Nuclear Data Section
International Atomic Energy Agency
P.O.Box 100, A-1400 Vienna, Austria

Memo CP-D/451

Date:
To:
From:

12 January 2006
Distribution
O. Schwerer

Subject:

Quantity codes for data in arbitrary units, chain and mass yields(Reply to CP-E/085)

Items 1) and 2) of CP-E/085
In my opinion, often the quantity code for relative data given in arbitrary units cannot be
uniquely determined. E.g., as outlined in CP-E/085, relative data for the production of certain
fission products can be coded both as relative fission yields or as relative fission cross sections.
This is not (or not only) a question of the EXFOR format but it is an objective fact that suchdata can be viewed from different sides. We have no general rule for such cases and I doubtthat it is possible to make one without creating other inconsistencies. I think the understanding
is to code it in a way appearing most reasonable to the compiler, taking into account, among
other things, what name the authors of the article use, and, under which quantity the users are
more likely to look for the data. I believe, that if many different fission products are measured,
this will most often be called fission product yields rather than cross sections.
Concerning PAR vs. DE: Again, this is normally answered by the units. If its "per MeV", thanit's DE, otherwise it's PAR. However, for PAR, it's sufficient to have a secondary energy value(sometimes fixed) given as additional independent variable, it does not have to be integrated
over a range.
In the case of 14044.002, the actual units given for Fig.2 are "number per unit energy" which
points to a single (but not double) differential cross section; since another secondary energy isgiven as an additional parameter, this is accounted for by PAR.
This was our argument; but again, once the data are coded with ARB-UNITS, it is hard toprove that this is the only correct solution.
Subentry 14044.003 and definition of mass yields
The main point here was that the data originally coded with SF6=DE are a mass spectrum andtherefore cannot be coded with DE. Another option would be to code them simply with….(N,F)MASS,PAR,FY,LF/HF,MXW/RELbut this leads to the conceptual problem that we do not have a fission yield type just PAR,FY.
FY always requires a very specific code (more specific than PAR) in SF5, such as : PRE, TER,CHN, IND, CUM, MAS. One reason for this (and for the need of the SF5 code MAS ingeneral) is that MASS in SF4 is not part of the dictionary code (dictionary 36/236 covers only
SF5-8 but not SF4). Therefore I have no way of explaining the quantity as mass spectrum in thedictionary (unless we add to it "This quantity always comes with MASS in SF4", which is notin line with the current way the dictionaries work).
Any ideas on better solutions for this problem (without radical changes in the dictionary
structure and usage) are very welcome.
The definition of MAS,FY has been proposed earlier for LEXFOR; this and the other types offission yields can be looked up in the revised LEXFOR page on fission yields which isappended to this memo, and will be included in the upcoming LEXFOR revision. See items 5
and 6 for the definitions of CHN,FY and MAS,FY.

Distribution:
oblozinsky@bnl.gov
vml@bnl.gov
drochman@bnl.gov
nordborg@nea.fr
manokhin@ippe.obninsk.ru
samaev@obninsk.ru
Mmarina@ippe.obninsk.ru
blokhin@ippe.obninsk.ru
feliks@polyn.kiae.su
chukreev@polyn.kiae.su
S.Dunaeva@iaea.org
taova@expd.vniief.ru
varlamov@depni.sinp.msu.ru
chiba@earth.sgu.ac.jp
kato@nucl.sci.hokudai.ac.jp
ohnishi@nucl.sci.hokudai.ac.jp
ohbayasi@meme.hokudai.ac.jp
yxzhuang@iris.ciae.ac.cn

gezg@iris.ciae.ac.cn
hongwei@iris.ciae.ac.cn
tarkanyi@atomki.hu
stakacs@atomki.hu
katakura.junichi@jaea.go.jp
vlasov@kinr.kiev.ua
kaltchenko@kinr.kiev.ua
ogritzay@kinr.kiev.ua
nklimova@kinr.kiev.ua
yolee@kaeri.re.kr
jhchang@kaeri.re.kr
ohtsuka@nucl.sci.hokudai.ac.jp
A.Mengoni@iaea.org
m.wirtz@iaea.org
schwerer@iaeand.iaea.org
v.zerkin@iaea.org
henriksson@nea.fr
exfor@nea.fr

