Journal of Nuclear and Radiochemical Sciences, Vol. 9, No.1, pp. 19-25, 2008

Empirical Formulas for Estimation of Fission Prompt Neutron Multiplicity for Actinide
NuclidesTakaaki Ohsawa*
Department of Electric and Electronic Engineering, School of Science and Engineering, Kinki University, 3-4-1
Kowakae, Higashi-osaka 577-8502, Japan
Received: January 11, 2008; In Final Form: May 1, 2008
Empirical formulas were obtained for estimation of the prompt neutron multiplicity for actinides as a function of
the incident neutron energy. Measured data for eleven nuclides (232Th, 233U, 235U, 238U, 237Np, 239Pu, 240Pu, 241Pu,
241
Am, 243Am, and 245Cm) were used as the basis to extract systematic relations of slopes and intercepts of a linear
function of the prompt neutron multiplicity. The obtained formulas were compared with available measured dataand existing evaluations. It was found that these formulas could be used to estimate the quantity for nuclides forwhich no or scarce data is available.

1. Introduction
With the increase of interest to extended burn-up of nuclear
fuel and incineration of long-lived actinide nuclides, the needfor accurate nuclear data for actinide nuclides has been risingthese years. However the quality of nuclear data for minor
actinides remains to be improved.1 The figure-of-merit of a
nuclide in nuclear design of a reactor is evaluated by the prod––uct ν (E n)σf (E n) of the average prompt neutron multiplicity ν(E n ) and fission cross section σf (E n ), which means that the
prompt neutron multiplicity is one of the important quantities
that determines the performance of the system. Efforts havebeen devoted to deduce formulas that can be used for evalua–tion of the quantity ν (En) for any actinides, but existing formulas were obtained on the basis of the measurements available inthe seventies. Thus it is useful to re-examine the preceding
works and experimental data available nowadays so as to construct formulas that makes it possible to evaluate the required
data in compiling evaluated nuclear data libraries. Actually,
the present formulas are planned to be used for evaluation ofprompt neutron multiplicity for some actinides in Japanese
Evaluated Nuclear Data Library, version 4 (JENDL-4) presently under compilation.
2. Preceding Studies
It would be useful to review the preceding studies on theprediction of the average number of prompt neutrons for
actinides. Here two models are discussed that have been used–
to evaluate the ν (En) -values in several nuclear data files.
–
2.1. Howerton’s Mode. Howerton 2, 3 assumed that ν (E n)can be expressed by a truncated pseudo-Taylor series expansion:–ν (E, A, Z) = C0 + C1(Z–92) + C2(A–235) +C3(En–Eth) + C4(A–235)·(En–Eth) + …. (1)The constant C 0 was evaluated from systematics of theprompt neutron multiplicity at fission thresholds for 235U and238
U. Other coefficients Ci were also obtained from experimental data. This led to the resulting formula:*Corresponding author. E-mail: ohsawa@mvg.biglobe.ne.jp. fax:
+81-6723-2721.

–
ν (Z, A, En) = 2.33 + 0.06[2–(–1) A+1–Z –(–1) Z ] + 0.15(Z–92)+ 0.02(A–235) + [0.130+0.006(A–235)](En–Eth).
(2)This formula was extended so as to be applicable in the neutronenergy region where multiple-chance fission can occur. (Seeeqs 9 – 11 of Reference 2.) This set of formulas has been usedin many nuclear data files, including JENDL-3.3, to estimate–
the ν (En)-values for nuclides for which no or scarce measured
data were available.
However, there seems to be some problems in this method:a) The experimental data used to derive the formula werelimited to those available at 1977. Many measurements havebeen performed during the last thirty years, especially forheavier actinides. It is desirable to take these data into consideration.
–b) It was assumed that ν (Z, A, En) was adequately expressedin terms of truncated pseudo-Taylor series expansion around235
U. However, it is rather questionable whether the functional
forms and relevant parameters determined on the basis of thedata in the narrow (U–Pu) region can be safely applied
throughout the wider region of actinides up to Cf.
–c) The value 3.73 used by Howerton 2, 3 for the ν -value for
spontaneous fission (abbreviated as sf hereafter) of 252 Cf is–
0.724% lower than the recent value of ν ( 252 Cf,sf) =3.757
4adopted by Boldeman and widely used. In the present work,
the experimental data were renormalized to this standard to
remove biases due to diversity of the standard.
2.2. Bois-Fréhaut’s Method. Bois and Fréhaut5 performed–
measurements on ν for 235U, 238U, 239Pu, 240Pu, and 241Pu as afunction of the incident neutron energy over the energy range
1.5–15 MeV, and proposed another method on the basis of theirmeasurements.
First, they assumed that the average number of prompt neutrons was expressed as a linear function,––
ν = a(En–Eth) + ν s ,(3)where Eth is the fission threshold energy (tabulated in Tableaux–
I of Reference 5), ν s the average number of prompt neutrons at
the threshold energy. They analyzed the measured data to–obtain the slope a and intercept ν s for each of nuclides. Then–they determined the quantities: ν = f(N, Z, Eth , En), a = f(N, Z),–ν s = g(N, Z), as functions of N, Z, Eth, and En . After comparison with the data of sf for U, Pu, Cm, and Cf isotopes, two newterms 0.153(N–145) and 0.082(–1) N were introduced to consider© 2008 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 06/02/2008

