High-resolution measurements of beta-delayed protons from 37Ca and 41Ti

Protons with energies from 870 keV to 5.4 MeV have been observed following bombardment of a ⁴⁰Ca target with ³He at beam energies of 29.5, 36.5 and 60 MeV, as well as from 40 MeV ³He bombardment of an ³⁶Ar gas target. These data, and those resulting from 20 MeV proton bombardment of ⁴⁰Ca, permit accurate identification of proton unbound levels in ⁴¹Sc, ³⁷K, and ⁴⁰Ca fed by allowed beta decay from ⁴¹Ti, ³⁷Ca or ⁴⁰Sc, respectively. Absolute ft values have been determined for beta decay to these levels. The half-life of ⁴¹Ti has been remeasured to be 80±2 ms and the log ft for its superallowed decay branch has been found to be 3.35±0.02, indicating an isospin purity for the lowest $\text{T =}\text{3}\text{2}\text{state in}{}^{41}\text{Sc of}\text{≈ 91 \%}$. The $\text{ft}\text{values for}{}^{37}\text{Ca}\text{β}{}^{\mathrm{+}}$ decay are compared to shell-model calculations for beta-decay in A = 37 nuclei.     

Fission characteristics of the composite system 32S+50Ti: (I). Correlations between coincident fragments

The characteristics of “fission-like” processes observed in the bombardment of ⁵⁰Ti with ³²S ions of 140 MeV energy are investigated in a coincidence experiment between a time-of-flight telescope and a position sensitive ΔE-E ionization chamber. Coincident particles were identified and their energy and angular correlations in and normal to the reaction plane were measured. The experiment proves the binary nature of the mass division. Both the width and the average value of the total kinetic energy distribution are consistent with the values extrapolated from fission of heavier nuclei. An average number of 3±1 nucleons are emitted during the reaction; α-particle emission is not an important decay mode.     

Nuclear photoexcitation and delbrück scattering studied in the energy range 2–8 MeV

Elastic scattering by nuclei in the range of mass numbers between 64 and 238 has been studied with monochromatic photons in the energy range between 2 and 8 MeV. These photons were provided either by a Ti(n,γ) source installed in the tangential through channel of the Grenoble high flux reactor, or by²⁴Na and⁵⁶Co sources produced by deuteron bombardment of Al or Fe at the Göttingen cyclotron. The photoexcitation of 23 nuclear levels has been observed and the decay properties and groundstate widths of the majority of these levels have been determined. For the lead scattering target the coherent elastic differential cross section has been studied in detail. There is evidence that below the photo-neutron threshold the elastic scattering via virtual photoexcitation of the nucleus can be approximated by extrapolating the real part of the Giant Dipole Resonance amplitude along a Lorentzian curve. Coulomb corrections to Delbrück scattering seem to play a small role at 6.5 MeV.     

Emission of high-energy charged particles at 0° in Ne-induced reactions

Inclusive energy spectra have been measured for light charged particles emitted in the bombardment of ²³²Th, ¹⁸¹Ta, ^natTi and ¹²C targets by ²²Ne ions at 178 MeV and ^natTi by ²⁰Ne ions at 196 MeV. The reaction products were analysed and detected by means of a ΔE ? E telescope placed in the focal plane of a magnetic spectrometer located at an angle of 0° with respect to the beam direction. In all the reactions studied light charged particles with an energy close to the respective calculated kinematic limit for a two-body exit channel are produced with relatively great probability. The results obtained make it possible to draw some conclusions about the reaction mechanism involving the emission of light charged particles.     

Gamma-gamma directional correlations and coincidence studies in154Gd

The intensities, placements andE2/M1 mixing ratios of transitions in the decay of¹⁵⁴Eu have been carefully studied to provide accurate data for microscopic calculations. Coincidence relationships in the decay of¹⁵⁴Eu have been studied extensively with a multiparameterγ-γ coincidence system with two large volume Ge(Li) detectors. Spectra in coincidence with twenty energy gates were analyzed. Twenty-nine new coincidence relationships were established and confirmed most, but not all, of several levels previously assigned by energy fits only. From an analysis of coincidence spectra and singles spectra with a 18% efficiency Ge(Li) detector new information on the gamma-ray intensities were obtained. Precise values of theE2/M1 mixing ratios of transitions from the gamma- and beta-vibrational bands to the g.s. band have been determined fromγ-γ directional correlation measurements with a NaI(Tl)-Ge(Li) detector coincidence system. Mixing ratios were obtained for a number of other transitions including those fromK ^π =0^? and 2⁺ bands from direct and skipped cascade correlations.     

