Prompt <Emphasis Type="Italic">γ</Emphasis> rays in <Superscript>77</Superscript>Ge and <Superscript>75</Superscript>Ge after thermal neutron capture

The reactions ⁷⁴Ge(n, γ) and ⁷⁶Ge(n, γ) have been measured with cold neutrons generated by the research reactor FRM II near Munich, Germany. The γ rays have been detected by two Compton-suppressed HPGe systems in single and coincidence mode. The number of identified prompt transitions and levels in ⁷⁷Ge was increased significantly and the decay scheme could be reconstructed for the first time. The decay scheme was also reconstructed for 68 prompt transitions in ⁷⁵Ge. Previously reported inconsistencies of the γ-ray intensities in the ⁷⁷Ge β decay could be resolved. In particular, the region around 2039 keV was investigated carefully, since the background to the neutrinoless double-beta decay of ⁷⁶Ge must be understood well for the upcoming Gerda and Majorana experiments.     

Decay of the very neutron-deficient isotope 131Pm

The decay of ¹³¹Pm has been investigated by means of γ-ray spectroscopy. The ¹³¹Pm nuclei were produced by fusion-evaporation reaction of ¹⁰⁶Cd(³²S,3p4n) at the beam energy of 170 MeV. A helium-jet technique and a tape transport system were used to collect the activities and transfer them to a detecting position for X and γ rays measurement. Two γ rays of 185.0 and 220.0 keV were unambiguously identified to follow the β⁺ decay of ¹³¹Pm by results of X-γ and γ–γ coincidence. A growth-decay feature of the decay curve for 87.8 keV γ-ray of ¹³¹Nd confirmed the production of ¹³¹Pm nuclei. The half-life of ¹³¹Pm was measured to be 6.3 ± 0.8 s. A partial decay scheme of ¹³¹Pm is proposed on the basis of X-γ and γ–γ coincidence data in this experiment and the known structure information deduced from in-beam experiments of the daughter nucleus ¹³¹Nd. Received: 11 January 1999 / Revised version: 20 May 1999     

Decay properties of neutron-deficient nuclei in the region Z = 86–92

Neutron deficient isotopes of elements Z = 86-92 have been produced by heavy-ion fusion reactions ¹²C + ²⁰⁸Pb, ²⁰⁹Bi, ²²Ne + ²⁰⁸Pb, ⁵¹V + ¹⁷⁰Er, and ⁵⁰Ti + ¹⁷⁰Er. The evaporation residues were investigated by means of α- and α-γ-spectroscopy after in-flight separation from the projectile beam by the velocity filter SHIP and implantation into a 16-strip position-sensitive Si-detector. New or improved decay data for ^{225, 226}U, ^{216, 217m, 218}Pa, ^{215, 216, 217}Th, ^{214, 215, 216, 216m}Ac, ²¹⁴Ra and ²¹³Rn have been obtained. Received: 5 April 2000 / Accepted: 28 July 2000     

The decay of the neutron–rich nucleus 216Bi

The decay of the neutron–rich isotope ²¹⁶Bi, produced by proton–induced spallation at the PS Booster–ISOLDE facility, was investigated by β-γγ, αγ coincidence and spectrum-multiscaling measurements. A new method for reducing isobaric contamination enabled to cover the unknown region “east” of ²⁰⁸Pb for the isobaric chain A=216. The half-life of the β decay of ²¹⁶Bi was found as T_1/2= 135 ± 5 s. Its decay scheme was extended and the possible shell model configurations are proposed. Received: 13 July 1999 / Revised version: 22 September 1999     

Conversion electron measurements of 152Nd

Abstact: Multipolarities of γ-rays in ¹⁵²Nd have been studied by conversion electron measurements in the β⁻ decay of ¹⁵²Pr. The praseodymium activities were obtained by the thermal neutron fission of ²³⁵U and followed with the on-line isotope separator KUR–ISOL. Conversion electrons and γ-rays were measured with a Si(Li) detector and a HPGe detector, respectively. The two γ-rays, 226 keV and 285 keV, were decided to have the multipolarities of the E1 transition. The spins and parities of the 1600 keV and 1542 keV levels were determined to be 3⁺ and 2⁺, respectively. Received: 14 April 1998     

