Decay of proton-rich nuclei between 39Ti and 49Ni

Decay studies of very neutron-deficient nuclei ranging from ³⁹Ti to ⁴⁹Ni have been performed during a projectile fragmentation experiment at the GANIL/LISE3 separator. For all nuclei studied in this work, ^{39, 40}Ti, ^{42, 43}Cr, ⁴⁶Mn, ^{45, 46, 47}Fe and ⁴⁹Ni, half-lives and decay spectra have been measured. In a few cases, γ coincidence measurements helped to successfully identify the initial and final states of transitions. In these cases, partial decay scheme are proposed. For the most exotic isotopes, ³⁹Ti, ⁴²Cr, ⁴⁵Fe and ⁴⁹Ni, which are candidates for two-proton radioactivity from the ground state, no clear evidence of this process is seen in our spectra and we conclude rather on a delayed particle decay. Received: 26 July 2000 / Accepted: 20 December 2000     

Production and identification of new neutron-rich fragments from 33 MeV/u86Kr beam in the 18≦Z≦27 region

The new nuclei⁴⁷Ar,⁵⁷Ti,^59,60V,^61,62Cr,^64,65Mn,^66,67,68Fe,^68,69,70Co haye been produced by fragmentation of a⁸⁶Kr beam and identified through time of flight andΔE×E measurements. The tentative observation of⁵⁶Ti,^57,58V,⁶⁰Cr and⁶⁵Fe by other groups is confirmed.     

Direct observation of new proton rich nuclei in the region 23≦Z≦29 using A 55A.MeV58Ni beam

Using magnetic separation and identification through time of flight andΔExE measurements, the nuclei⁵⁶Cu,⁵²Co (T _z =?1);⁵⁵Cu,⁵¹Co,⁴⁷Mn,⁴³V(T _z =?3/2)⁵²Ni,⁵⁰Co,⁴⁸Fe,⁴⁶Mn,⁴⁴Cr (T _z =?2); and⁵¹Ni (T _z =?5/2) are observed for the first time from interactions of 55A.MeV⁵⁸Ni projectiles with a Ni target. The predicted proton drip-line has probably been reached for the odd elements.     

Level densities for nuclei with 47 ≤ A ≤ 59

Nuclear level densities of ⁴⁷V, ⁴⁸V, ⁴⁹V, ⁵³Mn, ⁵⁴Mn, ⁵⁷Co, ⁵⁹Ni and their energy dependences are determined from measurements of the neutron evaporation spectra in the (p, n) reaction. Neutron spectra from the (p, n) reaction on nuclei of ⁴⁷Ti, ⁴⁸Ti, ⁴⁹Ti, ⁵³Cr, ⁵⁴Cr, ⁵⁷Fe, and ⁵⁹Co are measured at proton energies between 7 and 11 MeV. The data are analyzed in terms of statistical equilibrium and pre-equilibrium models of nuclear reactions.     

Hyperfine anomalies of Sc isotopes (A = 44, 44 m, 46 and 47) in iron

Nuclear magnetic resonance on oriented nuclei (NMR-ON) on Sc isotopes (A = 44, 44 m, 46, 47) in Fe were performed. Using the known magnetic moments the magnetic hyperfine fields were determined. The hyperfine anomalies of various Sc were deduced; ⁴⁴Δ⁴⁷ = 0.0 (12) %, ^44mΔ⁴⁷ = 1.2 (4) %, ⁴⁶Δ⁴⁷ = 2.7 (8) %. The measured hyperfine anomalies are briefly discussed based on the shell model.     

Nuclear charge radii of Sc,V, Fe,Co, Ni,Cu and Zn from elastic electron scattering at 60 MeV

Elastic electron scattering cross sections have been measured at 60 MeV for scattering angles between 45 and 153 degrees relative to⁴⁶Ti (for⁴⁵Sc),⁵⁰Ti (for⁵¹V) and¹²C (for the other nuclei). The following rms radii (in fm) have been deduced with a Fermi-type charge distribution (skin thickness 2.5 fm):⁴⁵Sc: 3.52(9);⁵¹V:3.62 (9); Fe: 3.71 (11);⁵⁹Co: 3.77 (5); Ni: 3.78 (8); Cu: 3.85 (5); Zn: 3.90 (5). The present uncertainty of the rms radius of¹²C increases the errors given by 0.01 fm. The rms radius differences 0.04 (5) fm for⁴⁶Ti-⁴⁵Sc and 0.06 (5) for⁵¹V-⁵⁰Ti were measured directly.     

