Potential Capabilities at Los Alamos Meson ... - ACS Publications

64 Potential Capabilities at Los Alamos Meson Physics Facility To Study Nuclei Far from Stability W. L . Talbert, Jr., and M . E . Bunker

Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on July 13, 2018 at 07:06:03 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Los Alamos National Laboratory, Los Alamos, N M 87545

Feasibility studies have shown that a He-jet activity transport line, with a target chamber placed in the LAMPF main beam line, will provide access to short-lived isotopes of a number of elements that cannot be extracted efficiently for study at any other type of on-line facility. The He-jet technique requires targets thin enough to allow a large fraction of the reaction products to recoil out of the target foils; hence, a very intense incident beam current, such as that uniquely available at LAMPF, is needed to produce yields of individual radioisotopes sufficient for detailed nuclear studies. We present the results of feasibility experiments on He-jet transport efficiency and timing. We also present estimates on availability of nuclei far from stability from both fission and spallation processes. Areas of interest for study of nuclear properties far from stability will be outlined. 1. Introduction A He-jet coupled on-line mass separator, used in conjunction with a target chamber placed in the LAMPF main beam, offers an especially attractive approach for the study of nuclei far from stability. Such a facility would provide access to isotopes of a number of elements that cannot be efficiently extracted for study at any other type of on-line separator system, and the use of a long capillary transport line would allow the separator ion source to be located outside the accelerator beam-line shielding, greatly reducing the installation cost. The He-jet technique requires thin targets in order for the reaction products to escape, and to produce a sufficient yield of radioisotopes far from stability for detailed nuclear studies, a beam intensity comparable to that available at LAMPF is needed. The mass-separated ion beams extracted from the proposed system would be directed to various experimental devices capable of determining basic nuclear properties such as half-life, spin, nuclear moments, mass, and nuclear structure. The data acquired would have broad application to theories of nuclear matter and to such related topics as nucleosynthesis of the elements. We 0097-6156/ 86/ 0324-0426S06.00/ 0 © 1986 American Chemical Society

Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

64.

TALBERT

estimate

that

427

Potential Capabilities at LAMPF

AND BUNKER

several

hundred

previously

unobserved

nuclei,

both

neutron-

d e f i c i e n t and neutron-rich, would become a v a i l a b l e f o r study. T h i s report presents bility

s t u d i e s , along

a b r i e f summary of the r e s u l t s of our He-jet

feasi

with estimates of which n u c l e i would become a v a i l a b l e

with our proposed f a c i l i t y .

S p e c i f i c areas f o r i n i t i a l s t u d i e s are a l s o sug

gested.

2.

He-jet

The

a c t i v i t y transport

concerns

transport

were:

studies

addressed 1)

Will

in

the

our

feasibility

He-jet

studies

technique work at

of

He-jet

activity

the beam i n t e n s i t i e s

that e x i s t at LAMPF?; 2) What transport e f f i c i e n c i e s can be expected f o r both fission

and

activity

s p a l l a t i o n products?;

transported?;

and

4)

3)

What

What

aerosols

is

the

time

and/or

dependence

aerosol

of

the

conditions

are

optimum? Using both s p a l l a t i o n - and we

determined that the He-jet

sities

(~800μΑ).

activities

Absolute

through

a

22-m

f i s s i o n - p r o d u c t targets i n the LAMPF H

efficiencies long

f o r transport

capillary

T r a n s i t time measurements appear convincing could

be

made a c c e s s i b l e

f o r study.

more e f f i c i e n t transport than KC1 Optimization employing two

of

the

We

were found

We

of

refractory-element

to average about

60%.

that a c t i v i t i e s as short as 300 found that P b C ^

aerosols

ms

provided

or NaCl a e r o s o l s .

target

chamber c o n f i g u r a t i o n

r a d i a l l y - d i r e c t e d i n l e t s at ± 135°

capillary outlet.

