Transcript Survival of Excited Compound Nuclei and Online Chemistry Experiments at Texas A&M University C.

Survival of Excited Compound Nuclei and
Online Chemistry Experiments at
Texas A&M University
C. M. Folden III
Cyclotron Institute, Texas A&M University
June 12, 2014
Research Goals
 We are interested in both the chemistry and physics of
heavy elements.
 Nuclear Reactions: Understand fusion-evaporation
reactions leading to the production of heavy elements.
 Understand the survival of excited compound nuclei.
 Chemistry: Perform “online” experiments with activity
collected from a physical pre-separator.
 Use “designer” molecules to study the complexation
behavior of transactinides and their homologs.
Projectiles with Z  20 Reacting with
Lanthanide Targets
MOTIVATION:
Prospects of SHE
Synthesis with Zp > 20
Rxns. Studied:
48Ca CN 50Ti CN
45Sc CN
54Cr CN
How do you make a heavy
nucleus?
 The evaporation residue
cross section can be
described as:
S n ,1
En ,1
S n,2
   cap PCNWsur ( E *, l )
  cap PCN Px
x

n
/  tot i
n
/  f i
i 1
  cap PCN Px
x

i 1
 n Pn


 f Pf
2mn gr02 A 2/3
2
En, 2
S n ,3
En,3
E1*
Fission
E2*
Fission
E3*
Fission
S n,4
En, 4



E *  Bn
0
E* B f
0
n ( E *  Bn   ) d
f ( E *  B f  K ) dK
Evaluation of n/f
 Do Taylor Series expansions around E = E* – Bn and E
= E* – Bf, and use d(ln /dE  1/T:
n exp( Bn / T )

f
exp( Bf / T )


E *  Bn
0
E* B f
0
 ( E * )exp( / T ) d
 ( E * )exp( K / T ) dK
E *  Bn
* T]
n / f 2 2exp[
(Bn B
f )/
/3
(
E
 Bn   ) d
n
2mn gr0 A
0


 n Pn


 This relationship
is2 approximately
true, but
E* B f
P
*
f
f
E trivial.
B f  K ) dK
determining the input values isf (not
0
Influence of Bf – Bn on Cross
Section
 The 48Ca-induced reactions show the influence of
Bf – Bn on survival and therefore cross section.
 The significant change in Bf – Bn for Z > 20 is
problematic.
8
213
Fr
Rn
207
At
202
Po
210
7
6
5
1
165
Ho(48Ca,4-5n)209,208Fr
162
Dy(48Ca,4-5n)206,205Rn
159
Tb(48Ca,4n)203At
154
Gd(48Ca,4n)198Po
10-1
180
4
3
2
185
190
195
200
205
Projectile Ecot (MeV)
210
215
st
1
nd
2
rd
3
th
4
Neutron Emitted from the CN, ACN to ACN-4n
Bf - Bn (MeV)
EvR (mb)
10
Heavy Element Reaction Studies at
the Cyclotron Institute
 Our focus has been on determining which projectile is most
likely to lead to the next new element.
 Substantially reduced cross sections are observed for 45Sc
and 50Ti compared to 48Ca.
 The data suggest that produced elements 119-120 will be
very difficult (cross sections ~ 10-50 fb are reasonable).
102
48
Ca + 162Dy
48
Ca +
48
Ca + 162Dy
159
Tb
101
EvR (mb)
100
10-1
50
Ti + 162Dy
50
Ti + 160Gd
10-2
50
Ti + 159Tb
10-3
30
35
40
45
50
55
60
65
35
40
45
50
55
60
65
CN Excitation Energy (MeV)
35
40
45
50
55
60
65
How does an online chemistry
experiment work?
 Making heavy atoms available for online chemistry
requires several steps.
Physical Pre-Separation
Rotating Degrader
Cyclotron
Gas Stopping
Chemistry Experiment
Recoil Transfer Chamber
Simulations
 STAR-CCM+ and SIMION were used for simulations.
Nozzle: 2.0 L/min
AC Inlet: 0.5 L/min
Vwindow – Vnozzle = 420 V
Lines are 10 V apart
Recoil Transfer Chamber
Performance
 Two modes of operation: fast extraction (<150 ms) or
maximum efficiency (several seconds for extraction).
 Results suggest that online chemistry experiments are be
feasible. An online laboratory is being installed.
 Next step: Aerosol transportation measurements.
Recoil Transfer
Chamber Schematic
New Gas Stopper at the
MARS Focal Plane
Extraction Efficiency for
118Sn(40Ar, 6n)152Er
Future Work
 Nuclear Reactions: Study reactions with lower cross
sections such as 48Ca, 45Sc, 50Ti, 54Cr + 181Ta, 197Au, etc.
 Products will be deformed and weakly shell-stabilized.
 Provides a complement to the current studies.
 Long term: Move toward light transactinide production
(Z ~ 104-105).
 Offline Chemistry: Start studying extraction of group 13
elements.
 Online Chemistry: Begin “manual” chemistry
experiments and switch to “automated” experiments.
 Using cryptands or crown ethers as extractants.
Future Online Chemistry: Crown
Ethers
 Crown ethers have
shown promise for
separation of
Group 4 elements.
 Good separation
factors.
 High extraction:
(Kd ~ 10).
 Fast extraction.
O
O
O
O
O
O
DC18C6
Courtesy of R. Sudowe.
LLNL is developing automated systems for atom-at-a-time
chemistry
Product transport
from cyclotron
Gas-Liquid Interface for
Transferring Transactinides to
Automated Radiochemistry
(GLITTAR)
Removes reaction products
from transport gas and
transfers them to aqueous
phase
Super Heavy Element Liquid
Automation (SHELA)
Macrocyclic ligands
for specific ion
extraction
Modular, rapid chemistry
system for low volume
separations
Slide courtesy of D. A. Shaughnessy.
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Gas-Filled Separator: AGGIE (nee
SASSYER)
 Acceptance cone: ±50 mrad horizontally and vertically
 Efficiency: 50-75% for 59Co + 209Bi → 267Ds + n
 Bmax = 2.2 T m
 Arrived at Texas A&M in January 2014.
Summary
 We have a broad program to study the chemical and
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physical properties of heavy elements.
Current experiments have demonstrated that the
production of new superheavy elements may be very
difficult.
We have a vibrant offline chemistry program and a
new gas stopper to enable online experiments.
We are leaders in a national collaboration to perform
online chemistry experiments.
A new gas-filled separator will substantially increase
the sensitivity of all of our experiments.
We are starting to receive national and international
interest in our program.
Acknowledgements
 Heavy Element
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Group Members:
M. C. Alfonso
M. E. Bennett
T. K. Bhardwaj
M. J. DeVanzo
L. D. Fields
M. M. Frey
D. A. Mayorov
E. E. Tereshatov
(not pictured)
T. A. Werke
Acknowledgements: Collaborators
 N. Gharibyan
 J. Despotopulos  M. E. Bennett
 R. A. Henderson
 J. Rolfes
 K. J. Moody
 R. Sudowe
 J. P. Greene
 D. A. Shaughnessy
 Funding agencies:
 Grant A-1710