The n-n S-wave scattering length from the neutron spectra of the reaction π− +d → 2n+γ

We present a measurement of the neutron-neutron S-wave scattering length, a_nn, from an analysis of the neutron energy and angular spectra for the reaction d(π^?, γ)2n. This reaction provides the unique advantage that while all three final-state particles are experimentally detectable, only the neutrons are strongly interacting. The data are analyzed using the treatment of this reaction given by Bander, taking the effects of experimental resolution into account with Monte Carlo techniques. Two independent analyses of 4200 events yield a_nn = ?16.7 ±1.3 fm assuming r_nn = 2.65 fm. This value is in good agreement with calculations of a_nn which assume charge symmetry of the nuclear components of p-p and n-n interactions.     

Investigation of224Ra in the226Ra(α, α′ 2n) reaction

Positive and negative parity bands have been followed up to 10⁺ (possibly 12⁺) and 11^? in²²⁴Ra and are compared to the corresponding bands in the isotone²²⁶Th. If a constant value of the intrinsic quadrupole moment is assumed for allE2 transitions in²²⁴Ra theE1/E2 branching ratios are consistent with an intrinsic dipole moment of ¦Q₁¦=0.032(3)e·fm. This small value, as compared to ¦Q₁¦=0.30(2)e·fm for²²⁶Th, can be explained by an almost complete cancellation of large positive liquid-drop and negative shell-model contributions.     

The neutron-neutron scattering length from a complete experiment on the 3H(d, 2n)3He reaction at 8.45 MeV

The spectrum of the time-differences between the two neutrons from the ³H(d, 2n)³He reaction detected by two plastic scintillators situated at 0.2 and 2.0 m from the target was measured at 0°. The spectrum was compared with a Jost-function final-state interaction enhancement factor and yielded a value of 16.2 ± 1.2 fm for a_n?n, the neutron-neutron scattering length.     

Investigation of the reaction 2H(n,np) at θn = 0°

The differential cross section of the ²H(n, np) reaction was measured at θ_n = 0°. Because of the applied special geometry the experimental data extend over a large fraction of the phase space, including several final state interaction regions as well as regions far from the dominance of quasi-two-body processes. The experiment was analysed with an exact three-body calculation using s-wave separable potentials (CEE). The analysis of the n-n and n-p final state interaction peaks gave a_nn = ?16.3 ± 1.6 fm for the n-n ¹S₀ scattering length and r_nn = 3.15 ± 0.7 fm for the effective range. Remarkable deviations from the calculated cross sections-were found in regions where no strong final state interaction was present.     

Neutron-neutron scattering length from the 2H(n,np)n reaction at bombarding energies up to 27 MeV

The n-n interaction has been investigated in a kinematically complete experiment with high statistical accuracy via the ²H(n, np)n reaction at bombarding energies up to 27 MeV, extending previous measurements to higher energies and to a different geometry. The analysis with exact three-body calculations yields ann = ?16.9 ± 0.6 fm.     

Fragmented 2d 5/2, 1g 7/2 and 1g 9/2 deep proton-hole states of207TI

The three proton-hole states ?2d_5/2, 1g_7/2 and 1g_9/2 are found to be fragmented as a result of coupling of these states with the 3^?, 5^?, 2⁺, 4⁺ and 6⁺ collective states of²⁰⁸Pb. The excited states in²⁰⁸Pb (t,α) reaction can be quantitatively explained in terms of altered 2d_5/2, 1g_7/2 and 1g_9/2 states with the hole-core coupling model.     