beam,

technique should work w e l l at LAMPF beam i n t e n

resulted

in a

design

to a s i n g l e r a d i a l l y - d i r e c t e d

have chosen an i n s i d e c a p i l l a r y diameter of 2.4

mm

as a

reasonable compromise between target chamber purge rate and helium flow r a t e . Two

target chambers have been designed, one

for s p a l l a t i o n targets. i n g , would be beam-stop.

l o c a t e d at

The

target

f o r f i s s i o n t a r g e t s and

one

These chambers, which are designed f o r remote s e r v i c the

end

of

a vertical

chambers incorporate

the

determined from our f e a s i b i l i t y experiments and

s h i e l d plug inlet

and

near

the

LAMPF

o u t l e t geometries

f e a t u r e double containment

to

allow use of a c t i n i d e t a r g e t s . One

concern

remains

in

our

experience i n coupling a He-jet

considerations.

to a mass separator

Despite

the

considerable

i o n source [M0L81,0KA81],


428

NUCLEI OFF THE LINE OF STABILITY

the

reported

achieved

the He-jet ress.

total

efficiencies

are

characteristically

with normal o n - l i n e separator systems. c o u p l i n g and

Current

less

that

efforts

those

to improve

i o n i z a t i o n e f f i c i e n c i e s are, however, showing

prog-

An i o n o p t i c a l design has been made that i n c o r p o r a t e s a non-dispersive

intermediate image to allow f o r c o r r e c t i o n of i o n source f l u c t u a t i o n s .

A con-

c e p t u a l layout f o r the o n - l i n e system with t h i s design i s shown i n F i g . 2.1.

Fig.

3.

2.1

Layout of the proposed o n - l i n e mass separator system at LAMPF, showing conceptual i o n o p t i c a l design f o r a s i n g l e magnetic stage.

Production estimates f o r n u c l e i f a r from s t a b i l i t y

To d e f i n e more a c c u r a t e l y the boundaries

of the mass regions that could

be accessed with the proposed He-jet coupled mass separator system, production cross

s e c t i o n s f o r both

stability product [RUD66].

n e u t r o n - d e f i c i e n t and

have been estimated

neutron-rich nuclei

f o r 800-MeV proton r e a c t i o n s .

cross s e c t i o n s were estimated

through

use

The

f a r from

spallation-

of the Rudstam systematics

For e s t i m a t i o n of the f i s s i o n - p r o d u c t cross s e c t i o n s , however, there

i s no e s t a b l i s h e d , s i m i l a r approach.

Thus, an e m p i r i c a l approach was


taken i n

64.

which two and


TALBERT AND BUNKER overlapping

cesium

Gaussian d i s t r i b u t i o n s were f i t t e d to e x i s t i n g rubidium

i s o t o p i c d i s t r i b u t i o n s obtained

at

156

[TRA72,BEL80] —

one Gaussian f o r the neutron-rich

and

neutron-deficient

one

f o r the

were then v a r i e d w i t h A and other d i f f e r e n c e s

portion.

we

between the

assume

that

needed f o r spectroscopic only

170

μb i s r e q u i r e d

i n t e n s i t y of 800

uA.

neutron-deficient

rubidium and was

atoms/s

cesium data.

of at l e a s t 10

a

measurements and

mass-separated

that

f o r the n u c l i d e

According

to

our

i n question,

cross-section

nuclei with calculated

accessible

over two

2 3 8

enormity of our by

7 6

S r and

high-energy

and

of

the

radionuclide

cross

Sn.

has

s e c t i o n of

assuming a LAMPF beam estimates, e s s e n t i a l l y

On

will

μb (assuming

I n t e r e s t i n g nuclear 1 0 0

are

system

the

the

regions

neutron-rich

and mass 60-140 can

U with a cross s e c t i o n of >1

current

be

Table

ignorance of n u c l e i f a r from s t a

s p a l l a t i o n and

decades of p r o l i f i c o n - l i n e

Table 3.1.

