H2 and Cl2 production in the radiolysis of calcium and magnesium chlorides and hydroxides

Article abstract of DOI:10.1021/jp044166o

The production of H₂ has been examined in the γ-ray and 5 MeV He ion radiolysis of CaCl₂·2H₂O, CaCl ₂· 6H₂O, Ca(OH)₂, MgCl ₂·2H₂O, MgCl₂·6H₂O, and Mg(OH)₂. The highest yield for the formation of H₂ is observed in the γ-radiolysis of MgCl₂·2H₂O (0.72 molecule/(100 eV), 75 nmol/J), but the yield decreases with dose due to the relative instability of the dihydrate. The H₂ yields with the other compounds range from 0.04 to 0.2 molecule/(100 eV) (4.2-21 nmol/J), which is lower than that from pure water or 2 M chloride solutions. There appears to be no relationship between the results for H₂ from waters of hydration with that from aqueous salt brines. No particular trend is observed in the radiation chemical yields of H₂ with respect to the cation or the degree of hydration. The production of Cl₂ is found only in the γ-radiolysis of CaCl₂ with a few weight percent of excess water. No Cl₂ was found in the 5 MeV He ion radiolysis of identical systems. None of the other compounds examined here showed detectable amounts of Cl₂ formation.

Full text of DOI:10.1021/jp044166o

J. Phys. Chem. A 2005, 109, 2861-2865
2861
H2 and Cl2 Production in the Radiolysis of Calcium and Magnesium Chlorides and
Hydroxides
Jay A. LaVerne*,† and Lav Tandon‡
Radiation Laboratory and Department of Physics, UniVersity of Notre Dame, Notre Dame, Indiana 46556, and
Chemistry DiVision, Los Alamos, National Laboratory, Los Alamos, New Mexico 87545
ReceiVed: December 22, 2004; In Final Form: February 1, 2005
The production of H2 has been examined in the γ-ray and 5 MeV He ion radiolysis of CaCl2‚2H2O, CaCl2‚
6H2O, Ca(OH)2, MgCl2‚2H2O, MgCl2‚6H2O, and Mg(OH)2. The highest yield for the formation of H2 is
observed in the γ-radiolysis of MgCl2‚2H2O (0.72 molecule/(100 eV), 75 nmol/J), but the yield decreases
with dose due to the relative instability of the dihydrate. The H2 yields with the other compounds range from
0.04 to 0.2 molecule/(100 eV) (4.2-21 nmol/J), which is lower than that from pure water or 2 M chloride
solutions. There appears to be no relationship between the results for H2 from waters of hydration with that
from aqueous salt brines. No particular trend is observed in the radiation chemical yields of H2 with respect
to the cation or the degree of hydration. The production of Cl2 is found only in the γ-radiolysis of CaCl2 with
a few weight percent of excess water. No Cl2 was found in the 5 MeV He ion radiolysis of identical systems.
None of the other compounds examined here showed detectable amounts of Cl2 formation.
Introduction
F centers are formed when electrons produced by the irradiation
are trapped in chloride vacancies.23 Less than 0.1% of electrons
Very little information exists on the nature of the stable
chemical products produced by the passage of ionizing radiation
in solid chloride salts despite the importance of these materials
in the storage of radioactive materials. Solid-state radiolytic
effects such as the production of F, H, or V centers have long
been examined in a number of chloride salts, especially NaCl.1,2
A variety of studies have also been performed on salt brines,
but as shown later there is very little relationship between the
radiation chemistry of brine and a solid salt.3-15 Pyrochemical
processing of plutonium in chloride salt media has been
proceeding for many decades. Significant amounts of plutonium-
containing materials have accumulated that are often associated
with large quantities of potassium, sodium, magnesium, and
calcium chloride salts.16-18 Salt content can be from about 8 to
20 wt %, depending on the degree of calcination. Self-radiolysis
of radioactive processed material in storage can lead to the
production of H2 from moisture, which is an important explosion
hazard, and Cl2, which can be converted to HCl giving a
corrosion potential. Chloride attack on metal storage containers
is well-documented.19-22 The production of gaseous products
such as H2 and Cl2 is especially important in the storage of
processed nuclear materials such as plutonium, which must be
stabilized, packaged, and stored for up to 50 years in sealed
containers.18 This issue will also be important for the storage
of nuclear waste in geologic salt repositories such as the Waste
Isolation Pilot Plant (WIPP), USA, and Gorleben, Germany.
