Reaction 40Ar Research Articles

Alpha decay properties of new protactinium isotopes

Evaporation residues produced in the reactions 40Ar + 181Ta and 40Ar + 184W were separated from the primary beam by the velocity filter SHIP and detected by a Δ E-E counter telescope. The technique of delayed coincidences was applied to individually identify the reaction products implanted into a Si surface barrier detector by their subsequent α-decays. The previously unknown nuclei 215Pa and 218Pa were identified by their known daughter decays. 215Pa was found to decay with E α = 8.085±0.015MeV and t 1/2 = 14± 2 3ms. For 218Pa two α-lines were found at 9.535±0.015MeV and 9.614±0.020MeV with a corresponding half-life of 120 +40 -20μs. The half-life of the 8.33 MeV α-decay of 217Pa. was determined to be 4.9 +0.6 -0.4 ms. Furthermore a new isomer was found in 217Pa which decays with E = 10.16±0.02MeV and t 1/2 = l.6 +1.0 -0.5ms. The decay of this isomer is tentatively interpreted as being hindered by an angular momentum of about 10ħ of the emitted α-particle. The ground state α-decay energies of these very proton-rich isotopes agree well with systematics but deviate considerably from theoretical mass predictions.

Transport theory of deeply inelastic heavy-ion collisions based on a random-matrix model. III. Calculation of cross sections. Comparison with the reaction Ar + Th

The transport equation deduced previously is cast into a form which allows for numerical computation of cross sections. The approximations, especially the moments approach, are exhibited, as are essential points of the numerical procedure. The validity of the Einstein relation is discussed. Doubly differential cross sections for various fragments produced in the reaction 40Ar + 232Th are calculated and compared with experimental data.

Large contribution of deep inelastic processes to reactions of40Ar and48Ca with238U

Differential recoil range distributions have been measured for heavy-reaction products ranging from Te(Z=52) to quasielastic transfer products near the charge and mass of the targets for the reactions of 276 MeV48Ca+238U, 237MeV and 250 MeV40Ar+238U, and 259 MeV40Ar+197Au. The measured recoil range distributions for the40Ar+197Au reaction agree with range distributions calculated from the known projectile-like fragment angular distributions for this reaction. The angular distributions of recoil products formed in the uranium target reactions are deduced and show that the products in the75Re to83Bi region have backward peaked angular distributions characteristic of deep inelastic reactions. The heavy product angular distributions smoothly vary from a (1/sinθ) shape to an exponential shaped backward peak as the atomic number of the product increases from 52 to 83. The trend in the deduced angular distributions for those elements for which recoil range distributions were determined in the40Ar+197Au reaction and the 250 MeV40Ar+238U reaction is similar, suggesting that just as for the Ar+Au system the composite system for the uranium target reaction is also not fully equilibrated along the mass asymmetry coordinate. These conclusions show that the fraction of the total reaction cross section resulting in complete fusion must be re-evaluated for the40Ar+238U reaction and similar heavy-target reactions.

The strength of the M2 transition from the 7-/2 hole state in43K

The mean life of the 738 keV level of 43K has been measured by direct electronic timing as tau m=265+or-15 ns. The reaction 40Ar( alpha ,p gamma )43K at 10.4 MeV was used to excite the level. A comparison is made with another recent measurement while the deduced M2 strength is compared with those in other potassium isotopes.

Deep inelastic collisions in the interaction of 280 MeV 40Ar with 58Ni

Masses and charges of all the nuclei with 5 ≦ Z ≦ 20 produced in the reaction 40Ar + 58Ni have been identified using combined ΔE · E and time-of-flight techniques. Energy spectra, angular distributions and cross sections have been measured. The formation of an intermediate composite system, in which charge equilibrium is achieved, is discussed. Also, the transition between the quasi-elastic and the deep inelastic process is studied. The angular distribution behaviour is shown to be related to the interaction time. The total cross section of the deep inelastic process has been found to be 700 mb and is compared to the evaporation residue cross section.

