Journal of Nuclear and Radiochemical Sciences, Vol. 1, No. 2, pp. 53−61, 2000

53

ArticlesPhotofission of 197Au at Intermediate Energies
H. Haba,*,a M. Igarashi,b K. Washiyama,a H. Matsumura,a M. Yamashita,aK. Sakamoto,†,a,b Y. Oura,c S. Shibata,d M. Furukawa,e and I. FujiwarafaDivision of Physical Sciences, Graduate School of Natural Science and Technology, Kanazawa University,
Kanazawa-shi, Ishikawa 920-1192, Japanb
Department of Chemistry, Faculty of Science, Kanazawa University, Kanazawa-shi, Ishikawa 920-1192, Japanc
Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji-shi, Tokyo 1920397, Japand
Research Reactor Institute, Kyoto University, Sennan-gun, Osaka 590-0494, Japane
Faculty of Environmental and Information Sciences, Yokkaichi University, Yokkaichi-shi, Mie 512-8512, Japanf
Department of Economics, Faculty of Economics, Otemon-Gakuin University, Ibaraki-shi, Osaka 567-8502,
Japan
Received: April 4, 2000; In Final Form: June 30, 2000
The reaction yields of 58 radionuclides with the mass number A = 42–131 produced in the photofission of 197Au
by bremsstrahlung of end-point energies (E0) from 300 to 1100 MeV have been measured using the catcher foil
technique. The reaction yields increase steeply with an increase of E0 up to 600 MeV and increase gradually
above 600 MeV, indicating the resonance-type excitation function attributed to the (3,3) resonance. The charge
distribution was found to be well reproduced by a Gaussian function with the most probable charge (Zp) expressedby a linear function of A, i.e., Zp = RA + S, and with the A-independent full width at half maximum (FWHMCD).
The charge distribution parameters R, S, and FWHMCD were found to be independent of E0 above 600 MeV,
reflecting the resonance nature in photonuclear reactions at intermediate energies. The weighted mean values at
E0 ≥ 600 MeV were R = 0.424 ± 0.001, S = 0.7 ± 0.1, and FWHMCD = 2.2 ± 0.1 charge unit (c.u.). Based on theseparameters, the symmetric mass yield distributions with the most probable mass Ap of 92 ± 1 mass unit (m.u.) andthe width FWHMMD of 39 ± 1 m.u. were obtained. The characteristics of the charge and mass yield distributions
were discussed by referring to the literature data including those of proton-induced reactions.

1. Introduction
Photofission processes at intermediate energies are expected
to be unique for investigating the complex dynamics of excitation in heavy nuclei when compared with hadron-induced
fission, because photons interact electromagnetically with
nuclei through giant dipole resonance, quasi-deuteron mechanism, and (3,3) resonance. For preactinide nuclei, the photofission processes opened by the quasi-deuteron mechanism andthe (3,3) resonance absorption are especially important due totheir high fission thresholds of > 20 MeV that suppress thefission channels opened by the giant dipole resonance. Thus aphoton of an energy above 20 MeV sees all nucleons inside a
nucleus identically and interacts with a nucleon-nucleon pairor a single nucleon, transferring its kinetic energy effectively
but comparatively little angular momentum to the nucleus. In
this context photofission is quite different from hadroninduced fission. A hadron, which possesses large angularmomentum, collides with a single nucleon in the surface
region of the nucleus through the strong nucleon-nucleon interaction. It is of interest to investigate whether there exist similarities or not in the final steps in these two types of nuclear
reactions.
Previously, we1–3 measured the photospallation yields fornat
V, 59Co, natCu, 89Y, 127I, 133Cs, natLa, and 197Au targets at thebremsstrahlung end-point energies (E0) of 30–1050 MeV, andanalyzed them by the five-parameter charge distribution andmass yield distribution (CDMD) formula given by Rudstam.4
From the slope of the mass-yield curve (P) and the total*Present address: Japan Atomic Energy Research Institute, Tokaimura, Naka-gun, Ibaraki 319-1195, Japan. E-mail: haba@popsvr.
tokai.jaeri.go.jp.
†Corresponding author. E-mail: kohsakamoto@par.odn.ne.jp.
FAX: +81-76-224-8253.

inelastic cross section (σ̂) in the formula, some anomalous
behaviors of the energy-absorption and energy-dissipation
mechanisms were suggested for heavy targets with the target
mass number At ≥ 150. Recently a systematic yield measurement of the (γ, π–xn) reactions for x = 0–9 on targets ranging
from 7 Li to 209 Bi were also reported by our group.5 It was
found that changes in the yield profiles for targets heavier thanAt = 100 might be associated with pronounced nuclear medium
effects giving rise to more excessive excitation as comparedwith medium-heavy targets with At < 100. These findings havemotivated us to an investigation on the fission process, which
is characteristic of heavy nuclei and competes with spallation,
fragmentation, and also simple photopion reactions.
The photofission study of 197 Au is appropriate for thispurpose, because the yields of the competing spallation, fragmentation, and simple photopion reactions have already beenobtained by our group.2,3,5,6 The total photofission yields and/or
cross sections on 197Au have been extensively measured withionization chambers, and solid-state track detectors so far.7–21
A few works22,23 measuring charge distribution and/or mass
distribution, which are further essential for fission mechanisms, were performed in the past. Komar et al.22 reported thesymmetric mass yield distribution with the full width at half
maximum FWHM MD = 40 m.u. by the coincident energy
measurements of fission fragment pairs at E0 = 1000 MeV,
assuming the mass number of the fissioning nucleus to be Af =194. On the other hand, Areskoug et al.23 measured the relative yields of 29 radionuclides produced from 197Au at E0 = 600
MeV using the catcher foil technique. They analyzed theyields of 22 fission products by a six-parameter charge distribution and mass yield distribution formula, and reported a
Gaussian mass distribution with the most probable mass Ap =92.6 ± 0.6 m.u. and FWHMMD = 30.9 ± 1.7 m.u. They concluded
that the larger width reported by Komar et al.22 at E0 = 1000

© 2000 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/28/2000

Haba

54 J. Nucl. Radiochem. Sci., Vol. 1, No. 2, 2000
MeV was attributed to the higher photon energy investigated.
In the present work the photofission of 197Au was investigated systematically in the wide E0 range of E0 = 300–1100
MeV using the thick-target thick-catcher method with the aidof intensive chemical separations. Reported in this paper are
the absolute reaction yields of the 58 fission products in themass range of 42 ≤ A ≤ 131. The charge and mass yield distributions, and total fission yields were deduced and comparedwith the literature data including those of proton-induced reactions. In a separate paper, 24 the recoil properties of the 29
product nuclei in the mass range of 24 ≤ A ≤ 131 are reported
and discussed together with the previous photospallation
results and also the literature data on the proton-induced reactions.

