RaLa Experiment
Encyclopedia
The RaLa Experiment, or RaLa, was a series of tests during and after the Manhattan Project
designed to study the behavior of converging shock wave
s to achieve the spherical implosion necessary for compression of the plutonium pit of the nuclear weapon
. The experiment used significant amounts of a short-lived radioisotope lanthanum-140, a potent source of gamma radiation; the RaLa is a contraction of Radioactive Lanthanum. The method was proposed by Robert Serber
and developed by the team of Bruno Rossi
.
The tests were performed with 1/8 inch spheres of radioactive lanthanum, equal to about 100 curie
and later 1000 Ci, located in the center of a simulated nuclear device. Their outcomes are said to be "the most important single experiment affecting the final bomb design". The explosive lens
es were designed primarily using this series of tests.
254 tests were conducted between September 1944 and March 1962.
s in the metal of the sphere as it underwent compression. The gamma ray source was located in the center of a metal sphere. The increase of thickness (of hollow shells) and density (of solid spheres) as the compression progressed was detected as a decrease of intensity of gamma rays outside of the sphere; the lower density explosives did not absorb gamma radiation enough to interfere with the experiment. The gamma rays had to be intense and of the right energy. Too low energy, and they are fully absorbed in the surrounding metal; too high energy and the difference of attenuation during the implosion is too low to be practical. The detectors had to provide high speed and large area; fast ionization chamber
s, then under development, were the only devices then available satisfying the requirements.
Lanthanum-140 was chosen for having the right emitted gamma ray energy (1.60 MeV, with fraction of 0.49 MeV), a suitable half-life (as it cleaned itself up from the environment) and a sufficient radiation intensity; a high-intensity source was required to provide satisfying signal from the ionization chambers. It was also potentially available in larger quantities because barium-140 (its precursor) was an abundant fission product. It was however contaminated with barium-140, caesium-140, and especially strontium-90
; the latter still presents a potential problem in the area of the tests. Lanthanum-140 has specific activity
of 5.57×105 Ci/g; a 1000 Ci La-140 source therefore equals about 1.8 mg of lanthanum.
A radiolanthanum sample, precipitated in a tip of a small cone, followed by a plug, was lowered into the center of the metal sphere of the experimental assembly with a device resembling a fishing rod
. The cone and the plug were mated to the metal center of the assembly, together forming a metal sphere. A section of the explosive lensing was then returned to its place above the sphere. Several, typically four, ionization chamber
s were located around the experimental setup. Immediately after the detonation they generated signals that were displayed on oscilloscope
s in a blast-proof shelter or a mobile laboratory in a tank, 150 feet (45.7 m) away, and the oscilloscope traces recorded on camera
s. A calibration measurement was performed before and after each test. The ionization chambers and their preamplifier
s were destroyed during the explosion, but their simple design allowed their production in sufficient quantities.
The ionization chambers were cylindrical, 2 inches in diameter, 30 inches long, with a wire along the longitudal axis. They were filled with a mixture of argon
and carbon dioxide
at 4.5 atmospheres. Eight chambers were arranged in a tray and connected in parallel; four trays were located in a tetrahedron
around the experimental assembly, recording the gamma radiation around the sphere, sufficiently close to give a signal and sufficiently far away to not be destroyed by the blast before they can record the required information.
The initiation of the explosives was initially performed by a multipoint Primacord
system. The results were however erratic, as the detonations weren't sufficiently synchronized. Much better results were obtained since February 1945, when exploding-bridgewire detonator
s, developed by the Luis Alvarez
's G-7 group, became available.
As plutonium was not available, it was substituted with material with similar mechanical properties. Depleted uranium
was used but was not optimal because of its opacity for radiation; iron
, copper
, or cadmium
were other choices. Cadmium was the choice for most of the tests. The first shot was performed with an iron mockup of the plutonium pit. Hollow shells were initially used, but a more robust approach with solid spheres was employed later.
The resulting signal was a fast dip, corresponding to the compression of the cadmium sphere, followed by slower increase, corresponding to the decompression and following dispersal of the sphere and the lanthanum. The differences between the four traces on the oscilloscope display, each indicating the average compression in the direction of the detector, allowed the assessment of the required synchronization accuracy for the detonators.
The RaLa sources were very radioactive. They had to be lowered to the test apparatus by a 10 feet (3 m) long rod. The tests were initially observed from a sealed military tank
; the mobile laboratory consisted of two M4 Sherman
tanks. Each experiment was supposed to contaminate an area of about 3000 square meters for about a half year. When radiobarium was removed from the radiolanthanum, however, the short term contamination levels turned out to be insignificant. Tanks were then replaced with fixed shelters. One of the tanks was later lead-plated, sealed, equipped with self-contained air supply, and used for sampling of fission products in the post-blast debris after the Trinity test
. The sources posed a considerable radiation exposure risk; the exposure rate of a 1000 Ci source at 1 meter was 1,130 R/h and 11,000 R/h at 1 foot (0.3048 m). Sources with activity up to 2,300 Ci were used in some tests.
The radioactive contamination posed a problem. The people working in the Bayo Canyon had to change their clothes and take showers after the work. Sometimes they would still trip detectors at security gates.
The tests were performed in a relatively isolated area in the Bayo Canyon, then called Technical area 10, in Los Alamos County. Large amounts of radioactive lanthanum were dispersed by the explosions; 254 tests were performed between 1944 and 1961. In 1948 two workers received radiation burn
s there. The experiments were generally performed when the wind blew to the north, but occasionally the wind would change direction in the early morning. In 1949 and 1950 the fallout
from the tests was blown over parts of the housing area and a road; the radiation levels on the road occasionally reached 5-10 mR/h and the road had to be closed for a while.
