[ RadSafe ] What's a "T unit?"

Cindy Bloom radbloom at comcast.net
Thu Oct 19 15:54:49 CDT 2006


I don't yet have an exact reference, but I found this quote:

"From about 1943 into 1945, MED also used the "T unit" for expressing beta 
exposure; a T unit is defined as "0.25 R/hr" (i.e., rep/hr) of beta 
radiation only."

Also there's a quote from H. L. Friedell (at Y-12?)  on 8/12/1944 that 
discusses readings taken to determine whether X1 and X2 could be 
concentrated in the systems and notes, "The readings, which are recorded as 
related to T metal mean that the beta activity which is related to X1 and 
X2 is the same as the beta activity  from material in equilibrium with 
T."   This quote is consistent with the T unit defined as 0.25 R/h.  Based 
on this I don't think T unit necessarily refers to tolerance.  I believe 
that when it is written as T unit, it probably refers to the beta dose rate 
from a slab of uranium (code named T) metal.  In some records, we've seen 
%Tol, and think that clearly refers to the tolerance level for the specific 
era and site, for which I've seen beta limit of 0.5 R/8h (not clear if this 
only applies to hands) and levels up to 5.5 R/wk for the hands.  It's 
possible that % Tol got shortened to T in some records, but I don't think 
that's the case you describe.  Based on the fact that the measurement 
reported in T units was taken at 1/2 foot from a pile of (presumably U) 
scrap metal, it seems most reasonable to assume that the reading was about 
equal to 0.125 R/h.  rad=rem=R=r give or take.


At 10:53 AM 10/19/2006 -0700, Strom, Daniel J wrote:
>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
>http://www.eh.doe.gov/advocacy/faclist/showfacility.cfm :
>Ventron Corporation
>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;
>1996-1997 (remediation)
>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
>Brief Resume: http://www.pnl.gov/bayesian/strom/strombio.htm
>Online Publications: http://www.pnl.gov/bayesian/strom/strompub.htm
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