A local versus non-local t-matrix in the N(p, 2p)C reaction at 46 MeV

The angular distributions for the ¹⁴N(p, 2p)¹³C reactions at 46 MeV incident proton energy are calculated in the distorted wave t-matrix approximation (DWTA) where approximate optical-model waves are used. A comparison is made between the calculation using a local t-matrix to that of a non-local t-matrix. The (p, 2p) angular distribution is smaller in magnitude where a non-local t-matrix is employed compared to the calculation using a local t-matrix which implies that there is an overall enhancement of absorption associated with the non-local t-matrix. This also implies that differences between the local and non-local off-energy-shell effects can be significant. Parameter studies were undertaken for the distorted waves and bound state wave function and the effects on the angular distributions were similar in the local and non-local cases. The distortion effect due to the final-state focus phase dramatically changes the shape of the angular distribution. The calculations are considered to be a test of the off-energy-shell effects due to non-local interaction. This calculation is also a test of the approximate distorted waves at 46 MeV and the comparison to the ¹⁴N(p, 2p)¹³C data indicates that the distortion is reasonably well described.     

Nuclear asymptotic normalization coefficients for <Superscript>14</Superscript>N → <Superscript>13</Superscript>C + <Emphasis Type="Italic">p</Emphasis> configurations and astrophysical <Emphasis Type="Italic">S</Emphasis> factor for radiative proton capture

Empirical values of the asymptotic normalization coefficient for proton bound states in the ¹⁴N nucleus for the first five levels were obtained from an analysis of the experimental differential cross sections known from our measurements and from the literature for the reaction ¹³C(³He, d)¹⁴N in the projectile-energy range between about 15 and 40 MeV. The values obtained in this way were used to calculate the astrophysical S factors for the reaction ¹³C(p, γ)¹⁴N in the case of the population of the first five levels of the 14N nucleus. The calculations were based on the R-matrix approach. The calculated values are in good agreement with the experimental astrophysical S factor at energies below 1 MeV.     

Shell model calculations on natural parity states in 10≦ A≦14 nuclei

Shell model calculations of natural parity states in the 10≦A≦14 mass region have been performed by assuming an inert⁴He core with the residual interaction in the 1p shell only. The modified surface delta interaction (MSDI) has been used as an effective two-body interaction. The MSDI parameters as well as the single-particle binding energies have been deduced from a least-squares fit to experimentally known levels in, firstly, the seperate¹⁰B,¹¹B-C,¹²C,¹³C-N and¹⁴N nuclei, and secondly, the whole mass region 10≦A≦14. Multipole moments for ground states and M1 and E2 radiative widths for excited states have been calculated with the resultant wave functions.     

Two-nucleon T = 0 transfer reactions in the 0p shell

The ¹⁶O(d, α)¹⁴N, ¹⁴N(d, α)¹²C and ¹²C(d, α)¹⁰B reactions at E_d = 40MeV and the ¹²C(α d)1¹⁴N at E_α = 55 MeV were investigated. A total of seventeen transitions are analysed in terms of one-step, zero-range DWBA calculations, using the two-particle coefficients of fractional parentage obtained from the Cohen-Kurath Op shell wave functions. For most transitions, fair agreement is obtained between experiment and calculation, possible exceptions being the transition to the E_x = 4.43 MeV, J^π = 2⁺ state in ¹²C and to the E_x = 2.15 MeV, J^π = 1⁺ state in ¹⁰B, for which the calculations predict too much L = 0 strength. Where possible, a comparison with previous (p, ³He) results is made. In ¹⁴N a state at E_x = 11.04 MeV was observed for which the values (J_π; T) = (3⁺; 0) are suggested. In ¹²C we found, in addition to the well known T = 0 states, two relatively sharp T = 0 states at E_x = 19.50 ± 0.10 and 20.55 ± 0.10 MeV. The shape and strength of the angular distribution for the transitions to these states can be approximately accounted for by the calculations, although no one-to-one correspondence between observed and predicted levels could be established.     

Spectroscopy of highly excited states in29Si

Particleγ-ray coincidences have been measured in the²⁸Si (d,pγ) reaction at 6.5 and 7 MeV bombarding energy, in the²⁶Mg (α,nγ) reaction at 12, 14 and 15 MeV, and in the²⁷A1 (τ,pγ) reaction at 9 MeV. Theγ-decay has been observed for all bound states of²⁹Si and for 56 unbound states up to 12,960 KeV excitation energy. Particleγ-ray angular correlations were measured in the²⁸Si (d,pγ) reaction at 6.5 MeV and in the²⁶Mg (α,nγ) reaction at 12 MeV. Spin (-parity) assignments or restrictions were obtained for nearly all bound states and some high-spin states above the binding energy. The assignment of mirror levels in²⁹Si and²⁹P has been extended to 8.2 MeV excitation energy. The excitation energies of 41 positive-parity states are reproduced by shell model calculations. The possible existence of aK ^π=5/2⁺ band with prolate deformation is discussed.     

