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Isobaric Multiplets of Light Nuclei

#1744


Investigation of Isobaric Multiplets of Light Nuclei with T=2 Near Neutron-Decay Thresholds Using Tritium Beam

Tech Area / Field

  • PHY-ANU/Atomic and Nuclear Physics/Physics

Status
3 Approved without Funding

Registration date
21.12.1999

Leading Institute
Russian Academy of Sciences / Physical Technical Institute, Russia, St Petersburg

Supporting institutes

  • VNIIEF, Russia, N. Novgorod reg., Sarov

Project summary

Threshold phenomena in nuclear reactions grant the unique opportunity of the detailed study of nuclear structure in the energy range, where new particles are nascent and new channels of reaction are opened. Near the threshold occurs the radical inner alteration of the nuclear system and, as effect, violent changes the energy dependence of the physical parameters of nucleus.

The energy thresholds of reactions are critical states of the nuclear matter. The most bright threshold irregularities manifest in experiments with 1p-shell nuclei. It is very complicated to investigate the phenomena among the middle and heavy nuclei, though the anomalous behavior of cross sections near the threshold of analogue channels is observed too.

In terms of nuclear theory to solve problem of the wave function reconstruction, it is necessary to determine all overlapping integrals, provided that its energy dependence is known. Near of the thresholds the strict analytic expression of the function versus energy may be derived by means of Feshbach’s microscopic theory of nuclear reactions [1], which we use as basis for creation the theory of threshold phenomena (TTP) [2].

The principal merit of the TTP is capability obtain the energy dependence of physical value in analytic form. The wave function parameters of the system have clear physical sense, and they are determined by overlapping integrals of the wave functions of different reaction channels. Analysis of experimental data by means of this approach gives opportunity to deduce valuable information about the reaction channel wave functions and nuclear interactions, on the mechanism of reactions, the quantum characteristics of excited states and decay parameters. Other well-known methods of the investigation cannot contend for quantity and accuracy of derivable data with the proposed TTP approach.

Isobaric multiplet is a set of nuclei at mass number A and with different mix of neutrons and protons. It is found, light nuclei with A < 20 and at minimal isospin value Т = 0 (A - even), 1/2 (A - odd) have a minimum energy of ground states. Nuclei with isospin value, differed from minimum one by T = 2 have the ground state energy higher by 20-30 MeV beside the ground states with T = 0, 1/2. As a rule, properties of the ground states with T = 2, 5/2 are insufficiently known.

Nuclei at isospin T = 2 are beta- or nucleon-unstable. To study these nuclei the efficient and accurate methods for experimental and theoretical research are needed. We had elaborated such methods and examined its at investigation of 10Be, 10Li nuclei of multiplet A = 10 with T = 2 [2,3,4]. The theoretical approach have been applied to analyze excitation functions of 7Li + p elastic scattering [2,5] and T(d,4He)n reaction [6,7,8]. Using TTP approach, we measured differential cross sections of 9Be(p,4He)6Li, 9Be(4He,n)12C and 10B(4He,p)13C reactions [9,10,11] in case of separately standing resonances.

It is proposed to investigate nuclei of T = 2 isobaric multiplets with A = 10 and 14 that have displayed the giant anomalies in the excitation function near neutron thresholds.

The present project dedicates investigation not separate nuclei at T = 2. In case of A = 10, we are going to study 10Li, 10Be, 10B,10C, 10N nuclei. This approach will permit to obtain additional information about Coulomb rearrangement energies and nuclear structure of the multiplet, and will raise the reliability of extrapolation of the level characteristics for the stable nuclei to the 10Li and 10N nucleon-unstable ones.

From formal point of view, solution of the defined project task supposes measurement of excitation functions near the threshold for all energetically opened reactions that lead to the A compound nucleus. There is technically hard to carry out such comprehensive research program.


The research method is based on precise measurement of reaction excitation functions near energy threshold of compound nucleus decay, and subsequent theoretical analysis of the threshold anomaly by meansof the TTP [2]. Energy resolution needed for the excitation function measurements and its reliable theoretical

analysis should not be worse of 10 keV, and the error of experimental data must be considerably less than value

of the threshold anomaly, i.e. 1-2% at most.