GeV

Gaussians

[TAK73] h a l f - l i v e s >300 ms

d i f f e r e n t target m a t e r i a l s ) .

produced i n high-energy f i s s i o n of

bility

the

the mass separator

side of s t a b i l i t y , most n u c l e i w i t h h a l f - l i v e s >300 ms

summarizes the

1

accomplished by i n t e r p o l a t i o n .

of

that could be reached i n c l u d e those near

3.1

and

Adjustment

be produced i n 800-MeV s p a l l a t i o n w i t h a cross s e c t i o n of >1 use

MeV,

parameters of

a one-percent o v e r a l l e f f i c i e n c y , a p a r t i a l production

about 0.7

all

1000

The

MeV,

p o r t i o n of the d i s t r i b u t i o n

Ζ to account f o r the mass-yield v a r i a t i o n s

c r o s s - s e c t i o n d i s t r i b u t i o n s to 800 MeV If

429

fission

reactions,

despite

studies.

Numbers of n u c l e i with unknown p r o p e r t i e s between known l i m i t s and 300-ms (according to the gross theory of beta d e c a y ) or l ^ b c r o s s - s e c t i o n l i m i t s ; Z*10-90. 9

Neutron-rich [ U(p,f)]

Mass Half-life Decay scheme Spin-parity

Of

Neutron-deficient [Spallation]

2 3 8

Property

281 170 243 300

those n u c l e i included i n Table 3.1,

436 198 630 484

we

expect that unique access to about

h a l f would come from a He-jet coupled mass separator

at LAMPF.

We


plan to

use

430

NUCLEI OFF THE LINE OF STABILITY

this

unique access

to advantage

i n proposed

s t u d i e s , to

complement

(rather

than compete with) s i m i l a r studies at other o n - l i n e f a c i l i t i e s .

4.

Possible Specific

Studies

Given the l a r g e v a r i e t y of new

n u c l e i that would become a v a i l a b l e with

the proposed o n - l i n e separator system, a focus i s needed f o r p o s s i b l e i n i t i a l studies.

On

the other hand, the

importance of making systematic

nuclear p r o p e r t i e s over s i z e a b l e regions must be recognized. novel f e a t u r e of shape coexistence was tematic s t u d i e s of nuclear decays.

s t u d i e s of

For example, the

e s t a b l i s h e d only through d e t a i l e d , sys-

A notable f e a t u r e of the proposed o n - l i n e

mass separator system i s the c a p a b i l i t y to make unique nuclear s t r u c t u r e s t u d i e s i n s e v e r a l i n t e r e s t i n g regions. One strong

such

deformation

support be

region

i s that

[MÔL81].

around

N=Z=38, p o s t u l a t e d

Although

this

to

p r e d i c t i o n has

be

a

some

region

of

experimental

[LIS82,PRI83,HEY84], other t h e o r i e s p r e d i c t n u c l e i i n t h i s r e g i o n

s p h e r i c a l , with

some softness

toward

deformation

[ÂBE82,BUC79].

to

Recent

work i n t h i s r e g i o n suggests an apparent quenching of p a i r i n g c o r r e l a t i o n s i n 81

*Zr, r e s u l t i n g i n moments of i n e r t i a at about rigid-body values The

neutron-rich n u c l e i near

deformed r e g i o n especially cated extent

of

A=100 — The

Zr

and

The

[PRI83].

comprise another r e c e n t l y e s t a b l i s h e d

[KHA77,WOL77,SCH80,AZU79].

abrupt,

[PEK85].

1 0 0

Here, the onset

of deformation

strong quenching of p a i r i n g c o r r e l a t i o n s seems

He-jet

technique

offers

the

t h i s unusual deformed r e g i o n i n the

capability

of

mapping

refractory-element

is

indi-

area

the

above

a region presently i n a c c e s s i b l e at other o n - l i n e f a c i l i t i e s . region around

1 0 0

Sn

also offers exciting p o s s i b i l i t i e s .

