Resonances in the reaction 56Fe(p, γ)57Co

Resonances in the reaction ⁵⁶Fe(p, γ)⁵⁷Co have been surveyed over the energy range 1.2 ? E_p ? 1.5 MeV wherein the analogues of the ground state $\text{(J}{}^{\mathrm{\pi }}\text{=}\text{1}\text{2}{}^{\mathrm{?}}\text{, 0.014}\text{MeV}$ state $\text{(J}{}^{\mathrm{\pi }}\text{=}\text{3}\text{2}{}^{\mathrm{?}}\text{)}$ and 0.136 MeV state $\text{(J}{}^{\mathrm{\pi }}\text{=}\text{5}\text{2}{}^{\mathrm{?}}\text{)}$ of ⁵⁷Fe are expected to occur. Gamma-ray angular distributions have been used to establish resonance and bound-state spins, and decay schemes have been determined. The analogue resonances appear to be severely fragmented, however the density of resonances of a given spin correlates quite well with (³He, d) results and with the expected analogue-state positions.     

High spin states in 57Co

High spin states of ⁵⁷Co have been studied via prompt γ-ray spectroscopy in the reactions ⁴⁸Ti(¹²C, p2n) and ⁵⁴Fe(α, p) at 26–48 MeV and 12–24 MeV, respectively. The energies and decay modes of these levels were determined from the analysis of γ-ray singles and γ-γ coincidence spectra, excitation functions, angular distributions and correlations. The relevant lifetimes were measured by the Doppler-shift attenuation method. The new levels established in this work are at 4037, 4814 and 5918 keV with the most probable J^π assignment of $\text{15}\text{2}{}^{\mathrm{?}}$, if $\text{17}\text{2}{}^{\mathrm{?}}$ and $\text{19}\text{2}{}^{\mathrm{?}}$, respectively. The previously known level at 2524 keV was assigned to have $\text{J}{}^{\mathrm{\pi }}\text{=}\text{13}\text{2}{}^{\mathrm{?}}$. These together with the known $\text{9}\text{2}{}^{\mathrm{?}}$(1224 keV) and $\text{11}\text{2}{}^{\mathrm{?}}$(1690 keV) levels constitute the yrast states of ⁵⁷Co. The measured lifetimes of the above six levels are (in order of increasing energies) 0.085±0.030, 0.32±0.10, 0.16±0.06, 0.10_?0.07^+0.06, 1.5_?0.5⁴ and 0.17_?0.07^+0.08 ps, respectively. Comparisons with some theoretical calculations are presented.     

16O(p,α0)13N cross-section measurements

Total cross sections for the ${}^{16}\text{O}\text{(}\text{p}\text{, α}{}_0\text{)}{}^{13}\text{N}$ reaction have been measured by observation of the positron decay of the residual ¹³N nuclei. These cross sections, covering the c.m. energy range 5.4 ≦ E ≦ 9.9 MeV, allow determination of reaction rates of astrophysical interest at temperatures in the neighborhood of 4 × 10⁹°K.     

Gamma-spectroscopic investigations on 67Ge

By γ-γ coincidence measurements following the ⁵⁷Fe(¹²C, 2nγ) reaction at E_12C = 40 MeV several new states above 1.5 MeV excitation energy in ⁶⁷Ge have been established. Spin and parity assignments on the basis of the angular distribution, linear polarization and γ-ray yield function indicate very similar structures in ^{67, 69}Ge. The positive-parity states can be followed up to the $\text{17}\text{2}{}^{\mathrm{+}}$ state at E_x = 3.07 MeV followed by a sequence of negative-parity high-spin states at nearly the same excitation energy relative to the $\text{9}\text{2}{}^{\mathrm{+}}$ single-particle state as in the neighbouring nucleus ⁶⁹Ge where these states were found to have strong single-particle admixtures. A reinvestigation of the spin of the E_x = 2.75 MeV level in ⁶⁹Ge resulting in a change of its spin from $\text{15}\text{2}{}^{\mathrm{+}}\text{to}\text{17}\text{2}{}^{\mathrm{+}}$ and for all spins above, removed the discrepancy concerning the spin assignments of corresponding levels in ^{67, 69}Ge. The excitation pattern of the Ge isotopes with 34 ≦ N ≦ 39 clearly indicate same structures probably due to the strong competition between collective and single-particle excitations along the whole chain similar to the results for the Zn isotopes.     

