RE: criticality accidents

["Franta, Jaroslav" <frantaj@aecl.ca>]

Arnold Dion [mailto:asdion@cyberenet.net] wrote on Friday November 03, 2000
12:55 AM

RADSAFE Community:

Many of you probably know that there are many myths associated with the =
two fatalities that resulted from criticality tests performed on a =
plutonium core in Los Alamos in 1945 (Harry Daghlian) and 1946 (Louis =
Slotin). In order to dispel some of these myths, I have a website, =
http://arnold_dion.tripod.com/Daghlian/, describing documented =
circumstances of the Daghlian accident and his subsequent death from =
acute radiation sickness.

In addition, I want to add a FAQs page to the website with a listing of =
myths and questions concerning both accidents. So, I would greatly =
appreciate receiving from the RADSAFE community any myths you've heard, =
or questions concerning these accidents (asdion@cyberenet.net). I will =
respond to all.
<><><><><><><><><><><><>

COMMENT:

In your web-posted document, "Los Alamos and the Omega Site Accident,"
(copied below) the following statements seem IMHO to require some
clarification : 

<BEGIN QUOTE>
Reacting instinctively, he pushed the brick from the assembly with his right
hand, which developed a tingling sensation as it became enveloped in the
blue glow surrounding the sphere. The time was 9:55 PM. 

....the bright flash of light hardly escaped his notice as he turned in the
direction of the assembly.
<END QUOTE>

I refer specifically to the "blue glow" phenomenon.
Kevin Roark of LANL says much the same thing in his article posted at URL
http://www.lanl.gov/worldview/news/releases/archive/00-099.html

<BEGIN QUOTE>
Criticality accidents report issued
LOS ALAMOS, N.M., July 19, 2000­ Since 1945 there have been 60 criticality
accidents world-wide 
<snip>
In most criticality accidents this chain reaction is very short lived,
causing a neutron population spike and resultant radiation, heat and, in
many cases, an ethereal "blue flash," a phenomenon of the air surrounding a
neutron burst becoming ionized and giving off a flash of blue light.
<END QUOTE>

But as I understand it, this is NOT CORRECT.
This "flash of blue light" would occur if the criticality had been inside a
tank of water, like a pool-type research reactor, due to Cerenkov radiation.
But Daghlian's and Slotin's plutonium sphere was in a dry air environment
with no way to produce Cerenkov radiation in the lab. 
But there's more to it than that. 
Recall that in the case of the Tokaimura criticality accident the excursion
occurred in an aqueous solution of enriched uranium. A blue flash of
Cerenkov radiation would therefore have been produced. But the liquid was in
a closed tank, so the light would not have shined outside. 
Nevertheless the victims of the accident, just like Daghlian, Slotin and
their colleagues, saw a blue flash. 
But this was not in the laboratory. It was INSIDE THEIR EYEBALLS, where the
gamma & neutron particles caused Cerenkov radiation to form "in-situ." (
BTW, the end of the "blue flash" also signalled the end of the fission
pulse, due to thermal expansion of the metal -- no point leaping at the
device to try to shut it down, since its all over by then anyway ! )

A number of web sites on this topic give the same information as yours. For
example,

http://www.geocities.com/Heartland/Park/2874/slotin04.html
Louis Slotin And 'The Invisible Killer'

The chain reaction was stopped when Slotin knocked the spheres apart, but
deadly gamma and neutron radiation had flashed into the room in a blue blaze
caused by the instantaneous ionization of the lab's air particles. 

http://collections.ic.gc.ca/heirloom_series/volume6/252-255.htm
Louis Alexander Slotin: 1910-1946 
Selfless Hero of the Manhattan Project 

While he was demonstrating the perilous techniques of the assembly to his
successor, an accident occurred. Instantly a blue glow, stronger than the
spring sunshine, filled the laboratory. There was a wave of unbearable heat.
Some present experienced a dry, prickly sensation on their tongues - a sign
of excessive radiation. Immediately Slotin threw himself forward, separating
the two hemispheres with his bare hands. The chain reaction ended; the blue
glow was gone; the unbearable heat subsided. It was 3:23 p.m. on Tuesday
afternoon, May 21, 1946. And Louis Slotin had begun to die traumatically. 
<><><><><><><><><>

Please verify with your colleagues that this indeed is incorrect
information.
If it is, would you please assist in correcting it, starting with your own
posting ?

Thank you very much.

