Doppler-shift Attenuation Lifetime Measurements Research Articles

Transition probabilities in 31P and 31S: A test for isospin symmetry

Excited states in the mirror nuclei 31P and 31S were populated in the 1p and 1n exit channels of the reaction 20Ne + 12C, at a beam energy of 33 MeV. The 20Ne beam was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident γ-rays and Doppler-shift attenuation lifetime measurements were performed using the multi-detector array GASP in conjunction with the EUCLIDES charged particle detector. In the observed B(E1) strengths, the isoscalar component, amounting to 24% of the isovector one, provides strong evidence for breaking of the isospin symmetry in the A=31 mass region. Self-consistent beyond mean field calculations using Equation of Motion method based on a chiral potential and including two- and three-body forces reproduce well the experimental B(E1) strengths, reinforcing our conclusion. Coherent mixing from higher-lying states involving the Giant Isovector Monopole Resonance accounts well for the effect observed. The breaking of the isospin symmetry originates from the violation of the charge symmetry of the two- and three-body parts of the potential, only related to the Coulomb interaction.

The Spectral difference method applied to plunger data: Lifetime determination at one distance

Abstract A generalization of an earlier proposed method for analysis of Doppler-shift attenuation lifetime measurements, namely the Spectral difference method, is presented for the case of Recoil distance Doppler-shift or plunger experiments. Using the data at only one distance between the target and stopper, the lifetime is derived directly by fitting the time dependence of the population of the level of interest using the line shape of the depopulating transition and the difference of the spectra of the depopulating and feeding transitions. Practical application to real data proves the applicability of the new procedure by reproducing literature lifetime values.

On the imprecisions that may be induced when applying the Blaugrund approximation for the analysis of Doppler-shift attenuation lifetime measurements

It is shown that the Blaugrund approximation could have led to some imprecise lifetime determinations in the past which used the Doppler-shift attenuation method (DSAM). Comparison with Monte Carlo simulations of the slowing-down process show that there is not an easy way to judge using them on the reliability of old data.

Robustness of the analysis of Doppler-shift attenuation lifetime measurements according to the coincidence differential decay curve method with respect to class of uncertainties in the stopping powers

It is shown that the Differential decay curve method applied to analyze coincidence Doppler-shift attenuation lifetime measurements with a gate on the shifted component of a directly feeding feeding transition is characterized by stable results within scaling variations of the stopping powers of up to 15% at least. This is due to cancellation in the formula used for the lifetime determination while when using the traditional data analysis methods the imprecision in the stopping powers cannot be surrounded.

Symmetries in mirror nuclei 31S and 31P

Excited states in mirror nuclei 31S and 31P were populated in the 1n and 1p exit channels, respectively, of the reaction 20Ne + 12C. The beam of 20Ne, with an energy of 33 MeV, was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident pairs and Doppler-shift attenuation lifetime measurements in 31S and 31P were performed using the multidetector array GASP in conjunction with the EUCLIDES charged particle detector. A comparison of the determined B(E1) strengths of the analog mirror 7/2- → 5/2+ transitions indicates the presence of a violation of isospin symmetry.

No evidence of reduced collectivity in Coulomb-excited Sn isotopes

In a series of Coulomb excitation experiments the first excited ${2}^{+}$ states in semimagic $^{112,116,118,120,122,124}\mathrm{Sn}$ isotopes were excited using a $^{58}\mathrm{Ni}$ beam at safe Coulomb energy. The $B(E2$; ${0}^{+}\ensuremath{\rightarrow}{2}^{+})$ values were determined with high precision $(\ensuremath{\sim}3%)$ relative to $^{58}\mathrm{Ni}$ projectile excitation. These results disagree with previously reported $B(E2\ensuremath{\uparrow})$ values [A. Jungclaus et al., Phys. Lett. B 695, 110 (2011).] extracted from Doppler-shift attenuation lifetime measurements, whereas the reported mass dependence of $B(E2\ensuremath{\uparrow})$ values is very similar to a recent Coulomb excitation study [J. M. Allmond et al., Phys. Rev. C 92, 041303(R) (2015)]. The stable Sn isotopes, key nuclei in nuclear structure, show no evidence of reduced collectivity and we, thus, reconfirm the nonsymmetric behavior of reduced transition probabilities with respect to the midshell $A=116$.

New procedures for analyzing Doppler-shift attenuation lifetime measurements

A generalization of an earlier proposed version of the Differential decay curve method is presented for the analysis of Doppler-shift attenuation lifetime measurements. The lifetime is derived directly from the line shapes of the depopulating and feeding transitions without any assumptions about or fitting of the time dependence of the population of the corresponding levels except for unobserved feeding when relevant. Fitting of the line shapes is also not necessary. The only approximation involved is related to the continuous treatment of the nuclear scattering events in the Monte Carlo simulation needed. Tests with simulated and real data reveal good reliability of this method. We propose also a new precise procedure where the lifetime is derived by fitting the time dependence of the population of the level of interest using the line shape of the depopulating transition and the difference of the spectra of the depopulating and feeding transitions. Practical application to simulated and real data proves the applicability of the new procedure.

Low-lying bands with different quadrupole deformation in155Dy

To investigate the interplay between collective and single particle degrees of freedom in odd nuclei, Recoil distance Doppler-shift and Doppler-shift attenuation lifetime measurements were carried out for levels in 155Dy in coincidence detection of gamma-rays. 26 lifetimes were determined using the Differential decay curve method. Particle plus triaxial rotor model (PTRM) calculations were performed to compare the experimental level scheme and transition strengths with theoretical ones in order to get information on the quadrupole deformation (є,γ) of the bands. As a result, different quadrupole deformations for the one-quasineutron bands at low and medium spins are deduced.

