Mass measurements for nuclear astrophysics with JYFLTRAP

Over 90 neutron-deficient nuclides between ¹⁰C and ¹¹¹I have been measured at the JYFLTRAP mass spectrometer with a precision of better than 10 keV. Masses of these nuclides are important for modeling astrophysical rp and ??p processes and nucleosynthesis occurring in novae. Here, a review of the mass measurement programme of the neutron-deficient nuclides performed at JYFLTRAP for nuclear astrophysics studies is given.     

Recent Results on Ne and Mg from the MISTRAL Mass Measurement Program at ISOLDE

The MISTRAL experiment (Mass measurements at ISOLDE with a Transmission and Radiofrequency spectrometer on-Line), conceived for very short-lived nuclides, has reached the end of its commissioning phase. Installed in 1997, results have been obtained consistent with all aspects of the projected spectrometer performance: nuclides with half-lives as short as 30 ms have been measured and accuracies of 0.4 ppm have been achieved, despite the presence of a systematic shift and difficulties with isobaric contamination. Masses of several nuclides, including ^25–26Ne and ³²Mg that forms the famous island of inversion around N=20, have been significantly improved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mass measurements of neutron-deficient radionuclides near the end-point of the rp-process with SHIPTRAP

Direct mass measurements of nuclides near to the supposed end-point region of the astrophysical rp-process were performed at SHIPTRAP, the Penning trap mass spectrometer at GSI Darmstadt. The masses of 24 nuclides were measured with relative uncertainties between 5 ^. 10^-8 and 2 ^. 10^-7 . Three of them, ¹⁰⁷Sb , ¹¹¹I and ¹¹²I , were determined experimentally for the first time. The data analysis and mass evaluation are presented in detail.     

Mass measurements of neutron-deficient nuclei and their implications for astrophysics

During the years 2005-2010 the double-Penning-trap mass spectrometer JYFLTRAP has been used to measure the masses of 90 ground and 8 isomeric states of neutron-deficient nuclides with a typical precision of better than 10keV. The masses of 14 nuclides -- ⁸⁴Zr , ^{88, 89}Tc , ^90-92Ru , ^92-94Rh , ^{94, 95}Pd , ^{106, 108, 110}Sb -- have been experimentally determined for the first time. This article gives an overview on these measurements and their impact on the modeling of the astrophysical rp -process.     

Mass measurements of neutron-deficient nuclides close to A = 80 with a Penning trap

The masses of ^{80, 81, 82, 83}Y, ^{83, 84, 85, 86, 88}Zr and ^{85, 86, 87, 88}Nb have been measured with a typical precision of 7keV by using the Penning trap setup at IGISOL. The mass of ⁸⁴Zr has been measured for the first time. These precise mass measurements have improved S_p and Q_EC values for astrophysically important nuclides.     

Study of Muon-Catalyzed Fusion in Ortho–Para Controlled Solid Deuterium

Recently, the applicability of Penning trap mass spectrometry has been extended to nuclides with a half-life of less than one second. The mass of ³³Ar (T _1/2=174 ms) was measured using the ISOLTRAP spectrometer with an accuracy of 4.2 keV. This measurement provided a stringent test of the Isobaric Multiplet Mass Equation (IMME) at mass number A=33 and isospin T=3/2. The fast measurement cycle that shows the way to other measurements of very-short-lived nuclides is presented. Furthermore, the results of the IMME test are displayed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Isochronous Mass Measurements of Hot Exotic Nuclei

A novel method for mass measurements of short-lived exotic nuclides is presented. Exotic nuclides were produced and separated in flight at relativistic energies with the fragment separator (FRS) and were injected into the experimental storage ring (ESR). Operating the ESR in the isochronous mode we performed mass measurements of neutron deficient fragments of ⁸⁴Kr with half-lives larger than 50 ms. However, this experimental technique is applicable in a half-life range down to a few μs. A mass resolving power of 110000 (FWHM) has been achieved. Results are presented for the masses of ⁶⁸As, ^70,71Se and ⁷³Br. This revised version was published online in July 2006 with corrections to the Cover Date.     