The solid-state effects due to the radiolysis of sodium chloride
have been fairly well-characterized, and similar results are
expected in the magnesium and calcium chlorides. The main
effects of concern to the radiolytic formation of H2 and Cl2 are
the formation of centers (F, V, and H, etc.); generation and
trapping of elemental chlorine in the salt; storage and release
of energy; and saturation and annealing effects.1,2 Highly colored
are expected to be trapped in this manner.24 F centers are thought
to be the source of H2 observed on dissolving NaCl in water
following irradiation.25,26 Hydrated electrons, a potential source
of H2, have also been observed when irradiated NaCl is
dissolved in water.27 H2 production following salt solvation is
accomplished by the transfer of an energetic species from the
solid salt to the water. Similar processes may occur when water
is associated with the chloride as in the case of waters of
hydration.
H centers are formed when electrons are stripped from the
chloride anions to give radicals that then diffuse to form
molecular chlorine anions trapped at interstitial sites.2 Several
studies have tried to measure Cl2 production because of its
immense corrosive potential. Minute amounts of Cl2 has been
detected in the radiolysis of NaCl to very high (>107 Gy)
doses.28 Other studies irradiated NaCl or MgCl2‚6H2O to 7
MGy, dissolved them in water, and searched for hypochlorite.29
Cl2 formation was suggested, but no accurate quantitative
measurements were made. Monitoring the headspace with a
mass spectrometer during the radiolysis of solid NaCl again
suggested the presence of Cl2, but without quantitative measure-
ment.30 Cl2- was observed in radiolysis of concentrated MgCl2
aqueous solutions.31 No consensus on the formation or yield of
Cl2 in the radiolysis of solid chloride salts has emerged. On the
other hand, excellent spectroscopic studies have been performed
recently on various chlorine species following the radiolysis of
aqueous solutions of NaCl, MgCl2, and multicomponent
brines.15,32 The formation of chlorine species may lead to the
oxidiation of actinide species (Pu, Am, Cm, Np, and U) to higher
oxidation states if they are present.10,33
In this work, the formation of gaseous H2 from the radiolysis
of CaCl2‚2H2O, CaCl2‚6H2O, MgCl2‚2H2O, and MgCl2‚6H2O
was examined. Cl2 formation from the hydrated, anhydrous, and
wet calcium and magnesium chlorides was also examined. The
irradiations were performed with both γ-rays and 5 MeV helium
† University of Notre Dame.
‡ Los Alamos National Laboratory.
10.1021/jp044166o CCC: $30.25 © 2005 American Chemical Society
Published on Web 03/03/2005

2862 J. Phys. Chem. A, Vol. 109, No. 12, 2005
LaVerne and Tandon
ions (R-particles) in order to examine the effect due to the linear
energy transfer (LET ) stopping power, -dE/dx) of the
radiation and to mimic the conditions in mixed storage with
high concentration of γ-emitting actinides (Am, Np, etc.) along
with R-emitting actinides such as Pu, Am, and U, etc. Calcina-
tion of the chlorides is expected to reduce the chlorides to the
oxides.18,34 The presence of water can then form hydroxides.
For this reason, H2 production was examined in the γ-ray and
5 MeV helium ion radiolysis of Mg(OH)2 and Ca(OH)2 powders.
The experiments give fundamental knowledge related to the
mechanism for the formation of H2 from hydroxides and from
waters of hydration and provide useful information for the
management of packaged nuclear materials and waste.
