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Nuclear Science and Engineering
ISSN: 0029-5639 (Print) 1943-748X (Online) Journal homepage: http://www.tandfonline.com/loi/unse20
Measurement of the Photonuclear (γ,n) Reaction
Cross Section for
Photons
129
I Using Bremsstrahlung
Abul Kalam Md. Lutfor Rahman, Shigeyuki Kuwabara, Kunio Kato, Hidehiko
Arima, Nobuhiro Shigyo, Kenji Ishibashi, Jun-ichi Hori, Ken Nakajima, Tetsuo
Goto & Mikio Uematsu
To cite this article: Abul Kalam Md. Lutfor Rahman, Shigeyuki Kuwabara, Kunio Kato, Hidehiko
Arima, Nobuhiro Shigyo, Kenji Ishibashi, Jun-ichi Hori, Ken Nakajima, Tetsuo Goto & Mikio
129
Uematsu (2008) Measurement of the Photonuclear (γ,n) Reaction Cross Section for I Using
Bremsstrahlung Photons, Nuclear Science and Engineering, 160:3, 363-369, DOI: 10.13182/
NSE160-363
To link to this article: http://dx.doi.org/10.13182/NSE160-363
Published online: 10 Apr 2017.
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Date: 27 October 2017, At: 04:27
NUCLEAR SCIENCE AND ENGINEERING: 160, 363–369 ~2008!
Measurement of the Photonuclear (g, n) Reaction Cross Section
for
129 I
Using Bremsstrahlung Photons
Downloaded by [University of Missouri-Columbia] at 04:27 27 October 2017
Abul Kalam Md. Lutfor Rahman,* Shigeyuki Kuwabara, Kunio Kato, Hidehiko Arima,
Nobuhiro Shigyo, and Kenji Ishibashi
Kyushu University, Department of Applied Quantum Physics and Nuclear Engineering
744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
Jun-ichi Hori and Ken Nakajima
Kyoto University Research Reactor Institute, Osaka 590-0494, Japan
and
Tetsuo Goto and Mikio Uematsu
Toshiba Corporation, Yokohama 235-8523, Japan
Received October 28, 2007
Accepted March 15, 2008
Abstract – Nuclear waste contains a significant amount of long-lived non-gamma-emitting nuclei such as
129
I and 14 C. A method of nondestructive detection for monitoring long-lived waste products is proposed
as an application of the (g, n) reaction. This method is useful for surveying long-lived “difficultto-measure” nuclides, e.g., 129 I. Iodine-128 produced from the reaction of 129 I(g, n) 128 I emits gamma
rays that can easily be measured by a gamma-ray counter. We measured the inclusive photonuclear
129 I(g, n) 128 I reaction cross section induced by bremsstrahlung photons. The photons were produced at a
Ta target bombarded by 30-MeV electrons from a linear accelerator. The intensity of the slow neutrons was
considered in the reactions of 127 I(n, g) 128 I and 129 I(n, g) 130 I. The activity of 128 I was measured by a
high-purity germanium spectrometer. The gamma-ray flux and the neutron flux were calculated using the
EGS and MCNP codes, respectively. The average activation cross section of the 129 I(g, n) 128 I reaction had
a 12% deviation from the evaluated International Atomic Energy Agency photonuclear data.
I. INTRODUCTION
nor actinides such as neptunium, americium, and curium; and long-lived fission products like technetium,
iodine ~ 129 I!, and cesium. The solution proposed for disposal of this waste is to isolate it from the biosphere for
periods of hundreds of thousands of years in deep underground geological repositories. Prior to disposal of longhalf-life radionuclides, it is necessary to know their
amounts in nuclear waste. Measurement based on neutroninduced reaction is sometimes not usable because it tends
to produce rather long half-life nuclides; for example,
the neutron capture reaction of 129 I produces 130 I, which
has a half-life of 12.36 h. In contrast, using the 129 I ~g, n!
reaction produces 128 I with a half-life of 25 min. Therefore, it is considered easy to measure the amount of 129 I
The production of electricity by nuclear power plants
is very effective; however, handling spent nuclear fuel is
still a very great challenge. Part of the nuclear waste
includes radioactive isotopes with half-lives on the order
of millions of years, and therefore, this material is an
unwanted legacy for future generations. Figure 1 is a
schematic diagram of the radioactive waste source.
