Decay studies of exotic nuclei

Krzysztof P. RykaczewskiPhysics Division, Oak Ridge National Laboratory

Oak Ridge, Tennessee

exotic nuclei:- fission products of 238U- super heavy nuclei produced in hot fusion

It is my first trip to Japanbut I had several joint publications with Japanese collaborators before:

“Beta decay of 20Mg”, Nucl. Phys. A 584, 509, 1995with S. Kubono and T. Nakamura

GANIL LISE exp in 1991 decay data relevant for the break-out from CNO cycle

several papers from 1998 to 2004with M. Shibata

Total Absorption Spectroscopy at GSI ISOL facility performed with M. Nitschke’s (Berkeley) TAS by Warsaw -Valencia-GSI teams

“True Gamow-Teller strength distribution around 100Sn and 146Gd”

many results on new and important s-isomers obtained afterwards at GANIL (LISE), GSI (FRS) , NSCL(A1900)

and more recently at RIKENsee, e.g., Kameda, Kubo,.. et al, PR C86, 054319, 2012

Early work in GANIL on 20Mg triggered the expansion of GSI ISOL program of Gamow-Teller β-transitions studies near 100Sn to fragmentation reactions.

It resulted the identification and studies of s-isomersR. Grzywacz et al.,Phys. Lett. B 355, 439,1995; PR C55, 1126, 1997; PRL 81, 766, 1998

R. Grzywacz et al., Phys. Rev.C55, 1126, 1997R. Grzywacz et al., Phys. Lett. B355, 439, 1995

among motivations of the HRIBF decay studies of fission products :

- understanding the evolution of nuclear structure -- single-particle levels around shell gaps-- beta strength function related to the structure of parent and daughter states

- beta-decay data for the analysis of post r-process isotopic distributions and nuclear fuel cycle -- half-lives-- properties of beta-delayed neutron emission-- decay heat -- antineutrino energy spectra (deduced from true β-transition probabilities)-- low-energy states, isomers ...

HRIBF based decay studies of fission products substantially contributed

to our understanding of neutron-rich nuclei

Holifield Radioactive Ion Beam Facilitycapable to produce and study nuclei at the neutron-rich

and proton-rich limits of nuclear landscape

IRIS-1

IRIS-2

ORIC

lasers

isobarseparator

Tandem

RMS

OLTF

= Holifield Radioactive Ion Beam Facility at Oak Ridge (1996 - 2012)

proton-induced fission of 238Ucreates a lot of neutron-rich nuclei

for spectroscopic studies

86Ga:HRIBF: ~10,000/hour at 15 A protons

pure beam at the HRIBF !RIKEN:10/hour at 0.2 pnA 238U

(now ~ 5 pnA)

J.R. Beene et al., J. Phys. G: Nucl. Part. Phys. 38, 024002, 2010

Decay studies of fission products at the

Range outexperiment

LeRIBSSexperiment

+/-40 keV+/-160 keV

Isobar separator M/M ~ 10000

Mass separatorM/ΔM ~ 1000

54 MeV protons12- 18 A

2-3 MeV/u

200 keV

charge exchange cell

(removes Zn, Cd)0% - 40% efficiency

typically 5% efficiency

Positiveions

Positive or negative ions

Tandem accelerator

(negative ions only)

~ 10% efficiency

IRIS-1

ORIC : ~6 g 238U

fission fragments

~1011/s

~7 % ~70%

gas cell

IRIS-1 and IRIS-2, laser ionization

beam kicker En

erg

y l

os

sTotal ion energy

76Cu

76Ga

76Ge

no 76Zn !!!

Range out expgas cell spectra

C.J.Gross et al., EPJ A25,115,2005

two-stage magnetic separation:

from molecular beams like A=118 86Ge32S+

to pure “nominal mass A-” ion beam

example: new 84-86Ge,84-87As- results

A variety of beam purification methods

selectivelaser ionization

Detectors for beta decay studies CARDS β- at LeRIBSS VANDLE n-TOF array at LeRIBSS

Hybrid 3Hen-β- array at LeRIBSS

εn~30%

3Hen array after “ranging-out”

850 liters of 3He at 10 atm

εn~80%

Ed Zganjar, LSURobert Grzywacz, UTK

nearly 80% efficient and segmented 3Hen neutron counter

ORNL, UTK LSU , Mississippi

UNIRIB

850 liters of 3He at 10 atm

εn~80%

Detectors for beta decay studies 2200 pounds of NaI(Tl) - Modular Total Absorption Spectrometer

(MTAS)and its 12,000 pound shielding

Decays studied at HRIBF Tandem-OLTF-MTAS are marked by yellow squares.