High-spin states in112Cd from the110Pd(α, 2n γ)-reaction

The decay scheme of¹¹²Cd has been studied by γ-ray spectroscopy with the¹¹⁰Pd(α, 2nγ) reaction. Spin and parity assignments were made on the basis of coincidence measurements, angular distributions and excitation functions. Twelve new energy levels were established. A vibrational-like positive-parity band up to spin 8⁺ and a negativeparity side band 5^?, (7^?), (9^?) were found. For the negative-parity states a (v_j, vh_11/2) configuration is suggested. Nuclear Reactions:¹¹⁰Pd(α,2nγ),E _α =15–22.5 MeV; measuredE _γ ,E _γ , (E,E _γ ),E _γ (θ),γ-γ- coincidence;¹¹²Cd deduced levels,J; enriched target.     

Observation of the (π−, π−n) and (π+, π+p) reactions at 165 MeV

The (π^?, π^?n) and the (π⁺, π⁺p) reactions were studied on C, Fe, and Bi at 165 MeV by coincidence measurement o outgoing particles. The nucleon-knockout reaction is the dominant inelastic process at backward pion-scattering angles at this energy. The quasifree (π^?, π^?n) and (π⁺, π⁺p) cross sections were determined from the π-N an correlations. Their σ_qf(π^?, π^?n)/σ_qf(π⁺, π⁺p) ratio is consistent with unity for C and is larger than the N/Z ratio for the heavier nuclei.     

Neutron-proton final state interaction in the 3H(3He,pα)n reaction at low bombarding energies

The ³H(³He, pα)n reaction has been studied in a kinematically complete experiment at ³He bombarding energies between 0.31 and 2.80 MeV in order to detect a possible resonant energy dependence of the spin singlet (T = 1) neutron-proton final state interaction (FSI). The data in the region of low n-p relative energies have been analyzed in terms of the Watson-Migdal formalism. Only a slight relative increase of the ¹S₀ n-p FSI is observed with increasing bombarding energy. This result is not easily related to the strong isospin violations found in the two-body reaction ³H(³He, d)⁴He at similar ³He energies.     

Charge states of atoms in the lattices of the high-temperature superconductors Tl2Ba2Ca n−1CunO2n+4 and Bi2Sr2Ca n−1CunO2n+4

To determine the charges of atoms in the lattices of the compounds Tl₂Ba₂Ca _n?1Cu_nO_2n+4 and Bi₂Sr₂Ca _n?1Cu_nO_2n+4 (n=1,2,3), the parameters of the electric field gradient tensor at the copper sites of the indicated lattices were found by emission Mössbauer spectroscopy on the isotopes ⁶¹Cu(⁶¹Ni) and ⁶⁷Cu(⁶⁷Zn), and a calculation of these parameters was performed in the point-charge approximation. A comparison of the resulting values and the published data on ⁶³Cu nuclear quadrupole resonance showed that agreement between the experimental and computed values of the parameters obtains for models in which the holes resulting from a reduction in the valence of some of the thallium (bismuth) atoms are localized predominantly at oxygen sites located in the same plane as the copper atoms (for the compounds Tl₂Ba₂Ca₂Cu₃O₁₀ and Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀—at oxygen sites in the same plane as the Cu(2) atoms).     

Investigation of 228Th in the (α, α'2n) reaction

The ²³⁰Th(α, α'2n)²²⁸Th reaction at E_α = 56 MeV was used to investigate states of moderately high spin in ²²⁸Th. Conversion electron and e^?-γ coincidence measurements were carried out, where the electrons were detected with an iron-free orange spectrometer. The ground state and low-lying K^π = 0^? rotational bands were observed up to I^π = 14⁺ and 13^?, respectively. The data are interpreted in terms of an ω-expansion for the ground-state rotational band, and an octupole vibrational band distorted by the Coriolis coupling to the K^π ? 1^? excitations for the K^π = 0^? band.     