Each test released a plume of dispersed radioactive lanthanum. Three tests in 1950 are documented where the released radioactivity was tracked by a B-17 aircraft carrying the Atmospheric Conductivity Apparatus; in one case radiation was detected over a town 17 miles (27.4 km) downwind. These tests were concurrent with the RaLa tests and their aim was development of airborne detectors for tracking air burst
nuclear tests.
The size and altitude of the radioactive cloud was determined by the quantity of the explosive used. For the first 125 tests between 1944 and 1949, the meteorology and fallout monitoring was rare; between 1950-1954 closer monitoring was phased in and was virtually complete afterwards. One cloud was reportedly tracked as far as 70 miles (112.7 km) downwind, over Watrous
, New Mexico
.
The site had several fixed structures. The lanthanum-140 was being isolated in a radiochemistry building, TA-10-1. The TA-10-21 was the personnel building. There were four firing sites. The instruments for firing the explosives and recording the data were housed in two detonation control buildings (TA-10-13 and TA-10-15).
.
To handle the logistics of the tests, Luis Alvarez
was appointed by Robert Oppenheimer
as the head of the RaLa program; his group was designated E-7, RaLa and Electric Detonators Group. On 15 April 1944, Alvarez outlined the needed items; on 26 April a committee was formed from Hans Bethe
, George Kistiakowsky
, Seth Neddermeyer
, Robert Oppenheimer
, Parratt, Bruno Rossi
, Staub, Edward Teller
, Richard Dodson, Gerhardt Friedlander, Lindsay Helmholtz, David Nicodemus, and Victor Frederick Weisskopf
. Rossi and Staub built the ionization chamber
s and electronics by late spring.
At first the work proceeded at a leisurely pace as the implosion was only a backup project; it was believed that the plutonium
bomb would be of the Thin Man
design. This however turned out to not be the case as first tests on the reactor-produced plutonium in early summer 1944 shown unacceptably high spontaneous fission
rates, precluding use of gun assembly and requiring implosion. On July 17 the Thin Man design was abandoned and all effort was focused to implosion. The Los Alamos laboratory was reorganized—the X-Division (Explosive Division) and the G-Division (Gadget Division, or Weapon Physics Division) were formed. The Rossi's group was assigned to G-Division as G-6, or RaLa Group; the Alvarez's group was G-7, or Electric Detonator Group.
On 25 July 1944 the first preliminary test was fired in the Bayo Canyon as a rehearsal, test of equipment, and measurement of collapse times and detonation and shock wave velocities. The program was however delayed by about a month by late radiobarium shipments, as the test scheduled for 15 August was not conducted until mid-September. The first test with radiobarium was fired on 22 September.
In late August and at the request of Rossi's group, the RaLa group was reformed under the leadership of Bruno Rossi
, and Alvarez and his group took over the exploding bridgewire detonator research.
At the suggestion of Robert Christy
solid spheres instead of the originally intended hollow ones were chosen for the pit, in order to reduce the problems with jets and spalling.
The first solid-sphere RaLa shot was performed in early December but the results were inconclusive. The shot from 14 December though, showed (in the words of Robert Bacher
) "definite evidence of compression".
The first tests using electric detonator
s and solid pits were performed on 7 and 14 February 1945; until then primacord
based initiation was employed. The electric detonators shown a significant improvement in the achieved compression degree and symmetry; they were used on all RaLa tests thereafter. Based on these results, by the end of February the design of The gadget was settled.
Other test methods were also necessary as the RaLa experiments provided only indirect indications about the formation of problematic jets that plagued the early implosion designs. RaLa however was the most important.
Currently several other methods are used for hydrodynamic testing.
of La-140 is 40.224 hours; it undergoes beta decay
to stable cerium-140. It was prepared from barium-140, a common fission product
isolated from the spent fuel from the Oak Ridge National Laboratory
(then known under its code name
X-10) X-10 Graphite Reactor
, and later, since around 1948, also from the Hanford Site
plutonium-239
producing nuclear reactor
s. Barium was isolated in a purpose-built hot laboratory
in Oak Ridge and shipped in a lead pig
to Los Alamos, where it was used to extract lanthanum. The Oak Ridge laboratory was the first laboratory where remote manipulators were used for work with radioactive materials. The delivery was performed by a truck with two person crew, driving 1500 miles (2,414 km) nonstop.
The uranium slugs were irradiated for 40 days, then left to cool down for 1 to 5 days, then dissolved. Barium then was extracted and the solution evaporated; the solid material was then shipped to Los Alamos. As of 1949, full production runs involved up to 1728 slugs (34.5 batches of 50 slugs). Until 1949 the Oak Ridge production site processed uranium slugs irradiated both on-site and at Hanford; afterward only Hanford material was processed.
At first the barium isolation was performed in the building 3026-C (706-C) where an existing laboratory was converted for this purpose in 5 months; the first run was finished in September 1944. The 3026-C was designed for work with sources between 1-10 Ci; however conditions forced it to be adapted to work with 100 Ci sources. The capacity was insufficient, and the demand grew. In May 1945 a dedicated building 3026-D (706-D) adjacent to 3026-C and designed to process sources up to 1000 Ci, was finished; the first run was on May 26, 1945, the same day as the last run in the 3026-C facility.
As of March 1949, 31 shipments averaging over 2000 Ci each were produced there for Los Alamos. The demand continued to grow though and by July 1950 the production goal per shipment was 10,000 Ci, and by early 1950s the requirements went up to 50,000 Ci. By 1954 the shipments went up to 64,805 Ci, and that year the AEC
decided to build a new facility in Idaho National Laboratory
for RaLa production. In October 1956, Oak Ridge completed their 68th RaLa run, the last one. In total, Oak Ridge processed over 30,000 uranium slugs and shipped over 500,000 Ci to Los Alamos.
