[en] A Monte-Carlo simulation code, named as SimCSR, has been developed for the isochronous mass spectrometry experiments in the experimental storage ring (CSRe). The revolution times of the fragments ions stored in the CSRe, which were produced in the fragmentation of ${}^{58}\mathrm{N}\mathrm{i}$ primary beam are reproduced very well by the SimCSR, although only linear components are considered. The standard deviation of the revolution time is found to be strongly affected by the phase slip factor, the width of the relative momentum difference and the instability of magnetic field. Based on the simulations, we outline and discuss the methods to reduce the standard deviation of the revolution time. (topical articles)

[en] Isochronous mass spectrometry (IMS) established in heavy-ion storage rings has proven to be a powerful tool for mass measurements of short-lived nuclides. In IMS, the revolution times of stored ions should be independent of their velocity spread. However, this isochronous condition is fulfilled only in the first order and in a small range of revolution times. To correct for non-isochronicity, an additional measure of the velocity or magnetic rigidity of each stored ion is required. For this purpose two new time-of-flight (TOF) detectors were installed in one of the straight sections of the experimental cooler storage ring in Lanzhou. It is expected that the resolving power of the IMS will significantly be improved with such a double-TOF arrangement. The double-TOF system was tested in a recent experiment with the "7"8Kr fragments. Some of the experimental results are presented in this contribution. (paper)

[en] Relative yields of fragments following the "7"8Kr projectile fragmentation in a beryllium target were measured in a storage ring by using isochronous mass spectrometry (IMS). Odd–even staggering of the relative fragment yields is observed and can be explained by the odd–even staggering of the particle-emission threshold energies. IMS is a complementary technique to γ-ray spectroscopy for measuring isomeric ratios, in particular for nuclides with long lifetimes. It was found that the isomeric yield ratios in "5"3Fe are almost constant for different longitudinal momenta. (paper)

[en] Masses of A=2Z-1 proton-rich nuclides were measured with the experimental cooler storage ring CSRe in Lanzhou by employing the isochronous mass spectrometry (IMS) method. The short-lived proton-rich nuclides were produced via ⁷⁸Kr projectile fragmentation, separated in the radioactive beam line RIBLL2 and then stored in CSRe. A typical mass resolving power of R=m/Δm∼1.7.10⁵ was achieved. After the improvement of the stability of CSRe dipole magnet power supplies, a new measurement with ⁵⁸Ni projectile fragments was carried out. The data analysis methods for both experiments are presented.

[en] Short-lived ⁴⁶Cr, ⁵⁰Fe and ⁵⁴Ni were studied by isochronous mass spectrometry at the HIRFL-CSR facility in Lanzhou. The measured precision mass excesses (ME) of ⁴⁶Cr, ⁵⁰Fe and ⁵⁴Ni are -29471(11) keV, -34477(6) keV and -39278(4) keV, respectively. The superallowed 0⁺→0+β-decay Q values were derived to be Q_EC(₄₆Cr) =7604(11) keV, Q_EC(₅₀Fe) =8150(6) keV and Q_EC(₅₄Ni) =8731(4) keV. The values for ⁵⁰Fe and ⁵⁴Ni are by one order of magnitude more precise than the adopted literature values. By combining the existing half-lives and branching ratios, we obtained the corrected ℱt values to be ℱt(₅₀Fe) =3103(70) s and ℱt(₅₄Ni) =3076(50) s. The main contribution to the ℱt uncertainties is now due to β-decay branching ratios, still, more high-precision measurements of the half-lives, the masses, and especially the branching ratios are needed in order to satisfy the requirements for a stringent CVC test.

[en] A novel isochronous mass spectrometry, termed as Bρ-defined IMS, has been established at the experimental cooler-storage ring CSRe in Lanzhou. Its potential has been studied through high precision mass measurements of ${}^{58}$Ni projectile fragments. Two time-of-flight detectors were installed in one of the straight sections of CSRe, thus enabling simultaneous measurements of the velocity and the revolution time of each stored short-lived ion. This allows for calculating the magnetic rigidity Bρ and the orbit length C of each ion. The accurate Bρ(C) function has been constructed, which is a universal calibration curve used to deduce the masses of the stored nuclides. The sensitivity to single stored ions, fast measurement time, and background-free characteristics of the method are ideally suited to address nuclides with very short lifetimes and smallest production yields. In the limiting case of just a single particle, the achieved mass resolving power allows one to determine its mass-over-charge ratio m/q with a remarkable precision of merely ∼ 5 keV. Masses of T${}_z$=-3/2 fp-shell nuclides are re-determined with high accuracy, and the validity of the isospin multiplet mass equation is tested up to the heaviest isospin quartet with A=55. The new masses are also used to investigate the mirror symmetry of empirical residual proton-neutron interactions.

[en] Revolution frequency measurements of individual ions in storage rings require sophisticated timing detectors. One of common approaches for such detectors is the detection of secondary electrons released from a thin foil due to penetration of the stored ions. A new method based on the analysis of intensities of secondary electrons was developed which enables determination of the charge of each ion simultaneously with the measurement of its revolution frequency. Although the mass-over-charge ratios of "5"1Co"2"7"+ and "3"4Ar"1"8"+ ions are almost identical, and therefore, the ions cannot be resolved in a storage ring, by applying the new method the mass excess of the short-lived "5"1Co is determined for the first time to be ME("5"1Co)=−27342(48) keV. Shell-model calculations in the fp-shell nuclei compared to the new data indicate the need to include isospin-nonconserving forces

[en] Isochronous mass spectrometry (IMS) in storage rings is a powerful tool for mass measurements of exotic nuclei with very short half-lives down to several tens of microseconds, using a multicomponent secondary beam separated in-flight without cooling. However, the inevitable momentum spread of secondary ions limits the precision of nuclear masses determined by using IMS. Therefore, the momentum measurement in addition to the revolution period of stored ions is crucial to reduce the influence of the momentum spread on the standard deviation of the revolution period, which would lead to a much improved mass resolving power of IMS. One of the proposals to upgrade IMS is that the velocity of secondary ions could be directly measured by using two time-of-flight (double TOF) detectors installed in a straight section of a storage ring. In this paper, we outline the principle of IMS with double TOF detectors and the method to correct the momentum spread of stored ions.

[en] Direct mass measurements of ⁷⁸Kr projectile fragments have been performed in the recently commissioned storage ring CSRe employing the isochronous mass spectrometry method. A new data-analysis technique has been developed to correct the drifts in the revolution frequencies caused by instabilities of the magnetic fields in the CSRe, thus yielding a mass resolving power of R=m/Δm∼1.7x10⁵ (sigma). Masses for ⁴⁵V, ⁴⁷Cr, ⁴⁹Mn and ⁵¹Fe nuclei are determined with a relative mass precision of δm/m∼2x10^-7 (sigma) which is an improvement by a factor of ∼2 compared to the literature values.