The Discoveryof Element 117
Presented toFriends of ORNL
Jim Roberto
Oak Ridge National Laboratory
Oak Ridge, Tennessee
July 21, 2010

The discovery of element 117
is a historic accomplishment•! An important advance in nuclear structure,
confirming the “island of stability”
for super-heavy elements•! Includes the discovery of 11 new heaviest
known isotopes with atomic numbers
105–117•! Featured on the cover of Physical Review
Letters, more than 250 news articles(New York Times, Science, etc.)•! Changes the periodic table(and eventually every high school
chemistry book)•! Even a new ice cream!
2

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Featured flavor at Razzleberry Ice Cream Lab

The discovery of chemical elements
began more than 10,000 years ago
1789:
LavoisierLddevelops
firstmodernlist ofcchemicaleelements

Copper, gold, lead,silver, iron, carbon,tin, sulfur, zincAncient history,
y 90
9000–1000000
BCE

Middle ages, ~800
Midd00 CE

Arsenic,
antimony,bismuth3

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21 elements:
Commongases,
metals, anduranium

1700ss1700

50 elements:
Noble gases,semiconductors,
rare earth metals,
and radium

1800s
00s

1869:
MendMendeleev
arrangesarrang 63
elementsele
in thefirstmodernm
periodic
petableBenefits of Mendeleev’s table•! Demonstrated trends/similarities
by arranging elements
in a two-dimensional network•! Reordered elements despite theiraccepted masses (early indicationthat atomic mass was not thedetermining factor)•! Allowed gaps in the table, predicting
10 new elements (7 actually exist)
In 1906, Mendeleev camewithin one vote of winning
the Nobel Prize

Mendeleev’s periodic table (1869)4

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The importance of atomic number•! In 1913, Moseley showed thatatomic number Z (the numberof protons in the nucleus)
is the determining factor
in the periodic law•! Moseley’s work revealed
gaps at atomic numbers
43 and 61 (later filledby the discoveryof technetiumand promethium)•! By 1939, there were
91 known elementswith uranium (Z = 92)
having the highest
atomic number
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X-ray spectraof the elements, showing
the proportionalityof frequency withatomic number [Moseley,Phil. Mag. (1913), p.1024]

Henry Gwyn
Jeffreys Moseleyy
7–(November 1887–August 1915)

The synthesis of transuranics
and element 61
Seaborg’s discoveryof the actinides led
him to modify theperiodic table•! Transuranic elements (atomic numbers
greater than 92, uranium) do not naturally
exist on Earth•! Fermi proposed creating heavier elements
by irradiating uranium with neutrons(he missed the discovery of fission)•! Seaborg and co-workers synthesized
elements 93–103 in the 1940s and 1950s–! To further this research, Seaborg wasa major advocate for construction of HFIR•! Scientists at ORNL separated the missing
element 61 from fission products in 1945,
completing the lanthanide series

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ORNL’s Graphite Reactor,
site of the discoveryof element 61 (promethium)by Marinsky, Glendenin,
and CoryellSuper-heavy elements, Z > 103•! 1960s: Existence of transactinides(super-heavy elements) first proposedby Seaborg–! Half-lives ranging from hours (Z = 104, 105)
to milliseconds (Z = 115, 116, 118)–! Expected to be analogous in chemical
properties to Hf, Ta, etc., and placed
immediately beneath these elementsin the periodic table•! 1964: First transactinide (element 104,rutherfordium) synthesized
at the Joint Institutefor Nuclear Research(JINR), Dubna, Russia

Neutron

Ne-22

Pu-242

242

2294Pu10Fusion

Compound Elementnucleus
104
263

264

Ne104

Rf*104

Rf + nTransactinides (super-heavy elements)
Lanthanides
Actinides

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Bombarding Pu (94 protons) with Ne (10 protons)
results in a compound nucleus, Z = 104 protons

Why study super-heavy elements?
Super-heavy element research advances nuclear scienceand atomic physics at the extreme limits of stability,
nuclear mass, and relativistic electron behavior

Key questions:
Oganessian,•! How many protons and neutrons can a nucleus
ENAM (2008)
hold together?

110•! Can we develop a comprehensive theoryof nuclei from the lightest to the heaviest?

108

106

•! Does the predicted “island of stability”
for super-heavy elements exist,
and what are its properties and boundaries?

104•! Can we understand the physical and chemical
behavior of elements with extreme numbersof neutrons, protons, and electrons?