During preparation of RaLa volatile fission products were released. When dissolved, a batch of 50 slugs produced 2500 Ci of xenon-133, 1300 Ci of iodine-131
(high amounts, as the fuel had to be processed "fresh"), and a small amount of krypton-85
. As few precautions were used for limiting the fission product releases the RaLa production was a major contributor to radioactive contamination at Oak Ridge. The iodine emissions were an important factor in the decision to move the facility to Idaho. Later improvements allowed reducing the iodine emissions to levels about 100 times lower.
A serious accident with radioactivity release occurred in the 3026-D facility at about 5 pm on April 29, 1954. After the dissolution of the third batch of uranium slugs, the liquid in the dissolver tank did not completely cover the slugs for about 29 hours, which overheated due to decay heat
. When the acid was added for the fourth batch, the violent reaction with the hot metal produced gases and forced the solution up the slug loading chute and the pipes. The building staff donned their gas masks and evacuated the building. Radiation levels on the third floor of the building reached 100 R/h, and were reduced to 100 mR/h by 7 am the next day. The highest exposure to a person was 1.25 R of hard radiation
and 4.7 rep of soft radiation
.
Shortly later the process was improved; barium was removed chemically, by double precipitation
from a solution as a barium sulfate
.
The process was improved again, to allow repeated separation of lanthanum from the barium solution, as the lanthanum built up. Initially, a phosphate process was used, where lanthanum was precipitated as lanthanum phosphate. This was later abandoned when an oxalate or hydroxide method was developed; lanthanum was precipitated as lanthanum hydroxide and then converted to a filterable precipitate by addition of oxalate
with a trace of fluoride
. The oxalate method had to be performed quickly, as the oxalate ion was susceptible to radiolysis
and the lanthanum had tendency to go back into solution. The oxalate process could be performed by remotely operated devices. The batches contained about 100 curies of radiolanthanum, the highest radiation levels people ever worked with at that time.
Special tools had to be developed for remote handling of the hot materials. Lead bricks
were used for shielding the sources. The radiation dose limit for the personnel was set to 500 mrem per source preparation. Sometimes this limit was exceeded; once the received dose was 2 rem.
The improved process that separated lanthanum from the barium chloride
solution had the advantage that barium could be "milked" repeatedly, increasing radiolanthanum yield and allowing more experiments. The problems with radioactive contamination with barium-140, with half-time of 12.5 days, were eliminated; the amount of contaminating strontium-90 was also significantly reduced. Use of purified lanthanum also allowed usage of much smaller amount of material in the tests themselves. Semiautomatic equipment for "lanthanum milking" (the barium-140 isotope was nicknamed a "cow") was built in a sufficiently distant area, which avoided time-consuming construction of a heavily shielded building. Early on, the process however hit a snag when impurities of iron and other metals, probably introduced from an irradiated shipping container, were found to impair the lanthanum phosphate precipitation by forming phosphate gels that clogged filters. This problem was solved with better shipping containers.
A similar "milking" process is used for preparation of technetium-99m
, used in nuclear medicine
, from molybdenum-99 "cow" in technetium-99m generator
s.
The separation process was performed in a dedicated facility in the Bayo Canyon, in the radiochemistry building, designated TA-10-1. The separated lanthanum was then shipped to the test site in a lead cask
on the back of a truck. In 1951, the separation work was moved to TA-35.
The tests were performed in a month-long series, as the barium source decayed and was periodically "milked" for lanthanum.
s, each using five gallons of a liquid scintillator
. The flashes from 100 gallons of burning scintillator were remarkably brilliant in the early morning times when the tests were usually performed.
After 1962 the RaLa tests were replaced by more advanced methods.
, can have long enough half-life to present a potential problem even decades after the tests; in 2002 the Los Alamos National Laboratory issued a warning to the Los Alamos county and the Forest Service
performing thinning
of trees in the area to not remove the trees cut in various parts of the Bayo Canyon due to possible content of residual radioactive materials. Five attempts for decontamination were performed between 1964–1976; much of the area ended up having to be covered over. The worst affected zones are fenced off; detectable levels of radioisotopes are present in the soil, insects and trees in the surrounding areas. The neighbouring population was not informed about the tests until mid-1990s. Los Alamos refused to declassify the documentation.
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...
designed to study the behavior of converging shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
s to achieve the spherical implosion necessary for compression of the plutonium pit of the nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
. The experiment used significant amounts of a short-lived radioisotope lanthanum-140, a potent source of gamma radiation; the RaLa is a contraction of Radioactive Lanthanum. The method was proposed by Robert Serber
Robert Serber
Robert Serber was an American physicist who participated in the Manhattan Project. He was born in Philadelphia, Pennsylvania; he was the eldest son of David Serber and Rose Frankel. He married Charlotte Leof in 1933. Rose Serber died in 1922; David married Charlotte's cousin Frances Leof in...
and developed by the team of Bruno Rossi
Bruno Rossi
Bruno Benedetto Rossi was a leading Italian-American experimental physicist. He made major contributions to cosmic ray and particle physics from 1930 through the 1950s, and pioneered X-ray astronomy and space plasma physics in the 1960s.-Biography:Rossi was born in Venice, Italy...
.
The tests were performed with 1/8 inch spheres of radioactive lanthanum, equal to about 100 curie
Curie
The curie is a unit of radioactivity, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit,...
and later 1000 Ci, located in the center of a simulated nuclear device. Their outcomes are said to be "the most important single experiment affecting the final bomb design". The explosive lens
Explosive lens
An explosive lens—as used, for example, in nuclear weapons—is a highly specialized explosive charge, a special type of a shaped charge. In general, it is a device composed of several explosive charges that are shaped in such a way as to change the shape of the detonation wave passing through it,...
es were designed primarily using this series of tests.