Appendix (from next LEXFOR revision)
Fission Yields(See also Fission).
TheoryThe fragments formed at the scission stage by a nucleus undergoing fission are called primary,initial, or pre-neutron emission fragments.
The primary fragments repel each other, obtain their full kinetic energy (e.g., 90 MeV), emit
prompt neutrons (<4x10-14 sec) and gamma rays (<10-11 sec), are slowed down in thesurrounding medium, and stopped. These fragments are called secondary fragments, postneutron-emission fragments, or primary fission products (the emitted γ-rays may cause
conversion β's and X-rays).
The secondary fragments undergo (after .01 sec and more) a series of β-decays forming
secondary products, and end up in stable nuclei. For certain products the emission of delayed
neutrons competes with γ de-excitation, both following the β-decay process. In most of thesestages mass yields and charge dispersions are measured as well as energy distributions.
The terms fragments and products are not clearly distinguished. Most frequently the borderline between fragments and products varies, and often the word fragments is used as anoverall term, including all stages of decay.
Fission fragments are often specified only by their mass, including all Z-numbers, so that thefragment yield remains constant during β decay. Fission products are usually specified by Z
and A. A specified fission product is obtained in two ways: either immediately from fission(primary yield) or from the decay of another fission product. Thus, the total amount of a
specified fission product varies with time. Very short-lived fission products may,nevertheless, be most important, because some have extremely high capture cross sections(106 b). Finally, all decay to stable end products, partially via metastable states. For odd Anumbers, only one stable end product exists that is significantly formed in fission; for even Anumbers, one or two exist.
The sum of the yield for all fission products will, in general,
add up to 200%, i.e., 100% for each of the heavy and light
product distributions (see example in figure 1 ). Since internary fission more than two fragments are formed perfission, the yields for all fragments sum up to a bit morethan 200%.
For further information, see Pappas [1] and Walker [2].

1

Taken from R.L. Walsh et al., Physics and Chemistry of Fission, Proceedings of a Symposium, Juelich, 1979
(I.A.E.A., 1980) p.129.

Fission Yields (continued)
Coding:1. Absolute Yields. (Fissions and fission fragments are counted independently.)
REACTION coding: The quantity code FY in SF6. The yield type is specified in SF5(Branch) (see under specific type of yield, following pages).
Units: a code from Dictionary 25 with the dimension FY (e.g., PC/FIS).
2. Relative yields.
REACTION Coding: same as above with modifier REL in SF8
Units: ARB-UNITS
However, emission of light particle in ternary fission does not change the sum of yields in thebinary fission mass range usually measured, and other mass splits in ternary fission arenegligible, therefore, relative yield measurements may be normalized to 200% if themeasurement was made for a sufficient large number of fragments. If this is done, the datatable may include some values that have not been measured but obtained by interpolation;such values must be labeled by flags.
The fission product considered is coded either in REACTION SF4 or as a variable in the datatable.
Examples for product nuclei coded within the reaction code:(92-U-235(N,F)54-XE-124,IND,FY) independent yield of the fission product124Xe(92-U-235(N,F)54-XE-133-G,CUM,SIG) cumulative production crosssection for the fission product 133gXefor coding product nuclei as variablesin the DATA tables:(92-U-235(N,F)ELEM/MASS,IND,FY) independent yield of specified productnuclei which are given in the DATA
table under the data headings
ELEMENT, MASS, and ISOMER (ifapplicable).
(92-U-235(N,F)MASS,CHN,FY) chain yield of several mass numbers given inthe DATA table under the data heading
MASS.
See Reaction Product and EXFOR Manual Chapter 6: Variable Nucleus for details.
Yield data to be compiled in EXFOR
1. Primary fission-fragment yield. The primary yield per fission of fission-fragment mass
A before prompt neutron emission. It may also be called pre-neutron-emission fragmentmass distribution. In all experimental techniques corrections for some prompt neutrons
already emitted cannot be avoided.