barium were employed for the Mylar catchers in a separate
irradiation at E0 = 1000 MeV. The identifications of radionuclides were made on the basis of their γ-ray energies and halflives. The γ-ray intensities were obtained with the automatic
peak search program “SPECanal98”.30 The detector efficiency
was determined with calibrated 152Eu and 182Ta sources withthe same size as the samples. The decay properties of interest
such as half-lives, γ-ray energies, and branching ratios 31–33 aresummarized in Table 1, together with formation types; I: independent yield, C–: cumulative yield by β – decay, and C+:
cumulative yield by β+ decay and/or electron capture. This
classification was made on the basis of charge distributions of
the product nuclei (See sect. 3. 2.), irradiation periods, andtimes required for chemical separations.

2. Experimental

3. Results and Discussion

Irradiations by electron-free bremsstrahlung beams with E0= 300–1100 MeV in steps of 100 MeV or less were carried out
using the 1.3 GeV electron synchrotron of the High Energy
Accelerator Research Organization (KEK) at Tanashi. The
target consisted of a stack of 40–50 sets of a Au foil (99.99%)
of 90 mg/cm 2 in thickness and 2.5 × 2.5 cm 2 in size sandwiched by one pair of Mylar foil of 7.0 mg/cm2 in thickness
and 2.5 × 2.5 cm2 in size, which collected the recoil nuclei inthe forward or backward directions with respect to the beamaxis. The stack was vacuum-encapsulated in a polyethylene
bag together with additional 40–50 Mylar foils (280–350
mg/cm2) on the downstream side of the beam, which served as
an activation blank. Details of the irradiation were almost thesame as described in the previous papers. 1,25,26 The photon
intensities evaluated from the monitor reaction of 27Al (γ, 2pn)
24
Na (Refs. 27, 28) were 109–1010 equivalent quanta per second(eq.q./s). A typical irradiation period was 5 h.
After irradiation, about 10 selected Au foils and all of theforward and backward catcher foils from one target pile werecollected separately and were assayed for radioactivities
nondestructively with high-purity Ge detectors each coupledwith a 4 k-channel pulse height analyzer. The other 30–40 Au
foils were divided into three portions and subjected to chemical separations of K, Fe, Ni, Zn, Ga, As, Rb, Sr, Y, Zr, Nb,
Mo, Ag, and Ba. All of the chemical procedures applied in thepresent work are described in a separate paper.29 Radioactivities
in the chemically separated samples were also assayed by γ-ray
spectrometry. In order to obtain the recoil data of productswith low reaction yields, chemical separations of scandium and3.1. Yield Curves. In the present work the radioactivities of
36 product nuclides in the mass range of A = 46–131 wereidentified both in the forward and backward catcher foils.
They are denoted with a label “C” in Table 1. In the nondestructive Au target and/or the chemically separated samples,
the radioactivities of 50 nuclides in the mass range of A =42–131 were identified as denoted with a label “T” in the sametable. From the fractions of each nuclide which has recoiled
out of the Au target of the thickness W in unit of mg/cm2 into
the forward and backward catcher foils, expressed as F =NF/(NF + NB + Ntarget) and B = NB/(NF + NB + Ntarget), N being thenumber of atoms, respectively, the effective mean ranges, FW
and BW, in Au were obtained. The mean ranges of 46Sc were
calculated by estimating the produced radioactivities in the target on the basis of our yield data at the same E0.6 It was foundthat the effective mean ranges FW and BW are independent of
E0 at the studied E0.24 A quantity approximately equal to themean range of the recoil in the target material, 2W(F+B) in
unit of mg/cm2 of Au, was calculated for 28 nuclides in themass range of A = 46–131, and they are indicated in Figure 1
by open circles as a function of the product mass number A,
together with the eight values reported by Areskoug et al.23 at
E0 = 600 MeV by closed squares. The present results agree
well with those by Areskoug et al.23 within the experimental
errors. The 2W(F+B) values decrease almost linearly with anincrease of A, and no effects attributed to the formation types(I, C+, C–) were found within the experimental uncertainties.
Then, a linear function of 2W(F+B) = (–0.067 ± 0.011) A +(14.7 ± 1.1), as the first approximation, was obtained by the

TABLE 1: Relevant Nuclear Data
*3

NuclideHalf life

E γ (keV)b.r.(%) TYPE

Detec.

Ba-131
Ba-129m
Ba-129Ba-128
Ba-126
Ag-113Ag-112
Ag-110m
Ag-106m
Ag-105
Rh-105
Ru-105
Ag-104Ag-103
Ru-103
Mo-99
Nb-98b
Ru-97
Nb-97
Zr-97

11.50d
2.17h
2.23h
2.43d
1.67h
5.37h
3.130h249.8d8.28d
41.29d
1.473d
4.44h
1.15h
1.10h
39.26d2.748d51.3min
2.9d
1.20h
16.91h

496.3
*1
182.3
*1
214.3
273.4
233.6
298.6
617.4
657.8
717.3
344.5
318.9
724.3
767.6
118.7
497.1
D140.5
787.4
215.7
657.9
743.4

46.8
*1
47
*1
9.9
14.5
20
10
43
94.0
28.9
41.4
19.2
47.3
66
31
90.9
90.7
93.4
85.6
98.4
93.1

T, C
T, C
T
T, C
T
T
T
T, C
T
T
C
C
T
T
T, C
T, C
T
C
T
T, C

C+
C+
C+
C+
C+
CI
I
I
C+
CCI
C+
CCI
C+
I
C-

*4

NuclideHalf life

E γ (keV)

Tc-96
Nb-96
Nb-95
Zr-95
Nb-92m
Sr-92
Sr-91
Y-90m
Zr-89
Zr-88
Y-88
Y-87m
Y-87
Sr-87m
Rb-86
Rb-84
Sr-83
Rb-83
Rb-82mBr-82

4.28d
23.35h
34.98d64.02d10.15d
2.71h
9.63h
3.19h
3.267d83.4d106.7d13.37h3.33d2.803h
18.63d32.77d1.350d86.2d6.472h
1.471d849.9*21091.3
765.8
756.7
934.5
1383.9
749.8
202.5
909.1
*2
392.9
898.0
380.8
484.8
388.5
1077.0
881.6
762.7
520.4
776.5
698.4

b.r.(%) TYPE Detec.
97.6
*2
48.5
99.8
54.5
99.1
90
23.6
97.3
99.9
*2
97.3
93.7
78.1
89.7
82.1
8.64
69.0
30
44.7
84.4
28.5

I
I
I
CI
CCI
C+
C+
I
C+
C+
I
I
I
C+
C+
I
I

Nuclear data are from Ref. 31 except for *1 from Ref. 33 and *2 from Ref. 32.
−+*3: I: independent yield; C-: cumulative yield by β decay; C+: cumulative yield by β decay and/or electron capture.
*4: Identification in Au target (T) or Mylar catcher (C).
D: γ-ray of the daughter in equilibrium.