Energy levels of 14C

The ⁹Be (⁶Li, p)¹⁴C reaction has been studied using 20 MeV ⁶Li ions and the Penn multiangle spectrograph. Proton groups are reported corresponding to thirty excited states of ¹⁴C with E_x < 18.2 MeV. The total cross section for formation of the six bound excited states, whose J^π are known, is proportional to 2J_f + 1. Possible new spin assignments are suggested for several unbound levels of ¹⁴C, based on the 2J_f + 1 rule and a comparison of the experimental widths and widths predicted from neutron penetration of a centrifugal barrier.     

Proton stripping to 14N

The ¹³C(³He, d) reaction at a beam energy of 43.6 MeV was used to examine levels of ¹⁴N up to 11.7 MeV over an angular region including the main stripping peaks. Many spectroscopic factors were determined reliably for known states and found to be mostly in good agreement with calculations for the stronger levels. Several new spin or parity assignments are made at high excitation.     

Microscopic and macroscopic aspects of 135 MeV proton scattering from 16O

Differential cross sections have been measured for the scattering of 135 MeV protons from ¹⁶O and data from the transitions to 13 states (up to 19.5 MeV excitation) have been analysed using microscopic and macroscopic nuclear reaction models. Extensive collective model calculations have been made of the transitions to all natural-parity states. The deformation parameters for the 4p4h rotational band are in good agreement with theoretical models. The inelastic scattering data from the excitation of the negative-parity states have also been analysed in the distorted-wave approximation using microscopic (shell and RPA) models of nuclear structure and with density-dependent two-nucleon t-matrices. For positive-parity states, we report the first shell-model calculation using the complete 2?ω basis space and find that the triplet of 2p2h states (4⁺, 2⁺, 0⁺) around 11 MeV excitation is quite well described by this model, as may be a 1⁺ state which is observed for the first time by proton scattering from ¹⁶O.     

The (p, π±) reactions on 12,13C at 200 MeV

Angular distributions from the (p, π^±) reactions have been measured at 200 MeV on ¹²C and ¹³C leading to discrete final states in the residual nuclei. A comparison of the cross sections is made between transitions to isobaric analog and non analog final states. Differences between the (p, π⁺) and (p, π^?) reactions are found in the shape and magnitude of the differential cross section as well as in the energy variation.     

Assignment of the HCOOH CW-submillimeter laser

Twenty one laser lines of the 250–1000 GHz range have been assigned in the v₆ and v₈ excited states of the H¹²COOH molecule. The microwave study of these two states has allowed us to determine the molecular constants and to calculate the energy levels up to J = 50. The values of the energy levels of the ground state are well known and allow the frequency calculation of infrared rovibrational transitions near the 9.6–10.6 μm region and the comparison with the frequencies of the CO₂ laser lines. A microwave infrared double-resonance experiment has also been performed to confirm assignment based on the calculation of the energy levels. The value of the two band centers has been determined.     

Alpha particle scattering to negative parity states of14N

Inelastic⁴He scattering on melamine targets is studied for negative parity excitations of¹⁴N. ElevenΔL=3 excitations are presented, for states up to 15.41 MeV; threeΔL=1 transitions are also studied. A microscopic DWBA calculation accounts for several of the octupole excitations, requiring an isoscalar effective strength about twice that expected for free alpha-nucleon scattering. Great purity of the structure of the three lowest 2^? states is noted, with the 5.11 MeV and 9.13 MeV levels excited byΔL=3, but with the 7.97 MeV state excited purely byΔL=1.     

The 14C(α, α')14C and 13C(d,p)14C reactions

The isoscalar transition rates and neutron-stripping probabilities to states of ¹⁴C have been measured using the 35 MeV ¹⁴C(α, α')¹⁴C and 17.7 MeV ¹³C(d, p)¹⁴C reactions. States showing great charge asymmetries in pion scattering at 8.32 MeV (2⁺) and 11.7 MeV (4^?) were examined in detail. Isoscalar transition rates B(02) were determined to be 168, 96 and 74 fm⁴ for the 7.01, 8.32 and 10.45 MeV 2⁺ states, with identical single-neutron spectroscopic factors of 0.065, from the (d, p) data, for the lowest two states.     

High-Temperature Infrared Emission Spectra of DCN and DCN

The infrared spectra of two isotopomers of deuterium cyanide, D¹²C¹⁴N and D¹³C¹⁴N, were measured in emission at temperatures of 1370 K and 1520 K, respectively, in the range from 450 to 850 cm⁻¹ and, for D¹²C¹⁴N, also from 1800 to 2800 cm⁻¹. Assignments were made for rovibrational transitions to high bending states, v₂=9 for D¹³C¹⁴N and v₂=11 for D¹²C¹⁴N. To aid and verify the assignments, bands of the lower bending states, up to v₂=3, were also measured in absorption at room temperature. A global fit was made of all measurements available to us for each isotopomer. In addition to giving the rovibrational constants for each state measured, the power series expansion constants are also given and compared with those of the other deuterium cyanide isotopomers. The D¹²C¹⁴N laser transitions are verified as arising from the consequences of the Coriolis interaction between the J=21 levels of the 02⁰2 and 09^1e0 states.     

