Absolute Excitation Research Articles

Measurement and Analysis of Ground-State Band Transitions and2+′States inKr78,80,82,84from (α,xnγ)

Ground-state band levels to ${6}^{+}$ in $^{84}\mathrm{Kr}$, ${6}^{+}$ in $^{82}\mathrm{Kr}$, ${8}^{+}$ in $^{80}\mathrm{Kr}$, and ${10}^{+}$ in $^{78}\mathrm{Kr}$ have been identified with 20-65-MeV ($\ensuremath{\alpha},xn\ensuremath{\gamma}$) reactions on enriched Se targets with $x=2, 3, \mathrm{and} 4$. The data are in-beam and radioactive $\ensuremath{\gamma}$ spectra, angular distributions, relative and absolute excitation functions and \ensuremath{\sim}3-nsec time distributions. All transitions in the ground-state bands are \ensuremath{\gtrsim}95% prompt (\ensuremath{\gtrsim}3 nsec) except for $^{84}\mathrm{Kr}$, in which the 6 \ensuremath{\rightarrow} 4, 4 \ensuremath{\rightarrow} 2, and 2 \ensuremath{\rightarrow} 0 transitions have the same intensities of long-lived (\ensuremath{\gtrsim}200-nsec) component in addition to the prompt component. Multipole mixing ratios of three other transitions in $^{82}\mathrm{Kr}$ are obtained from the angular distributions. The systematics of level energies in the ground-state bands of various Se, Kr, Mo, and Ru isotopes are analyzed with a phenomenological equation. This reveals three limiting types of nuclei.

Absolute excitation cross sections for the 41 S-, 41 D- and 31 P-levels of helium excited by fast protons

We have measured absolute cross sections for proton excitation of the 31P-,41S- and 41D-levels of He in the energy range from 200 keV to 1 MeV. Calibration with a tungsten lamp mounted in the collision chamber and normalization on the high energy first Born approximation 31P values for protons and electrons were used to obtain absolute data. At 1 MeV the experimental results agree within 10% with the first Born approximation values.

Excitation of the CO Fourth Positive Band System by Electron Impact on Carbon Monoxide and Carbon Dioxide

Absolute excitation cross sections were measured for five vibrational bands of the CO(A 1Π–X 1Σ+) Fourth Positive band system. The bands were produced by electron impact on CO and CO2 and the cross sections were measured from threshold to 350 eV. Relative intensity measurements on 28 bands were used to determine the dependence of Re on the r centroid, which is Re = 1.9(1.0 − 0.6r̄υ′υ″). Absolute transition probabilities were computed using this functional form for Re and normalizing the total transition probability of the υ′ = 2 level to published experimental results. The total f-value for this transition is then 0.15. Absolute excitation cross sections for the first five vibrational levels (υ′ = 0 → 4) of the A 1Π state were determined for each parent gas using the measured cross sections of specific bands and the absolute transition probabilities. When CO was the parent gas, the relative populations of these vibrational levels were proportional to the Franck–Condon factors, qυ′0. The sum of the cross sections for these levels is 1.87 × 10−17 cm2 ± 15% at 300 eV. This represents 87.4% of the total excitation cross section for the A 1Π state. The relative populations of the first five vibrational levels were also determined for dissociative excitation of CO2 and they differed from the relative populations which resulted from direct excitation of CO. The sum of the cross sections for these five levels is 1.4 × 10−18 cm2 ± 17% at 300 eV.

