A Novel LaBr3 based γ-ray

detection array for use at RIBFP. Doornenbal1, H. Scheit1, N. Aoi1, T. Motobayashi1, H. Sakurai1, and S. Takeuchi1

1RIKEN Nishina Center for Accelerator-Based Science, 2-1 Hirosawa, Wako, Saitama 0351 - 0106, Japan

Motivation

Simulated exemplary experiments

With the Radioactive Ion Beam Factory (RIBF) at RIKEN being on the cusp to deliver the worldʼs most intense RI beams at energies of several hundred MeV/u, a new γ-ray detection array is required to exploit the new experimental possibilities coming along with it. The material LaBr3(Ce) possesses an unprecedentedly high intrinsic energy resolution for scintillators of 2 % (FWHM) at 1332.5 keV and an excellent time resolution below 500 ps and is therefore well suited for high-resolution in-beam γ-ray experiments at relativistic energies. To minimize Doppler effects, the total array will comprise of up to one thousand individual crystals. The array will be placed around the secondary target area of the large acceptance fragment separator BigRIPS. Alternatively, the array can be used in a different configuration for stopped beam, delayed γ-ray decay experiments.

Configuration for stopped beam experiments

Energy [keV]500 1000 1500 2000 2500 3000

FEP

Effic

ienc

y / %

10

20

30

40

50

60

70

80

90

1000 mm Al

0.5 mm Al

1. mm Al

• 960 LaBr3 detectors in a simple boxed shaped geometry,

• 15 x 40 x 80 mm3 crystal size• 12 cm distance to target,• Simulations performed with Al

housings of 0, 0.5 and 1.0 mm thickness,

• ≈ 85 % solid angle coverage,• High granularity is kept for high

energetic γ-rays.

Gamma Fold0 2 4 6 8 10 12

Rela

tive

Inte

nsity

1

10

210

310

410

500 keV1000 keV1500 keV2000 keV2500 keV3000 keV

Conclusions

Configuration for fast beam experiments

DALI2 array: 160 NaI detectors

Energy [keV]0 200 400 600 800 1000 1200 1400 1600 1800 2000

Coun

ts /

10 k

eV

0

5

10

15

20

25

30

35

40

453LaBr

DALI2Au197Sn*)102Sn,102Au(197

Energy [keV]500 1000 1500 2000 2500 3000

FEP

Effic

ienc

y / %

10

20

30

40

50

60

70

80100 MeV/u

150 MeV/u

200 MeV/u

250 MeV/u

Energy [keV]500 1000 1500 2000 2500 3000

Ener

gy R

esol

utio

n (F

WHM

) / %

2

2.5

3

3.5

4

4.5

5

5.5100 MeV/u

150 MeV/u

200 MeV/u

250 MeV/u

Relativistic Coulomb excitation of 102Sn

•25 particles per second 102Sn beam 150 MeV/u at secondary target,

•Secondary target thickness of 500 mg/cm2 Au,

•B(E2; 0+ → 2+) = 0.044 e2b2 from shell model calculations*,

•5 days beam on target.

Isomer spectroscopy at the limits

*A. Banu et al., PRC 72, 061305(R) (2005)

130Cd

1325

1864 1992 2130 8+

4+

2+

0+

6+

RI Beam Factory

SRC

BigRIPSLocation of LaBr3 array

IRC

•50 implanted 130Cd isomers.

Objectives and considerations•Construct a 4π LaBr3 fast beam γ-ray detection array of up to 1000 detectors with an optimized geometry for RIBF energies of v/c = 0.6,

•Energy resolution of less than 3 % (FWHM) at Eγ = 1332.5 keV and Ebeam = 100 MeV/u,

•Full energy peak efficiency (FEP) of 40 %,•Simple detector geometry for a maximum of flexibility and to allow for an easy reconfiguration of the array for stopped beam experiments,

•In the first instance, the uncompleted array can be used in addition to a modified DALI2 array*.

*S. Takeuchi et al., RIKEN Acc. Rep. 36, 148 (2003)

• 960 LaBr3 detectors,• Arranged in a configuration that

ke e p s t h e s a m e D o p p l e r broadening due to the detectors’ opening angle for all polar angles at v/c = 0.6,

• 15 x 40 x 80 mm3 crystal size,• Simulations are performed with a

0.5 mm thick Al housing.

Beam direction

ZeroDegree

•The LaBr3 array in a configuration of 960 detectors with the dimensions of 15 x 40 x 80 mm3 fulfills the set requirements on energy resolution and photopeak efficiency at the relativistic secondary beam energies of the RIBF.

•The high granularity and efficiency of the array make it a powerful tool to study γ-γ angular correlations.

•Only few implanted isomers are necessary to reconstruct level schemes. Therefore, the array is a dedicated equipment for the spectroscopy of very weakly produced isomers.

Energy [keV]0 200 400 600 800 1000 1200 1400 1600 1800 2000

Coun

ts /

4 ke

V

02468

10121416182022

>Gamma0 200 400 600 800 1000 1200 1400 1600

<Gam

ma

0

100

200

300

400

500

600

0

0.5

1

1.5

2

2.5

3

3.5

4γ-γ coincidences