Effect of shell closure N=50,82. Measurements of neutron emission

probability with high efficiency3He neutron detector TETRA

Dmitry Testov

09 November 2011

Introduction

78NiN/Z1,79

132Sn N/Z=1,64

Ni

Sn

Nuclei of interest

Qβ = 5-25 MeVSn = 0–5 MeV

For nuclei with N > Z, the neutron drip line islocated where the neutron separation energyequals zero

The blue areas indicate the nuclei which couldpotentially be produced and accelerated intobeams by SPIRAL2

One- and two-β-delayed neutronemission scheme of strongly neutronrich nucleus Az. In a daughter nucleusAz+1 the strength function of β—decay Sβ(E) depending on excitation energy Exis shown.

Introduction

Precursor

Emitter

Yu.Lyutostansky and I.Panov, Z.Phys.A, 313,235 (1983)

Known β-2n emitters

Nuclides T1/2,ms xn Pxn,%11Li 8.5 2n 4.1(4)

3n 1.9(2)14Be 14.5 2n 0.80(8)

3n 0.2(2)15B 10.4 2n 0.4(2) 17B 5.1 2n 11(7)

3n 3.5(7)4n 0.4(3)

30Na 48 2n 1.17(16)32Na 13.5 2n 8(2)34Na 5.5 2n ~ 5098Rb 110 2n 0.38(6)100Rb 51 2n 2.7(7)

Predicted β-2n emitters

Nuclides T1/2,ms Qb-B2nPxn,%

(MeV)86As 0.9 1.33 0.02 94Br 0.07 3.78 3.12112Nb 0.10 3.79 1.28134In 0.1 5.54 99136Sb 0.8 2.25 10.6/0.28142J 0.2 2.28 0.76150Cs 0.15 2.97 1.48

(a) Total β-decay half-lives for Ga/Cu isotopescalculated from the 1) DF3+CQRPA including the allowed and first-forbidden transitions, 2) FRDM+RPAfor the allowedtransitions in comparison with the experimental data. (b) Delayed neutron emission probabilities for Ga isotopes calculatedfrom DF3+ CQRPA: 1) including allowed and first-forbidden transitions, 2) for allowed transitions.

Gamow-Teller and first-forbidden decays near the r-process paths at N = 50, 82 (1)

78Ni

____ 1f7/2

-------- μ(n)____ 2d5/2

____ 1g9/2

____ 1f5/2

____1p3/2

____1f7/2

____ 1p1/2

____ 1g7/2

____ 2d5/2

neutrons

____ 1g9/2

____ 2p1/2

____ 1f5/2

-------- μ(p)

____ 2p3/2

protons

FF , L=1

GT, L=0

N=50

____ 1f7/2

-------- μ(n)____ 2d5/2

____ 1g9/2

____ 1f5/2

____1p3/2

____1f7/2

____ 1p1/2

____ 1g7/2

____ 2d5/2

neutrons

____ 1g9/2

____ 2p1/2

____ 1f5/2

-------- μ(p)

____ 2p3/2

protons

FF , L=1

GT, L=0

N=50

N<50 GT transitions dominate N>50 FF transitions 2d5/2 → 1f5/2 dominates

The experimental β-decay half-lives for the Cd/Snisotopes(1) DF3 + CQRPA for allowed and first-forbiddentransitions, (2) experimental data (see text).Comparison between DF3 + CQRPA calculations of thedelayed neutron emission probabilities and experimentaldata:(1) DF3 + CQRPA for allowed and first-forbiddentransitions, (2) experimental data).

Gamow-Teller and first-forbidden decays near the r-process paths at N = 50, 82 (2)

N ≈ 82; Z < 50

N ≈ 82; Z ≥ 50

Nuclei at r-process path produced at ALTO (78Ni region)