Labels “1” and “2” indicate the priorityfor decay heat measurements established

by the Nuclear Energy Agency (NEA) in 2007

January 2012

Beta decay of very neutron-rich nuclei is very rich in interesting features

β and MTAS

neutron detection

3Hen, VANDLE

22 parent radioactivities in 78Ni region studied by means of β spectroscopy at the HRIBF 78Ni to 132Sn region (~ 10), + MTAS (22), + VANDLE (29)

80As

79Ge

78Ga

77Zn

76Cu

75Ni

81As

80Ge79Ga

78Zn

77Cu

76Ni

82As

81Ge

80Ga

79Zn

78Cu

77Ni

83As

82Ge81Ga

80Zn

79Cu

78Ni

84As

83Ge82Ga

81Zn

80Cu

79Ni

85As

84Ge

83Ga

86As

85Ge84Ga

87As

86Ge

85Ga

83Se 84Se 85Se 86Se 87Se 88Se

82Zn 83Zn

Z=28

N=50

79As

78Ge77Ga

76Zn

75Cu

74Ni

78As

77Ge

76Ga

75Zn

74Cu

73Ni

86Ga

88As

87Ge

89Se

77As

76Ge75Ga

74Zn

73Cu

72Ni

D. Miller, R Grzywacz et al., to be published

~ 2 days exp

detected 79Cu ions:NSCL 2005 (2010): 754HRIBF 2006: ~16 000RIKEN 2010: ~ 10 000HRIBF 2011: ~158 000

81Zn

81Ga

78Ni

79Cu

79Zn

initial yields : 79Zn ~ 105 pps 79Cu+ ~ 40 pps

after charge exchange : 79Zn 0.0 pps 79Cu- ~ 2 ppspure beam of 79Cu ions → single neutron-hole states in N=49 79Zn

78Zn

79Cu decay (HRIBF LeRIBSS) N=50

0.29(2) s

half-life of 79Cu Kratz 1991 : 188(25) ms (multi βn fit)Hosmer 2010 : 257(+ 29,- 26) ms (ion-β)Miller 2013: 290(20) ms (β- 730 keV)

Beta-delayed neutron emission: counting identified ions → absolute branching ratios

HRIBF results pointed to much higher β-delayed neutron branching ratios in comparison to earlier measurements and calculations

see, e.g., Pfeiffer, Kratz, Moeller (PKM 2002) Progress in Nucl. Energy, 41, 5 (2002)

similar conclusions: P. Hosmer, H. Schatz et al., PR C82 , 025806, 2010

J. Winger et al., PRL 102, 142501 (2009) PRC 80, 054304,2009; PRC 81,044303,2010;

PRC 82, 064314 (2010); PRC 83, 014322 (2011); PRC 86, 024307,2012

all βn-precursorsgiven in this plot

have T1/2 < 1 s

Delayed Neutron Yield following 235U fission

0.1 1 10 10010-6

10-5

10-4

10-3

10-2

Del

ayed

neu

tron

yie

ld (

n/s/

fissi

on)

Time after fission (s)

ORIGEN Keepin (IAEA 6 group)

Integral β,n measurementsused for reactor analysis

-n isotopic decay data

ORIGEN is missing data for very short-lived

fission products

from Ian C. Gauld, ORNL Reactor Science Group (2010)

Note log scales !

Example of MTAS data – 139Xe decay (A. Fijałkowska et al., ND2013)(139Xe ~5% cumulative fission yield for nth+ 235U)

MTAS data (black) compared to ENDSF-based simulations (red).

Lack of β-feeding and following -energy release from highly excited states in current data base !

MTAS-revised decay of 139Xeaverage -energy release

increased from 935 keV to 1146 keV (23%)

May 2010 : the Department of Energy creates the first nuclear energy innovation hub -- the Consortium for Advanced Simulation of Light Water Reactors (CASL) -- headquartered at Oak Ridge.

The first task will be to develop computer models that simulate nuclear power plant operations, forming a "virtual reactor" for the predictive simulations of light water reactors. Other tasks include using computer models to reduce capital and operating costs per unit of energy, safely extending the lifetime of existing U.S. reactor and reducing nuclear waste volume generated by enabling higher fuel burn-ups.

http://www.ornl.gov/sci/casl/

We should remember that even the very best simulations of nuclear fuel cycles require correct experimental input data.

“Conquering nuclear pandemonium”KR’s Viewpoint in Physics, 3, 94, 2010

(credit to A. Algora et al., PRL 105, 202501, 2010)

79Cu, 81,82,83Zn, 85,86Ga, 86Ge, 86,87As .....

