple differential cross section for angle,atomic number and energy (or angular momentum transfer) calculated for the 280MeV40Ar+58Ni (or 365MeV63Cu+197Au) system in a simple model

Highly excited levels of³³S populated by α-particle capture in²⁹Si have been investigated forE _α=1.962 MeV to 4.287 MeV. Excitation curves measured with Ge(Li) and BF₃ detectors are reported. More than fifty resonances can be identified with levels in³³S. (α, γ) angular distributions measured on five strong resonances have yieldedJ ^π values 1/2+, 3/2 +, 5/2?, 5/2?, 5/2? and 3/2+ respectively, for theE _x =10.054, 10.466, 10.523, 10.721, 10.758 and 10.776 MeV levels in³³S. Elastic scattering experiments have been performed and theJ ^π assignments are found to be consistent with thel-values inferred from the elastic scattering data. Decay schemes from the above³³S levels have been proposed. A new level at 9.245 MeV is also suggested and theJ ^π values for the 4.425 and 2.87 MeV states are shown to be consistent with 7/2+ and 3/2+ assignment, respectively. Nuclear Reactions²⁹Si(α, γ) and²⁹Si(α, α),E _α=1.962-4.287 MeV. Measured relative σ(E). DeducedJ ^π andE _γ of³³S levels. New³³S level atE _x =9.245 MeV. Enriched targets.     

Alpha-particle decay widths and narrow cluster states in15N

The total widths of¹⁵N* excited cluster states with E_x, J^π=12.55 MeV, 9/2⁺ and 13.00 MeV, 11/2^? are estimated by measuring the total alpha-particle decay probability and assuming that the reduced width does not exceed the Wigner limit for alpha-particle decay.     

High-spin states in 34CI

High-spin yrast states in ³⁴Cl have been studied with the reactions ³¹P(α, nγ)³⁴Cl at E_α = 11.7?16.3 MeV and ²⁴Mg(¹²C, pnγ)³⁴Cl at E(¹²C) = 32–35 MeV. Ambiguities in the ³⁴Cl level scheme for levels at E_x = 4.82 and 5.32 MeV have been resolved through combination of threshold measurements with the ³¹P + α reaction and gamma-gamma coincidence and E_γ-measurements with the ²⁴Mg + ¹²C reaction. Gamma-gamma coincidence and in-beam γ-γ angular correlation experiments have been performed employing a Compton-suppression spectrometer with a solid angle of 120 msr.Unambiguous spin-parity assignments of J^π = 6^?, 5⁺ and 7⁺ to the ³⁴Cl levels at E_x = 4.74, 4.82 and 5.32 MeV, respectively, are obtained.Previously unreported levels of high spin are found at E_x = 7.25 and 7.80 MeV with J^π = (9⁺) and (8⁺); τ_m = 200 ± 70 fs and 100 ± 70 fs, respectively. Excitation energies, mean lives, branching ratios and multipole mixing ratios are reported. The experimental results are compared with large-scale shell-model calculations. The high-spin yrast levels can be characterized by a rather simple shell-model structure.     

Study of theω π + system

The mass spectra of theω π ⁰ system, produced inπ ^? p charge-exchange reactions at 38 GeV/c and 100 GeV/c, show a new neutral state with a mass of 2200±20 MeV and a width of 260±50 MeV. Likeρ ₃(1690), this meson,X(2200), is produced through one-pion-exchange.X(2200)J ^PC is likely 1^??. It might be a 2³ D ₁ radial-orbital excitation ofρ ⁰. Its production cross section falls with energy quadratically, in agreement with one-pion-exchange. The cross sections forb ₁(1235) andρ ₃(1690) production have also been measured; their energy dependences have been determined.     

A study of the 230Th (α, α′f) reaction at 50 MeV

The total kinetic energy release (TKE) of the fissioning nucleus ²³⁰Th is measured as a function of the excitation energy E_x, for various mass splittings. A small rise in the TKE(E_x) of 0.2 ± 0.1 MeV per 1 MeV rise in E_x is observed. The mass-yield distributions show fine structure for E_x around 6.7 MeV. The mass yield is presented as function of the TKE.     

A study of 28Si(α, γ)32S resonances below Eα = 3.83 MeV

The γ-decays of eleven resonances in the ²⁸Si(α,γ)³²S reaction below E_α = 3.83 MeV have been studied using a large Ge(Li) detector. Results for branching ratios differ considerably from previous NaI work. The previous discrepancy in radiative strengths for the 2.61 MeV resonance is explained by this data. The strengths of the first five resonances at E_α = 1.77, 1.99, 2.19, 2.37 and 2.42 MeV appear to be (39 ± 13)% lower than previously reported. Spin-parities of l^?, 2⁺ and 2⁺ have been assigned to the levels at 8.50, 8.69 and 8.86 MeV respectively. The radiative width of the E_p = 1.467 MeV, J^π = 3^? resonance in the ³¹P(p,γ)³²S reaction has also been measured.     

The 6− analog-antianalog states of 28Si

A resonance is observed in the ²⁷Al(p, γ)²⁸Si reaction at E_p=2876±2 keV, which corresponds to an excitation energy of 14356±2 keV. The 14.36 MeV level decays to a new level at 11577±2 keV, which is turn decays to the known level at 9701.8±0.5 keV. With previous information on the 9.70 MeV level and the present γ-ray angular distributions, obtained from singles spectra as recorded by a 40 cm³ Ge(Li) detector, the spins of the three levels can be limited to J=5, 6; J=6; and J=5, respectively. Transition strength arguments based on measurements of the strength of the 2876 keV resonance and the lifetime of the 11.58 MeV level indicate that the 14.36 MeV level has J^π=6^?, T=1 and that the 11.58 MeV level has J^π=6^?, T=0.     

Radiative width of the first T = 2 state in 8Be

The lowest T = 2 state (J^π = 0⁺) in ⁸Be was observed as a resonance at E_d = 6962.8 ± 3.0 keV (E_X = 27495.8 ± 2.4 keV, λ_c.m. = 5.5 ± 2.0 keV) in the ⁶Li(d, γ)⁸Be reaction. The resonant capture yield to the 17.6 MeV J^π = 1⁺, T = 1 state gives λ_γ = 23 ± 4 eV (1.14 ± 0.20 W.u.), in good agreement with the intermediate coupling model.     

Measurement of the π−n→π−π−p cross section near threshold

The cross section for the reaction π^?n→π^?π^?p has been measured in a deuterium bubble chamber. The cross section at E_π,lab = 226, 250 and 312 MeV was found to be equal to 9.4 ± 2.3, 25.0 ± 5.3 and 57 ± 10 μb, respectively.