MEASUREMENT OF ISOMERIC CROSS-SECTION RATIO IN 133Cs(n,γ) 134Cs REACTION

The isomeric absolute cross-section have been measured for the reaction ¹³³Cs (n,c) ¹³⁴ Cs at 14.8 MeV neutron energy.The results are:σ_n,γ^134mCs=1.76±0.14mb;σ_n,γ^134gCs=5.17±0.41mb;σ_n,γ^134+gCs=6.93±0.55mb.The isomeric cross-section ratio is σ^134m_Cs/σ^134gCs=0.34±0.03 The experimental results are in agreement with the values given by S.M. Qaim andcompared with the theoretical results calculated by Huizenga-Vandenbosch theory.From this, the spin cut-off paramenter σ and the number of γ-Cascades have been de-termined.     

CHARGE DISTRIBUTION IN THE FISSION OF 232Th BY 14MeV NEUTRON

Independent yields of ⁸²Br, ⁹⁶Nb, ¹¹²Ag, ¹³⁰I,¹³²I, ¹³⁴I, ^134mCs, ^135mCs, ¹³⁶Cs and upper limitof independent yield for ¹⁴⁰La in the fission of ²³²Th induced by neutrons of 14 MeVwere determined with nuclear chemistry techniques. The correlation of the fractionalindependent yields in the high yield mass chains with a Gaussian curve of charge dis-tribution has been investigated using various mass formulae and charge distributionhypotheses. The results indicate that the hrpothesis of minimum potential energy witha shell-effected mass equation gives the best fit to the data. The width parameter Cof the charge distribution is found to be 0.80. The large deviations of ³²Br and ¹¹²Ag from the Gaussian curve seem to show that the low yield in very asymmetric fissioncan be attributed to a narrower width of charge distribution, whereas the high yield insymmetric fission may correlate with a wider width. The trends have been explainedqualitatively in terms of a liquid drop model. There is no evidence for 40-proton subshell effect on the fission yield.     

124Ba Decay to the 55 124 Cs69 low-spin levels

The decay of¹²⁴Ba to the levels of odd-odd¹²⁴Cs has been studied with on-line mass-separated sources delivered at the Isocele facility. The energy level scheme has been established fromγ-ray singles,γ?γ?t coincidence ande?γ?t coincidence spectra. Spin and parity of several low-lying levels have been assigned on the basis of internal conversion coefficient measurements andβ-branchings. A completely new level pattern including approximately 50 levels and 180γ-rays is proposed for¹²⁴Cs. Several features of this level scheme are discussed and compared to those of neighbouring isotopes.     

Superdeformation in lead nuclei

For the first time, collective bands have been observed in the doubly-odd nucleus¹²⁴Cs. They are proposed to result in the coupling of an h_11/2 proton to h_11/2 and positive parity neutrons. The relative residual protonneutron interaction in¹²⁴Cs is calculated and compared to that of neighbouring odd-odd nuclei.     

Entrance Channel Dependence of the Correlation Function of IMFs in 36Ar+112,124Sn at 35MeV/u

The reduced velocity correlation functions of the Intermediate Mass Fragments (IMFs) were measured in the reactions of ³⁶Ar+^112,124Sn at 35MeV/u. The anti-correlation at small reduced velocities is more pronounced in ³⁶Ar+¹²⁴Sn system than that in ³⁶Ar+¹¹²Sn system. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three-body Coulomb repulsive trajectory code (MENEKA) is employed to calculate the emission time scale of IMFs for the both systems. The time scale is 150fm/c in the ³⁶Ar+¹¹²Sn system and 120fm/c in the ³⁶Ar+¹²⁴Sn system, respectively. A calculation based on an Isospin dependence Quantum Molecular Dynamics code (IQMD) reveals that the emission time spectrum of IMFs is shifted slightly leftwards in ³⁶Ar+¹²⁴Sn compared with that in the ³⁶Ar+¹¹²Sn system, indicating a shorter emission time scale. Correspondingly, the central density of the hot nuclei decreases faster in ³⁶Ar+¹²⁴Sn than in ³⁶Ar+¹¹²Sn.     

Conditioning the γ spectrometer for activity measurement at very high background

The application of a high purity Germanium (HPGe) γ spectrometer in determining the fuel element burnup in a future reactor is studied. The HPGe detector is exposed by a ⁶⁰Co source with varying irradiation rate from 10× 10³m s^-1 to 150× 10³m s^-1 to simulate the input counting rate in real reactor environment. A ¹³⁷Cs and a ¹⁵²Eu source are positioned at given distances to generate a certain event rate in the detector with the former being proposed as a labeling nuclide to measure the burnup of a fuel element. It is shown that both the energy resolution slightly increasing with the irradiation rate and the passthrough rate at high irradiation level match the requirement of the real application. The influence of the background is studied in the different parameter sets used in the specially developed procedure of background subtraction. It is demonstrated that with the typical input irradiation rate and ¹³⁷Cs intensity relevant to a deep burnup situation, the precision of the ¹³⁷Cs counting rate in the current experiment is consistently below 2.8%, indicating a promising feasibility of utilizing an HPGe detector in the burnup measurement in future bed-like reactors.     