Fission Yields (continued)
REACTION coding: Branch code PRE in SF5.
Example:(....(N,F)ELEM/MASS,PRE,FY)

2. Secondary fission-fragment yield. The secondary yield per fission of fission-fragment
mass A after prompt-neutron emission, but before β decay and delayed-neutron emission. It
may also be called post-neutron-emission fragment-mass distribution.
REACTION coding: Branch code SEC in SF5.
Example: (....(N,F)MASS,SEC,FY)
3. Independent fission-product yield. The direct or independent yield per fission of a
primary fission product specified by Z and A; i.e., after prompt neutron emission, but before βdecay and delayed-neutron emission, including only the direct yield and not the yield obtained
from decay of other fission products.
REACTION coding: Branch code IND in SF5.
Example: (…(N,F)ELEM/MASS,IND,FY)
Sum rule: The secondary yield is equal to the sum, over all Z (for one A) of the independentyields.
Experimental data for independent yields of the product Z,A include yields from the delayedneutron emission of the product Z,A + 1 or from the beta decay of the product Z-1,A, if
separation times are not short against the relevant decay times. Corrections are required andshould be mentioned under the keyword CORRECTION. Fragment-mass yields are notaffected by beta decay but only by delayed-neutron emission.
4. Cumulative fission-product yield: the cumulative yield per fission of a secondary fission
product specified by Z and A, i.e., after prompt-neutron emission, and including theindependent yield plus the yield from decay of other fission products.
REACTION coding: Branch code CUM in SF5.
Example: (…(N,F)ELEM/MASS,CUM,FY)
Sum rule:

CUM,FY for the β-decaying product Z-1,A + IND,FY for product Z,A =CUM,FY for product Z,A, if the products Z-1,A and Z,A+1 are not delayedneutron emitters.

The following events may add to the cumulative yield of the fission-product Z,A in its groundstate:• independent yield from fission• β decay from product Z-1,A in ground state• β decay from product Z-1,A in a metastable state• delayed-neutron emission from product Z,A + 1• internal transition from a metastable state of product Z,AFission Yields (continued)
In addition, the product Z,A may be formed from neutron capture in the product Z,A-1; thisproduct is not included in the "cumulative yield".
The cumulative yield is often given for an isomeric state of a fission-product Z,A; the isomeris entered in EXFOR as a separate data field, see EXFOR Manual Chapter 6: Variable
Nucleus.
5. Total chain yield. The total chain yield per fission of fission-fragment mass A is the sumof the cumulative yields of all stable fission products having the same mass A. When only
one stable fission product per mass A exists, the total chain yield for mass A is identical withthe cumulative yield of the stable end product Z,A.
REACTION coding: Branch code CHN in SF5.
Example: (…(N,F)MASS,CHN,FY)
6. Total mass yield The total mass yield per fission of fragment mass A is the sum of theindependent yields of all fission products with the mass A.
REACTION coding: Branch code MAS in SF5.
Example: (…(N,F)MASS,MAS,FY)
7. Fractional yields The distribution of charge Z within a given fragment mass chain A iscalled charge dispersion. It can empirically be approximated by a Gaussian distribution witha most probable charge Zp (see following).
The fractional independent yield of a fission product (after prompt neutron emission) is givenby:[P ( Z ) = ( cπ ) −1 / 2 exp − ( Z − Z p ) 2 / c]whereas the fractional cumulative yield is given by

1ZZ +1 / 2∑ P = σ 2π ∫ en =0n⎡ − ( n − Z p )2 ⎤⎢⎥2⎢⎣ 2σ⎥⎦dn−∞The parameters c and σ are widths of the distributions related by:c ≈ 2(σ 2 + 1 / 12 )For charge dispersion, fractional yields are defined only as ratios to total chain yield.
For further information, see Wahl [3].
REACTION coding: coded as an explicit ratio, and followed by the keyword RESULT.
In all cases, the data are entered as ratios with values from 0 to 1 and data units NO-DIM.