C
T, C
T, C
T, C
C
T, C
T, C
T, C
T, C
T, C
T, C
T
T, C
T
T, C
T, C
T
T, C
T
C

NuclideHalf life

E γ (keV) b.r.(%)

Rb-81
Br-77
As-76
Se-75
As-74
Ga-73
As-72
Ga-72
Zn-72
As-71
Zn-71mZn-69m
Ni-66
Ni-65
Fe-59
Mn-56
Sc-46
K-43
K-42

4.576h
2.377d
1.097d119.8d17.77d
4.86h
1.08d
14.10h1.94d2.720d3.96h
13.76h2.28d
2.517h
44.50d
2.579h83.79d22.3h
12.36h

190.3
520.7
559.1
264.7
595.8
297.3
834.0
834.0
144.7
175.0
386.3
438.6
D1039.2
1481.81099.3
846.8
889.3
617.5
1524.7

64.0
22.4
45
58.5
59.4
79.8
79.5
95.6
82.9
82
93
94.8
7.4
23.6
56.5
98.9
100
79.2
18.1

TYPE Detec.
C+
C+
I
C+
I
CI
I
CC+
CI
CCCCI
CI

T
C
T
T, C
T, C
T
T
T, C
T, C
T
T, C
T
T
T, C
T, C
C
C
T
T

Photofission of 197Au at Intermediate Energies

J. Nucl. Radiochem. Sci., Vol. 1, No. 2, 2000 55(3,3) resonance. It is noted that the saturation of the reaction
yield above 600 MeV is reasonably consistent with the E0independent recoil properties such as forward-to-backward
yield ratios and the kinetic energies of the residual nuclei.24
3.2. Charge Distribution. In the present work, the charge
distribution Y CD (Z) among the isobars of a certain productmass number A, was assumed to be represented by the following Gaussian function:
2

YCD (Z) = YCD (Zp) ·exp)
{ –(Z–Z}, (1)Cp

Z

Figure 1. Measured mean ranges 2W(F+B) in unit of mg/cm2 of Au
as a function of product mass number A. The present results areshown by open circles, and those by Areskoug et al.23 at E0 = 600
MeV are shown by closed squares.

least squares fitting as shown by a dashed line in the figure.
The quality of this fitting is fairly good because all of the2W(F+B) values can be well reproduced within 2 σ of theexperimental errors. By using this relation the reaction yieldsof the nuclides observed only in the target were obtained after
correcting their recoil losses, and the relative yields of thenuclides found only in the catcher foils were normalized to theabsolute ones. Thus the absolute yields of the 58 products inthe mass range of A = 42–131 were obtained, and they are
given in unit of µb per equivalent quanta (µb/eq.q.) in Table
A1 in Appendix. The yield values in italics were obtained
from the radioactivities assayed in the catcher foil. In general
the yield values increase steeply with an increase of E0 up to
600 MeV and increase gradually at higher E0, indicating theresonance-type excitation function mainly attributed to thewhere, YCD (Zp) is the maximum yield of the charge distribution, Zp being the most probable charge. The width parameter
CZ was assumed to be constant, irrespectively of A, and Zp tobe a linear function of A, i.e., Zp = RA + S. By assuming the
Unchanged Charge Distribution (UCD), the parameter R isrelated to a charge-to-mass ratio of a fissioning nucleus as R =79 / (197–νpre), νpre being the number of prefission neutrons.
The parameter S is a measure of the number of average post
fission neutrons νpost as S = 79νpost / (197–νpre). The eq 1 wasfitted to the experimental yields by a least squares method.
For cumulative yields, a sum of the yields of a suitable number
of isobars was fitted. The yields of the product nuclei in ametastable state were excluded from the present analysis. The
results of yield measurements of 46,47,48Sc and 56,57,58,60Co from197
Au target in the previous study6 were also included in thepresent analysis. The four free parameters YCD (Zp), CZ, R, andS were determined at representative eleven energies of E0 =1100, 1000, 900, 800, 700, 600, 500, 450, 400, 350, and 300
MeV. As an example, the charge distributions obtained at E0 =1100 MeV are shown in Figure 2 by solid curves for the representative mass chains of A = 56, 72, 83, 88, 95, 97, 103, and105, in which more than two yield data were obtained. The
independent yields (I), the cumulative yields by β– decay (C–)
and by β+ decay and/or electron capture (C+) are shown by
open circles, closed triangles, and closed squares, respectively.

Figure 2. Charge distributions for the mass chains of (a) 56, (b) 72, (c) 83, (d) 88, (e) 95, (f) 97, (g) 103, and (h) 105 at E0 = 1100 MeV. The independent yields (I), the cumulative yields by β– decay (C–), and by β+ decay and/or electron capture (C+) are shown by open circles connected by asolid curve, closed triangles connected by a dotted curve, and closed squares connected by a dashed curve, respectively.

Haba

56 J. Nucl. Radiochem. Sci., Vol. 1, No. 2, 2000
The cumulative yields calculated are shown by a dotted curve
for C– and by a dashed curve for C+ by integrating the independent Y CD (Z p ) curve. It seems that the results of these
fittings are fairly good and the present assumptions in eq 1 arereasonable.