Various radioactive products are formed during the
operation of nuclear reactors. Some are long-lived and
highly radiotoxic. The main products are plutonium; mi*E-mail: [email protected]
363
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364
RAHMAN et al.
Fig. 1. Schematic diagram of the source of radioactive
waste.
by gamma-induced reaction. In this context, photoninduced reaction has the potential to measure long-lived
radionuclides nondestructively in nuclear waste.
Some efforts were recently directed 1,2 toward
photonuclear reaction as laser transmutation of 129 I.
The technology of laser transmutation may be usable as
a “nondestructive detection” method in the future.
The present work proposes to measure the photonuclear 129 I~g, n! 128 I reaction cross section using bremsstrahlung photons produced by an electron linac. When a
fast electron interacts with matter, part of its energy is
converted into electromagnetic radiation in the form of
bremsstrahlung. The fraction of the energy converted
into bremsstrahlung increases with electron energy and
is the largest for absorbing materials of high atomic number. The process is important in a conventional X-ray
tube. In a typical bremsstrahlung spectrum, low-energy
photons are predominant, and the average photon energy
is a small fraction of the incident electron energy.
Radioactive waste contains long-lived non-gammaemitting nuclides. They are deemed “difficult-to-measure”
radioisotopes. For safe disposal, it is necessary to know
their radioactivities. The measurement of such isotopes
is usually determined using an indirect method such as
the scaling factor method.3 This method works by exploiting a radiochemical process that uses mixed bed
and cation bed resins. The resins remove ionic fission
products such as anionic iodine with a cation. Although
its effective removal efficiency is high, this method is
costly and time-consuming.
If a long-lived beta radionuclide such as 129 I ~halflife ⫽ 1.57 ⫻ 10 7 yr! can be changed into the short-lived
gamma emitter 128 I ~half-life ⫽ 25 min!, its radioactivity
can easily be measured by counting gamma rays. We
have devised a nondestructive detection technique for
this purpose. The nondestructive detection method measures gamma rays that are emitted from the beta decay of
~g, n! products in a photon-irradiated waste drum ~asphalt solidification drum! without any destruction. In the
destructive process, radionuclides are separated from the
waste and then analyzed by the radiochemical technique.4 The concept of the nondestructive detection
method is illustrated in Fig. 2. The method consists of an
electron accelerator, a heavy metal target ~Ta, W, etc.!, a
radioactive waste drum ~asphalt drum!, and a Ge gammaray detector. High-energy electrons strike the heavymetal target and generate high-energy bremsstrahlung
photons. The photons directly react with the long-lived
radionuclide, and the result is conversion of long-lived
beta-radio nuclei into short-lived gamma emitters. The
radioactivity of the residual nuclide is measured using a
Ge detector. Since the photonuclear cross section is high
at the giant resonance region, the electron energy is chosen so that the bremsstrahlung photon spectrum covers
the giant resonance region. Table I lists typical longlived nuclides. Among these, 129 I comprises a significant amount of nuclear waste. It can easily be measured
because the half-life of the residual nuclide 128 I is 25 min.
As far as we know, there are no experimental photonuclear cross-section data available for 129 I. The photoabsorption cross sections were thus evaluated from giant
dipole resonance ~GDR! and quasi-deuteron model calculations.5 Figure 3 shows the evaluated photoabsorption cross section of 129 I. In addition, the production
cross sections were calculated with the GNASH code.6
The aim of this study is to measure the average
inclusive 129 I~g, n! 128 I reaction cross section using
continuous-energy bremstrahlung photons emittted from
a Ta target bombarded by a 30-MeV electron linac. The
EGS5 ~Ref. 7! and MCNP ~Ref. 8! Monte Carlo codes
were used in the data analysis.
Fig. 2. Concept of nondestructive detection method.