Fission Yields (continued)
Examples:a.)

REACTIONb.)

RESULT
REACTIONRESULT((92-U-235(N,F)ELEM/MASS,IND,FY)/(92-U-235(N,F)MASS,CHN,FY))(FRIND)((92-U-235(N,F)ELEM/MASS,CUM,FY)/(92-U-235(N,F)MASS,CHN,FY))(FRCUM)

8. Most probable charge. The most probable initial charge Zp for a given mass chain.
REACTION Coding: the process code ZP in SF6
Example: (…(N,F)MASS,,ZP)
Note: The Gaussian width parameter is assumed to be approximately constant for all A
chains, as given by Wahl, et al. Therefore Zp has sometimes been determined from a single
fractional yield measurement. However, there is evidence for a variation of c and σ with massA, and they may be determined together with Zp. Therefore, the Gaussian width parameterused should be explained (value or reference).
9. Most Probable Mass. The most probable mass Ap is the mean mass for a given element.
REACTION Coding: AP in SF6
Example: (…(N,F)ELEM,,AP)
10. Charge yields. The charge yield (or elemental yield) is defined as the sum of theindependent yields for all products with a specified Z.
Definition: Charge distribution (primary charge function) is defined as the distribution ofprimary charge about Zp as a function of primary mass.
This quantity is deduced, either from other quantities (charge dispersion, mass distribution),or from instrumental measurements of fragment mass (kinetic energy) and X-rays; bothmethods involving uncertain corrections for prompt-neutron emission.
REACTION Coding: Branch code CHG in SF5.
Example:(……(N,F)ELEM,CHG,FY)

10. R-values. An R-value is a ratio of measurement results for 2 different energies or energyspectra (one of which is considered to be a monitor reaction), each of which is relative to thesame standard reaction.
REACTION Coding: coded as an explicit ratio, followed by an entry under RESULT withthe code RVAL.
Example:REACTIONRESULT(((92-U-238(N,F)ELEM/MASS,CUM,FY,,FIS)/(92-U-238(N,F)42-MO-99,CUM,FY,,FIS))//((92-U-238(N,F)ELEM/MASS,CUM,FY,,MXW))(92-U-238(N,F)42-MO-99,CUM,FY,,MXW)))(RVAL)

Fission Yields (continued)
Yields of correlated fragment pairs
The Z and A of the correlated pair are entered under the field headings ELEM1, MASS1, and
ELEM2, MASS2.
1. Yields of correlated fragment pairs.
REACTION coding:: Process code FY/CRL in SF6.
Example:BIB
REACTION…
ENDBIB
COMMONELEM1NO-DIM
56.
ENDCOMMON
DATA
MASS1
NO-DIM
138.
138.
…
ENDDATA(…(N,F)ELEM/MASS,IND,FY/CRL)ELEM2NO-DIM
42.

MASS2
NO-DIM
104.
105.
…

DATA
PC/FIS…
…
…

2. Kinetic energy of correlated fragment pair.
The total kinetic energy of the fragment pair is given.
REACTION coding: Process code KE/CRL in SF6.

References[1.] A. C. Pappas, J. Alstad, and E. Hagebo, Mass, Energy, and Charge Distribution inFission, Physics and Chemistry of Fission, Symposium, Vienna, 1969 (I.A.E.A., 1969),p. 669[2.] W. H. Walker, Status of fission product yield data for thermal reactors, Fission-product
Nuclear Data, IAEA Panel, Bologna, 1973, report IAEA-169, Vol. I, (1974) p. 285[3.] A.C. Wahl, et al., Nuclear Charge Distribution in Low-Energy Fission, Phys. Rev. 126,1112 (1962)