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OhsawaJ. Nucl. Radiochem. Sci., Vol. 9, No. 1, 2008

fluctuations due to even-odd difference of N. The final formwas

It should be noted that the coefficient of (E n – E th) in eq 4 issmaller than the coefficient 0.130 + 0.006(A–235) of Howerton3
in the region heavier than 239Pu.
There are some problems to be discussed on this method.
a) The term 0.082(–1) N dependent on the even-odd nature of
N was deduced from the data in the narrow region of U to Pu,
so it remains to be verified if the term is applicable to wider
range of actinides.
b) The N-dependent term 0.153(N–145) was obtained by–using the ν (sf)-data. It is now known that the excitation energies of the fission fragments are lower in sf compared withneutron-induced fission (n,f), since the initial excitation energyof the fissioning nucleus is zero in sf, and it is equal to Bn + En
in (n,f), where Bn is the neutron binding energy of the fissioning nucleus. Thus the present author considers that the sf-datashould be treated separately and not to be included in deriving–
systematic relations in ν .
–c) The standard value ν (252Cf, sf)=3.732 of Axton6 was usedby the authors as the reference. This value is 0.67% lower than
the newer standard value of 3.757, determined by Boldeman4
and adopted in the present evaluation.

Prompt neutron multiplicity–
ν = (2.767 ± 0.010) + (0.200 ± 0.006)(Z – 94) +0.153(N – 145) + 0.082(–1) N + [(0.1496 ± 0.0006) +(0.0031 ± 0.0004)(N – 145)](En – Eth)(4)[for 94≤Z≤96],

7
6
Am243

5
Cm245
4 Pu240

U238
3

U233
U235

Np237
Th232

2
1

0

2

4

6

8

10

12

14

16

18

20

E n / MeV––
Figure 1. Comparison of least-squares fitting lines ν = aEn + ν 0 for
11 nuclides

4.0

� 0 � 0.27318Z � 22.7734

3.5

�0

3.0

Np
237

U
233

2.5

3. Analyses of Experimental Data
3.1. Experimental Data Base. Experimental data weretaken from the experimental nuclear reaction data base EXFOR
available at the web site of IAEA. Measured data relative to–
252
Cf (sf) were renormalized by using ν (252Cf, sf)=3.757, and–235
those relative to U were renormalized by using the ν (235U)values of the current version of the Japanese Evaluated Nuclear
Data Library (JENDL-3.37).
As the first step, every renormalized data were plotted, andbest-fit lines were obtained for 11 actinides (232Th – 245Cm) by––least-squared method assuming a simple formula ν =aE n +ν 0.
Some notes should be given here: (a) Small structures observed
near (n,f), (n,n’f) and (n,2nf)-thresholds were ignored, because
our aim was to obtain global systematic relations; (b) Non-uniform frequency distribution of measured data points on theincident energy axis (in many cases more experimental data
are available in the low-energy region) results in effectively
placing more emphasis on low-energy region in the leastsquared analysis. While being aware of this tendency, theauthor did not try to exclude some of the low-energy data, considering that low-energy data are more important in reactor
physics. (c) For 241Am, it was found that the data of Khokhlov
cited in the recent paper of Kuzminov8 are different from thoseregistered in EXFOR. Considering that this is due to some
additional correction made after the measurement, we used thevalues reported in Reference 8.
The best-fit lines for 11 nuclides ( 232 Th, 233U, 235 U, 238 U,
237
Np, 239Pu, 240Pu, 241Pu, 241Am, 243Am, and 245Cm) are compared in Figure 1. Two apparent tendencies can be observed:–(1) In general, the ν -values are greater for higher-Z nuclides;–
i.e. the intercept ν 0 is an increasing function of Z. This is due
to higher total energy release E R just after fission for heavier
elements (e.g. ER =177.1, 198.9, and 209.4 MeV for 232Th, 239Pu,
and 245Cm, respectively, at an incident energy 2 MeV, assuming
Wang-Hu model9 for fission fragment mass distribution, and
TUYY mass formula10) ; (2) From the lines for U and Pu isotopes, it is observed that the slope of the lines becomes steeper