NUCLEAR SCIENCE AND ENGINEERING
VOL. 160
NOV. 2008
PHOTONUCLEAR CROSS SECTION FOR
129
I
365
TABLE I
Example of Photonuclear Reactions Applicable to Nondestructive Detection
Nuclide
14
C
36 Cl
59 Ni
79 Se
99 Tc
129
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93
I
Zr
Half-Life
~yr!
5.73 ⫻ 10 3
3.01 ⫻ 10 5
7.50 ⫻ 10 5
6.50 ⫻ 10 4
2.13 ⫻ 10 5
1.57 ⫻ 10 7
1.53 ⫻ 10 6
Giant
Estimated Cross
Resonance Peak
Section s
Residual
Reaction
~MeV!
~mb!
Nuclide Half-life
~g, p!
~g, 2n!
~g, p!
~g, p!
~g, 3n!
~g, n!
~g, p!
Fig. 3. Evaluated cross section of
25
25
20
20
22
15
22
129 I~g,
10
8
30
25
20
300
20
13
B
34m Cl
58 Co
78As
96m Tc
128
92
I
Y
Decay Mode
Major
Gamma Energy
~keV!
17.4 ms
b⫺
32.3 min
b⫹
70.9 days Electron capture
1.5 h
b⫺
51.5 min Electron capture
25 min
b⫺
3.54 h
b⫺
3684
2128
811
614, 1309
778
443
934, 1405
abs!.
Fig. 4. Irradiation room of the electron linac facility at
Kyoto University Research Reactor Institute.
II. EXPERIMENTAL
II.A.
129 I(g, n)
Reaction Measurement
TABLE II
For the analysis of the photonuclear ~g, n! reaction
cross section of radioactive 129 I ~activity of 3 MBq!, an
irradiation experiment was carried out at the electron
linear accelerator facility of Kyoto University Research
Reactor Institute. The experimental layout is shown in
Fig. 4. The irradiation conditions are summarized in
Table II. Bremsstrahlung photons were generated at a
thick tantalum target ~50-mm diameter and 61-mm thickness! near the extraction port of the accelerator. The target was actually 29 mm thick. Inside the target capsule
there were some channels through which cooling water
flowed. A shielded source of radioactive iodine was used
as a sample, and it was covered with a titanium metal
sheet. The iodine sample ~27.8-mm diameter and 2.8-mm
thickness! contained radioactive 129 I at 68% proportion
and stable 127 I at 32% proportion. The sample was irradiated together with 197Au foils placed in the front and
the back of the iodine sample to measure the photon and
NUCLEAR SCIENCE AND ENGINEERING
VOL. 160
NOV. 2008
Irradiation Condition in the Experiment
Electron
Energy
Irradiation
Time
Beam
Current
Pulse
Width
Frequency
30 MeV
30 min
27.8 mA
100 ns
100 Hz
neutron fluxes at the sample position. The gold foil at the
back of the iodine was covered by a cadmium sheet to
estimate the low-energy neutron flux. Gold foils of different sizes were used to ensure uniform distribution of
the flux in the iodine sample. The geometry of the sample and the gold foils is presented in Fig. 5. The sizes and
weights of the foils are listed in Table III. Gamma rays
from residual nuclides of irradiated iodine and foils were
366
RAHMAN et al.
TABLE IV
Standard Calibration Sources Used in the Experiment
Calibration
Source
109
Cd
Co
137 Cs
60 Co
60 Co
57
Gamma Energy
~keV!
88.03
122.1
661.6
1173
1333
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Fig. 5. Position of iodine and gold foils in the experiment
~inset below: All samples are packed together in a holder!.
measured by a high-purity germanium detector for 30 min.
The cooling time for the iodine sample was 24 min. The
gold foils were placed 4 mm and the iodine sample
170 mm from the end surface of the detector.