New mass data for the rp-process above Z = 32

High-accuracy mass measurements have been performed with the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. The short-lived nuclides ^{70, 71, 72, 73}Se , ^{72, 73, 74, 75}Br , and ^{98, 99, 100, 101, 103}Ag have been measured with an average uncertainty of a few keV. The data are important input for nucleosynthesis calculations of the rp-process beyond Z = 32 .     

ISOLTRAP: An on-line Penning trap for mass spectrometry on short-lived nuclides

ISOLTRAP is a Penning trap mass spectrometer for high-precision mass measurements on short-lived nuclides installed at the on-line isotope separator ISOLDE at CERN. The masses of close to 300 radionuclides have been determined up to now. The applicability of Penning trap mass spectrometry to mass measurements of exotic nuclei has been extended considerably at ISOLTRAP by improving and developing this double Penning trap mass spectrometer over the past two decades. The accurate determination of nuclear binding energies far from stability includes nuclei that are produced at rates less than 100 ions/s and with half-lives well below 100ms. The mass-resolving power reaches 10⁷ corresponding to 10keV for medium heavy nuclei and the uncertainty of the resulting mass values has been pushed down to below 10^-8. The article describes technical developments achieved since 1996 and the present performance of ISOLTRAP.     

Mass excesses of 79As, 81As,and 80Ge

Accurate mass measurements for the nuclides ⁷⁹As, ⁸¹As, and ⁸⁰Ge have been measured. Good agreement has been found for ⁷⁹As and ⁸¹As with the Garvey-Kelson transverse mass relation and with several mass model predictions. The agreement for ⁸⁰Ge is not as satisfactory and presents a challenge for understanding mass values far off the line of stability.     

Improvement of the Applicability, Efficiency, andPrecision of the Penning Trap Mass Spectrometer ISOLTRAP

With the Penning trap mass spectrometer ISOLTRAP, close to 200 nuclides have already been investigated and their masses determined with a typical relative precision of δm/m=10⁻⁷. Recently, ISOLTRAP's beam preparation system was replaced by an RFQ ion beam cooler and buncher. The principle and the characteristics of this new beam preparation system will be presented. It is planned to use ions of various carbon clusters C⁺ _n (n>1) as reference ions for mass measurements. Apart from negligible molecular binding energies, these clusters have masses that are exact multiples of the unified atomic mass unit. This will allow ISOLTRAP to carry out absolute mass measurements as well as to investigate possible mass-dependent systematic errors. The results of tests of the production, transport, and trapping of such carbon clusters will be presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Exploring new mass regions with the ISOLTRAP spectrometer

First direct mass measurements on rare earth isotopes around ¹⁴⁶Gd have been performed with the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. More than 40 isotopes of the elements Pr, Nd, Pm, Sm, Eu, Dy and Ho have been measured with an accuracy of typically 1 × 10^-7. In the case of ¹⁴¹Sm isomeric and ground state (ΔE = 175 keV) were resolved. Since isobaric contaminations are present in the ISOLDE beam, these measurements on rare earth isotopes became only possible after the installation of a new cooler trap which acts an isobar separator. This revised version was published online in August 2006 with corrections to the Cover Date.     

钐原子的两步激发共振光电离光谱

采用两步激发共振光电离技术研究了Sm原子的偶宇称高激发态光谱.实验采用了两条激发路线：1)第一束激光的波长固定在478.44nm以便将Sm原子从4f⁶6s²［⁷F₁］态激发至4f⁶6s6p［⁷D₁］态,再用第二束激光使其波长从480nm扫描至530nm,将Sm原子进一步激发至待测的高激发态;2)第一束激光的波长固定在574.8 关键词： Sm原子 光谱 分步激发 共振电离     