Experimental Section
The salts used in this work were as follows: calcium chloride
anhydrous, CaCl2 (Alfa Aesar, ACS grade); calcium chloride
dihydrate, CaCl2‚2H2O (Aldrich, 99.99%); calcium chloride
hexahydrate, CaCl2‚6H2O (Aldrich, 98%); calcium oxide, CaO
(Aldrich, 99.995%); calcium hydroxide, Ca(OH)2 (Aldrich,
99.995%); magnesium chloride anhydrous, MgCl2 (Alfa Aesar,
ACS grade); magnesium chloride hexahydrate, MgCl2‚6H2O
(Aldrich, 99.99%); magnesium oxide, MgO (Aldrich, 99.99%);
and magnesium hydroxide, Mg(OH)2 (Alfa Aesar) powders. The
oxides, hydroxides, and anhydrous chlorides were baked at 100
°C for 24 h to remove adsorbed water. No major changes in
these compounds occur under this drying condition as suggested
by the relatively small weight changes. The hydrates were dried
under vacuum at room temperature or in a drybox with Drierite
(calcium sulfate). No difference in the two drying techniques
was observed. Variation in weight was used to confirm that
only excess water was removed and not waters of hydration.
Drying the hydrates at temperatures of 100 °C often resulted in
the loss of waters of hydration. Magnesium chloride dihydrate,
MgCl2‚2H2O, was made by baking the hexahydrate at 100 °C
under vacuum. The change in weight corresponds to formation
of the dihydrate. Furthermore, the dried compound dissolves
in water, whereas magnesium oxide does not.
Figure 1. Dose dependence of H2 production in the radiolysis of CaCl2‚
4
2H2O: (9) γ-rays; (O, b) 5 MeV He ions. The slopes of the fitted
lines correspond to G-values of 0.20 and 0.21 molecule/(100 eV),
respectively.
Notre Dame. The dose rate was 150 Gy/min, as determined
using the Fricke dosimeter.38 The sample cell was made from
a quartz cuvette with inlet and outlet ports for purging the sample
before and after irradiation. The same cuvette was used for both
dosimetry and sample irradiation. The ambient temperature of
the irradiation chamber was about 30 °C, and samples would
rise to this temperature during long irradiations.
Hydrogen was determined using an inline technique with a
gas chromatograph. Ultrahigh purity argon was used as the
carrier gas with a flow rate of about 50 mL/min. The argon
passed through a constant flow regulator, an injection septum,
and a four-way valve and into a 3 m 5× molecular sieve column
of an SRI 8610C gas chromatograph with a thermal conductivity
detector. Calibration of the detector was performed by injecting
pure gases with a gastight microliter syringe. The sample cell
was connected to the gas analysis system using the four-way
valve, which was used to purge the sample and then isolate it
during irradiation. Following the irradiation, the four-way valve
was opened and the radiolytic gases analyzed. Estimated error
in gas measurements is estimated to be about 10%.
Samples for molecular chlorine determination from γ-
radiolysis were placed in Pyrex tubes (φ ∼ 1 cm, L ∼ 10 cm),
purged with argon, and heat-sealed. Following irradiation the
tubes were broken, the solid mixed with water, and Cl2
determined by the DPD colorimetric technique, EPA Method
330.5, using a Chemetrics I-2001 analytical kit.39 This technique
involves the hydrolysis of Cl2 to the hypochlorite ion or
hypochlorous acid followed by reaction with KI at pH 4 or less
to give iodine. Iodine reacts with N,N-diethyl-p-phenylenedi-
amine, DPD, to give a red color with two wide absorption bands
at 510 and 550 nm. Calibration was performed with known
NIST traceable Cl2 standards. Error in Cl2 determination is
estimated to be 10%. Helium ion radiolysis was performed in
cells similar to that used for H2 measurements, and following
irradiation the sample was transferred to a closed vessel
containing water.
The heavy ion radiolysis experiments were performed using
the facilities of the Nuclear Structure Laboratory of the
4
University of Notre Dame Physics Department. He ions were
produced and accelerated using a 10 MV FN Tandem Van de
Graaff. After acceleration, the ions were energy and charge-
state selected magnetically. The window assembly was the same
as reported earlier and gave a beam diameter of 6.4 mm with a
uniform flux across the sample surface.35,36 Energy loss of the
helium ions in passing through all windows was determined
from a standard stopping power compilation.37 The samples were
irradiated with completely stripped ions at a charge beam current
of about 1.5 nA. Absolute dosimetry was obtained from the
product of the integrated beam current and the particle energy.
