Decay studies of exotic nuclei
Krzysztof P. Rykaczewski
Physics Division, Oak Ridge National Laboratory
Oak Ridge, Tennessee exotic nuclei:
fission products of 238 U
super heavy nuclei produced in hot fusion

It is my first trip to Japan but I had several joint publications with Japanese collaborators before:
“Beta decay of 20 Mg”, Nucl. Phys. A 584, 509, 1995 with 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 2004 with 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 100 Sn and 146 Gd”

Early work in GANIL on 20 Mg triggered the expansion of GSI ISOL program of Gamow-Teller β-transitions studies near 100 Sn to fragmentation reactions.
It resulted the identification and studies of
 s-isomers
R. 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, 1997
R. Grzywacz et al., Phys. Lett. B355, 439, 1995 many results on new and important
 s-isomers obtained afterwards at GANIL (LISE), GSI (FRS) , NSCL(A1900) and more recently at RIKEN see, e.g., Kameda, Kubo,.. et al, PR C86, 054319, 2012

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

capable to produce and study nuclei at the neutron-rich and proton-rich limits of nuclear landscape
ORIC
Tandem
IRIS-1
OLTF
IRIS-2 isobar separator lasers
RMS

= Holifield Radioactive Ion Beam Facility at Oak Ridge (1996 - 2012)
J.R. Beene et al., J. Phys. G: Nucl. Part. Phys. 38, 024002, 2010 proton-induced fission of 238 U creates a lot of neutron-rich nuclei for spectroscopic studies
86 Ga:
HRIBF: ~10,000/hour at 15

A protons pure beam at the HRIBF !
RIKEN: 10/hour at 0.2 pnA 238 U
(now ~ 5 pnA)

ORIC : 54 MeV protons
12- 18  A e g ~7 % e b ~70% b g b g g g
200 keV
LeRIBSS experiment fission fragments
~10 11 /s
~6 g 238 U
+/-40 keV
Mass separator
M/ΔM ~ 1000
Positive ions
+/-160 keV
Tandem accelerator
(negative ions only)
~ 10% efficiency
Isobar separator
M/ D M ~ 10000
Positive or negative ions charge exchange cell
(removes Zn, Cd)
0% - 40% efficiency typically 5% efficiency
C.J.Gross et al.,
EPJ A25,115,2005
Range out exp gas cell spectra
Range out experiment gas cell
2-3 MeV/u beam kicker
76 Cu
76 Ga no 76 Zn !!!
76 Ge
Total ion energy

selective laser ionization two-stage magnetic separation: from molecular beams like A=118 86 Ge 32 S
+
to pure “nominal mass A ” ion beam example: new 84-86 Ge, 84-87 As
results

CARDS βg at LeRIBSS
VANDLE n-TOF array at LeRIBSS
ε n
~80% array at LeRIBSS
ε n
~30%
850 liters of 3 He at 10 atm

nearly 80% efficient and segmented 3 Hen neutron counter
ε n
~80%
ORNL, UTK
LSU , Mississippi
UNIRIB
850 liters of 3 He at 10 atm

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 priority for decay heat measurements established by the Nuclear Energy Agency (NEA) in 2007
January 2012

neutron detection
3Hen, VANDLE
β g and MTAS

22 parent radioactivities in 78 Ni region studied by means of β g spectroscopy at the HRIBF
78 Ni to 132 Sn region (~ 10), + MTAS (22), + VANDLE (29)
83 Se 84 Se 85 Se 86 Se 87 Se 88 Se 89 Se
77 As 78 As 79 As 80 As 81 As 82 As 83 As 84 As 85 As 86 As 87 As 88 As
76 Ge 77 Ge 78 Ge 79 Ge 80 Ge 81 Ge 82 Ge 83 Ge 84 Ge 85 Ge 86 Ge 87 Ge
75 Ga 76 Ga 77 Ga 78 Ga 79 Ga 80 Ga 81 Ga 82 Ga 83 Ga 84 Ga 85 Ga 86 Ga
74 Zn 75 Zn 76 Zn 77 Zn 78 Zn 79 Zn 80 Zn 81 Zn 82 Zn 83 Zn
Z=28
73 Cu 74 Cu 75 Cu 76 Cu 77 Cu 78 Cu 79 Cu 80 Cu
72 Ni 73 Ni 74 Ni 75 Ni 76 Ni 77 Ni 78 Ni 79 Ni
N=50

