Superheavy Element Research at Berkeley

Ken GregorichLawrence Berkeley National Laboratory

Festcolloquium and Workshop on the Future of Superheavy ElementsFebruary 17-18, 2004

Gesellschaft für Schwerionenforschung

The LBNL 88-Inch Cyclotron

First Operation in 1961K130 Sector focused cyclotronA/q < 5 for Coulomb Barrier

AECRU(present)

andVENUS

(Spring ’05)

Accelerator Capabilities

0

5

10

15

20

25

30

35

0 50 100 150 200 250

En

erg

y in

MeV

/am

u

Particle Mass in amu

Evolution of the 88-Inch Cyclotron Performance for

Heavy Ions at 1pnA

VENUS

AECR-U 1995

ECR- 1989

PIG-1984

0.01

0.1

1

10

100

H+3He+14N4+16O6+22Ne6+25Mg7+37Cl9+40Ar9+48a10+Ti5064Ni14+65Cu15+86Kr19+136Xe26+136Xe28+

Be

am o

n T

arg

et [

pµ

A]

1 pµA

Xe26+Xe28+

86Kr

Ar9+

25Mg

Ne6+O6+N4+

He+H+

37Cl48Ca

64Ni65Cu

Mass

50Ti .3 pµA

2 pµA

.06 pµA

Mass range andmaximum energy

Routinely availableCoulomb barrierbeam intensities

Present Operating Status

$2M/year - National Reconnaissance Office and US Air ForceBerkeley Accelerator Space Effects Facility (BASEF)to study the effect of radiation on microelectronics, optics, and materials for spacecraft

$3M/year - US. Department of Energy Office of Sciencefor basic Nuclear Science Research

This funding plan is guaranteed for at least two years

Is This Good for Heavy Element Experiments in Berkeley?YES! BGS could get up to 2000 hr/year of beamtimeNO! Scheduling and political conflicts with BASEF have already set back the Heavy Element Program

Berkeley Gas-filled Separator (BGS)

Construction “completed” fall 1999 Recycled Bevalac magnets Innovative design gives =45msr 70º bend gives superior separation ~1 mBar He fill gives full

momentum and charge acceptance

Beam rejection up to 1015

Transit time ~s Rotating target allows beam

intensities up to pA range Beam intensity, target

thickness, and efficiency give 1 event/(picobarn*week)

3000 3500 4000 4500 5000 5500 60000

1000

2000

3000

4000

5000

6000

7000

8000

Calibrated Spectrum with148Gd, 239Pu, 241Am, 244Cm

co

unts

per

5 k

eV

Energy (KeV)

Automated Energy and PositionCalibration Procedure

T = top channel B = Bottom channelET = mBT - aT

EB = mBB -aB

P = (ET - EB) / (ET + EB)

E = (ET + EB)(cP2 + dP +f )

Understanding the Position Resolution

BTBT

BTBT

EEBT

EB

ET

P

EEBT

EB

ET

E

E

P

E

P

E

P

E

P

E

E

E

E

E

E

E

E

2

2

2

2

2

2

2

2

2

2

2

2

Ignoring the (cP2 + dP + f) factor: E=ET + EB

This is standard error propagation,BUT

The CROSS TERM is important, because the fluctuations in thesignals from the top and bottom of a strip are ANTI-CORRELATED

Understanding the Position Resolution

Plugging in the derivatives and solving:

4

22222

222

844

2

E

EEEEBTBT

BT

BT

EEBTETEBP

EEEEE

This one is easy, because the partial derivatives are 1

This one is harder, becausehigh school was a long time ago

Note: is known from the widths of the peaks and can be found by . . .

E

TEBE

Understanding the Position Resolution

measuring the ET and EB signals through a NARROW slit ORfitting the end of the ET (or EB) spectrum with an error function . . .

600 610 620 630 640 650 660 670 6800

50

100

150

200

250

300

350315

0

cnts i

calcCnts i

680600 i

Strip 24 top, gated on 244Cm peak, mT = 9.44 keV/ch

Understanding the Position Resolution

From calibration data taken one week ago (room temperature):

(E = 17 keV, FWHM = 40 keV)

(T = B = 33 keV, FWHM = 78 keV)

(<0 indicates anti-correlated)

22 keV290E

0 2000 4000 6000 8000 10000 120000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

P (

mm

)

Energy (keV)

The result is . . . P is very weakly position dependent and nearly proportional to 1/E

FWHM for 8 MeV - 8 MeV- correlation should be 0.93 mm

FWHM for 8 MeV - 1 MeV-escape corr. should be 5.3 mm

2keV940BT EE

222 keV1090 BT

Notes on the Position Resolution Equations(or . . . These Equations Behave as Expected)

