MeV State Of 12C Research Articles

Measurement of the 3-α decay from the Hoyle and the broad 10 MeV states in12C

The measurements of the 3-α decay from the Hoyle and the broad 10 MeV state in12C have been performed using an inverse kinematic method of the12C(12C,3α)12C reaction at E12C = 110 MeV. In the measurement of the Hoyle state, the upper limit of the direct decay was improved to be 0.2 %. This was inconsistent with the recent reported nonzero value of 0.9 %, but an order larger than the direct decay branch predicted in the 3-α model. The branching ratios of the sequtial decay for the broad 10 MeV state were also obtained. They were higher than those obtained in the RCNP experiment, since they contained the contributions of higer multipole components. Their contributions will be estimated.

Complete kinematical study of the 3 $\alpha$ breakup of the 16.11 MeV state in 12C

The reaction $^{11}B+p$ has been used to populate the $(J^{\pi},T)=(2^+,1)$ state at an excitation energy of 16.11 MeV in $^{12}$C, and the breakup of the state into three $\alpha$ particles has been studied in complete kinematics. A two-step breakup model which includes interference effects is found to provide the most accurate description of the experimental data. The branching ratio to the ground state of $^8$Be is determined to be 5.1(5)% in agreement with previous findings, but more precise by a factor of two, while the decay to the first-excited state in $^8$Be is found to be dominated by $d$-wave emission.

Nature of 10 MeV state in 12C

We performed a coincidence measurement of decay-α particles by using inelastic scattering of 386 MeV α particles on 12C. We obtained further evidence for the second 2+ state at 9.84 MeV, which we found in previous work, from angular correlation functions for decay-α particles. The coincidence energy spectra with the α-decay to the ground state and the first excited 2+ state in 8Be from the 10 MeV states in 12C were obtained. They indicated the broad 0+ state at 10 MeV consists of two components. The lower 0+ state do α decay to the ground state of 8Be only. The higher 0+ state has a distinct peak at 10.8 MeV with a width of 0.4 MeV in the coincidence spectrum for the first excited state of 8Be channel. They have consistent properties predicted for a higher nodal state of the Hoyle state and a linear-like 3α state, respectively.

α + 12C scattering at 110 MeV: Has exotic 7.65 MeV Hoyle’s state signatures “alpha-condensate” structure?

We present new measurements of the α + 12C elastic and inelastic (to the states 4.44, 7.65, and 9.64 MeV) scattering at Elab = 110 MeV in the wide angular range from ∼10° to 175°, which enable us to examine the condensate and cluster properties of the low-lying excited states in 12C. We present the diffraction-radius analysis of our data together with a considerable amount of the existing data. The magnitudes of the diffraction radii for the ground and the first excited (4.44 MeV) states are found to be equal, whereas they appear to be enhanced by ∼0.6 fm both for 7.65 and 9.64 MeV states. This result shows that the radius of the Hoyle’s 02+, 7.65 MeV state in 12C is by a factor of ∼1.2–1.3 larger than that of the ground state. It is demonstrated that the direct transfer mechanism of 8Be dominates at the largest angles in all four reactions reported here. The configuration corresponding to the transfer of 8Be in its ground state (Iπ = 0+) with L = 0 turns out to be the most important for the 7.65 MeV state of 12C. Evidence of existence of some features of α-condensed structure of the Hoyle’s 02+ state in 12C was obtained: its enhanced radius and large contribution of α-particle configuration with L = 0.

Observation of γ-delayed 3α breakup of the 15.11 and 12.71 MeV states in 12C

The reactions B10(He3,pααα) at 4.9 MeV and B11(He3,dααα) at 8.5 MeV have been used to investigate the γ decay of states in 12C. By measuring the four-body final state in complete kinematics we are able to detect γ transitions indirectly. We find γ transitions from the 15.11 MeV state in 12C to the 12.71, 11.83, 10.3 and 7.65 MeV states followed by their breakup into three α particles. The relative γ-ray branching ratios obtained are (1.2±0.3), (0.32±0.12), (1.4±0.2) and (4.4±0.8)%, respectively, with the remaining (92.7±1.0)% of the γ decays going to the bound states. We obtain Γα/Γ=(2.8±1.2)% for the isospin-forbidden α decay of the 15.11 MeV state. From the 12.71 MeV state we find γ transitions to the 10.3 and 7.65 MeV states. The relative γ-ray branching ratios are (0.9−0.5+0.6) and (2.6−1.2+1.6)%, respectively, with the remaining (96.6−1.3+1.7)% of the γ decays going to the bound states. Finally, we discuss the relation between the β decay of 12N and 12B to states in 12C and the γ decay of the 15.11 MeV analog in 12C to the same states.