79
~ 2 days exp N=50
81 Ga
78 Zn 79 Zn 81 Zn
79 Cu
0.29(2) s
78 Ni initial yields : 79 Zn ~ 10 5 pps 79 Cu
+
~ 40 pps after charge exchange : 79 Zn 0.0
pps 79 Cu
-
~ 2 pps pure beam of 79 Cu ions → single neutron-hole states in N=49 79 Zn detected 79 Cu ions:
NSCL 2005 (2010): 754
HRIBF 2006: ~16 000
RIKEN 2010: ~ 10 000
HRIBF 2011: ~158 000 half-life of 79 Cu
Kratz 1991 : 188(25) ms (multi βn fit)
Hosmer 2010 : 257(+ 29,- 26) ms (ionβ)
Miller 2013: 290(20) ms ( βg
730 keV)
D. Miller, R Grzywacz et al., to be published

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) all βn-precursors given in this plot have T
1/2
< 1 s
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 similar conclusions: P. Hosmer, H. Schatz et al., PR C82 , 025806, 2010

Delayed Neutron Yield following 235 U fission
10 -2
Integral β,n measurements used for reactor analysis
10 -3
10 -4 b
-n isotopic decay data
ORIGEN is missing data for very short-lived fission products
10 -5
ORIGEN
Keepin (IAEA 6 group)
10 -6
0.1
1 10
Time after fission (s)
100 from Ian C. Gauld, ORNL Reactor Science Group (2010)
Note log scales !

Example of MTAS data – 139 Xe decay (A. Fijałkowska et al., ND2013)
( 139 Xe ~5% cumulative fission yield for n th
+ 235 U)
MTAS data (black) compared to
ENDSF-based simulations ( red ).
Lack of β-feeding and following g
-energy release from highly excited states in current data base !
MTAS-revised decay of 139 average
Xe g
-energy release increased from 935 keV to 1146 keV (23%)

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

g
79 Cu, 81,82,83 Zn, 85,86 Ga, 86 Ge, 86,87 As .....
molecular beams
GeS, AsS
861ms
86 As
484 ms
87 As
83 Ge 84 Ge
494 ms
85 Ge
226 ms
86 Ge
81 Ga 82 Ga
83 Ga 84
85 ms
Ga
304 ms
81 Zn
228 ms
82 Zn
117 ms
83 Zn
93 ms
85 Ga 86 Ga
290 ms
79 Cu
78 Ni
~ 3 ions/s, April 2012 pure Ga beams from laser ion source and hybrid 3Hen array

78
β-half-lives of 84,85,86 Ge and
84,85,86,87 As isotopes
C. Mazzocchi , KR, et al., → Phys. Rev. C87, 034315, 2013
I.N. Borzov’s DF3a+CQRPA

(HRIBF measurements → I.Borzov’s analysis → R.Surman’s modeling)
M. Madurga et al., Phys. Rev. Letters, 109, 112501, 2012
R. Surman 2012 experiment
FRDM Moeller 2003
DF3a+CQRPA Borzov 2011
+ post r-process abundances simulations with Moeller’sT
1/2
’s simulations with Borzov’s T
1/2
’s

Evolution of single-particle states beyond N=50 evolution of neutron 3s
1/2 vs 2d
5/2 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
(energy of s
1/2
Emerging N=58 d
5/2
-s
1/2 subshell ?
state dropping down towards d
5/2 gs for n-rich nuclei)

Neutron states in N=51 isotones, from Z=30 81 Zn to Z=50 101 Sn
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0
-200
28 30 32 34 36 38 40 42 44 46 48 50 52 n
1g
7/2 n
3s
1/2 n
2d
5/2
Darby, Grzywacz et al.,
PRL 105, 162502,2010
101 Sn 103 Sn 105 Sn ...
81 Zn decay, PR C82, 064314, 2010

Interesting experiment for RIKEN: 82 Cu β-decay to s
1/2 state in N=51
( 80,81,82 Cu β-decay experiments were accepted at the HRIBF, but ...)
81 Zn
T.Ohnishi,T.Kubo .. JPSJ 2010
0.2 pnA 238 U
82 Cu
(4-,5-)
Q
β
~ 17 MeV
T
1/2
~ 60 ms
βn
S n
~ 5 MeV
~ 0.6 MeV s
1/2 d
5/2
0 +
81 Zn
N=51
82 Zn with 100 part*nA of relativistic 238 U beam (RIKEN, FRIB ?) we can go for more ambitious study of
80 Co βndecay to the s
1/2 excited state in N=51 79 Ni 

Decay of N=55 86 Ga studied with “hybrid 3Hen” at LeRIBSS in April 2012. Pure and intense beams of 83,85,86 Ga 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 85 Ga, ~ 1- 3 pps of 86 Ga

