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.     

The energy levels of79Br and81Br

The low-lying energy level and decay schemes of the stable bromine isotopes were studied by observing the γ-rays from the (n, n′γ) reactions in a natural bromine sample with the aid of a Ge (Li) detector. A pulsed neutron source and time-of-flight methods were used to reduce background due to neutron events in the detector. Most of the γ-rays observed could be assigned to transitions in either⁷⁹Br or⁸¹Br. In addition to those levels previously known from γ-decay or Coulomb excitation experiments, several new levels were excited in each isotope.     

First Experimental Determination of Half-Life for New Nuclide 65Se

By using experimental data obtained from the measurement of beta-delayed proton decay of ⁶⁵Se produced in ⁴⁰Ca(²⁸Si,3n)reaction,the absolute detection efficiency of particle telescope for rotating radioactive source was imitatively calcu-lated.The half-life of ⁶⁵Se was thus accurately determined to be 9.6_-4.1^+5.3 ms.The β-delayed proton energy of ⁶⁵Se was 3.70±0.08MeV.The partial decay scheme of ⁶⁵Se β-delayed proton decay was revised and proposed.     

The decay of a new nuclide: 71Br

The decay of mass-separated samples of the previously unknown nuclide ⁷¹Br have been investigated by means of the Chalk River on-line isotope separator. Eleven γ-rays were assigned to the decay of this nuclide, and its half-life was measured to be 21.4 ± 0.6 s. A simple decay scheme for ⁷¹Br has been constructed incorporating six levels in its daughter, ⁷¹Se. Two long-lived excited states were found in ⁷¹Se, and the transition from the least energetic one to the ground state was found to be heavily converted. Systematic trends in the level schemes of the N = 37 isotones ⁶⁷Zn, ⁶⁹Ge and ⁷¹Se are investigated.     

Candidate of the member of three-phonon multiplet observed in the β + +EC decay of 76Br

The decay scheme of ⁷⁶Br is established by the ⁷⁶Br(T _1/2?=?16.2 h) β ^?+?/EC study. The 1791.31 keV level, which was identified initially by Müller et al with ⁷⁶Se(p, p ^′) reaction more than three decades ago, is reconfirmed. However, the spin and parity have not been assigned by Müller et al. Now we consider it reasonable to assign the 1791.31 keV level as a new candidate of the three-phonon multiplet in ⁷⁶Se. In addition, in order to study the deformation of ⁷⁶Se which lies in transitional region between strongly deformed and spherical nuclei, we calculate the total Routhian surfaces (TRS) of positive-parity states by cranking shell model formalism.     

On-line orientation of bromine isotopes

Assignments for the principal Nilsson configuration in light β⁺-decaying bromine isotopes were proposed in a contribution to the OLNO-1 conference. These assignments were made on the basis of magnetic moments derived from the temperature dependence of anisotropies in daughter Se isotopes observed in the DOLIS-COLD facility at Daresbury. Anisotropy measurements have since been extended to a lower base temperature in^74m Br and^72g Br decay, leading to more stringent limits on the ground state moment of⁷²Br. The proposed π[312]3/2 configuration for⁷⁵Br has also now been confirmed by a measurement of the sign of its magnetic moment. This was done by observing the β-asymmetry in⁷⁵Br decay using high purity Si detectors mounted within the dilution refrigerator.     

DISCOVERY OF MULTIPLE,COLLECTIVE BAND STRUCTURES IN NUCLEI WITH A=60—80

Recent studies of levels in even-even ^68,70,72Ge,^70,72,74Se,^74,76,78,80Kr and ⁶⁵Ga and ⁷⁴Br have led to the discovery of a wide variety of different collective band structures.These include bands built on near spherical ground states and excited more well de-formed shapes that may include triaxial shapes,rotation-aligned bands built on thesame orbital （g_（9/2））² for both protons and neutrons,RAL negative parity bands witheven and odd spins,and ΔI=1 γ-type vibrational bands in even-even nuclei.As recent as 1974,a survey of the energy level in the even-even Ge and Se iso-topes^[1] revealed little was known above a spin of 4⁺ （see for examples Figs.1 and 2 of Ref.1）.With the exception of the unusally low-lying excited 0⁺ states in ^70,72Ge,first discovered in ⁷²Ge in 1948 at Vanderbilt^[2],the theoretical treatment of thesenuclei was limited primarily to some variation of the vibrational model.However,very recently there has been a surge of information on nuclei in this region that hasrevealed fascinating new features and also provided new insight into the excited 0^+’states.Particularly striking are the multiple,independent and highly collective bandstructures which we have discovered in our in-beam γ-ray spectroscopy studies fol-lowing heavy-ion induced reaction.Evidence for and the theoretical understandingof the richness of the collective band structures that are found in our studies of^68,70,72Ge （Refs.3—6）,^70,72,74Se （Refs.7—13） and ^74,76,78,80Kr （Refs.14—18）,as illustratedby the at least seven different bands found in our studies of the levels of ⁶⁸Ge ⁷⁴Se,and ⁷⁶Kr （Figs.1—3）,are described in this paper.These multiple structures includethe following:a) coexistence of ground bands built on near-spherical shapes andexcited bands with larger deformation built on O^+′ band heads;b) bands with 8⁺ band heads interpreted as rotation-aligned,RAL,bands built on both neutron and/orproton （g_（9/2））² quasiparticle configurations coexisting with the ground-state band;c)RAL neutron and proton odd-parity bands formed from coupling of a g_{（9/2 ）}quasipar-ticle and a p_（1/2）,p_（3/2） or f_（5/2）,quasiparticle with the core;d) ΔI=1 even-parity bands,which are best characterized as gamma-vibrational bands;and e) additional bandswhose nature are presently not known.     

