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Concerning the time dependence of the decay rate of 137Cs.

01 Apr 2013-Applied Radiation and Isotopes (Pergamon)-Vol. 74, pp 50-55

TL;DR: It is found that the PTB measurements of the decay rate of (137)Cs show no evidence of an annual oscillation, in agreement with the recent report by Bellotti et al., and is consistent with the finding that different nuclides have different sensitivities to whatever external influences are responsible for the observed periodic variations.
Abstract: The decay rates of eight nuclides (85Kr, 90Sr, 108Ag, 133Ba, 137Cs, 152Eu, 154Eu, and 226Ra) were monitored by the standards group at the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany, over the time frame June 1999 to November 2008. We find that the PTB measurements of the decay rate of 137Cs show no evidence of an annual oscillation, in agreement with the recent report by Bellotti et al. However, power spectrum analysis of PTB measurements of a 133Ba standard, measured in the same detector system, does show such evidence. This result is consistent with our finding that different nuclides have different sensitivities to whatever external influences are responsible for the observed periodic variations.
Topics: Nuclide (52%)

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University of Nebraska - Lincoln
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
Concerning the time dependence of the decay rate
of 137 Cs
J H. Jenkins
Purdue University
E Fischbach
Purdue University
D Javorsek II
Air Force Test Center
R H. Lee
U.S. Air Force Academy
P A. Sturrock
Stanford University
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Applied Radiation
and
Isotopes
74
(2013)
50-55
Contents
lists
available
at
SciVerse
ScienceDirect
Applied Radiation and Isotopes
ELSEVIER
journal
homepage:
www.elsevier.com/locate/apradiso
Concerning the time dependence
of
the decay rate
of
137
Cs
j.H. Jenkins a,b,*,
E.
Fischbach b,
D.
Javorsek
nc,
R.H.
Lee
d,
P.A.
Sturrock e
CrossMark
" School
of
Nuclear Engineering, Purdue University,
West
Lafayette,
IN
47907,
USA
b Department
of
Physics, Purdue University,
West
Lafayette,
IN
47907,
USA
C Air
Force
Test Center, Edwards
AFR,
CA
93524
USA
d Physics Department,
U.s.
Air
Force
Academy,
2354
Fairchild Drive,
USAF
A,
CO
80840,
USA
e Center for Space Science and Astrophysics, Stanford University, Stanford,
CA
94305,
USA
HIGHLIGHTS
~
Analysis
of
measured
decay
data
for
two
isotopes
measured
on
the
same
detector
has
been
performed.
~
The spectral analysis found periodicities for one isotope,
133Ba,
but
not
the
other,
137CS.
~
This
supports
an
explanation
not
involving
systematic/environmental
causes.
~
The results are
consistent
with
others
where
periodicities have
and
have
not
been
observed.
~
Failure to observe periodicities in one isotope does
not
exclude
their
presence in others.
ARTICLE
INFO
ABSTRACT
Article history:
Received 9 November 2012
Accepted 18 December 2012
Available online
31
December 2012
Keywords:
Radioactivity
Beta decay
Sun
Neutrinos
The decay rates
of
eight nuclides (
8S
Kr,
90Sr,
108Ag,
133Ba,
137CS,
1S2Eu,
1S4Eu,
and
226Ra)
were
monitored
by
the
standards
group
at
the
Physikalisch-Technische Bundesanstalt
(PTB),
Braunschweig, Germany,
over
the
time frame June
1999
to November
2008.
We find
that
the
PTB
measurements
of
the
decay rate
of
137
Cs
show
no evidence
of
an annual oscillation, in
agreement
with
the
recent
report
by Bellotti
et
al.
However,
power
spectrum
analysis of
PTB
measurements
of
a
133Ba
standard,
measured
in
the
same
detector
system, does
show
such evidence. This result
is
consistent
with
our
finding
that
different
nuclides have different sensitivities
to
whatever
external influences are responsible for
the
observed
periodic variations.
1. Introduction
Bellotti
et
al.
