Lifetimes Of Excited Nuclear States Research Articles

Lifetimes of nuclear excited states with neutron gated recoil distance method

A motor driven plunger has been constructed for measuring lifetimes of nuclear excited states in pico second region. An array consisting of six neutron detectors was used to clean up γ-spectra obtained with CS-HPGe detectors. Lifetimes of low excited states in neutron deficient nuclei with low production cross-section e.g.81Y,77Kr and78Rb are reported.

Nuclear spectroscopy with slow neutrons

The aim of nuclear spectroscopy is to study nuclear excitations with a view to improving our knowledge of the forces play within the nucleus. Many complementary techniques have been developed to unravel the complex interplay of these forces and it is usually the combination of several experimental approaches such as the study of radioactive decay, transfer reactions, neutron capture, inelastic scattering, Coulomb excitation and other charged particle reactions which allows us to construct detailed level schemes and interpret them. We will concentrate, within the frame of this Workshop on the advanced instrumentation of the neutron capture gamma-ray spectroscopy, which plays an important and specific role in the comprehensive testing of nuclear models. Neutron capture gammaray spectroscopy now employs very sophisticated techniques to study nucear structure. The combination of precise measurements of primary gamma transitions with the precision obtained to data with curved and flat crystal and conversion electron spectrometers has considerably extended the possibilities in the study of nuclear structure. The nearly perfect resolution obtained with the most modern double flat crystal spectrometers allows the measurement of lifetimes of excited nuclear states in the range < 10−12 s via the observation of the Doppler broadening of gamma rays due to the recoil of the nucleus following emission of a primary gamma ray.

Electromagnetic transition probabilities in 130Ce

Lifetimes of excited nuclear states have been measured in 130Ce using the coincidence-plunger technique. The employed nuclear reaction was 98Mo( 36S, 4n) 130Ce at a beam energy of 150 MeV. The measurement has been performed at the NSF Daresbury using the ESSA 30 set-up. It was possible to determine lifetimes for the 4 + to 16 + states in 130Ce. The experimental B(E2) values could be well reproduced by calculations using the triaxial rotor model with β = 0.26 and γ = 21° as well as the rotation vibration model ( β = 0.25).

The application of the linearized boltzmann transport equation to low energy atomic collisions in solids

A new method has been developed for the solution of the linearized Boltzmann equation far from thermal equilibrium. The solution has been applied to the interpretation of the slowing down of atoms with kinetic energies of a few hundreds of eV as obtained from measured γ-peak profiles, using the gamma ray induced doppler broadening (GRID) technique. From this solution, lifetimes of nuclear excited states can be extracted. These results are compared with the predictions of other models.

Transition probabilities in transitional nuclei in the A=130 region

Lifetimes of excited nuclear states have been measured in 124Ba, 128Ba and 130Ce using the coincidence-plunger technique. The nuclear reactions employed were 100Mo( 28Si,4n) 124Ba, 114Cd( 18O,4n) 128Ba and 98Mo( 36S,4n) 130Ce at beam energies of 115 MeV, 75 MeV and 150 MeV, respectively. The measurements have been performed at the INFN Legnaro and at the University of Cologne using the OSIRIS-MIPAD and the OSIRIS spectrometer, respectively as well as at the NSF Daresbury using the ESSA 30 set-up. It was possible to determine lifetimes in 130Ce for the 4 + to 16 + states and in 128 Ba for the 2 + to 8 + states of the ground state band (gsb), the 4 +, 6 + and 8 + state of the γ -band as well as for 3 negative parity states. Preliminary results are obtained for 124 Ba. The corresponding B(E2) values support the interpretation that 128Ba is a good example of an O(6)-type nucleus. The B(E2) values for 130Ce indicate that the nucleus is less γ-soft than 128 Ba. The experimental values could be well reproduced by calculations using the triaxial rotor model with β = 0.26 and γ = 21 0 as well as the rotation vibration model (β = 0.25).

New reactor based methods to measure short lifetimes of nuclear excited states

Abstract In an atomic nucleus three of the four basic forces manifest themselves: the strong force between the nucleons determines the nuclear structure, while the weak force leads to beta decay and the electromagnetic force rules over the decay of the nucleus in an excited state to the stable ground state. The nuclear domain differs from many other physical systems, since typically only a few tens of nucleons participate in collective motion. Therefore, thenucleus is aunique laboratory in which the interplay of single particle motion and collective many-body correlations can be probed and the attendant finite body phase transitions (e.g., in shape) will exhibit dramatic fluctuations absent from an atomic environment. These aspects make the study of the atomic nucleus a fascinating, yet challenging, pursuit.

Lifetime measurements with a new Doppler shift technique

A method is described to measure the lifetimes of excited nuclear states with a new Doppler shift technique which combines the recoil-distance method, the Coulomb excitation of beam projectiles and the inverse kinematics. An annular parallel-plate position-sensitive avalanche counter has been designed for that purpose. The results of tests experiments using xenon beams, in particular the measurement of the lifetime of the first 2 + level in 132Xe, are reported.

Methods and new techniques in neutron capture gamma-ray spectroscopy

Neutron capture gamma -ray spectroscopy now employs the most sophisticated techniques to study nuclear structure, yet efforts are continuing to improve still further sensitivity and resolving power of the spectrometers used. The combination of precise measurements of primary gamma -transitions with the precision obtained to date with curved and flat crystal and conversion electron spectrometers has considerably extended the possibilities in the study of nuclear structure. Techniques are also available for the investigation of multiple neutron capture leading to nuclei which are up to three neutrons beyond stability. The nearly perfect resolution obtained with the most modern double flat crystal spectrometers allow the measurement of lifetimes of excited nuclear states in the range <10-12 s via the observation of the Doppler-broadening of gamma -rays due to the recoil of the nucleus following emission of a primary gamma -ray.

