Re: Cm-244/C-13 Source

[baumbaug@nosc.mil (Joel T. Baumbaugh)]

Paul,

     This  is probably more detail than you really want to  know,
but here goes:

     The  reaction  you are interested in is caused by  a  Prompt
Gamma  Reaction  ->  Gamma  radiation  accompanying  the  fission
process without measurable delay.  As I understand it, the Cm-244
source  alphas  excite  the C-13 producing an  excited  state  of
Oxygen-16.  The O-16 then produces the "big boy" gamma.


242       240         4      0
   Cm -->    Pu  +     He  +  gamma
95        94          2      0

13      4       16      1      0
  C  +   He -->   O  +   n  +    gamma
6       2       8       0      0


The shorthand nomenclature for this reaction is:
        13           16
     The  C (gamma,n)  O

     The  (gamma,n)  reaction results in some of the O-16  in  an
excited energy level.  This decays to the stable ground state of
O-16  with a half life of 17 pico seconds and a gamma ray  energy
of 6.13 Mev.

     This  energy  is so unusually high that it is of value as  a
reference  lint  to calibrate spectrometers in this  high  energy
region.

     The  prompt  gamma  sources will be very  inefficient.   The
(gamma,n)  reaction  cross-section is low,  so only a few of  the
particles  from the decay of Cm-244 will be absorbed by the C-13;
most  of  them will slow down to thermal energies by  interaction
with  the  surrounding material and end up as helium  atoms.   Of
those  which do react with the C-13 nucleus, only 1% or so of the
reactions  will produce O-16 in the excited state at the 6.13 Mev
level,  the remainder will result in ground state O-16 which will
not emit gamma rays.

     In  case  you  plan  to make your  own,  the  efficiency  of
reaction also depends on the mixing of the Cm-244 and C-13 and on
the  average  energy  of the alpha particles  emitted  from  CmO2
particles.  There is a threshold energy below which the (gamma,n)
reaction  will not occur.  If the alpha energies from Curium  are
degraded too much before they interact with C-13 then no reaction
will  occur.   Thus the C-13 and Curium oxide particle sizes  are
very important parameters to consider when attempting to assemble
a source.

     If  you  want a picture of the prompt gamma spectrum  and/or
the neutron spectrum, let me know and I'll fax them to you.

Joel Baumbaugh
NRaD, San Diego CA

The  info/opinions  herein are mine, you can't blame them on  the
government this time.


Date: Wed, 30 Nov 94 12:17:00 -0600
Sender: radsafe@romulus.ehs.uiuc.edu
From: paterpd@ucssun1.sdsu.edu (Paul Pater)
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Subject: Cm-244/C-13 Source

I  am  interested  if someone could explain  a  reaction  between
Cm-244 and C-13
as  a  sealed  source  for the production of  a  6.1  MeV  gamma.
Apparently, this
source  exists and a Principal Investigator at our university  is
interested
in using it.

Paul Pater
Radiation Safety Officer
San Diego State University
(619) 594-6098
paterpd@ucssun1.sdsu.edu