(2012)
have recently reported the result of
measurements of the activity of a
137(S
source (T1/2 = 30.08 yr,
100%
[r
(Browne and Tuli,
2007
),
as determined by an experi-
ment
installed deep underground in the Laboratori Nazionali del
Gran Sasso
(LNGS).
They report
that
"no signal with amplitude
larger
than
9.6 x
10-
5
at
95%
c.L.
has been detected," concluding
that
this result
is
"in clear contradiction with previous experi-
mental results and their interpretation as indication of a novel
field (or particle) from the
Sun."
In
reviewing
the
case for
variability, Bellotti
et
al. refer to articles by Jenkins
et
al.
(2009)
,
Fischbach
et
al.
(2011)
, Parkhomov (201
Oa
,b), and Javorsek et
al.
(2010)
. However, none of these articles cites decay rates for
137(S.
* Corresponding
author
at: School
of
Nuclear Engineering, Purdue University,
West
Lafayette,
IN
47907,
USA.
Tel.: + 1
7654963573.
E-mail address: jere@purdue.edu
(J.H.
Jenkins).
0969-8043/$ -
see
front
matter
© 2012 Elsevier
Ltd.
All
rights reserved.
http://dx.doi.org/1
0.1
016fj.apradiso.2012.12.01 0
©
2012
Elsevier
Ltd.
All
rights reserved.
Measured decay data for
137
(s
have previously been examined
for similar periodicities, and none have been found. A small
source of
137(S
is
onboard the
MESSENGER
spacecraft, and decay
data have been collected periodically from an onboard high purity
germanium detector. These data, from
just
prior to launch on
Earth to
just
after orbital insertion
at
Mercury, are consistent
with
no modulation of
137(S,
as reported by Fischbach
et
al.
(2012)
.
Ellis
(1990)
also reported no annual or
other
variations in
measured
137(S
decay data.
What
is
striking about Ellis' result,
however,
is
that
there was an annual variation in the measure-
ments of
56Mn
decay data, which were taken on
the
same
detector system (over
the
same time period)
that
was used to
measure
the
137(S
calibration standards, for which no annual
oscillatory behavior was observed. We shall discuss the Ellis
results in greater detail in Section 3. There
is
one group
that
has
reported periodicities shorter
than
a year in
137(S,
(Baurov
et
aI.,
2000
, 2001
),
but
none of those experiments had a long enough
duration to conclusively observe an annual period.
The question of periodic or
other
non-random behaviors in
nuclear decay rates has long been of interest to
the
scientific
This article
is
a U.S. government work, and is not subject to copyright
in
the United States.

community (Emery, 1972; Hahn et al., 1976; Dostal et al., 1977),
and the results presented in Jenkins and Fischbach (2009), Jenkins
et al. (2009), Javorsek et al. (2010), and Sturrock et al. (2010a,
2010b), as well as others, have generated renewed interest in this
topic. In an effort to further explore the possible existence of
periodicities in nuclear decays, an examination of historical data
collected during extended studies of half-lives of long-lived
radionuclides and of detector stability has been carried out at
the Physikalisch-Technische Bundesanstalt (PTB). Included in this
program was an analysis of
137
Cs data, as reported by Schrader
(2010). The goal of the present paper is to examine the results of
these PTB measurements for comparison with the result of the
Bellotti experiment.
2. Analysis of PTB measurements
Schrader (2010) reports extended half-life measurements of
eight nuclides (
85
Kr,
90
Sr,
108
Ag,
133
Ba,
137
Cs,
152
Eu,
154
Eu, and
226
Ra). The
137
Cs data were collected from late 1998 to November
2008. All of the measurements were made with a 4
p
ionization
chamber (IG12/A20, Centronic 20th Century Electronics, Ltd.). In
principle, these measurements could be affected by influences on
the particular radionuclide under study, on the detector, or on the
measuring electronics. As is clear from Figs. 2–5 of Schrader
(2010), the record of measurements (residuals of a half-life fit)
superficially resembles a scatter diagram. It follows that periodi-
cities in the decays of any of these nuclides will be revealed only
by some form of power-spectrum analysis. The purpose of the
present paper is to carry out such an analysis for
137
Cs (residuals
of a half-life fit) and also (for reasons that will become clear) for
133
Ba and
226
Ra.