85Ga≥150ns

86Ge≥150ns

87As0.57s

86Ga≥150ns

87Ge≈0.14s

88As≥300ns

84Ge

83Ga

85As

82Zn>150ns

84Ga

85Ge

86As

83Zn>150ns

74Co>150ns

75Co>150ns

81As

76Ni

80Ge

79Ga

77Cu

78Zn

82As

77Ni>150ns

81Ge

80Ga

79Zn

78Cu

82Ge

81Ga

83As

80Zn

79Cu

83Ge

82Ga

84As

81Zn

80Cu>300ns

88Ge≥300ns

89As≥300ns

90As≥150ns

91As≥150ns

76Co 77Co

78Ni>150ns

75Fe 76Fe

r-process path

N = 50; Z = 28N = 82; Z = 50

Mechanisms of detecting neutrons

3He (n,p) cross-section as a function of neutron energy

Energy, MeV

3He gasmoderator

a neutron source

nn

n

As can be seen, the cross-section is much larger for thermal neutrons (~ 0.0253eV) than for fast neutrons (~ 1 MeV). Fission neutrons are born fast. Thus, tomaximize the efficiency of the 3He tubes, the neutrons must be slowed (ormoderated) to thermal energies. Neutron moderation is most often achieved viaelastic scattering collisions with hydrogenous material. For this reason, 3He tubesare often embedded in high-density polyethylene (C6H12).

Table of Nuclides, http://atom.kaeri.re.kr/, Nuclear Data Evaluation Laboratory, Korea Atomic Energy Research Institute (2007).

th = 5320 barns

3He + n = 3H + p + 780 keV

CELL

Zero energy threshold

Zero cross-talk

Low gamma sensitivity

Free geometry

Easy in use

High efficiency

Low internal background

Preprint JINR P13-2007-154

Neutron detectors TETRA with 3He filled counters

Pressure of 3He 7 atm90 counters (d=32 mm; L = 50 cm)Eff. 60% (0.4 – 1.5 MeV)

3He-detector Scintillator

Neutron energy ? VThreshold 0 ~30÷300 keVCross talk no yesEfficiency 30-60% 10-30%

Multiplicity Yes ?

Angle correlation Yes (<200) ?

Time scale 10 µs ns

Chemistry of 112 Fobos

Vassilissa Shin

Uses of 3He detectors in different setups

Neutron-Neutron coincidence

Neutron-Fragments coincidence

Efficiency of TETRA as a function of 3He gas pressure (MCNP-simulations)

2 4 6 8 10 12 14 16 18 20 220

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Efficiency of TETRA as a function of 3He-pressure for different neutron energies

0.5 MeV 1 MeV 2 MeV 5 MeV 8 MeV

3He pressure, atm

Eff

7 atm

0.5 MeV1 MeV2 MeV

5 MeV

8 MeV

0 0,01 0,02 0,03 0,04 0,05 0,06 0,07

Efficiency Difference between 7 atm & 20 atm

0.5 MeV 1 MeV 2 MeV 5 MeV 8 MeV

4 atm 7 atm 10 atm 20 atm

0,130,08 0,06 0,03

0,520,57 0,59 0,63

Efficiency/atm; Efficiency/$ (En=1MeV)

Eff/atm (%)Eff, %

3He pressure

Eff

ration = efficiency / pressure% per atm

1.0300%

Nucl. Instr. and Meth. A540 (2005) 430-436

Van de Graaff Accelerator, Charles University, Prague

Calibration for average delayed neutron energy measurementsEn=400-1500 keV

moderatorcounters

Neutron flux

Neutron flux

Neutron efficiency depends on neutron energy

2n/1n = 3.10-4

Probably the observed two neutronactivity belong to 136Sb, then

Pβ-2n(136Sb)~ (1.4±0.2)%

Predictions: Pβ-2n(136Sb)= (10.6 - 0.28) %*

Delayed neutron emitters in the 136Sb region

Intensity: calculation [1], primary electron beam, 50MeV, 10μA[1] Nucl. Instrum. and Mety. in Phys. Res. B 204 (2003) 246–250

136Sb0.923 s

β- : 100.00 %β-n : 16.30 % 8,85•103 [1/s]

136Te17.63 s

β- : 100.00 %β-n : 1.31 % 9,8•106 [1/s]

135Te134Te

136In

135Sb1.679 s

β- : 100.00 %β-n : 22.00 %

134Te

136Cd

135I134I 136I

136Sn0.25 s

β- : 100.00 %β-n : 30.00 %

9•101 [1/s]

133Te

2n 1n β

1n β

Z

N

84 85 86

52

51

50

1n β

JINR proposal at IPN Orsay: approved

e-LINAC

ECS bunker

PARRNe mass separator

ISOL installation at ALTO

Secondary beam lines

Laser, located one level up

Laser arrives here

Experiment 2009 = upgrade needed

paraffin + polyethylene shielding (very bulky)