Jaro
frantaj@aecl.ca


http://arnold_dion.tripod.com/Daghlian/accident.html
Los Alamos and the Omega Site Accident 
 
As scheduled, Baker, Holloway, King and Schreiber arrived at the Los Alamos
facility in the autumn of 1943, while Daghlian stayed behind to help with
rebuilding the Purdue cyclotron, restoring it to produce 10-MeV deuterons.
At this point, he also needed to complete his course work at Purdue,
typically two years in duration, which would then allow him to devote
full-time to his doctoral thesis project at Los Alamos. Daghlian probably
started working at Los Alamos in the late spring of 1944 as a member of the
"Water Boiler" group at the Omega Site; he later joined the Critical
Assembly Group or "crew" that was headed by Otto Frisch, also located at
Omega. These studies included the well-known "tickling the dragon's tail"
experiments. Daghlian's last major assignment was as an assistant in
preparing the plutonium core at the MacDonald Ranch House for the Trinity
test in Alamogordo, NM (16 July, 1945). [ Inset : Embroidered shoulder patch
awarded to 3500 participants of the Manhattan Project.] 

On 21 August, 1945, Daghlian was involved with a series of experiments at
Omega Site concerning the critical masses of a 6.2 kg sphere of plutonium
(Pu-239 or "49 metal") in various tungsten carbide (WC) tamper arrangements.
On the morning of August 21, 1945, he constructed a hollow cube on a square
base (14-7/8 inches per side) from WC bricks (2-1/8 x 2-1/8 x 4-1/4 inches)
surrounding the 49 metal sphere. This assembly was found to be critical when
five layers were completed and two additional bricks were placed in the
middle of the sixth layer. 

That afternoon, Daghlian constructed another cube on a 12-3/4 inch square
base of WC bricks for enclosing the same 49 metal sphere. This time, the
assembly became critical when five layers were completed, and the task of
designing an appropriate assembly configuration, i.e., the 49 metal sphere
enclosed in a completed cube, remained to be determined. As he disassembled
the afternoon experiment and returned the Pu-239 sphere to the vault,
Daghlian began planning the next criticality test and, after making some
final remarks in his notebook, he decided to construct the next assembly on
a 10-5/8 inch square base. [ Inset: Photo of the critical assembly after the
accident and dismantling by Daghlian. A nickel-plated sphere of 49 metal is
shown supported by a WC cradle and surrounded by a base of WC bricks. During
a test, a neutron source is first placed into the hollow center of the shere
(composed of two hemispheres) and covered with a matching top WC cradle. The
assembly is subcritical in this configuration. The WC tamper functions to
"reflect" neutrons back to the center sphere of plutonium causing increasing
fissions which also release additional neutrons. In Daghlian's case, too
much tamper was accidently added when the WC brick fell from his hand and
the assembly became "critical".] 

After dinner, Daghlian attended a scientific lecture at theatre #2, and
began thinking about returning to Omega Site that evening to test the third
assembly, rather than the following morning as originally planned. He was
well aware that this was against "official" safety regulations on two
counts, i.e., performing a potentially hazardous experiment alone
after-hours. By the end of the lecture at 9:10 PM, his mind was made up, for
reasons that are even today unknown, and he proceeded directly to Omega,
arriving there at 9:30 PM. 

Entering the laboratory, he found Private Robert J. Hemmerly, a Special
Engineer Detachment (SED) guard, seated at a desk and reading a newspaper.
Hemmerly looked up apprehensively at a somewhat anxious Daghlian, who tried
to mask his nervousness by walking directly to the assembly bench. SED
guards were stationed at Omega whenever fissionable material was onsite, in
case of fire and, especially, as a deterrent to theft. Hemmerly's
responsibilities did not extend to policing conduct or enforcing laboratory
regulations, and his apprehension quickly faded with a return to his
newspaper and a "Hi, Harry" in the direction of the moving figure. 

Daghlian immediately set about removing the 49 metal sphere from the vault
and constructing the planned assembly. Using the audible "clicks" of the
monitoring instruments as a guide, he quickly completed four layers. His
pace slowed as he started the fifth layer and he finished half of it. As he
attempted to place another brick over the center of the assembly with his
left hand, the "clicks" alerted him to the possibility that this addition
would be supercritical, and he immediately started withdrawing his left hand
when the brick fell from his grasp into the center of the assembly. Reacting
instinctively, he pushed the brick from the assembly with his right hand,
which developed a tingling sensation as it became enveloped in the blue glow
surrounding the sphere. The time was 9:55 PM. 

When the accident occurred, Hemmerly was seated with his back to the
assembly some twelve feet away. Even so, the rapid succession of instrument
"clicks", the thud of the falling brick, and the bright flash of light
hardly escaped his notice as he turned in the direction of the assembly. At
that moment, Daghlian's large figure was standing limply with his arms
suspended at his sides, attempting to rationally assess the situation in
spite of a flood of varied emotions ranging from embarrassment to fear of
the possible consequences he had created. For now, he decided to partially
dismantle the assembly to a more stable configuration, and subsequently
informed Hemmerly of the situation. By chance, another graduate student had
just arrived at Omega and she drove Daghlian to the hospital at Los Alamos,
while Hemmerly stayed behind to alert Sargeant Starner, who was in a
protected office area at Omega separated by a five-foot-thick concrete wall
from the laboratory, that an accident had occurred. 

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