Decay 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 + b n-branching ratio
2. Measurements with Modular Total Absorption Spectrometer MTAS
MTAS energy spectra in segmented array
→ beta strength within bg
-window (decay heat)
3. Measurements involving 3Hen and VANDLE → b
-delayed neutrons
βn-intensities and βn-energy spectra /Robert Grzywacz/
→ beta strength above neutron separation energy
g
→ determination of a full b
-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. Stracener
UT 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-Cichocka
Mississippi : J. A. Winger, S. Ilyushkin
Louisiana : Ed Zganjar, B.C. Rasco
UNIRIB : J.C. Batchelder , S. H. Liu
Vanderbilt : N. Brewer, J.H. Hamilton, J.K. Hwang, A. Ramayya, C. Goodin
Warszawa : A. Korgul , C. Mazzocchi
Krak ów : W. Kr ólas 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 )

~ 250 mg
252 Cf
~ 8
 g
254 Es

J. Roberto et al., workshop on SHE studies at the Dubna SHE Factory
College Station, TX, 12-13 th March 2013 about 12 mg to 15 mg of actinide material is needed for one SHE target

243 Am/ 244 Cm/ 248 Cm seed material and its n-capture/decay path to 249 Bk, 252 Cf, 253,254 Es and 257 Fm
94 Pu
Z
93 Np
96
95
Pu 238
Np 237
98
97
Cf
Bk
100
99
Fm
Es
Cf 249
, (n,f)
Cm
Am
Pu 239
, (n,f)
Np 238
Cm 242
Am 241
Pu 240
Cm 243
, (n,f)
Cm 244 Cm 245
, (n,f)
Cm 246 Cm 247
, (n,f)
Am 242 Am 243 Am 244 Am 245 Am 246
-
, EC
-
Pu 241
-
, (n,f)
Pu 242 Pu 243
-
Pu 244 Pu 245
-
Cf 250
Bk 249
-
Cm 248
, SF
Cf 251
, (n,f)
Bk 250
-
Cm 249 Cm 250
-
SF
Fm 254 Fm 255 Fm 256
Es 253 Es 254
SF
Es 255
-
Cf 252
,
, SF
Bk 251
-
Cf 253
-, (n,f)
Cf 254
SF
Pu 246
-
Fm 257
N

2012 – a very good year for SHE studies !
see 278 113 among the “Inventions of the year 2012” according to Time magazine
(most experiments were performed with ORNL-made actinide target materials)
(+1 TASCA)
16
(+25 TASCA) (+1 TASCA)
(+1 TASCA)
Yu.Ts. Oganessian et al.,
PRL 104, 142501, 2010; PRL 108, 022502, 2012; PRL 109, 162501, 2012; PR C 87, 014302, 2013 and submitted to PR C.

•
248 Cm+ 54 Cr,
33 out of 140 days, April-May 2011 (also 2012), beam dose ~5*10 18
search for isotopes of new element Z=120, 298,299 (120)
178,179
(T
1/2
~ 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
SHIP analog data acquisition GSI Annual Report 2011 (2012) dead time
~ 11
 s
 recoil
UTK Digital Signal Processing Laboratory recoil dead time
~ 0.3
 s

New ORNL-UTK detectors and digital data acquisition system
(similar DAQ at SHIP Z=120 exp was serving PSSD+Si-box+MCPs)
MICRON detectors
128 x48 mm,1 mm strips
300
 m DSSD
500
 m single Si-veto matching DSSD design six 120 x 65 mm single Si
300
 m Si-box
LF 250 flange
MESYTEC lin-log preamps
ISEG NIM HV
XIA Pixie16 rev D
(208 channels)
Dell Power Edge

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 48 Ca beam at Dubna.
(50% of 249 Cf, 35% of 251 Cf and 15% of 250 Cf and very low content of 252 Cf)

Experiment with 48 Ca beam and 240 Pu ORNL target material at Dubna
T
SF
~10-100
 s ?

Staszczak, Baran, Nazarewicz; Phys. Rev. C 87, 024320, 2013
Spontaneous fission modes and lifetimes of superheavy nuclei in the nuclear density functional theory only even-even nuclei plotted here
284 Fl (4n, 240 Pu)
?
296 118 (3n, 251 Cf)

1.
Impressive SHE harvest in 2012 at JINR , GSI and RIKEN !
2. ORNLmade 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 48 Ca beam ( 44 Ca, 40 Ca) and 240 Pu ( 239 Pu, 245 Cm, 248 Cm..) can help to connect nuclear mainland to the “Hot Fusion Island” and provide important data on fission/alpha competition.