Vector analyzing power and cross section for the reactions [formula omitted

Angular distributions of vector analyzing power and cross section for the reactions 40Ar(d, p)41Ar and40Ar(d, t)39Ar have been measured at an incident deuteron energy of 14.83 MeV. The bound-state data in the (d, p) reaction and the (d, t) data are compared to DWBA calculations. The data for the neutron-unbound states are analyzed in the framework of the DWBA using (i) a form factor for weakly bound neutron and (ii) a resonance form factor, following the approach of Vincent and Fortune. The j-dependence of the (d, p) vector analyzing power permits definitive spin-parity assignments to be made for 19 neutron-bound and 4 neutron-unbound states in 41Ar with excitation energy up to 6.57 MeV. Tentative Jπ assignments have been made for 3 states. The l-value for the 5.62 MeV state has been determined. Data for the observed unbound states are found to be equally well reproduced by the type (i) calculations as by the type (ii) calculations. The (d, t) vector analyzing power data show definite j-dependence although not as strongly as in the (d, p) reaction. For relatively weakly excited states a pre-knowledge of the l-value of the transition is desirable for an unambiguous spin assignment. In general, the j-dependence in the (d, t) vector analyzing power can be utilized for definitive Jπ assignments. On this basis, Jπ values have been assigned for seven states in 39Ar with excitation energies up to 4.47 MeV excitation. Possible spin values for three other states are suggested. Spectroscopic factors for the states in 41Ar and 39Ar have been extracted and are in fair agreement with those obtained by other workers.

Evidence for the temporary existence of a ?composite? system in deep inelastic nuclear interactions

Masses and charges have been identified for the light fragments (6<A<40) produced in the reactions (40Ar+58Ni), (40Ar+64Ni), (40Ca+58Ni) and (40Ca+64Ni). From the study ofN and Z distributions, it has been shown that the ratioN/Z of thecomposite system has a dominant role in the determination of theN/Z of the product. Then there should be at least a charge equilibration during the damped collision.

Cyclotron production of 38S by the reaction 40Ar ( p, 3 p) 38S

Cyclotron production of 38S by the reaction 40Ar ( p, 3 p) 38S

Properties of potassium atoms trapped in a solid argon matrix

Argon crystals were doped with 0.2 ppm of 41K through the nuclear reaction 40Ar(n, β −) 41K. The X-band electron spin resonance of 41K was observed during a simultaneous irradiation into the various optical absorption bands. In this way optical and ESR-data of potassium atoms trapped at multiple sites in the argon matrix could be correlated.

Multiple trapping sites for potassium atoms in argon matrices

Argon crystals were dopes with 0.2 ppm of 41K through the nuclear reaction 40Ar(n, β -) 41K. The X-band electron spin resonance spectrum of 41K was observed. The recorded spectra clearly show the existence of different trapping sites for potassium in argon. Zero-field hyperfine splittings and g-values of potassium on these sites are determined.

Annealing studies on the absorption spectrum of 41K-atoms trapped in an argon matrix

Argon crystals were doped with 0.2 ppm of 41K through the nuclear reaction 40Ar (n, β -) 41K. The absorption spectrum from 300 nm to 800 nm was measured as a function of the annealing temperature. Absorption ← 4 2s 1 2 transition of the free atom could be bands corresponding to the 4 2p 1 2 , 3 2 ← 4 2s 1 2 and 5 2p 1 2 , 3 2 ← 4 2s 1 2 transition of the free atom could be observed. The absorption bands depend strongly on the annealing temperature. An increase in the annealing temperature results in a blue shift of the absorption bands.

Excitation functions and α-decay from compound nuclei in Ar induced reactions on 144Sm and 166Er

Excitation functions for the reactions 40Ar + 144Sm → Pt and 40Ar + 166Er → Po radionuclides, in which the observed nuclei have two protons less than the product of the complete fusion of projectile and target, have been found to be characterized by two peaks. Independent of whether the target was Sm or Er, and independent of the mass of the product, the two peaks were consistently found to be separated by ≈ 40 MeV of excitation energy. Consideration of other experiments with 40Ar ions, and with lighter projectiles, leads us to the conclusion that the two peaks are due to different compound-nuclear de-excitation processes: the first peak involves the evaporation of an α-particle, (Ar, α( x − 2)n), and the second peak, the emission of nucleons only, (Ar, 2p xn).

Mass and charge identification of the light products of the reaction 40Ar + natNi

Mass and charge identification of the light products of the reaction 40Ar + natNi

Reactions of 40Ar with 159Tb, 142Nd and 144Sm; New α-activities from 189Bi, 173Pt and 177Au

Reactions of 40Ar ions with targets of 159Tb, 142Nd, and 144Sm have been studied at energies below 300 MeV with a helium gas-jet system. Excitation functions for (Ar, xn) reactions, where x = 5–10, were obtained for the radioactive products that decay by α-emission. Based on the characteristics of these excitation functions and on the systematics of α-decay, evidence is presented for the existence of the nuclides 189Bi with α-particle energy E α = 6.67±0.01 MeV and half-life < 1.5 sec, and 173Pt with E α = 6.19±0.01 MeV; and for the emission from 177Au of an α-particle with E α = 6.15±0.01 MeV.