Studies of 213g, mRa and 214g, mRa by α and γ decay

The decay of ^{213, 214}Ra was studied by α-γ and γ-γ coincidence measurements. The nuclei were produced in the reactions ¹⁷⁰Er(⁴⁸Ca, xn)^218-x Ra and ¹⁷⁰Er(⁵⁰Ti, 3n)²¹⁷Th and subsequent α decay of ²¹⁷Th to ²¹³Ra. Evaporation residues recoiling out of the target were separated in-flight by the velocity filter SHIP and implanted into a position-sensitive 16-strip PIPS detector in order to study their subsequent decays. Associated γ-rays were detected by a four-fold Ge-Clover detector. In the present work we extracted new and improved data for ^{213, 214}Ra including isomeric transitions. The results are discussed and compared with previously published data.     

Total strength of the magnetic dipole resonance in <Superscript>31</Superscript>P

The γ decay of the resonance-like structure observed in the ³⁰Si(pγ)³¹P reaction in the energy range E _p = 1.4–2.7 MeV of accelerated protons has been investigated. The excitation function of this reaction and the spectra and angular distributions of the γ rays formed in the decay of resonances with E _p = 1482, 2350, and 2505 keV have been measured. The M1 resonance on the ground and the first excited states of ³¹P with E _p = 1266 keV is identified. The total strength of the M1 resonance on the ground state of this nucleus is determined. The position and total strength of this resonance on the ground state are explained taking into account pairing forces.     

(EC +β+) decay study of 128Ce

The (EC+β⁺) decay of ¹²⁸Ce was reinvestigated in the ¹¹⁶Sn (¹⁶O, 4n) reaction by using a helium-jet tape transport system. The close half-lives of ¹²⁸Ce and ¹²⁹Ce made it difficult to separate the decay γ rays of both nuclei apart. Instead of the excitation-function measurements, both reactions of ¹⁶O+¹¹⁶Sn and ¹⁶O+¹¹⁷Sn were carried out, and from their comparisons, the decay γ rays of ¹²⁸Ce were clearly told from those of ¹²⁹Ce. Based on X-γ and γ-γ coincidence measurements, a detailed (EC +β⁺) decay scheme of ¹²⁸Ce has been proposed, which revises the previous one. Received: 29 September 1999 / Revised version: 5 November 1999     

Beta decay of 94Pd and of the 71 s isomer of 94Rh

The β decay of ⁹⁴Pd and of the 71s isomer of ⁹⁴Rh was investigated by using total γ-ray absorption techniques. Several levels in ⁹⁴Rh are established, including a new low-lying isomer characterized by a half-life of 0.48(3)μs and a de-exciting transition of 55keV. E2 multipolarity is determined for this transition by measuring the intensities of its γ-rays and the characteristic X-rays from its electron conversion. On the basis of the measured reduced β-decay transition rates to known ⁹⁴Ru levels and shell model considerations, the spin-parity of the 71s and the 0.48μs isomers of ⁹⁴Rh is assigned to be (4⁺) and (2⁺), respectively. The β-decay strength distributions measured for ⁹⁴Pd and the 71s isomer of ⁹⁴Rh yield Q _EC values of 6700(320) and 9750(320)keV for these decays and give evidence for the population of those states below and above the magic N = 50 gap that belong to both components of the 0g spin-orbit doublet.     

Radon loss from encapsulated sediments in Ge gamma-ray spectrometry for the annual radiation dose determination in luminescence dating

In Ge gamma-ray spectrometry for the annual radiation dose determination in the luminescence dating of sediments, the picture of ²²⁶Ra enrichment or depletion (in the ²³⁸U decay series) obtained via measurement of its ²¹⁴Pb and ²¹⁴Bi daughters may be disturbed by the ²²²Rn-content of the sample being decreased due to manipulations such as drying and pulverizing. Therefore, it is common practice to start the measurement only about 1 month after encapsulating the material, after which the ²²⁶Ra(1600 a)- ²²²Rn(3.82 d) mother-daughter equilibrium is re-established. Evidently, this only holds on condition that no significant escape of Rn occurs out of the sediment after making it up for counting. In order to experimentally investigate this effect, in the present work measurements were carried out with various types of dried and pulverized sediments that were either encapsulated in screw-cap polystyrene vials or in sealed glass containers, or that were mixed with molten wax followed by solidification in a cylindrical geometry. From the results obtained, it could be concluded that preparation and counting of the sediment-wax mixture is the method of choice.     

