Memo issued on behalf of
National Nuclear Data Center
Brookhaven National Laboratory
USA
Memo CP-C/389
Date:
To:
From:

14 April 2010
Distribution
O. Schwerer

Subject:

Final and intermediate reaction products

In EXFOR REACTION coding, as a rule, the final products of a nuclear reaction will be coded in
REACTION SF4 and/or SF3. Intermediate states, such as excited states unstable against prompt
particle emission, will not normally appear as reaction products. Such levels may be defined using
EN-SEC and E-LVL or E-EXC, in particular, when competing channels have to be distinguished.
This rule is, in general, sufficiently clear for neutron reactions and has been largely observed.
However, for charged-particle and heavy-ion-induced reactions, more complicated reactions occur
and clarification is required, in particular in view of recent discussions.
1. Neutron reactions
An important case concerns "inelastic" excitation of states unstable against particle emission,
followed by prompt decay into the final products.
A classical case is the reaction which in the literature is usually written as
C(n,n')3α12This reaction must be coded as 6-C-12(N,N+2A)2-HE-4(see LEXFOR, "Light-Nuclei Neutron Reactions", page L.3).
Note that this is the only correct coding for this reaction. SF3=INL is not a valid option for thischannel.
This LEXFOR page lists several other reactions which are likely to occur in the literature as"inelastic" or (n,n') reactions followed by prompt particle decay. None of them should be compiled
with INL in SF3 but all with the final products in SF3 and SF4. Examples are11
B(n,nα)7Li, 10B(n,n3He)7Li, 9Be(n,nd)7Li, etc.
The LEXFOR page "Light-Nuclei Reactions" (page L.1) also says that competing
reactions leading to the same end products may exist (implying that still those end products will begiven in the REACTION while the different channels will be defined using EN-SEC and E-LVL).
2. Charged-particle and heavy-ion induced reactions
With charged particles and heavy ions as projectiles, the situation of excitation of states unstableagainst prompt particle emission extends also to the projectile. In particular in view of experiments

in inverse kinematics or, generally, with the projectile sometimes heavier than the target, there is
no reason why excited and decaying projectiles should be treated differently from excited targets.
We therefore propose to clarify the situation by making this rule (to always code the final reaction
products in SF4, or SF3 and SF4), which exists implicitly in LEXFOR for neutron reactions,explicitly a general one.
Suggested addition to LEXFOR, "Reaction Product":Intermediate and final reaction products
In general, the final reaction products are to be coded in REACTION SF4 (or, if several products
are produced, in SF4 and SF3). Intermediate states unstable against prompt particle decay will notnormally appear as products but may be specified using the keyword EN-SEC and data headings
E-LVL or E-EXC.
Typical cases where such intermediate states are produced are inelastic reactions leading topromptly decaying excited states. See LEXFOR "Light-Nuclei Neutron Reactions" for examples
of excited target nuclei and how these reactions must be coded. Note that the same rule applies
also to excited heavy projectiles unstable against prompt particle emission.
3. Recent example: 9Be(10C,2p+2α)9Be and 12C(10C,2p+2α) 12C
On these reactions, a group including authors R.J. Charity, K. Mercurio et al. recently published 3papers:(1) PR/C,80,024306,2009(2) PR/C,78,031602,2008(3) PR/C,75,51304,2007

EXFOR C1732 (on PRELIM/TRANS C095)
EXFOR C1660
EXFOR C1580(1) The preliminary version of entry C1732 (PRELIM C095) was compiled with SF1-SF4 as
explained above. In the final version, additional information about intermediate states was addedusing EN-SEC and E-LVL1,2. In addition, in some cases free text explanations about the reaction
channels is added as "footnotes" using FLAG. This is not strictly necessary because the data are
distinguishable by the information given in COMMON and DATA sections, but is considered
useful for the users.
(2) Entry C1660 (on master): REACTION coding(6-C-12(6-C-10,2P+2A)6-C-12....)
is in agreement with the present proposal.
(3) Entry C1580 (on master): REACTION coding(4-BE-9(6-C-10,INL)4-BE-9....)
is inconsistent with both, the coding of entry C1732 (describing a repetition of the sameexperiment) and the present proposal. This entry will be retransmitted replacing REACTION
SF3=INL with the final products.

