Tables of angular distribution coefficients for gamma rays of mixed multipolarities emitted by ...

135 Pages·2005·4.62 MB·English

BNL 18235
PD 121
BROOKHAVEN NATIONAL LABORATORY
Associated Universities, Inc.
Upton, L.I., N.Y. 11973
PHYSICS DEPARTMENT
Informal Report
TABLES OF ANGULAR DISTRIBUTION COEFFICIENTS FOR GAMMA RAYS
OF MIXED MULTIPOLARITIES EMITTED BY ALIGNED NUCLEI
l£. der Mateosian and A. W. Sunyar
September 1973
NOTICE
This report was prepared as an account of work
sponsored by the United States Government. Neither
the United States nor the United States Atomic Energy
Commission, nor any of their employees, nor any of
their contractors, subcontractors, or their employees,
makes any warranty, express or implied, or assumes any
Ufal liability or responsibility for the accuracy, com-
pleteness or usefulness of any Information, apparatus,
product or process disclosed, or represents that its use
would not infringe privately owned tfjhts.
N 0 T I, C E
This report was prepared as an account of work sponsored by the United States
Government. Neither the United States nor the United States Atomic Energy Com-
mission, nor any of their employees, nor any of their contractors, subcontractors,
or their employees, makes any warranty, express or implied, or assumes any legal
liability or responsibility for the accuracy, completeness or usefulness of any
information, apparatus, product or process disclosed, or represents that its use
would not infringe privately owned rights.
MASTER
DISTRIBUTION Of THIS DOCUMENT IS UNLIMITED
h
-1-
ABSTRACT
Tables of angular distribution coefficients have been calculated
for gamma rays of mixed multipolarities emitted by aligned nuclei in transi-
tions both between states of integer spins and half integer spins.
CONTENTS
INTRODUCTION
TABLE OF ANGULAR DISTRIBUTION COEFFICIENTS
A. INTEGER SPIN
B. HALF INTEGER SPIN
-2-
INTRODUCTION
The ability to product nuclei in high angular momentum and excitation
states through the use of heavy ion reactions, and to produce them relatively well
aligned in respect to the beam direction, has stimulated the investigation of the
properties of high angular momentum states of nuclei. In 1967 T. Yamazaki pub-
lished a set of tables which were useful in the analysis of the angular distribution
of gamma rays emitted from aligned and partially aligned nuclei, a standard tech-
nique for determining the multipolarity of the y~ray transitions originating from
such states. However, these tables were explicitly for fully aligned nuclei and
for pure gamma ray transitions of unmixed multipolarity. Expressions were given
which could be used to make the necessary calculations to cover the cases of par-
tially aligned nuclei and transitions of mixed multipolarities. Since these cal-
culations are tedious, a table of attenuation coefficients for the angular distri-
bution of gamma rays from partia^'y aligned nuclei to be used with the Yamazaki
2
tables was calculated and published elsewhere. Since the appearance of the Yamazaki
tables, nuclear states with angular momenta as high as 22 have been identified.
Because the Yamazaki tables were calculated for spins up to 15, an extension of the
2
Yamazaki tables to spin 26 was added to the table of attenuation coefficients.
The following tables obviate the need for lengthy calculations in the
case of electromagnetic transitions of mixed multipolarities. They have been cal-
culated for integer and half-integer spins up to J * 20 and for AJ * 0, ±1, dt-2.
Yamazaki expresses the angular distribution function for a transition between two
states of angular momenta 1, - I, as
W(6) = 1 + A P (cos9) + A P (cose) (1)
2 2 4 4
where the angular distribution coefficients are given by
LJLJJJ) = Pk(J1)/l+62){Fk(JfL1L1J1) + 26]rk(JFI1L2Ji) + a^JjLjLy^)) k«2,4 (2)
An extension of these tables to higher spins may be obtained by writing the authors.
-3-
and
P, (J) = (2J+1)^ £ (-)J'm(JmJ-m|k0)P (J) (3)
km m
is a statistical tensor which, with the population parameters P (J), specifies the
m
degree of alignment of the nuclear state. Explicit expressions far the F-coefficients
are given in reference 1, equation 4. The ratio of the amplitudes of the mixed multi-
polarity is given by
<j ||L ||J >
6 = . . . . . fAI
In the case of complete alignment, P lJ) assumes the value
k
(2J+l)'!(-) (JOJO|kO) for integer spin
!