254 tests were conducted between September 1944 and March 1962.
Experimental setup
The idea behind the experiment was about measuring the spatial and temporal symmetry of explosive compression of a metal sphere. The test measured changes of absorption of gamma rayGamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s in the metal of the sphere as it underwent compression. The gamma ray source was located in the center of a metal sphere. The increase of thickness (of hollow shells) and density (of solid spheres) as the compression progressed was detected as a decrease of intensity of gamma rays outside of the sphere; the lower density explosives did not absorb gamma radiation enough to interfere with the experiment. The gamma rays had to be intense and of the right energy. Too low energy, and they are fully absorbed in the surrounding metal; too high energy and the difference of attenuation during the implosion is too low to be practical. The detectors had to provide high speed and large area; fast ionization chamber
Ionization chamber
The ionization chamber is the simplest of all gas-filled radiation detectors, and is used for the detection or measurement of ionizing radiation...
s, then under development, were the only devices then available satisfying the requirements.
Lanthanum-140 was chosen for having the right emitted gamma ray energy (1.60 MeV, with fraction of 0.49 MeV), a suitable half-life (as it cleaned itself up from the environment) and a sufficient radiation intensity; a high-intensity source was required to provide satisfying signal from the ionization chambers. It was also potentially available in larger quantities because barium-140 (its precursor) was an abundant fission product. It was however contaminated with barium-140, caesium-140, and especially strontium-90
Strontium-90
Strontium-90 is a radioactive isotope of strontium, with a half-life of 28.8 years.-Radioactivity:Natural strontium is nonradioactive and nontoxic, but 90Sr is a radioactivity hazard...
; the latter still presents a potential problem in the area of the tests. Lanthanum-140 has specific activity
Specific activity
In nuclear sciences and technologies, "activity" is the SI quantity related to the phenomenon of natural and artificial radioactivity. The SI unit of "activity" is becquerel, Bq, while that of "specific activity" is Bq/kg. The old unit of "activity" was curie, Ci, while that of "specific activity"...
of 5.57×105 Ci/g; a 1000 Ci La-140 source therefore equals about 1.8 mg of lanthanum.
A radiolanthanum sample, precipitated in a tip of a small cone, followed by a plug, was lowered into the center of the metal sphere of the experimental assembly with a device resembling a fishing rod
Fishing rod
A fishing rod or a fishing pole is a tool used to catch fish, usually in conjunction with the pastime of angling, and can also be used in competition casting. . A length of fishing line is attached to a long, flexible rod or pole: one end terminates in a hook for catching the fish...
. The cone and the plug were mated to the metal center of the assembly, together forming a metal sphere. A section of the explosive lensing was then returned to its place above the sphere. Several, typically four, ionization chamber
Ionization chamber
The ionization chamber is the simplest of all gas-filled radiation detectors, and is used for the detection or measurement of ionizing radiation...
s were located around the experimental setup. Immediately after the detonation they generated signals that were displayed on oscilloscope
Oscilloscope
An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional graph of one or more electrical potential differences using the vertical or 'Y' axis, plotted as a function of time,...
s in a blast-proof shelter or a mobile laboratory in a tank, 150 feet (45.7 m) away, and the oscilloscope traces recorded on camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
s. A calibration measurement was performed before and after each test. The ionization chambers and their preamplifier
Preamplifier
A preamplifier is an electronic amplifier that prepares a small electrical signal for further amplification or processing. A preamplifier is often placed close to the sensor to reduce the effects of noise and interference. It is used to boost the signal strength to drive the cable to the main...
s were destroyed during the explosion, but their simple design allowed their production in sufficient quantities.
The ionization chambers were cylindrical, 2 inches in diameter, 30 inches long, with a wire along the longitudal axis. They were filled with a mixture of argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
at 4.5 atmospheres. Eight chambers were arranged in a tray and connected in parallel; four trays were located in a tetrahedron
Tetrahedron
In geometry, a tetrahedron is a polyhedron composed of four triangular faces, three of which meet at each vertex. A regular tetrahedron is one in which the four triangles are regular, or "equilateral", and is one of the Platonic solids...
around the experimental assembly, recording the gamma radiation around the sphere, sufficiently close to give a signal and sufficiently far away to not be destroyed by the blast before they can record the required information.
The initiation of the explosives was initially performed by a multipoint Primacord
Primacord
Primacord is a registered trademark of detonating cord used in blasting, originally manufactured by the Ensign-Bickford Company. Ensign Bickford sold the trademark to Dyno Nobel Inc in 2003 and it is now manufactured in Graham, Kentucky...
system. The results were however erratic, as the detonations weren't sufficiently synchronized. Much better results were obtained since February 1945, when exploding-bridgewire detonator
Exploding-bridgewire detonator
The exploding-bridgewire detonator is a type of detonator used to initiate the detonation reaction in explosive materials, similar to a blasting cap in that it is fired using an electric current...
s, developed by the Luis Alvarez
Luis Alvarez
Luis W. Alvarez was an American experimental physicist and inventor, who spent nearly all of his long professional career on the faculty of the University of California, Berkeley...
's G-7 group, became available.
As plutonium was not available, it was substituted with material with similar mechanical properties. Depleted uranium
Depleted uranium
Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...
was used but was not optimal because of its opacity for radiation; iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, or cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
were other choices. Cadmium was the choice for most of the tests. The first shot was performed with an iron mockup of the plutonium pit. Hollow shells were initially used, but a more robust approach with solid spheres was employed later.
The resulting signal was a fast dip, corresponding to the compression of the cadmium sphere, followed by slower increase, corresponding to the decompression and following dispersal of the sphere and the lanthanum. The differences between the four traces on the oscilloscope display, each indicating the average compression in the direction of the detector, allowed the assessment of the required synchronization accuracy for the detonators.