4. Concerns about retrievability
The main motivation for the standardization of REACTION coding for light-particle reactions(where a priori often several possibilities exist), as described in LEXFOR "Light-Nuclei
Reactions", was the unambiguous retrievability. Nevertheless, a novice user may need more than
one trial to find the 12C(n,n')3α data under the (n,n+2a) reaction. Anyway our rule makes sure thatthese data are compiled under only one REACTION code.
On the other hand, this problem is actually less severe in cases of "decaying projectiles" as
described above under 3. Even if we think of such data as "inelastic", REACTION SF1, SF2, andSF4 remain the same, and therefore the data can conveniently be retrieved with these 3 parameters,
ignoring the contents of SF3 (which may be thought of being "INL" but is actually something like
2P+2A).

5. General considerations
When clarifying our rules for more precise REACTION coding, I believe the following
considerations are important:•Detailed coding for certain types or branches of REACTIONs is defined not only through
REACTION SF1-SF4 but also using SF5-SF8 (e.g. with branch codes SEQ or PAR) andsometimes specified further using EN-SEC and the related numerical values for secondaryenergies.

•SF3=INL is used (only) for inelastic scattering as the process which was measured but notin combination with other outgoing particles. The only combination of INL with anothercode within SF3 occurring in the master file is (...,INL+F) e.g. for (n,n'f). I believe that thisrestriction is correct and need not be changed. (One could even discuss changing(N,INL+F) to (N,N+F).)•When proposing changes in REACTION coding rules, the following practicalconsiderations should be taken into account:•Reasonable simplicity for compilers (i.e., they can determine the correct REACTION coding
easily enough from the publication, normally without much checking back with the authors)•

Reasonable simplicity for the users (i.e., for data which are usually retrieved together andhave SF1-SF4 in common, it may be a good option to be compiled under the same
REACTION and be distinguished only by "secondary" elements such as different values of
E-LVL or different nuclides under EN-SEC). In other words, we should check how useful it
is to split certain reactions into (too) many branches•

How will the new rule affect existing entries - how many will have to be retransmitted forconsistency, and how easy will it be to do this accurately

Distribution:
blokhin@ippe.ru
chiba@earth.sgu.ac.jp
claes.nordborg@oecd.org
emmeric.dupont@oecd.org
ganesan@barc.gov.in
gezg@ciae.ac.cn
hongwei@ciae.ac.cn
jhchang@kaeri.re.kr
j.roberts@iaea.org
kaltchenko@kinr.kiev.ua
katakura.junichi@jaea.go.jp
kato@nucl.sci.hokudai.ac.jp
kirarlyb@atomki.hu
l.vrapcenjak@iaea.org
manuel.bossant@oecd.org
manokhin@ippe.ru
mmarina@ippe.ru
mwherman@bnl.gov
nicolas.soppera@oecd.org
nklimova@kinr.kiev.ua

n.otsuka@iaea.org
nrdc@jcprg.org
oblozinsky@bnl.gov
ogritzay@kinr.kiev.ua
otto.schwerer@aon.at
pronyaev@ippe.ru
r.forrest@iaea.org
samaev@obninsk.ru
s.babykina@polyn.kiae.su
scyang@kaeri.re.krs.dunaeva@iaea.org
stakacs@atomki.hu
stanislav.hlavac@savba.sk
taova@expd.vniief.ru
tarkanyi@atomki.hu
varlamov@depni.sinp.msu.ru
vlasov@kinr.kiev.ua
vmclane@optonline.net
v.zerkin@iaea.org
yolee@kaeri.re.kr