The full width at half maximum of the charge distribution(FWHMCD) in charge unit (c.u.) instead of CZ and the parameters R and S are shown as a function of E0 by open circles in
Figures 3a–3c, respectively, together with those reported by
Areskoug et al.23 at E0 = 600 MeV by closed squares. The
FWHMCD (Figure 3a) shows E0-independence at the studied E0
within the quoted errors, and the weighted mean value of 2.2 ±0.1 c.u. agrees well with that reported by Areskoug et al.23 at
E0 = 600 MeV. On the other hand, the parameter R (Figure 3b)
increases slightly with an increase of E 0 and becomes aconstant value of R = 0.424 ± 0.001 above 600 MeV, which
implies eleven-neutron emission before fission (νpre = 11) as
deduced from the UCD assumption. The parameter S (Figure3c) is also independent of E0 above 600 MeV and the weighted
mean value of 0.7 ± 0.1 implies the average two post neutrons(νpost = 2). The variations of the R and S values below 600
MeV may reflect a change in the excitation energy, though thenumber of the measured isobars is small and the yield data areaccompanied with large errors at lower energies. The R and S
values reported by Areskoug et al. 23 at E 0 = 600 MeV areconsistent with the present results within 2 σ of the experimental uncertainties.
3.3. Mass Yield Distribution. By using the charge distribution parameters YCD (Zp), CZ, R, and S determined above, thetotal chain yields in unit of µb/eq.q. were evaluated for themass chains of A = 42, 43, 46–48, 56–60, 65, 66, 71–77,
82–84, 86–89, 91, 92, 95–97, 99, 103, 105, 112, 126, 128, 129,
and 131. The total chain yields calculated at E0 = 1100, 900,
700, 500, and 300 MeV are shown in Figure 4 as a function of
the product mass number (A) by open circles, closed triangles,
open squares, closed inverse triangles, and open diamonds,
respectively. The mass yield distributions seem to be symmetric with a maximum around A = 90. In the present work themass yield distribution, YMD (A), is assumed to be represented
by the following Gaussian function,
2

Figure 3. Charge distribution parameters (a) FWHMCD, (b) R, and (c)S as a function of E0. The present results are shown by open circles,
and those by Areskoug et al.23 at E0 = 600 MeV are shown by closed
squares.

YMD (A) = YMD (Ap) ·exp){–(A–A}, (2)C
p

A

where, YMD (Ap) is the maximum of the mass distribution, Ap
being the most probable mass, and CA is the width parameter.

Figure 4. Mass yield curves of the photofission of 197Au at E0 = 1100, 900, 700, 500, and 300 MeV. See text for the details.

Photofission of 197Au at Intermediate Energies

The total chain yields, except for the data at A = 42, 47, 82,
and 96, which were largely deviated from the expected
Gaussian curve, were fitted by eq 2 as shown by the different
curves for each energy in Figure 4. The shape of the mass
yield curves are almost the same above 500 MeV, though theabsolute yields increase slightly with an increase of E0. The
mass yields at E0 = 300 MeV, however, are quite smaller andthe Ap value is somewhat higher than those at higher energies.
The relative mass yield curves reported by Komar et al.22 at
E0 = 1000 MeV and Areskoug et al. 23 at E0 = 600 MeV are
applied to a comparison. In order to investigate the consistency of the mass yield curves obtained by the different
methods and at the different energies, the Ap value and the full
width at half maximum (FWHMMD) are shown as a function of
E0 in Figures 5a and 5b, respectively. The Ap value decreases
with an increase of E0 from 97 ± 2 m.u. at E0 = 300 MeV to a
constant value of 92 ± 1 m.u. at E0 ≥ 600 MeV. This constantvalue at E0 ≥ 600 MeV is reasonable because the mass numberof the fissioning nucleus was estimated to be Af = 186 m.u.
(νpre = 11) from the charge distribution parameter R based on
the UCD assumption. The Ap value reported by Areskoug etal.23 at E0 = 600 MeV agrees well with the present result, butthat by Komar et al.22 at E0 = 1000 MeV is higher by 5 m.u.
because they assumed the mass number of the fissioning
nucleus to be Af = 194 m.u. On the other hand, the FWHMMD
values are independent of E0 at the studied energies within theexperimental uncertainties, though a slightly increasing trend
appears at E0 < 600 MeV. The weighted mean value of 39 ± 1
m.u. at E0 ≥ 600 MeV is equal to that measured by Komar etal.22 by the coincident energy measurements of fragment pairs.
However the FWHMMD value reported by Areskoug et al.23 at
E0 = 600 MeV is lower by about 8 m.u. (FWHMMD = 30.9 ± 1.7
m.u.). As mentioned above, the charge distribution parameters
FWHMCD, R, and S reported by Areskoug et al.23 at E0 = 600
MeV are consistent with those obtained in the present work
(See sect. 3. 2.). The discrepancy of FWHMMD may be attributed to the smaller mass range analyzed by Areskoug et al.23(72 ≤ A ≤ 111). Also noted is that Areskoug et al.23 measured
the cumulative yield of 59Fe, but eliminated it from the analysis
because the value of 59 Fe is anomalously higher than that
deduced from their mass yield curve obtained at A = 72–111.

Figure 5. Variations of (a) the most probable mass Ap and (b) the full
width at half maximum of the mass distribution FWHMMD as a function of E0. The present results are shown by open circles, and those by
Komar et al.22 at E0 = 1000 MeV and by Areskoug et al.23 at E0 = 600
MeV are shown by closed triangles and closed squares, respectively.