If , top and bottom signals are fully anti-correlated TBEE BT 22

221

2

E

EE

EBTT

p

If and , top and bottom are uncorrelated BT EE 0

BT EE

ETE

p

2 position resolution is independent

of vertical position

At the top or bottom edge (EB or ET = 0, respectively)position resolution is the same as in the anti-correlated case. Position resolution at center is better by a factor of 2

1

238U(48Ca,3n)2831121999: Vassillissa 2 SF observed 5.6 pb @ 231 ± 3 MeV half-life = 81 sec No SF observed < 4.0pb @ 238 ± 3 MeV 1999: Vasillissa SF observed after 10.29-MeV -decay of 287114 new 283112 half-life = 3 min

2001: BGS No SF observed < 1.6 pb @ 228-234 MeV B(in He) = 2.19-2.31 Tm

2001: Dubna Chemistry ~2.0 pb fissions could be long-lived 283112 with Rn-like Chemistry

2002: BGS No SF observed < 0.7 pb @ 228-234 MeV B(in He) = 2.19-2.31 Tm

2003: PSI@GSI Hg-Rn chemistry gave inconclusive result (sensitive only to long-lived SF activity)

2003: DGFRS 9.5-MeV after 10.0-MeV -decay of 287114 half-life ~ 5s seen in both 244Pu(48Ca,5n)287114 and 242Pu(48Ca,3n) reactions

2003: Vassilissa No SF observed < 1.2 pb @ 231±3 MeV 2 SF observed ~ 4.0 pb @ 234± 3 MeV new 283112 half-life = 5.1 min

2004: DGFRS 9.5 MeV ~3.0 pb @ 234±3 MeV half-life ~ 5s None observed <1.0 pb @ 240±3 MeV

283112 Summary

The 5-minute SF activity reported by Vassilissa is incorrectBased on information in 1999 and 2004 reports, random probabilities for correlation to an EVR on a several-minutes time-scale are HIGH

Determination of mass based on q/A and TOF for two events is NOT POSSIBLE

Implied -decay hindrance factor for 283112 is unusually large

~5-sec 9.5-MeV -decay of 283112 is more likely correctfollowed by ~200-ms SF of 279110 provides strong signature

E and half-life are consistent with decay systematics in the region

279110 occasionally decays by , resulting in a long -decay chain

Optimum 48Ca beam energy is between 234 and 237 MeV

238U(48Ca,xn)286-x112 experiments begin at the BGS on February 9 February 25 March 2----------------- --------------------

Are the UF4 Targets Any Good?

Targets are ~600g/cm2 UF4 evaporated onto 2-m Al foils

-spectroscopy of the 238U shows no large change in the thickness or uniformity of the UF4 layer

-particle energy loss measurements indicate that there is no large change in of UF4 thickness or Al thickness during the experiments

-particle energy loss measurements show the Al is actually 2.2 m(in-target beam energies are about 0.6 MeV lower than expected)

Atomic Force Microscopy shows a change in the UF4 structure (pictures to come)

Conclusion: Targets are good (although not perfect)

AFM of the edge of the UF4 layer(outside the visible beam stripe)

Overall UF4 thickness is 900 nm

Crystalline structure

Thickness variations up to +/- 2%

AFM of the center of the UF4 layer(inside the visible beam stripe)

Overall UF4 thickness 900 nm

large-scale melting of UF4

Variations up to +/- 20%

RMS thickness variations aremuch less than 10%

What is the 283112 Magnetic Rigidity?

Shell structure of the stripped ion is important

B/

A(T

m*1

0-3)

New Fit to B DataNo correction for stripped ion electronic configuration

6 8 10 12 14 16 18 20 223

4

5

6

7

8

9

10

11

12

13

14

15

q = 0.475(v/v0)Z1/3 + 1.15

v/v0 < 11.1

q = 0.706(v/v0)Z1/3 - 1.42

v/v0 >= 11.1

aver

age

char

ge in

He

gas

(v/v0)Z1/3

SASSY data 54<=Z<=96 BGS data 99<=Z<=110

New Fit to Br Datasinusoidal correction for stripped ion electron

configuration

6 8 10 12 14 16 18 20 223

4

5

6

7

8

9

10

11

12

13

14

15 SASSY elastic scattering BGS heavy element EVR fit to corrected average q

q = mx+b + c*sin((2/32)(Z-(mx+b)-d))

x = (v/v0)Z1/3

m = 0.641b = -0.235c = 0.517d =74.647

qex

p - c

orr

ect

ion

(v/v0)Z1/3

283112 from238U(48Ca,3n) should have:

v/v0Z1/3 = 11.3

q = 6.86

B = 2.21 Tm

New BGS Focal Plane DetectorsCover 9% in B

New experimentwill be run at 2.21 Tm(2.11-2.31 Tm)

compared to previous expt. @(2.19-2.31 Tm)

Do We Know the Beam Energy?