The RaLa sources were very radioactive. They had to be lowered to the test apparatus by a 10 feet (3 m) long rod. The tests were initially observed from a sealed military tank
Tank
A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...
; the mobile laboratory consisted of two M4 Sherman
M4 Sherman
The M4 Sherman, formally Medium Tank, M4, was the primary tank used by the United States during World War II. Thousands were also distributed to the Allies, including the British Commonwealth and Soviet armies, via lend-lease...
tanks. Each experiment was supposed to contaminate an area of about 3000 square meters for about a half year. When radiobarium was removed from the radiolanthanum, however, the short term contamination levels turned out to be insignificant. Tanks were then replaced with fixed shelters. One of the tanks was later lead-plated, sealed, equipped with self-contained air supply, and used for sampling of fission products in the post-blast debris after the Trinity test
Trinity test
Trinity was the code name of the first test of a nuclear weapon. This test was conducted by the United States Army on July 16, 1945, in the Jornada del Muerto desert about 35 miles southeast of Socorro, New Mexico, at the new White Sands Proving Ground, which incorporated the Alamogordo Bombing...
. The sources posed a considerable radiation exposure risk; the exposure rate of a 1000 Ci source at 1 meter was 1,130 R/h and 11,000 R/h at 1 foot (0.3048 m). Sources with activity up to 2,300 Ci were used in some tests.
Radiation safety
The system for remote handling of the samples had flaws; it took about six months to catch them all. The chemists, who operated on mixtures of fission products with batches reaching up to 2300 curie each, were frequently exposed (accidentally) to undesirably high doses of radiation. The group handling the experiments themselves was less at risk; they operated in close coordination with the Health Group, who was in charge of ensuring that radiation exposure of the people involved was survivable.The radioactive contamination posed a problem. The people working in the Bayo Canyon had to change their clothes and take showers after the work. Sometimes they would still trip detectors at security gates.
The tests were performed in a relatively isolated area in the Bayo Canyon, then called Technical area 10, in Los Alamos County. Large amounts of radioactive lanthanum were dispersed by the explosions; 254 tests were performed between 1944 and 1961. In 1948 two workers received radiation burn
Radiation burn
A radiation burn is damage to the skin or other biological tissue caused by exposure to radio frequency energy or ionizing radiation.The most common type of radiation burn is a sunburn caused by UV radiation. High exposure to X-rays during diagnostic medical imaging or radiotherapy can also result...
s there. The experiments were generally performed when the wind blew to the north, but occasionally the wind would change direction in the early morning. In 1949 and 1950 the fallout
Fallout
Fallout or nuclear fallout is the residual radiation hazard from a nuclear explosion.Fallout may also refer to:*Fallout , a 1997 post-apocalyptic computer role-playing game released by Interplay Entertainment...
from the tests was blown over parts of the housing area and a road; the radiation levels on the road occasionally reached 5-10 mR/h and the road had to be closed for a while.
Each test released a plume of dispersed radioactive lanthanum. Three tests in 1950 are documented where the released radioactivity was tracked by a B-17 aircraft carrying the Atmospheric Conductivity Apparatus; in one case radiation was detected over a town 17 miles (27.4 km) downwind. These tests were concurrent with the RaLa tests and their aim was development of airborne detectors for tracking air burst
Air burst
An air burst is the detonation of an explosive device such as an anti-personnel artillery shell or a nuclear weapon in the air instead of on contact with the ground or target or a delayed armor piercing explosion....
nuclear tests.
The size and altitude of the radioactive cloud was determined by the quantity of the explosive used. For the first 125 tests between 1944 and 1949, the meteorology and fallout monitoring was rare; between 1950-1954 closer monitoring was phased in and was virtually complete afterwards. One cloud was reportedly tracked as far as 70 miles (112.7 km) downwind, over Watrous
Watrous (La Junta)
Watrous, also named La Junta, is a historic district in New Mexico.The National Park Service's Statement of Significance for the site was:Trail ruts remain, and the district includes 21 structures:...
, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
.
Bayo Canyon Site
The experiments were performed in the Bayo Canyon in a location designated TA-10 ("Technical Area 10") (but more commonly referred to as the Bayo Canyon Site) in Los Alamos County and close to the border with Santa Fe County, northeast from the Los Alamos townsite.The site had several fixed structures. The lanthanum-140 was being isolated in a radiochemistry building, TA-10-1. The TA-10-21 was the personnel building. There were four firing sites. The instruments for firing the explosives and recording the data were housed in two detonation control buildings (TA-10-13 and TA-10-15).
Logistics and schedule
The experiment was suggested on 1 November 1943 by Robert SerberRobert Serber
Robert Serber was an American physicist who participated in the Manhattan Project. He was born in Philadelphia, Pennsylvania; he was the eldest son of David Serber and Rose Frankel. He married Charlotte Leof in 1933. Rose Serber died in 1922; David married Charlotte's cousin Frances Leof in...
.
To handle the logistics of the tests, Luis Alvarez
Luis Alvarez
Luis W. Alvarez was an American experimental physicist and inventor, who spent nearly all of his long professional career on the faculty of the University of California, Berkeley...
was appointed by Robert Oppenheimer
Robert Oppenheimer
Julius Robert Oppenheimer was an American theoretical physicist and professor of physics at the University of California, Berkeley. Along with Enrico Fermi, he is often called the "father of the atomic bomb" for his role in the Manhattan Project, the World War II project that developed the first...
as the head of the RaLa program; his group was designated E-7, RaLa and Electric Detonators Group. On 15 April 1944, Alvarez outlined the needed items; on 26 April a committee was formed from Hans Bethe
Hans Bethe
Hans Albrecht Bethe was a German-American nuclear physicist, and Nobel laureate in physics for his work on the theory of stellar nucleosynthesis. A versatile theoretical physicist, Bethe also made important contributions to quantum electrodynamics, nuclear physics, solid-state physics and...