The T = 2 isobaric multiplet with A = 10 will be investigated by means of following beams: 3H, 3He and the 7Li

targets. Characteristics and properties of the 10Li, 10N nuclei will be derived from data on the 10Be and 10B

nuclei, using the extrapolation method [12] based on the Coulomb energy systematic.

The same methodology will be used to study the T = 2 multiplet with A = 14 (14B, 14C, 14N, 14O, 14F). In this

case the number of basic reactions with T = 1 a little more: 10Be(4He,p)13B , 11B(t,p)13B , 11B(3He,p)13C ,

13C(p,p’)13C* (T = 3/2). Investigation of 11B+t reaction is planned in this project.

The theoretical analysis of the excitation functions will be carry out using Feshbach’s theory [1] and the

approach TTP [2], developed on it base. The investigation may cover all interesting energy interval,

however, most precise analysis is found in the range Ethr1 MeV near reaction thresholds. In this region the

analytical energy dependence of collision matrix and, hence, excitation function are known. Due to known

energy dependence near the thresholds, reduced overlapping integrals of channel wave functions will be

determined, in particular, reduced partial and total widths of compound nucleus levels, orbital moments and

parities of levels, branching ratio of direct interactions and compound contributions to the reaction mechanism.

The investigation of isobaric multiplet with T = 2 allows to carry out comparative analysis of Coulomb

rearrangement energies and structure of the nuclei, theirs radii, densities, reduced partial widths and the

amplitudes of interaction. The comparison of properties two and more the T = 2 multiplets with different A

enables to reveal new regularities in structure of light nuclei.

Duration of the proposed supplement to the Project is equal to 36 months. The project activities will take

place at A.F.Ioffe Physical Technical Institute, RFNC All-Russia Scientific Research Institute of Experimental

Physics. Expected scope of activity is approximately equal to 580 person-months.

References

1. Feshbach H. Ann. of Phys., v. 5, p. 357-390 (1958).


2. Abramovich S.N., Guzhovskii B.Ja., Lazarev L.M. Sov.J.Part.Nucl. v. 23(2), p.129, March-April 1992.
3. Abramovich S.N., Guzhovskii B.Ja., Lazarev L.M. Phys. Part. Nucl. v. 26(4), p.423, July-August 1995.
4. Abramovich S.N., Guzhovskii B.Ja., Zvenigorodskii A.G., Trusillo S.V. Sov.J.Nucl.Phys., v.30, p. 665, 1979.
5. Malmberg P.R. Phys.Rev.,v.101,p.114-118, 1956.
6. Lazarev L.M.,Izv.RAN , Ser. Fiz.,v.59,p.171,1995.
7. Jarmie N.,Brown R.E.,Hardekopf R.A.-Phys.Rev.,v.C29,p.2031,1984.
8. Brown R.E.,Jarmie N., Hale G.M.-Phys.Rev.,v.C35,p.1999,1987.
9. S.N.Abramovich, L.N.Generalov, A.G.Zvenigorodskii, L.M.Lazarev, V.G.Kiptily, Proc. International Workshop on Precise Measurements in Nuclear Spectroscopy, September 2-5, 1996, Sarov, Russia. Topics of Atomic Power Science and
Technology (VANT), item: Physics of Nuclear Reactors. Special Issue, 1997, p.194.

10. V.G.Kiptily, D.N.Doinikov, V.O.Naidenov, I.A.Polunovskii, I.N.Chugunov, A.E.Shevelev, S.N.Abramovich, V.A.Agureev,


S.V.Trusillo, Proc. International Workshop on Precise Measurements in Nuclear Spectroscopy, September 2-5, 1996,

Sarov, Russia. Topics of Atomic Power Science and Technology (VANT), item: Physics of Nuclear Reactors. Special

Issue, 1997, p.223.

11. V.G.Kiptily et. al. Final Report of ISTC Project 161B-96, Moscow, 1998 ( unpublished).


12. Antony M.S., Britz J., Bueb J.B., Pape A. Atomic Data and Nucl. Data Tables, v.33, p. 447, 1985.


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