Study of the124Xe and126Xe structure

The level structure of¹²⁴Xe and¹²⁶Xe is studied on the basis ofβ ⁺ decay of¹²⁴Cs and¹²⁶Cs. The Cs isotopes were produced in the Xe(p, n) Cs reactions at a proton energy ofE≈9.5 MeV. Decay schemes are proposed for these nuclei. The available experimental data are compared with the predictions of various models.     

INFLUENCE OF THE NEUTRON NUMBER OF TARGET NUCLEUS ON CROSS SECTIONS OF PARTICLES EMISSION IN 12C+112,124Sn

The energy spectra and angular distributions of Li, Be, B particles emitted from the ¹²C+¹¹²Sn and ¹²C+¹²⁴Sn reactions at E_L=70.0MeV are measured. The angular distributions of the Li, Be, and B particles are found to be peaked around the grazing angle, without any forward peaked component.
The experimental results also showed that the cross section for emission is larger in ¹²C+¹¹²Sn reaction than that in ¹²C+¹²⁴Sn reaction, in contrast with the cross sections for Li, Be and B emissions. The indicates the effect of the neutron number of the target nucleus on the emission probability.     

Variable Phase Method Used to Calculate Ultracold Scattering Properties of 7Li33Cs

Elastic scattering properties of singlet and triplet states of ^7 Li^133 Cs at ultralow temperatures are calculated using the constructed potential curves gleaned from high-precision spectroscopy measurement. We show how to reach the scattering length and the number of bound states via the vaxiable phase method. The scattering lengths of the singlet and triplet states of^7 Li^133 Cs are 50.5 a.u. and -135.7 a.u., respectively. We derive two corrections, arising from long range interactions, accurately to at least first order, which provide upper and lower computed bounds to the scattering length. Our results are consistent with the recent experimental data and the theoretical calculation.     

Isospin Effect on Relative State Population Temperature in the Reactions 40Ar+ 112,124Sn at 30MeV/u

An array of 13 detector telescopes has been used for detecting small-angle particle-particle correlations in the reactions ⁴⁰Ar+^112,124Sn at 30MeV/u. The α-α correlation functions were extracted from two-particle coincident events. A three-body trajectory code MENEKA was used to calculate the background correlation function. The detection efficiency was calculated by using the Monte-Carlo method. After subtracting the background correlation and making the detection efficiency correction, the temperatures of 4.18±0.25 0.21 MeV and 4.10±0.22 0.20MeV are obtained from relative populations of ⁸Be states for the reaction systems with different isospin,⁴⁰Ar+¹¹²Sn and ⁴⁰Ar+¹²⁴Sn, respectively. From the relationship between the state population temperature and outgoing particle energies, it is found that the emission temperature decreases with increase of the particle energies for both studied reaction systems. For the neutron deficient system ⁴⁰Ar+¹¹²Sn the emission temperature is 5.13±0.30 0.26MeV for the lower emitting particle energies and 3.87±0.37 0.29MeV for the higher emitting particle energies. And for the neutron rich system ⁴⁰Ar+¹²⁴Sn the emission temperature is 5.39±0.30 0.26MeV for the lower emitting particle energies and 3.32± 0.28 0.23MeV for the higher emitting particle energies. This kind of isospin dependence is discussed.     

Measurement of 125Ba High Spin States

The high spin states of ¹²⁵Ba populated via the ¹⁰⁹Ag(¹⁹F,3n) reaction are measured by using a BGO Compton suppressed HPGe detector array.The negative and positive parity bands built respectively on the h_11/2 and g_7/2 neutron hole states are extended to 35/2^－ and 23/2⁺.Backbending occurs in both signature branches of the negative band at the frequencies close to that of the ¹²⁴Ba yrast band.An onset of backbending in the positive band has been seen.     

A New Level Scheme of 127I

Study of in beam γ ray spectroscopy of ¹²⁷I has been performed using ¹²⁴Sn(⁷Li, 4n)¹²⁷I reaction at 32 MeV beam energy. A new level scheme of ¹²⁷I has been established including 25 new levels and 52 new γ transitions. Negative parity levels based on 11/2^－ π h_11/2 particle state have been observed up to (35/2^－) extending our knowledge of decoupled structures to the heavier iodine isotope. Two ΔI=2 yrast positive-parity levels have been proposed to be associated mainly with the πg_7/2 configuration due to observations of several strong inter band transitions. Two weakly populated ΔI=2 positive parity levels and a high-lying ΔI=1 cascade have been newly identified and tentatively assigned as πd_5/2 one-quasiparticle and three quasiparticle bands, respectively.     

New isomers and their decay in odd-odd neutron-deficient cesium isotopes

By a systematic on-line cesium mass separation fromA=122 toA=132 and subsequent gamma and electron decay spectroscopy at very low energy, new isomers have been precisely identified:^122m Cs (T _1/2=0.36±0.02 s),^124m Cs (T _1/2=6.3±0.2 s) and^130m Cs (T _1/2=3.46±0.06 min). Detailed level schemes are given for both^124m Cs and^130m Cs. Comparison of excited levels known in the odd-odd nuclei of the same region shows that more experimental informations are needed to propose a clear and realistic picture of the nuclear states structure. Radioactivity:^{122m, 124m, 130m} Cs [from La or Ce,³Hexn]-measuredT _1/2,E _γ,I _γ,E _CE ,I _CE ,γ-γ-t, γ-ce coinc.; deduced ICC,^{124, 130}Cs deduced levels,J, π. Online mass separated sources, Ge(Li), intrinsic Ge, Si(Li), magnetic electron selector.     