Search for 4n IN π− double charge exchange reactions with heavy nuclei

A search for the existence of the tetraneutron has been made using the double charge exchange reaction $\text{π}{}^{\mathrm{?}}\text{+}{}^{208}\text{Pb}\text{→}{}^4\text{n + π}{}^{\mathrm{+}}\text{+}$ residuals for ⁴n production and the capture process in the same target, ${}^{208}\text{Pb}\text{+}{}^4\text{n}\text{→}{}^{212}\text{Pb}\text{+ γ}$, for the ⁴n detection. No event has been found, giving an upper limit for the product of the production cross section σ_p, the detection cross section σ_d and the ⁴n lifetime τ. Assuming 10^?18 ≦ τ ≦ 10^?9 sec it follows that σ_pσ_dτ ≦ 2.5 × 10^?65cm⁴ sec with 90 % confidence, and for $\text{τ ≧ 10}{}^{\mathrm{?9}}\text{sec}\text{, σ}{}_{\mathrm{<mtext>p</mtext>}}\text{σ}{}_{\mathrm{<mtext>d</mtext>}}\text{≦ 2.5 × 10}{}^{\mathrm{?56}}\text{cm}{}^4$ with 90 % confidence. The magnitude of this value is comparable to the experimental limit of the ⁴He(π^?, π⁺)⁴n cross section.     

Nuclear polarization of high-spin levels and the sign of the quadrupole moment of 54Fe(10+)

The determination of the sign of the quadrupole deformation at high spins requires an observation of the electric quadrupole interaction of polarized isomers in single crystals of non-cubic metallic hosts. The ⁵⁴Fe(10⁺) isomer was polarized, subsequent to its population by the (¹²C, p2n) reaction, by passage through an array of tilted carbon foils. The isomers were then recoil implanted into single crystals of zinc and cadmium and the tune differential modulations of the angular distribution of decay γ-rays were observed. Nuclear polarization values of P_I = 0.08(3)?0.18(5) were found for 13–17 polarizing foils, respectively, and a positive sign of the quadrupole moment was deduced. An improved value was established for the quadrupole moment: $\text{Q[}{}^{54}\text{Fe}\text{(10}{}^{\mathrm{+}}\text{)] = + 29.7(4) e ·}\text{fm}{}^2$, in agreement with current shell-model predictions.     

A study of some resonances in the 54Fe(p, γ)55Co reaction

Excitation functions for the ⁵⁴Fe(p, γ)⁵⁵Co reaction have been recorded in the energy region E_p = 1100–1760 keV. The decay schemes and branching ratios of ten resonances have been investigated. Angular distributions of primary γ-rays have been measured for three resonances to establish resonance spins. Resonance strengths for six resonances and gamma widths for three resonances have been determined. The isobaric analogues of the ground ($\text{J}{}^{\mathrm{\pi }}\text{=}\text{7}\text{2}{}^{\mathrm{?}}\text{)}\text{and}\text{1919}\text{keV}$$\text{J}{}^{\mathrm{\pi }}\text{=}\text{3}\text{2}$^?) states of the parent nucleus ⁵⁵Fe have been identified at 4722 and 6712 keV respectively in ⁵⁵Co. The Coulomb displacement energies of the observed analogue pairs (0–4722 keV) and (1919–6712 keV) have been obtained. The strengths of the possible analogue-antianalogue transitions for the proton capture state at E_p = 1679 keV have also been determined.     

Recoil-distance lifetime measurements in 51Cr, 53Cr, 53Mn and 53Fe

Levels in ⁵¹Cr, ⁵³Cr, ⁵³Mn and ⁵³Fe were excited via (α, n) or (α, p) reactions. Using the recoil-distance method, mean-lives (in ps) have been obtained for excited states (keV) in the residual nuclei: ${}^{51}\text{Cr}\text{(2256) = 66±2,}{}^{53}\text{Cr}\text{(1536) = 21.5±3.5,}{}^{53}\text{Cr}\text{(2173) = 6.7±3.1,}{}^{53}\text{Mn}\text{(2564) = 20}{}^{\mathrm{+8}}{}_{\mathrm{?6}}\text{and}{}^{53}\text{Fe}\text{(1424) = 4.0±1.0}$. Reduced transition probabilities calculated from these values are compared with the available theoretical values.     

The GT matrix elements in the decay of the mirror nuclei 47Cr, 51Fe and 55Ni

Three new mirror nuclei, ⁴⁷Cr, ⁵¹Fe and ⁵⁵Ni, have been identified in (³He, 2n) reactions. The measured half-lives were as follows: ${}^{47}\text{Cr}\text{, 452 ± 18}\text{ms}\text{;}{}^{55}\text{Fe}\text{, 245 ± 7}\text{ms}\text{;}{}^{55}\text{Ni}\text{, 189 ± 5}\text{ms}$. Known mass data were utilized to deduce log $\text{?t}$ values and Gamow-Teller matrix elements for the three mirror β-decays. The experimental GT matrix elements are compared to the results of shell-model calculations.     

