Computer program reduces time manually required to compute neutron age and to provide definite plan of procedural choices. Program allows convenient comparison of several fitting and error analysis procedures. Program code provides for error estimation of various integration options

Semler, T. T.

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October 1970	 Brief 70-10557 
NASA TECH BRIEF H 
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nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Neutron Ages Computed from Experimental Activation Data 
The problem: 
To devise a computer program for determining 
neutron ages from experimental activation data. The 
neutron or Fermi age is related to the mean-square 
distance traveled by a neutron from its point of genera-
tion to its point of thermalization. 
The solution: 
This program was written to reduce the time man-
ually required to compute a neutron age and to pro-
vide a definite plan of procedural choices. It allows 
convenient comparison of several fitting and error-
analysis procedures. 
How it's done: 
For the purpose of integration, the experimentally 
determined activation energy versus distance-squared 
curve is separated into two portions. The shape of 
curve I has not been analytically determined, whereas 
curve II is assumed to be exponential. The breakpoint 
or division between curves I and II may be determined 
by the program or by the experimenter. If the program 
option is selected, a difference method is used for 
calculation of the breakpoint. 
After the breakpoint is determined, curve I is 
integrated in any of several ways that are left as op-
tions in the code. The first option available for the 
integration of curve I is the trapezoidal integration. 
This option should be used if many finely spaced 
points are to the left of the division point. The second 
option available is a least-squares polynomial curve 
fitted to the data. This option also allows the speci-
fication of the significance of the fit; that is, a certain
confidence level for the polynomial fit may be inserted 
as program input. The third option available is an 
averaged parabolic fit. This option fits one parabola 
to the first three and another parabola to the last 
three of four successive points. The coefficients thus 
generated are averaged and the curve is integrated. 
A considerably better approximation to the integral 
is produced with this option than with the trapezoidal 
option, since curvature is allowed between points. 
The exponential region of the curve (curve II) is 
fitted by a weighted least-squares exponential ap-
proximation. It is then integrated analytically from 
the division point to infinity. A fourth option allows 
the value of the index number of the breakpoint to be 
specified as part of the program input. 
The remaining options of the code provide for error 
estimation of the various integration options. 
Notes: 
1. This program is written in FORTRAN IV language 
• for use on the IBM 7094 computer. 
2. Inquiries concerning this program may be directed 
to:
COSMIC 
Barrow Hall 
University of Georgia 
Athens, Georgia 30601 
Reference: B70-10557
Source: T.T. Semler
Lewis Research Center

(LEW- 10949) 
Category 09 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United -States
	 will be free from privately owned-rights.
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Neutron ages computed from experimental activation data

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