Cross section measurements of the Pd(p, γ)Ag, Sn(p, γ)Sb, and Sn(α, γ)Te reactions relevant to the astrophysical rp- and γ-processes

Total cross section measurements for the ¹⁰²Pd(p, γ)¹⁰³Ag and ¹¹⁶Sn(p, γ)¹¹⁷Sb reactions have been performed in the proton energy range 2.6 to 4.25 MeV, and for the ¹¹²Sn(α, γ)¹¹⁶Te reaction over the alpha beam energy range 7.0 to 10.5 MeV. An activation technique was used in which gamma rays from decays of the reaction products were detected off-line by two hyper-pure germanium detectors in a low background environment. Where possible, reaction rates are derived and the results compared to those of calculations generated by the NON-SMOKER and the MOST statistical model codes so as to judge their applicability for describing the cross sections needed for network calculations of nucleosynthesis in explosive astrophysical environments via the γ- and rp-processes.     

Comparative study of compound components in N(N, α) and C(O, α) reactions

Experimental spectra of the reaction ¹⁴N(¹⁴N, α) were measured at 111 MeV. Continuum spectra extending to high excitation energy of ²⁴Mg do not show any structure which is completely at variance with the reaction ¹²C(¹⁶O, α). A compound evaporation calculation reproduces the smooth components of the spectra of both reactions. The same theoretical prediction, however, seems to contradict the conjecture that the compound process yields the broad peaks in the ¹²C(¹⁶O, α) reaction.     

No pre-critical enhancement observed in C(π, γ)N(g.s.) at q 2mπ

The cross section and angular distribution for the reaction ¹³C(π⁺, γ)¹³N(g.s.) have been measured from 37 to 85° in the laboratory, at a pion energy of 115.5 MeV. The observed cross section ranges from 320 to 660 nb/sr. These results do not show the large magnitude and wide-angle peaking expected if pre-critical effects due to nascent pion condensation were present. In addition, the observed cross section is less than one-half of the predictions of available theoretical calculations which do not include the pre-critical effect. Data on the reaction ¹H(π⁻, γ)n at T_π = 116.6 MeV were also obtained for calibration purposes. These data agree with expectations based on knowledge of the inverse reaction and previous measurements.     

Al production cross sections from the Na(α, n)Al reaction

Cross sections have been determined for the production of ^{26g, m}Al from the ²³Na(α, n) reaction. Total ²⁶Al production cross sections were obtained from measurements of the thick-target neutron yield. ^26mAl cross sections were measured using an activation technique. ^26gAl cross sections were deduced by subtracting the ^26mAl cross sections from the total (α, n) cross sections. The principle of detailed balance has been applied to the low-energy data to obtain cross sections for the astrophysically interesting ^26gAl(n, α₀)²³Na reaction. These results are compared with the results of Hauser-Feshbach calculations.     

Energy dependence of the C(O, α) reaction

The energy dependence of the ¹²C(¹⁶O, α) reaction was measured at incident energies of E_lab=112−191 MeV. In the range ofE_x(²⁴Mg)=30−56 MeV, the excitation energies of the structures in the inclusive α spectrum were found to vary continuously as a function of incident energy in this region. This fact indicates that these structures do not represent excitations in ²⁴Mg, but rather that they originate from a different process such as a sequential ejectile decay.     

A reassessment of the O(αs) three-jet cross section for ee annihilation

Results of a new evaluation of the O(α_s²) dressed three-jet cross section for e⁺e⁻ annihilation are summarized. For vanishing cutoffs, the different results in published three-jet cross section formulae are due to differing definitions of resolvable four-jet events. Subleading terms which were ignored in previous calculations are evaluated and found to be sizeable in the phase space region where three-jet events become more two-jet-like. A simple calculation demonstrates that α_s values determined according to the three-jet cross section formulae of Gutbrod, Kramer and Schierholz are systematically too large.     

Proton reactions with 17O: (II). The 17O(p,d)16O reaction

Differential cross sections for the ¹⁷O(p, d₀)¹⁶O reaction have been measured at the incident proton energies 8.62, 9.56, 10.5, 11.16 and 11.44 MeV. Both the BHMM and DWBA theories have been applied to these data, and to published analysing power data for the reactions ¹⁶O(d, p₀)¹⁷O and ¹⁶O(d, p₁)¹⁷O¹. While some parameter adjustment is necessary to obtain good fits with the BHMM theory, the adjusted parameters produce predictions in good agreement with analysing power data. The DWBA theory, however, produces good fits with proton parameters deduced from measurements of proton elastic scattering from ¹⁷O, provided the deuteron parameters used give good predictions for both differential cross section and vector analysing power data for the reaction ¹⁶O(d, d₀)¹⁶O.     