J. Nucl. Radiochem. Sci., Vol. 1, No. 2, 2000 57
In the present work the product mass range measured was
expanded widely to A = 42–131, and almost all of the total
chain yields fell on the Gaussian curve. The anomaly of the59
Fe yield suggested by Areskoug et al.23 was not observed in
the present work.
The total fission yields in unit of mb/eq.q. determined abovefrom the mass yield curves are shown as a function of E0 by
open circles in Figure 6. As mentioned in Introduction, thetotal fission yields on 197 Au in unit of mb/eq.q. have been
extensively measured with ionization chambers7 and solid-state
track detectors.8,10–16 These results are compared in Figure 6 by
the different symbols as shown in the inset of the figure. The
results by the different authors are consistent with each otherin the range of a factor of 2 except for the result by Kiely etal.16 at E0 = 580 MeV (an open diamond). The total fission
yields increase steeply by about three orders of magnitude withan increase of E 0 from 100 MeV to 600 MeV and increaseslightly at energies higher than E0 = 600 MeV, indicating boththe quasi-deuteron mechanism and the (3,3) resonance aremain photoabsorption channels to induce fission process. In
recent years the total fission cross sections have been intensively measured by quasi-monochromatic photon beams ofenergies up to 300 MeV,17–21 and the detailed structure of theexcitation function of the photofission of 197Au has become
clear. Unfortunately these beams are too low in intensities atpresent for our radiochemical studies.
The many radiochemical cross section measurements were
performed for the proton-induced fission of 197 Au at thevarious proton energies.34–44 Since almost all of the proton data
were obtained by a nondestructive γ-ray measurement of theirradiated Au target, the number of nuclides measured are quite
small and insufficient for the same analysis as applied in thepresent work. Therefore, the ratios of the reported crosssections of the proton reaction at Ep = 1000, 800, 600, 400,
300, and 200 MeV to the yields of the photon reaction at E0 =1000 MeV were calculated for some representative products of46
Sc (I), 58Co (I), 59Fe (C–), 60Co (I), 74As (I), 75Se (C+), 82Br(I), 83,84,86Rb (C+, I, I), 87,88Y (C+, I), 89,95Zr (C+, C–), 96Tc (I),103
Ru (C–), 105Ag (C+), and 131Ba (C+), based on our compilation of the cross section data in References 34–44. They are
shown as a function of the product mass number A in Figure 7,
all normalized to 1 at A = 103 ( 103 Ru), because the crosssections of the neutron rich isotope of 103Ru are independent of
Ep in the range of Ep = 200–1000 MeV.38,39,41,42,44 The ratios at
Ep = 300 and 400 MeV are almost unity (a dashed line), indicating the same mass yield shape as the photofission at E0 =1000 MeV. This may be reasonably understood, because theeffective photons to induce fission process are mainly in the(3,3) resonance with a peak energy around 300 MeV. This fact

Figure 6. Total photofission yields of 197Au in unit of mb per equivalent quanta (mb/eq.q.) as a function of E0. See text for the details.

Haba

58 J. Nucl. Radiochem. Sci., Vol. 1, No. 2, 2000

Figure 7. Ratios of the cross sections of the proton reactions at Ep =1000, 800, 600, 400, 300, and 200 MeV to the yields of the photon
reaction at E0 = 1000 MeV as a function of product mass number A,
normalized to 1 at A = 103 (103Ru). See text for the details.

may imply that the difference in the initial interactions ofphotons and protons with nuclei does not affect the fissioning
process. A few physical investigations of the mass yield
curve, which is based on the coincident energy measurementsof the fragment pairs, are also available at Ep = 1000 MeV.45,46
The FWHMMD values of 54.5 ± 0.6 m.u. reported by Kotov etal.45 and 46.9 m.u. by Andronenko et al.46 are discrepant witheach other and both are higher than the present photon result of
39 ± 1 m.u. at E 0 ≥ 600 MeV. The intensive cross section
measurements in the proton-induced fission of 197 Au arestrongly desired in order to determine charge and mass yield
distributions and to compare them further with the present
photofission results.
The contributions of the spallation process in the observed
yields were estimated by the CDMD formula4 using the parameter set reported in Reference 2. The spallation yields were
estimated to be one order of magnitude higher than theobserved yields for the barium isotopes, for which the spallation contributions are deduced to be the largest. The parameter
set in Reference 2 was determined based on the yield data of
the near-target isotopes produced in the (γ, 0–5pxn) reactions,and might not be appreciable to such far-target isotopes as
those in the barium region. An extensive yield measurementsof rare earth elements are under study in order to clarify thedifference in the charge and mass yield distributions between
fission and spallation in the region of barium and light rareearth isotopes. Recently, the yields of light nuclei such as
7,10Be, 22,24Na and 28Mg from 197Au were measured.6 It was
found that they are more than one order of magnitude higher
than those extrapolated from the mass yield curve of fission,indicating different reaction mechanism; fragmentation. All of
the mass yield data in Figure 4 are well reproduced by theGaussian curves, indicating that the contributions of otherreaction processes such as spallation and fragmentation are
negligible within the experimental uncertainties.
It is interesting to compare the charge and mass yield distributions obtained in the present study with those calculated by aMonte-Carlo intranuclear cascade-evaporation code forphotonuclear reactions. Previously, the cross sections and/or
reaction yields of the photopion and photospallation reactions
and the kinetic energies of the photospallation products weresystematically compared with the Photon-Induced Intranuclear
Cascade Analysis (PICA) code, 47,48 and various important
information related to the nuclear structure and reaction mechanism was pointed out;5,25,26,49–53 especially a requirement of
nuclear medium effect in heavy nuclei with At ≥ 100 in the
PICA model was emphasized. Very recently, several modifications have been performed for the original PICA code andthe fission process will be included in the calculation by Sato.54
A comparison with the advanced PICA calculation54 will bereported elsewhere, together with the same yield measurements of the photofission of 209Bi, which are under study in ourgroup.55
It was found that the charge distribution parameters (CZ, R,
and S) and the mass yield distribution parameters (Ap and CA)
as well as the recoil properties discussed in the separate paper24
are all independent of E0 above 600 MeV. It is concluded thatthe photofission process of 1 9 7 Au attains to the limiting
behavior above 600 MeV as found in our previous studies ofphotospallation1–3 and simple photopion reactions.5,25,26 The
measurements at E0 < 300 MeV are strongly desired, because
the different contributions of the giant dipole resonance, thequasi-deuteron mechanism, and the (3,3) resonance areincluded, and the change in the fission characters with E0 is
expected. A measurement at E0 = 65 MeV, where only the
giant dipole resonance and the quasi-deuteron mechanism
contribute, was performed by using the 300 MeV electron
linac of the Laboratory of Nuclear Science (LNS) of Tohoku
University. The preliminary result of the symmetric mass
yield distribution with A p = 99 ± 1 and FWHMMD = 20 ± 1
m.u., which is quite different from the present results at E0 ≥300 MeV, was obtained. The results will be reported elsewhere.
Acknowledgment. The authors would like to express their
gratitude to Drs. H. Okuno and K. Masumoto, and the ES
crew members of the High Energy Accelerator Research
Organization at Tanashi, for their invaluable cooperations in
the course of experiments. This work was supported in part by
the Grant-in-Aid for Scientific Research (07304077) of the
Ministry of Education, Science and Culture of Japan.