Levels ofCu61,Cu64,Ga67, andGa68Excited by the (p, n) Reaction

Neutron time-of-flight techniques were used to study the ($p, n$) reaction on the nuclei $^{61}\mathrm{Ni}$, $^{64}\mathrm{Ni}$, $^{67}\mathrm{Zn}$, and $^{68}\mathrm{Zn}$. The locations of excited states in the residual nuclei were measured with an energy resolution of about 10 keV. The absolute excitation energies are accurate to \ifmmode\pm\else\textpm\fi{}2 keV for low-lying states and to \ifmmode\pm\else\textpm\fi{}5 to 7 keV for the highest states (2-3-MeV excitation). The following results were obtained: $^{61}\mathrm{Cu}$, 17 levels (0 to 2.6 MeV); $^{64}\mathrm{Cu}$, 66 levels (0 to 2.75 MeV); $^{67}\mathrm{Ga}$, 57 levels (0 to 3.3 MeV); and $^{68}\mathrm{Ga}$, 32 levels (0 to 1.6 MeV). Comparisons with other information on these nuclei indicate that the ($p, n$) reaction is a very effective tool for locating all the levels. The relative intensities of the neutron groups displayed distinctive patterns. However, quantitative yields of a succession of closely spaced proton energies showed typically 30% fluctuations. To maintain good energy resolution and yet reduce the fluctuations we averaged many individual runs in order to have more meaningful comparisons with the Hauser-Feshbach predictions. Spin assignments were made to 10-20 levels in $^{64}\mathrm{Cu}$, $^{67}\mathrm{Ga}$, and $^{68}\mathrm{Ga}$. The results are generally consistent with other available information on spin parities.

Cross Section for Excitation of the Fourth Positive Band System in Carbon Monoxide by 20-120 keV Protons

Excitation cross sections for the fourth positive band system in carbon monoxide have been determined from studies of the energy-loss spectra of 20-120-keV protons incident on gaseous CO targets. The energy-loss spectra had an energy resolution of about 2 eV. Prominent peaks in the spectra were observed at 8.5 and 13.8 eV. The first peak is believed to be due to excitation of the fourth positive band system of $\mathrm{CO} (X^{1}\ensuremath{\Sigma}^{+}\ensuremath{\rightarrow}A^{1}\ensuremath{\Pi}$, while the 13.8-eV peak covers a number of possible states, including the $B^{2}\ensuremath{\Sigma}^{+}$ and the $C^{1}\ensuremath{\Sigma}^{+}$ states. Changes in the slope of the ionization continuum were noted at 16.5 eV, corresponding to the $A^{2}\ensuremath{\Pi}_{i}$ state of C${\mathrm{O}}^{+}$, and at 20.5 eV, corresponding to the $B^{2}\ensuremath{\Sigma}^{+}$ state of C${\mathrm{O}}^{+}$. Absolute excitation cross sections for the fourth positive band system of CO are presented, as well as the total inelastic cross sections and the total ionization cross sections for 20-120-keV protons incident on CO.

Dissociative Excitation of Some Oxygen-Containing Molecules: Lifetimes and Electron-Impact Cross Sections

Decay lifetimes of seven vacuum-ultraviolet O I and O II emission multiplets have been measured using a pulsed electron beam in low-pressure samples of ${\mathrm{O}}_{2}$, CO, NO, and ${\mathrm{H}}_{2}$O. The lifetimes and cascade patterns of the lines are consistent with known autoionization processes. In two cases, spin-orbit-induced autoionization rates are determined. Absolute electron excitation functions for 8447---\AA{} O I have been measured in the above gases. Relative excitation functions for 1304-\AA{} O I are normalized to the 8447-\AA{} absolute cross section by means of a time-domain cascade analysis. A method for computing relative cross sections from $N$-exponential decays is outlined.

Absolute excitation cross section of the K + resonance states in collisions with argon atoms

To measure absolute values of the intensity of spectral lines in the vacuum ultraviolet a photoionization chamber of a new design has been constructed. The absolute values of the cross sections for the excitation K II resonance lines have been determined.

Electron impact excitation of the B 3capital $\Pi$g state of N2

Absolute excitation cross sections for the emission of the first positive bands of nitrogen under electron impact have been obtained. The maximum total cross section of the B 3capital Pig level was found to be 659 × 10-18 cm2. From measurements made on the cascade contribution from the D 3Σu level an approximate maximum cross section for excitation of this level of 3 × 10-18 cm2 was obtained. Other cascade features were observed and discussed. The results are compared with those of other workers.

