Properties of the lighest known caesium isotopes 114–118Cs

Neutron-deficient caesium isotopes with mass numbers from 114 to 118 have been studied at the ISOLDE facility. Half-lives have been determined from counting of β-particles, β-delayed protons, and γ-rays. A short-lived isomer ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.7}\text{sec}$) in ¹¹⁶Cs has been observed and the new delayed-particle precursors ¹¹⁶Cs (protons and α-particles), ¹¹⁵Cs (protons), and ¹¹⁴Cs (protons and α-particles) have been identified. Coincidences between delayed particles and γ-rays have been measured for ¹¹⁸Cs (pγ and αγ) and ¹¹⁶Cs (pγ). A search for the possible proton-radioactive isotope ¹¹³Cs has been performed and an upper limit for its production yield is given.     

Decay properties of very neutron-deficient isotopes of silver and cadmium

The β-decay properties of the lightest known silver and cadmium isotopes are investigated. Data for β-delayed γ-ray emission of ^95–97Ag and for β-delayed proton emission of ⁹⁶Ag and ⁹⁷Cd are presented. The experimental findings are compared with predictions of shell-model calculations in which a variety of model spaces and effective interactions are considered.     

The neutron binding energy in the neutron-rich nucleus93Sr

The neutron binding energy in⁹³Sr has been determined to (5230±6) keV from energy correspondences between levels defined by γ-ray transitions and β-delayed neutron emission.     

The doubly closed shell nucleus 13250Sn82

The structure of excited states in ¹³²Sn, fed in the β-decay of ¹³²In, has been investigated. Absolute intensities were deduced from γ-singles measurements. From multi-spectrum analysis of γ-lines the half-life of ¹³²In was determined to be 186 ± 22 ms. A level scheme based on γγ and βγ coincidences is presented. The conversion electron spectrum has been studied and internal conversion coefficients deduced for two low-energy transitions. The total decay energy of ¹³²In was determined, from γ-gated β-spectra, to be Q_β = 13.6 ± 0.4 MeV. A lower limit of 6.968 MeV for the neutron separation energy in ¹³²Sn was deduced from the β-delayed neutron spectrum. The experimental results on the level structure of the doubly closed shell nucleus ¹³²Sn show that the shell model is applicable even far from the valley of stability.     

Spectroscopic studies of the βp and β2p decay of 23Si

²³Si isotopes have been produced as projectile fragments of a ³⁶Ar primary beam at 95 MeV/nucleon at the LISE3 spectrometer of GANIL. After implantation in a detector telescope, β-delayed one-proton and β-delayed two-proton emission has been observed. The main one-proton peaks are at (1.32±0.04)MeV, (2.40±0.04)MeV, and (2.83±0.06)MeV. The total decay energy for the β2p decay is (6.18±0.10)MeV for the decay to the ground state and (5.86±0.10)MeV for the decay to the first excited state in the daughter nucleus. However, energetically possible decays via βpα and β3p emission have not been identified. The spectra allowed us to determine the excitation energy of the isobaric analogue state in ²³Al. This enabled us to calculate the coefficients of the T = 5/2 isobaric multiplet mass equation for A = 23. The mass excess of the ²³Si ground state was deduced. This value is compared to different theoretical predictions. Additionally, we determined the branching ratios for the different decay branches. A half-life measurement yielded T_1/2 = (40.7±0.4)ms.     

Beta-delayed proton emission around N=50 and the rp-process

Detailed information on the decay modes of very proton-rich heavy nuclei is a prerequisite for p-process nucleosynthesis models. We have therefore measured β-delayed protons and γ-rays from mass-separated sources of ⁹⁶Ag, ⁹⁸Ag and ⁹⁸Cd, and obtained βp branching ratios of 3.7(9) × 10^{t ?2}, (1.1 _?0.4 ^+0.5 ) × 10^?5 and <2.5 × 10^?4, respectively. The consequences of the experimental data for rp-process calculations and the results from a statistical model are briefly discussed.     

40Ti β decay and the neutrino capture cross section of 40Ar

⁴⁰Ti β decay was studied at GANIL using the LISE3 spectrometer. A decay scheme was deduced from twenty-one observed β-delayed proton transitions feeding the ground and first excited states of ³⁹Ca. The ⁴⁰Ti half-life was found to be 51.7(6) ms. These results imply that the ICARUS ⁴⁰Ar detector has an effective absorption cross section for ⁸B solar neutrinos of 14.5(4) × 10⁻⁴³ cm²; 73% of the total cross section arises from Gamow-Teller transitions that were neglected in early estimates of the ICARUS efficiency.     