Since oscillations when they occur are typically intermit-
tent rather than steady, it is more illuminating to examine time–
frequency displays (‘‘spectrograms’’) than simple power spectra
(Sturrock, 2008). To form spectrograms, we first prepare the data
by means of the RONO (Rank-Order NOrmalization) operation
(Sturrock et al., 2011a) that maps the measurements onto a
normal distribution, as is appropriate for power-spectrum ana-
lyses such as the Lomb–Scargle procedure (Lomb, 1976; Scargle,
1982) or a likelihood procedure (Sturrock et al., 2006). We then
carry out a sequence of likelihood power-spectrum analyses of
sections of the data. For present purposes, we have found it
convenient to adopt sections of 500 measurements. The power, S,
is then displayed by a color code in a time–frequency diagram. (In
power-spectrum analysis, the probability of finding a power of S
or greater at a given frequency arising from normally distributed
random noise, the null hypothesis, is given by e
S
, Scargle, 1982.)
The spectrogram formed in this way from the PTB
137
Cs data is
shown in Fig. 1. We see that there is only slight evidence of an
annual oscillation (frequency 1 year
1
) between 2002 and 2004.
The feature near 0.2 year
1
may be related to the finite duration
of the dataset. In contrast, we show in Fig. 2 the spectrogram
formed from the
133
Ba (T
1=2
¼ 10:551 yr, 100% K-capture, Khazov
et al., 2011) measurements taken on the same detector system.
This spectrogram exhibits a strong annual oscillation from 2003
to 2005. We also see evidence of an oscillation with frequency
close to 2 yr
1
. This could be a harmonic of the annual oscillation,
but it is more likely to be a Rieger oscillation (an r-mode
oscillation with spherical harmonic indices l ¼ 3, m ¼ 1), which is
prominent in power spectra formed from Brookhaven National
Laboratory (BNL) and PTB data (Sturrock et al., 2011a).
We have also analyzed the PTB measurements in terms of
‘‘phasegrams,’’ which are analogous to spectrograms, displaying
the power as a function of time and phase for an assumed annual
oscillation. The plot derived from
133
Ba data is shown in Fig. 3.
As we expect from Fig. 2, the power is found mainly over the time
interval 2003 to 2005. The power is centered on a phase of
approximately 0.43, corresponding to a date on or about 6 June.
Comparable plots for
226
Ra (T
1=2
¼ 1600 yr, 100%
a
-decay,
Akovali, 1996) measurements are shown in Figs. 4 and 5.We
see from these figures that the
226
Ra results are similar to those
for
133
Ba, but the power levels are not as strong. We note that
while
226
Ra is 100%
a
-decay, it is in equilibrium with most of its
daughters, several of which are
b
-decays. These
b
-decaying
daughters contribute a significant portion of the photons emanat-
ing from the sealed source (Chiste et al., 2007). Therefore, we
cannot discern which isotope or isotopes would be the source of
the observed fluctuations and note that there could be more
than one.
Central Time of Sample
Frequency (yr
−1
)
2002 2003 2004 2005 2006
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
1
2
3
4
5
6
7
8
9
10
Fig. 1. Time–frequency display (spectrogram) of measurements of the decay-rate
of
137
Cs made at PTB over the time interval June 1999 to November 2008. There is
only a slight suggestion of an annual oscillation from 2002 to 2003. The power, S,
is represented by the color bar. (For interpretation of the references to color in this
figure legend, the reader is referred to the web version of this article.)
