Measurement of β - delayed neutrons around the third r-process peak

ROGER CABALLERO FOLCH,

FRS User meeting 2011 - GSI, 28th November 2011

S410 EXPERIMENT GSI – SEPTEMBER 2011

Introduction and astrophysics motivation

Setup: FRS – SIMBA – BELEN

Current analysis status and its outlook

Contents

1/14

Analysis Future goalsIntroduction Setup

Summary and future goals

Experiment

2/14

S410: Beta-decay measurements of new isotopes near the third r-process peak (N~126)

- Performed at GSI in September 2011 with a week of beam time

- Shared setup with S323 experiment

The measurements settings were

centered on two isotopes: 215Tl, 211Hg.

We have preliminarily identified the

following nuclei:

207-214Hg 205-210Au

203,206Pt 199,202Ir

211-217Tl

Analysis Future goalsIntroduction SetupIntroduction

Motivation

3/14

Nuclear structure knowledge: beta decay studies of these nuclei

provide information about their decay mechanism and nuclear structure in this mass region

Half lives (T1/2)

Beta delayed neutron emission probabilities (Pn)

Astrophysics (r-process): nucleosynthesis aspects of the heavy mass

elements. The new values for T1/2 and Pn, will provide valuable information

for the test of theoretical models.


“Ignorance”-Curve

Exp. T. Kurtukian et al.Phys. Lett. B (Submitted)

DF3 + QRPA

+ FRDM + QRPA(P.Moeller, et al. 2003)

(I.Borzov, et al. 2003)

State of the art

4/14


N=126

t1/2 exists identifiedArea of interestPn (%) QRPABn= 2-3 MeV

Centered

Introduction


5/14

Setup

Fragment separator spectrometer (FRS). Beam characteristics.

SIMBA +BELEN

1.6 g/cm2 Be target

2x109 ions/spill intensity

Bρ settings for: 215Tl, 211Hg and as references 216Po, 205Bi, 135Sb

Spill length ~1s with a period around 4s

Separation in flightBρ – ΔE – Bρ

Introduction

Experimental hall (S4) configuration and settings

6/14TPC

MUSIC

SLITS

SCI

DEGRADER

ITAG SIMBA &BELEN

Analysis Future goalsIntroduction SetupSetup

Implantation detector: SIMBA (Silicon Implantation Detector and Beta Absorber)

7/14

SIMBA detector

Multilayer silicon detector

Allows to measure both ion implants and

β-decays.

Decay events can be correlated in time

with the detection of neutrons.

2 SSSD (7 segm.) 60x40 mm2 (1mm thick)

XY FRONT A B C REAR

Tracking layers XY (60 segm.) 60x60 mm2 (0.3mm thick)2 SSSD (7 segm.) 60x40 mm2 (1mm thick)3 DSSD (implantation area, 60x40 segm.): 60x40 mm2 (0.7mm thick)

Front view


8/14

Neutron detector: BELEN (Beta Delayed Neutron Detector)

- Neutron detector designed by UPC GRETER research group (Barcelona)

- The detection of the neutron is based on the detection of products of the reaction

of the neutron with 3He counters: 3He + n 3H + 1H + 765 keV

Ion beam

n

n

n

Polyethylenemoderator

Proportional 3He counterSilicon

β decay detector

- 30 3He counters:


8/14

Neutron detector: BELEN (Beta Delayed Neutron Detector)

BELEN-30 neutron detector

· 10 with 10 atm pressure

· 20 with 20 atm pressure

Neutron shielding

SIMBA inside the matrix

BEAMLINE



Analysis procedure (Preliminary plots / ongoing)

9/14

Analysis Setup

Tracking detectors calibrations & particle ID

Particle ID check via 205Bi isomers,216Po α-decays

SIMBA calibrationimplantation patterns

Analysis of half lives and Pn

Digital data acquisition system features

A/Q

BiPbTl

HgAu

Pt

Po

215Tl

FRS setting 215Tl

SCI21-SCI41 ToF

TPC21-22 – TPC41-42 Position calibration

MUSIC 41-42-43 Energy Loss calibration

PRELIMIN

ARY


9/14

Analysis






BiPb

TlHg

AuPt

Po

Ir


SCI21-SCI41 ToF

TPC21-22 – TPC41-42 Position calibration

MUSIC 41-42-43 Energy Loss calibration

FRS setting 211Hg

A/Q

211HgPRELIM

INARY

10/14

Analysis Future goalsIntroduction Setup Analysis






205Bi setting has been used as Z identification

reference via isomer gamma rays and 216Po setting

as A/Q checking in the region of interest.