β-decay studies of the neutron-rich 18,21N isotopes

The β-decay studies of neutron-rich ^18,21N isotopes have been performed using β-n, β-γ, and β-n-γ coincidence methods. The ^18,21N ions were produced by the fragmentation of the ²²Ne and ²⁶Mg beams, respectively, on a thick beryllium target. The time of flight of the emitted neutrons following the β-decay of ^18,21N was measured by a neutron detector system with wide energy detection range and low-energy detection threshold. In addition, several clover germanium detectors were used to detect the β-delayed γ-rays. The half-lives of the β-decays of ¹⁸N and ²¹N were determined to be (619±2) ms and (82.9±7.5) ms, respectively. Several new β-delayed neutron groups were observed with a total branching ratio of (6.98±1.46)% and (90.5±4.2)% for ¹⁸N and ²¹N, respectively. The level schemes of ¹⁸O and ²¹O were deduced. The experimental Gamow-Teller β-decay strengths of ¹⁸N and ²¹N to these levels were compared with the shell model calculations.     

(3He, 2n) excitation functions for some light nuclei

Excitation functions have been measured for the reaction ⁹Be(³He, 2n)¹⁰C over the range $\text{E(}{}^3\text{He}\text{) = 10–41}\text{MeV}$ and for the reaction ²⁷Al(³He, 2n)²⁸P over the range $\text{E(}{}^3\text{He}\text{) = 14–41}$ MeV by detecting β-delayed γ-rays. An excitation function has also been measured for the reaction ²⁴Mg(³He, 2n)²⁵Si over the range $\text{E(}{}^3\text{He}\text{) = 21–43}\text{MeV}$ by detecting β-delayed protons.     

The β-delayed α-spectrum of 16N,and its role in defining the astrophysical cross section for 12C(α,γ)16O

It has proven to be very difficult to determine the astrophysically important cross section for ¹²C(α, γ)¹⁶O at the relevant energies (∼300 keV) from radiative capture measurements. The present paper summarizes a new measurement of the β-delayed α-spectrum of ¹⁶N that substantially improves our knowledge of the E1 α-capture cross section on ¹²C at 300 keV. The paper concludes with a brief discussion of the status of the total ¹²C(α, γ)¹⁶O cross section at 300 keV.     

Half-lives of ground and isomeric states in Cd and the astrophysical origin of Ru

First experimental evidence for a high-spin isomer (25/²⁺$25/2^{+}$) in ⁹⁷Cd, a waiting point in the astrophysical rapid proton capture process, is presented. The data were obtained in β-decay studies at NSCL using the new RF Fragment Separator system and detecting β-delayed protons and β-delayed γ rays. Decays from ground and isomeric states were disentangled, and proton emission branches were determined for the first time. We find half-lives of 1.10(8) s and 3.8(2) s, and β-delayed proton emission branches of 12(2)% and 25(4)% were deduced for the ground and isomeric states, respectively. With these results, the nuclear data needed to determine an rp-process contribution to the unknown origin of solar ⁹⁶Ru are in place. When the new data are included in astrophysical rp-process calculations, one finds that an rp-process origin of ⁹⁶Ru is unlikely.     

锗、硅、锑化铟和砷化镓的热膨涨——用X射线衍射法测量

本工作是用X射线衍射法测量锗、硅和合金InSb及GaAs在不同温度的点阵常数,观察它们的热膨涨,并求得它们的膨涨系数。     

Inclusive neutron and proton energy spectra following the negative pion absorption at rest in 12C

The results of a measurement of the inclusive energy spectra of the neutrons and protons emitted following the absorption at rest of negative pions on ¹²C are presented. The spectra have been measured with the time-of-flight method with an overall resolution of 650 psec. From the neutron spectrum the rate of 1.7 × 10^?2 neutrons per stopped pion has been deduced for the single-neutron emission reaction ¹²C(π^?, n)¹¹ B. Comparisons are made with calculated spectra and other experimental spectra.     