Inelastic Proton Scattering Analyses and Ambiguities in Spin–Parity Assignments of States in 12C

Data from the excitation of the 13�35, 18�35, 19�20 and 19�40 MeV states in 12C by the inelastic scattering of protons have been analysed using a fully microscopic distorted wave approximation to determine optimal assignments from amongst the current and ambiguous J π; T values of each state involved. While not conclusive, the present analysis suggests the assignments of 4-1; 0, 2-2; 0, 4-2; 0 and 22-2; 1 respectively.

Elastic and inelastic scattering of 12C ions at intermediate energies

Abstract Elastic and inelastic scattering of 12C ions on 12C and 208Pb targets have been measured at the incident energies per nucleon E / A = 120 MeV/u and E / A = 200 MeV/u. Optical-model analysis is reported and nuclear surface transparency effects are discussed, together with the nuclear potential-energy dependence. The transparency region extends down to a radial internuclear distance of about 3 fm for the 12C-12C system and 8 fm for the 12C-208Pb system. A decrease of the imaginary potential with increasing incident energy is deduced for the two systems. Anomalous collapse of the real potential in the surface region is observed for 12C-208Pb system at 200 MeV/u. DWBA analysis of data on the 2+, 4.4 MeV state of 12C is reported and trends for the energy dependance of mean-field excitations are deduced.

Spin-dipole strength in 12N

Data are presented for the 12C(p, n) 12N reaction at 120, 160 and 200 MeV. Angular distributions at 160 MeV show that the spectrum between 2 and 17 MeV excitation energy is dominated by l = 1 spin excitations. The (p, n) spectrum for l = 1 transitions is calculated based on a Cohen-Kurath type of shell-model calculation. The shape of the calculated spectrum agrees well with the experimental spectrum, but with a factor of 2 larger cross section. This is consistent with electron-scattering data for the 19.4 MeV state in 12C, the analogue of the 4.2 MeV state in 12N. Two broad structures at 4 and 7 Me V are identified as being mainly 2 − and 1 − states.

Study of the 18.30 and 19.40 MeV states in 12C in intermediate energy proton scattering

Angular distributions of the cross section and analyzing power have been measured for proton inelastic scattering from 12C at 398, 597, and 698 MeV. Angular distributions of the spin-flip probability have been measured at 398 MeV. Comparison of these data with DWIA calculations strongly suggests 2 −( T = 0) and 2 −( T = 1) assignments to states at 18.30 and 19.40 MeV, respectively; their wave functions are well described by recent calculations of Millener.

A study of the 13C(p, p′) reactions at 135 MeV

Differential cross sections have been measured for the elastic scattering, and inelastic scattering to all excited states below 11 MeV excitation, of 135 MeV protons from 13C. Two different sets of optical model parameters, and two different forms of the nucleon-nucleon effective interaction were used in distorted-wave analyses of the data. It is suggested that the 8.86 and 11.08 MeV ( 1 2 −) states, neither of which is fitted by this form of analysis, may be predominantly formed by coupling a Op 1 2 neutron to the 7.66 MeV state of 12C.

Elastic and inelastic scattering of 1.03 GeV 12C projectiles

Elastic scattering cross sections of 86 MeV/N 12C ions on 12C, NATCa, 89Y and 208Pb targets has been measured together with inelastic scattering to the 4.4 MeV state of 12C. There is some indication for giant (quadrupole) resonance excitation in 40Ca. Optical model and DWBA analyses are reported. Nuclear transparency effect is discussed.

Beta decay of12B and12N to the first excited state of12C (4.44 MeV)

The branching ratios of the beta-decay of12B and12N to the 4.44 MeV state in12C were determined by (βγ-coincidences to be (1.182±0.019)% and (1.898±0.032)% of the total rate, resp. This givesft−=(1.407±0.023) · 105 s andft+=(1.406±0.024) · 105 s. For theft-asymmetryδ=(ft+/ft−)−1 the valueδ=−(1±14) · 10−3 was obtained. This is in contrast to other GT mirror transitions which show positiveδ of a few percent.

Analyzing power measurements for the 13C( [formula omitted],d) 12C reaction at 200 and 400 MeV

Cross sections and analyzing powers for the 13C( p ,d) reaction have been measured at 200 and 400 MeV to the 0 +, ground state and 2 +, 4.44 MeV state of 12C. While the cross sections are rather structureless, DWBA calculations in exact finite range account well for both the magnitude and shape of the angular distributions. On the other hand, the measured analyzing powers are in serious disagreement with the DWBA calculations.

