Pis’ma v ZhETF, vol. 111, iss. 8, pp. 483 - 484

April 25

States of¹²N with enhanced radii

A. S. Demyanova^a,¹⁾ A. N. Danilov^a, A. A. Ogloblin^a, V. I. Starastsin^a, S. V. Dmitriev^a, W. H. Trzaska^b,

S. A. Goncharov^c, T. L. Belyaeva^d, V. A. Maslov^e, Yu. G. Sobolev^e, Yu. E. Penionzhkevich^e, S. V. Khlebnikov^f ,

G. P. Tyurin^f , N. Burtebaev^g, D. Janseitov^e,g, Yu. B. Gurov^h, J. Louko^b, V. M. Sergeev^a,c

^aNational Research Centre Kurchatov Institute, 123182 Moscow, Russia

^bDepartment of Physics, University of Jyväskylä, FI-40014 Jyväskylä, Finland

^cLomonosov Moscow State University, 119991 Moscow, Russia

^dUniversidad Autónoma del Estado de México, 50000 Toluca, México

^eFlerov Laboratory for Nuclear Research, Joint Institute for Nuclear Research, 141980 Dubna, Russia

^fV. G. Khlopin Radium Institute, 194021 St. Petersburg, Russia

^g Institute of Nuclear Physics, National Nuclear Center of Republic of Kazakhstan, 050032 Almaty, Republic of Kazakhstan

^hNational Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409 Moscow, Russia

Submitted 18 March 2020

Resubmitted 18 March 2020

Accepted 24

March 2020

DOI: 10.31857/S1234567820080017

Recently the evidence of the excited states of light

presumable have halos are determined in a more com-

nuclei with enlarged radii, located close to and above the

plicated manner: replacing the neutron in the halo state

particle emission threshold, was convincingly demon-

with a proton does not necessarily lead to the appear-

strated (see, e.g., [1] and references therein). The ex-

ance of a similar proton structure. The fact is that the

istence of neutron halos in the short-lived excited states

appearance of a halo is determined by the proximity of

of some stable and radioactive nuclei was revealed, in

the valence nucleon to the emission threshold, and it can

particular, by the asymptotic normalization coefficient

be very different for a neutron and a proton. One notable

(ANC) analysis of the neutron-transfer reactions [2, 3].

example is the IAS of mirror¹³C and¹³N nuclei.¹³C

The ANC analysis of the¹¹B(d,p)¹²B reaction at

in the 1/2⁺, 3.09-MeV state has a neutron halo [2, 3]

E_lab = 21.5 MeV was carried out in our group [4]. Radii

that satisfies all halo criterions. The 1/2⁺, 2.37-MeV

of the valence neutron for the first five excited states of

IAS in¹³N does not lie in the discrete spectrum, but in

¹²B were determined. Calculations showed that the rms

the continuum spectrum, and therefore the proton wave

radii of the last neutron in the second 2^-(1.67 MeV)

function differs from the neutron one. An increase of the

and the third 1^-(2.62 MeV) excited states of¹²B far

¹³N radius in this state is also observed [5].

exceed those for the ground state (g.s.) and the first

Now we study excited states of¹²N, namely the

2⁺(0.95 MeV) excited state. Moreover, a probability of

2⁺(0.96 MeV), 2^-(1.19 MeV), and 1^-(1.80 MeV) states

the last neutron to be outside the range of the interac-

of 12N. We propose to use the Modified Diffraction

tion radius, so-called D₁ coefficient, was obtained to be

Model (MDM) method [5-7] and apply it to analyze the

53 and 62 %, respectively. It should be noted that a for-

(3He,t) reaction data. Obtained radii for12N in the 2-

mal criterion of a halo state is that D₁ should be more

and 1^- states will be compared with those received for

than 50 % and it is fulfilled in both cases.

the excited states of¹²B [4]. The problem is that existing

Accordingly to charge independence of nuclear

data are not completed enough to make definite conclu-

forces, mirror nuclei are isobars that have proton

sion about the radii of the 2^- and 1^- states in¹²N.

and neutron numbers interchanged. Some states of

The existing in the literature data are presented only at

mirror nuclei with the same quantum numbers (isospin,

three energies: 36 [8], 49.8 [9], and 81 MeV [10]. The data

spin/parity), isobaric analogue states (IAS), can form

at 36 MeV contain only the angular distributions for

the isospin or isotopic multiplets (doublets, triplets,

the g.s. and the 0.96-MeV states. The data at 49.8 MeV

etc.) and then approximately have the same structure

contain the angular distributions for the g.s., 0.96-MeV,

and radii.

and 1.20-MeV states. The data at 81 MeV contain all

Natural question arises: what we can expect in the

interested for us states, but they present only one in-

IAS of¹²B in the mirror¹²N nucleus? The IAS that

dinstinct oscillation in the angular distributions. The

angular distribution for the 0.96-MeV state obtained at

¹⁾e-mail: a.s.demyanova@bk.ru

81 MeV [10] is not comparable with others, if it would

Письма в ЖЭТФ том 111 вып. 7 - 8

2020

483

4^∗

484

A. S. Demyanova, A. N. Danilov, A. A. Ogloblin et al.

be drawn as a function of linear transferred momentum.

the 1.80 MeV state is 3.0±0.1 fm. These values are larger

This fact stimulate us to carried out a new experiment

than rms radius of the g.s. of¹²N 2.47 ± 0.07 fm [12].

on the¹²C(³He,t)¹²N reaction at E(³He)= 40 MeV.