The Fe(α, γ)Ni reaction at excitation energies in the region of the giant dipole resonance

Excitation functions for the ⁵⁶Fe(α, γ₀)⁶⁰Ni and ⁵⁶Fe(α, γ₁)⁶⁰Ni reactions have been measured at 90° to the beam direction over the bombarding energy range 8.0–17.6 MeV. Gamma-ray angular distributions were measured at ten bombarding energies. Excitation functions for the ⁵⁹Co(p, γ₀)⁶⁰Ni and ⁵⁹Co(p, γ₁)⁶⁰Ni reactions were measured over the range E_x = 16.58–16.92 MeV and compared with the (α, γ) data. The angular distribution data indicate that the (α, γ₀) and (α,γ₁) reactions proceed through 1⁻, and 1⁻ and 3⁻ states, respectively. The (α, γ) excitation functions are discussed with respect to isospin splitting of the ⁶⁰Ni giant dipole resonance. The fine structure observed in the excitation functions is shown to be most probably due to Ericson fluctuations. The gross (α, γ) cross sections are shown to be in reasonable agreement with the results of calculations made using the theory of Hauser and Feshbach assuming excitation of the giant dipole resonance.     

Preequilibrium α-emission in the Au(p,αx)-reaction at Ep = 72 MeV

Proton-induced α-spectra from ¹⁹⁷Au have been measured at E_p = 72.3 MeV and the angle-integrated cross section is compared to an exciton model Monte-Carlo calculation and to the spectral distribution of α-particles emitted after the absorption of negative pions at rest.     

The Bi(d,γ)Po reaction

The yield of the ²⁰⁹Bi(d, γ)^211g.s.Po and ^211mPo (T_1/2 = 25.2s) reaction was measured for deuteron energies E_d = 8–11.5 MeV. The reaction was identified by the -activities of the Po isotope. At E_d = 10.43 MeV, the (d, γ) cross section for the population of the ground state of ²¹¹Po is σ_g.s. = 16 ± 3 μb, the ratio relative to the cross section for the metastable state is σ_g.s./σ_m = 25.4 ± 0.9. These values and the yield curves were compared with calculations using a simple model for the population of the two states. In the excitation region E* = 15–19 MeV, the branching ratio of γ- to particle emission is nearly constant and has a value of about 0.4 × 10⁻⁴.     

Changes in electrical properties in α- and γ-exposed PADC track detector

The changes in the dielectric properties and temperature dependence of the d.c. conductivity of α-exposed poly allyl diglycol carbonate (PADC) have been studied. On α-irradiation the dielectric constant (′) as a function of frequency has been found to decrease significantly. The temperature dependence of resistivity in pristine and γ-irradiated samples is of the form ρ(T)=ρ_∝ exp(T₀/T) which can be attributed to conduction of thermally generated carriers. In case of (γ+α) irradiated samples the temperature dependence of resistivity is of the form ρ(T)=ρ_∝ exp(T₀/T)^1/2 which is due to one-dimensional hopping of carriers.     

Messung der Neutronenpolarisation bei der Reaktion12C(d,n 0)13N mit Hilfe der Mott-Schwinger-Streuung

The polarization of neutrons produced in the reaction¹²C(d, n ⁰)¹³N was measured. Deuterons from the Karlsruhe isochronous cyclotron were used to induce this reaction at 51,5 MeV laboratory energy. The degree of polarization was determined by using the special features of Mott-Schwinger scattering. With an uranium scatterer analysing efficiencies of up to 0.92 can be obtained at very small angles (0.23°). The analysing efficiency can be calculated if the differential cross section at 0° and the total cross section is known. These quantities were experimentally determined. The differential cross section for 49.4 MeV neutrons, scattered by uranium, was measured between 0.88° and 2.10°. By an extrapolation the value 43.4±2.6 b/sr was found for the nuclear differential cross section at zero degree. A total cross section ofσ _t=4.80±0.22 b was obtained. The neutron polarization was measured at a reaction angle of 24.5° and the result isP=?0.45±0.07. This value is fairly above the semiclassical 1/3 limit and can be only explained, if spin orbit forces are taken into account. For (d, n) reactions this is the first neutron-polarization measurement above an energy of 20 MeV.     

Angular distribution measurements of Li(p,α)He reaction at 140 keV proton energy using nuclear track detectors

Angular distributions of a ⁶Li(p,α) ³He reaction were measured at six angles for 140 keV proton energy using nuclear track detectors (NTDs). The measurements were carried out over 60°–160° lab. angles in 20° increments using a scattering chamber of 80° beam line of the 350 kV accelerator. A semiconductor silicon surface barrier (SSB) detector was placed at +160° and was used as a monitor. The results have shown that the CR-39 detector has excellent capabilities to distinguish 1.4–2.7 MeV α+ ³He particles from the ⁶Li(p,α) ³He reaction and 8–9.4 MeV α-particles from the ⁷Li(p,α) ⁴He reaction through their track diameters. However, it was not possible to distinguish between the 2.3 MeV ³He ions and the 1.7 MeV ⁴He ions from the ⁶Li(p,α) ³He reaction from their track diameter measurements, but it was possible to differentiate between the two, from the darker contrast of the ³He particles caused by its deeper tracks as compared to those of ⁴He.     