Beta-delayed proton emitter kr

The nucleide ⁷³Kr has been identified by on-line mass separation as a precursor of β-delayed proton emission. The proton branch is (6.8 ±1.2) × 10⁻³ proton/decay. The protons populate the ground state and also the first excited 2⁺ state at 866 keV in ⁷²Se with a relative intensity of (35±9) %. The value of Q_EC−B_p, where B_p is the proton separation energy for the nucleus ⁷³Br, is found to be 4.85 ±0.30 MeV based on the fraction of proton events preceded by positron decay.     

29 P(p, γ)30 S in explosive hydrogen burning

The very neutron-deficient nucleus¹⁰¹In has been identified for the first time by studying the β-delayed γ rays of on-line mass-separated samples. The deduced half life is 16(3)s. This study assigns a hitherto unplacedγ ray cascade of a recently published in-beam study to¹⁰¹Cd.     

Beta-delayed proton emission from 97Cd and 99Cd

Two new β-delayed proton precursors, ^97,99Cd, have been identified at the ISOLDE on-line isotope separator. The proton branching ratio for ⁹⁹Cd is (1.7^+1.1_?0.5) × 10^?3. The ⁹⁹Cd proton spectrum is discussed in terms of the statistical model with Porter-Thomas fluctuations. The half-life of ⁹⁹Cd was determined to be 16±3 sec. A search for ⁹⁸Cd was also performed and it was found to be a pure β-emitter with a probable half-life of ≈ 8 sec.     

Cross-section measurements and thermonuclear reaction rates for 46Ti(p, γ)47V, 47Ti(p, γ)48V, 47Ti(p,n)47V and 48Ti(p, γ)49V

The yield of γ-rays from the reaction ⁴⁶Ti(p, γ)⁴⁷V has been measured as a function of bombarding energy over the range 0.72–3.00 MeV, from ⁴⁷Ti(p, γ)⁴⁸V over the range 0.74–3.50 MeV, and from ⁴⁸Ti(p, γ)⁴⁹V over the range 0.72–4.40 MeV. The yields of γ-rays following (p, p') reactions on all three targets were also measured and (p, p') cross sections were deduced for the first excited state proton groups for ⁴⁶Ti and ⁴⁸Ti and for the first ten proton groups for ⁴⁷Ti. The yield of neutrons from the reaction ⁴⁷Ti(p, n)⁴⁷V has been measured over the range from threshold to 4.40 MeV. All these data are compared with statistical-model calculations, and good agreement is achieved. Thermonuclear reaction rates for the (p, γ) and (p, n) reactions are calculated for the temperature range 5 × 10⁸–10¹⁰ K which includes the range of temperatures of interest in nucleosysnthesis calculations.     

Average excited state lifetimes in 73Br

Lifetimes in the region of 10^?16 s have been measured for excited states between 4 and 6.6 MeV in ⁷³Br. The states were produced by the β⁺(EC) decay of a mass-separated source of ⁷³Kr, and they decayed by the emission of protons or γ-rays; their lifetimes were measured by the particle X-ray coincidence technique. The data yield information on both γ-ray and proton partial widths as well as on the level density, a level density parameter-a = 13.7 MeV^?1 is obtained. With the level widths so determined, a statistical model calculation yields excellent agreement with the delayed proton spectrum if a smooth gaussian β-strength function is employed. It is concluded, however, that without the lifetime data, β-strength function information could not have been reliably extracted.     

β-delayed charged particles from 9Li and 11Li

β-delayed emission of α-particles from ⁹Li and of both α and ⁶He particles from ¹¹Li is observed. Singles energy spectra and two-dimensional energy spectra of coincident particles are measured. A time-of-flight versus energy measurement is used to identify the mass of the particle. New β-branches are observed which populate high-energy levels in the daughter nuclei. The branching ratios are measured and the β-delayed neutron emission probabilities $\text{P}{}_{\mathrm{<mtext>n</mtext>}}\text{for}{}^9\text{Li and}\text{P}{}_{\mathrm{3n}}\text{for}{}^{11}\text{Li}$ are deduced.     

Beta-delayed proton emission around N=50 and the rp-process

Detailed information on the decay modes of very proton-rich heavy nuclei is a prerequisite for p-process nucleosynthesis models. We have therefore measuredβ-delayed protons andγ-rays from mass-separated sources of⁹⁶Ag,⁹⁸Ag and⁹⁸Cd, and obtainedβp branching ratios of 3.7(9)×10^?2, (1.1 _?0.4 ^+0.5 )×10^?5 and <2.5×10^?4, respectively. The consequences of the experimental data for rpprocess calculations and the results from a statistical model are briefly discussed.