First decay scheme of 113Tc and identification of 113Ru m

Very neutron–rich fission products of the mass chain A=113 obtained from the IGISOL on–line mass separator have been investigated by γγ coincidence techniques and γ-spectra multiscaling. Gamma–rays following β–decay of ¹¹³Tc have been observed for the first time and a new 0.5 s isomeric state has been found in ¹¹³Ru. Received: 10 February 1998     

β-delayed proton decays and spin assignments for 133Sm and 149Yb

The proton-rich isotope ¹³³Sm was produced via the fusion evaporation reaction ⁴⁰Ca + ⁹⁶Ru. Its β-delayed proton decay was studied by p-γ coincidence in combination with a He-jet tape transport system, and half-lives, proton energy spectra, γ-transitions following the proton emission, as well as β-delayed proton branching ratios to the low-lying states in the grand-daughter nucleus were determined. Comparing the observed β-delayed proton branching ratios with statistical model calculations, the best agreement is found assuming that only one level with the spin of 3/2 in ¹³³Sm decays or two levels with the spins of 1/2 and 5/2 decay with similar half-lives. The configuration-constrained nuclear potential energy surfaces of ¹³³Sm were calculated using the Woods-Saxon-Strutinsky method, which suggests a 1/2^- ground state and a 5/2⁺ isomer with an excitation energy of 120keV. Therefore, the simple (EC+β⁺) decay scheme of ¹³³Sm in Eur. Phys. J. A 11, 277 (2001) has been revised. In addition, our previous experimental data on the β-delayed proton decay of ¹⁴⁹Yb reported in Eur. Phys. J. A 12, 1 (2001) was also analyzed using the same method. The spin-parity of ¹⁴⁹Yb is suggested to be 1/2^-.     

Alpha decay of the new isotopes 188,189Po

New neutron-deficient isotopes ^188,189Po have been produced in the complete fusion reaction of ⁵²Cr ions with a ¹⁴²Nd target at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of α-γ and α-conversion electron coincidence measurements and of α-α position and time correlations. In ¹⁸⁹Po a ground state to ground state α decay with E_α1= 7540(20) keV, T_1/2= 5(1) ms and two fine structure α-decays at E_α2= 7264(15) keV and E_α3= 7316(15) keV have been observed. In ¹⁸⁸Po (T_1/2= 400⁺²⁰⁰ ₋₁₅₀μs) a ground state to ground state α decay at E_α= 7915(25) keV and a fine structure α decay at E_α= 7350(40) keV have been found. Improved data on the α-decay of ¹⁸⁹Bi were obtained. Received: 15 October 1999     

Bremsstrahlung emission accompanying the α -decay of 214Po

We analyze the bremsstrahlung emission obtained by the α -γ coincidence measurements to investigate on the α -decay dynamics of the ²¹⁴ Po nucleus. We performed the experiment using a radioactive ²²⁶ Ra source leading, by α -decays, to the ²¹⁴ Po nucleus, and the apparatus with the Si detector for α -particles, the NaI(Tl) detector able to collect photons with energies up to about 1 MeV. We compare the experimental data with the quantum-mechanical calculations and find a good agreement between theory and experiment for photon energies up to 765 keV. In the experimental data of the bremsstrahlung spectrum one can see the presence of slight oscillations.     

Beta-gamma-gamma directional correlation in103Rh

β-γ-γ directional correlation studies for the cascades (i)β-rays ofE _max=0.12 MeV,γ-rays of 557 keV andγ-rays of 53 keV and (ii)β-rays ofE _max=0.21 MeV,γ-rays of 444 keV andγ-rays of 53 keV have been made. The triple correlation functionsW(θ) were obtained to beW(θ)=1+(−0.153±0.031)P ₂(cosθ)+(0.004±0.035)P ₄(cosθ) forβ-rays ofE _max 0.12 MeV→557→53 keV cascade andW(θ)=1+(0.163±0.042)P ₂(cosθ)+(−0.035±0.058)P ₄(cosθ) forβ rays ofE _max=0.21 MeV→444 keV→53 keV cascade. Spins and parities of the 650, 537 and 93 keV levels of¹⁰³Rh are deduced by triple angular correlation and the internal conversion coefficient studies. Multipolarities of the transitions are also determined.     