Photoneutron Disintegration of 40Ar

Photoneutron energy spectra from 40Ar have been measured at bremsstrahlung end-point energies from 13 to 23 MeV in 1 MeV steps. The differential cross section at 90° for the reaction 40Ar(γ, n0)39Ar revealed some 26 previously unreported excited states of 40Ar in the region below 13 MeV. The envelope of these states suggests a single particle resonance involving the valence 1f7/2 neutrons. The measured total neutron cross section exhibits a marked change from this single particle behavior at about 14 MeV where collective effects begin to dominate and neutrons are emitted to highly excited states of 39Ar.

Polarization and angular correlation measurements following the 40Ar(p, nγ) 40K reaction

Gamma-ray angular distributions and polarization correlations have been measured using the reaction 40Ar(p, nγ) 40K. All the experiments were carried out with bombarding energies close to threshold for the states under investigation. Comparison with compound nuclear predictions has yielded the following spin assignments to states in 40K; 1.959(2 +), 2.047(2 −), 2.070(3 −), 2.103(1 −), 2.261(3 +), 2.290(1 +), 2.291(4, (3)), 2.419(2,3), 2.575(2,4) and 2.625(0 −). Multiple mixing ratios together with the gamma-ray branching ratios have been determined for all these levels. A short theoretical treatment of the polarization of gamma rays from aligned nuclei using the phase-consistent formalism of Brink and Rose is included.

Thermal and 14.4 MeV neutron activation cross sections of argon

Thermal and 14.4 MeV neutron activation cross sections of argon were measured with argon quinol-clathrate powder as target material. The thermal neutron activation cross section of the 40Ar(n, γ) 41Ar reaction was measured to be 510±25 mb. The 14.4±0.3 MeV neutron activation cross sections for the reactions 38Ar(n,p) 38Cl, 40Ar(n,p) 40Cl(1.4 min), 40Ar (n, np+n, pn+n, d) 39Cl and 40Ar(n, α) 37S were measured to be 75±20, 15.7±2.0, 1.40±0.15 and 10.5±1.0 mb, respectively. These values are compared with prior measurements and with semi-empirical predictions of Levkovskii and of Gardner.

14·8 MeV neutron activation cross-sections of argon

The 14·8 MeV neutron activation cross-sections for the reactions 38Ar( n, p) 38Cl, 40Ar( n, p) 40Cl, 40Ar( n, np) 39Cl and 40Ar( n, α) 37S have been measured to be 110±22 mb; 15±2 mb; 1·7±0·2 mb and 10±1·5 mb, respectively. The data are in reasonably good agreement with the theoretically calculated values of Gardner.

Production ratios of the 38K isomers in nuclear reactions

The production ratios of 38mK and 38gK have been measured in the reaction 40Ar(p, 3n) 38K over the range E p = 29–48 MeV and in the reaction 37Cl( 3He, 2n) 38K over the range E( 3 He) = 10–23 MeV . The results show a fair agreement with calculations assuming a compound-nucleus model with a nuclear moment of inertia about one-half the rigid-body value and a nuclear temperature varying with excitation energy. A prediction is made of the isomer ratio to be expected in high-energy (spallation) reactions.

Fine structure and neutron decay of the isobaric analogue resonances

The mechanism of the distribution of an isobaric analogue resonance over its fine structure peaks is studied in the frame of the shell-model theory of nuclear reactions. A two-channel model is constructed, where the isobaric analogue doorway state is dominated by the entrance proton channel which, in turn, is coupled to the outgoing neutron channel only via complicated shell-model states. The energy averages of the differential elastic scattering, total and reaction cross sections are calculated. It is shown that these averages do not display the same resonance energies and widths, unless the background of the (p, n) cross section reaches its maximum value. This holds in spite of the fact that the diagonal and off-diagonal S-matrix elements have the same poles. The elastic, scattering and total cross sections in the absence of the isobaric analogue resonance are studied from a microscopic point of view and the connection with the phenomenological optical-model treatment is given. The extraction of the spectroscopic factor from the experimental data is discussed. The fluctuations of the differential elastic scattering cross section around its average are investigated. The distribution of the fine structure resonance parameters is derived for overlapping as well as isolated peaks; the results are compared with the experimental data obtained at Duke University for the reaction 40Ar(p, p)40Ar.