ANP QUARTERLY PROGRESS REPORJ 41%
ORNL-LR-DWG 2657
5 0 - c C ION
Fig. 13A,
Gamma-Ray Dose Measurements
hind AGHT Graphite.
1-ft graphite thickness between the reactor face and the end of the spectrometer collimator i s shown i n Fig. 13,5. The spectrum measured w i t h the end of the collimator against the reactor face i s also s t1own. Removal cross sections have been calculated for each thickness of graphite by use of a method suggested by E. P. Blizard.4 The resulting cross sections are 0.82 barn/atom for the 1-ft slab, 0.84 b a d a t o m for the 2-ft slab, and 0.80 barn/atom for the 3-ft slab. These removal cross sections are i n goad agreement w i t h measurements made on graphite a t the LTSF. R E A C T O R A I R GLOW
R. G. Cochraii K. M. Henry
T. A. L o v e F. C. Maienschein
R. W. P e e l l e
Attempts t o theoretically determine the amount of v i s i b l e l i g h t which may surround a nuclear-powered airplane in f l i g h t have resulted i n widely differing
~ a l u e s . ~ 'Therefore ~ an experiment was performed at the BSF t o provide an experimental basis for future estimates. The end of an a i r - f i l l e d aluminum periscope tube was placed a t the reactor face, and the amount of l i g h t produced in the tube was measured by a photomultiplier w i t h spectral response similar t o that of the average human eye. Other relative measurements were token w i t h a photomultiplier which was sensitive chiefly in the blue and nearultraviolet range. The latter measurements are plotted i n Fig. 13.6 as functions o f the air pressure i n the tube. Measurements w i t h argon i n the tube demonstrate that nei ther the approximate amount of l i g h t produced nor the exact spectrum emitted i s strongly dependent on the atomic number of the gas. It i s also interesting t o note that the l i g h t production i n a given volume of air appears t o have a maximum a t a pressure corresponding to an altitude of about 30,000 ft. It i s demonstrated i n Figs. 13.7 and 13.8 that t h e air glow i s largely caused by gamma radiation rather than by neutrons. Figure 13.7 shows the decay of the l i g h t plotted along w i t h the decay of the reactor gamma ion chamber current just after reactor shutdown. The attenuation by water of the radiation which produces the air glow i s shown i n Fig. 13.8. T h i s attenuation rather c l o s e l y follows that o f gamma rays. The photomultiplier was used t o compare the quantity of l i g h t given off i n the air-glow tube w i t h that from a small tungsten lamp mounted a t the reactor end of the ti~be, T h i s comparison showed
that 7.2 x lom5 lumen was given off b y the glow for c1 reactor power of 100 kw and atmospheric pressure. Presumably, the amount of light should be proportional t o the integral of the gamma-ray dose rate over the volume of the air in t h e measuring 10 tube. T h i s integral was estimated to be 1.1 x 10 (r.cm3)/hr. Therefore the effective l i g h t production J ~air ~ is per u n i t V O ~ L of
L
6.5 x
:
(Iumen/cm3)/(r/hr).
If i t i s assumed that all the l i g h t i s given off a t 4E. P. B l i z a r d , Procedure /or Obtaining E / / e c t i v e Rernoval Cross T e r t z o n s f r o i n L i d T a n k Data, QRNL CF-54-6-164 ( J u n e 22, 195.1)5T. A. Welton a s quoted by C, E. Moore, Visual Detectability o/ Azrcralt at N i g h t , LP.C-15, p 24 (Aug. 14, 1953). 6J. E a Faulkner,_Vrsible 1.1ght Produced in A i r Around Reactors, O R N L Lt -54-5-99 (to be i s s u e d ) .