Studies

of

nearby n u c l e i have been unable to determine the a p p l i c a b l e coupling scheme or the i n t e r p l a y of the nearly symmetric neutron-proton

configurations.

more, heavy-ion r e a c t i o n cross s e c t i o n s pose a severe

limit

Further-

i n extending

the

previous studies i n t h i s region. L a s t , but not l e a s t , i t i s important the Pt

region

i n which

the

nuclear

supersymmetric

boson-fermion

theory.

regions

bring

step

would

us

one

to search f o r other regions

s t r u c t u r e can The

closer

proven to

a

be

described

existence

of

comprehensive

besides

i n terms of several

theory

nuclei.


such

of a l l

64.

TALBERT AND BUNKER


431

Acknowledgment s This work was supported by the U.S. Department of Energy.

References [ÅBE82] S.Åberg, Phys. Scr. 25, 23 (1982). [AZU79] R. E. Azuma, G. L. Borchert, L. C. Carraz, P. G. Hansen, B. Jonson, S. Mattsson, O. B. Nielsen, G. Nyman, I. Ragnarsson, and H. L. Ravn, Phys. Lett. 86B, 5 (1979). [BEL80] B. N. Belyaev, V. D. Domkin, Yu. G. Korbulin, L. N. Androneko, and G. E. Solyakin, Nucl. Phys. A348, 479 (1980). [BUC79] D. Bucurescu, G. Constantinescu, and M. Ivascu, Rev. Roum. Phys. 24, 971 (1979). [HEY84] K. Heyde, J . Moreau, and M. Waroquier, Phys. Rev. C 29, 1859 (1984). [KHA77] T. A. Khan, W. D. Lauppe, K. Sistemich, H. Lawin, G. Sadler, and H. A. Selic, Z. Phys. A283, 105 (1977). [LIS82] C. J. Lister, B. J. Varley, H. G. Price, and J. W. Olness, Phys. Rev. Lett. 49, 308 (1982). [MÖL81] P. Möller and J. R. Nix, At. Data Nucl. Data Tables 26, 165 (1981). [MOL81] D. M. Moltz, Nucl. Instr. and Meth. 186, 135 (1981) and references therein. [OKA81] K. Okano, Y. Kawase, K. Kawade, H. Yamamoto, M. Hanada, and T. Katoh, Nucl. Instr. and Meth. 186, 115 (1981). [PEK85] L. K. Peker, F. Κ. Wohn, J. C. Hill, and R. F. Petry, to be published. [PRI83] H. G. Price, C. J. Lister, B. J. Varley, W. Gelletly, and J. W. Olness, Phys. Rev. Lett. 51, 1842 (1983). [RUD66] G. Rudstam, Z. Naturforsch. 21a, 1027 (1966). [SCH80] F. Schussler, J. A. Pinston, E. Monnand, A. Moussa, G. Jung, E. Koglin, B. Pfeiffer, R. V. F. Janssens, and J. van Klinken, Nucl. Phys. A339, 415 (1980). [TAK73] K. Takahashi, M. Yamada, and T. Kondoh, At. Data and Nucl. Data Tables 12, 101 (1973). [TRA72] B. L. Tracy, J. Chaumont, R. Klapisch, J. M. Nitschke, A. M. Poskanzer, E. Roeckl, and C. Thibault, Phys. Rev. C 5, 222 (1972); J. Chaumont, Ph.D. thesis, Faculté des Sciences Orsay, 1970 (unpublished). [WOL77] H. Wollnik, F. K. Wohn, K. D. Wunsch, and G. Jung, Nucl. Phys. A291, 355 (1977). RECEIVED

July 15, 1986


Potential Capabilities at Los Alamos Meson ... - ACS Publications

Recommend Documents