J(2J+1)''(-) "*(J%J-^(kO) for half-integer spin
The directional distribution coefficients for complete alignment may then be written
as
I.L.L J ) - -~ {B (J )F. (J.L.L.J ) + 26 B. (J.)F. (J L.LjJ.) (5)
2 f
The sign of 6 may differ under different circumstances, and the second term
in the expression for A, may be positive or negative. This is apparent in the
following tables, which list A max(+) and AmaX(-).
k k
The attenuation coefficient for partially aligned states mentioned above
is precisely
P (J )
k t
In the following tables, the quantities L^U^F^JJI^LJJJ) and the direc-
tional distribution coefficients A.m ax(J,L.U..J ) are listed as functions of J and 6
{
where J takes on values of 1 Co 20 in steps of 1 in the integer table and 1/2 to
'2 in the half integer table, and 6 varies from 0.01 to 100, or six decades, in
2
6
steps of 10 or 20 in each decade. The quantity Q = ~ is included as a conven-
1+6Z
ience for those who wish to make plots of A 's of the kind first suggested by R. G.
4
Arn and M. L. Wiedenbeck. See figure 1.
When mixed multipolarity transitions take place in partially aligned
nuclei the analysis of experimental data becomes somewhat complex. The angular
distribution function may be written (in Yamazaki's notation) as
i<(Q\ l + a A max P (c s8^ + a A max P ( aft^ (7)
=
Experimentally, values are obtained for the coefficients (a A raax) and (a A,max) and
i
it may be desired to determine, say for example, the ratio 6. Both the o's and
A, 's may be varied independently and the proper values of the coefficients can
be determined only through considerations of consistency.
Assume that a transition under study is between states of known J's so
that A.1"3* and A,max may be obtained from Yamazaki's tables or reference 2 for
the case of pure transitions. In general, these coefficients will differ from the
experimentally determined quantities A. and A , which will be less in value
than the A,max's in the case of partial alignment. If attenuation coefficients a
and a can be found associated with the same value of o/J (a parameter measuring
{
the degree of alignment of the nuclei emitting the detected gamma ray) so that
. max... . exp . . max.,. . exp .
/o
o? A (J) = A r and ar^ (J) = A^ r (8)
2 2 2
then one may assume that a particular set of conditions have been found as a possi-
ble description of the existing state of the nucleus. If this is not possible to
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do, one may then attempt to match the experimentally determined directional dis-
exp
tribution coefficients A, by assuming that the transition is not a pure multi-
pole but is mixed.
The method of approach to the problem is best illustrated by taking an
example. Assume that a transition between states with J = 6 and J = 5 takes place
in a partially aligned set of nuclei resulting from perhaps a heavy ion-Xn reaction
and that the directional distribution of the gamma ray emitted has been determined,
yielding experimental values of A. and A^ P. Assume that the transition has
mixed multipolarity. If we further assume that the ratio & for the transition is
0.5 and that the alignment Is described by a/J » .4 we can calculate with the help
of the tables what values of A, and A, to expect. From the following tables we
see that for a transition between atates of J. • 6 and J, • 5 with 6 - 0.5,
A?ma* " "1-09423 and A max * 0.12468 (assuming that the sign of 6 it negative).
/
From reference 2 we obtain attenuation coefficients a. » 0.61070 and Of, • 0.22547.
Our expected coefficients are
* A max - 0.61070 x (-1.09423) - -0.66825
2 2
and
a,.A,max - 0.22547 x 0.12468 - 0.02811
4 4
Returning to our initial problem, let us assume we have obtained experimentally the
Information that A_cxp = -0.66825 and A,exp » 0.0281. Both a and 6 are unknown
and we wish to determine 6. By referring to the tables we soon find that there
are many combinations of a and 6 which will give us the above values for the angu-
lar distribution coefficients. A set of such choices of a/J and 6 are given in
table I and are plotted in figure 2. Every pair of values of a/J and 6 represented
-6-
by the curve labeled a A- and every pair of values represented by the «,A.
curve will givo the experimentally determined values for the angular distribution
coefficients A and A . But only at one point, where the curves intersect, will
/
one pair of values of o/J and 6 give the proper values for both A. and A, at the
same time. This then is the proper set of values for o/J and 6; namely, o/J = 0.4
and 6 = 0.5. In a real experiment the values of ajA, would have errors and
the lines in figure 2 would be replaced by bands whose widths would reflect the
errors of the measurements.