A/Q

Z

205Bi

keV

Cou

nts

11/14







Implants keV

Ch

Bet

a di

sint

egra

tion

s

- SIMBA calibrations are being performed with a 137Cs source

- β- decay curves will provide half lives values

ImplantationCo

un

ts

Energy deposited (ch)

Noise

Beta decay


- Time correlation between neutron and beta decay

-252Cf for BELEN efficiency and can be checked with

135Sb

12/14







N

NP n

nn

1

Pulser

Noise Neutron signal

Cou

nts

Energy (ch)


DDAS- Triggerless digital data acquisition system used for the first time in thistype of experiments at GSI.

- It allows to eliminate the dead timeof conventional acquisition systemsthanks to the double memory digitalcards which allow to acquire data and reading of previously taken data at the same time.

- Advantages:1. Increase the efficiency by about 8% (from 27 to 35%)2. Flexibility for large time correlation (fundamental to

obtain correlations with all neutron and to change the gates offline)

3. Allows to correct some experimental effects, e.g. To reduce neutron background from uncorrelated neutrons.

13/14








Outlook

14/14

Analysis Future goalsIntroduction Setup Future goalsAnalysis

Improved ID-Plot via final calibrations of frs detectors

Determine implantation rates for each identified isotope

Determine implant-beta correlations and neutron-beta correlations

Implement an analysis method for deriving half-lifes and for determining beta-delayed

neutron emission probabilities.

In collaboration with theoreticians, study the impact of these results on nuclear

models, as well as on r-process nucleosynthesis calculations.

Future goals

Upgrade of detector: up to 90 counters (detection efficiency ~70%): collaboration with Dubna

Combine with AIDA implantation detector (first separate tests in August 2011): talk Robert

Page (Tue, 10:10)

Optimize detection system (BELEN) and its acquisition (DDAS) for future experiments with

more exotic beams (FAIR).

Prepare for first experiments closer to the r-process path @FAIR/DESPEC (>2018)

Measure Pxn

The end!

Thanks to collaborators:

Institut de Física Corpuscular de València (IFIC)

Universitat Politècnica de Catalunya (UPC)

Helmholtzzentrum für Schwerionenforschung GmbH (GSI)

NSCL, Michigan State University (MSU-USA)

CIEMAT (Madrid)

Universidade de Santigo de Compostela (USC)

Department of Physics, University of Surrey (UK)

CFNUL Universidade de Lisboa (Portugal)

School of Physics & Astronomy, U. Edinburgh (UK)

Department of Physics, University of Liverpool (UK)

STFC, Daresbury Laboratory (UK)

Laboratori Nazionali di Legnaro, INFN (Italy)

Flerov Laboratory, JINR, Dubna (Russia)

CENBG, Université Bordeaux (France)

State of the art

4/16

Analysis status Data analysisIntroduction Setup Outlook & futureIntroduction

Effect of half-lives

The Astr. Jour., 579 (2002), H. Schatz et al.

Proc. CGS-13 (2009), G. Martinez-Pinedo

“Ignorance”-Curve

Focus of present proposal

r-path

State of the art

4/14


FRDM + QRPA

K.-L. Kratz, (private communication)

r-proce

ss path

T1/2

Pn

Exp. T. Kurtukian et al.Phys. Lett. B (Submitted)

DF3 + QRPA + FRDM + QRPA(P.Moeller, et al. 2003)(I.Borzov, et al. 2003)

Effect of half-lives

The Astr. Jour., 579 (2002), H. Schatz et al.

Proc. CGS-13 (2009), G. Martinez-Pinedo

K.-L. Kratz, (private communication)

Particle identification

9/16

Analysis status Data analysisIntroduction Setup Outlook & futureAnalysis status

The method is based in Time of Flight (ToF) measurement according to the

energy loss (ΔE) in the (MUSIC) ionisation chambers and the B fields (Bρ) set.

205Bi setting has been used as Z identification reference via isomer gamma

rays and 216Po setting as A/Q checking in the region of interest.

A/Q

Z

205Bi

keV

Cou

nts

Setup

Measurement of β - delayed neutrons around the third r-process peak

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