Mass measurements of relativistic projectile fragments in the storage ring ESR

Two experimental methods of measuring masses of exotic nuclei in the storage ring ESR are presented. Bismuth and nickel fragments were produced via projectile fragmentation, separated and investigated with the combination of the fragment separator FRS and the ESR: (i) Direct mass measurements of relativistic projectile fragments were performed using Schottky mass spectrometry (SMS), i.e., exotic nuclei were stored and cooled in the ESR. Applying electron cooling, the relative velocity spread of circulating low intensity beams can be reduced below 10⁻⁶. Under this condition a mass resolving power of up to m/Δm=6.5·10⁵ (FWHM) was achieved in a recent measurement. Previously unknown masses of more than 100 neutron-deficient isotopes have been measured in the range of 60≤Z≤84. Using known Q _α values the area of known masses could be extended to more exotic nuclei and to higher proton numbers. The results are compared with mass models and extrapolations of experimental values. In a second experiment with ²⁰⁹Bi projectiles the area of the measured masses was extended to lower proton numbers. Due to various improvements at the ESR the precision of the measurements could be raised. (ii) Exotic nuclei with half-lives shorter than the time needed for SMS (present limit: T _1/2 ≈ 5 sec) can be investigated by time-of-flight measurements whereby the ESR is operated in the isochronous mode. This novel experimental technique has been successfully applied in first measurements with nickel and neon fragments where a mass resolving power of m/Δm=1.5·10⁵ (FWHM) was achieved.     

On-line nuclear orientation of the deformed neutron-deficient Eu,Sm and Pm isotopes

Low-temperature nuclear orientation measurements made on-line at the SERC Daresbury Laboratory on^142m Eu,^141m Sm, and¹⁴¹Pm, with known magnetic dipole moments, have yielded the magnitude of the hyperfine fields of these isotopes in an iron host lattice. Thus measurements for the isotopes^{139, 138}Eu,^139m Sm, and¹³⁸Pm yielded values for the respective magnetic moments. Limits on the thermal relaxation times of Eu and Sm isotopes in Fe were also deduced. The results for¹³⁸Eu appear to contradict the earlier πh_11/2⊗νh_11/2 ground-state configuration assignment.     

Beta-decay of148,150,152Pr into levels of148,150,152Nd

Theβ ^?-decay of^148,150,152Pr into levels of^148,150,152Nd has been studied byγ-singles,γγ-coincidence and for¹⁴⁸Pr also byγγ-angular correlation measurements. The praseodymium activities have been obtained by thermal neutron-induced fission of²³⁵U followed by on-line mass separation with the helium-jet coupled mass separator HELIOS. Decay schemes for these heaviest praseodymium nuclides are proposed. From the angular correlation measurements spin values for the seven lowest levels of¹⁴⁸Nd are deduced. Spin and parity assignments for the lower levels in^150,152Nd have been extrapolated from level systematics.     

Structure analysis of 159Sm and properties of odd-mass neutron-rich nuclei in mass-160 region

Recent fission experiment data provide interesting structure information for neutron-rich nuclei in the mass A ∼ 160 region. We apply the projected shell model to study the strongly-deformed, neutron-rich Sm isotopes. We perform calculations for rotational bands up to spin I = 20 (29/2) for even-even (odd-neutron) Sm isotopes, and analyze the band structure of low-lying states with quasiparticle excitations. Emphasis is given to rotational bands based on one-quasiparticle (1-qp) configurations in the odd-mass ¹⁵⁹Sm. The ¹⁵⁹Sm result is discussed together with those of the even-even isotopes ^158,160Sm. New bands in ¹⁵⁹Sm based on neutron 1-qp 1/2⁻ and 5/2⁺ configurations are predicted. Electromagnetic transition probabilities are discussed.

     

ISOLTRAP results 2006–2009

Since 2006 the ISOLTRAP mass spectrometer has provided high-precision masses of many short-lived nuclides located all across the nuclear chart with half-lives down to a few 10 ms. These nuclides range from the two-proton halo candidate ¹⁷Ne, via the neutron-rich magic ⁸⁰Zn and ¹³²Sn, up to ²²⁹Rn which was identified for the first time. The results show that ISOLTRAP is a versatile tool well suited to address physics topics such as nuclear structure, stellar nucleosynthesis, or the weak interaction.     

Light-ion-induced reactions in mass measurements of neutron-deficient nuclides close to A = 100

A survey of neutron-deficient nuclides which can be produced via proton- and ³He -induced fusion-evaporation reactions in the A = 100 region was made using a Penning trap as a high-resolution mass filter. A comparison of the measured isotopic rates with a statistical model calculation for the proton-induced reactions shows the importance of using the precise binding energy values for the final reaction products. In particular, proton separation energies were found to play an important role in the evaporation process. In addition, accurate masses of 12 nuclides, ^{97-99, 101}Pd , ¹⁰⁰Ag , ^101-105Cd and ^{102, 104}In , were determined with uncertainties of less than 10keV.