Decay of 95Ru

1.65h ⁹⁵Ru was produced and studied by y ray spectroscopy of ⁹²Mo(a, n)reaction, 34 of the 130 obversed y rays following ⁹⁵Ru decay are new. According to coincidence relations, 29 new γ rays were flited into level scheme, the placement of 7 γ rays in level scheme were confirmed, 3 new levels were assigned, a modified and expanded decay scheme was proposed.     

THE POSSIBILITY OF EXITENCE OF NEW ISOTOPE 65Se

A new beta-delayed proton precussor ⁶⁵Se has was probably produced via the reaction ⁴⁰Ca (²⁸Si,3n)⁶⁵Se and identified from its beta-delayed proton emission.A single proton group at 3.75±0.05MeV with half-life of 10.8±4.1/3.7ms was observed,corresponding to superallowed beta decay of ⁶⁵Se to the isobaric analog state of ⁶⁵As (the lowest T=3/2 state in ⁶⁵As) then proton emitting to the ground state of ⁶⁴Ge.Because of poor statistics further experimental effort is required to confirm this discovery.     

Study of Excited States in Neutron-Deficient 197Bi

High-spin states in ¹⁹⁷Bi were populated by bombarding natural Re target and isotope ¹⁸⁷Re target with ¹⁶O beam of 100 MeV. Using comprehensive γ-γ-t coincidence measurements,three new isomers in ¹⁹⁷Bi were established and eleven new y-transitions were identified,while errors in the existing level scheme were corrected.From the level structure systematics of the odd-mass Bi isotopes, the configuration and decay properties of a new isomer with t_1/2n=19.3±4.9ns in ¹⁹⁷Bi were discussed.The y-ray angular distributions were also measured.A new level scheme of ¹⁹⁷Bi was proposed.     

Study of Quasiparticles Bands in Odd-Odd 188Au

High-spin level structure of ¹⁸⁸Au has been studied via the ¹⁷³Yb(¹⁹F, 4nγ) reaction using techniques of in-beam γ-ray spectroscopy. Based on the experimental results, the level scheme of ¹⁸⁸Au has been revised significantly. The previously reported positive parity levels have been modified and a new 20⁺ level was proposed to feed the 18⁺ states via two low-energy transitions. The existence of the 20⁺ and the level structures above it are similar to those in the neighboring odd-odd ^190,192Au,therefore, the π h_{11/2}^{-1}\otimes \upnu i_{13/2}^{-2} h_{9/2}^{-1} configuration was assigned to the 20⁺ state.     

The decay of83gSe and83mSe

The decay of the isomeric pair^83gSe (T1/2=22.6 min,I ^α = 9/2⁺) and^83mSe (T1/2=70 s,I ^α = 1/2^?) has been reinvestigated using straight Ge(Li) (^83gSe and^83mSe) and Ge(Li)-Ge(Li) coincidence spectrometry (^83gSe). Both decays populate entirely different⁸³Br levels, 11 of them being previously unreported. Fromγ-ray unbalances and from the known isomeric cross-section ratio of⁸²Se, β^?-branchings have been obtained, including a 34% branching of^83mSe to the ground state of⁸³Br. Logft-values are deduced, spin and parity values proposed and discussed.     