High-spin states in206Bi populated in the205Tl(α, 3n) reaction

Using alpha-particles in the energy range 35–51MeV and in-beam gamma ray and conversion electron spectroscopy techniques the reaction²⁰⁵Tl(α, 3n)²⁰⁶Bi was studied. A 15±1ns isomeric 15⁺ state was found at an excitation energy of 3147keV in²⁰⁶Bi. The main configuration of the isomeric state is suggested to beπh _9/2 vp ₁ ^2/?1 i ₁₃ ^2/?2 . The isomeric state decays mainly through a stretched cascade of five gamma rays to the previously known 0.88ms 10^? state of theπh _9/2 vi ₁₃ ^2/?1 (j ^?2)₀₊ configuration at an excitation energy of 1045 keV. A shell model calculation of the yrast states has been performed and it is found that the calculation agrees fairly well with the experiments. The average deviation between experimental and calculated energies for the yrast states with angular momenta in the region 6–18 is +4keV and the root mean square deviation is 22 keV.     

A coexistence model for 18F

Three intrinsic four-particle-two-hole core-deformed states, labelled by the K-quantum number of the holes, are introduced to aid in describing the low-lying T = 0 even-parity levels in ¹⁸F. Since states of good angular momentum projected from only two of these three states can admix with the even-J two-particle states, the paucity of the even-J relative to the odd-J states can be explained in this fashion. The emphasis is on the reproduction of the empirical spectra using realistic potentials. However, calculations of the E2 transition probabilities and comparison of results with particle transfer data serve as tests of the model. A notable feature is that the T = 0 matrix elements between the 2p and 4p2h states are found to be considerably smaller than the T = 1 ones.     

Investigation of 16O excited states via the 14N(3He,p) reaction

The reaction ¹⁴N(³He, p)¹⁶O has been investigated at a bombarding energy of 15.0 MeV, using a differentially pumped gas target. Angular distributions were measured for 30 levels below 16.5 MeV in excitation. Data were compared with shell-model calculations of Zuker, Buck and McGrory for states whose correspondence with theory is established. Many states are found to possess a large compound-nucleus reaction component. Several previously unreported levels are observed at high excitation. Angular distributions for all except the weakest levels have been compared with DWBA calculations.     

Continuum shell model calculations for 15C

Microscopic calculations of the discrete and continuous spectrum of ¹⁵C are carried out within the framework of the continuum shell model, using a recently developed generalization of the extended R-matrix formalism. Comparison is made with the predictions of a conventional shell model calculation and also with the presently rather meager experimental data. The calculated total elastic and total reaction cross sections for the ¹⁴C+n reaction exhibit some interesting resonance phenomena which it would be desirable to investigate experimentally. The calculated stripping form factors for the ¹⁴C(d, p) reaction are similar to Woods-Saxon eigenfunctions for those states in ¹⁵C which have strong single-particle character, but differ markedly from this shape when the single-particle component is small. The effect on the calculated results of the addition or removal of closed channels is shown to be small. The present calculational method is found to be convenient, flexible and economical.     

Negative parity states in 16O from coupled-cluster equations

The extension of the coupled-cluster theory to excited states of closed-shell nuclei is presented. The method is applied to the negative parity particle-hole spectrum of ¹⁶O. Some approximations found necessary in the application of the theory at the three-body level are discussed. Numerical calculation bears out characteristic discrepancies to experimental energy levels for some T = 0 states whereas agreement with experiment is found for T = 1 states.     

The11B(p,p′)11B* reaction: An extended coupled-channels treatment

The predictions of a multi-configurational shell model continuum calculation for the¹¹B(p, p) and¹¹B(p,p′) reaction channels are discussed. In the calculated excitation function for the (p, p ₁) channel theT=1, 2^? resonances play a dominant role in the region of 22 MeV to 24 MeV excitation in¹²C. These model predictions are consistent with the known parent states in the¹²B system. Corroborative evidence is also obtained by comparing theory with the differential cross section data.     

Lifetime of the second excited state of K

Energy distributions of neutrons from the (d, n) reactions on ^12–14C leading to unbound states of ^13–15N have been measured at 6.3 or 6.5 MeV deuteron energy. Angular distributions have been extracted for ^{13, 14}C(d, n) transitions and analysed with DWBA using the extra-polation technique to give l-values and transition strengths for ten unbound states in ¹⁴N and six in ¹⁵N. For the ¹⁵N level at 10.541 MeV it is concluded that J^π is $\text{3}\text{2}$^?. A new ¹⁵N level is observed at 11.44 MeV. The 0° (d, n) cross sections have been set in proportion to (p, p₀) resonance cross sections, and a pronounced l-dependence of the ratio is obtained.