The authors wish to thank E. Auerbach, W. Bornstein, and K. Fuchel for
programming help and E. Auerbach for the use of his routines for generating
Clebsch-Gordan and Racah coefficients. Computations were made with the Brookhaven
National Laboratory CDC 6600 computer.
REFERENCES
1) T. Yamazaki, Nuclear Data A 3, 1 (1967).
2) E. der Mateosian and A. W. Sunyar, Nuclear Data, to be published.
3) P. Thieberger et al., Phys. Rev. Letters 28, 972 (1972).
4) R. G. Am and M. L. Wledenbeck, Phys. Rev. JJJ,, 1631 (1958).
-7
TABLE I. Values of o/J and 6 ocrurring in the hypothetical problems of text.
max. . . max . max . max
O/J 6 o/J 6
A2 °2A2 <*4 A4 4 4
0.15 0.2 0.94416 -0.70777 -0.66825 0.25 0.3 0.54614 0.05147 0.02811
0.30 0.3 0.76997 -0.86789 -0.66825 0.34 0.4 0.32694 0.08598 0.02811
0.35 0.4 0.67023 -0.99705 -0.66825 0.40 0.5 0.22547 0.12468 0.02811
0.40 0.5 0.61070 -1.09423 -0.66825 0.44 0.6 0.17035 0.16501 0.02811
0.43 0.6 0.57532 -1.16152 -0.66825 0.48 0.7 0.13712 0.20500 0.02611
0.44 0.7 0.55557 -1.20281 -0.66825 0.51 0.8 0.11555 0.24327 0.02811
0.44 0.8 0.54650 -1.2278 -0.66825 0.54 1.0 0.09019 0.31169 0.02811
0.44 I.0 0.54918 -I.21682 -0.66825 0.64 3.0 0.05010 0.56104 0.02811
0.39 1.5 0.61774 -1.08176 -0.66825
0.32 2.0 0.72415 -0.92281 -0.66825
0.23 2.5 0.84573 -0.79015 -0.66825
0.12 3 0 0.97421 -0.68594 •0.66825
-B-
TABLE IIA
Angular Distribution Functions for Integer Spin
Explanation of Table
JI = J - Initial J.
t
JF = J - Final J.
f
Delta =6 - Ratio of amplitudes of the mixed multipole
transition.
B2F2(11) = B (J )F (J L =l,L =l,J ) - See Eq. (5).
2 i 2 f 1 2 1
B2F2(12) = B (J )F (J L =l,L =2,J ) - See Eq. (5).
2 i 2 f 1 2 i
B2F2(22) = B (J )F (J L =2,L =2,J ) - See Eq. (5).
2 i 2 f 1 2 1
A2MAX(+) = A max for positive ft - See Eq. (5).
2
A2MAX(-) = A max for negative 6 - See Eq. (5).
2
B4F4 = B^(J )F - See Eq. (5).
i 4
A4MAX = A.maX - See Eq. (5).
7
6
Q = o
1+6Z
TABLE IIB
Angular Distribution Functions for Half Integer Spins
Explanation of Table
JI « J - Initial J.
t
JF = J - Final J.
f
Delta =6 - Ratio of amplitudes of the mixed multipole
transitions.
B2F2(ll) = B (J )F (J L =l,L =l,J ) - See Eq. (5).
2 i 2 f 1 2 i
B2F2(12) = B (J )F (J L =l,L =2,J.) - See Eq. (5).
2 1 2 f 1 2
B2F2(22) - B (J )F (J L =2,L =2,J ) - See Eq. (5).
2 i 2 f 1 2 i
-9-
A2MAX(+) = A maX for positive 6 - See Eq. (5).
2
A2MAX(-) = A maX for negative 6 - See Eq. (5),
2
B4F4 = B (J )F - See Eq. (5),
4 1 4
A4MAX = A maX - See Eq. (5).
1+6l