β spectroscopy - new beta decays

83Ge

81Zn

83Ga

84Ge

81Ga

78Ni

82Zn

84Ga

85Ge

85Ga

79Cu

83Zn

86Ga

86Ge

82Ga

117 ms228 ms304 ms

93 ms85 ms

226 ms

87As86As484 ms

494 ms

290 ms

molecular beams GeS, AsS

~ 3 ions/s, April 2012 pure Ga beams from

laser ion sourceand hybrid 3Hen array

861ms

Departing from 78Ni into a deformed region β-half-lives of 84,85,86Ge and 84,85,86,87As isotopes C. Mazzocchi , KR, et al., → Phys. Rev. C87, 034315, 2013

I.N. Borzov’s DF3a+CQRPA

Exp half-lives → β-theory → r-process(HRIBF measurements → I.Borzov’s analysis → R.Surman’s modeling)

experiment

FRDM Moeller 2003

DF3a+CQRPA Borzov 2011

M. Madurga et al., Phys. Rev. Letters, 109, 112501, 2012

+ post r-process abundances

simulations with Moeller’sT1/2’s

simulations with Borzov’s T1/2’s

R. Surman 2012

Evolution of single-particle states beyond N=50

evolution of neutron 3s1/2 vs 2d5/2 states in N=51 isotones (N=58 sub-shell closure)

see J. Dobaczewski’s global calculations along N=50 isotones in J. Winger, KR, .. et al., PR C 81, 044303, 2010

Emerging N=58 d5/2-s1/2 subshell ? (energy of s1/2 state dropping down towards d5/2 gs for n-rich nuclei)

Neutron states in N=51 isotones, from Z=30 81Zn to Z=50 101Sn

-200

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

28 30 32 34 36 38 40 42 44 46 48 50 52

Z

E (

ke

V)

1g7/2

3s1/2

2d5/2

Darby, Grzywacz et al.,PRL 105, 162502,2010 101Sn-103Sn-105Sn ...

Padgett , Madurga, Grzywacz et al., 81Zn decay,PR C82, 064314, 2010

Interesting experiment for RIKEN: 82Cu β-decay to s1/2 state in N=51 81Zn( 80,81,82Cu β-decay experiments were accepted at the HRIBF, but ...)

82Cu

Qβ~ 17 MeVT1/2 ~ 60 ms

82Zn

81ZnN=51

Sn~ 5 MeVs1/2

d5/2

0+

(4-,5-)

βn

~ 0.6 MeV

with 100 part*nA of relativistic 238U beam (RIKEN, FRIB ?) we can go for more ambitious study of

80Co βn-decay to the s1/2 excited state in N=51 79Ni

T.Ohnishi,T.Kubo .. JPSJ 2010

0.2 pnA 238U

Beta-delayed multi-neutron emission Decay of N=55 86Ga studied with “hybrid 3Hen” at LeRIBSS in April 2012. Pure and intense beams of 83,85,86Ga isotopes were produced at the IRIS-2 RIB platform using laser ion source RILIS Y. Liu et al., Nucl. Instr. Meth. Phys. Res. B298, 5, 2013.

pure beams: 100 pps of 85Ga, ~ 1- 3 pps of 86Ga

SummaryDecay studies of fission products at the HRIBF created a lot of new and reliable data on fission products decays

1. High energy resolution measurements with pure beams of known intensities (when post accelerated)ranging-out technique and gamma-beta-conversion electron detectors → basic “high energy resolution” decay scheme + n-branching ratio

2. Measurements with Modular Total Absorption Spectrometer MTASMTAS energy spectra in segmented array → beta strength within -window (decay heat)

3. Measurements involving 3Hen and VANDLE → -delayed neutronsβn-intensities and βn-energy spectra /Robert Grzywacz/ → beta strength above neutron separation energy

Combining high-res -data, 3Hen, MTAS, VANDLE → determination of a full -strength function and its consequences → comparison with theory and further development of modeling

2008-2012 LeRIBSS – OLTF (MTAS) HRIBF campaigns

ORNL : C.J. Gross, Y. Liu, T. Mendez, K. Miernik, KR , D. Shapira, D. StracenerUT Knoxville : R. Grzywacz, K.C. Goetz, M. Madurga, D. Miller, S. Paulauskas, S. Padgett, L. Cartegni , A. Fijałkowska, M. Al-Shudifat and C.R. Bingham ORAU/ORNL : C. Jost, M. Karny, M. Wolińska-CichockaMississippi : J. A. Winger, S. Ilyushkin Louisiana : Ed Zganjar, B.C. Rasco UNIRIB : J.C. Batchelder , S. H. LiuVanderbilt : N. Brewer, J.H. Hamilton, J.K. Hwang, A. Ramayya, C. GoodinWarszawa : A. Korgul , C. Mazzocchi Kraków : W. Królas IAEA: I. Darby NSCL-MSU: S. Liddick