Study of penetration effects in the <Emphasis Type="Italic">E</Emphasis>1 and <Emphasis Type="Italic">M</Emphasis>1 transitions in <Superscript>44</Superscript>Sc

Conversion coefficients for the E1 and M1 transitions in the ⁴⁴Ti decay have been measured with high accuracy using the sum peak and multidimensional coincidence methods. The following values have been obtained: α_K(E1) = 0.077 ± 0.003 and α_K(M1) = 0.014 ± 0.001. A significant contribution of the penetration effects for the M1 transition has been shown. The penetration parameter λ is determined to be ?260 ± 30 has been determined.     

The conversion electron spectrum in the decay of195Au

Twenty-four internal conversion lines in the decay of¹⁹⁵Au have been studied at high resolution by means of the Vanderbilt iron-free spectrometer. The electron intensities of this work and previously published photon intensities were used to calculate the percentage decay to each level in¹⁹⁵Pt. Conversion coefficients andL subshell ratios were used to assign the following multipolarities: 30.8 keV, pureM1; 98.8 keV, (99±1)%M1; 129.8 keV, pureE2; and 210 keV, pureE2. MeasuredL subshell ratios are not in good agreement with theoretical values.     

The reactions 50,52Cr(d, 6Li) 46,48Ti at Ed = 651 MeV

The ^50,52Cr(d, ⁶Li) ^46,48Ti reactions have been studied at E_d = 65 MeV bombarding energy. Angular distributions of outgoing Li particles were measured for final states in ^46,48Ti nuclei from 15° to 50° (lab). These were compared with zero-range and finite-range DWBA calculations in an α-cluster pick-up approximation to obtain relative α-spectroscopic factors.     

Measurement of mean lifetimes, γ-ray angular distributions and linear polarizations for low-lying levels of 50V

Levels of ⁵⁰V were populated with the ⁵⁰Ti(p, n)⁵⁰V reaction at E_p = 4.50, 4.62 and 4.80 MeV. Gamma rays were measured in singles. From Doppler shift attenuation measurements mean lifetimes have been deduced for 9 levels below E_x = 2 MeV. The J^π assignments for 8 of these levels follows from γ-ray angular distribution and linear polarization measurements. The transition strengths have been compared with calculations based on the wave functions of McCullen, Bayman and Zamick.     

An internal conversion study of the decay of193Au

The internal conversion spectrum following the decay of¹⁹³Au has been studied in the electron energy region 0.8 to 700 keV, with the use of high-resolution magnetic beta-ray spectrometers. Several not previously reported transitions have been estabblished. Multipolarities and mixing ratios have been deduced fromK/L and subshell intensity ratios, and the majority of the transitions were found to be ofM1 and/orE2 characters. A revised level scheme for¹⁹³Pt, which consistently accomodates most transitions, has been constructed. Tentative spin-parity values have been assigned to all levels.     

Evidence for the Auger neutralization mechanism in secondary ion emission

Secondary ion yields, S⁺(E), for Cu⁺ ejected from Cu(111) and Cu(110) have been determined for the secondary ion kinetic energy range from l to 50 eV. A plot of log S⁺(E) versus $\text{E}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ falls on a single straight line over three orders of magnitude of S⁺(E). The slope. $\text{A}\text{a}$ is 2 × 10⁶ cm/s, in good agreement with values reported for the related process, the survival probability of excited neutral copper atoms ejected from a copper surface by ion bombardment. This provides strong evidence that Auger neutralization is the dominant factor governing secondary ion survival.     