A plunger device for in-beam measurements of nuclear lifetimes

An experimental apparatus was built to measure life-times of excited nuclear states with the recoil-distance method (RDM). A millesimal micrometer and an electromagnetic gauge-head are used to measure the target-stopper distance, and their parallelism is tested by optical and capacitance methods. Measurements were performed in the nuclei 22Na and 153Dy, populated by the reactions 19F(α, n) and 144Nd( 12C, 3n), respectively. A minimum target-stopper distance of ≅3 ωm has been reached.

A new method for studying the nuclear and electronic mechanisms of heavy ion stopping in matter

It is shown that by using a semi-thick target in Coulomb excitation experiments permits, by analyzing the shape of the γ-line which is Doppler-broadened as a result of de-excitation of excited recoil nuclei emerging into vacuum, to study the stopping of the latter in the target material. The method proposed is not based on the use of reference lifetimes of excited nuclear states and enables to simultaneously investigate both the electronic and nuclear parts of the stopping losses. The γ-line shape calculations include multiple scattering of recoil nuclei in the target material and perturbations in the angular correlation resulting from the recoil nuclei emerging into vacuum. A technique is described and experimental results are presented on the parameters of electronic and nuclear energy losses for the cases of Cr stopping in Cr, Ni in Ni, and Cd in Cd. In these cases, the factors ƒ e and ƒ n characterizing the deviation of the nuclear and electronic stopping loss parameters from the predictions of the LSS theory turned out to be, accordingly, 1.1 and 0.8 for Cr, 0.9 and 0.5 for Ni, and 1.3 and 0.6 for Cd. The values of the parameters obtained were used to determine the lifetimes of some excited states in 111Cd, 58, 60, 61, 62Ni and 52, 53Cr by the DSAM.

Mesure de vies moyennes de niveaux excités par effet Doppler γ après émission α ( [formula omitted

Using the γ Doppler shift following α decay, a method is described to measure the lifetimes of nuclear excited states in the picosecond range. This method should be applicable to many α-emitters. Five excited states in 219Rn were measured and gave the following results • T 1 2 : 159 keV = (42.3±5.0) × 10 −12 s , • 269 keV = (14.2±2.3) × 10 −12s, • 338 keV = (6.1±2.8) × 10 −12s, • 376 keV = (6.9±3.9) × 10 −12s, • 445 keV = (6.2±3.1) × 10 −12s.

Electronic measurements of nuclear lifetimes in the region 1 ps < τ < 100 ps

A system is desribed which measures electronically lifetimes of excited nuclear states of radioactive probes in the region 1 ps < τ < 100 ps. The principle of the centroid-shift self-comparison method is applied. The technique which is developed allows to control all systematic errors to better than 0.2 ps in favourable cases. The half-lives of the first excited states of 60Ni and 46Ti were measured as t 1 2 (2 + state of 60 Ni) = (0.90±0. ps , and t 1 2 (2 + state of 46 Ti) = (4.65±0.35) ps .

The measurement of subnanosecond lifetimes using a rotating target systems

A rotating target system has been developed for use in the measurement of lifetimes of excited nuclear states by a direct timing technique using a pulsed proton or deuteron beam. The target system which is capable of speeds up to 7 000 r.p.m. can be used with two targets simultaneously. The system has the electronics capable of routing into two separate regions of the on-line computer the information obtained from each target. The technique has a distinct advantage over most previous centroid shift delayed-coincidence methods in that data are obtained at the same time for both the prompt and delayed time distribution curves. Thus errors that may occur due to electronic drifts and shifts between alternate experimental runs to obtain the prompt and delayed time distribution curves separately are avoided. As an illustration of the use of the rotating target system, the lifetime of the first excited state of 47Ti at 160 keV was measured to be (295 ± 24) ps.

A new version of the microwave method

Abstract Description and analysis are presented for a new version of the microwave method for measuring short lifetimes of excited nuclear states.

Measurement of nuclear reaction times by the use of the blocking effect

Abstract A new method is presented to measure nuclear reaction times and lifetimes of excited nuclear states from 1 as to 10 fs, based on the blocking effect of charged particles in single crystals. Reaction time measurements are described for the 28Si(p, p')28Si (1.78 MeV, 2+), 70Ge(p, p')70Ge (1.04 MeV, 2+) and 72Ge(p, p')72Ge (0.835 MeV, 2+) reactions at E = 3.61–5.91 MeV. Planar blocking patterns by the (111) crystal plane of thin single crystals were observed for protons scattered at 90° leaving residual nuclei in definite states. Clear reduction of the blocking effect from that of the elastic scattering was found for the 70Ge(p, p')70Ge* and 72Ge(p, p')72Ge* reactions and not for the 28Si(p, p')28Si* reaction. Reaction times τ derived from the reduction were 36±23 and 42±19 as for the 70Ge(p, p')70Ge* and 72Ge(p, p')72Ge* reactions at E = 4.84MeV and τ ≦ 6 as for the 28Si(p, p')28Si* reaction at E = 3.61–5.86MeV.

Measurement of lifetimes of nuclear excited states by doppler shift attenuation method

Measurement of lifetimes of nuclear excited states by doppler shift attenuation method