Energy levels of Na from the Na(d, pγ)Na reaction

Excited states in ²⁴Na have been investigated by means of the ²³Na(d, pγ)²⁴Na reaction at incident deuteron energies of 2.5 and 2.8 MeV. Excitation energies and γ-ray decay for levels up to 4.2 MeV have been determined from proton-gamma coincidence spectra obtained with a surface barrier detector and a Ge(Li) detector on-line with a computer. Two new levels at 3944 ± 2 and 4195 ± 3 keV excitation energies are reported.     

Investigation of the^3 He(\vec d,p)^4 He reaction between 1 and 13 MeV

High-precision measurements of the cross section, the vector analyzing poweriT ₁₁ and the three tensor-analyzing powersT ₂₀,T ₂₁, andT ₂₂ of the³He(d, p)⁴He reaction have been performed in the energy range between 1.0 and 13.0 MeV in steps of 1 or 2 MeV. Angular distributions of the cross section have been obtained between 22.5° and 157.5° in the laboratory system. The polarization observables have been measured between 10° and 170°.     

Observation of χb production in the exclusive reaction ′→γγχb→γγ→γγ(eeorμμ−)

We report on the observation of 1 ³P_J (χ_b) production in the reaction ′→γχ_b→γγ→γγ(e⁺e⁻ or μ⁺μ⁻). The data were recorded with the nonmagnetic CUSB detector at the Cornell Electron Storage Ring, CESR. We observe 124 γγ events with either an electron or muon pair in the final state. In the γγ correlation plot about 40% of the events cluster around (120, 430) MeV.     

The differential cross section and polarization quantities in the 4He(d,p)n4He and 2H(α, n)p4He reactions

The differential cross section and the polarization quantities (T₁₁, T₂₀, T₂₁, T₂₂, P_γ') in the deuteron breakup reaction by an α-particle are calculated in the framework of the recently developed three-body model. All values are discussed under the incomplete kinematical condition. All polarization quantities are caused by the difference of the potential between $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ waves of the N-α interaction. Results of the calculation are compared with the available measurement of (i) the differential cross section and the deuteron vector analysing power in the ⁴He($\text{d}$, p)n⁴He reaction and (ii) the differential cross section and neutron polarization in the ²H(α, $\text{n}$)p⁴He reaction. The agreement with experiment is very satisfactory in each case. Among the tensor analysing powers of the deuteron the absolute value of T₂₀ is very large. Observables at the FSI peak corresponding to ⁵He_g.s. are discussed systematically in the energy region of 5.4–20 MeV of the incident deuteron in the ⁴He(d, p)n⁴He reaction. Although the differential cross section is not sensitive to the energy of the three-body resonance, the polarization quantities T₁₁, T₂₀, P_γ' are quite sensitive to it.     

Search for γγ→ηb in ee collisions at LEP 2

A search for the pseudoscalar meson η_b is performed in two-photon interactions at LEP 2 with an integrated luminosity of 699 pb⁻¹ collected at e⁺e⁻ centre-of-mass energies from 181 GeV to 209 GeV. One candidate event is found in the six-charged-particle final state and none in the four-charged-particle final state, in agreement with the total expected background of about one event. Upper limits of Γ_γγ(η_b)×BR(η_b→4 charged particles)<48 eV, Γ_γγ(η_b)×BR(η_b→6 charged particles)<132 eV are obtained at 95% confidence level, which correspond to upper limits of 9.0% and 25% on these branching ratios.     

Widths for s- and d-wave α-decay of neutron-deficient isotopes with Z 82

The α-decay of the nucleides ^188–192Pb, ¹⁸⁰Hg, and ¹⁷⁶Pt has been studied after on line mass separation of spallation products from reactions with 600 MeV protons. For the lead isotopes, the K X-ray/α ratios were determined, and from these partial α half-lives were deduced. In the decay of 6 sec ¹⁷⁶Pt, a 1.4% α-branch was found to the 228 keV 2⁺ level of ¹⁷²Os, while for ¹⁸⁰Hg an upper limit of 10⁻³ (relative to the ground-state α-branch) could be put on the intensity of an assumed rotational fine-structure component. The systematics of reduced s-wave (0⁺ → 0⁺) α-widths is discussed. The lead isotopes show a surprising trend: the reduced s-widths vary from a very small value for ¹⁸⁶Pb (deduced from the heavy-ion cross sections of Gauvin et al.) to a quite large value for ¹⁹²Pb. The systematics of d-wave (0⁺ → 2⁺) hindrance factors (relative to the ground-state branch) shows that these range from 1 to 4 for the actinides, while for platinum and mercury one finds 8 and ≈ 50, respectively.     

3He D-state effects in (d, 3He) reactions

The tensor analysing power of the ²⁷Al(d, ³He)²⁶Mg reaction has been measured at E_d = 12.4 MeV. The results are reproduced by predictions of the DWBA including D-state components in the ³He wave function. The magnitude of the tensor analysing power provides information on the asymptotic D-state to S-state ratio in the ³He wave function. The value obtained for ³He is in agreement with the corresponding value for ³H.