160

162

164

The island of enhanced stability•! The possibility of an “island of stability” of superheavy elements with greatly increased lifetimes(perhaps millions of years) was originally postulated by Seaborg•! When neutrons and protons completely fill the energy levels of a given nucleus,
the nuclear binding is strongest, leading to longer lifetimes•! Heaviest stable isotope (Pb-208): Closed nuclear shells for both protons (82) and neutrons (126)•! Next “doubly magic” nucleus: Occurs around Z = 114 and N = 184,
the presumed center of the island of stability

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Isotopes of element 113
demonstrate increased stability
with increasing neutron number! " 1 pb
249Bk + 48Ca

294! = 4.2 pb

117

243Am + 48Ca! = 0.03 pb

287

288

290

115

115

115

209Bi + 70Zn

237Np + 48Ca

278

282

283

284

286

113

113

113

113

113

0.07 s

0.1 s

0.5 s

10 s

0.24 ms
RIKEN (Tokyo)

Half-life

JINR, LLNL, ORNL collaboration
Y. Oganessian. Perspectives of JINR–ORNL collaboration in the studies ofsuperheavy elements, JINR Scientific Council, September 24–25. 2009, Dubna

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1990s: Cold fusion experiments at GSI
in Germany extended the periodic
table to Z = 112•! Bombardment of a heavy target(Pb, Bi) with a heavy ion(Fe, Ni, etc.) at energies
just above the Coulomb barrier•! Imparts minimum internal energy
to the compound nucleus•! Cross sections decrease steadily
with increasing atomic number,making the technique impracticalabove Z = 112

Cold fusion cross sections for compound
nucleus formation up to Z = 113

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1 atom/year!

2000s: Hot fusion techniques using 48Ca
beams were pioneered in Russia•! 48Ca is a “doubly magic” neutron-rich isotope•! Bombardment of actinide targets(Cm, U, Cf, etc.) with 48Ca beam createsa highly-excited compound nucleus•! At higher neutron numbers, these nuclei
stabilize by emission of 3–4 neutrons•! Overall cross sections increase, reversing
the cold fusion trend and extending the rangeof synthesis experiments to Z = 118
and above•! For element 117, this techniquerequires a berkelium target
At higher neutron numbers, spontaneous fission
is suppressed, allowing excited compound nuclei
to stabilize via multiple neutron emissions
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The development of 48Ca hot fusion has
extended the periodic table to Z = 118
Year

ElementLaboratory

Reaction

2000

114

JINR, Russia1

48Ca # 244 Pu (ORNL)

50 atoms

2004

113

JINR, Russia1

Decay product of element 115

8 atoms

2004

115

JINR, Russia1

48Ca # 243 Am (ORNL)

30 atoms

2005

116

JINR, Russia1

48Ca # 248 Cm (RIAR/ORNL)

30 atoms

2006

118

JINR, Russia148Ca # 249 Cf (ORNL)

3 – 4 atoms

2010

117

JINR, Russia2

48Ca # 249 Bk (ORNL)

6 atoms

1 In collaboration with LLNL
2 In collaboration with ORNL, LLNL, Vanderbilt, and UNLVAll of these discoveries used ORNL isotopes

13

Number of atoms
synthesized to date

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The periodic table in 2009
Period
13
IIIA

2
IIA

14
IVA

15
VA

16
VIA

17
VIIA

2H

2345678910

LiBeB

CNO

FNe

1112131415161718NaMg

AlSiPS

ClAr

345671411He

1920

21

2223

24

252627

28

2930

3132

33

3435

36

K

Ca

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr

37

38

39404142

434445

46

4748

49

50

51

52

53

54

Rb

Sr

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

55

56

57

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

Cs

Ba

La

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Po

At

Rn

87

88

89

104

105

106

107

108

109

110

111

112

113

114

115

116

Rg

Cn

Uut

Uuq

Uup

Uuh

117

Uuo

Fr

Ra

AcLanthanide Series

5859

60

61

6263

64

65

66

67

68

69

70

71

CePr

NdPm

SmEu

GdTb

Dy

HoErTmYb

Lu

Actinide Series

90

91

92

93

94

95

96

97

98

99

100

101

102

103

Th

PaU

Np

Pu

Am

Cm

Bk

Cf

EsFm

Md

No

Lr

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Rf

Db

Sg

Bh

Hs

Mt

Ds118

What it takes to produce a few atomsof element 117
3 g of Ca-48
20 mg of Bk-249
Chemical separation of Bk
from irradiated targets