The ranges of the helium ions are smaller than the sample
thickness, so the ions are completely stopped in the sample and
the radiation chemical yields represent all processes from the
initial particle energy to zero and are therefore track-averaged
yields. The sample cell (φ ∼ 1 cm, L ∼ 0.3 cm) was made of
quartz with a thin (∼4-6 mg/cm2) mica window epoxied to
the front for the beam entrance. Inlet and outlet ports allowed
the cell to be purged before and after the irradiation. Irradiations
were performed at room temperature (23 °C), and the dose rate
was sufficiently small that no significant macroscopic heating
was observed; see below.
Results and Discussion
H2 Production from Calcium Compounds. H2 production
in the radiolysis of CaCl2‚2H2O and Ca(OH) 2 with both γ-rays
and 5 MeV helium ions gave linear responses as a function of
total adsorbed dose. A typical response for CaCl2‚2H2O is shown
in Figure 1. The slopes of the dose responses shown in Figure
1 are proportional to the radiation chemical yields, or G-values.
Radiolysis with γ-rays was performed using a Shepherd 109
60Co source at the Radiation Laboratory of the University of

H2 and Cl2 Production through Radiolysis
J. Phys. Chem. A, Vol. 109, No. 12, 2005 2863
TABLE 1: Radiolytic Yields of H2 with γ-rays and 5 MeV
He Ionsa
γ-rays
0.20
0.098
0.49
5 MeV He
CaCl2‚2H2O
CaCl2‚6H2O
2 M CaCl2
Ca(OH)2
MgCl2‚2H2O
MgCl2‚6H2O
Mg(OH)2
0.21
0.038
0.77
0.051
0.38 (0.22)c
0.14
0.038
1.34
0.20
0.72 (0.51)c
0.042
0.051
0.56
2 M MgCl2
b
CeO2
0.018
0.08
0.018
0.018
0.018
0.018
b
ZrO2
b
UO2
a In units of molecule per 100 eV. b With 1 wt % water adsorbed.29,30
c High-dose yield in parentheses.
Radiation chemical yields are traditionally given in units of
molecules of product per 100 eV of total energy deposited in
the medium. The G-values reported here for helium ions are
track-averaged yields since the ions are completely stopped in
the sample. Figure 1 shows that the radiation chemical yields
of H2 from CaCl2‚2H2O are nearly the same (∼0.2 molecule/
(100 eV)) for both γ-rays and 5 MeV helium ions. A similar
value is observed in the γ-radiolysis of Ca(OH)2, as shown in
Table 1. The 5 MeV He ion radiolysis of Ca(OH)2 gives a
significantly lower yield (∼0.05 molecule/(100 eV)). Linear
responses to dose are observed for both of these compounds
with both types of radiation, indicating straightforward radiolytic
processes are responsible for H2 production.
The yield of H2 in the radiolysis of water is about 0.45
molecule/(100 eV) and mainly due to reactions of the hydrated
electron or its precursor.40 H2 yields in the radiolysis CaCl2‚
2H2O are about half of this value, indicating the compound
readily decomposes to give H2. Ionizing radiation deposits
energy to the electrons of a medium so most of the initial energy
loss is to the CaCl2 moiety. Presumably energy is transferred
to the water resulting in the formation of the oxide or hydroxide,
but no specific analysis was performed. H2 yields with the 5
MeV He ion radiolysis of Ca(OH)2 are lower than that observed
with γ-rays even though samples were irradiated under identical
conditions. There is no reason to assume that the decomposition
of Ca(OH)2 in helium ion radiolysis is less than in γ-radiolysis,
so radical or other reactive precursors to H2 must be recombining
in the high LET helium ion track to give other products. No O2
was observed in these systems as also suggested in earlier studies
by Jenks and Walton.4
The γ-radiolysis of CaCl2‚6H2O is complicated by heating
of the sample by the source. With long irradiations, the sample
temperature increased to that of the γ source, which was about
30 °C. A previous work reports that CaCl2‚6H2O acts like a
single compound with a melting point at about 29 °C.41 The
heat capacity of this compound was shown to start rising at
about 25 °C, indicating some structural changes occurring at
very near room temperature. Short doses with new samples
repetitively gave yields of 0.098 and 0.038 molecules of H2
per 100 eV of energy absorbed for γ-rays and 5 MeV helium
ions, respectively. Under longer irradiations, higher doses, the
yields in γ-radiolysis increased and approached the yield found
with 2 M aqueous solutions. The samples visually appeared to
be melted in γ-radiolysis. An increase in H2 yields could be
observed in helium ion radiolysis, especially at higher dose rates.
