Nuclear Data Section
International Atomic Energy Agency
P.O.Box 100, A-1400 Vienna, Austria
Memo CP-D/622
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11 March 2010
Distribution
N. Otsuka, V. McLane, O. Schwerer, S. Dunaeva
Reaction Coding (SF1-SF2)
Memo CP-D/607

Below is update of the EXFOR Formats Manual and LEXFOR entries “Center-ofMass System” and “Incident-Projectile Energy” We plan to follow up shortly with amemo on Reaction Coding (SF3-SF4).

1) Proposed revision of the EXFOR Formats Manual 6:
Reaction field…
Notes on SF1 and SF2Target is given in SF1 and the incident projectile is given in SF2. If the incident
energy is given in center-of-mass energy (EN-CM) or laboratory incident energy pernucleon (MEV/A, etc.), and reversing the order of the target and the projectile does notchange the numerical data, the REACTION is coded using the tautology formalism. See
LEXFOR Incident Particles for use of the tautology formalism for inverse
kinematics. When such a tautology is given, an explanation about the sample andincident particle beam must be given under SAMPLE and INC-SOURCE.
Example:REACTION((1-H-2(9-F-19,P)9-F-20,,SIG)=(9-F-19(1-H-2,P)9-F-20,,SIG))(Cross section for 2H(19F,p)20F given with incident energy in center-of-mass)

2) Proposed revision of LEXFOR “Center-of-Mass System”:

Center-of-Mass System…
Note: Only one representation (i.e., either laboratory or center-of-mass) for eachparameter may be coded as a variable in the data table. The other representation
may be added under the data heading MISC if considered desirable by the compiler.
In case of doubt, the laboratory system is preferred.

Centre-of-Mass Energy and Incident Energy per Nucleon
Note that the centre-of-mass energy (EN-CM) is defined as
E cm = E proj,lab M targ / (M proj + M targ ) = E proj,cm + E targ,cm = Mc 2 − (M proj + M targ ) c 2(M: invariant mass in relativistic kinematics). It is clear from the 3nd and 4th term thatthe centre-of-mass is invariant under exchange of the incident projectile and the target.
Because the numerator of the 2nd term can be rewritten as (E proj,lab / M proj ) M proj M targ ,the incident energy in laboratory system per projectile mass (number) (MeV/A, etc.)
is also invariant under this exchange. This invariance is not valid when the Debyeeffect (shielding of the nuclear Coulomb field by bound atomic electrons) enhances
the cross section.
This is observed in several reactions such34
6
3
as He(d,p) He, Li(p,α) He, 6Li(d,α)4He and 6Li(p,α)4He at low energy.

3) Proposed revision of LEXFOR “Incident-Projectile Energy (to be renamed)”:Incident Particles
In general, the incident projectile is coded in REACTION SF2 and the target is givenin SF1. (Particles resulting from the REACTION to be defined are given in SF3 andSF4, see Outgoing Particles 1).
Incident-Projectile Energy(See also Spectrum Average.)
The energy of the incident projectile is entered in the COMMON or DATA section
under the appropriate data heading (i.e., a data heading from Dictionary 24 having an
A in column 66).
…
Information on the characteristics of the resolution and the spectrum of theincident-projectile beam is entered in free text under the keyword INC-SPECT. (SeeEXFOR Exchange Formats Manual Chapter 7: INC-SPECT).
Inverse kinematics
If the incident energy is given in center-of-mass energy (EN-CM) or laboratory incident
energy per nucleon (MEV/A etc.), A targ ≤ 4 and A proj ≥ 5 in the experiment, andreversing the order of the target and the projectile does not change the numerical data,
REACTION must be coded using the tautology formalism. This helps users when
inverse kinematics technique is applied. The target and projectile used in theexperiment should be in the left hand side of REACTION.
Examples:
REACTION((1-H-2(9-F-19,P)9-F-20,,SIG)=(9-F-19(1-H-2,P)9-F-20,,SIG))(Cross section for 2H(19F,p)20F given with center-of-mass energy)

11

LEXFOR entry to follow in memo on REACTION SF3-SF4.

REACTION((1-H-1(9-F-19,EL)1-H-1,,DA,P)=(9-F-19(P,EL)9-F-19,,DA,RSD))(Proton angular distribution for 1H(19F,p)19F given with center-of-mass energy andcentre-of-mass angle.)
See also, Center-of-Mass System.
Nuclear Quantities…
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