Fragmentation of relativistic

9Be and 14N nuclei in nuclear track emulsionD. A. Artemenkov

JINR, DubnaBECQUREL Collaboration

web site: http://becquerel.jinr.ru/

Contents• Introduction• Roots• Fragmentation of relativistic 9Be nuclei• Fragmentation of relativistic 14N nuclei• Summary

Introduction• The fragmentation of a large variety of light nuclei was investigated using the emulsions exposed to few A GeV nuclear beams at JINR. In this energy range, the pattern of the relativistic fragmentation loses sensitivity either to the collision energy or to the particular properties of a target nucleus.•The results of investigations of the relativistic 9Be, 14N nuclei fragmentation in emulsion which entails the production of He fragments are presented.•The study of the 9Be fragmentation at relativistic energies gives the possibility of observing the reaction fragments which are the decay products of unbound 8Be nuclei(without combinatorial background). •The results obtained for the 9Be, 14N nuclei are compared with similar data for the 12C, 16O and 22Ne nuclei.

RootsThe 12С3 and 16O4 fragmentation at the energy of 3.65 A GeV was studied at JINR Synchrophasotron* .

*V.V. Belaga et al., Phys. At. Nucl., vol. 58 1905 (1995)

12C3 , 3.65 A GeV

The 16О4 fragmentation were investigated using a large amount of information (641 events). An analysis of the angular correlations gave evidence that the angular momentum was transferred to the systems of fragments and that the cascade decays via 8Be and 12C nuclei were nonessential**.

(PAVICOM image)16О4 , 3.65 A GeV

**F.A. Avetyan et al., Phys. At. Nucl., vol. 59 №1 (102-108) 1996

Fragmentation of relativistic 9Be nuclei at 1.2 A GeVNuclear emulsions were exposed to relativistic 9Be nuclei at the JINR Nuclotron. The beam of relativistic 9Be nuclei was obtained in the 10B9Be fragmentation reaction with polyethylene target.

with heavy fragment of target nucleus

“white” star (PAVICOM image)

.mov.avi

.avi .mov

9Be8Be

n4He4He

The method of nuclear emulsions used in the present report allows one to observe the charged component of the relativistic 9Be 2He+n fragmentation channel. Owing to a good angular resolution of this method it is possible to separate the 9Be fragmentation events which are accompanied by the production of an unstable 8Be nucleus with its subsequent breakup to two alpha-particles.

find: ~200 events of 9Be 2He fragmentation Angular measurements for 131 events were carried out with an accuracy not worse then 4.5 10-3 rad.

n4He

4He

Energy Level Diagram 9Be

Opening angle between two He fragments for the channel 9Be2He

Θ9Be

HeHe

.2.27 mrad

.7.4 mrad

Excitation energy Q2 for the channel 9Be2

mMQ 222

22

1

22

ii

PM

2+, 8Be(2. 9 MeV, 1. 5 MeV)

0+, 8Be(92 keV, 6.8 еV)

Transverse momentum of He fragments (laboratory system )

Transverse momentum of He fragments (c.m.s.)

)sin(0 ApPT

n

iTiTiTi n

1

* /PPPp0 =1.9 A GeV/cA=4 (in the assumption 4He)

cMeVPT /3.24*1

cMeVPT /1.103*2

cMeVPT /5.107

9Be2

12C3

22Ne5

In this case we clearly see a tendency toward an increase of the mean particle momentum with increasing their multiplicity . This implies a growth of the total coulomb interaction of clusters arising in nuclei.

<P*T1>≈24 MeV/c, <P*

T2>≈103 MeV/c

<P*T>≈141 MeV/c

<P*T>≈200 MeV/c

The *T velocity distribution in the c.m.s. of

particles

Fragmentation of relativistic 14N nuclei at 2.1 A GeV

A stack of layers of BR-2 emulsion of a relativistic sensitivity was exposed to a beam of 14N nuclei accelerated to an energy of 2.1 A GeV at the Nuclotron (JINR).

14N3He+H, 2.1 A GeV

find: 950 events of 14N fragmentation.

Angular measurements for 132 events of 14N3+H were carried out.

.avi .mov

Azimuthal angle *ij

of pairs in the c.m.s. for 14N3+X

He

14N

HeHe

8Be ?

14N3

Excitation energy Q2for the channel 14N3+X

0+, 8Be

Excitation energy Q3 for the channel 14N3+X

)(1233 CmMQ

23

1

23

ii

PM

1: all events

2: “white” stars

Excitation energy Q3 for the channel 14N3+X (with 8Be cut)

14N

Summary The results of investigations of inelastic interactions of

9Be, 14N nuclei are presented. The main features of 9Be2 relativistic fragmentation:In the P*T distribution of particles there is observed the

formation of two peaks with the mean values 24.3 MeV/c and 103.1 MeV/c.

In the Q2 invariant energy distribution of an particle pair there is observed a separation of virtually all the events over the two energy intervals : from 0 to 1 MeV with a peak at 100 keV and from 2 to 4 MeV.

This facts suggests the dominance of the 9Be 8Be+n fragmentation accompanied by a 8Be decay from the ground (0+) and the first excited (2+) states to two particles.

The *ij distribution in the c.m.s. of particles for 14N is asymmetric with an abundance at 140 – 180°.

The energy scale of the 3 alpha system production has been estimated. According to the available statistics 80% of interactions are concentrated at 10-14 MeV. The fraction of the 14N→3α+X channel involving the production of an intermediate 8Be nucleus is about (25-30)%.

The results obtained for the 9Be, 14N nuclei are compared with similar data for the 12C, 16O and 22Ne nuclei.

The data obtained from 9Be angular measurements can be employed for the estimation of the role of 8Be in more complicated N systems.