No visual change to the sample was observed in the 5 MeV He
radiolysis, but the penetration is only expected to be about 15
µm. The heating of such a small volume would be difficult to
observe or measure. Sample heating by the heavy ion irradiation
Figure 2. Temperature dependence of H2 production in the radiolysis
of CaCl2‚6H2O with γ-rays. The lower line shows the yield at 22 °C,
while the upper line shows the yield in 2 M aqueous CaCl2 solution.
must be due to low-level heating due to the slow transport of
heat from the irradiation zone. On the other hand, the 5 MeV
He ion radiolysis of CaCl2‚6H2O at higher temperatures is
expected to give H2 yields approaching that observed in 2 M
CaCl2 solutions. A temperature of 30 °C is certainly expected
in many nuclear material storage conditions, and the variation
of H2 yields as the CaCl2‚6H2O melts is significant.
An attempt was made to estimate the relative heating with
respect to dose with γ-rays by measuring the temperature rise
of the sample, and the results are shown in Figure 2. The lack
of good thermal conductivity probably leads to an uneven
heating of the sample, so the present method of estimating
temperature rise is crude and intended to only show the general
increase in H2 yield as the sample approaches its melting point.
An increase in H2 yield to about 0.57 molecule/(100 eV) was
observed in He radiolysis. The variation in H2 yield between
the 2 M solutions and the solid compounds show that data from
salt brine studies are not suitable for relatively dry solid salts.
This is true although 2 M MgCl2 and 2 M CaCl2 solutions give
similar radiation chemical yields of H2 to those obtained by
previous researchers.4,42 The radiation chemistry of the brines
are characterized by the chloride anion reaction with excited
water to give H2.3-6
An attempt was made to measure the production of H2 from
CaO and MgO with small amounts of adsorbed water in order
to compare with previous results on CeO2, ZrO2, and UO2.43,44
There is partial or complete conversion of both magnesium and
calcium chloride salts to CaO and MgO under some of the
conditions associated with plutonium processing for storage.34,45
The H2 yields were found to increase with increasing water
weight percent for both CaO and MgO powders. However, when
these oxides are left for long periods of time in humid conditions
they slowly convert to the corresponding hydroxides. Calcium
oxide converts to the hydroxide more rapidly than does
magnesium oxide, which may be the reason that H2 yields with
Ca(OH)2 are higher than Mg(OH)2.46 At low water loadings, it
could never be ascertained that the oxides had adsorbed water
or that a small fraction had simply converted to the hydroxides
and the results represented that found with mixtures. Total H2
yields from CeO2, ZrO2, and UO2 are significantly lower than
the hydrates or hydroxides examined here; see Table 1.
Hydroxides may have a substantial contribution to H2 formation
in certain waste storage conditions.
H2 Production from Magnesium Compounds. The produc-
tion of H2 in Mg(OH)2 was found to be linear with dose for

2864 J. Phys. Chem. A, Vol. 109, No. 12, 2005
LaVerne and Tandon
Figure 3. Dose dependence of H2 production in the radiolysis of
MgCl2‚2H2O: (9) γ-rays; (b) 5 MeV 4He ions. The dashed lines show
the low-dose limiting yields.