The gamma decay of analogue states in61Cu

Resonances in the reaction⁶⁰Ni(p, γ)⁶¹Cu have been studied in the proton energy rangesE _p=1840–1880 keV and 2220–2300 keV. Decay schemes and branching ratios have been determined for a number of resonances, three of which are identified as analogue fragments of the 283 keV (1/2^?) and 656 keV (3/2^?) states in⁶¹Ni. The split analogue components of the 283 keV state atE _x≈6.6 MeV are seen to decay significantly to a group of states in the region of excitation 3–4 MeV. Gamma ray angular distributions yield the following resonance spins:E _p=2248 keV,J=3/2;E _p=2263 keV,J=5/2. Also, the⁶¹Cu ground stateβ ⁺ decay to parent levels in⁶¹Ni has been compared to the respective analogue stateM1 gamma decay to the⁶¹Cu ground state.     

The reaction 36S(p,γ)37Cl: (I). Excitation energies and γ-ray branchings of bound states deduced from resonances in the range Ep = 500–2000 keV

Yield curves of the reaction ³⁶S(p, γ)³⁷Cl have been measured over the range E_p = 500–2000 keV with a highly enriched (81%) ³⁶S target. Proton energies, with a precision of typically 0.3 keV, and strengths are presented for the nearly 200 observed resonances. Several previously reported resonances, among which the well-known $\text{J}{}^{\mathrm{\pi }}\text{=}\text{7}\text{2}{}^{\mathrm{?}}\text{, E}{}_{\mathrm{p}}\text{= 1887}\text{keV}$ analogue resonance, are proven to be multiplets.At 75 selected resonances in the ranges E_p = 500–1200 and 1800–2000 keV the decay schemes have been studied. These measurements also provide rather detailed information on the γ-ray branching ratios of more than 50 bound states of which the majority has not been observed previously. Precision excitation energies have been determined; for the levels with E_x < 5 MeV the median uncertainty amounts to 30 ppm. The reaction Q-value is Q = 8386.34 ± 0.23 keV.These precision data invalidate several previous spin and parity assignments to low-lying bound states of ³⁷Cl. They also provide a basis for the lifetime measurements and spin and parity assignments to be discussed in the following paper.     

Energy distributions of atomic and molecular ions sputtered by C60 projectiles

In the process of investigating the interaction of fullerene projectiles with adsorbed organic layers, we measured the kinetic energy distributions (KEDs) of fragment and parent ions sputtered from an overlayer of polystyrene (PS) oligomers cast on silver under 15 keV C₆₀⁺ bombardment. These measurements have been conducted using our TRIFT™ spectrometer, recently equipped with the C₆₀⁺ source developed by Ionoptika, Ltd. For atomic ions, the intensity corresponding to the high energy tail decreases in the following order: C⁺(E^−0.4) > H⁺(E^−1.5) > Ag⁺(E^−3.5). In particular, the distribution of Ag⁺ is not broader than those of Ag₂⁺ and Ag₃⁺ clusters, in sharp contrast with 15 keV Ga⁺ bombardment. On the other hand, molecular ions (fragments and parent-like species) exhibit a significantly wider distribution using C₆₀⁺ instead of Ga⁺ as primary ions. For instance, the KED of Ag-cationized PS oligomers resembles that of Ag⁺ and Ag_n⁺ clusters. A specific feature of fullerene projectiles is that they induce the direct desorption of positively charged oligomers, without the need of a cationizing metal atom. The energy spectrum of these PS⁺ ions is significantly narrower then that of Ag-cationized oligomers. For characteristic fragments of PS, such as C₇H₇⁺ and C₁₅H₁₃⁺ and polycyclic fragments, such as C₉H₇⁺ and C₁₄H₁₀⁺, the high energy decay is steep (E⁻⁴ − E⁻⁸). In addition, reorganized ions generally show more pronounced high energy tails than characteristic ions, similar to the case of monoatomic ion bombardment. This observation is consistent with the higher excitation energy needed for their formation. Finally, the fraction of hydrocarbon ions formed in the gas phase via unimolecular dissociation of larger species is slightly larger with gallium than with fullerene projectiles.     

