Appendix: "Radiohalos in Coalified Wood"
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References and Notes
- J. Jedwab, Coal Science (American
Chemical Society, Washington, D.C., 1966).
- I. A. Breger, in Formation of Uranium
Ore Deposits, Proceedings of a Symposium, Athens, 6-10 May
1974 (International Atomic Energy Agency, Vienna, 1974),
- I. A. Breger donated Colorado Plateau coalified
wood specimens from the following mines: (i) Jurassic—Peanut
and Virgin No. 3, Colorado; Corvusite, Utah; and Poison Canyon,
New Mexico; (ii) Triassic—Lucky Strike No. 2, Dirty Devil
No. 2, Adams, and North Mesa No. 9, all in Utah; and (iii) Eocene—Docamour,
Colorado. J. S. Levinthal provided 16 other specimens. However,
only those from the Rajah 49 mine [Salt Wash member of the Morrison
Formation (Jurassic)] were sufficiently well preserved to exhibit
halos. The Chattanooga shale coalified wood (Devonian), which
came from near Nashville, Tennessee, was donated by I. A. Breger
and V. E. Swanson. Breger's analysis of this coalified wood yielded
0.001 to 16 percent U, 54 to 84 percent C, 3 to 7.5 percent H,
0.3 to 1.8 percent N, 6 to 38 percent O, and 0.6 to 14.5 percent
S. Except where stated, all experimental results refer to work
on Colorado Plateau coalified wood (Triassic and Jurassic formations).
A thin section of a coalified wood specimen (earlier obtained
from I. A. Breger) was provided by J. Jedwab and was used along
with Breger's other specimens. Although personal communications
with Breger and Jedwab proved of great value, this in no way
implies that either Jedwab or Breger necessarily concurs with
the results presented here.
- R. V. Gentry. Annu. Rev. Nucl. Sci.
23, 347 (1973). The halo in Fig. 1a would extend another
20 μm if fully developed.
- C. A. Andersen and J. R. Hinthorne. Science
175, 853 (1972).
- R. V. Gentry, ibid. 184, 62
- If the appropriate formulas [G. Friedlander,
J. W. Kennedy, J. M. Miller, Nuclear and Radiochemistry (Wiley,
New York, ed. 2, 1964), pp. 95-98] are used for computing α-ranges
in various solids, the ranges of a 5.3-Mev α-particle
in coalified wood [see (3)] of density
1.3 and 1.6 g/cm3 would be 31 and 25 μm
respectively. Uniform shrinkage of the matrix could also reduce
- G. H. Henderson, Proc. R. Soc. London
Ser. A 173, 250 (1930).
- R. V. Gentry, Science 160,
- ______. Nature (London) 252,
564 (1974); ibid. 258, 269 (1975).
- This occurrence of Po halos refers to the
Colorado Plateau coalified wood.
- L. R. Stieff, T. W. Stern, R. G. Milkey,
U.S. Geol. Surv. Circ. 271 (1953).
- Dual halos have thus far been found in
specimens from the North Mesa No. 9 mine in Utah and the Virgin
No. 3 and Rajah 49 mines [see (3)].
- The coloration pattern of the dual halo
provides the key to understanding its rarity. If U with its daughters
were concurrently flushed out of some Precambrian ore deposit,
even with a relatively short transit time from the ore deposit
to the wood, equilibrium conditions still require that more than
50 times as much 210Pb as 210Po be available
for accumulation. If the wood exhibited constant sensitivity
to α-induced coloration, then the outer circular
halo resulting from 210Pb accumulation would be expected
to be much darker than the elliptical halo resulting from 210Po
accumulation. The fact that just the opposite is true is in good
agreement with the evidence found by Jedwab [(1)
and private communication] indicating that during the U infiltration
the gel-like wood exhibited much higher sensitivity to a induced
coloration as compared to the later stages of coalification.