The efficiency measured for the neutron detector is up to 35%

Neutron lifetime in the detector is 35 μs

BEAM

Germanium Detectors

Tape axis

Collection Chamber

3He counters

Detection chamber is inside

(0.47 ≤ Pn(136Te) ≤ 4.89)%

Pn(136Te) 1.31 %

beta

Neutron detector TETRA installation at ALTO

0,1 1 100

0,1

0,2

0,3

0,4

0,5

0,6

0,7

Internal Layer 1 Layer 2 Layer 3 Outer Layer 4Overall efficiency

En, MeV

Effi

cien

cybeam

Efficiency of the TETRA (MCNP simulations)

* For neutron energy 0.144 – 1.5 MeV** For gamma energy 1 MeV

0.1 1 100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Efficiency of TETRA in respect to different schielding

no schielding

En, MeV

Effi

cien

cyEffect of background shielding on efficiency (MCNP simulations)

No shielding at all (00 cm)Green line

A layer of 5 cm of polyethylenegives an advantage to anefficiency of neutron registrationfrom a neutron source placed atthe center of the detector up to 5 –10 % at neutron energy more than2 MeV0.1 1 10

00.050.1

0.150.2

0.250.3

0.35Efficiency of the inner layer

no schieldingCH2, 20 cm15 borated +5 CH2Borated, 20 cm

En, MeV

Effi

cien

cy

0.1 1 100

0.02

0.040.060.08

0.10.120.14

Efficiency of the outer layer

no schieldingCH2, 20 cm15 borated +5 CH2Borated, 20 cm

En, MeV

Effi

cien

cy

ONLY polyethylene (20 cm)Orange line

0.1 1 100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Efficiency of TETRA in respect to different schielding

no schielding CH2, 20 cm

En, MeV

Effi

cien

cy

ONLY Boron polyethylene 20cmBlue line0.1 1 10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Efficiency of TETRA in respect to different schielding

no schielding CH2, 20 cm Borated, 20 cm

En, MeV

Effi

cien

cy

Mixed shielding piepolyethylene (5 cm) +

Boron polyethylene (15 cm)Yellow Line

0.1 1 100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Efficiency of TETRA in respect to different schielding

no schielding CH2, 20 cm 15 borated +5 CH2 Borated, 20 cm

En, MeV

Effi

cien

cy

82,83,84,85 Gallium precursors

84Ga 84Ge 84As

83Ge 83As

n n

Ф1 Ф2 Ф3

A general scheme presenting the relevantnuclei participating in the decay chain of aneutron reach Ga isotope

0 2 4 6 8 10 1270

75

80

85

90

95

100

105

9293

9495

969798

99100

101102

7980

8182

8384

8586

Ga Rb

Emax(neutron), MeV

Isto

pes

Plasma ion source,Ф1, Ф2, Ф3 are ON

Laser ion source,Ф1 is ON; Ф2=0, Ф3=0

First experiment is scheduled on march 2012

Maximum En of neutrons

624 keV2+→0+84Ge nouvelle scientifique

Red: ionisation laser, aftera few hours of beamtimerouge

Blue: total statistic (surfaceionisation) from the thesis ofM. Lebois (previousexperiment on the samemass)

84Ga→84GeT1/2= 0.085 s

Laser beam of 84Ga at ALTO October 2011

136Sb

84Ga

TETRA Neutron Detector Setup: prototype for DESIR

Moderator: polyethylene, distance between parallel faces - 5 cm.

Efficiency: 30-60% (depends on geometry)

Life time: 15-30 µs (depends on geometry)

close to 4-π geometry

Geometry: Ø 3 cm, 3He at 7 atm Ø 3 cm, 3He at 7 atmlength 50 cm length 25 cm

Total numberof counters: 90 342

TETRA Detector

Why does it call TETRA ????

Greek prefixes (Cardinal) – “4”:- 4Pi-geometry

- Study multiple neutron emission (4 neutrons ?!) …. and more

Kingdom: Animalia Phylum: ChordataClass: ActinoptervaiiOrder: Characiformes Family: - Alestiidae- Characidae- Lebiasinidae

Tetra species (from biology, some):Pygmy tetra, Odontostilbe dialepturaCopper tetra, Hasemania melanuraBlack neon tetra, Hyphessobrycon herbertaxelrodiCoffe-bean-tetra, Hyphessobrycon takasei……..New tetra species to be added (from nuclear physics):

Antimony tetra, Stibium duplicemGallium tetra, Dives Insolens

Tetra are species of small freshwaterfish from Africa, Central America andSouth America belonging to thebiological family Characidae and to itsformer subfamilies Alestiidae (the"African tetras") and Lebiasinidae.

Fish “TETRA”

TETRA