Pu241

Pu239

Am241

2.0

235

Th

245
243

241
239

Cm

241
Am

240
Pu

238

232

�������

1.5

89

90

91

92

93

94

95

96

97

Proton number Z–
Figure 2. Correlation between the intercept ν 0 and the atomic number Z of target nuclides.
4.0

3.5

� 0 � 0.04674 ER � 6.40326

3.0

241
239

245
243

�0

U
233

2.5

2.0

Np
237

240
Pu

Cm

241
Am

235

Th

238

232

��������
1.5

170

180

190

200

210

220

Total Energy Release E R / MeV–
Figure 3. Correlation between the intercept ν 0 and the total energy
release of fission E R of target nuclides.

for heavier isotopes of the same element.
–
3.2. Intercept ν 0 . We searched for correlations between–
the intercept ν (En = 0 MeV) and other physical quantities, such
as Z, N, ER, fissility Z2 /A. After examination we found out two
good correlations (Figures 2 and 3):

Empirical Formulas for Estimation of Fission Prompt Neutron–ν 0 = 0.27318Z – 22.7734, (σ = 0.073),––
ν 0 vs. ER : ν 0 = 0.04674 ER – 6.40326, (σ = 0.090),

21

J. Nucl. Radiochem. Sci., Vol. 9, No. 1, 2008

(5a)

0.20

(5b)

where σ stands for the standard deviation. The two equations
agree to within 1.6%, except Th, Pa, and 233U for which they–agree to within 3%. Good correlation between ν 0 and E R , eq–
5b, is self-evident, because ν 0 is approximately proportional to
the total excitation energy of the fission fragments, which in–turn is proportional to ER. Good correlation between ν 0 and Z,
eq 5a, is to be expected, because there is an explicit linear relation between ER and Z.
The need for a term depending on even-odd character of N
and/or Z of the target nucleus was not confirmed as long as theavailable experimental data are concerned. From physicalpoint of view, the even-odd effect outstands in sf, because theexcitation energy is not strong enough to break nucleon pairs,
but this effect disappears at higher excitation energies.
3.3. Slope a. We searched for another correlation for theslope a, on the basis of empirical relations obtained in the previous subsection, and obtained two types of linear functions(Figures 4 and 5):

0.18
Am241 Am243

U238

0.16

Slope a–ν 0 vs. Z :

Th232

0.14

Np237

Present fit:a = ��0.1636+0.0013A

U233

0.12

Cm245

Pu240 Pu241

Pu239

U235

Howerton:� = �1.28+0.006A

0.10
0.08
230

232

234

236

238

240

242

244

246

248

Mass number A
Figure 4. Correlation between the slope a and the mass number A oftarget nuclides. Howerton’s relation was obtained only from U isotope data.

0.20

a vs. A: a = –0.1636 + 0.0013A [Howerton (H) type],(6a)a vs. N: a = –0.2256 + 0.00256N [Bois-Fréhaut (BF) type]. (6b)– –
ν = ν 0 + aEn

0.16
Slope aThese equations should be compared with the corresponding
terms in eqs 2 and 4. Figure 4 shows that, when a is considered as a function of A, fit to the data for all nuclides resulted
in a line that is considerably different from Howerton’s line.
This is due to the fact that Howerton’s line was obtained fromfitting to limited data for U and Pu isotopes that were available
at that time. Figure 5 shows that, regarded as a function of N,
the present evaluations of a are rather close to Bois-Fréhaut’sline. This figure also shows that fit to specific nuclides, suchas U or Pu isotopes, yields lines different from overall fitting.
Figure 6 compares the evaluations of a by Howerton, BoisFréhaut, and the present author. It is worth noting that the two
eqs 6a and 6b, obtained independently by different correlation
analyses of H- and BF-type, provide results that are quite close
to each other. This is one of the results of including the data of
Am and Cm isotopes not considered in previous works.
3.4. New Proposal. In summary, we propose here two setsof empirical relations for the formula

Np237

0.14

Am241
U238

Pu239
U235

0.12

Pu240

Am243

Pu241

Cm245

Fit to all nuclides (present):a = �0.22557+0.00256N

U233

Fit to Pu-isotopes:a = �0.54086+0.00473N

0.10
0.08

140

142

144

146

148

150

Neutron number N

Figure 5. Correlation between the slope a and the neutron number Nof target nuclides. Correlations observed among U data ( a = –0.79519 + 0.00651N ) and Pu data ( a = –0.54086 + 0.00473N ) arealso shown. The present evaluation was obtaines by least-squares fitting to all the data.