Absolute Luminescence Spectra via Digital-Technique and Time-Resolved Spectroscopy

Most instruments intended for luminescence spectroscopy fall in the category of uncorrected spectrofluorimeters. In many routine analyses, uncorrected spectra are useful, especially if they do not have to be compared with others from different laboratories. However, for theoretical work, results must be on an absolute basis. This paper describes a method and the related equipment that have been developed and used to obtain, on an absolute basis, many of the parameters that are important in photochemical research. The system can provide absolute emission spectra, absolute excitation spectra, and quantum efficiencies for luminescence, fluorescence, delayed fluorescence, and phosphorescence. Also, it can measure the half-life of phosphorescence and of delayed fluorescence. Provision is made for the independent and continuous control of the time between excitation and detection pulses, thus allowing the measurement of the half-life at any wavelength of emission. With these provisions it is possible to resolve overlapping fluorescence, delayed fluorescence, and phosphorescence spectra.

Semiempirical Model for Atom–Atom Ionization Rates

Numerical calculations are carried out to help interpret ionization rates for rare-gas atoms (particularly argon) obtained in shock-heating experiments. A simplified semiempirical model with three adjustable parameters is used for electronic transitions induced by atom–atom collisions. The three parameters are a measure of the absolute excitation rate from the ground state to the first excited state and of the ratios of different excitation and ionization rates. Numerical results are presented for the total ionization rate as a function of temperature and time for different values of the parameters. Present experiments determine one of the parameters, limit the other two parameters, and yield a relation between them. The possibility for determining all three parameters uniquely from future experiments is discussed.

Excitation of O2+ bands by electron impact

Absolute excitation cross sections for the emission of the first negative bands of O2+ under electron impact on O2 have been obtained. The peak cross section for the b 4Σg- state was found to be 32·5 × 10-18 cm2 at 100 eV. The results are compared with proton and other electron impact data. Some preliminary results on the second negative system are also given.

Absolute cross sections for electron excitation of the second positive bands of nitrogen

Absolute excitation cross sections for the emission of the second positive bands of nitrogen under electron impact have been obtained. Peak level cross sections for the νprime = 0, 1, 2 levels of the c 3IIu state were found to be, respectively, 23·5 × 10-18 cm2, 14·4 × 10-18 cm2 and 4·9 × 10-18 cm2. Good agreement is found with the theoretical A coefficients for the relative intensities of the different vibrational bands. The results are compared with those of other workers and various secondary effects which were observed are discussed.

Étude expérimentale et analyse des fonctions d'excitation 165Ho(α, χn) et 169Tm (α, χn)

Absolute cross sections and excitation functions for α-induced reactions have been measured from 15 to 55 MeV by activation and stacked-foil techniques. The following reactions were observed: 165Ho(α, 5n) 164Tm, 165Ho(α, 4n) 165Tm, 165Ho(α, 3n) 166Tm, 165Ho(α, 2n) 167Tm, 165Ho(α, n) 168Tm, 169Tm(α, 5n) 168Lu, 169Tm(α, 4n) 169Lu, 169Tm(α, 3n) 170Lu, 169Tm(α, 2n) 171Lu and 169Tm(α, n) 172Lu. The experimental results agree fairly well with the theoretical value for T = 1.66 MeV except for the high-energy “tail” of these reactions. Interpretations were proposed with the help of a quantal process instead of Monte-Carlo calculation.

Absolute cross sections and excitation functions for deuteron-induced reactions on the nickel isotopes between 2 and 12 MeV

Absolute cross sections and excitation functions for the reactions 58Ni(d, n) 59Cu, 61Ni (d, n) 62Cu, 62Ni(d, 2n) 62Cu, 60Ni(d, n) 61Cu and 58Ni(d, t) 57Ni have been measured by activation using the stacked-foil technique. The (d,n) experimental excitation functions are compared to the theoretical calculations of F. Perey based on a non-local, optical-model potential.

Coincidence study of the reactions 39K(n, pγ) 39Ar and 39K(n, αγ) 36Cl

The reactions 39K(n, p) 39Ar and 39K(n, α) 36Cl were investigated by bombarding a KI(TI) scintillator with fast mono-energetic neutrons in the energy range 4–8 MeV. Information on the level and decay schemes of the final nuclei, especially 39Ar, was obtained by spectroscopy of γ-radiation in coincidence with protons and α-particles. For the strongly populated final states 39 Ar ∗ = 1.27, 1.52, and 2.10 MeV and 36 Cl ∗ = 0.79 MeV , absolute excitation functions and γ-angular distributions were measured and analysed for spectroscopic information assuming a compound nucleus reaction mechanism. The experimental techniques are described, and the results are discussed together with information available from other reactions leading to the same final nuclei.