Central Time of Sample
Frequency (yr
−1
)
2002 2003 2004 2005 2006
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
2
4
6
8
10
12
14
16
18
20
Fig. 2. Spectrogram of measurements of the decay-rate of
133
Ba made at PTB over
the time interval June 1999 to November 2008. There is evidence of an annual
oscillation from 2003 to 2005. There is also evidence of the first harmonic of this
oscillation. The power, S, is represented by the color bar. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
this article.)
J.H. Jenkins et al. / Applied Radiation and Isotopes 74 (2013) 50–55 51

3. Discussion
We next review in more detail previous reports concerning the
decay rate of
137
Cs. In the Ellis (1990) experiment, a set of
137
Cs
standards was measured on a large, uncollimated, NaI system (Cohn
et al., 1969) designed for low background, high spectral resolution
counting of human subjects undergoing in vivo neutron activation
analysis (NAA). The counting system, described in detail in Cohn
et al. (1969), comprised two planar, parallel 3 9arraysof
15 cm 5 cm matched NaI(Tl) crystals with low-background photo-
tubes, for a total of 54 detectors. This system was located in a
heavily shielded, low-background room at BNL. Additional mea-
sures, such as a recirculating, filtered air system, were also incorpo-
rated to reduce background, as described by Cohn et al. (1969).
The
137
Cs standard set referenced above, which was used to
determine system stability and calibration, consisted of nine
individual sources of 0:5
m
Ci each. Over a six month period of
initial set-up and calibration, as reported in Cohn et al. (1969), the
standard deviation of the
137
Cs counts was 0.54%, implying good
stability, and the background over the same period was 2:32
10
4
7 0:56% counts/min over a 2:5 MeV spectrum window. The
overall spectral resolution (ratio of peak width to spectrum-
window width) for the
137
Cs source geometry was 8.7%. Careful
controls to monitor and quickly correct for drift were maintained
for the system to prevent counting errors. Additional corrections
were calculated for geometry and other parameters which could
lead to other systematic variations in the measured counting rate,
as described in Cohn et al. (1969). The result was a very well
designed, sensitive and stable counting system, with sensitivities
of order 0.1 nCi. Calibration was performed on the system daily
with the aforementioned
137
Cs sources.
This counting system was utilized in conjunction with a broad
beam neutron irradiator (Cohn et al., 1972), for the in vivo NAA
experiments described in Ellis (1990), as mentioned above. The
irradiator was specifically designed for high reproducibility (Cohn
et al., 1973), and comprised an array of fourteen 50 Ci encapsu-
lated
238
Pu/Be sources. In 1976, a second standard set was
incorporated to be used on a weekly basis to monitor the
reproducibility of the activation and counting systems together
(Ellis, 1990). This was a lucite rod which contained nine regions
each of 10 cm
3
volume containing powdered manganese metal.
The rod was placed in the neutron irradiator for 5 min, activated,
and then was placed in the counting bed and counted for fifteen
minutes. When placed in the counting bed, the activated regions
of the rod were in the same locations as the
137
Cs sources with
respect to the detector arrays (Ellis, 1990).