Surface lifetime degradation in Si and Ge under low energy electron irradiation

The bombardment of n-type Ge and Si by 10–30 keV electron beams is shown to reduce the surface lifetime τ_P of minority carriers but not to affect mobility μ_P or diffusion constant D_P. For experiments, the electron beam in a scanning electron microscope is replaced a chopped light source to perform modified Haynes-Shockley experiment, and the measurements is used to calculate μ, D and τ. The reduction in τ is interpreted in terms of an increase in surface recombination velocity s. At a dose of approximately 10¹⁷ electrons cm^?2 for Ge and 10¹⁵ electrons cm^?2 for Si, a saturation value for s appears to be reached after which further bombardment has no effect. The values of τ obtained from both light and SEM Haynes-Shockley experiments performed in vacuum agree within approximately 5% both prior to and after bombardment. The initial values of lifetime can be restored by etching the samples.     

Dominance of α decay from the isoscalar giant quadrupole resonance in 16O

The charged particle (c) decay of the isoscalar giant quadrupole resonance in a ¹⁶O has been studied in a ¹⁶O(α,α'c) coincidence experiment at E_α=155 MeV. The J=2 character of this resonance was established by angular correaltion measurements. Its dominant decay proceeds through the α₁ channel which contains about 40% of the E2 energy weighted sum rule. This explains difficulties of capture reactions to locate the GQR.     

The reaction 36S(α, γ)40Ar: Yield curve,excitation energies and decay of 40Ar resonance levels

The 8 to 10 MeV levels in ⁴⁰Ar have been studied for the first time through the reaction ³⁶S(α, γ)⁴⁰Ar (Q-value 6.80 MeV). Energy and strength of 51 resonances have been determined in the bombarding energy range E_α = 2.3 to 3.55 MeV. The decay schemes have been studied for 13 resonances.     

Investigation of the e<Subscript>0</Subscript>-electron yield from the surface of thin films under bombardment by α and β particles from radioactive sources

The yields of near-zero (e₀) electrons from the surface of targets with different Z under their bombardment by α particles from ²²⁶Ra decay were measured by the method of e_α coincidences. The ratios of the e₀-electron yields for α particles with different energies E _α are described well by the dependence Y _e (E _α) ～ υ _α ^?1 , where υ _α is the α-particle velocity. The e₀-electron yield from the surface of thin films under their bombardment by β particles from radioactive sources with ¹⁵²Eu, ¹⁵⁴Eu, and ²²⁶Ra has been investigated by the method of eγ coincidences. It is established that ionization rate of target atoms in this case is inversely proportional to the velocity of incident β particles (υ _β ^?1 ), i.e., is proportional to the time of atomic electron perturbation induced by a β particle passing near an atom.     

Levels of146Ce studied through the decay of high-spin isomer of146La

The decay of 10.0 s high-spin isomer of¹⁴⁶La to levels of¹⁴⁶Ce has been studied using the on-line isotope separator KUR-ISOL. Gamma-ray singles,γ -γ coincidence and conversion-electron spectra have been measured. A level scheme containing 90 levels and 206γ-ray transitions has been constructed for¹⁴⁶Ce, populated in the decay of the high-spin isomer of¹⁴⁶La. Among these, 39 levels are reported for the first time. Spins and parities for some levels are proposed on the basis ofγ-decay mode, logft values and conversion-electron measurements. The band structure of the low-lying levels in¹⁴⁶Ce is discussed.     

Field ion microscopy of cascades of atomic displacements in metals and alloys after various types of irradiation

Experimental results on atomic-spatial investigation of radiative defect formation in surface layers of materials, initiated by neutron bombardment (of Pt, E > 0.1 MeV) and ion implantation (in Cu₃Au: E = 40 keV, F = 10¹⁶ ion/m², j = 10^?3 A/cm²), are considered. Quantitative estimates are obtained for the size, shape, and volume fraction of cascades of atomic displacements formed under various types of irradiation in the surface layers of the materials. It is shown that the average size of radiation clusters after irradiation of platinum to a fast neutron fluence of 6.7 × 10²² m^?2 (E > 0.1 MeV) is about 3.8 nm. The experimentally established average size of a radiation cluster (disordered zone) in the alloy after ion bombardment is 4 × 4 × 1.5 nm.