Study of the (3He,d) reactions on 58, 60Ni and 56Fe near the Coulomb barrier

Using spectroscopic information gained by earlier measurements of the proton bound states populated by stripping reactions, (³He, d) reactions on ^{58, 60}Ni and ⁵⁶Fe targets are studied at energies near the Coulomb barrier and evaluation is made of the vertex function . This value is then used to determine spectroscopic factors for low-lying states in ⁵⁷Co.     

Interference effects in 12C(p, γ)13N and direct capture to unbound states

Excitation functions of the capture reaction ¹²C(p, γ₀)¹³N have been obtained at θ_γ = 0° and 90° and E_p = 150–2500 keV. The results can be explained if a direct radiative capture process, E1(s and d → p), to the ground state in ¹³N is included in the analysis in addition to the two well-known resonances in this beam energy range $\text{[E}{}_{\mathrm{p}}\text{= 457(}\text{1}\text{2}{}^{\mathrm{+}}\text{)}$ and 1699 $\text{(}\text{3}\text{2}{}^{\mathrm{?}}\text{) keV]}$. The direct capture component is enhanced through interference effects with the two resonance amplitudes. From the observed direct capture cross section, a spectroscopic factor of C²S(l = 1) = 0.49 ± 0.15 has been deduced for the $\text{1}\text{2}{}^{\mathrm{?}}$ ground state in ¹³N. Excitation functions for the reaction ${}^{12}\text{C(p,γ}{}_1\text{p}{}^1\text{)}{}^{12}\text{C}$ have been obtained at θ_γ = 0° and 90° and E_p = 610–2700 keV. Away from the 1699 keV resonance the capture γ-ray yield is dominated by the direct capture process E1 (p → s) to the $\text{2366 (}\text{1}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound state. Above E_p = 1 MeV, the observed excitation functions are well reproduced by the direct capture theory to unbound states (bremsstrahlung theory). Below E_p = 1 MeV, i.e., E_p → 457 keV, the theory diverges in contrast to observation. This discrepancy is well known in bremsstrahlung theory as the “infrared problem”. From the observed direct capture cross sections at $\text{E}{}_{\mathrm{p}}\text{? 1 MeV}$, a spectroscopic factor of C²S(l = 0) = 1.02 ± 0.15 has been found for the $\text{2366 (}\text{1}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound state. A search for direct capture transitions to the $\text{3512 (}\text{3}\text{2}{}^{\mathrm{?}}\text{)}$and $\text{3547 (}\text{5}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound states resulted in upper limits of C²S(l = 1) ≦ 0.5 and C²S(l = 2) ? 1.0, respectively. The results are compared with available stripping data as well as shell-model calculations. The astrophysical aspect of the ¹²C(p, γ₀)¹³N reaction also is discussed.     

Spectroscopy of 62Ni with the 61Ni(d, p) reaction

Differential cross sections, vector and tensor analysing powers have been measured for the ⁶¹Ni(d, p) reaction at a deuteron energy of 12.3 MeV. Most of the 30 transitions observed below 8.5 MeV excitation are dominated by a single j-value, which was determined from behaviour of the analysing power data. For a number of transitions it was possible to make unambiguous j-assignment relying on the established j-dependence of the T₂₂ tensor analysing power. The deduced spectroscopic factors indicate that the full strength of neutron transfer to the ($\text{2p, 1f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$) and $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ orbits was found and seven $\text{5}\text{2}{}^{\mathrm{+}}$ transitions were located above 5.3 MeV. The separated strengths of the $\text{3}\text{2}{}^{\mathrm{?}}\text{,}\text{1}\text{2}{}^{\mathrm{?}}\text{and}\text{5}\text{2}{}^{\mathrm{?}}$ transitions are compared with shell-model calculations for the low-lying states of ⁶²Ni.     