Interestingly, the data collected on the activation product,
56
Mn (T
1=2
¼ 2:5789 h, 100%
b
-decay, Huo et al., 2011), showed
fluctuations with an annual period, as reported by Ellis (1990),
and later confirmed by our group in Javorsek et al. (2010). The
important result from Ellis’ work was that even though annual
fluctuations appeared in the
56
Mn data, they were not observed in
the
137
Cs standard, which was measured on the same detector
system daily to confirm the calibration and efficiency of the
detector system. It should be noted that both the Mn and Cs
standards were contained in similar lucite fixtures. Therefore, the
Central Time of Sample
Phase
2002 2003 2004 2005 2006
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
2
4
6
8
10
12
14
16
18
20
Fig. 3. Time-phase display (phasegram) of measurements of the decay-rate of
133
Ba made at PTB over the time interval June 1999 to November 2008. The phase
of the annual oscillations is approximately 0.43, corresponding to a peak in the
modulation on or about June 6. The power, S, is represented by the color bar. (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
Central Time of Sample
Frequency (yr
−1
)
2002 2003 2004 2005 2006
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Fig. 4. Spectrogram of measurements of the decay-rate of
226
Ra made at PTB over
the time interval June 1999 to November 2008. There is evidence of an annual
oscillation from 2002 to 2005. The power, S, is represented by the color bar. (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
Central Time of Sample
Phase
2002 2003 2004 2005 2006
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Fig. 5. Time-phase display (phasegram) of measurements of the decay-rate of
226
Ra made at PTB over the time interval June 1999 to November 2008. The phase
of the annual oscillation is approximately 0.36, corresponding to a peak in the
modulation on or about 12 May. The power, S, is represented by the color bar. (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
J.H. Jenkins et al. / Applied Radiation and Isotopes 74 (2013) 50–5552

thermal expansion of the lucite, which has an expansion coeffi-
cient of 7:1 10
5
cm=cm=1C(10.02, 2012), would have been
the same for the two standards, and hence expansion due to
temperature would not be a likely source of any seasonal varia-
tions. Furthermore, as described in Javorsek et al. (2010), if the
phase of the outdoor temperature is assumed to be similar to any
annual variation in indoor temperature, it does not match the
phase of the annual variation in the
56
Mn data reported by Ellis
(1990).
Based on the care and thorough effort in the design, construc-
tion and calibration of the counting system in the Ellis experi-
ment, aimed at reducing possible background and systematic
variations, it seems probable that the observed differences in the
fluctuations in the measured decay rates are intrinsic to the
56
Mn
and
137
Cs decays themselves. Of course, the possibility also exists
that something was changed in the activation process, either in
the production of neutrons in the PuBe sources, or the (n,
g
)
capture process in the conversion of
55
Mn to
56
Mn. Therefore, in
light of all of the examples previously mentioned where decay
rate variations were observed in long-lived isotopes, the possibi-
lity that the
56
Mn decay rate changed over the course of the year
cannot be excluded.
In the spirit of the above analysis it is instructive to examine
the PTB counting system where variations in the
133
Ba count rate
were observed, but not in
137
Cs as described in Section 2.As
previously noted, the isotopes were measured on a 4
p
ionization
chamber system, and the current generated in the ion chamber
was measured with a Keithley electrometer, model 6517A. This
ionization chamber current is the result of the deposition of
energy by the interaction of the decay photons of the isotope
being measured in the detector, generally in the detector walls.
Much of that energy is transferred to the working gas of the
detector (in this case argon) via Compton electrons or photo-
electrons. Direct interaction of photons in the gas itself can also
occur, but even at a pressure of 2 MPa (20 atm), this probability is
very low. However, this is not true for the lower energy Compton
photons resulting from the original wall interactions.
One of the significant factors leading to the selection of
ionization chambers in these types of measurements is their
inherent stability with respect to systematic and environmental
effects. It is well known that the output of the detector is
relatively insensitive to changes in the detector bias voltage,
since the voltage is high enough to prevent recombination of
the electron/ion pairs generated, but too low to cause electron
multiplication. Hence there is a fairly large width to this ‘‘plateau’’
such that the response is insensitive to voltage variations.
Furthermore, as described in detail in Jenkins et al. (2010), the
construction of the detector is such that the geometry and
functional parameters of the detector will experience only negli-
gible changes as a result of changes to ambient variables such as
temperature, pressure and humidity. Possible backgrounds and
their seasonal variations were also analyzed in Jenkins et al.
(2010) with respect to the annual fluctuations in the
226
Ra
measurements reported in Siegert et al. (1998). These were found
to be too small an effect to account for the observed fluctuations
in the
226
Ra currents. It is reasonable to conclude that none of the
known possible influences on the detector system were the likely
cause of the fluctuations.
It should be pointed out that the previously discussed results
of the analysis of
226
Ra data acquired at PTB over the interval June
1999 to November 2008 differ from the earlier results of the
analyses (Jenkins et al., 2009; Sturrock et al., 2010b) of data
acquired at PTB over the interval November 1983 to October 1998
(Siegert et al., 1998). Notably, the decay rate of
226
Ra shows
strong evidence of an annual oscillation in the earlier dataset but
weaker evidence for such an oscillation in the later dataset (Fig. 4).