Magnetic hyperfine field of Hg in nickel and the sign of magnetic moment of 197mAu by NMR-ON

Nuclear magnetic resonance on oriented nuclei (NMR-ON) measurements were performed on the successive decay of ^197mHg–^197mAu in Ni. The NMR-ON resonance spectra of ^197mHgNi were obtained by detecting the 134 keV γ-ray from the decay of ^197mHg and the 279 keV γ-ray from the decay of ^197mAu. The magnetic hyperfine splitting frequency of ^197mHgNi in an external magnetic field of 0.2 T has been determined as 16.55(6) MHz. With the known g-factor of ^197mHg the hyperfine field of B₈₂(^197mHgNi)= -13.53(6) T was deduced. The anisotropy of the 279 keV γ-ray (^197mAu to ¹⁹⁷Au) increased at the resonance. This phenomenon was explained using the spin inversion process including the lifetime of the isomer and the spin–lattice relaxation time. The sign of the g-factor of ^197mAu was determined to be positive. This revised version was published online in August 2006 with corrections to the Cover Date.     

Experimental investigation of the angular dependence of photon-induced differential cross-sections of L X-rays from U,Th and Bi at 59.5 keV

Summary The differential cross-sections for the emission of L_ρ, L_α, L_β and L_γ groups of L X-ray lines from U, Th and Bi have been measured at different angles varying from 45° to 135° at intervals of 15°. The vacancies were created by 59.5 keV γ-rays from²⁴¹Am source and L X-rays were measured using a Si(Li) detector. It is found that the L_γ and L_β groups of L X-rays are isotropic, the L_ρ and L_α groups are anisotropic in the spatial distribution. The authors of this paper have agreed to not receive the proofs for correction.     

Beta decay of 101Sn

The β decay of the very neutron-deficient isotope ¹⁰¹Sn was studied at the GSI on-line mass separator using silicon detectors for recording charged particles and germanium detectors for γ-ray spectroscopy. Based on the β-delayed proton data the production cross-section of ¹⁰¹Sn in the ⁵⁰Cr + ⁵⁸Ni fusion-evaporation reaction was determined to be about 60nb. The half-life of ¹⁰¹Sn was measured to be 1.9(3)s. For the first time β-delayed γ-rays of ¹⁰¹Sn were tentatively identified, yielding weak evidence for a cascade of 352 and 1065keV transitions in ¹⁰¹In. The results for the ¹⁰¹Sn decay as well as those from previous work on the ¹⁰³Sn decay are discussed by comparing them to predictions obtained from shell model calculations employing a new interaction in the ⁸⁸Sr to ¹³²Sn model space.     

Interactions of the solar neutrinos with the deuterons

The beta decay of ³¹Cl has been studied with a silicon detector array and a HPGe detector at the IGISOL facility. Previously controversial proton peaks have been confirmed to belong to ³¹Cl and a new proton group with an energy of 762(14) keV has been found. Proton captures to this state at 6921(15) keV in ³¹S can have an effect on the reaction rate of ³⁰P(p,γ) in ONe novae. Gamma rays of 1249.1(14) keV and 2234.5(8) keV corresponding to the de-excitations of the first two excited states in ³¹S have been measured. No beta-delayed protons from the IAS have been observed.     

Study of the N = 50 major shell effect toward 78Ni at PARRNe⋆

The γ-ray de-excitations following the β-decay of ⁸³Ga and the β-n decay of ⁸⁴Ga have been studied. The radioactive species were produced using the PARRNe on-line mass-separator installed at the IPN Orsay Tandem accelerator. Two γ-lines were attributed to ⁸³Ge with the aid of β-γ and γ-γ coincidences. The Z identification of the γ-lines was provided by time analysis of a buid-up/decay cycle. The excited levels of ⁸³Ge can be explained by the coupling of the single neutron state ν2d _5/2 to the first 2⁺ excitation of the ⁸²Ge core.