179 research outputs found
Three-body correlations in direct reactions: Example of Be populated in reaction
The Be continuum states were populated in the charge-exchange reaction
H(Li,Be) collecting very high statistics data ( events) on the three-body ++ correlations. The
Be excitation energy region below MeV is considered, where the
data are dominated by contributions from the and states. It is
demonstrated how the high-statistics few-body correlation data can be used to
extract detailed information on the reaction mechanism. Such a derivation is
based on the fact that highly spin-aligned states are typically populated in
the direct reactions.Comment: submitted to Physical Review
New insight into the low-energy He spectrum
The spectrum of He was studied by means of the He(,)He
reaction at a lab energy of 25 MeV/n and small center of mass (c.m.) angles.
Energy and angular correlations were obtained for the He decay products by
complete kinematical reconstruction. The data do not show narrow states at
1.3 and 2.4 MeV reported before for He. The lowest resonant
state of He is found at about 2 MeV with a width of 2 MeV and is
identified as . The observed angular correlation pattern is uniquely
explained by the interference of the resonance with a virtual state
(limit on the scattering length is obtained as fm), and with
the resonance at energy MeV.Comment: 5 pages, 4 figures, 2 table
Cannibalism as a life boat mechanism
Under certain conditions a cannibalistic population can survive when food for the adults is too scarce to support a non-cannibalistic population. Cannibalism can have this lifeboat effect if (i) the juveniles feed on a resource inaccessible to the adults; and (ii) the adults are cannibalistic and thus incorporate indirectly the inaccessible resource. Using a simple model we conclude that the mechanism works when, at low population densities, the average yield, in terms of new offspring, due to the energy provided by one cannibalized juvenile is larger than one
10He low-lying states structure uncovered by correlations
The 0+ ground state of the 10He nucleus produced in the 3H(8He,p)10He
reaction was found at about MeV (\Gamma ~ 2 MeV) above the
three-body 8He+n+n breakup threshold. Angular correlations observed for 10He
decay products show prominent interference patterns allowing to draw
conclusions about the structure of low-energy excited states. We interpret the
observed correlations as a coherent superposition of the broad 1- state having
a maximum at energy 4-6 MeV and the 2+ state above 6 MeV, setting both on top
of the 0+ state "tail". This anomalous level ordering indicates that the
breakdown of the N=8 shell known in 12Be thus extends also to the 10He system.Comment: 5 pages, 5 figure
Detector array for the H nucleus multi-neutron decay study
Setup fitting the requirements for the detailed study of the five-body decay
of the 7H nucleus obtained as a result of the proton transfer from the 8He
projectiles to the deuterium target nuclei is being built at the radioactive
beam line of ACCULINNA-2 separator in the G.N. Flerov Laboratory of Nuclear
Reactions. Described here is the assembly of 100 BC-404 plastic scintillators,
intended for neutron detection, the annular Si detector telescope for the 3He
recoils, and the detector array providing the --TOF registration
of 3H nuclei emitted at the 7H decay. Results obtained by the Monte Carlo
simulations made for the energy values and flight passes of all these particles
are given together with the luminosity expected for the discussed experiments
Search for 2p Decay of the First Excited State of 17 Ne
Structure of nuclei located near and beyond the drip-lines plays important role in the explosive astrophysical processes. The problem of two-proton decay of the 17Ne first excited state is a good example of such situation. The two-proton radiative capture is a possible bypass of the 15O waiting point in the rp-process. The rate of this process drastically depends on the value of the weak
Study of Proton and Deuteron Pickup Reactions 2H(10Be,3He)9Li an 2H(10Be,4He)8Li with 44 A MeV 10Be Radioactive Beam at ACCULINNA-2 Fragment Separator
The proton and deuteron pickup reactions 2H(10Be,3He)9Li and\\
2H(10Be,4He)8Li radioactive beam produced by the new fragment separator
ACCULINNA-2 at FLNR, JINR\@. These measurements were initially motivated as
test reactions intended for the elucidation of results obtained in the study of
the extremely neutron-rich 7H and 6H systems created in the 2H(10Be,3He)9Li and
2H(10Be,4He)8Li reactions using the same setup. In the 2H(10Be,3He)9Li reaction
the 9Li ground-state () and its first excited state (2.69~MeV, )
were identified in the low-energy region of its excitation spectrum. The
differential cross sections for the 9Li g.~s.) population were extracted at
forward center-of-mass angles () and compared with the FRESCO
calculations. Spectroscopic factor of , derived by a model for the
10Be9Li(g.s.) clustering was found in accord with the experimental
data. The energy spectrum of 8Li populated in the 2H(10Be,4He)8Li reaction
shows the strong peak which corresponds to excitation of the second excited
state of 8Li (2.25 MeV, ). The fact that the ground and the first excited
states of 8Li were not observed is fully consistent with Shell-Model
calculations carried out for the 10Be g.\,s. and 8Li level structure applying
momentum selection rules
The H states studied in the reaction and evidence of extremely correlated character of the H ground state
The extremely neutron-rich system H was studied in the direct
H transfer reaction with a 26
MeV secondary He beam. The measured missing mass spectrum shows a
resonant state in H at MeV relative to the H+ threshold.
The population cross section of the presumably -wave states in the energy
range from 4 to 8 MeV is
b/sr in the angular range . The
obtained missing mass spectrum is free of the H events below 3.5 MeV
( b/sr in the same angular
range). The steep rise of the H missing mass spectrum at 3 MeV allows to
show that MeV is the lower limit for the possible resonant state
energy in H tolerated by our data. According to paring energy estimates,
such a MeV resonance is a realistic candidate for the H ground
state (g.s.). The obtained results confirm that the decay mechanism of the
H g.s.\ (located at 2.2 MeV above the H+ threshold) is the
``true'' (or simultaneous) emission. The resonance energy profiles and the
momentum distributions of the sequential H \,\rightarrow \,
^5H(g.s.)+n\, \rightarrow \, ^3H+ decay fragments were analyzed by the
theoretically-updated direct four-body-decay and sequential-emission
mechanisms. The measured momentum distributions of the H fragments in the
H rest frame indicate very strong ``dineutron-type'' correlations in the
H ground state decay.Comment: 9 pages, 11 figure
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