In fact, Schrader (2010) shows that strong annual periodicities
were also present in
85
Kr,
108m
Ag,
152
Eu and
154
Eu measured from
1990 to 1996.
The difference between the two sets of measurements, as
described by Schrader (2010), is that the current measuring
system used in the PTB measurements prior to October 1998
was a Townsend balance, but for data taken after 1998, a Keithley
electrometer was used, as described in Schrader (2007, 2010).
With the introduction of the electrometer, the observed annual
periodicity was reduced significantly. However, Schrader (2007)
points out in his 2007 article (8 years after the switch to the
electrometer) that ‘‘for high accuracy measurements in metrol-
ogy, a Townsend induction balance, i.e. a capacitor with voltage
compensation, is used ...’’. While it remains to be seen which
current measurement method will prove to be the more accurate,
it is still evident as noted in Section 2 that there clearly
remains an annual periodicity in the
133
Ba data that is similar to
those observed prior to the introduction of the electrometer, in
addition to a weak one in the
226
Ra data, as shown in Fig. 4.
Further support for the existence of the annually varying
periodic behavior in the
133
Ra data is presented in Table 1, which
lists other experiments where annual and sub-annual periodici-
ties have been observed. What is important to note here is that 17
of the 23 results listed in Table 1 were collected by counting
methods utilizing pulse processing from a variety of detector
classes, and not the current measurement from an ion chamber.
The systematics of pulse processing are significantly different
from the measurement of small currents, such as those of the PTB
ionization chamber, and are not subject to the same set of
challenges and uncertainties.
An additional important feature of the data in Table 1 is that
there are 10 in the list that exhibit sub-annual periodicities in
addition to the annual variations. While it is possible to attribute
the annual periods to a ‘‘seasonal’’ influence with a clear annual
variation, such as temperature, periodicities on the order of six
months, one month, or less, are not. Furthermore, as shown in
Sturrock et al. (2010a,b), Sturrock et al. (2011a), Shnoll et al.
(1998) and Veprev and Muromtsev (2012), the observed decay
frequencies align closely with known solar periodicites. This
tends to support the original hypotheses of Jenkins and
Fischbach (2009), Jenkins et al. (2009), and Fischbach et al.
(2009), suggesting that there is a solar influence on radioactive
decay rates on Earth. Even more interesting are the results
presented by our group in Sturrock et al. (2012), which indicate
that the data originally presented in Parkhomov (2010a,b), exhibit
a frequency structure similar to solar diameter measurements
from the Mt. Wilson Solar Observatory. Thus, the evidence
supporting a putative solar evidence seems at least as reasonable
as simply attributing the decay rate variations to unspecified
environmental or systematic effects.
Further support for concluding that the source of the varia-
tions being observed is not simply an environmental or systema-
tic effect can be found in the
137
Cs and
133
Ba data presented in
Section 2. These measurements were made in the same time
frame, with the same detector, and with the same current
measuring electronics. It is difficult to produce a viable conven-
tional scenario to account for this difference, particularly in light
of the results of Ellis (1990). Similar results were observed in an
experiment by Alburger et al. (1986), who measured
32
Si
(T
1=2
¼ 153 yr, 100%
b
-decay, Ouellet and Singh, 2011) and
36
Cl
(T
1=2
¼ 301, 000 yr, 98.10%
b
-decay, 1.90% K-capture, Nica et al.,
2012) alternately on a differential gas proportional detector
system (Harbottle et al., 1973) using 30 min counts each for
twenty hours total. For each isotope, the 30-min counts were
aggregated into an integral count for the day. By taking the ratio
of the two integrated counts, i.e.,
32
Si/
36
Cl, systematic and
J.H. Jenkins et al. / Applied Radiation and Isotopes 74 (2013) 50–55 53

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