, George Kistiakowsky
George Kistiakowsky
George Bogdan Kistiakowsky was a Ukrainian-American chemistry professor at Harvard who participated in the Manhattan Project and later served as President Eisenhower's Science Advisor...
, Seth Neddermeyer
Seth Neddermeyer
Seth Henry Neddermeyer was an American physicist who co-discovered the muon, and later championed the implosion design of the plutonium atomic bomb, at the Manhattan Project....
, Robert Oppenheimer
Robert Oppenheimer
Julius Robert Oppenheimer was an American theoretical physicist and professor of physics at the University of California, Berkeley. Along with Enrico Fermi, he is often called the "father of the atomic bomb" for his role in the Manhattan Project, the World War II project that developed the first...
, Parratt, Bruno Rossi
Bruno Rossi
Bruno Benedetto Rossi was a leading Italian-American experimental physicist. He made major contributions to cosmic ray and particle physics from 1930 through the 1950s, and pioneered X-ray astronomy and space plasma physics in the 1960s.-Biography:Rossi was born in Venice, Italy...
, Staub, Edward Teller
Edward Teller
Edward Teller was a Hungarian-American theoretical physicist, known colloquially as "the father of the hydrogen bomb," even though he did not care for the title. Teller made numerous contributions to nuclear and molecular physics, spectroscopy , and surface physics...
, Richard Dodson, Gerhardt Friedlander, Lindsay Helmholtz, David Nicodemus, and Victor Frederick Weisskopf
Victor Frederick Weisskopf
Victor Frederick Weisskopf was an Austrian-born Jewish American theoretical physicist. He did postdoctoral work with Werner Heisenberg, Erwin Schrödinger, Wolfgang Pauli and Niels Bohr...
. Rossi and Staub built the ionization chamber
Ionization chamber
The ionization chamber is the simplest of all gas-filled radiation detectors, and is used for the detection or measurement of ionizing radiation...
s and electronics by late spring.
At first the work proceeded at a leisurely pace as the implosion was only a backup project; it was believed that the plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
bomb would be of the Thin Man
Thin Man nuclear bomb
The "Thin Man" nuclear bomb was a proposed plutonium gun-type nuclear bomb which the United States was developing during the Manhattan Project...
design. This however turned out to not be the case as first tests on the reactor-produced plutonium in early summer 1944 shown unacceptably high spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
rates, precluding use of gun assembly and requiring implosion. On July 17 the Thin Man design was abandoned and all effort was focused to implosion. The Los Alamos laboratory was reorganized—the X-Division (Explosive Division) and the G-Division (Gadget Division, or Weapon Physics Division) were formed. The Rossi's group was assigned to G-Division as G-6, or RaLa Group; the Alvarez's group was G-7, or Electric Detonator Group.
On 25 July 1944 the first preliminary test was fired in the Bayo Canyon as a rehearsal, test of equipment, and measurement of collapse times and detonation and shock wave velocities. The program was however delayed by about a month by late radiobarium shipments, as the test scheduled for 15 August was not conducted until mid-September. The first test with radiobarium was fired on 22 September.
In late August and at the request of Rossi's group, the RaLa group was reformed under the leadership of Bruno Rossi
Bruno Rossi
Bruno Benedetto Rossi was a leading Italian-American experimental physicist. He made major contributions to cosmic ray and particle physics from 1930 through the 1950s, and pioneered X-ray astronomy and space plasma physics in the 1960s.-Biography:Rossi was born in Venice, Italy...
, and Alvarez and his group took over the exploding bridgewire detonator research.
At the suggestion of Robert Christy
Robert Christy
Robert F. Christy is an American theoretical physicist and later astrophysicist who worked on the Manhattan Project. He was also briefly president of Caltech....
solid spheres instead of the originally intended hollow ones were chosen for the pit, in order to reduce the problems with jets and spalling.
The first solid-sphere RaLa shot was performed in early December but the results were inconclusive. The shot from 14 December though, showed (in the words of Robert Bacher
Robert Bacher
Robert Fox Bacher was an American nuclear physicist and one of the leaders of the Manhattan Project.-Early life and career:...
) "definite evidence of compression".
The first tests using electric detonator
Detonator
A detonator is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the latter two being the most common....
s and solid pits were performed on 7 and 14 February 1945; until then primacord
Primacord
Primacord is a registered trademark of detonating cord used in blasting, originally manufactured by the Ensign-Bickford Company. Ensign Bickford sold the trademark to Dyno Nobel Inc in 2003 and it is now manufactured in Graham, Kentucky...
based initiation was employed. The electric detonators shown a significant improvement in the achieved compression degree and symmetry; they were used on all RaLa tests thereafter. Based on these results, by the end of February the design of The gadget was settled.
Other test methods were also necessary as the RaLa experiments provided only indirect indications about the formation of problematic jets that plagued the early implosion designs. RaLa however was the most important.
Currently several other methods are used for hydrodynamic testing.
Barium-lanthanum preparation
The half-lifeHalf-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of La-140 is 40.224 hours; it undergoes beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
to stable cerium-140. It was prepared from barium-140, a common fission product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...
isolated from the spent fuel from the Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...
(then known under its code name
Code name
A code name or cryptonym is a word or name used clandestinely to refer to another name or word. Code names are often used for military purposes, or in espionage...
X-10) X-10 Graphite Reactor
X-10 Graphite Reactor
The X-10 Graphite Reactor at Oak Ridge National Laboratory in Oak Ridge, Tennessee, formerly known as the Clinton Pile and X-10 Pile, was the world's second artificial nuclear reactor and was the first reactor designed and built for continuous operation.When President Roosevelt in December 1942...