Natural abundance enriched 500 times at Sverdlovsk-45
Produced by 250-day neutron irradiation in the world’s highest
thermal neutron flux at Oak Ridge
Impurities less than 2 ng (one part in 107), performed at Oak Ridge

Preparation of Bk target foils Specially produced at Dimitrovgrad to survive massive ion bombardment
Target irradiation with Ca-48

150 days continuous irradiation in the world’s most intense Ca-48 beam at Dubna

Detection

One superheavy atom per 1012 reaction products at Dubna

Analysis

Nuclear data analysis of thousands of candidate reactions (Dubna and LLNL)

HFIR/REDC reactor/hot cell complex (ORNL)15

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Flerov Laboratory (Dubna)

The element 117 research team•! Joint Institute for Nuclear Research (Dubna)
Yu.Ts. Oganessian, F. Sh. Abdullin, S. N. Dmitriev, M. G. Itkis, Yu. V. Lobanov, A.N. Mezentsev,
A. N. Polyakov, R. N. Sagaidak, I. V. Shirokovsky, V. G. Subbotin, A. M. Sukhov, Yu. S. Tsyganov,V. K. Utyonkov, A. A. Voinov, G. K. Vostokin•! Oak Ridge National Laboratory
P. D. Bailey, D. E. Benker, J. G. Ezold, C. E. Porter, F. D. Riley, J. B. Roberto, K. P. Rykaczewski•! Lawrence Livermore National Laboratory
R. A. Henderson, K. J. Moody, S. L. Nelson, D. A. Shaughnessy, M. A. Stoyer, P A. Wilk•! Vanderbilt University
J. H. Hamilton, A. V. Ramayya•! University of Nevada, Las Vegas
M. E. Bennett, R. Sudowe•! Research Institute for Advanced Reactors (Dimitrovgrad)
M. A. Ryabinin

ORNL staff were involved in all aspects of the research
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Lead-up to the discovery•! Yuri Oganessian (JINR) proposes element 117
experiment to ORNL•! Oganessian presents colloquium at ORNL•! JINR/ORNL/LLNL/Vanderbilt collaboration
February 2005
established•! Experiment awaits next Cf campaign•! Oganessian, Roberto, and Joe Hamilton
September 2008 (Vanderbilt) meet in Nashville to coordinate
planning for the experiment•! DOE authorizes Cf separation including research
November 2008use of Bk•! ORNL and JINR sign Scientific Collaboration
December 2008
and Material Transfer Agreement•! Cf targets removed from HFIR
January 2009
(Bk decay clock starts ticking)•! REDC-separated Bk shipped on schedule
June 15, 2009
to Russia•! Bk target preparation at Dimitrovgrad
July 2009(30 layers hand-painted on target wheel)•! Experiment begins at Dubna
July 28, 2009
(Ca-48 beam on target)
December 2004

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Academician Yuri Oganessian (right)
with JINR staff member Vladimir Utyonkov

Reactor irradiationof Am/Cm targets at HFIR•! Targets specially designed for reactor conditions:–! Composition controls fission and gamma heating–! Targets remain in the reactor for 11 cycles(approximately 18 months)•! Irradiation in the HFIR flux trap–! Thermal neutron fluxof 2.5 ! 1015 neutrons/cm$%s(world’s highest steadystate neutron flux)–! 31 target positions(10–13 targets
typically irradiated)–! Produces ~35 mg
252Cf per target(smaller quantities
of Bk, Es, Fm, others)
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Target positionsin the flux trap of a
HFIR fuel element
Fuel change-out at theHigh Flux Isotope Reactor (ORNL)

Bk production/separation cycle (18–20 months)
Radiochemical Engineering Development Center, ORNL
Irradiatedtargets

Aluminum
dissolution

Causticsoluble FP

HFIR
irradiation

Targetfabrication

Nitric aciddissolution
HDEHP
extraction

Waste organic

LiCl anion
exchange 1

Final 249Bk productBk
22 mg (320 d)

CfEs

AHIB cationexchange

Microspherepreparation

Lanthanide FP

LiCl anion
exchange 2

Fm
Hydroxide
precipitation

Trans CmOxalatePurification
Am/Cm (40g)More than 50 ORNL staff contributed
to the Bk production and separation•!RadiochemicalEngineeringDevelopmentCenter•!High Flux
Isotope Reactor•!Nuclear Scienceand TechnologyDivision•!ChemicalSciences Division