Levels in 156Gd studied in the (n, γ) reaction

Levels up to 2.3 MeV in ¹⁵⁶Gd have been studied using the (n, γ) reaction. Energies and intensities of low-energy γ-rays and electrons emitted after thermal neutron capture have been measured with a curved-crystal spectrometer, Ge(Li) detectors and a magnetic electron spectrometer. High-energy (primary) γ-rays and electrons have been measured with Ge(Li) detectors and a magnetic spectrometer. The high-energy γ-ray spectrum has also been measured in thermal neutron capture in 2 keV resonance neutron capture. The neutron separation energy in ¹⁵⁶Gd was measured as S_n = 8535.8 ± 0.5 keV.About 600 transitions were observed of which ~50% could be placed in a level scheme containing more than 50 levels up to 2.3 MeV excitation energy. 42 of these levels were grouped into 15 excited bands. In addition to the β-band at 1050 keV we observe 0⁺ bands at 1168, 1715 and 1851 keV. Other positive-parity bands are: 1⁺ bands at 1966, 2027 and 2187 keV; 2⁺ bands at 1154 (γ-band) and 1828 keV; and 4⁺ bands at 1511 and 1861 keV. Negative-parity bands are observed at 1243 keV (1^?), 1366 keV (0^?), 1780 keV (2^?) and 2045 keV (4^?). Reduced E2 and E0 transition probabilities have been derived for many transitions. The ground band, the β- and γ-bands and the 0⁺ band at 1168 keV have been included in a phenomenological four-band mixing calculation, which reproduces well the experimental energies and E2 transition probabilities.The lowest three negative-parity (octupole) bands of which the 0^? and the 1^? bands are very strongly mixed, were included in a Coriolis-coupling analysis, which reproduces well the observed energies. The E1 transition probabilities to the ground band are also well reproduced, while those from the higher-lying 0⁺ bands to the octupole bands are not reproduced. Absolute and relative transition probabilities have been compared with predictions of the IBA model and the pairingplus-quadrupole model. Both models reproduce well the E2 transitions from the γ-band, while strong disagreements are found for the E2 transitions from the β-band. The IBA model predicts part of the decay features of the higher lying 2⁺₂, 4⁺₁ and 2^?₁ bands.     

n-n Effective range from the photon spectrum of the reaction π−d→γnn

Notable improvements in the treatment of the reaction π^?d→γnn, extending the validity of the calculation to lower photon energies, permit a new analysis of a high statistics photon spectrum. A precise value of the effective range parameter γ_nn = 2.83 ± 0.11 fm has been obtained. The theoretical uncertainty is 0.11 fm. The value of the scattering length previously extracted from the same spectrum is confirmed, with a_nn = ? 18.6 ± 0.5 fm.     

Search for narrow resonances in the reaction γ + Be → e+e− + X at 1.8 ⩽ Me+e− ⩽ 2.6 GeV

The reaction γ + Be → e⁺e^? + X was studied with a bremsstrahlung beam of 7.2 GeV maximum energy. For invariant pair masses 1.8 ? M_e⁺e^? 2.6 GeV, no evidence for narrow resonance of width smaller than 40 MeV was found. For the mass interval 2.1 ? M_e⁺e^? ? 2.6 GeV, we obtained an upper limit of σ · B_e⁺e^? < 2 × 10^?35 cm²/nucleon (90% confidence level), assuming a production mechanism similar to the θ (1019) meson.     

Determination of the longitudinal and the transverse part in π+ electroproduction

We report on an experiment where the different contributions from the transverse and longitudinal polarization of the virtual photon are measured separately for the reaction e^?p→e^?π⁺n. The data taken above the resonance region at small ∣t∣ values in the q² range of ∣q²∣ < 0.5 GeV² show a clear dominance of the longitudinal part of the cross section and are well described by a generalized Born-term model. Using this model the electromagnetic form factor of the pion is determined. At q² = ?0.35 GeV² one gets F_π = 0.598 ± 0.021.     