Appendix
TABLE A1: Yields of 58 Fission Products from 197Au in Unit of µb per Equivalent Quanta (µb/eq.q.)
E 0 (MeV)
1100
1000
950
900
800
700
650
550
500
450
400
350
300

131

Ba (C+)

6.79 ± 0.73
6.5 ± 0.4

131

Ba (C+)

4.4 ± 1.1129m

Ba (C+)

1.57 ± 0.11
2.1 ± 0.5129m

Ba (C+)

1.5 ± 0.5

129

Ba (C+)

4.70 ± 0.52
3.9 ± 2.3

128

Ba (C+)
5.37 ± 0.49
9.7 ± 1.6

1.01 ± 0.18

2.31 ± 0.84

7.73 ± 1.71

0.413 ± 0.090

0.591 ± 0.387

4.96 ± 1.04

128

Ba (C+)

6.4 ± 2.1

126

Ba (C+)
0.981 ± 0.164
2.7 ± 0.8

1.36 ± 0.65

113

Ag (C-)
7.20 ± 0.76

9.48 ± 0.53
8.59 ± 0.61
7.19 ± 0.36

5.82 ± 0.45
1.62 ± 0.63

6.37 ± 0.34
3.82 ± 0.86−+

I: independent yield; C-: cumulative yield by β decay; C+: cumulative yield by β decay and/or electron capture.
Yield values in italics were obtained from the activities in the catcher foils.

Photofission of 197Au at Intermediate Energies

J. Nucl. Radiochem. Sci., Vol. 1, No. 2, 2000 59

TABLE A1: (Continued)
E 0 (MeV)
1100
1000
950
900
800
700
650
550
500
450
400
350
300

112

Ag (I)

110m

Ag (I)

110m

Ag (I)

106m

Ag (I)

105

Ag (C+)

7.91 ± 0.80

9.62 ± 0.89

9.2 ± 1.2
13 ± 5

3.41 ± 0.51
3.24 ± 0.59

6.90 ± 0.79

11.8 ± 0.5
12.0 ± 0.5
8.73 ± 0.29

7.9 ± 3.6
11 ± 413 ± 47.33 ± 0.32
4.23 ± 0.28
6.43 ± 0.26

11.1 ± 1.2
10.1 ± 1.3
7.88 ± 0.83
10.3 ± 2.1
11.1 ± 2.1
8.80 ± 0.92
5.07 ± 0.84
6.38 ± 0.85

6.04 ± 0.67
5.72 ± 0.91
3.01 ± 0.42
4.07 ± 0.68
5.86 ± 1.25
2.37 ± 0.32
1.54 ± 0.69
1.56 ± 0.39

8.66 ± 0.99
8.23 ± 1.25
7.04 ± 0.66
10.0 ± 2.9
5.08 ± 1.32
4.58 ± 0.31
3.46 ± 0.46

5.55 ± 0.93

9.71 ± 6.71

105

105

104

103

Rh (C-)
60 ± 565 ± 466 ± 873 ± 564 ± 468 ± 458 ± 566 ± 943 ± 6

22
19
19
24
21
23
19
18
16

Ru (C-)
± 2
± 2
± 2
± 2
± 2
± 2
± 1
± 2
± 1

Ag (I)
1.85 ± 0.20

Ag (C+)
0.905 ± 0.125
0.769 ± 0.192

2.03 ± 0.13
1.90 ± 0.12
1.34 ± 0.10

0.815 ± 0.089
0.871 ± 0.071
0.511 ± 0.082

0.891 ± 0.138
0.778 ± 0.087

0.189 ± 0.127

32 ± 436 ± 535 ± 912 ± 1
11 ± 18.0 ± 1.2

0.580 ± 0.070

0.295 ± 0.134

0.279 ± 0.144

TABLE A1: (Continued)
E 0 (MeV)

103

1100
1000
950
900
800
700
650
550
500
450
400
350
300

61.3 ± 2.3
64.5 ± 2.8
58.6 ± 2.6
65.8 ± 2.5
60.2 ± 3.0
60.0 ± 2.5
53.3 ± 2.6
48.7 ± 7.5
42.4 ± 2.6

62 ± 364 ± 359 ± 365 ± 357 ± 257 ± 354 ± 354 ± 439 ± 250.4 ± 2.3

40.0 ± 2.6

60 ± 254 ± 262 ± 361 ± 261 ± 351 ± 353 ± 349 ± 339 ± 231.8 ± 1.7
26.3 ± 2.0
17.8 ± 2.2

32 ± 224 ± 218 ± 726.0 ± 1.8
39 ± 812 ± 232 ± 229 ± 222 ± 2

Ru (C-)

103

Ru (C-)

99

Mo (C-)

57

± 2

48

± 3

99

Mo (C-)

98b

Nb (I)

11 ± 2
11.5 ± 1.0

9.0 ± 0.7

97

Ru (C+)
9.6 ± 0.6
9.8 ± 0.7
8.9 ± 2.1
8.8 ± 0.6
9.6 ± 0.7
8.0 ± 0.6

97

Nb (I)
29 ± 233.4 ± 1.5

30

± 2

26
22

± 2
± 3

30

± 20

97

Zr (C-)
9.06 ± 0.62
8.5 ± 0.7
9.6 ± 0.7
9.0 ± 1.1
11.1 ± 0.7

6.45 ± 0.53

Zr (C-)
9.1 ± 0.6
10 ± 1
10 ± 29.6 ± 0.6
9.5 ± 0.5
8.5 ± 0.5
8.7 ± 0.5
7.9 ± 1.3
6.7 ± 0.7

4.87 ± 0.34
5.3 ± 0.5
5.07 ± 0.97

5.3 ± 0.6
4.9 ± 0.9
4.6 ± 1.0

10.6 ± 0.7
9.6 ± 1.0
14 ± 397

TABLE A1: (Continued)96

E 0 (MeV)
1100
1000
950
900
800
700
650
550
500
450
400
350
300

Tc (I)

96

96

Nb (I)

8.7 ± 0.9
9.9 ± 1.1
7.7 ± 1.3
8.8 ± 0.7
9.1 ± 0.9
5.6 ± 0.8
5.3 ± 1.2
13 ± 45.4 ± 1.2

29 ± 230.1 ± 1.3

22
22

± 2
± 3

2.5 ± 1.2

20

± 10

± 1

20

95

Nb (I)

± 2
± 2
± 4
± 2
± 2
± 2
± 2
± 4
± 2

28
28
25
26
24
24
21
24
17

Nb (I)

40 ± 448.1 ± 2.0

± 3

40

± 3
± 14

40
25

14 ± 27.5 ± 1.2
7.7 ± 1.7

95

Nb (I)

52 ± 360 ± 450 ± 654 ± 351 ± 344 ± 341 ± 350 ± 738 ± 324 ± 325 ± 395

Zr (C-)
47.0 ± 2.3
36 ± 440 ± 743 ± 342.3 ± 2.8
29.9 ± 2.7
29.2 ± 1.7
20.0 ± 1.6
16 ± 613.2 ± 6.4