II.B. Efficiency Calibration
of the Ge Detector
Detection efficiency is essential to measure the absolute emission rates of gamma rays. The efficiency of
the Ge detector was measured using standard sources
listed in Table IV. The detector efficiency was also calibrated by the EGS5 code to determine the shape of the
efficiency curve. Figure 6 plots the measured and calculated efficiencies at different energies. The calculated
values agree well with the measured ones. The absolute
value of the efficiency was taken from the following
fitting function of the standard source value:
Efficiency ⫽ K0 ⫹ K1 ⫻ [email protected]⫺~ln~ x0K2 !0K3 !# ,
~1!
where K0 , K1 , K2 , K3 are fitting parameters and x is
energy in kilo-electron-volts.
Fig. 6. Efficiency at different energy ~17-cm distance from
detector surface to sample!.
III. RESULTS AND DISCUSSION
III.A. Results and Discussion on Photon
and Neutron Fluxes
Photon fluxes were derived from data of gold foils
irradiated together with the iodine sample. The measured fluxes were then checked by the EGS5 code taking combinatorial geometry. The photon flux at the iodine
TABLE III
Sizes and Weights of Different Gold Foils
Sample
Position
Size
Weight
~mg!
Small Au
Small Au
Big Au
Small Au covered by Cd
Front of I
Back of I
Back of I
Back of I
6-mm diameter ⫻ 15 mm
6-mm diameter ⫻ 15 mm
20-mm diameter ⫻ 10 mm
6-mm diameter ⫻ 30 mm
8.32
8.33
76.67
17.81
NUCLEAR SCIENCE AND ENGINEERING
VOL. 160
NOV. 2008
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PHOTONUCLEAR CROSS SECTION FOR
sample’s position was determined by averaging the fluxes
on the gold foils at the front and the back of the iodine.
Since 32% of the radioactive iodine sample was 127 I,
the contribution of the 127 I~n, g! 128 I reaction to the yield
of total 128 I was considered to determine only the
129 I~g, n! 128 I reaction cross section. To obtain the ~n, g!
reaction contribution, the fast neutron flux was calculated using the MCNP code. In addition, low-energy
neutron fluxes in the thermal and epithermal regions
were derived from experimental data on gold foils with
and without cadmium covers. The thermal neutron flux
was assumed to have a Maxwellian distribution with
amplitude and temperature parameters. The two parameters were determined from the gold activation results
with and without cadmium sheets. The neutron attenuation through the cadmium sheet was taken into account. The temperature of the thermal neutrons was
2.69 ⫻ 10⫺2 keV. The contribution of ~n, g! was mainly
from the thermal neutron flux.
129
Activity ⫽ A 0 ⫽
I
367
l ⫻ net gamma-ray counting area
« ⫻ exp~⫺l ⫻ t1 ! ⫺ exp~⫺l ⫻ t2 !
~2!
where
l ⫽ decay constant
« ⫽ counting efficiency of the Ge detector
t1 , t2 ⫽ start and finish times of the gamma counting.
Activation rates were derived as follows:
Activation rate ⫽ sfN ⫽
A0
~1 ⫺ exp~⫺l ⫻ t !!
,
where
f ⫽ flux
Since the photonuclear reaction cross section of gold
is known, gold foil was irradiated together with radioactive 129 I to check the evaluated cross section of the
129 I~g, abs! reaction. In the gold foil irradiation, occurring reactions are 197Au~g, n! 196Au and 197Au~n, g! 198Au.
At high energy, the cross section of the Au~g, n! reaction 5 is dominant over the Au~n, g! reaction.9 Figure 7
shows an example of a gamma-ray spectrum of the irradiated gold. The peaks are at 355.73 keV ~Ig ⫽ 87%!
for 196Au decaying through the 197Au~g, n! 196Au reaction and at 411.80 keV ~Ig ⫽ 95.6%! for 198Au decaying through 197Au~n, g! 198Au. Activities of the decaying
isotopes were calculated at the end of irradiation by
Eq. ~2!:
N ⫽ number of nuclides
t ⫽ irradiation time.
The activation rates measured for 197Au~g, n! and
197Au~n, g! at different positions are summarized in
Table V. It is obvious from Table V that the ~g, n!
reaction is dominant over the ~n, g! reaction. The photon flux on the gold foil was calculated with the EGS5
code taking 8 million particles per batch ~Fig. 8!. The
average statistical error in the calculation was 4%.
