Pis’ma v ZhETF, vol. 110, iss. 1, pp. 7 - 8

Pauli-principle driven correlations in four-neutron nuclear decays

P. G. Sharov⁺¹⁾, L. V. Grigorenko^+∗×, A. N. Ismailova⁺, M. V. Zhukov^◦

⁺Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, 141980 Dubna, Russia

^∗National Research Nuclear University “MEPhI”, 115409 Moscow, Russia

^×National Research Centre “Kurchatov Institute”, 123182 Moscow, Russia

^◦Department of Physics, Chalmers University of Technology, S-41296 Göteborg, Sweden

Submitted 29 March 2019

Resubmitted 24 April 2019

Accepted 24

May 2019

DOI: 10.1134/S0370274X19130022

In the last decade there was a great progress in the

of the correlation space, but there should be still a lot.

studies of three-body decays (e.g. two-proton radioactiv-

The question can be asked here “How we should look for

ity) [1]. In contrast to “conventional” two-body decays,

physically meaningful signals in this wealth of informa-

three-body decays encrypt a lot of additional informa-

tion?”

tion in the momentum (energy and angular) correla-

The concept of “Pauli focusing” was proposed in [14]

tions of the decay products. Theoretical studies indicate

and further discussed, e.g., in [15, 16] for the bound

that both effects of the initial nuclear structure and the

state structure of three-body core+n+n systems. It was

decay mechanism may show up in the core+n+n and

demonstrated that due to the Pauli exclusion principle,

core+p+p fragment correlation patterns in various ways

the population of orbital configurations [lj1 ⊗lj2 ]_J for the

[2-13].

valence nucleons may induce strong spatial correlations

With the development of experimental techniques,

depending on the specific values of j₁, j₂, and J. Various

more and more “complicated” nuclear systems become

forms of such correlations were actively discussed as an

available for studies. One of such complicated cases

integral part of the two-nucleon halo phenomenon.

are isotonic neighbors of the 4n-halo systems located

Pauli focusing for 5-body systems was discussed in

beyond the neutron dripline, which are expected to

[17, 18] by example of8He nucleus described by the

have narrow resonance ground state decaying via 4n-

α+4n model. The complicated spatial correlation pat-

emission. The examples of such systems, which are now

terns were predicted. However, Pauli focusing has never

actively studied by experiment, are⁷H and²⁸O. The

been discussed for decays of the systems located above

4n-emission phenomenon is known to be widespread be-

the five-body core+4n breakup threshold.

yond the neutron dripline, and other possible candidates

The theoretical model we develop in this work for dy-

for such a decay mode, e.g.,¹⁸Be can be mentioned.

namics of 5-body decay is generalization of the improved

Their ground states are expected to be unbound with

direct 2p-decay model [19] to the 4n emission case. In di-

E_T ≲ 2 MeV (E_T is energy above the 4n decay thresh-

rect decay models it is assumed that emitted particles

old), and the decay mechanism can be assumed as “true”

are propagating to asymptotics in fixed quantum states,

4n emission: there are no sequential neutron emissions,

while the total decay energy is shared among single-

which mean that all neutrons are emitted simultane-

particle configurations described by R-matrix-type am-

ously.

plitudes. In the three-body case the direct decay model

In the 4n-emission (core+4n decay) the five-body

is powerful and reliable phenomenological tool broadly

correlations encrypt enormously more information com-

used in the application to 2n and 2p decays for lifetime

pared to the three-body decay. In five-body case

estimates [12,20-22] studies of two-nucleon correlations

the complete correlation pattern is described by 8-

[1, 19] and transitional dynamics [19, 23, 24].

dimensional space compared to the 2-dimensional space

As a result, in this work we have for the first time

in the three-body decay. The core+4n system permuta-

theoretically studied the correlations in emission of four

tion symmetries should decrease the effective dimension

nucleons in the nuclear 5-body decay. We have demon-

strated that for true five-body decays of core+4n sys-

¹⁾e-mail: sharovpavel@jinr.ru

tems the Pauli focusing - the cumulative effects of anti-

Письма в ЖЭТФ том 110 вып. 1 - 2

2019

P. G. Sharov, L. V. Grigorenko, A. N. Ismailova, M. V. Zhukov

symmetrization and population of definite orbital con-

I. Mukha, L. Grigorenko, K. Sümmerer et al. (Collabo-

figurations - may lead to distinctive correlation pat-

ration), Phys. Rev. C 77, 061303 (2008).

terns. These patterns are not very expressed in the one-

L. V. Grigorenko, T. D. Wiser, K. Miernik et al. (Collab-

dimensional energy and angular distributions. Here they

oration), Phys. Lett. B 677, 30 (2009).

