Cf-252 FTC-CFZ-431

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Overview

An official document for the CF-252 source with serial number FTC-CFZ-431 provides a value for the neutron rate and CF-252 mass as of 03/19/1993.

The initial neutron rate and mass of cf-252 are stated to be [math]\displaystyle{ 10^{7}s^{-1} }[/math] and 4.2[math]\displaystyle{ \mu g }[/math], respectively.

4.2 [math]\displaystyle{ \mu g }[/math] would generate [math]\displaystyle{ 9.67 \times 10^{6} }[/math] neutrons per second. The discrepancy between these two numbers gives a 2% error.

Initial source composition

CF252 used in the US is produced in batches at Oak Ridge National Laboratory which all have similar isotopic make up. I found the isotopic composition of a batch produced in 1991, two years before the production date of our source<ref> http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-12-22883 </ref>. Assuming our source has the same isotopic composition as the 1991 batch and a total mass of 4.2 [math]\displaystyle{ \mu }[/math]g, the values in the following table can be calculated.

nuclide	Atom %	[math]\displaystyle{ T_{1/2} }[/math] [y]	as of 1993
			n atoms [math]\displaystyle{ *10^{15} }[/math]	decays [math]\displaystyle{ [s^{-1}]*10^3 }[/math]
				[math]\displaystyle{ \alpha }[/math]	SF
[math]\displaystyle{ ^{249}Cf }[/math]	5.76	351	0.58	36.0	0
[math]\displaystyle{ ^{250}Cf }[/math]	9.22	13.1	0.93	1,560	1.25
[math]\displaystyle{ ^{251}Cf }[/math]	2.85	898	0.29	7.02	0
[math]\displaystyle{ ^{252}Cf }[/math]	81.99	2.65	8.25	66,300	2120

Table of rates

Click here to open a table giving neutron rates and C-252 activity from dates 1/2017 to 12/2029. This calculation only includes neutrons from Cf-252, since all other daughter nuclei and possible impurities have a very low SF rate compared to Cf-252.

Formulas

As the Cf252 source ages, neutrons from the SF of Cf250 become significant since it's has a half-life is 13 yrs, vs 2 yrs for CF252. Aside from Cf 252/250, there are no other significant neutron sources present.

The formula used for neutron rate [[math]\displaystyle{ s^{-1} }[/math]]:

[math]\displaystyle{ k=(0.5)^{\frac{(year-1993)+\frac{month-3}{12}}{2.645}} }[/math]

[math]\displaystyle{ n_{0}rate=9.835\times10^6\times k }[/math]

and for Cf-252 activity [[math]\displaystyle{ \mu Ci }[/math]]:

[math]\displaystyle{ activity=2283.3\times k }[/math]

References

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