Identification of High-Spin States in Odd-Odd 126I

Excited states in odd–odd ¹²⁶I have been studied via the heavy–ion induced fusion–evaporation reaction ¹²²Sn(¹¹B,5n2p) at beam energies of 55 and 60 MeV with beams provided by the HI–13 tandem accelerator of CIAE in Beijing.A level scheme consisting of 20 new γ transitions assigned to ¹²⁶I is established.The assignment of the established level scheme to ¹²⁶I is based on the observed coincidences between the newly identified γ–transitions and two previously known cascade γ transitions feeding the ground state of ¹²⁶I, and supported by a cross measurement using the ¹²⁴Sn(^7lI,5n) reaction performed at UTTAC,Japan.The observed structures of ¹²⁶I at high spins show typical properties of collective rotation in a deformed nucleus. their possible configurations are discussed briefly on the basis of knowledge from the neighboring nuclei.     

Isospin Effect on the Emission Mechanism of Hot Nuclei in 35MeV/u 40Ar +112Sn/124Sn Reactions

As an extension of radioactive ion beam physics, the research on isospin dependent properties of hot nuclei has increasingly attracted considerable interest. The isospin effect on the decay of hot nuclei in reactions 35MeV/u ⁴⁰Ar+¹¹²Sn/¹²⁴Sn has been investigared. It is concluded that due to Coulomb repulsion and instability, proton-rich hot nuclei probably emit prides such as a with high energy to increase their neutron-proton ratio. Moreover, the decay chain for those particles is seemingly long and the emission Probability is high. Thus, the conventional observations, for instance, the ‘slope temperature’ extracted from energy spectrum, may very appreciably with the measured particles.     

BaF2 Scintillator Coupling with a Low-pressure Multistep Avalanche Chamber

We studied the properties of a UV light sensitive low-pressure multistep avalanche chamber containing pure TMAE vapour.The gain of two chambers with different constructure at various temperatures is measured.With pure TMAE vapour at 40°C the gain of one chamber was 4×10⁵,the time resolution was 4.1ns.Coupling the chamber with a 2×2×2.4cm³ BaF₂ scintillator we successfully observed the signal of ¹³⁷Cs γ-ray of 0.661MeV.     

Parities of strong dipole ground state transitions in88Sr

By on-line mass separation and subsequent gamma and electron decay-spectroscopy at very low energy, two new isomers,^124mCs (T_1/2=6.3 ±0.3 seconds) and^127mBa (T_1/2=1.9±0.2 seconds) have been identified.     

Study on Stiffness of the Symmetry Energy at High Densities by π－/π+ Ratio

using the isospin–and momentum–dependent transport model, for three different symmetry energies, we have calculated the π^–/π⁺ ratio as a function of time and tranverse–momentum in central 132sn+124 sn collision at e_beam/A=400mev. the results show that the π^–/π⁺ ratios is very sensitive to the stiffness of the symmetry energy. thus we can probe the stiffness of the symmetry energy at high densities by using the π–/π+ ratio at different time or transverse momentum more accurately than before. comparing experimental data with the calculations will reveal crucial information about the stiffness of the symmetry energy more accurately.hadronic transport model, symmetry energy, π–/π+ ratio     

In-trap decay spectroscopy for 2�ͦ¦� decay experiments

Knowledge of 2??|? nuclear matrix elements is essential to probe the theoretical framework of 0??|? decays. At TITAN, TRIUMF??s Ion Trap for Atomic and Nuclear science, a novel technique has been developed to measure electron capture branches of virtual intermediate nuclei in ?|? decays. During two experiments with radioactive ^{124, 126}Cs isotopes the feasibility of this new method was proven.     

Relaxation of Isospin Degree of Freedom in the Reactions 36Ar+112,124Sn at 35MeV/u

Isotope ratios,defined as the yield ratio of two isotopes with the same charge,were analyzed as a function of kinetic energy of outgoing particles at 20° in the reactions of ⁴⁰Ar+^112,124Sn and 5°in³⁶Ar+^112,124Sn at incident energy of 35MeV/u. Isotope ratios between the neutron-deficient isotopes and stable isotope increase with kinetic energy,while those between the neutron rich isotopes and stable isotope decrease. This different behavior was observed similar for both ¹¹²Sn and ¹²⁴Sn targets. The isotope ratios show rather obvious target dependence at 20° and little target dependence at 5°. As the outgoing energy getting down,the N/Z ratio of the fragmentation products at 5° diverts gradually from the N/Z ratio of the projectile to that of the system. These observations indicate that the isospin degree of freedom does not reach complete equilibrium in the peripheral or semi-peripheral collision at this bombarding energy.