Evidence for deformed states in 75Br

The excited states in ⁷⁵Br have been studied via the reactions ⁷⁴Se(p, γ), ⁷⁴Se(d, n), ⁷⁴Se(³He, pn) and ⁷⁴Se(α, p2n) by using in-beam γ-ray spectroscopy. In addition to measurements of γ-γ coincidences, excitation functions and angular distributions of γ-rays, ns lifetime measurements have also been carried out. As a result 19 levels have been identified up to spin ($\text{17}\text{2}$) and excitation energies up to 2.6 MeV. The B(E2) value of 88 W.u. derived for the 88.4 keV γ-ray indicates strong collectivity within a positive-parity band. A comparison of the excitation energies of the unique-parity states in ⁷⁵Br and ⁷⁷Br with those in ¹⁵³Tb and ¹⁵⁵Tb reveals that the average deformation increases when going from ⁷⁷Br (N = 42) to ⁷⁵Br (N = 40).     

First Study of Weak (EC+β+) Decay Branch for the Neutron-Deficient Isotoep 209Fr

²⁰⁹Fr has been produced by irradiation of ¹⁹⁷Au with ¹⁶O from SFC accelarator uia the fusion-evaporation 4n channel.The(EC+β⁺)decay of ²⁰⁹Fr has been studied by a He-jet tape transport system.The decay scheme is proposed for the first time based on γ-t,X-γ-t,γ-γ-t coincidece and γ-γ delay coincidence measurements,which takes account of 20 observed γ ray.Five members of low-lying states in ²⁰⁹Rn can be explained by the multi-plet [(²¹⁰Rn2⁺)(νf_5/2)^－1].The branching ratio for(EC+β⁺) decay of ²⁰⁹Fr has been estimated experimentaly to be(3.0±1.5)%.     

The Efficiency Mearurement of NaI(Tl) Detector for a Long Tube Volume Source of 6.13MeV Gamma-Ray

The relation of the ¹⁶N leak rate of the nuclear reactor to the efficiency and counting rate of γ–ray detector, velocity of high pressure vapor, is deduced. a conclusion of the efficiency independent on the velocity of high pressure vapor and decay constant of ¹⁶N is drawn. experimentally the space distribution of the relative efficiencies and the absolute efficiency at a refe~rence point are measured with Puc source emiting 6.13mev gamma ray detected by nai(tl) counter. The measured efficiency is consistent with monte carlo calculation in 7%. the compton small angle scattering contribution to the convergence length and the effect of the energy difference between 7.12mev and 6.13mev gamma ray on measured ¹⁶N leak rate are discussed.     

Evaluation of the 1077 keV γ-ray emission probability from 68Ga decay

⁶⁸Ga decays to the excited states of ⁶⁸Zn through the electron capture decay mode. New recommended values for the emission probability of 1077 keV γ-ray given by the ENSDF and DDEP databases all use data from absolute measurements. In 2011, JIANG Li-Yang deduced a new value for 1077 keV γ-ray emission probability by measuring the ⁶⁹Ga(n,2n) ⁶⁸Ga reaction cross section. The new value is about 20% lower than values obtained from previous absolute measurements and evaluations. In this paper, the discrepancies among the measurements and evaluations are analyzed carefully and the new values are re-recommended. Our recommended value for the emission probability of 1077 keV γ-ray is (2.72± 0.16)%.     

An IBM description of 76Se and neighbouring Se-isotopes

The level structure of ⁷⁶Se is discussed within the framework of Interacting Boson Models. The calculated energy levels, transition probabilities, mixing ratios, \({Q_{2_1^ + }}\) and \({g_{2_1^ + }}\) are compared with experimental data. Mixed-symmetry states are investigated in the isotopes ⁷²Se, ⁷⁴Se, ⁷⁶Se, ⁷⁸Se and ⁸⁰Se. Two mixed symmetry states with spin 1⁺ and 3⁺ are proposed for ⁷⁶Se, and also six other 1⁺ and 2⁺ levels in the neighbouring selenium isotopes.     

Der Zerfall des77Kr

⁷⁷Kr (T _1/2=1.2 h) was produced by bombarding⁷⁶Se with 48 MeV-α-particles. After irradiation the radioactive⁷⁷Kr gas was collected in glass ampoules filled with charcoal and cooled by liquid air. The decay of⁷⁷Kr has been investigated using Ge(Li)-counters and a Ge(Li)-Ge(Li)-coincidence circuit. 27 γ-transitions, 13 of them unknown up to the present, have been found and their relative intensities have been determined. A level scheme for⁷⁷Kr→⁷⁷Br having 14 levels is proposed. This accounts for all the observed γ-transitions.     

Half-Life and the Nuclear Matrix Element of the 2νββ Decay in 76Ge

We apply the shell-model wave functions of ⁷⁶Ge to calculate the nuclear matrix elements and the half-life of the 2νββ decay of ⁷⁶Ge. Our result is comparable to the recent observed 2νββ decay half-life of ⁷⁶Ge. Furthermore it provides the upper limit of the effective neutrino mass is about 0.4eV with the recent experimental data of the 0νββ decay half-life.