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

Franz Schönhofer franz.schoenhofer at gmail.com
Thu Oct 19 16:42:42 CDT 2006

Thank you Cindy, for providing this historic note and I hope that persons
engaged in the history of nuclear power will make use of it.

I rather referred it to the much later established and among hydrogeologists
still used "TU" unit for "tritium unit" as you can see from my previous

Best regards,


2006/10/19, Cindy Bloom <radbloom at comcast.net>:
> Dan,
> 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.
> Cindy
> 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
> >International.
> >----------*-----------
> >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
> >Laboratory
> >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
> >Pagemaster for  http://www.pnl.gov/bayesian   http://qecc.pnl.gov
> >http://bidug.pnl.gov
> >
> >
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