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]10^{7}s^{-1}[/math] and 4.2[math]\mu g[/math], respectively. I am skeptical about the quoted neutron rate since 4.2 [math]\mu[/math]g of pure Cf252 would not have a neutron rate that high. So, I did my calculations assuming that there was initially 4.2 [math]\mu[/math]g of Cf with a isotopic composition that is typical for the date of production.

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]\mu[/math]g, the values in the following table can be calculated. Cf250 is of particular important since as the source becomes aged it will contribute significantly to neutron rate.

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

Table of rates

Click here to open a table giving neutron/alpha rates of the source for the next ten years.

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]s^{-1}[/math]]:

[math]\Delta t=\frac{(year-1993)+\frac{month-3}{12}}{2.645}[/math]

[math]n_{0}rate=(r_{252})(3.7)(0.5)^{\frac{\Delta t}{t252_{1/2}}}+(r_{250})(3.5)(0.5)^{\frac{\Delta t}{t250_{1/2}}}[/math]

where [math]r_{252}[/math] and [math]r_{250}[/math] are the initial SF rates of Cf252 and Cf250, respectively. 3.7 and 3.5 are the neutron multiplicities for Cf252 and Cf250, respectively.

References

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