For optimal transportation of your crystals it is imperative that you look after your dry shipping dewars. Here are some tips on how to make sure that you don't lose your crystals or introduce ice onto your pucks and pins.
Handling and loading
Charging with liquid nitrogen
A well cared for dewar that is properly charged with liquid nitrogen before use should keep crystals safe for at least a week without refilling being required.
Dry shippers rely on two things to keep your samples cold during transit; an absorbent that immobilises a certain mass of liquid nitrogen and a vacuum dewar that insulates the contents and reduces the loss of this liquid nitrogen. Once the liquid nitrogen is all lost, the dewar warms up. We suggest you assess your dewars regularly as outlined below to ensure their integrity and fitness to ship your valuable samples.
The quantity of nitrogen held is dependent on the condition of the absorbent material (degraded absorbent can sometimes be seen as a fine white powder in your dewar). As the absorbent degrades, the amount of nitrogen stored decreases. The easiest way to damage the absorbent is to cool the dry shipper before the absorbent material has fully dried. Dry shippers should be warmed upside down and left until completely dry before cooling. You can speed this process up by directing a flow of dry air into the dry shipper
You can easily assess the absorbent material condition. Weigh your dry shipper when it is dry and warm. Now cool the shipper as you would prior to shipping, pour off any residual liquid and weigh it again.
Cold weight – warm weight = mass of stored nitrogen
This should be around 3kg depending on dry shipper model. On some models this material can be replaced. Do this test periodically and compare values over time.
The loss rate of nitrogen relates to the insulating performance of the dewar (mainly the vacuum level, but also the neck plug condition).
The combined effect of these can be measured by simply weighing the dry shipper when cold over a period and calculating the rate of mass loss. Once at a stable temperature (leave the dry shipper for an hour or so after charging), the mass loss is very linear and two measurements 24h or so apart should give a good estimate.
For a new dry shipper, this mass loss should be around 150-200g a day depending on model.
Diamond colour classifications based on weight loss are as follows:
Total lifetime can be easily calculated from the previous two experiments.
Mass of stored nitrogen/ mass loss per day = maximum storage lifetime of dry shipper
We would recommend relying on no more than half of this value as a sensible safety margin for your samples. At Diamond, dry shippers are topped up in storage every five days.
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
Copyright © 2022 Diamond Light Source
Diamond Light Source Ltd
Harwell Science & Innovation Campus
Diamond Light Source® and the Diamond logo are registered trademarks of Diamond Light Source Ltd
Registered in England and Wales at Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom. Company number: 4375679. VAT number: 287 461 957. Economic Operators Registration and Identification (EORI) number: GB287461957003.