The diffraction and rms radii of¹²C in the IAS were

The measurements were conducted at the University

determined by the MDM from the inelastic³He +¹²C

of Jyväskylä (Finland) using the K130 cyclotron [11] to

scattering [9]. Within the error bars, the rms radii of

produce a³He beam at E(³He) = 40 MeV. The 150 cm

¹²C in the 15.11-MeV 1⁺ and the 16.57-MeV 2^- states

diameter Large Scattering Chamber was equipped with

agree with the rms radii of their IAS in¹²N. The pre-

four ΔE-E detector telescopes, each containing two in-

liminary ANC analysis in which excited states of¹²C

dependent ΔE detectors and one common E detector.

are considered as a weakly bounded (effective positive

So each device allowed carrying out measurements at

energy of a valence proton, ε ≈ 0.01 MeV), gives ap-

two angles. The measurements in c.m. angular range 10^◦

proximately the same radii. Moreover, D₁ coefficient for

were conducted in one exposure. The differential cross

the 2^- state is more than 50 %, which indicate that the

sections of the¹²C(³He,t)¹²N reaction were measured

16.57-MeV 2^- state of¹²C can be considered as a proton

in the c.m. angular range of 8^◦-69^◦. Self-supported¹²C

halo-like state. Complete results of the ANC analysis

foils of 0.23 and 0.5 mg/cm² thicknesses were used as

will be published later.

targets. The beam intensity was about 20 particle nA.

Finally, we revealed that¹²B,¹²N, and¹²C in the

Triton angular distributions for the g.s. and three

IAS with T = 1, and spin-parities 2^- and 1^- have in-

first excited states of¹²N: 0.96-MeV 2⁺, 1.19-MeV 2^-,

creased radii and exhibit properties of neutron and pro-

and 1.80-MeV 1^- were measured. The resulting differ-

ton halo states.

ential cross sections for the¹²C(³He,t)¹²N reaction with

Full text of the paper is published in JETP Letters

DWBA calculations are presented in Fig. 1.

journal. DOI: 10.1134/S0021364020080020

A. A. Ogloblin, A. N. Danilov, A.S. Demyanova,

S. A. Goncharov, T. L. Belyaeva, and W. Trzaska, in Nu-

clear Particle Correlations and Cluster Physics, World

Scientific, Singapore (2017), p. 311.

Z. H. Liu, C. J. Lin, H. Q. Zhang, Z. C. Li, J. S. Zhang,

Y. W. Wu, F. Yang, M. Ruan, J. C. Liu, S. Y. Li, and

Z. H. Peng, Phys. Rev. C 64, 034312 (2001).

T. L. Belyaeva, R. Perez-Torres, A. A. Ogloblin,

A. S. Demyanova, S. N. Ershov, and S. A. Goncharov,

Phys. Rev. C 90, 064610 (2014).

T. L. Belyaeva, S. A. Goncharov, A. S. Demyanova,

A. A. Ogloblin, A. N. Danilov, V. A. Maslov,

Yu. G. Sobolev, W. Trzaska, S. V. Khlebnikov,

G. P. Tyurin, N. Burtebaev, D. Janseitov, and

E. Mukhamejanov, Phys. Rev. C 98, 034602 (2018).

A. S. Demyanova, A. A. Ogloblin, A.N. Danilov,

T. L. Belyaeva, S. A. Goncharov, and W. Trzaska, JETP

Fig. 1.

Triton angular distributions from the

Lett. 104, 526 (2016).

¹²C(³He,t)¹²N reaction at E(³He) = 40 MeV popu-

A. S. Demyanova, A.A. Ogloblin, S. A. Goncharov,

lated the

1+(g.s),

2⁺(0.96 MeV),

2-(1.19 MeV), and

A. N. Danilov, T. L. Belyaeva, and W. Trzaska, Phys.

1^-(1.80 MeV) states of¹²N. The curves correspond to the

Atom. Nucl. 80, 831 (2017).

DWBA calculations

A. N. Danilov, T. L. Belyaeva, A. S. Demyanova,

S. A. Goncharov, and A. A. Ogloblin, Phys. Rev. C 80,

054603 (2009).

Let us discuss the results of the MDM analysis of

K. P. Artemov, Y.A. Glukhov, V.Z. Goldberg,

the existing and our new data on the¹²C(³He,t)¹²N re-

V. V. Davydov, I. P. Petrov, and V. P. Rudakov, Yad.

action at 40 MeV.

Fiz. 11, 43 (1970).

We try to make estimations of rms radius of the g.s

G. Ball and J. Cerny, Phys. Rev. 177, 1466 (1969).

of¹²N and got value: 2.8 ± 0.4 fm, which is consistent

10.

W. A. Sterrenburg, M. N. Harakeh, S. Y. van Der Werf,

with the estimates resulting from our DWBA analysis -

and A. van Der Woude, Nucl. Phys. A 405, 109 (1983).

2.9 fm.

11.

W. H. Trzaska, P. Heikkinen, A. N. Danilov, A.S. De-

myanova, S. V. Khlebnikov, T. Yu. Malamut,

Also the rms radii for the 1.19 MeV and 1.80 MeV

V. A. Maslov, A. A. Ogloblin, and Yu.G. Sobolev,

states were determined using MDM. The 1.19 MeV state

Nucl. Instrum. Methods Phys. Res. A 903, 241 (2018).

is excited by transfer of two angular momentums L = 0

12.

A. Ozawa, T. Suzuki, and I. Tanihata, Nucl. Phys. A

and L = 2 and complicates analysis a bit. An average

693, 32 (2001).

value was found to be 2.8 ± 0.3 fm. The rms radius for

Письма в ЖЭТФ том 111 вып. 7 - 8

2020