Pionic modes of excitation in nuclei: Inelastic electron and proton scattering to the (1 +, T=1; 15.1 MeV) state in 12C

The M1 form factor for the transition into the 15.1 MeV state in 12C is calculated with inclusion of large-space pionic polarisation involving both nucleon- and Δ-hole excitations. The corresponding particle-hole interaction incorporates one- and two-pion-exchange, the latter represented by the relevant ππ → N N helicity amplitude squared, plus additional short range correlations. We find that the non-resonant Born part of two-pion exchange, in addition to ϱ exchange, plays a crucial role to obtain the proper enhancement of the M1 form factor at large q. We conclude that a reduction of the repulsive correlations accompanying OPE to unreasonably small amounts is not required, hence the “critical opalescence” situation is unlikely to be encountered in this process. The excitation of the same state with 800 MeV protons is also investigated, with the aim of obtaining further independent information on a possible amplification of the nuclear pion field at q ∼ 2−3 m π. Measurable enhancement effects are suggested, but a more precise knowledge of the spin-isospin dependent NN amplitudes is required to draw further conclusions.

Electron scattering with the excitation of the 15.11 MeV state of12C and the? 12B12C coupling constant

Theπ12B12C coupling constant is extracted from the data on theM1 form factor of12C using the PCAC and CVC hypotheses. The extrapolation of the form factor to the pion pole using analyticity arguments leads to the value\(f_{\pi ^{12} B^{12} C}^2 = 0.052\). Our present knowledge of this coupling constant is discussed.

Excitation of the 15.110 MeV state of 12C by neutrinos or antineutrinos

Formulae for cross sections of ν 12 C(g.s.) → ν 12 C ∗(15.110) and ν 12 C(g.s.) → ν 12 C ∗(15.110) and for angular distributions and circular polarizations of the subsequent decay photons are derived in a model-independent (elementary-particle) approach. Our results indicate that, granting validity of the isotriplet hypothesis which relates the isovector components of the hadronic neutral weak current to the hadronic charged weak polar and axial currents, the numerical predictions of these quantities are strikingly different between solutions A and B.

Inelastic scattering of 14.8 MeV neutrons from deuterons

The double differential inelastic scattering cross sections of 14.8 MeV neutrons by deuterons have been measured using the time-of-flight technique and a NE 230 scintillator as a scatterer. The total neutron emission cross section in a forward hemisphere has been determined as 240+or-30 mb. The present measurements have been compared with previous measurements on neutron and proton emission. The differential cross sections for the excitation of the 9.63 MeV state in 12C decaying through emission of charged particles have been measured to be 5.3+0.5, 5.6+or-0.6 and 6.2+or-0.6 at 78 degrees , 89 degrees and 99 degrees in the centre-of-mass (CM) system.

Absolute excitation energy measurements using an electrostatic analyzer

The excitation energies of several states in 6Li, 11B, 12C, 27Al and 56Fe have been measured in terms of the standard meter and the standard volt. The energy of the electron beam from a FN Tandem Accelerator was measured absolutely with a 61 cm radius electrostatic analyzer to an uncertainty of 0.037%. Thin target bremsstrahlung produced by this beam was used to excite the states in question. The excitation energies are as follows: (2126.5 ± 1.5) keV for the 2.12 MeV state in 11B; (2984.2 ± 1.5) keV for the 2.98 MeV state in 27Al; (3451.3 ± 1.7) keV for the 3.45 MeV state in 56Fe; (3569.0 ± 1.7) keV for the 3.56 MeV state in 6Li; (4439.4 ± 1.6) keV for the 4.44 MeV state in 12C; (4446.4 ± 1.8) keV for the 4.44 MeV state in 11B; and (5021.1 ± 1.8) keV for the 5.02 MeV state in 11B. These results are compared with particle-reaction and gamma ray spectroscopy measurements.

A measurement of Γ rad/Γ for the 7.654 MeV state of 12C and the rate of the stellar 3α reaction

The branching ratio Γ rad/Γ for the radiative de-excitation of the 7.654 MeV, 0 + state in 12C has been measured. Coincidences between α-particles from 12C(α, α') 12C(7.654 MeV) and recoil 12C ions at the proper energy and angle were the signature of radiative decay. Conservative techniques were used throughout to avoid the need for large corrections. A value, of Γ rad/ Γ = (3.87±0.25) × 10 −4 was obtained in good agreement with other recent results but substantially higher than the previously accepted value of (2.9±0.3) × 10 −4. Available results are reviewed and a recommended value of Γ rad/ gG is presented. The implication of this result for the rate of the 3α process in stellar helium burning is discussed and a recommended reaction rate is presented.

Isospin mixing in 12C

Gamma-ray decays of the 12.71 and 16.11 MeV states of 12C are investigated in a coincidence study of the 10B(τ, pγ) reaction, and using the 163 keV 11B(p, γ) resonance. This information together with existing data on M1 transitions and stripping and pickup spectroscopic factors is used to determine the isospin mixing between the 12.71 and 15.11 MeV levels. A charge dependent mixing matrix element of 110 ± 30 keV is deduced.