95

Zr (C-)
40 ± 242 ± 338 ± 746 ± 338 ± 337 ± 333 ± 436 ± 526 ± 492m

Nb (I)

3.90 ± 0.41

4.5 ± 2.1

92m

Nb (I)
2.3 ± 0.6
4.4 ± 0.6
6.0 ± 1.1
3.9 ± 0.6
3.4 ± 0.8
2.4 ± 0.7
3.4 ± 1.1

4.6 ± 1.8
2.5 ± 1.1

22 ± 422 ± 5TABLE A1: (Continued)
E 0 (MeV)
1100
1000
950
900
800
700
650
550
500
450
400
350
300

92

Sr (C-)

7.9 ± 0.6

92

Sr (C-)91

Sr (C-)

16.3 ± 1.2

5.0 ± 0.5

8.4 ± 0.5
9.7 ± 1.0
11 ± 211 ± 18.1 ± 0.6
9.0 ± 0.6
8.7 ± 0.7
9.6 ± 1.3
7.0 ± 0.8

3.8 ± 0.3
2.7 ± 0.6
2.9 ± 0.2

5.1 ± 0.5
5.4 ± 0.8
3.6 ± 0.8

7.5 ± 0.4
6.2 ± 0.5

91

Sr (C-)

15.2 ± 1.0

18
19
26
24
21
18
16

± 3
± 2
± 4
± 2
± 2
± 2
± 2

10.2 ± 1.0

13

± 2

9.72 ± 0.60
7.65 ± 0.93
7.92 ± 1.46

12 ± 29.8 ± 2.5

15.9 ± 1.0

90m

Y (I)

90m

89

88

56.4 ± 3.0
46.6 ± 1.2
48.0 ± 2.0
48.7 ± 1.2
43.1 ± 1.6
41.6 ± 1.2
39.3 ± 1.5
32.5 ± 1.0
33.5 ± 2.4
27.0 ± 2.7
16.0 ± 0.6
10.0 ± 0.6

23 ± 117 ± 113 ± 14.72 ± 0.64
6.6 ± 1.1
4.49 ± 1.26

7.3 ± 1.3

Y (C+)

87

± 2.6
± 1.4
± 3.0
± 1.2
± 3.0
± 1.1
± 1.9
± 0.9
± 1.5

Y (C+)
± 2
± 2
± 3
± 2
± 2
± 2
± 2
± 2
± 2

87m

41
38
40
40
38
31
26
23
16

Sr (C+)
3.53 ± 0.30

Rb (I)
68 ± 858 ± 1072 ± 2879 ± 873 ± 1066 ± 91.40 ± 0.18

Rb (I)
56.7 ± 5.6
55.6 ± 6.7
75.8 ± 23.4
67.2 ± 7.5
48 ± 566 ± 957 ± 846.3 ± 12.7
23.8 ± 6.2

12 ± 16.9 ± 1.3

1.05 ± 0.14

28.4 ± 7.7

32 ± 1162 ± 210.729 ± 0.273

36.6 ± 21.8

29.2
26
20
26
21.5

Zr (C+)
± 1.9
± 3
± 3
± 2
± 1.5

89

Y (I)
55 ± 254 ± 350 ± 256 ± 249 ± 246 ± 243 ± 236 ± 231 ± 2

17.2 ± 1.3
11.3 ± 1.0

29
26
22
25
22
19
15
13
11

Zr (C+)
± 2
± 2
± 3
± 1
± 2
± 1
± 3
± 2
± 2

Zr (C+)
14.9 ± 1.011± 29.3 ± 2.015
± 24.80 ± 1.33

1.94 ± 0.71
6.7 ± 2.5

4.99 ± 0.70

TABLE A1: (Continued)
E 0 (MeV)
1100
1000
950
900
800
700
650
550
500
450
400
350
300

88

13
13

Zr (C+)± 1± 2

13 ± 17.2 ± 0.9
8.8 ± 1.0
6.4 ± 2.1

88

Y (I)

88

Y (I)

48.8 ± 3.6
46.8 ± 2.2

39 ± 4

± 1.7
± 2.4
± 1.5
± 2.3
± 2.2
± 3.1

44 ± 337 ± 433 ± 334 ± 5

19.6 ± 2.9

19 ± 2

42.9
36.2
35.3
28.3
30.3
31.1

3.11 ± 2.20

28 ± 387m

Y (C+)

43.0
34.1
33.4
32.9
27.1
21.2
21.8
15.0
18.0

± 2.4
± 0.9
± 2.1
± 0.7
± 1.0
± 0.7
± 1.0
± 0.6
± 1.4

10.9 ± 1.2
5.41 ± 0.35
3.11 ± 0.38

87

46.1
39.0
36.4
39.4
36.0
30.2
26.6
18.5
19.1

12.8 ± 1.4
6.83 ± 0.59
3.93 ± 0.79

3.17 ± 0.23
3.15 ± 0.22868679 ± 2242 ± 11Haba

60 J. Nucl. Radiochem. Sci., Vol. 1, No. 2, 2000
TABLE A1: (Continued)
E 0 (MeV)
1100
1000
950
900
800
700
650
550
500
450
400
350
300

84

Rb (I)

± 3.2
± 4.5
± 5.2
± 3.3
± 2
± 4
± 2

56.0
62.1
63.9
63.2
43
54
34

21.5 ± 4.9
21.6 ± 3.7
15.4 ± 5.2
7.32 ± 2.89

84

Rb (I)

56 ± 351 ± 354 ± 457 ± 550 ± 341 ± 344 ± 341 ± 331 ± 383

Sr (C+)

3.63 ± 0.71

3.99 ± 0.65
3.20 ± 0.95

83

Rb (C+)

52.1 ± 2.5
57.8 ± 3.9
54.3 ± 2.8
42.3 ± 4.2
40.2 ± 3.3
36.1 ± 3.7

21 ± 318 ± 383

Rb (C+)

48 ± 244 ± 347 ± 1051 ± 341 ± 433 ± 329 ± 542 ± 634 ± 412 ± 482m

Rb (I)
14.0 ± 1.0
12.4 ± 1.1
13.3 ± 0.7
10.1 ± 0.6
9.21 ± 0.65
5.27 ± 0.55
5.39 ± 0.55
4.01 ± 1.02
3.55 ± 0.69
1.45 ± 0.62
1.05 ± 0.28