+ VANDLE collaboration (talk by R. Grzywacz)

theoretical analysis : I.N. Borzov (JIHIR/Dubna/Obninsk), K. Sieja (Strasbourg), R. Surman(NY-

JINA) R. Grzywacz (UTK), J. Dobaczewski (Warszawa/Jyväskylä)

Studies of Super Heavy Elements

ORNL, Oak Ridge

~ 250 mg 252Cf

~ 8 g 254Es

J. Roberto et al., workshop on SHE studies at the Dubna SHE FactoryCollege Station, TX, 12-13th March 2013

about 12 mg to 15 mg of actinide material is needed for one SHE target

Fm

E s

F m 254 F m 255 F m 256

SF

F m 257

Es 254 Es 255

- EC -

CfC f 249

, (n ,f)

C f 250 C f 251 C f 253 C f 254

, ,

, (n ,f) ,

B k 249B k

Bk 250 Bk 251

-

C m 242

A m

Cm

Pu 246

C m 243

Pu 239

, (n ,f)

, (n ,f)

C m 244 C m 245

, (n ,f)

C m 246

, (n ,f)

C m 247

, SF

C m 248

SF

C m 249 C m 250

Pu 240

N p 237

Pu 238 Pu 241 Pu 242 Pu 243

N p 238

Pu 244 Pu 245

-, (n ,f)

, (n ,f)-

Am 241

, EC-

Am 242 Am 243 Am 244 Am 245 Am 246

94

93

95

96

N

Z

98

97

100

99

SF

--

-

---

- - -P u

Np

Es 253

C f 252

, SF

243Am/244Cm/248Cm seed material and its n-capture/decay path

to 249Bk, 252Cf,253,254Es and 257Fm

2012 – a very good year for SHE studies !see 278113 among the “Inventions of the year 2012” according to Time magazine(most experiments were performed with ORNL-made actinide target materials)

16

(+25 TASCA) (+1 TASCA)

Yu.Ts. Oganessian et al., PRL 104, 142501, 2010; PRL 108, 022502, 2012; PRL 109, 162501, 2012; PR C 87, 014302, 2013and submitted to PR C.

(+1 TASCA)

(+1 TASCA)

new experiments at SHIP (GSI Darmstadt) • 248Cm+54Cr, 33 out of 140 days, April-May 2011 (also 2012), beam dose ~5*1018

- search for isotopes of new element Z=120, 298,299(120)178,179 (T1/2 ~ 3 s)

- expected short -decay half-life required ORNL/UTK fast digital electronics

- cross section limit of about 560 femtobarn reached at ~ 400 pnA beam current

dead time~ 11 s

dead time~ 0.3 s

UTK Digital Signal Processing Laboratory

SHIP analog data acquisition

recoil

recoil

GSI Annual Report 2011 (2012)

New ORNL-UTK detectors and digital data acquisition system

MICRON detectors

128 x48 mm,1 mm strips 300m DSSD

500 m single Si-vetomatching DSSD design

six 120 x 65 mm single Si300 m Si-box

MESYTEClin-log preampsISEG NIM HV

XIA Pixie16 rev D(208 channels)

Dell Power Edge

(similar DAQ at SHIP Z=120 exp was serving PSSD+Si-box+MCPs)

LF 250 flange

Preparations for experiment searching for 293(118), 295(118) and 296(118) isotopes with ORNL’s mixed-Cf target , new ORNL/UTK detection system and 48Ca beam at Dubna.

(50% of 249Cf, 35% of 251Cf and 15% of 250Cf and very low content of 252Cf)

Experiment with 48Ca beam and 240Pu ORNL target material at Dubna

TSF ~10-100 s ?

Staszczak, Baran, Nazarewicz; Phys. Rev. C 87, 024320, 2013Spontaneous fission modes and lifetimes of superheavy nuclei

in the nuclear density functional theory

284Fl (4n,240Pu)

296118 (3n,251Cf)

only even-even nuclei plotted here

?

Summary for the SHE section:

1.Impressive SHE harvest in 2012 at JINR , GSI and RIKEN !

2. ORNL-made actinide materials are used to make “SHE targets”. New mixed-Cf target can help to reach the heaviest atomic nuclei, the isotopes of element 118

3. Digital data acquisition system, initially developed for the studies of s- proton emitters at the HRIBF RMS (R. Grzywacz et al., UTK Digital Pulse Processing Laboratory), continues to be a system of choice in other experiments including the synthesis of super-heavy nuclei and fragmentation-based spectroscopy. 4. Experiment s on new short-lived super heavy nuclei with 48Ca beam (44Ca, 40Ca) and 240Pu (239Pu, 245Cm, 248Cm..) can help to connect nuclear mainland to the “Hot Fusion Island” and provide important data on fission/alpha competition.