The structure of the light exotic nucleus
8He was investigated using direct reactions of the
8He SPIRAL beam on a proton-rich target. The (p,p') scattering to the
2
1
+
state, the (p,d)
7He and (p,t)
...6He transfer reactions, were measured at the energy
E
l
a
b
=
15.7
A.MeV
. The light charged particles (p,d,t) were detected in the MUST Si-strip telescope array. The excitation spectrum of
8He was extracted from the (p,p') reaction. Above the known
2
1
+
excited state at 3.6 MeV, a second resonance was found around 5.4 MeV. The cross sections were analyzed within the coupled-reaction channels framework, using microscopic potentials. It is inferred that the
8He ground state has a more complex neutron-skin structure than suggested by previous
α
+
4
n
models assuming a pure
(
1
p
3
/
2
)
4
configuration.
The odd-Z 251Md nucleus was studied using combined γ-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the 5211/2- configuration, another ...rotational structure has been identified using γ-γ coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Using the transition intensities that depend on the gyromagnetic factor, a 5147/2- single-particle configuration has been inferred for this band, i.e., the ground-state band. A physical background that dominates the electron spectrum with an intensity of ≃60% was well reproduced by simulating a set of unresolved excited bands. Moreover, a detailed analysis of the intensity profile as a function of the angular momentum provided a method for deriving the orbital gyromagnetic factor, namely gK = $0.69$ $^{+0.19}_{-0.16}$ for the ground-state band. The odd-Z 249Md was studied using γ-ray in-beam spectroscopy. Evidence for octupole correlations resulting from the mixing of the Δl = Δj = 3 5213/2- and 6337/2+ Nilsson orbitals were found in both 249,251Md. Here, a surprising similarity of the 251Md ground-state band transition energies with those of the excited band of 255Lr has been discussed in terms of identical bands. Lastly, Skyrme-Hartree-Fock-Bogoliubov calculations were performed to investigate the origin of the similarities between these bands.
A gas secondary electron detector Drouart, A; Mazur, C; Alamanos, N ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2002, Letnik:
477, Številka:
1
Journal Article
Recenzirano
A new Secondary Electron gas Detector (SED) is under development to be used in conjunction with an emissive foil to detect low energy heavy ions as an alternative to micro-channel plates. It could ...measure position and time of flight. Secondary electrons are accelerated to
10
keV
so that they can cross through the
0.9
μm
Mylar entrance window. The electrons then are multiplied in the isobutane gas of the detector at 4–
10
Torr
. A time resolution of
150
ps
and a spatial resolution of
3
mm
have been obtained by using californium fission fragments on a prototype detector of
7×7
cm
2
. The advantage of the SED against MCP is that its size is not limited. Our final goal is to build a large size detector
(15×40
cm
2)
that will operate at the focal plane of the VAMOS magnetic spectrometer at GANIL.
Study of N = 16 for Ne isotopes Gillibert, A.; Obertelli, A.; Alamanos, N. ...
The European physical journal. ST, Special topics,
11/2007, Letnik:
150, Številka:
1
Journal Article
Recenzirano
27Ne has been investigated through the one neutron transfer reaction 26Ne(d,p)27Ne in inverse kinematics at 9.7MeV/nucleon. The results support the existence of a low lying negative parity state in ...27Ne which is a signature of a reduced sd-fp shell gap in the N = 16 neutron rich region, at variance with stable nuclei.
The study of nuclei far from stability interacting with simple target nuclei, such as protons, deuterons,
3He and
4He implies the use of inverse kinematics. The very special kinematics, together with ...the low intensities of the beams calls for special techniques. In july 2002 we tested a new detector, in which the detector gas is the target. This allows in principle a 4π solid angle of the detection, and a big effective target thickness without loss of resolution. The detector developped, called Maya, used isobuthane
C
4
H
10 as gas in present tests, and other gases are possible. The multiplexed electronics of more than 1000channels allows the reconstruction of the events occuring between the incoming particle and the detector gas atoms in 3D. Here we were interested in the elastic scattering of
8He on protons for the study of the isobaric analogue states (IAS) of
9He. The beam, in this case, is stopped in the detector. The resonance energy is determined by the place of interaction and the energy of the recoiling proton. The design of the detector is shown, together with some preliminary results are discussed.
Quantum tunnelling through a potential barrier (such as occurs in nuclear fusion) is very sensitive to the detailed structure of the system and its intrinsic degrees of freedom. A strong increase of ...the fusion probability has been observed for heavy deformed nuclei. In light exotic nuclei such as 6He, 11Li and 11Be (termed 'halo' nuclei), the neutron matter extends much further than the usual nuclear interaction scale. However, understanding the effect of the neutron halo on fusion has been controversial--it could induce a large enhancement of fusion, but alternatively the weak binding energy of the nuclei could inhibit the process. Other reaction channels known as direct processes (usually negligible for ordinary nuclei) are also important: for example, a fragment of the halo nucleus could transfer to the target nucleus through a diminished potential barrier. Here we study the reactions of the halo nucleus 6He with a 238U target, at energies near the fusion barrier. Most of these reactions lead to fission of the system, which we use as an experimental signature to identify the contribution of the fusion and transfer channels to the total cross-section. At energies below the fusion barrier, we find no evidence for a substantial enhancement of fusion. Rather, the (large) fission yield is due to a two-neutron transfer reaction, with other direct processes possibly also involved.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The blocking technique in single crystals is a direct method to investigate the presence of long fission time components. With a lead beam impinging on a germanium single crystal, we tried to produce ...compound nuclei (CN) with atomic number Z = 114 at high excitation energy. Blocking patterns for reaction products are reconstructed with position sensitive detectors at 20 deg relative to the beam direction. The Z and the energies of all products are measured with DeltaE-E telescopes of the 4pi INDRA array, so that all reaction channels are unambiguously identified. With this setup, we can reach long fission times ( > 10-18 s) that can be associated with CN fissions. However, in contrast to previous experiments in which such long fission times could be measured for Z = 120 and 124, no hint of long lifetimes within our sensitivity limit for Z = 114 was observed, which may be due to the neutron deficiency of the formed isotopes.
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