The3He(γ,2p)n reaction for Eγ=80-170MeV

The cross section for the³He(γ, 2p) reaction has been measured in a complete kinematics experiment in the energy rangeE _γ=80–170 MeV, forθ _P1=θ _P2=90°. This configuration was selected in order to investigate the role of proton-proton final state interactions in the three-body breakup process. The measured proton spectra are seen to be consistent with a prediction using the Watson-Migdal formalism. The magnitude of the observed cross section clearly indicates an enhancement over phase space, presumably due to the strong proton-proton interaction in the final state. The experimental results agree, within their limited statistical accuracy, with a theoretical calculation which includes this effect.     

Reaction dependence of nuclear decay linewidths

Various light- and heavy-ion reactions, 20 < E < 100 MeV, have been used to study the reaction dependence of α-decay widths for ⁸Be¹(2 ⁺ , 2.9 MeV) and ¹⁶O¹(1^?, 9.6 MeV). Although slight differences (< 20 %) are found for the observed line shapes (Γ), the resonance widths inferred (Γ_R) are self-consistent and indicate little if any reaction dependence (< 10 %). Near a decay threshold one may expect Γ < Γ_R by 20 % or more, however, and thus care must be taken in comparing decay widths inferred from nuclear reactions with those from scattering resonances. Reduced formal α-decay widths of γ_λ² = 680 ± 100 keV (s = 4.8 fm) and γ_λ² = 350 ± 50 keV(s = 5.4 fm), corresponding to θ_λ² = 0.50 and θ_λ² = 0.49 are deduced for ⁸Be¹(2 ⁺ , 2.9 MeV) and ¹⁶O¹(1^?, 9.6 MeV) using the nuclear-reaction Γ_R values and a particular set of α-nucleus potentials.     

Structures of proton solvates in the HCl-H2O-(CH3)2NCHO system as determined by IR spectroscopy and quantum-chemical calculations

The structures of proton solvates in the HCl-H₂O-(CH₃)₂NCHO (DMFA) system at H₂O: DMFA ratios ranging from 1: 1 to 21: 1 are studied by the IR spectroscopy method. It is demonstrated that H₂O?H⁺?OH₂ ions and (CH₃)₂NCHO?H⁺?OH₂ mixed solvates with a strong quasi-symmetrical hydrogen bond are formed in solutions. With an increase in the DMFA concentration, the fraction of H₅O ₂ ⁺ ions decreases. At HCl: H₂O ≥ 1: 3 and arbitrary DMFA concentrations, only mixed proton solvates are formed. The continuous absorption coefficients for the (CH₃)₂NCHO?H⁺?OH₂ ions are determined. The results obtained are compared with the results of quantum-chemical calculations of the structure and relative stability of the (DMFA) _m H⁺(H₂O) _n (m = 0–2, n = 0–3) positively charged complexes which were performed by the B3LYP/6-31++G(d,p) DFT method. We identified 19 stable configurations with chain, cyclic, and branched structures. Most of these configurations contain the (CH₃)₂NCHO?H⁺?OH₂ fragment. The parameters of the O?H⁺?O bridge show that some configurations have a strong quasi-symmetrical hydrogen bond. In some cases, the proton is located between two DMFA molecules. The H₂O?H⁺?OH₂ bridge is observed in none of the stable configurations of the (DMFA) _m H⁺(H₂O) _n (m ≠ 0) complexes.     

Half-life and configuration of the 1/2+ intruder state in203Bi

The decay properties of theJ ^π=1/2⁺,E _exc=1,098 keV state in²⁰³Bi were studied. The state was populated via the²⁰⁴Pb(p, 2n) reaction and the activity was studied with the ion guide isotope separator on-line system IGISOL. The half-life of the 1/2⁺ state was measured to beT _1/2=303 ±5 ms. From this value the partial half-lives of the three depopulating branches 1/2⁺ →7/2^? (E3), 1/2⁺→5/2^? (E3 +M2) and 1/2⁺→9/2 _g.s. ^? (M4) were deduced. Since all the transitions are configuration forbidden in first order, a detailed study of second-order shell-model configuration mixing could be performed.