Isotope shift of calcium isotopes withA=40, 42, 43, 44, 46 and 48 by laser spectroscopy

Isotope shifts of all the stable Ca isotopes in the intercombination lineλ=6573Å have been studied by laser spectroscopy. The nuclear volume effect for⁴³Ca and⁴⁶Ca could be evaluated from the measurements and the quadrupole moment of⁴³Ca was obtained.     

Measurement and hybrid-model analysis of proton-induced reactions with V,Fe and Co

On target elements V, Fe and Co (natural isotopic composition) proton-induced reactions were investigated in the energy region from 12 to 45 MeV using the stacked-foil technique. The product nuclides observed were ⁴⁸Cr, ⁴⁹Cr, ⁵¹Cr, ⁴⁸V, ^{46m + g}Sc, ⁴⁷Sc and ⁴⁸Sc from V, ⁵⁵Co, ⁵⁶Co, ⁵⁷Co, ^{58m + g}Co, ⁵²Fe, ^{52m + g}Mn, ⁵⁴Mn, ⁵¹Cr and ⁴⁸V from Fe, and ⁵⁶Ni, ⁵⁷Ni, ⁵⁶Co, ⁵⁷Co, ^{58m + g}Co, ⁵⁴Mn and ⁵⁶Mn from Co. The comprehensive set of excitation functions extending and improving earlier studies is compared with calculations considering equilibrium as well as preequilibrium reactions according to the hybrid model of Blann. The overall agreement between experiment and theory is good. Certain discrepancies, however, indicate the necessity to revise the hybrid model with respect to the emission of complex particles.     

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.     

Magnetic moments of low-lying states in medium weight odd nuclei

The magnetic moments of several short-lived states in¹⁰³Rh,^1111113Cd and^1231125Te isotopes have been measured by the transient field technique. The results, together with those obtained earlier in the^1071109Ag isotopes, have been compared to predictions of various models and calculations. In the Z=45, 47 isotopes, the odd proton seems to deform the vibrational core. The data are best explained within the framework of a triaxially deformed nucleus. In the odd neutron isotopes with 50<N<82, and Z=48, 52, weak coupling states coexist with single particle states in a mix of configurations.     

Recoil properties of spallation products from bombardment of Z = 13–29 targets with 150,300 and 600 MeV protons

A semi-empirical relation developed using the classical model of high-energy nuclear reactions has been applied to spallation data obtained from thick-target — thick-collector recoil experiments. The ²⁴Na, ⁴²K, ⁴³K, ^44mSc, ⁴⁶Sc, ⁴⁷Sc ranges produced in Al, Sc, Ti, V, Fe, Co, Cu targets by 150, 300 and 600 MeV protons were determined. The excitation energies of the residual nuclei, deduced from the ranges, have been compared with theoretical calculations. The analysis shows that if the mass difference of the target and product nucleus is ΔA ? 10 the cascade plays a privileged role. If ΔA>10 an averaging effect is observed. In this case the number of prompt nucleons is about one-third of the total number and the excitation energy per evaporated nucleon is about 11 MeV.     

Experimental evidences of clusters with different short range order in amorphous alloys

⁵⁶Fe,⁵⁷Fe,¹⁰B and¹¹B isotopes were used for binary alloys. The signals of B (40,5 MHz) and Fe (43 MHz) from α-Fe in binary Fe−B crystalline and amorphous alloys were found besides the signals of these nuclei in t-and o-phase or clusters like these phases. The NMR on (51)V impurity nuclei in Fe−B alloys was used as well. Only amorphous Fe-(^<15 at.%B) alloys had the clusters with o-, t-Fe₃B and α-Fe short range order.     

On the stability of the nuclei of element 108 withA=263–265

In bombarding²⁰⁹Bi and^{207, 208}Pb targets by⁵⁵Mn and⁵⁸Fe ions the yields of “cold fusion” reactions have been determined using a sensitive technique for detectingT _1/2≧1 ms spontaneous fission and theα-decay of heavy actinide elements. It has been shown that theA = 263–265 isotopes of element 108, including the even-even isotope²⁶⁴108, undergo mainlyα-decay. The obtained results, together with the known data on the properties of the isotopes of elements 104 and 106, provide evidence for the enhanced stability of theZ=108 nuclei against spontaneous fission.     

