The neutron diffusion parameters of water and ice were measured by the pulsed source method at two temperatures; 1.0°C. and -19°C.
Neutron pulses were obtained at one millisecond intervals by modulating the beam in a Cockcroft-Walton type accelerator. The ₁H³(d,n)₂He⁴ reaction was used to generate neutrons.
The samples were contained in cylindrical aluminum cans covered with cadmium. The experiment was conducted inside a large paraffin block which served as a neutron shield and thermal insulator. The temperature of the samples was maintained constant to within ±1°C.
Neutrons leaving one surface of the sample were counted in a BF₃ proportional counter. The time distribution of these neutrons was recorded by an eighteen channel time analyzer. The width of each channel was 20 microseconds. The opening of the first channel was delayed 100 microseconds with respect to the start of the neutron burst to minimize harmonics in the neutron decay.
A geometric buckling was calculated for each sized sample from
B²=[2.405/(R+∈)]²+[π/(H+∈)]²
where B² = geometric buckling
2.405 = first zero of J<sub>o</sub> Bessel Functions
R = radios of cylinder
H = height of cylinder
∈ = extrapolation distance
The extrapolation distance ∈ was calculated from
∈ =0.71 λ<sub>tr</sub>
where λ<sub>tr</sub> = mean free path of neutrons in water
The extrapolation distance was assumed to vary as T<sup>½</sup> where T is the temperature in degrees Kelvin.
The measured decay constants, α, were fitted by the method of least squares to a polynomial in B² of the form
α = (∑<sub>a</sub>v) ÷ D<sub>o</sub>B² - CB⁴
where
∑<sub>a</sub> = the macroscopic absorption cross-section
v = the neutron velocity
D<sub>o</sub> = diffusion coefficient
C = diffusion cooling coefficient
The resultant values of (∑<sub>a</sub>v) and D<sub>o</sub> for each temperature are below. The data did not permit a determination of C.
1.0°C. (∑<sub>a</sub>v) = 4595 ± 365 sec⁻¹ D<sub>o</sub> = 29600 ± 840 cm²/sec
-19°C. (∑<sub>a</sub>v) = 4355 ± 263 sec⁻¹ D<sub>o</sub> = 27050 ± 630 cm²/sec / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/53838 |
| Date | January 1962 |
| Creators | McClure, John Arthur |
| Contributors | Physics |
| Publisher | Virginia Polytechnic Institute |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | 63 leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 20186685 |
Page generated in 0.0018 seconds