Memo 4C-3/374 (Rev.4)-----------------------------

4 May 1995

To:Distribution

From:

M. Lammer

Subject:

CINDA manual revision: coding of (2n,f), (n,n'f) and (n,2nf) reactions

CINDA Action no. 59 from the 1992 NRDC meeting was to draft coding hints for reactions(2n,f) and (n,n'f) as proposed manual revision for pages II.2.8 (hints for coding such cases)
and II.2.17 (note under the heading "fission quantities"). Action 44 from the 1994 NRDC
meeting was to reviewthe original memo; the revised wording is given below:

Addition to Page II.2.8:(2n,f) reaction
In this process, 2 neutrons are captured almost simultaneously before the compund nucleus(Z,A+2) undergoes fission.
Cross sections for this process as well as "eta" and "alpha" should be entered for the target
nucleus and the quantity NF with an appropriate comment, e.g.: "(2N,F)" or "(2N,F) REAC".
Other fission quantities (NU,NFY,FRS,etc.) are determined by the compound nucleus whichis the same as after (n,f) reaction for the target nucleus (Z,A+1). Therefore entries should bemade for the "target nucleus" (Z,A+1) with the corresponding quantity. The comment should
contain the real target nucleus and "(2N,F)" or "(2N,F) REAC" or "YLD FROM U235(2N,F)"
etc.

(n,n'f) and (n,2nf) reactions: instant fission
In the (n,n'f) resp. (n,2nf) reaction, 1 resp. 2 neutrons are emitted, leading to an excited levelwith negligible lifetime which undergoes instant fission (second resp. third chance fission).
These processes can experimentally not be separated from the (n,f) reaction and areconsidered as part of it. Therefore entries for all quantities should be made as for (n,f)
reactions.

(n,n'f) reaction: delayed fission
In this case, the (n,n') reaction leads to the formation of a spontaneously fissioning (shape)isomer of non-negligible lifetime with the same (Z,A) as the target nucleus. Therefore thetarget nucleus is always entered.
Cross sections for the whole process: entries should be made for the quantities NF and DIN(since it is a partial inelastic scattering cross section) with the incident neutron energy andappropriate comments, e.g.: "(N,N'F)" or "(N,N'F) REAC" or "SIG FOR (N,N'F)".

Other fission quantities: entries should be made for the quantity measured using "SPON" forthe energy. An appropriate comment is required, e.g.: "SPONT FISS ISOMER" or "FROMISOMER AFTER (N,N')" or "FROM U235(N,N')U235M(SF)". If no information on the (n,n')reaction is given, no corresponding entry for DIN should be made.

Memo 4C-3/374 (Rev.4)

page 2

Note: If the inelastic scattering cross section for the formation of the spontaneously fissioning
isomer is given together with other fission quantities, entries should be made for the the target
nucleus and the (n,n') reaction as well as for the reported quantities for the spontaneously
fissioning isomer as above, with appropriate comments.

(n,2nf) reaction: delayed fission
This case is similar to the (n,n'f) reaction except that 2 neutrons are emitted before formationof the spontaneously fissioning isomer (Z,A-1). The considerations of the processes andcoding rules for CINDA follow those of the (n,n'f) reaction except that for the cross section
for the whole process, N2N replaces DIN, and for the other fission quantities the target
nucleus is the spontaneously fissiong isomer (Z,A-1).

Revision of Page II.2.11:
under DIN

Diff Inelast:

Definition: Angular distributions orenergy spectra of inelastically scattered neutrons, or partial crosssections.
Examples of use:.......
4) cross-section for (n,n'f) reaction(see also pages II.2.8 and II.2.17)

Revision of Page II.2.13:
under N2N

(N,2N)

Definition: ... no change
Use: For cross sections .............. emitted.
Include: cross-section for (n,2nf) reaction (seealso pages II.2.8 and II.2.17)
Exclude: (n,f) and (n,3n) reaction.

Revision of Page II.2.17 (at top of page before NF):
Fission quantities
Summary table of coding rules for (2n,f), (n,n'f) and (n,2nf) reactions (for details and coding
hints see page II.2.8):||

delayed|quantities/ what to be coded| (2n,f) | (n,n'f) | (n,2nf) |==============================================|==========|==========|==========|| target nucleus +)| (Z,A)| (Z,A) | (Z,A)|
whole process:|------------------------|----------|----------|----------|| neutron energy| incident | incident | incident |NF RIF ALF ETA|------------------------|----------|----------|----------|| additional quantity *) |
|
DIN|
N2N
|
==============================================|==========|==========|==========|
other quantities:| target nucleus +)| (Z,A+1) | (Z,A)| (Z,A-1) |NU NUD NUF SFN SFG |------------------------|----------|----------|----------|FPG FPB NFY FRS CHG | neutron energy| incident |
SPON|
SPON
|
================================================================================+) target nucleus for CINDA, where (Z,A) is the published target nucleus*) only if information on the cross section is given