Are nuclei withN∼43 deformed?

The level schemes of⁷⁵Se and⁷⁹Kr have been established through gamma ray and conversion electron spectroscopy following⁷⁵As (p, nγ ^?e) and⁷⁹Br (p, nγe^?) reactions. The data on these nuclei and the nuclei in the neighbourhood of this mass region are discussed and evidence is presented to show that the nuclei withN～43 are deformed.     

Statistical properties of excited nuclei in the mass range 47 ? A ? 59

Level densities and their energy dependences for nuclei in the mass range of 47 ?? A ?? 59 were determined from the results obtained by measuring neutron-evaporation spectra in respective (p, n) reactions. The spectra of neutrons originating from the (p, n) reactions on ⁴⁷Ti, ⁴⁸Ti, ⁴⁹Ti, ⁵³Cr, ⁵⁴Cr, ⁵⁷Fe, and ⁵⁹Co nuclei were measured in the proton-energy range of 7?C11 MeV. These measurements were performed with the aid of a fast-neutron spectrometer by the time-of-flight method over the base of the EGP-15 pulsed tandem accelerator installed at the Institute for Physics and Power Engineering (Obninsk, Russia). A high resolution of the spectrometer and its stability in the time of flight made it possible to identify reliably discrete low-lying levels along with the continuum part of neutron spectra. Our measured data were analyzed within the statistical equilibrium and preequilibrium models of nuclear reactions. The respective calculations were performed with the aid of the Hauser-Feshbach formalismof statistical theory supplemented with the generalized model of a superfluid nucleus, the back-shifted Fermi gas model, and the Gilbert-Cameron composite formula for nuclear level densities. Nuclear level densities for ⁴⁷V, ⁴⁸V, ⁴⁹V, ⁵³Mn, ⁵⁴Mn, ⁵⁷Co, and ⁵⁹Ni and their energy dependences were determined. The results are discussed and compared with available experimental data and with recommendations of model-based systematics.     

Energy levels of136Pm and136Nd via beta decay of136Sm and136Pm

¹³⁶Pm and¹³⁶Nd were studied using theβ decay of¹³⁶Sm and¹³⁶Pm. The radioactive nuclei were produced by the⁹²Mo (⁴⁸Ti,xpyn) and¹¹²Sn (²⁸Si,xpyn) reactions. The UNISOR isotope separator enabled mass identification. The previously unknown level scheme of¹³⁶Pm was constructed and the half-life of¹³⁶Sm was determined to be 47±2 s. Six new levels and thirteen newγ-ray transitions have been added to the level scheme of¹³⁶Nd.     

New neutron-rich isotopes in the scandium-to-nickel region,produced by fragmentation of a 500 MeV/u86Kr beam

We have measured production cross-sections of the new neutron-rich isotopes⁵⁸Ti,⁶¹V,⁶³Cr,⁶⁶Mn,⁶⁹Fe,⁷¹Co and neighbouring isotopes that have been identified as projectile fragments from reactions between a 500 MeV/u⁸⁶Kr beam and a beryllium target. The isotope identification was performed with the zero-degree magnetic spectrometer FRS at GSI, using in addition time-of-flight and energy-loss measurements. The experimental production cross-sections for the new nuclides and neighbouring isotopes are compared with an empirical parametrization. The resulting prospects for reaching even more neutron-rich isotopes, such as the doubly-magic nuclide⁷⁸Ni, are discussed.This work is part of the Ph.D. Thesis of M. Weber     

Q β measurements and mass excess values for neutron deficient isotopes nearN∼Z∼40

Neutron deficient isotopes of⁸⁶Nb,⁸⁷Nb,⁸⁷Mo and⁸⁸Mo have been produced and identified. Their total decay positron energy have been measured and used to deduce mass excesses.     

Seven new neutron rich nuclides observed in deep inelastic collisions of 340 MeV40Ar on238U

The new nuclides⁵⁴Ti,⁵⁶V,^58–59Cr,⁶¹Mn,^63–64Fe, have been produced through⁴⁰Ar+²³⁸U reactions. The identification combining two (ΔE×E) informations as well as two time of flight measurements was quite unambiguous. Only those isotopes showing more than some twenty events were retained. Hints are given for production of 3 additional nuclides.