Lifetimes and electromagnetic transition strengths in155Dy

Recoil distance Doppler-shift and Doppler-shift attenuation lifetime measurements were carried out for levels in ${}^{155}$Dy through the coincident detection of $\ensuremath{\gamma}$ rays. Twenty-six lifetimes, most of them for the first time, were determined using the differential decay curve method for the analysis of the data. At low and medium spins, particle-plus-triaxial-rotor calculations reveal different quadrupole deformations for the one-quasineutron bands in this transitional nucleus. At high spin, the reduced $B(E2)$ transition probabilities confirm with a better precision the results of a previous study implying decreased collectivity with increasing spin.

A new version of the differential decay curve method for Doppler-shift attenuation lifetime measurements

A new version of the differential decay curve method is proposed for the analysis of Doppler-shift attenuation lifetime measurements. The lifetime is derived directly from the line shapes of the depopulating and feeding transitions on the basis of the Blaugrund approximation without including any assumptions or fitting of the time dependence of the population of the corresponding levels. For specific simulated cases, the method shows promise for its applicability. In the future, we intend to generalize the method for the case of an arbitrary multi-detector setup.

Transitional quadrupole moments in83Y

Doppler shift attenuation lifetime measurements have been carried out for the 3qp and isomeric rotational bands in Y-83 using the reaction (Ni(Si,3p))-Ni-58-Si-28. While the transitional quadrupole moments in the 3qp bands are slightly lower than in the 1 qp bands, we found evidence for a strong reduction in \Q(t)\ for the isomeric band.

Nuclear structure studies of high-spin states in 79Rb and 79Kr

Fluorine and carbon induced fusion-evaporation reactions were used to excite high-spin states in 79Rb and 79Kr. The level scheme of 79Rb was established on the basis of neutron multiplicity measurements, γγ coincidence data and excitation functions. From recoil distance and Doppler shift attenuation lifetime measurements, E2 strengths of the positive-parity yrast states in 79 Kr ( up to I π = 21 2 + ) and the favored and unfavored states in 79 Rb ( up to I π = 25 2 + ) were derived. An interpretation of these data in terms of the asymmetric rotor-plus-particle model and the interacting boson fermion model (with or without separate proton and neutron bosons) is proposed. Energies and lifetimes of a second stretched band in 79Rb (probably with negative parity) were also measured.

DSA lifetime measurements in21Ne at high recoil velocity

States in21Ne up to 5 MeV excitation energy have been populated using the inverted reaction2H(20Ne,pγ). The Doppler shift attenuation (DSA) analysis of thepγ coincidence spectra taken in a Ge(Li) detector at 45° and 135° and an annular silicon surface barrier detector near 0° yielded the lifetimes of 8 states in21Ne. Due to the large recoil ofπi/c∼ 4% three new lifetimes were determined for the short lived levels at 2.80, 4.68 and 4.73 MeV, namely 10±4 fs, 16±4 fs and 10±4 fs, respectively. The results are compared with rotational and shell model calculations.

Nuclear spectroscopy with lithium beams. I. High-spin states inFe55,Mn55, andCr53

The $^{7}\mathrm{Li}$ bombardment of $^{51}\mathrm{V}$ has been used in conjuction with recoil distance lifetime (RDM), $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence, angular distribution, and Doppler shift attenuation lifetime (DSAM) measurements to gain information on the properties of high-spin states in the nuclei $^{55}\mathrm{Fe}$, $^{55}\mathrm{Mn}$, and $^{53}\mathrm{Cr}$. Mean lifetimes ($\ensuremath{\tau}$) determined by RDM were as follows---in $^{55}\mathrm{Fe}$: 1409-keV level ($\ensuremath{\tau}=57.8\ifmmode\pm\else\textpm\fi{}3.5$ psec), 2813 (14.5\ifmmode\pm\else\textpm\fi{}3.1 psec), 5099 (32.3\ifmmode\pm\else\textpm\fi{}1.1 psec); in $^{55}\mathrm{Mn}$: 126-keV level ($\ensuremath{\tau}=382\ifmmode\pm\else\textpm\fi{}16$ psec); in $^{53}\mathrm{Cr}$: 2173-keV level ($\ensuremath{\tau}=47\ifmmode\pm\else\textpm\fi{}15$ psec); 3084 ($\ensuremath{\tau}=43\ifmmode\pm\else\textpm\fi{}15$ psec). Tentative spin assignments were made as follows---in $^{55}\mathrm{Fe}$: 5099-keV level $J=(\frac{19}{2})$, 6528, $J=(\frac{21}{2})$, in $^{55}\mathrm{Mn}$: 3056-keV level $J=(\frac{15}{2})$. Lifetimes (or limits) were also established from DSAM measurements for a number of other levels in the above nuclei. The results are compared to shell model calculations.NUCLEAR REACTIONS $^{51}\mathrm{V}(^{7}\mathrm{Li}, 3n)$, $^{51}\mathrm{V}(^{7}\mathrm{Li}, p2n)$, $^{51}\mathrm{V}(^{7}\mathrm{Li}, \ensuremath{\alpha}n)$ $E=25$ MeV; measured $\ensuremath{\gamma}\ensuremath{\gamma}$ coin.; deduced levels in $^{55}\mathrm{Fe}$, $^{55}\mathrm{Mn}$, $^{53}\mathrm{Cr}$; measured $\ensuremath{\sigma}({E}_{\ensuremath{\gamma}}, \ensuremath{\theta})$; deduced ${J}^{\ensuremath{\pi}}$ for high spin states; measured recoil distance; deduced ${T}_{\frac{1}{2}}$, $B(E2)$, effective charges. Natural target, Ge(Li) detectors.