13.3 Co-precipitation
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Carriers can be of three types:
1. Isotopic carrier,
2. Non-isotopic carrier and
3. Hold-back carrier.
13.3.1.1 Isotopic Carrier
Isotopic carriers are those, which should be of the same chemical element as that of the
radioactive substance but should be a stable isotope of the tracer. For example, iodide
ions can be used as an isotopic carrier for
131 I-ions. The disadvantage of this type of
carrier is that it lowers the specific activity of the material, because the radioactive
species cannot subsequently be chemically separated from the carrier. Hence, when
a thin, virtually weightless deposit of the material is required for counting; the use
of isotopic carriers should be avoided. Moreover, a stable isotope of iodine cannot
be used as a carrier for
131 I-ions, because though both belongs to the same element,
but their valences are different. In such cases, it is preferred to carry out at least a
couple of oxidation and reduction processes to make sure that both the carrier and
the radioactive isotope are in the same chemical form.
13.3.1.2 Non-isotopic Carrier
A “non-isotopic” carrier is an element, which has similar chemical properties as
the radioactive isotope, but is not an isotope of the tracer. A non-isotopic carrier
is sometimes used where there is no stable isotope available (e.g., barium is used
for radium isotope separation) or when it is desirable that the carrier should be
subsequently separated from the radioactive nuclide, especially when the original
specific activity is to be recovered. For example, the separation of Protoactinium-233
from neutron irradiated thorium nitrate solution is carried out by adding manganese
nitrate and precipitating manganese dioxide from the solution by the addition of
potassium permanganate. The advantage of this carrier is that the specific activity of
the tracer does not change, provided at the end of chemical separation, added inactive
carrier could be removed from the tracer.
Another type of non-isotopic carrier is called “scavenger”. Such carriers are
mainly gelatinous precipitates, such as ferric hydroxide or aluminum hydroxide.
Since freshly prepared hydroxides have a large surface area, adsorption of radioactive
isotopes present in the solution may remove the nuclides present in trace amounts in
the mixture.
203
Carriers can be of three types:
1. Isotopic carrier,
2. Non-isotopic carrier and
3. Hold-back carrier.
13.3.1.1 Isotopic Carrier
Isotopic carriers are those, which should be of the same chemical element as that of the
radioactive substance but should be a stable isotope of the tracer. For example, iodide
ions can be used as an isotopic carrier for
131 I-ions. The disadvantage of this type of
carrier is that it lowers the specific activity of the material, because the radioactive
species cannot subsequently be chemically separated from the carrier. Hence, when
a thin, virtually weightless deposit of the material is required for counting; the use
of isotopic carriers should be avoided. Moreover, a stable isotope of iodine cannot
be used as a carrier for
131 I-ions, because though both belongs to the same element,
but their valences are different. In such cases, it is preferred to carry out at least a
couple of oxidation and reduction processes to make sure that both the carrier and
the radioactive isotope are in the same chemical form.
13.3.1.2 Non-isotopic Carrier
A “non-isotopic” carrier is an element, which has similar chemical properties as
the radioactive isotope, but is not an isotope of the tracer. A non-isotopic carrier
is sometimes used where there is no stable isotope available (e.g., barium is used
for radium isotope separation) or when it is desirable that the carrier should be
subsequently separated from the radioactive nuclide, especially when the original
specific activity is to be recovered. For example, the separation of Protoactinium-233
from neutron irradiated thorium nitrate solution is carried out by adding manganese
nitrate and precipitating manganese dioxide from the solution by the addition of
potassium permanganate. The advantage of this carrier is that the specific activity of
the tracer does not change, provided at the end of chemical separation, added inactive
carrier could be removed from the tracer.
Another type of non-isotopic carrier is called “scavenger”. Such carriers are
mainly gelatinous precipitates, such as ferric hydroxide or aluminum hydroxide.
Since freshly prepared hydroxides have a large surface area, adsorption of radioactive
isotopes present in the solution may remove the nuclides present in trace amounts in
the mixture.