Possibly then, a relatively dark halo could have formed rather
quickly from as few as 104 to l05 Po atoms,
whereas some 20 to 50 years later the change in the coloration
sensitivity of the matrix might require an α-dose
50 to several hundred times higher from the 210Pb
decay sequence to produce even a light halo. Thus possibly only
in rare cases would the Pb-Se inclusions accumulate large enough
quantities of 210Pb to subsequently generate the outer
- The variation in the 238U/206Pb
ratios may be attributed primarily to the "old" radiogenic Pb
component and secondarily to 226Ra and 210Pb,
which, in varying amounts, were also incorporated into the U-rich
radiocenters. Evidence for this "old" radiogenic Pb was also
found in larger, millimeter-size U-rich regions which also contained
varying amounts of Na, Al, K, Ca, Ti, V, Fe, Y, Zr, Ba, and the
rare earths. Such regions exhibit variable (but not very high)
U/Pb ratios and very little common Pb.
- D. H. Smith, W. H. Christie, H. S. McKown,
R. L. Walker, G. R. Hertel, Int. J. Mass Spectrom. Ion Phys.
10, 343 (1972-1973).
- R. P. Fischer, in Proceedings of the
International Conference on the Peaceful Uses of Atomic Energy,
Geneva, August 1955 (United Nations, New York, 1956), vol.
6, p. 605; Econ. Geol. 65, 778 (1970).
- S. C. Lind and C. F. Whittemore, U.S.
Bur. Mines Tech. Pap. 88 (1915), p. 1; T. W. Stern and L.
R. Stieff, U.S. Geol. Surv. Prof. Pap. 320 (1959), p.
151; J. N. Rosholt, in Proceedings of the Second U.N. International
Conference on the Peaceful Uses of Atomic Energy, Geneva, September
1958 (United Nations, New York, 1958), vol. 2, p. 231.
- Nondestructive γ-ray spectrometry
was utilized to check on U disequilibrium in gram-size specimens
of the Colorado Plateau coalified wood. We found significant
differences in the γ-spectra that could reasonably
be attributed to U disequilibrium. By removing microportions
of U-rich areas and physically smearing the material onto steel
planchets for α-counting, we observed one α-spectra
that unambiguously indicated U disequilibrium between 234U
and 230Th, or 230Th and 226Ra,
or both. Excess α-activity in the ~ 4.7-Mev region
was not attributed to excess 234U because mass spectrometry
measurements on a separate specimen showed an equilibrium 238U/234U
- Less than 2.5 percent of the halos with
U radio-centers have any trace of an outer ring. It is difficult
to associate these with sequential α-decay from 238U
because such weak rings do not correlate with the U content.
These weak rings may have resulted from diffusion of α-radioactivity
out of the radiocenter prior to induration of the halo region
by the α-radioactivity. Alternatively, these weak
rings may have resulted from the accumulation of small amounts
of 222Rn, 214Pb, or 226Ra. In
fact, the size of the dark halo region around the U-rich sites
admits of the possibility that the inner halos may have formed
from the accumulation of minute amounts of 226Ra or
210Pb, or both. Their more diffuse radiocenters, however,
would prevent the formation of well-defined boundaries as in
the case of the Pb-Se inclusions.
- This would be true even if coalified wood
is only 1/10 as sensitive to α-coloration as biotite.
- I. A. Breger and J. M. Schopf, Geochim.
Cosmochim. Acta 7, 387 (1955); V. E. Swanson, U.S.
Geol. Surv. Prof. Pap. 300 (1956), p. 451. J. Jedwab informed
me of halos in this material.
- I thank I. A. Breger, J. S. Levinthal,
V. E. Swanson, and J. Jedwab for supplying coalified wood specimens.
Research sponsored by the Energy Research and Development Administration
under contract with Union Carbide Corporation, and by Columbia
Union College under NSF research grant DES 74-23451.
15 September 1975, revised 30 June 1976
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