0.22–
with ν 0 as given by eqs 5a or 5b and the slope a as given by eqs
6a or 6b.

0.20

HowertonBois-Frehaut
Present (BF-type)
Present (H-type)

0.18

Slope �The empirical formulas obtained in the preceding section
are verified by comparing with experimental data and existingevaluations such as Evaluated Nuclear Data File, format B, version VI, (ENDF/B-VI,11 USA), Joint Evaluated Fission and
Fusion File, version 3 (JEFF-3.0,12 EU), Karlsruhe EvaluatedNuclear Data File, version 4 (KEDAK-4,13 Germany).
U-235: The present formulas agree well with JENDL-3.3
evaluation and experimental data within errors below 6 MeV,
but a bit lower than that at higher energies. The evaluated val–ues of ν (E n) for 235U in JENDL-3.3 are based mainly on themeasurement by Gwin14, 15 and Fréhaut.16, 17 (Figure 7)–
U-238: Three evaluations of ν (En) in JENDL-3.3, ENDF/BVI, JEFF-3.0 are all based on the data of Fréhaut.18 The present formulas agree quite well above 6 MeV but higher than
measurements below 6 MeV. (Figure 8)–
Np-237: The evaluation of ν (En) in ENDF/B-VI is a smooth

Bois-Frehaut's slope
Th232

(7)

4. Verification

Fit to U-isotopes:a = �0.79519+0.00651N

0.18

0.16
0.14
0.12
232

234

236

238

240

242

244

246

248

250

Mass number A
Figure 6. Comparison of evaluations of the slope a by Howerton,
Bois-Fréhaut, and the present author of H- and BF-type function. It
is worth noting that the present two equations 6a and 6b, obtained
independently by different correlation analyses of H- and BF-type,give results that are very close to each other.

22

OhsawaJ. Nucl. Radiochem. Sci., Vol. 9, No. 1, 2008
19, 2 0approximation to the measurements by Malinovsky,–
Veeser,21 and Fréhaut.16 The evaluation of ν (En) in JENDL-3.3
22in addition considers Boikov and Mughabghab.23 The present
formulas agree quite well with JENDL-3.3 evaluation. (Figure9)–
Pu-239: The evaluation of ν (En) in JENDL-3.3 is based on
the experimental data of Gwin24,26 and Fréhaut.25 The evalua–tion of ν (E n ) in ENDF/B-VI is based on the evaluation of
27
Fort, after minor renormalization for consistency with thestandards of the Cross Section Evaluation Working Group(CSEWG, Brookhaven National Laboratory). JEFF-3.0
adopted the evaluation of Fort,27 supplemented by calculation
by Vladuka28 above 650 keV. No considerable difference wasobserved between the three evaluations. The present formulas
give results that are essentially the same as the three evaluations. (Figure 10)
Am-241: No description is given on the evaluation methodin the comment part of ENDF/B-VI file. Seemingly the line
was adjusted to the value of 3.216 of Jaffy 29 at the thermalenergy. The data of Khokhlov seem to be modified after publication at Gatlinburg Conference (1994).30 In the present work,
the data described in a recent report INDC(CCP)-435 (2002)31–
was used. The evaluation of ν (En) in JEFF-3.0 is higher than
6

U-235

JENDL-3.3
ENDF/B-VI(＝JEFF-3.0)