Analyzing powers of the continuum spectra: 65 MeV polarized protons on 12C, 28Si, 45Sc, 58Ni, 93Nb, 165Ho, 166Er and 209Bi

Analyzing powers of the continuum spectra were measured for 65 MeV protons from ¹²C, ²⁸Si, ⁴⁵Sc, ⁵⁸Ni, ⁹³Nb, ¹⁶⁵Ho, ¹⁶⁶Er, ${}^{209}\text{Bi}\text{(}\text{p}\text{,}\text{p\#}\text{prime;}\text{X}\text{)}$ and ($\text{p}$, dX) reactions and from ⁹³Nb, ²⁰⁹Bi($\text{p}$, αX) reactions. The analyzing powers of the continuum spectra were found to be small at forward angles where the pre-equilibrium process is important. However they do not show a systematic tendency. This feature indicates the importance of the spin-dependent interaction as well as nuclear structure effects. On the other hand, the analyzing powers were very large and positive at backward angles where the shape of the energy spectra resembles that of an evaporation spectrum. The maximum values of the analyzing power in the backward hemisphere depend on the target mass for the A < 45 mass region and they are as large as 15%, 20% and 35% for ${}^{93}\text{Nb}\text{(}\text{p}\text{,}\text{p}\text{′}\text{X}\text{)}$, ($\text{p}$, dX), ($\text{p}$, αX) reactions at E_X = 20 MeV, respectively. These large values are mainly due to the entrance channel effect. There is no appreciable even-odd mass effect on the analyzing power for medium-mass nuclei. These features were unexpected from the conventional pre-equilibrium reaction models.     

g-factors of 2.7 h 93Tc, 4.9 h 94Tc and 20 h 95Tc

The hyperfine splitting frequencies gμ_NB_H.F./h of 2.7 h ⁹³Tc $\text{(J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{+}}\text{)}$, 4.9 h ⁹⁴Tc (J^π = 7⁺) and 20 h ⁹⁵Tc $\text{(J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{+}}\text{)}$ as dilute impurities in Fe have been measured with NMR on oriented nuclei as 336.36(5) MHz, 175.11(1) MHz and 315.97(2) MHz, respectively. From the resonance shifts with an external magnetic field B₀ the hyperfine field of Tc$\text{Fe}$ has been determined as -317(5) kG. Taking this into account the nuclear g-factors are deduced as $\text{g(}{}^{93}\text{Tc}\text{) = 1.392(22), g(}{}^{94}\text{Tc}\text{) = 0.725(11)}\text{and}\text{g(}{}^{95}\text{Tc}\text{) = 1.308(21)}$.     

The 7Li(d, n0)8Be reaction with polarized 800 keV deuterons

The analysing power of the ${}^7\text{Li}\text{(}\text{d}\text{, n}{}_0\text{)}{}^8\text{Be}$ reaction for vector and tensor polarization of an 800 keV deuteron beam, as well as the relative cross section for the unpolarized beam were measured at 7 to 9 angles between 0° and 160°, using a thick target. Analysis in terms of (l, s, J^π) matrix elements shows that two intermediate states with $\text{J}{}^{\mathrm{\pi }}\text{=}\text{3}\text{2}{}^{\mathrm{+}}$ and $\text{J}{}^{\mathrm{\pi }}\text{=}\text{5}\text{2}{}^{\mathrm{?}}$ present, strongly interfering with each other. Assignments to known ⁹Be levels and to threshold resonances as suggested by Hackenbroich and Seligman are briefly discussed. The magnitude of the vector analysing power makes the reaction interesting as a monitor for the vector polarization of low-energy deuteron beams.     

The interaction of 33 MeV polarised helions with 30Si

Distributions of cross sections and analysing powers have been measured over the range ～ 14°–100° c.m. for the $\text{(}{}^3\text{H}\text{,}{}^3\text{He), (}{}^3\text{H}\text{,}{}^4\text{He), (}{}^{\mathrm{<mtext>3</mtext><mtext>H</mtext>}}\text{,}{}^2\text{H)}$ reactions at 33.4 MeV incident e using a ～ 95 % enriched ³⁰Si target. Phenomenological optical-model analyses of the elastic-scattering data have been carried out. A DWBA analysis of the inelastic-scattering data for the 2.24 MeV (2⁺) and 5.49 MeV (3^?) states of ³⁰Si has yielded values of the deformation β₂ and β₃. The j-dependence of the analysing powers for the (³He, ⁴He) and (³He, ²H) reactions has identified the 6.71 MeV level of ²⁹Si as a $\text{5}\text{2}{}^{\mathrm{+}}$ state, and a level near 9.5 MeV in ³¹P as a possible $\text{7}\text{2}{}^{\mathrm{?}}$ state. Spectroscopic factors for ten states in ²⁹Si and seven states in ³¹P have been deduced and are compared with other work. The extent to which the data defines the ³He spin-orbit potential is discussed.     