82

21
32
35
23
25
22
22

Br (I)
± 3
± 3
± 5
± 2
± 2
± 2
± 3

15

± 3

5.8 ± 2.1
12 ± 481

Rb (C+)
8.91 ± 0.73
8.77 ± 1.03
9.38
6.66
6.2
4.06
3.55
2.22

± 0.66± 0.68± 0.7± 0.77± 0.87± 0.7077

Br (C+)
16 ± 321 ± 424 ± 813 ± 312 ± 39.5 ± 2.1
13 ± 5

1.78 ± 0.46
0.626 ± 0.318

TABLE A1: (Continued)76

E 0 (MeV)
1100
1000
950
900
800
700
650
550
500
450
400
350
300

As (I)

32
23

± 2
± 1

25
20
22
16
14

± 2
± 1
± 2
± 1
± 2

75

Se (C+)

75

Se (C+)

18.3 ± 1.0
18.6 ± 1.7

14 ± 214 ± 416.3 ± 1.8
11.6 ± 1.3
11.9 ± 1.5
9.58 ± 1.74

13 ± 415 ± 414 ± 411 ± 1
11 ± 34.7 ± 1.1

74

As (I)

24.4 ± 1.7
19.6 ± 2.1

7473

As (I)

23 ± 113.5 ± 2.3
18 ± 2
13.1 ± 1.8
14 ± 226 ± 230 ± 228 ± 327 ± 222 ± 221 ± 222 ± 222 ± 315 ± 25.3 ± 0.8

11 ± 2

Ga (C-)

23 ± 227.4 ± 1.1

18.2 ± 0.9
18.5 ± 0.7

72

As (I)
5.4 ± 0.4
4.37 ± 0.26

2.9 ± 0.5
1.99 ± 0.16
2.7 ± 0.4
1.3 ± 0.4

10.2 ± 0.8

72

Ga (I)

23± 2
27.0 ± 1.5

18.0 ± 0.9
17.4 ± 0.8

7.07 ± 0.62

4.1 ± 1.4

72

27
27
26
25
24
21
20
16
14

Ga (I)
± 1
± 2
± 1
± 1
± 1
± 1
± 1
± 2
± 1

9.9 ± 0.6
7.9 ± 0.8
6.0 ± 0.8

TABLE A1: (Continued)
E 0 (MeV)
1100
1000
950
900
800
700
650
550
500
450
400
350
300

72

Zn (C-)

72

Zn (C-)

3.47 ± 0.49

8.6 ± 0.5
8.9 ± 0.5
10 ± 29.9 ± 0.4
8.5 ± 0.5
8.2 ± 0.4
7.0 ± 0.5
5.1 ± 0.8
4.0 ± 0.5

3.70 ± 0.24
2.8 ± 1.0
3.30 ± 0.61

4.8 ± 0.6
4.9 ± 1.0
4.5 ± 1.1

8.0 ± 0.6
6.0 ± 0.5
8.6 ± 1.3

71

As (C+)

2.9 ± 0.3
1.56 ± 0.15

1.3 ± 0.3
0.949 ± 0.13671m

Zn (C-)

5.3 ± 0.371m

3.3 ± 0.3
3.1 ± 0.3
3.2 ± 0.5
2.8 ± 0.4

2.9 ± 0.3
2.5 ± 0.5
2.6 ± 0.6

6.6 ± 0.4
7.3 ± 1.0

1.18 ± 0.2269m

Zn (C-)

5.8 ± 0.4
6.8 ± 0.6
5.5 ± 1.0
6.2 ± 0.6
6.3 ± 0.5
4.9 ± 0.6
4.9 ± 0.5
4.3 ± 0.7
3.6 ± 0.4

19
14
15

Zn (I)

± 1
± 1
± 2

8.79 ± 0.46
7.39 ± 0.35
5.3 ± 0.7
2.96 ± 0.47

66

65

15

Ni (C-)± 3

Ni (C-)
18.9 ± 0.9

19

± 4

15

16
16

± 10
± 4

16.5 ± 1.4
11.8 ± 0.9

8.7 ± 4.1
8.7 ± 3.6
5.5 ± 2.1

10.2 ± 0.9
6.2 ± 0.8
6.19 ± 0.82
7.6 ± 1.0
6.41 ± 1.33

± 2

65

17
22
24
17
16
14
13

Ni (C-)
± 2
± 3
± 4
± 2
± 2
± 2
± 2

11

± 3

6.4 ± 1.5
8.5 ± 2.0
8.0 ± 0.3

TABLE A1: (Continued)
E 0 (MeV)
1100
1000
950
900
800
700
650
550
500
450
400
350
300

59

Fe (C-)

17.7
16.7
18.2
17.8
15.9
12.4
10.9

± 0.9
± 1.0
± 1.2
± 1.1
± 1.1
± 0.8
± 1.0

15 ± 217 ± 220 ± 416 ± 215 ± 212 ± 27.2 ± 2.1

59

4.53 ± 1.34
3.54 ± 0.69

Fe (C-)56

Mn (C-)

43

K (C-)

42

K (I)2.73 ± 0.15

2.3 ± 0.3

1.2 ± 0.3

1.9 ± 0.4

1.9 ± 0.2

2.2 ± 0.2

7.9 ± 2.2

13 ± 114 ± 112 ± 113 ± 1
11 ± 19.4 ± 0.5
8.2 ± 0.5
6.4 ± 0.8
3.8 ± 0.5

4.6 ± 2.2
8.3 ± 4.0

3.3 ± 0.4
2.7 ± 0.6

0.4 ± 0.3
0.22 ± 0.18
0.26 ± 0.21

0.92 ± 0.29
0.53 ± 0.12

References(1) S. Shibata, M. Imamura, T. Miyachi, M. Mutou, K.
Sakamoto, Y. Hamajima, M. Soto, Y. Kubota, M.
Yoshida, and I. Fujiwara, Phys. Rev. C 35, 254 (1987).
(2) S. R. Sarkar, M. Soto, Y. Kubota, M. Yoshida, T.
Fukasawa, K. Matsumoto, K. Kawaguchi, K. Sakamoto,S. Shibata, M. Furukawa, and I. Fujiwara, Radiochim.
Acta 55, 113 (1991).
(3) S. R. Sarkar, Y. Kubota, T. Fukasawa, K. Kawaguchi, K.
Sakamoto, S. Shibata, and I. Fujiwara, Radiochim. Acta
55, 139 (1991).

0.5 ± 0.2

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