A combination magnetic plus Si(Li)-Si(Li) sum-coincidence technique for in-beam studies of internal pair transitions

Abstract An intermediate-image magnetic plus Si(Li) combination pair spectrometer featuring an excellent energy resolution and a pair-line efficiency of 10 −3 , recently presented and demonstrated, has been made more universally applicable by reducing the background underlying the pair lines. The best background reduction is achieved by using two standard Si(Li) detectors and a sum-coincidence method. An experimental coincidence pair-line efficiency of 2.1 × 10 −4 for the 1911 keV E0 pair line in 64 Zn is achieved. In this typical case, the high-energy background (mainly caused by β + activity) is reduced by a factor of about 200 as compared with the direct spectrum of a single detector.

Cross Sections of232Th (p,xn+yp) Reactions at Ep= 6.8 to 20.2 MeV

Cross-sections for the (p, n), (p, 2n), (p, 3n) and (p, pn) + (p, d) reactions on 232Th targets were measured, by comparison with the K-shell ionization cross-section, for proton energies between 6.8 and 20.2 MeV. The results are compared with the predictions of the statistical and the pre-equilibrium model. For the (p, pn) reaction, the "clean knock-out" model is also considered.

Decay of 0 2 + states in88,92,94Zr andE0 systematics of Zr isotopes

Branching ratios ofE0 andE2 transitions depopulating the 0 2 + states of88, 92, 94Zr have been determined using conversion-electron and γ-ray spectroscopy. Two different lifetime-measurement methods were applied in the remeasurement of the half-lives of the 0 2 + states in92, 94Zr, yielding consistent results ofT 1/2(0 2 + ,92Zr)=85(15) ps andT 1/2(0 2 + ,94Zr)=280(40) ps. The monopole strengths extracted areρ 2(92Zr)=8.4(17) ×10−3 andρ 2(94Zr)=11.9(20)×10−3. The proton configurations of the 0 2 + states are discussed in view of these values and proton transfer data.

A walk-free centroid method for lifetime measurements with pulsed beams

Abstract A delayed-coincidence lifetime measurement method based on a comparison of walk-free centroids of time spectra is presented. The time is measured between the cyclotron rf signal and the pulse from a plastic scintillation detector followed by a fixed energy selection. The events to be time-analyzed are selected from the associated charge-particle spectrum of a silicon detector which is operated in coincidence with the scintillator, i.e. independently of the formation of the signal containing the time information. With this technique, with the micropulse fwhm of typically 500 to 700 ps, half-lives down to the 10 ps region can be measured. The following half-lives are obtained with th…

A method for high-resolution in-beam studies of internal pair transitions

Abstract A combination intermediate-image magnetic plus Si(Li) electron spectrometer has been adapted to internal pair formation measurements of cyclotron-induced reactions. The system is especially intended for the study of E0 transitions in the energy range from 1.5 to 8.6 MeV and to measurements of coincidences between internal pairs and heavy particles. The method is based on the fact that the electron and the positron spiral from the target to the detector simultaneously, the sense of rotation being of opposite sign. The energies of the particles are summed in a high-resolution cooled Si(Li) detector. Calculations of the spectrometer pair-line efficiency for E0 transitions versus trans…

AbsoluteE0 andE2 transition rates and collective states in116Sn

AbsoluteE0 andE2 transition rates in116Sn have been measured using several newly developed techniques. ManyE2 transitions are observed to have a collective character withB(E2) values of up to 60 W.u. The presence of deformed excited states in116Sn is discussed in view of the results obtained.

E0study of0+states near 5 MeV in208Pb

Strong E0 lines from the 4866 and 5237 keV ${0}^{+}$ states in $^{208}\mathrm{Pb}$ have been identified using a new high-energy conversion-electron spectrometry technique in the study of the $^{207}\mathrm{Pb}$(d,p${)}^{208}$Pb and $^{208}\mathrm{Pb}$(p,p'${)}^{208}$Pb reactions at ${E}_{\mathrm{d}=10}$ MeV and ${E}_{\mathrm{p}=17.3}$ MeV, respectively. No evidence for an E0 transition from the expected third ${0}^{+}$ state was found.