Absolute cross sections and excitation functions for α-particle-induced reactions of 165Ho, 164Er, 166Er and 167Er

Absolute cross sections and excitation functions for α-induced-reactions have been measured from 16 to 40.5 MeV by activation and stacked-foil techniques. The following reactions were observed: 165 Ho(α, n) 168 Tm, 165 Ho(α, 2 n) 167 Tm, 165 Ho(α, 3 n) 166 Tm, 165 Ho(α, 4 n) 165 Tm, 164 Er(α, n) 167 Yb, 164 Er(α, 2 n) 166 Yb, 164 Er(α, 3 n) 165 Yb, 166 Er(α, 3 n) 167 Yb, 166 Er(α, 4 n) 166 Yb, 166 Er(α, pn) 168 Tm, 167 Er(α, 4 n) 167 Yb and 167 Er(α, p2 n) 168 Tm .

Direct Electron Excitation Cross Sections Pertinent to the Argon Ion Laser

Absolute direct excitation cross sections from the neutral ground state have been measured for upper levels of the strongest laser transitions in Ar II to within errors of \ensuremath{\approx}20%. Reasonable agreement is obtained with calculated values of these cross sections based on the "sudden" approximation made by Koozekanani with Hartree-Fock wave functions and intermediate coupling.

Compound-statistical features of deuteron-induced reactions: (I). Radiative capture of 4–15 MeV deuterons

Absolute cross sections and excitation functions for the 30Si(d, γ) 32P and 138Ba(d, γ) 140La reactions from ≈ 4 to 15 MeV have been measured radiochemically using the stacked target technique. The 30Si(d, γ) cross sections above 5 MeV are 110 to 160 μb and exhibit little energy dependence. The 138Ba(d, γ) excitation function peaks at ≈ 22 μb near 10 MeV. The compound nucleus mechanism, formulated from continuum-theory cross sections and statistical-model calculations using Fermi gas level densities, reproduces both the magnitudes and the dissimilar energy dependences of the two excitation functions. Inverse E1 photonuclear cross sections were calculated both for the giant resonance shape used by Carver and Jones and for that proposed by Lane and Lynn, the former providing more satisfactory agreement with experiment, especially in the Si reaction. It is concluded that these radiative deuteron capture reactions can be explained in terms of compound nucleus formation followed by statistical de-excitation.

Absolute cross sections and excitation functions for deuteron induced reactions on chromium between 2 and 12 MeV

Absolute cross sections and excitation functions between 2 and 12 MeV have been measured for the following reactions: 52Cr(d, 2n) 52mMn, 21 min, 52Cr(d, 2n) 52Mn, 5.6 d, 50Cr(d, n) 51Mn, 45 min. This was done by activation and stacked foil techniques. The experimental results show that the (d, 2n) reactions proceed via the compound nucleus mechanism whereas the (d, n) excitation function shows a mixture of compound nucleus and direct reaction mechanism. Measurements of the cross section ratio σ 21 min σ 5.6 d show that the ground state (5.6 d) is preferentially formed at low deuteron energies.

Absolute cross-sections and excitation functions for α-particle induced reactions on Zn between 11 and 24 MeV

Absolute cross-sections and excitation functions between 11 and 24 MeV have been measured for the following reactions: 64Zn(α, n)67Ge 19 min, 64Zn(α, pn)66Ga 9.4 h, 66Zn (α, n) 69Ge 40 h, 66Zn(α, 3p)67Cu 61 h, 66Zn(α, pn)68Ga 68 min, 67Zn(α, 2n)69 Ge 40 h, 67Zn(α, p2n)68Ga 68 min and 68Zn(α, αp)67Cu 61 h. This was done by activation and stacked foil techniques.The experimental results have been compared with theoretical predictions based on optical model and statistical analyses. The magnitude of the total cross-section is closer to the optical model one, but the excitation function seems to be shifted in energy. For the 64Zn +α compound nucleus the order of occurence of the various reactions with increasing energy is (α, n) and (α, pn), whereas for the 66Zn+α compound nucleus the order is (α, n), (α, 3p) and (α, pn). The excitation functions for both (α, pn) reactions are very similar.