Figure 4. Production of Cl2 as a function of dose from CaCl2 for
various amounts of added water: (9) 1.5 and (b) 5.5 wt % water.
both types of irradiation. G-values for H2 of 0.051 and 0.038
molecule/(100 eV) were determined for γ-rays and 5 MeV
helium ions, respectively; see Table 1. The yield with 5 MeV
He ions is comparable to those found in the radiolysis of
Ca(OH)2. However, the H2 yield in the γ-radiolysis of Ca(OH)2
is considerably greater than that of Mg(OH)2. Previous work
has shown that Mg(OH)2 is converted to MgO with radiolysis,
but the mechanism is not established.47 The formation of water
may predominate over the production of H2 in the radiolysis of
Mg(OH)2 since MgO is relatively inert.46
There is a variation of about a factor of 3 in the H2 yields
between the calcium and magnesium chloride hexahydrates. No
obvious trend exists for the yields as a function of cation or
radiation type. Even the relative H2 yields in CaCl2‚6H2O
decrease from the γ-radiolysis to the 5 MeV He ion radiolysis,
while the inverse is found for MgCl2‚6H2O. In many of the
solids examined here, the H2 yield in γ-radiolysis is greater than
or equal to that in 5 MeV He radiolysis. This result is very
different from that of liquid water or the salt brines, which again
shows that the results with salt brines cannot be used to predict
the yields in solid salts.
detected using the present technique. The present experiments
focused on the determination of Cl2 trapped or otherwise
associated with the solid salts. Of course, any loss of Cl2 to the
cell walls or atmosphere will not be observed in the experiments
reported here. A further search for Cl2 will have to be undertaken
in which both the solid and gas phases are sampled. The results
reported here are meant to be a survey for possible Cl2 formation
in the solid salt.
Radiolytic chlorine production was examined for all the
chlorides in this work. The salts were either dry or loaded with
known amounts of water, irradiated, and then dissolved in water
and chlorine determined. Chlorine was never observed in any
of the dried salts at doses up to about 1 MGy. This dose
corresponds to G-values of Cl2 production in γ-radiolysis of
less than 0.002 molecule/(100 eV). Significantly higher doses
may lead to observable Cl2, but those doses are far too large
for normal radiation chemistry studies. An exhaustive search
of the appropriate conditions for Cl2 formation was not made,
but a few systems did lead to measurable and reproducible Cl2
production.
The radiolysis of MgCl2‚2H2O with γ-rays and 5 MeV helium
ions exhibit nonlinear responses as a function of dose; see Figure
3. H2 yields are found to decrease with increasing dose. The
G-values measured at the lowest doses in this work are 0.72
and 0.38 molecule/(100 eV) for γ-rays and 5 MeV helium ions,
respectively. These values decrease to 0.51 and 0.22 molecule/
(100 eV), respectively, and may be slowly approaching the
yields observed with MgCl2‚6H2O or Mg(OH)2 as the dihydrate
decomposes. This finding is similar to an earlier work that
suggested heating the samples to liquefaction temperature leads
to the release of H2.4 All the H2 yields for MgCl2‚2H2O are
high, indicating the relative ease of this system to radiolytically
decompose. Hydrogen yields are probably highly dependent on
the presence and form of water on the salts, i.e., adsorbed,
absorbed, water of hydration, or inclusion fluid and on the
storage temperature of the nuclear material.8,13
Cl2 Production from Calcium Compounds. Previous results
in the literature are inconclusive in showing the formation of
Cl2 in the radiolysis of chloride salts.28-33 A trace of gaseous
Cl2 was detected in the radiolysis of NaCl.30 However, gaseous
Cl2 is extremely reactive, especially with water or metal surfaces,
and difficult to observe reliably using gas sampling techniques.