The final product (starting from 40 g of irradiatedAm/Cm) is the green speck at the bottomof the glass vial, 22 mg of ultrapure Bk

A race against time•! Bk-249 has a 320-day half-life–! 40% decay loss over the experiment•! Seamless coordination required–! HFIR operations (11 on-time cycles)–! REDC processing–! Transportation–! Target preparation–! Accelerator operations (24/7 for 5 months)•! Customs issues added drama

Bk packages being inspected
at Sheremetyevo Airport–! 5 flights across the Atlantic (lots of frequent flyer miles for our Bk)–! Still the fastest U.S.-Russia actinide transfer in history

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Heavy element production and detection
at the Dubna Gas Filled Recoil Separator•! 48Ca beam suppliedby the U400 cyclotron•! Total beam dose
>1019 particles•! Rotating target
distributes beam
heating•! Rapid separation
allows detectionof nuclei with shorthalf-lives•! Suppression factors
are 1015 for beam
particles and 104
for target-like particles

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Heavy Ion Cyclotron U-400 at theFlerov Laboratory, JINR (Dubna)

The element 117 experimentoffers the possibility of making
16 new neutron-rich isotopes

293

294

297

117

117
10.75 MeV
0.1 s

289

•! Closer to the island of stability

115
10.4 MeV
0.25 s•! Longer half-lives
for chemistry experiments

285

Z = 114286

113
9.9 MeV
1.5 s•! New information on shellstabilization, fission barriers,
and the next magic numbers

281

N = 184282

111
9.1 MeV
1–12 min
277

278

109
?5
9.1–9.4 MeV

A. Sobiczewski,
Acta. Phys. Pol.
B41, 157 (2010)290

2 s–1.5 min
274

107

16 new neutron-richisotopes of theheaviest elements

8.6–8.8 MeV
0.5–10 min
270

105
8.2–8.3 MeV
5–40 min
TEC > 10 h

TSF > 50 d 266
6.8 MeV 103
266
Ta > 600 d
6.8 MeV23

TEC > 10 d 102

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249Bk + 48Ca !297117* ! 294–293117 + 3–4n

Energy spectra in the detector•! Evaporation residues (including element
117 nuclei) are implanted into a silicondetector array•! Emitted alpha particles are registered inthe implantation detector or side detectors•! Total energy spectra of !-like signals
with beam on and off•! Arrows denote observed events•! The probability of a random sequence initiating
any given decay chain is 10-6 or less•! The beam is switched off following
candidate events (identified ion
implantation followed by a fast !-likesignal from the same location within the
expected energy range for Z = 117)•! With the beam off, detection system ismonitored for subsequent decay chain!-signals from the same location(with the decay chain endingin spontaneous fission)•! If no additional !’s are detected, beamon target is resumed after 15 minutes
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Energy (MeV)New isotopes from element 117
decay chains expand our knowledgeof neutron-rich nuclei•! Closer approachto the shell at N = 184
results in a decreasein "-decay energy
and an increase in lifetime•! Continued trend toward
increasing stability forhigher neutron numbers

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Elements
119 and 120(and possibly 121)
appear to bewithin reach

251Cf + 50Ti

254Es + 50Ti

249Cf + 50Ti

120
249Bk + 50Ti

254Es + 48Ca

118
116

251Cf + 48Ca

Z = 114114

N = 184

112

110

Challenges:•! Cf-251 requires special handling/processing•! Ti-50 beams need development,
and cross sections are small•! HFIR can produce Es-254,
but only in small quantities

108
106
104

160

162

164

166

168

170

Summary•! A new chemical element with atomic number Z = 117 has been synthesized–! 2nd element discovered by ORNL, 9th discovery using ORNL isotopes•! 11 new heaviest known isotopes observed in element 117 decay chains•! General trend toward increased stability with increasing neutron number•! Longer half-lives offer the potential
for chemistry studies to establish locationin periodic table–! On-line experiments in progress at Dubna•! A consistent picture of nuclear propertiesof heaviest nuclei is emerging–! Critical role of nuclear shells–! Experimental verification of the island of stability•! New targets and beams offer the potential
for higher neutron numbers and extending
the periodic table to even heavier elements
27

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