CALIBRATION OF THE ISOMER SHIFT OF THE TWO MÖSSBAUER ISOTOPES 127I AND 129I

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JOURNAL DE PHYSIQUE
Colloque C1, supplkment au n O 1, Tome 41, janvier 1980, page Cl-125
CALIBRATION OF THE ISOMER SHItT OF THE THO &SBAUER ISOTOPES 1271 AND 1 2 ' 1
P.E. Miiller and W. ~Gndig
1. Introduction.- The Mijssbauer isomer shift 6 be-
tween a pair of chemica_l compounds i s given by
R AA hp = c AP,
where Apis the difference of the electron densities
gets for the measured difference current
A1(t) = I-- I+ = (AI(o) - 1(0)AXt)exp(-At).
Thus the difference current corrected for the decay
18)
65-5- 4 a ~ e 2 (1)
A1(t)exp(Xt) w i l l increase linearly with time with
a slope proportional t o AX.
at the nucleus for the two chemical states, and C i s
the "calibration constant" which depends on B, the
change of the nuclear radius during the y-transition.
An experiment to determine absolute values of
Apbased on the influence of the chemical environ-
ment on the lifetime of the electron capture decay
in 125~ i s described. From a correlation of the l i f e
time measurements with the corresponding Miissbauer
isomer shift data, the calibration constants C (or
B ) for 127~ and 12', were determined.
An early analysis of the iodine isomer shift
data revealed /1/
( L S / R ) ~ ~ ~ / ( & R / R ) ~ ~ ~
For the individual values of AR/R only estimates
( ARlR),,, - - 3 . 3 ~ 0 - ~ , ( l / ~ ) ~ ~ ~
The decay probability for electron capture i s
= -0.78 0.05 (2)
exist /2/.
= +)1.2~10-~ (3)
given by /3/:
X " T - '
= const 2 pi(Eo - E ~ ) ~ , (4)
where Eo i s the transition energy and Ei the binding
energy of the captured electron. For 125~ Eq. (4)
reduces t o
(AXI'X),~~
= 1.553 (Ap/p)
(5)
where the values Eo = 147 keV and Els = 33.2 keV
were used. This expression combined with (1) gives
( AR/R),,g
The total electron density a t the nucleus was extra-
polated from Mallow et al./4/ to be 2.65~10 ag3. In
the experiment described here the isomer shift values
= 0.01166 61z9/ {e2RfZg P(9)125
(6)
5
6129 were taken from the literature. The correspond-
ing Ah/A values were measured with a differential
ionization chamber.
2. Experimental.- The chamber used in the experiment
is shown in Fig.1. The currents produced in the two
chamber halves are
I+(t) = I+(O) exp(-X+t),
- -
with two sources of approximately equal strength one
(7)
-
ELECTROMETER t
Fig. 1 : Cross-section of the left half of the ioni-
zation chamber. The chamber i s filled with 15 atm of
high purity argon. The sources are exchanged pneu-
mat ically .
For the current measurements the vibrating reed
electrometer C A R Y 401 was used in the rate of charge
mode. In one chamber half a fixed 'source was used
(source SO). The source in the other half was C?;langed
every two hours. The measurements were done automa-
tically over a period df more than 1 y. A l l the meas-
urements were normalized.with respect t o a lifetime
corrected 241~m standard (T
Altoghether 6 sources (%5 mCi each) were pre-
pared from the same ' high purity, aged, and carrier
= 458 y).
Y 2
free batch of 125~.
S 0,1,2 : Na3H2106 (reference: 6129 = 0 mm/s)
S 3
S 4
s 5
:KI04
: K I O j
:csrc14 (6=7.43mm/s)
(6=1.5mm/s)
(6 = 5.0 mm/s)
(9)
The sources containing about 100 mg non-radioactive
iodine each, were immobilized by, prissing with qu~0.t~
,
.
powder and then sealed into glass ampoules.
3. ~ e s u l t s .- Once a week the Ahlh experiment was in-
terrupted for 6 h in order t o determine the absolute
source strength of one of the sources ( N a 3 ~ 2 ~ ~ 6 ) ,
see Fig. 2.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980127

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JOURNAL DE PHYSIQUE
the various possible difference currents, the total
set of data was fitted t o
20- 1 0 0
TlME [dl
Fig. 2 : Section of the 125~ decay curve. The errozs
of the experimental points are approximately a fac-
tor 10 smaller than the poirlts sbown.
The half life of 1251 determined by a weighted f i t
Of the data points was found t o be
T~ = 59.666 5 0.016 d .
a value which may be compared with the present aver
age of Ty2 = 60.14 f 0.11 d given in the Nucl. Data
Sheets.
Examples of the AX/X measurements are shown in
(10)
Fig.3. The observed deviation from this linear re-
lation must be explained by source instabilities.
It may be assumed that the deviations show an expo-
nential behaviour.
IIIIII
I
I 0 0 200 300
TlME [DAYS]
Fig. 3 : Lifetime corrected current of the diffe-
rential ionization chamber plotted. as a function of
time. The three sources were measured relative t o a
Na3H2106 source.
The calculated linear slopes are only approximately
proportional to the corresponding isomer shifts. In
order to account for the known correlations between
For this f i t 1 1 independent parameters are required.
The fitted exponential factor was assumed to be the
same for a l l the sources. The result i s
= (1.22 k 0.08) x 10-5 x 6129 (mm/s).
The result from the individual difference currents
( A X / X ) ~ ~ ~
(Fig. 3) is
(8
with an estimated average of (1.55 + 0.35) x 10-5
one gets using Eq. 6 with R124
= + (7.2 f 1.7) x 10-4.
The error is increased by a factor or aDouz r In
order to account for various inconsistencies. This
~1~)~~~
= (1.68 f 0.20) x 10-5 x 6129 (mmls)
= 6.12 a:
( A R / R ) ~ ~ ~
value i s approximately a factor two higher than
earlier estimates (3).
TlME [DAY]
Fig. 4 : Lifetime corrected current for all combin-
ations of the sources S 1,2,4, and 5. The vertical
scale for the various curves is arbitrarily shifted.
The lines plotted are from one general f i t t o Eq.Y.
The relative isomer shifts are indicated, they are
proportional t o the slope of the curves given.
The authors would like t o thank Dr. B. Sawicka
for her help in the early phase of this experiment.
References
/1/ S.L. Ruby and G.K. Shenoy, Phys. Rev.
186, 326 (1969).
-
/2/ G.M. Kalvius and G . K . Shenoy, Atomic Data
and Nucl. Data Tables &, 639 (1974).
/3/ K. Alder, J. Hadermann, and U. Raff,
Phys. Lett. 30,
487 (1969).
/4/ J.V. Mallow, A.J.
Freeman, and J.P. Des-
claux, Phys. Rev. By
1884 (19'16).