Reproducibility of beam energies is good to within 0.5% FWHM

Absolute beam energies accurate to within 2 MeV (comparison of 208Pb(48Ca,xn)256-xNo excitation functions)

New beam TOF detectors to be installed this week in adjacent beamline

Will be available for all 88-Inch Cyclotron users

Beam energy measurement should take 5-10 minutes

Future SHE Experiments at the BGS

238U(48Ca,xn)286-x112 : Independent confirmation of SHE production

Systematic study of production cross sections and magnetic rigiditiesfor asymmetric reactions with actinide targets

Heavier projectiles: 238U(50Ti,xn)288-x114, etc.

Design and construction of an actinide target capability for BGS

SHE chemistry using BGS as a preseparator

Enhanced sensitivity with high-intensity beams from VENUS

Cross Section Systematics

The “California Plot”

0.68 0.70 0.72 0.74 0.76 0.78 0.80 0.82 0.84 0.86 0.88 0.90 0.9210-1

100

101

102

103

104

105

106

107

108

109

27Al+236U

26Mg+238U

26Mg+232Th

22Ne+236U

16O+242Pu

51V+208Pb

124Sn+90Zr (3n)

124Sn+92Zr (3n)

124Sn+94Zr (3n)

124Sn+96Zr (3n)

86Kr+121Sb (3n)

86Kr+123Sb (3n)

40Ar+176Hf

40Ar+178Hf

40Ar+180Hf

19F+248Cm

24Mg+232Th

25Mg+232Th

48Ca+184W (3n)

48Ca+197Au (3n)

48Ca+208Pb (3n)

48Ca+180Hf (3n)

48Ca+176Yb (4n)

48Ca+209Bi

50Ti+208Pb

50Ti+209Bi

54Cr+208Pb54Cr+209Bi

70Zn+208Pb

64Ni+209Bi

64Ni+208Pb58Fe+209Bi

58Fe+208Pb

48Ca+208Pb

40Ar+238U

37Cl+238U48Ca+238U

48Ca+208Pb (4n)

48Ca+226Ra

48Ca+186W (4n)

22Ne+238U

18O+249Cf

22Ne+244Pu

22Ne+244Pu

18O+249Bk18O+248Cm

22Ne+238U

22Ne+232Th

16O+238U

13C+248Cm

ex

pe

rim

en

tal c

ros

s s

ec

tio

n (

pb

)

effective fissility

cold fusion (1n) w/ 208Pb & 209Bi tgt.s shell stabilized hot fusion (3n) hot fusion (3n-5n) w/ actinide targets

hot fusion (3n-4n) w/ 48Ca beams

22Ne+243Am22Ne+248Cm

22Ne+249Bk

26Mg+248Cm34S+238U

48Ca+244Pu

48Ca+243Am48Ca+245Cm

48Ca+248Cm48Ca+249Cf

48Ca+173Yb (4n)48Ca+172Yb (4n)

22Ne

16O

34S

48Ca

26Mg

30Si

31P

27Al

Recoil Transfer Chamber v.3

Smaller (fixed) volumeHoneycomb grid allows thinner MYLARCatcher foil holder for yield measurementUsed w/ heated capillary for gas-phase volatile organometallic chemistry

Transactinide Element Liquid-Liquid Extractions using

Berkeley Gas-filled SSeparator

Rf and Db (Z=104,105) isotopes are produced at the LBNL 88-Inch Cyclotron by bombardment of Pb and Bi targets with 50Ti. Rf and Db are separated from other nuclear reaction products with the BGS.

Recoil Transfer Chamber

At the end of the BGS, Rf or Db atoms pass through a Mylar foil into the RTC and stop in He gas. These products become attached to aerosols are then transported through a 20-m long capillary to SISAK.

Result: Successful proof-of-principle experiments demonstrating atom-at-a time chemical separations of transactinide elements with half-lives of only a few seconds, an important new capability for heavy element studies.

These experiments were performed in collaboration with the U. of Oslo, the U. of Gothenburg, and U. of Mainz.

For more details please see: http://folk.uio.no/jonpo/SISAK_and_preseparation_ASR2001_Aug2001_v6.pdfResult

SShort-lived Isotopes Studied by the AKufve technique

Continuous liquid-liquid extractions are performed with SISAK. The alpha-decay of the separated transactinide atoms is assayed by performing liquid scintillation pulse-height analysis on the flowing solution.

BGS RTC SISAK