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In Beam Chirality Study with the Warsaw Cyclotron

 

Nuclear Physics Division, Warsaw University

Ch. Droste, E. Grodner, M. Kowalczyk, J.Mierzejewski, T. Morek, J. Srebrny, M. Sałata, P. Tarnowski, I. Zalewska

A. F. Ioffe Physical-Technical Institute St.-Petersburg

A. Pasternak

Heavy Ion Laboratory, Warsaw University

J. Kownacki, A. Kordyasz, P. Napiorkowski, M. Wolińska-Cichocka

The A. Sołtan Institute for Nuclear Studies, Świerk

M. Kisieliński, R. Kaczarowski, W. Płóciennik, E. Ruchowska, A. Wasilewski

Łódź University

J. Perkowski

Department of Physics and Astronomy, SUNY at Stony Brooks

D. B. Fossan, T. Koike, K. Starosta

 

Thanks are due to :

• IKF Julich (R. Lieder) for OSIRIS frame, BGO ball , electronics and 6 ACS Ge spectrometers ( + 3 Ge)
• Nuclear Physics Institute – Kraków (W. Męczyński) for 2 ACS Ge spectrometers
• NORDBALL collaboration and Jyvaskyla for 2 ACS and 4 Ge detectors

Recent theoretical and experimental works have attracted attention to the problem of chirality in atomic nuclei with odd numbers of protons and neutrons. In these nuclei the total nuclear spin is built from the valence proton and valence neutron momenta and angular momentum of the even-even core. These three vectors can be mutually perpendicular and coupled in two manners forming systems (left- and right-handed) with opposite chirality in the intrinsic frame of the nucleus. In the laboratory frame it manifests itself as the presence of two rotational bands, nearby degenerated, with the same parities. The study of the chiral twin bands is in its very early stage. For example, there is a lack of data on the lifetimes of states belonging to the chiral bands. Such data carry important information on nuclear wave functions.

We plan to study lifetimes in the ¹³⁰La and ¹³²La nuclei in which candidates for chiral bands have been found.

The ¹³²La and ¹²⁸Cs nuclei were produced in in the following reactions:

• ¹²²Sn(¹⁴N,4n)¹³²La     E(¹⁴N) = 75 MeV
• ¹²²Sn(¹⁰B,4n)¹²⁸Cs     E(¹⁰B) = 55 MeV

The Warsaw Cyclotron and the OSIRIS II multidetector spectrometer were used. For general information on the OSIRIS-II spectrometer please refer to the OSIRIS page.

History of Chirality in Nuclear Physics

New phenomena of chiral symmetry breaking first theoretical prediction (Frauendorf and Meng, Nucl.Phys. A617(1997)131) and reinterpretation of 134Pr data (Petrache et al., Nucl.Phys. A597(1996)106) Experimental identification of chiral doublets based on energy levels only – about 10 cases for A ~ 130 CPHC model formulated and firstly applied to 132La (K. Starosta et al. Phys. Rev. C65(2002) 044328) First lifetime measurements in supposed chiral bands 132La – Warsaw Cyclotron and OSIRIS II, DSAM New third band in 132La , OSIRIS II 128Cs lifetime measurements Warsaw Cyclotron and OSIRIS II, DSAM Chirality confirmed and survived ! ?

1997 19962001-20032002 2003 2003 2004 2004

Preliminary results on ¹²⁸Cs – June 2004 run

First results show that in ¹²⁸Cs differences in B(E2) values between the “yrast” band (band 1) and supposed partner chiral band (band 2 ) are much smaller than in the case of ¹³²La (see figures below)