5�measurements and other evaluations; the reason is not clear
because no description on the evaluation method is given in the
file. The present formula is consistent with Khokhlov, althougha discrepancy of maximum 4% is observed in the 2 – 4 MeV
region. (Figure 11)–
Am-243: The evaluation of ν (En) in JENDL-3.3 is based on
32
Maslov’s calculation. ENDF/B-VI adopted the Madland-Nix
model calculation.33 These two evaluations are more or lesssimilar. However, JEFF-3.0 evaluation, based on Howerton’s
method, is steeper than the two. The present formulas givelines with intermediate slopes. (Figure 12)
Cm-243: Both JENDL-3.3 and ENDF/B-VI adopted
Maslov’s calculation. 32 JEFF-3.0 is based on Howerton’s
method renormalized to the measured data of Jaffy 29 andZhuravlev34 at the thermal energy and gives a steeper line.
Generally speaking, Maslov’s calculations tend to be less steep
than Howerton’s formula, as can be confirmed for othernuclides. The present formulas provide lines with intermediateslopes. (Figure 13)–
Cm-244: The evaluation of ν (E n ) in JENDL-3.3 was
obtained by Howerton’s method. ENDF/B-VI also adopted
Howerton’s method but the value was renormalized to the thermal value computed from semi-empirical work of Gordeeva
and Smirenkin 35 as revised by Manero and Konshin.36 The
evaluation of JEFF-3.0 was taken from KEDAK-413 but thedetails of the method are not known. The present formula6

Np-237v = 2.359+0.1419En [H]� � 2.668+0.1432En [H] (≒JENDL-3.3)

5

4

�

v = 2.358+0.1405En[B]3

ENDF/B-VI=JEFF-3.0
4

� � 2.632 � 0.1405 En [ B]

2

3

0

2

4

6

8
10
E n / MeV

12

14

16

Figure 7. Prompt neutron multiplicity vs. incident neutron energy for235
U. The present evaluations are compared with existing evaluations(JENDL-3.3, ENDF/B-VI, JEFF-3.0) and experimental data. The
equality sign, such as in “ENDF/B-VI = JEFF-3.0”, means that thetwo evaluations are exactly identical. The symbol [B] stands for an
evaluation using Bois-Fréhaut-type equations 5a and 6a, while [H]stands for an evaluation using Howerton-type equations 5b and 6b.

0

2

4

6
8
En / MeV

10

12

14

16

Figure 9. Prompt neutron multiplicity vs. incident neutron energy for
237
Np. See the caption of Figure 7 for further explanation. The sign “” means that the two evaluations are not identical but very close.

6

6
ENDF/B-VI

U-238

Pu-239� � 2.359+0.1482 En [B]

5

0

2

4

6

8 10 12E n / MeV

14

16

18

� 4

ENDF/B-VI

� � 2.894+0.1456 E n [B]JEFF-3.0

� � 2.358+0.1458 En [H]3� � 2.906+0.1471En [H]5
JENDL-3.3(=JEFF-3.0）

� 4

2

2

3

20

Figure 8. Prompt neutron multiplicity vs. incident neutron energy for238
U. See the caption of Figure 7 for further explanation.

2

JENDL-3.3

0

2

4

6

8
10
E n / MeV

12

14

16

Figure 10. Prompt neutron multiplicity vs. incident neutron energy
for 239Pu. See the caption of Figure 7 for further explanation.

Empirical Formulas for Estimation of Fission Prompt Neutron

J. Nucl. Radiochem. Sci., Vol. 9, No. 1, 2008

6

23

7

� � 3.228+0.1497En [H]Am-241

Cm-243� � 3.179+0.1482En [B]5

JEFF-3.0

6(Howerton's E-dependence)

JEFF-3.0

��

4

ENDF/B-VI� � 3.452+0.1523 En [H]5

JENDL-3.3

� � 3.416+0.1508En [B]34
JENDL-3.3(=ENDF/B-VI =Maslov's calc.)Exp. data: Khokhlov (as cited in INDC(CCP)-435(2002) [ref.30] )

2

0

2

4

6

8

10

12

14

Jaffey(1970) [ref.29]

3

16

En / MeV

4

6

8

10

12

14

16

Figure 13. Prompt neutron multiplicity vs. incident neutron energy
for 243Cm. See the caption of Figure 7 for further explanation.

6

7

JEFF-3.0(Howerton's method)� � 3.179+0.1533 En [B]Cm-244� � 3.162+0.1523En [H]52

En / MeV

Figure 11. Prompt neutron multiplicity vs. incident neutron energy
for 241Am. See the caption of Figure 7 for further explanation.

Am-2430

ENDF/B-VI

6
JENDL-3.3

JENDL-3.3

� 4

�

(Maslov's calc.)5

� � 3.461+0.1536 En [H]JEFF-3.0

ENDF/B-VI(Madland-Nix model calc.)