The peak energy at the giant dipole resonance for the
197
Au~g, n! 196Au reaction is 13.5 MeV. The calculated
average flux deviated by 20% from the experimental
one and can be expressed by Eq. ~4!:
Measured activation
Calculated activation~sevl fcal N !
⫽ 20% ,
TABLE V
Measured Activation Rate of Different Gold Foils
Fig. 7. Gamma-ray spectrum of irradiated gold.
VOL. 160
~3!
s ⫽ cross section
III.B. Results and Discussion on the
Gold Foil Experiment
NUCLEAR SCIENCE AND ENGINEERING
,
NOV. 2008
196Au
198Au
Gold Foil
~Bq!
~Bq!
Small Au ~front of I!
Small Au ~back of I!
Big Au ~back of I!
Au with Cd cover
2.39 ⫻ 10 5
2.32 ⫻ 10 5
2.00 ⫻ 10 6
2.17 ⫻ 10 5
1.39 ⫻ 10 4
1.19 ⫻ 10 4
1.34 ⫻ 10 5
5.28 ⫻ 10 3
~4!
Downloaded by [University of Missouri-Columbia] at 04:27 27 October 2017
368
RAHMAN et al.
Fig. 8. Photon flux from 30-MeV incident electron by
EGS5 code.
Fig. 9. Gamma-ray spectrum of irradiated iodine.
TABLE VI
where
sevl ⫽ evaluated cross section of the 197Au~g, n! 196Au
reaction
fcal ⫽ flux calculated by the EGS5 code.
The calculated flux was normalized by Eq. ~5! to reproduce the experimental gold foil data at the iodine sample
position:
Activation Yields Obtained from Measurement of Iodine
Yield of
128
I
Bq
5.19 ⫻ 10 6 ~62.6 ⫻ 10 5 !
5.10 ⫻ 10 6 ~62.5 ⫻ 10 5 !
9.69 ⫻ 10 4 ~64.9 ⫻ 10 3 !
Total
129 I~g, n! 128 I
127 I~n, g! 128 I
Normalized flux, fnor ⫽ Normalizing factor ⫻ fcal ,
~5!
where Normalizing factor is the ratio of the measured
and calculated activation rates.
III.C. Results and Discussion on the Iodine
Sample Experiment
Figure 9 shows the irradiation spectrum of the iodine sample. The spectrum peaks at 442.9 keV ~Ig ⫽
12.62%! and 526 keV ~Ig ⫽ 1.2%! originate from 128 I
decaying through the 129 I~g, n! 128 I reaction, and those
at 536 keV ~Ig ⫽ 99%!, 668.5 keV ~Ig ⫽ 96%!,
and 739.5 keV ~Ig ⫽ 82%! are from 130 I decaying
through 129 I~n, g! 130 I. As the iodine sample contained
32% 127 I, 128 I was also produced through the reaction
of 127 I~n, g! 128 I. The contribution of the 127 I~n, g!
reaction to the production of 128 I was estimated on
the basis of the neutron flux by using the following
relation:
Activation rate of
127
I(n,g) 128 I
⫽ @~Normalizing factor
⫻ activation at the fast neutron energy region!
⫹ activation at the thermal neutron energy# ,
where Normalizing factor is reproduced from the ratio of
measured and calculated gold activation in the fast neutron energy region.
The total and individual activation yields of 128 I obtained from the irradiation of the iodine sample are listed
in Table VI. The contribution of the ~n, g! reaction was
1.9% of the total amount of 128 I production, due to the
flow of cooling water inside the tantalum target capsule
through some narrow channel that reduced the thermal
neutron production. The average cross section of the
129 I~g, n! 128 I reaction was 0.099 6 0.005 b, as determined by Eq. ~6!:
Activation rate
N ⫻ fnor
⫽s ,
~6!
where
fnor ⫽ normalized flux
s ⫽ cross section of the
129 I~g, n! 128 I
reaction.
