Nuclear Data Section
International Atomic Energy Agency
P.O.Box 100, A-1400 Vienna, Austria
Memo CP-D/569
Date:
To:
From:

2 July 2009
Distribution
N. Otsuka

Subject:

Dictionaries 31 and 236- provisional fragment mass (PRV)

In prelim 2211 (and also in prelim.2191 and 2207), several entries give fission datafor “provisional mass” of fission fragment. This should be distinguished from preneutron emission fission fragment mass (primary fission fragment mass PRE) andpost-neutron emission fission fragment mass (secondary fission fragment mass SEC).
In general, there are momentum and mass conservations for fission:
m 1 *E 1 *=m 2 *E 2 * (momentum conservation in center-of-mass system)m 1 *+m 2 *=m f(mass conservation), where m i (i=1, 2) and m f denote the mass of fission fragment and compound nucleus,respectively. Asterisk means the quantity before neutron emission. If we assume thevelocity of fission fragment is unchanged by prompt neutron emission (v i = v i *), we
can derive the pre-neutron emission fission fragment mass from above equations:m 1 *= m f v 2 /(v 1 +v 2 ),m 2 *= m f v 1 /(v 1 +v 2 )E* tot = (1/2) m f v 1 v 2m 1 = 2E 1 /v 1 2,m 2 = 2E 2 /v 2 2Therefore we can obtain pre-neutron emission fission fragment masses m i *, preneutron emission total kinetic energy E* tot and post-neutron emission fission fragment
masses m i * if we can measure velocities (v i ) and kinetic energies (E i ) of two postneutron emission fragments (2v2E method) [1].
Authors of old articles sometimes introduced the provisional fission fragment mass μ iwhich satisfies the following relation:
μ 1 E 1 =μ 2 E 2
μ 1 +μ 2 =m f, and obtained μ i from measurement of the kinetic energies of post-neutron emission
fission fragments E i [2]. I would propose to the following new branch code andquantity codes for provisional fission fragment mass.
Dictionary 31 (Branch codes)
PRV
Provisional (For use in fission)
Dictionary 236 (Quantities)
PRV,AP,HF
Most probable provisional mass for heavy fragment
PRV,AP,LF
Most probable provisional mass for light fragment

Sum rule: If sum of two fragment masses is equal to compound mass, they are preneutron emission fragment masses PRE or provisional fragment masses
PRV.

Checking of the following entries is necessary:
PRELIM.2191: 21752,PRELIM.2207: 21313, 21543, 21544, 21545, 21771.

References[1] For example, I. Nishinaka et al., Phys.Rev.C70(2004)014609[2] H. W. Schmitt et al., Phys. Rev. 141 (1966) 1146

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