Radiative capture of protons by the deformed nuclide232Th

The excitation function for the radiative capture232Th(p, γ)233Pa has been determined in the proton energy range 7 to 20 MeV by an activation method. The results are compared with a compound nucleus model prediction and earlier experimental data for another deformed nuclide176Yb. As in previous cases an enhancement over the CN-model prediction is observed and the excitation of the giant dipole resonance via the direct-semidirect reaction process is a likely explanation. Supplementary measurements of the232Th (p, f) excitation function in the proton energy range 11–20 MeV have been performed.

A combination intermediate-image magnetic plus Si(Li) electron spectrometer for in-beam experiments

Abstract A magnetic lens plus Si(Li) combination in-beam beta spectrometer with focusing properties and field shape similar to those of an intermediate-image spectrometer is described. A high transmission and a large momentum band-width are achieved by placing both the target and the detector in a high magnetic field inside the lens. The beam enters the lens axially, and the Faraday cup is placed inside the lens. The spectrometer is well suited to singles conversion-electron spectroscopy, to electron-heavy particle coincidence measurements, to lifetime measurements and to studies of internal-pair transitions.

A swept-current magnetic lens plus Si(Li) electron spectrometer with simultaneous momentum and energy selection

Abstract A combined swept-current magnetic lens plus Si(Li) electron spectrometer with simultaneous momentum and energy selection is presented. The spectrometer is intended for in-beam measurements of conversion electron lines up to several MeV in energy and for nanosecond lifetime determinations, as well as for off-beam studies of continuous beta-ray spectra and conversion lines from short-lived activities. The sweeping of the lens current is automatized and the energy selection, synchronously with the momentum, is performed using a simple digital window arrangement. The performance of the spectrometer is demonstrated in conversion electron and continuous spectrum measurements. Different v…

Collective states in 116Sn

Determination of ion-induced K-shell ionization cross sections by comparison with nuclear Coulomb excitation

Abstract A new method for the determination of cross sections for K-shell ionization of heavy atoms by charged particles is proposed. The method is based on a comparison of photon lines due to K X-rays and low-energy γ-rays, the latter ones being produced in nuclear Coulomb excitation with accurately known cross sections. This procedure applies within a limited energy range to the study of targets comprising deformed even nuclei, but can also be extended to other targets having Z≳30. A test of the new technique has been carried out for Gd, W, Th and U natural targets irradiated by 4.75 MeV protons. For Th, also energies of 6.80–10.10 MeV were used. The results are briefly discussed with ref…

Electromagnetic properties of low-spin states in102, 104Pd

Electromagnetic transitions from low-lying 0+, 2+, 4+ and 3− states in102, 104Pd have been studied using (p, 2n) and (p, p′) reactions and Coulomb excitation. TheE2 transition probabilities from the 0 3 + state in102Pd (13 W.u.) and from the 02/+ state in104Pd (14 W.u.) are somewhat low for two-phonon states. Generally, theE2 transition rates are reasonably well reproduced by the IBA-2 and by the boson-expansion description. The intruding 0 2 + state (t1/2=14.3 ns) in102Pd is connected to the 22/+ and 2 3 + states via strong E2 transitions: B(E2; 0 2 + → 2 2 + )=96±40 W.u.; B(E2; 2 3 + → 0 2 + =17±11 W.u.

Decay characteristics of 0 2 + and 0 3 + states in112Cd and114Cd

Absolute rates ofE0 andE2 transitions depopulating 0 2 + and 0 3 + states in112Cd and114Cd have been determined using conversion-electron andγ-ray spectroscopy, and double Coulomb excitation. The collectivity of these states is established and discussed.