, and later, since around 1948, also from the Hanford Site
Hanford Site
The Hanford Site is a mostly decommissioned nuclear production complex on the Columbia River in the U.S. state of Washington, operated by the United States federal government. The site has been known by many names, including Hanford Works, Hanford Engineer Works or HEW, Hanford Nuclear Reservation...
plutonium-239
Plutonium-239
Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and is currently the secondary isotope. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in...
producing nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s. Barium was isolated in a purpose-built hot laboratory
Hot cell
Shielded nuclear radiation containment chambers are commonly referred to as hot cells. The word "hot" refers to radioactivity.Hot cells are used in both the nuclear-energy and the nuclear-medicines industries....
in Oak Ridge and shipped in a lead pig
Lead shielding
Lead shielding refers to the use of lead as a form of radiation protection to shield people or objects from radiation. Lead can effectively attenuate certain kinds of radiation because of its high density and high atomic number; principally, it is effective at stopping alpha rays, gamma rays, and...
to Los Alamos, where it was used to extract lanthanum. The Oak Ridge laboratory was the first laboratory where remote manipulators were used for work with radioactive materials. The delivery was performed by a truck with two person crew, driving 1500 miles (2,414 km) nonstop.
The uranium slugs were irradiated for 40 days, then left to cool down for 1 to 5 days, then dissolved. Barium then was extracted and the solution evaporated; the solid material was then shipped to Los Alamos. As of 1949, full production runs involved up to 1728 slugs (34.5 batches of 50 slugs). Until 1949 the Oak Ridge production site processed uranium slugs irradiated both on-site and at Hanford; afterward only Hanford material was processed.
At first the barium isolation was performed in the building 3026-C (706-C) where an existing laboratory was converted for this purpose in 5 months; the first run was finished in September 1944. The 3026-C was designed for work with sources between 1-10 Ci; however conditions forced it to be adapted to work with 100 Ci sources. The capacity was insufficient, and the demand grew. In May 1945 a dedicated building 3026-D (706-D) adjacent to 3026-C and designed to process sources up to 1000 Ci, was finished; the first run was on May 26, 1945, the same day as the last run in the 3026-C facility.
As of March 1949, 31 shipments averaging over 2000 Ci each were produced there for Los Alamos. The demand continued to grow though and by July 1950 the production goal per shipment was 10,000 Ci, and by early 1950s the requirements went up to 50,000 Ci. By 1954 the shipments went up to 64,805 Ci, and that year the AEC
United States Atomic Energy Commission
The United States Atomic Energy Commission was an agency of the United States government established after World War II by Congress to foster and control the peace time development of atomic science and technology. President Harry S...
decided to build a new facility in Idaho National Laboratory
Idaho National Laboratory
Idaho National Laboratory is an complex located in the high desert of eastern Idaho, between the town of Arco to the west and the cities of Idaho Falls and Blackfoot to the east. It lies within Butte, Bingham, Bonneville and Jefferson counties...
for RaLa production. In October 1956, Oak Ridge completed their 68th RaLa run, the last one. In total, Oak Ridge processed over 30,000 uranium slugs and shipped over 500,000 Ci to Los Alamos.
During preparation of RaLa volatile fission products were released. When dissolved, a batch of 50 slugs produced 2500 Ci of xenon-133, 1300 Ci of iodine-131
Iodine-131
Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical...
(high amounts, as the fuel had to be processed "fresh"), and a small amount of krypton-85
Krypton-85
Krypton 85 is a radioisotope of krypton.It decays into rubidium-85, with a half-life of 10.756 years and a maximum decay energy of 0.687 MeV.Its most common decay is by beta particle emission with maximum energy of 687...
. As few precautions were used for limiting the fission product releases the RaLa production was a major contributor to radioactive contamination at Oak Ridge. The iodine emissions were an important factor in the decision to move the facility to Idaho. Later improvements allowed reducing the iodine emissions to levels about 100 times lower.
A serious accident with radioactivity release occurred in the 3026-D facility at about 5 pm on April 29, 1954. After the dissolution of the third batch of uranium slugs, the liquid in the dissolver tank did not completely cover the slugs for about 29 hours, which overheated due to decay heat
Decay heat
Decay heat is the heat released as a result of radioactive decay. This is when the radiation interacts with materials: the energy of the alpha, beta or gamma radiation is converted into the thermal movement of atoms.-Natural occurrence:...
. When the acid was added for the fourth batch, the violent reaction with the hot metal produced gases and forced the solution up the slug loading chute and the pipes. The building staff donned their gas masks and evacuated the building. Radiation levels on the third floor of the building reached 100 R/h, and were reduced to 100 mR/h by 7 am the next day. The highest exposure to a person was 1.25 R of hard radiation
Hard radiation
Hard radiation is a term used to describe high-energy electromagnetic radiation, typically high energy X-rays or gamma rays. The term refers to the ability of the rays to penetrate a given thickness of material, typically a lead shield....
and 4.7 rep of soft radiation
Soft radiation
Soft radiation is a term used to describe high-energy electromagnetic radiation, typically high energy X-rays or gamma rays. The term refers to the ability of the rays to penetrate a given thickness of material, typically a lead shield....
.
Lanthanum preparation
After delivery of the barium-lanthanum material to Los Alamos, it was stored in a dedicated building in the Bayo Canyon Site. At first, the mixture was used as-is, both barium and lanthanum together. This however led to unpleasant radioactive contamination that took long time to disappear, due to the 12.5 days of half-life of barium-140.Shortly later the process was improved; barium was removed chemically, by double precipitation
Precipitation (chemistry)
Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...
from a solution as a barium sulfate
Barium sulfate
Barium sulfate is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and materials prepared from it...
