Atomic Clocks....Should
We Worry ?
A great many laboratories, manufacturing facilities
and transmission stations now use frequency standards that owe their
accuracy to atomic physics. Given that cesium and rubidium are classified
as dangerous goods, how safe are users?
Caesium
The cesium (now internationally agreed to be spelled "caesium")
used in Agilent 5071A Primary Frequency Standards, Agilent 10890A/10891A
Caesium Beam Tubes, and prior HP caesium-based products contain
Cs-133. This is a naturally-occurring non-radioactive isotope. Although
considered a hazardous substance, it is completely contained in
the Caesium Beam Tube, which is itself a tested and certified steel
container, providing a safe means of transport.
The amount of Cs-133 used is less than 6 grams, as currently defined
by the US Department of Transportation (DOT). Due to the proven
strength of the tube, the DOT extends to Agilent an exemption from
normal hazardous material shipment regulations. This is documented
under exemption number E-11401 and refers to markings on the outside
of the packaging and includes clearance to use passenger aircraft
for shipments within the United States. International shipments
are governed by International Air Transport Association (IATA) and
International Civil Aviation Organization (ICAO) regulations which
have different requirements for the marking and transport. Consult
the US DOT and IATA websites before packaging and shipping this
type of product.
Rubidium
There are similar land and air transport controls concerning
rubidium which is used in lower performance frequency standards.
However, effective 1 July 2001, rubidium is reclassified by ICAO/IATA
as a non-radioactive substance for shipping. This means that it
no longer requires a radiation hazard warning.
In our obsolete 5065A Rubidium Vapor Standard and RVFR, two isotopes
of rubidium were used. The first, Rb-85, is the most abundant isotope
in nature at 72.2% and is non-radioactive. The rest of the natural
material (27.8%) is Rb-87, a radioactive isotope with a half-life
of 49 billion years. However, it is such a weak beta emitter that
it cannot be detected by normal means (i.e. it cannot be detected
by Geiger or scintillation detectors).
Jack Kusters, Agilent's premier scientist in this field was asked
to calculate how much rubidium a person could be exposed to and
still remain within the allowable radiation dose. He determined
that an individual would have to consume 5 tons per day (!) and
as rubidium is a very alkaline material, would have dissolved long
before more than a few pounds could be eaten.
—Cautionary Notice—
Despite the previous paragraph, the experimental consumption of rubidium
is not recommended and will not help as part of a calorie controlled
diet !
Further Advice
Atomic frequency standards contain hazardous materials
and their transportation is regulated.
Agilent can offer advice on shipping your Agilent/HP products,
for example, back to our service facilities.
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