34
� � 3.452+0.1533En [B]

Khokhlov(1994) [ref.27]

2

0

2

4

6

8

10

12

14

16

3

0

2

4

6

En / MeV
Figure 12. Prompt neutron multiplicity vs. incident neutron energy
for 243Am. See the caption of Figure 7 for further explanation.

gives lines located between ENDF/B-VI and JEFF-3.0, withrather smaller slopes. (Figure 14)
Cm-245: Both JENDL-3.3 and ENDF/B-VI adopted
Maslov’s calculation. JEFF-3.0 is based on the measurementsof Khokhlov.37 The present formulas are closer to Khokhlov’s
experiments than to Maslov’s calculation,38 the energy- dependence of which is rather weak. (Figure 15)
Cm-246: JENDL-3.3, ENDF/B-VI, and JEFF-3.0 all adopt
Maslov’s calculation. The slope of the present formulas is
steeper than that of Maslov’s calculation. (Figure 16)
Cm-247: JENDL-3.3 and JEFF-3.0 adopted Zhuravlev’s
measured value34 at the thermal energy with the energy dependence calculated with Hower ton’s method. However,
Zhuravlev’s thermal data is exceptionally high among curium
isotopes. ENDF/B-VI adopted a thermal value computed fromsemi-empirical work of Gordeeva and Smirenkin35 as revisedby Manero and Konshin,36 together with the energy dependenceof Howerton. The present evaluation gives values lower thanany of the existing evaluations. (Figure 17)
Cm-248: JENDL-3.3 adopted the Howerton’s method which
was also adopted by JEFF-3.0. ENDF/B-VI evaluation was
obtained by the same method as for Cm-247. The present evaluations are less steep. (Figure 18)
5. Conclusions– –1) Assuming a linear function of the form ν = ν 0 +aE n, the810
En / MeV

12

14

16

Figure 14. Prompt neutron multiplicity vs. incident neutron energy
for 244Cm. See the caption of Figure 7 for further explanation.

7
Howe(1983) [ref.34]
Khokhlov(1994) [ref.34]

Cm-245
6

JEFF-3.0

� � 3.452+0.1559En [B]� 5

JENDL-3.3=ENDF/B-VI=Maslov's calc.

4� � 3.385+0.1549E n [H]

3

0

2

4

6

8
10
En / MeV

12

14

16

Figure 15. Prompt neutron multiplicity vs. incident neutron energy
for 245Cm. See the caption of Figure 7 for further explanation.

–author determined the parameters ν 0 and a by least-squared
fitting to experimental data for 11 actinides. Two empirical–equations 5a and 5b for ν 0 and 6a and 6b for a, respectively,
with nearly equal standard deviations were obtained. The present formulas give the slope parameter a that is considerably

24

OhsawaJ. Nucl. Radiochem. Sci., Vol. 9, No. 1, 2008

smaller than Howerton’s formula and rather close to (actually a
bit smaller than) Bois-Fréhaut’s formula for actinides with
A>237.
2) The obtained equations were verified by comparing the–predicted ν -values with experimental as well as evaluated data

7
JENDL-3.3=ENDF/B-VI=JEFF-3.0=Maslov's calc.

Cm-2466�

54
� � 3.430+0.1562 En [H]

0

2

4

6

8

10

12

14

16

En / MeV
Figure 16. Prompt neutron multiplicity vs. incident neutron energy
for 246Cm. See the caption of Figure 7 for further explanation.

7

Cm-2476

� � 3.452+0.1610 En [B]JENDL-3.3=JEFF-3 (Howerton'senergy-dependence)

� 5
� � 3.419+0.1575 E n [H]

ENDF/B-VI

4

Exp.data: Zhuravlev(1973) [ref. 34]

3

0

2

4

6

8

En / MeV

10

12

14

16

Figure 17. Prompt neutron multiplicity vs. incident neutron energy
for 247Cm. See the caption of Figure 7 for further explanation.

7

Cm-248� � 3.452+0.1636En [B]6

ENDF/B-VI� 5

JENDL-3.3=JEFF-3.0
� � 3.431+0.1588En [H]4Exp. data: Zhuravlev(1973) [ref. 34]

3

0

2

4

6
8
En / MeV

10

12

Acknowledgment. The present work was performed undercontract between Kinki University and Japan Atomic Energy
Agency (JAEA). The author is indebted to Nuclear Data
Center, JAEA, for the support to this study.
References� � 3.452+0.1584 En [B]3

for 11 nuclides. It was found that the proposed formulas provide overall good representation without any ad hoc adjust–ment. These formulas can be used to predict ν -values for
nuclides for which no or scarce data is available.

14

16

Figure 18. Prompt neutron multiplicity vs. incident neutron energy
for 248Cm. See the caption of Figure 7 for further explanation.

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