.
The process was improved again, to allow repeated separation of lanthanum from the barium solution, as the lanthanum built up. Initially, a phosphate process was used, where lanthanum was precipitated as lanthanum phosphate. This was later abandoned when an oxalate or hydroxide method was developed; lanthanum was precipitated as lanthanum hydroxide and then converted to a filterable precipitate by addition of oxalate
Oxalate
Oxalate , is the dianion with formula C2O42− also written 22−. Either name is often used for derivatives, such as disodium oxalate, 2C2O42−, or an ester of oxalic acid Oxalate (IUPAC: ethanedioate), is the dianion with formula C2O42− also written (COO)22−. Either...
with a trace of fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
. The oxalate method had to be performed quickly, as the oxalate ion was susceptible to radiolysis
Radiolysis
Radiolysis is the dissociation of molecules by nuclear radiation. It is the cleavage of one or several chemical bonds resulting from exposure to high-energy flux...
and the lanthanum had tendency to go back into solution. The oxalate process could be performed by remotely operated devices. The batches contained about 100 curies of radiolanthanum, the highest radiation levels people ever worked with at that time.
Special tools had to be developed for remote handling of the hot materials. Lead bricks
Lead castle
A lead castle, also called a lead cave or a lead housing, is a structure composed of bricks made of lead. Lead castles are a type of lead shielding and are used to enclose small radioactive sources and/or radiation detectors. They are used during nuclear research and testing...
were used for shielding the sources. The radiation dose limit for the personnel was set to 500 mrem per source preparation. Sometimes this limit was exceeded; once the received dose was 2 rem.
The improved process that separated lanthanum from the barium chloride
Barium chloride
Barium chloride is the inorganic compound with the formula BaCl2. It is one of the most common water-soluble salts of barium. Like other barium salts, it is toxic and imparts a yellow-green coloration to a flame. It is also hygroscopic....
solution had the advantage that barium could be "milked" repeatedly, increasing radiolanthanum yield and allowing more experiments. The problems with radioactive contamination with barium-140, with half-time of 12.5 days, were eliminated; the amount of contaminating strontium-90 was also significantly reduced. Use of purified lanthanum also allowed usage of much smaller amount of material in the tests themselves. Semiautomatic equipment for "lanthanum milking" (the barium-140 isotope was nicknamed a "cow") was built in a sufficiently distant area, which avoided time-consuming construction of a heavily shielded building. Early on, the process however hit a snag when impurities of iron and other metals, probably introduced from an irradiated shipping container, were found to impair the lanthanum phosphate precipitation by forming phosphate gels that clogged filters. This problem was solved with better shipping containers.
A similar "milking" process is used for preparation of technetium-99m
Technetium-99m
Technetium-99m is a metastable nuclear isomer of technetium-99, symbolized as 99mTc. The "m" indicates that this is a metastable nuclear isomer, i.e., that its half-life of 6 hours is considerably longer than most nuclear isomers that undergo gamma decay...
, used in nuclear medicine
Nuclear medicine
In nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
, from molybdenum-99 "cow" in technetium-99m generator
Technetium-99m generator
A technetium-99m generator, or colloquially a technetium cow or moly cow, is a device used to extract the metastable isotope 99mTc of technetium from a source of decaying molybdenum-99...
s.
The separation process was performed in a dedicated facility in the Bayo Canyon, in the radiochemistry building, designated TA-10-1. The separated lanthanum was then shipped to the test site in a lead cask
CASK
Peripheral plasma membrane protein CASK is a protein that in humans is encoded by the CASK gene. This gene is also known by several other names: CMG 2 , calcium/calmodulin-dependent serine protein kinase 3 and membrane-associated guanylate kinase 2.-Genomics:This gene is located on the short arm of...
on the back of a truck. In 1951, the separation work was moved to TA-35.
The tests were performed in a month-long series, as the barium source decayed and was periodically "milked" for lanthanum.
Post-war progress
RaLa tests continued even after the war, until 1962. The technology was improving. By 1951 the four ionization chambers were replaced by twenty scintillation counterScintillation counter
A scintillation counter measures ionizing radiation. The sensor, called a scintillator, consists of a transparent crystal, usually phosphor, plastic , or organic liquid that fluoresces when struck by ionizing radiation. A sensitive photomultiplier tube measures the light from the crystal...
s, each using five gallons of a liquid scintillator
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
. The flashes from 100 gallons of burning scintillator were remarkably brilliant in the early morning times when the tests were usually performed.
After 1962 the RaLa tests were replaced by more advanced methods.
Long-term contamination
Lanthanum-140 has a short half-life and is not a threat after a fairly short time. Other radioisotopes, present as impuritiesImpurity
Impurities are substances inside a confined amount of liquid, gas, or solid, which differ from the chemical composition of the material or compound.Impurities are either naturally occurring or added during synthesis of a chemical or commercial product...
, can have long enough half-life to present a potential problem even decades after the tests; in 2002 the Los Alamos National Laboratory issued a warning to the Los Alamos county and the Forest Service
United States Forest Service
The United States Forest Service is an agency of the United States Department of Agriculture that administers the nation's 155 national forests and 20 national grasslands, which encompass...
performing thinning
Thinning
Thinning is a term used in agricultural sciences to mean the removal of some plants, or parts of plants, to make room for the growth of others.- Forestry :...
of trees in the area to not remove the trees cut in various parts of the Bayo Canyon due to possible content of residual radioactive materials. Five attempts for decontamination were performed between 1964–1976; much of the area ended up having to be covered over. The worst affected zones are fenced off; detectable levels of radioisotopes are present in the soil, insects and trees in the surrounding areas. The neighbouring population was not informed about the tests until mid-1990s. Los Alamos refused to declassify the documentation.