HCl may be even more important for corrosion effects. It may
also be formed in the radiolysis of these compounds but not
CaCl2 was dried and then reloaded with known amounts of
water and irradiated with γ-rays. The production Cl2 was very
dependent on the amount of water present. No Cl2 was observed
when water was absent. The G-value for Cl2 rose to 0.035
molecule/(100 eV) at 1.5 wt % water loading and decreased to
a value of 0.013 molecule/(100 eV) at 5.5 wt % water loading;
see Figure 4. There appears to be optimum water loading for
producing Cl2. A small amount of water or OH groups is
probably required to stabilize Cl2 formation on the salt, but water
decomposition products may dominate at higher water concen-
trations. Gaseous Cl2 may be predominately formed with no
water. The yield of H2 with CaCl2‚2H2O is relatively high,
indicating that decomposition to H2 may be preferred over that
to Cl2. Another possibility for the low production of Cl2 is due
to the preferential formation of HCl.
In the 5 MeV He ion radiolysis, no Cl2 was observed in any
CaCl2 or MgCl2 system. These systems included the same water
loadings that gave observable Cl2 production with γ-radiolysis.
Either the Cl2 yield with R-particles is very low or they have a
very different water loading dependence than that observed with
γ-radiolysis.18,48 It is also possible that the 5 MeV He ion
radiolysis leads to more production of gaseous Cl2 than in
γ-radiolysis or in more favorable conditions for the production
of HCl. A thorough search may eventually discover the optimum

H2 and Cl2 Production through Radiolysis
J. Phys. Chem. A, Vol. 109, No. 12, 2005 2865
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(15) Hartmann, T.; Paviet-Hartmann, P.; Wetteland, C.; Lu, N. Radiat.
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conditions for observing Cl2 formation, but the Cl2 yields
associated with the solid phase are certainly low for the salts
examined here.
(16) Tandon, L.; Penneman, R. A.; Eller, P. G. Information Search on
Chloride Salt Radiolytic Effects in Plutonium Storage Environments; Report
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Conclusions
These experiments have examined the production of H2 in
the radiolysis of CaCl2‚2H2O, CaCl2‚6H2O, Ca(OH)2, MgCl2‚
2H2O, MgCl2‚6H2O, and Mg(OH)2. Radiation chemical yields
of H2 do not show any particular trend with respect to the cation
or the degree of hydration. The radiolysis of MgCl2‚2H2O leads
to the greatest yield for the formation of H2, but the yields from
both γ-radiolysis and helium ion radiolysis decrease with dose
due to the radiolytic instability of the dihydrate. The H2 yields
with the other compounds are between 0.04 and 0.2 molecule/
(100 eV), which is considerably lower than that from pure water
or 2 M chloride solutions. However, these yields are consider-
ably greater than that observed in the bulk radiolysis of CeO2
and ZrO2 with adsorbed water.
Molecular chlorine was determined in association with the
solid salt and not in the gas phase. The production of Cl2 is
found only in the γ-radiolysis of CaCl2 with a few weight
percent of excess water loading. No Cl2 was found in the 5
MeV He ion radiolysis of identical systems. None of the other
compounds examined here showed detectable amounts of Cl2
formation.
(23) Burns, W. G.; Williams, T. F. Nature 1955, 175, 1043.
(24) Wardle, M. W. Color-Center and Radiation-Damage Effects in
Alkali Halides Irradiated to High Particle Fluence. Ph.D. Thesis, University
of Delaware, 1975.
(25) Rabe, J. G.; Rabe, B.; Allen, A. O. J. Phys. Chem. 1966, 70, 1098.
(26) Jenks, G. H.; Sonder, E.; Bopp, C. D.; Walton, J. R.; Lindenbaum,
S. J. Phys. Chem. 1975, 79, 871.
(27) Gopinathan, C.; Damle, P. S.; Hart, E. J. J. Phys. Chem. 1972, 76,
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Acknowledgment. The authors thank Professor A. Apra-
hamian for making the facilities of the Notre Dame Nuclear
Structure Laboratory available. The latter is funded by the
National Science Foundation. The 94-1 Program from Los
Alamos National Laboratory of the U. S. Department of Energy
supported the work described herein. The DOE Nuclear Materi-
als Stewardship Program, through the Nuclear Materials Project
Office in the Albuquerque Operations Center, supports the 94-1
Program. This contribution is NDRL-4576 from the Notre Dame
Radiation Laboratory, which is supported by the Office of Basic
Energy Sciences of the U. S. Department of Energy.
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