can also be masked by other dynamical effects. However,

L. V. Grigorenko, T. D. Wiser, K. Mercurio, R. J. Char-

we have found a way to reliably extract the information

ity, R. Shane, L. G. Sobotka, J. M. Elson, A. H. Wuos-

maa, A. Banu, M. McCleskey, L. Trache, R. E. Tribble,

on internal structure from correlations. In addition to

and M. V. Zhukov, Phys. Rev. C 80, 034602 (2009).

the one-dimensional distributions, the correlated two-

I. A. Egorova, R.J. Charity, L. V. Grigorenko et al. (Col-

dimensional energy {ε_ik, ε_nm} and angular {θ_ik, θ_nm}

laboration), Phys. Rev. Lett. 109, 202502 (2012).

(i = k, n = m) distributions may be constructed. For

10.

L. V. Grigorenko, I. G. Mukha, and M. V. Zhukov, Phys.

core+4n decays in total five topologically nonequivalent

Rev. Lett. 111, 042501 (2013).

two-dimensional distributions exist. The reconstruction

11.

K. W. Brown, R. J. Charity, L. G. Sobotka et al. (Col-

of all these distributions requires a complete kinemat-

laboration), Phys. Rev. Lett. 113, 232501 (2014).

ical characterization of the core+4n decay, which is

12.

K. W. Brown, R.J. Charity, L. G. Sobotka et al. (Col-

within the reach of the modern experiment. We pro-

laboration), Phys. Rev. C 92, 034329 (2015).

pose to study the full set of the two-dimensional corre-

13.

L. V. Grigorenko, J. S. Vaagen, and M. V. Zhukov, Phys.

lated energy or/and angular distributions for derivation

Rev. C 97, 034605 (2018).

of the information concerning the quantum-mechanical

14.

B. V. Danilin, M. Zhukov, A. Korsheninnikov, V. Efros,

4n-decay configuration. We predict that taken together

and L. Chulkov, Sov. J. Nucl. Phys. 48, 766 (1988).

these distributions form a unique “fingerprint” of the

15.

M. V. Zhukov, B. Danilin, D. Fedorov, J. Bang,

decaying quantum state.

I. Thompson, and J. S. Vaagen, Phys. Rep. 231, 151

This work for P. G. Sharov and L. V. Grigorenko was

(1993).

supported in part by the Russian Science Foundation

16.

P. Mei and P. V. Isacker, Annals of Physics. 327, 1162

grant #17-12-01367.

(2012).

17.

M. V. Zhukov, A. A. Korsheninnikov, and M. H. Smed-

Full text of the paper is published in JETP Letters

berg, Phys. Rev. C 50, R1 (1994).

journal. DOI: 10.1134/S0021364019130046

18.

P. Mei and P. V. Isacker, Ann. Physics 327, 1182 (2012).

19.

T. A. Golubkova, X.-D. Xu, L. Grigorenko, I. Mukha,

1. M. Pfützner, M. Karny, L. V. Grigorenko, and K. Riis-

C. Scheidenberger, and M. Zhukov, Phys. Lett. B 762,

ager, Rev. Mod. Phys. 84, 567 (2012).

263 (2016).

2. L. V. Grigorenko and M. V. Zhukov, Phys. Rev. C 68,

20.

B. A. Brown and F. C. Barker, Phys. Rev. C 67, 041304

054005 (2003).

(2003).

3. I. Mukha, E. Roeckl, L. Batist, A. Blazhev, J. Döring,

21.

F. C. Barker, Phys. Rev. C 68, 054602 (2003).

H. Grawe, L. Grigorenko, M. Huyse, Z. Janas, R. Kirch-

22.

E. Olsen, M. Pfützner, N. Birge, M. Brown,

ner, M. L. Commara, C. Mazzocchi, S. L. Tabor, and

W. Nazarewicz, and A. Perhac, Phys. Rev. Lett 110,

P. V. Duppen, Nature 439, 298 (2006).

222501 (2013).

4. L. V. Grigorenko and M. V. Zhukov, Phys. Rev. C 76,

23.

I. Mukha, L. V. Grigorenko, X. Xu, L. Acosta et al. (Col-

014008 (2007).

laboration), Phys. Rev. Lett. 115, 202501 (2015).

5. L. V. Grigorenko and M. V. Zhukov, Phys. Rev. C 76,

24.

X.-D. Xu, I. Mukha, L. V. Grigorenko et al. (Collabora-

014009 (2007).

tion), Phys. Rev. C 97, 034305 (2018).

Письма в ЖЭТФ том 110 вып. 1 - 2

2019