[ RadSafe ] What's a "T unit?"
Strom, Daniel J
strom at pnl.gov
Thu Oct 19 12:53:47 CDT 2006
I need to interpret a declassified report dated June 15, 1944 concerning
a company called (at the time) Metal Hydrides. Here's what one finds at
Also Known As: Metal Hydrides Corp.
Also Known As: Ventron Div., Morton Thiokol, Inc.
State: Massachusetts Location: Beverly
Time Period: AWE 1942-1948; Residual Radiation 1949-1995; DOE 1986;
Facility Type: Atomic Weapons Employer Department of Energy
Facility Description: From 1942 to 1948, Metal Hydrides Corp. was under
contract to the Manhattan Engineer District and the Atomic Energy
Commission to convert uranium oxide to uranium metal powder. This work,
as well as later operations to recover uranium from scrap and turnings
from a fuel fabrication plant at Hanford, was conducted at a foundry at
the site. During this period, Metal Hydrides was the AEC's primary
uranium scrap recovery contractor.
Cleanup activities at this location included the removal of an
underground storage tank in 1986. Further remediation was performed
between May 1996 and August 1997 by Bechtel National Inc. and a number
of local subcontractors as part of the Formerly Utilized Site
Remediation Action Program (FUSRAP).
The plant is currently owed by the Ventron Division of Morton
The report gives one pair of readings as "0.04 r/8-hr. day (gamma)" and
"0.5 T units (beta and gamma)" at "1/2 foot from 14000 pounds of scrap
metal." For measurements reported in "T units," the report states,
"Shield was removed from chamber, hence both beta and gamma radiation,
if present was measured with no differentiation possible."
In those days, the "Tolerance Dose" was 0.1 "r/day." It is possible that
a "T unit" was simply a fraction of the tolerance dose, when the beta +
gamma [open window or shield off] reading was interpreted as simply the
r/d divided by 0.1.
The limit for extremities was evidently 5 times higher, because there
are a whole series of readings inside of a left glove and a right glove
from 10 Apr. 1944 such as "Beta Rad. R/8 hr." of 0.15 and "Times
Tolerance" of 0.3, indicating a Tolerance Dose for the hands of 0.5 r/d
(usually one sees "r" and sometimes "R", as in a column heading where
all words or abbreviations began with an uppercase letter). I would
infer that these measurements must have been made with film, the only
contemporary technology that would fit into a glove. "Times Tolerance"
values ranged from 0.1 ("inside-back of hand") to 0.5 ("inside-base of
3rd and 4th fingers").
Intriguingly, a paragraph states, "The above figures indicate that these
gloves were not contaminated beyond the tolerance limit with beta
radiating materials as of 21 March 1944 or within a week prior to that
date. Corrections for the decay of radioactive materials were made to
the 21st of March, because that is when the gloves were shipped, but if
most of the radioactive contamination was accumulated two or three weeks
before the 21st, the beta radiation to the hands of the wearer at that
time was in the neighborhood of tolerance." This would imply a half-life
of a few weeks. The material in question may have been U-238 alpha decay
product Th-234, with a 24.1-day half-life, if it had been chemically
separated from uranium for some reason.
I would be grateful for any references to information that can confirm
what a "T unit" was.
- Dan Strom
The opinions expressed above, if any, are mine alone and have not been
reviewed or approved by Battelle, the Pacific Northwest National
Laboratory, or the U.S. Department of Energy.
Daniel J. Strom, Ph.D., CHP
Environmental Technology Directorate, Pacific Northwest National
Mail Stop K3-56, PO BOX 999, Richland, Washington 99352-0999 USA
Overnight: Battelle for the U.S. DOE, 790 6th St., Richland WA 99354
ATTN: Dan Strom K3-56
Telephone (509) 375-2626 FAX (509) 375-2019 mailto:strom at pnl.gov
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