Proton spectra from the 6,7Li(γ,p) 5,6He reactions at Eγ = 60 MeV

The ${}^{\mathrm{6,7}}\text{Li}\text{(γ,}\text{p}\text{)}$ reactions have been investigated for E_γ = 60 MeV. Excitation of residual (1p)^?1 and (1s)^?1 hole states is evident from the proton spectra measured at ?_p = 45°. The data are compared with a theoretical calculation which includes short-range correlations.     

Alpha capture to the giant dipole resonances of 42Ca, 44Ca and 52Cr

Differential cross sections for the ${}^{38}\text{Ar}\text{(α, γ}{}_0\text{)}{}^{42}\text{Ca}\text{,}{}^{40}\text{Ar}\text{(α, γ}{}_{\mathrm{0,\; 1}}\text{)}{}^{44}\text{Ca and}{}^{48}\text{Ti}\text{(α, γ}{}_{\mathrm{0,\; 1}}\text{)}{}^{52}\text{Cr}$ reactions were measured at 90° to the beam direction in 50 or 100 keV steps over the bombarding energy ranges 6.0–15.0 MeV, 5.5–11.1 MeV and 6.0–12.0 MeV respectively. Gamma-ray angular distributions were measured at forty bombarding energies. These show that the (α, γ₀) reaction proceeds through 1^? levels and to a lesser extent 2⁺ levels, whereas the (α, γ₁) reaction most probably proceeds through 1^? and 3^? levels. It is deduced that 〈Γ〉/〈D〉 ≦ 1 for the ⁴⁰Ar(α, γ)⁴⁴Ca. reaction whereas the fine structure observed in the ⁴⁸Ti(α, γ)⁵²Cr reaction is probably due to fluctuations. From a comparison with other data it is shown that the (α, γ) reaction is most probably statistical in nature. Using Hauser-Feshbach theory it is deduced that the ³⁶Ar(α, γ)⁴⁰Ca. reaction is inhibited by isospin selection rules and an estimate is made of isospin mixing in the ⁴⁰Ca giant dipole resonance. The ${}^{38}\text{Ar}\text{(α, γ)}{}^2{}^{42}\text{Ca and}{}^{40}\text{Ar}\text{(α, γ)}{}^{44}\text{Ca}$ data are considered with respect to theories of isosopin splitting of the giant dipole resonance.     

Spin assignments in 59Ni from the 58Ni(d, p)59Ni reaction

Angular distributions of the vector analyzing power and the absolute cross section were measured for the ⁵⁸Ni(d, p)⁵⁹Ni reaction at a deuteron energy of 10 MeV. The observed j-dependence of the vector analyzing power allowed unambiguous spin assignments for the following states in ⁵⁹Ni with excitation energies in $\text{MeV}\text{: 0.0,}\text{3}\text{2}{}^{\mathrm{?}}\text{; 0.341,}\text{5}\text{2}{}^{\mathrm{?}}$; $\text{0.465,}\text{1}\text{2}{}^{\mathrm{?}}\text{; 0.879,}\text{3}\text{2}{}^{\mathrm{?}}$; $\text{1.303,}\text{1}\text{2}{}^{\mathrm{?}}\text{; 1.686,}\text{5}\text{2}{}^{\mathrm{?}}\text{; 3.454,}\text{3}\text{2}{}^{\mathrm{?}}\text{; 3.858,}\text{3}\text{2}{}^{\mathrm{?}}\text{; 4.495,}\text{5}\text{2}{}^{\mathrm{+}}$. The data are well reproduced by DWBA calculations employing deuteron and proton optical model parameters obtained from analyses of elastic scattering cross sections and polarizations. A tentative spin assignment of $\text{9}\text{2}{}^{\mathrm{+}}$ is made for the level at 3.061 MeV. A $\text{5}\text{2}{}^{\mathrm{+}}$ assignment to the level at 3.538 MeV is suggested on the basis of the empirical behavior of the j-dependence of the vector analyzing power for l = 2 transitions. Measurements of the vector analyzing power for the four low-lying ⁵⁹Ni states formed by l = 1 transfer were made for angles from 2.5° to 15° using a magnetic spectrograph. A very strong j-dependence was observed for these far-forward-angle measurements in agreement with DWBA predictions.     

The octupole giant resonance strength in 16O

Angular distributions for polarized proton inelastic scattering cross sections along with the analysing power for the reaction ${}^{16}\text{O}\text{(}\text{p}\text{,}\text{p}\text{′)}{}^{16}\text{O}{}^1\text{(2}{}^{\mathrm{?}}\text{, 8.88}\text{MeV}\text{)}$ at E_p=42.5, 44.0 and 49.3 MeV have been measured. A semidirect reaction analysis augments the evidence for octupole giant resonance strength in the 30 to 50 MeV energy region.