The average was made taking the continuous-energy
bremsstrahlung photons, and the energy range was 9.0 to
30.0 MeV. On the other hand, the International Atomic
Energy Agency ~IAEA! evaluated photonuclear data library gives an average of 0.113 b ~Ref. 5!. The crosssection ratio ~measured0evaluated! is 88%. The evaluated
value deviates from the experimental data by 12%.
NUCLEAR SCIENCE AND ENGINEERING
VOL. 160
NOV. 2008
PHOTONUCLEAR CROSS SECTION FOR
Because of lack of a photonuclear cross section on
the photoabsorption cross section was calculated
from the GDR and quasi-deuteron model adopting the
GDR parameters of 127 I ~Ref. 5!. The present 129 I~g, n!
value is based on the experiment and is supposed to be
more reliable than the IAEA calculation. For this reason,
the experimental ~g, n! reaction cross-section value is
considered to be useful for the assessment of the longlived radioactive 129 I nuclide.
129
I
369
REFERENCES
129 I,
Downloaded by [University of Missouri-Columbia] at 04:27 27 October 2017
2. J. MAGILL, H. SCHWOERER, F. EWALD, J. GALY, R.
SCHENKEL, and R. SAUERBREY, “Laser Transmutation of
Iodine-129,” Appl. Phys. B Laser Optics, 77, 387 ~2003!.
3. K. H. HWANG and K. J. LEE, “Modeling the Activity of
129 I and 137 Cs in the Primary Coolant and CVCS Resin of an
Operating PWR,” J. Nucl. Mater., 350, 2, 153 ~2006!.
IV. CONCLUSION
Long-lived waste management is one of the major
problems in the nuclear world. In this study, we measured the 129 I~g, n! 128 I reaction cross section using
continuous-energy bremsstrahlung photons. An important aspect of this measurement was measuring the influence of the ~n, g! reaction caused by low-energy
neutrons in the experimental room. The influence of the
127 I~n, g! 128 I reaction on the 128 I yield was obtained with
the help of the well-known 197Au~n, g! 198Au reaction measurement. The contribution of the ~n, g! reaction was
1.9% to the 128 I production in this experiment. The average cross-section value obtained from the experiment
is 0.099 6 0.005 b. The IAEA evaluated data deviate by
12% from the measured data. The use of the measured
average cross section of the 129 I~g, n! 128 I reaction may
give reliability in the assessment of long-lived betaactive radionuclides.
The authors express their gratitude to the staffs of the
Kyoto University Research Reactor Institute for giving us the
opportunity and support to perform the experiment.
VOL. 160
4. P. ORMAI, A. FRITZ, J. SOLYMOSI, I. GRESITS, E.
HERTELENDI, Z. SZOCS, N. VAJDA, ZS. MOLNAR, and P.
ZAGYVAI, “Inventory Determination of Low and Intermediate Level Radioactive Waste of Paks Nuclear Power Plant
Origin,” J. Radioanal. Nucl. Chem., 211, 2, 443 ~1996!.
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~1996–1999!.
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“Comprehensive Nuclear Model Calculations: Theory and Use
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REFFO, Eds., World Scientific Publishing, Ltd. ~1998!.
7. H. HIRAYAMA et al., “The EGS5 Code System,” SLACR-730~2005! and KEK Report 2005-8, Stanford Linear Accelerator Center and High Energy Accelerator Research
Organization ~2005!.
8. L. J. COX et al., “MCNP Version 5,” LA-UR-02-1527, Los
Alamos National Laboratory ~2002!.
ACKNOWLEDGMENT
NUCLEAR SCIENCE AND ENGINEERING
1. K. W. D. LADINGHUM et al., “Laser-Driven PhotoTransmutation of 129 I—A Long-Lived Nuclear Waste Product,” J. Phys. D Appl. Phys., 36, L79 ~2003!.
NOV. 2008
9. P. G. YOUNG, “Evaluated Nuclear Data File ~ENDF!0VII,” LA-10069-PR, DIST-DEC 06 ~2006!.
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