Effects of 25 minutes of beta radiation exposure?

[Kiwimaster76]

So in chem lab we were doing experiments in radiation and the TA seems to have no idea how to do stuff, he told us to hold the samples at certain distances from a Geiger counter for 2 minutes at a time. I was tasked with holding an Sr90 sample for roughly 25 minutes, it was a very small sample encased in plastic that only emitted beta radiation. Is this a thing to worry about or am I probably ok?

He also made my lab partner hold Co60 a gamma radiation source, but for only about 8 minutes.

 

[Kiwimaster76]

This is the same type of sample as the on in the lab

 

[jim mcnamara]

If you are worried, go to the head of the department and voice your concerns. We have some senior members on PF who are conversant with this kind of thing, but PF is not in a position to give advice like this. I'm going to ask for help.

@Astronuc could you please help on directing @Kiwimaster76 to get help? Thanks.

PS: In what country/state are you located? Might help get you going.

 

[Kiwimaster76]

Not so much worried as mildly concerned, I know strontium-90 is used as a tracer isotope in medical imaging and as radiotherapy treatment for skin cancers so its probably not too major.

Arkansas, USA. Its a pretty reputable college so i doubt they'd keep anything that could do real damage around a freshman lab.

 

[Astronuc]

It should not be a concern based on the low activity, 0.1 microcurie, which is 3700 decays/sec. The beta energies are 0.546 MeV from Sr-90 and 2.28 MeV from Y-90. On the other hand, Co-60 has two gamma rays of 1.17 and 1.33 MeV, which are more penetrating, so one should handle as little as possible, and preferably with forceps or some device to preclude direct contact.

One can handle such activity safely for short times, but one would not want to handle it for long periods.

Note that it is a sealed source.

 

[mfb]

It should not be a concern based on the low activity, 0.1 microcurie, which is 3700 decays/sec.

As comparison: This is about the activity of potassium-40 inside a human body. As the source was outside and partially shielded, the exposure to anyone holding it is even lower than the natural internal dose from K-40 during the same time. It is also limited to the hand.

We don't know the Co-60 activity.

 

[Kiwimaster76]

The Cobalt was in the exact same casing and had 1μ on it which I assume means 1 microcurie

 

[Kiwimaster76]

Also thanks for your help guys! I appreciate the reassurance. :)

 

[Astronuc]

The Cobalt was in the exact same casing and had 1μ on it which I assume means 1 microcurie

Yes, 1μ would indicate 1 microcurie.

The energies I gave for Sr-90 and Y-90 are the maximum beta energy, and the most probably energy is approximately 1/3 of the maximum. One could integrate the activity over time and multiply by the energy per decay (1/3 of max) and get an estimate of the energy absorbed at some distance, with correction for geometry.

The best practice is to avoid unnecessary exposure, and handle sources with implements. One could place a specimen in a holder, or on a sheet of paper, rather than hold it in one's hand, if that's what was meant in the OP.

 

[Choppy]

If you look at the label on the picture, you'll see the words "exempt quantity" on the label. All radioactive materials have an exemption limit - the activity below which the source is not considered to be harmful to the public. Presumably for Sr-90, that's 0.1 microCi.

Your lab would have needed a specific license for radioactive materials and designated you a nuclear energy worker if you were handling a source above this limit. The nature of this question would suggest this is not the case.

Of course that doesn't mean you got zero dose, but it's highly unlikely that you'd get anything that would put you over a threshold for what's considered a safe exposure for a member of the general public, i.e. it's just noise in the background.

 

[Astronuc]

I too noticed the words "exempt quantity" on the source, which means that it is below certain strict regulatory limits. However, there are still appropriate handling and storage practices.

From the Health Physics Society
http://hps.org/sciencesupport/documents/hps_scisupport_guidance_exempt-quantities-school.pdf

General Handling Procedures
Although the radiation from exempt quantity sources is not hazardous, the basic principle of minimizing radiation dose should be followed:

• No eating, drinking, or applying cosmetics while handling the sources.
• Do not hold sources unless necessary.
• Only hold edges of disk. Avoid touching the unlabeled flat side of disk.
• Place sources away from living organisms with labeling facing up when not in use.
• Wash hands after handling sources.
• Sources must be accounted for. Take an inventory before and after each class period.
• Sources must be locked up at the end of each day.

As I indicated earlier, on should avoid unnecessary handling/touching of radioactive sources, even those of "exempt quantity".

See https://www.nrc.gov/reading-rm/doc-collections/cfr/part030/part030-0018.html regarding exempt quantities and § 30.71, Schedule B. for limits
https://www.nrc.gov/reading-rm/doc-collections/cfr/part030/part030-0071.html

Sr-90 limit = 0.1 microcurie, and
Co-60 limit = 1 microcurie

Nevertheless, one should avoid handling the sources to the extent possible.

 

[PSRB191921]

Hi,
Sr90 is a beta emetter. With beta emetter skin dose can be high
Sr 90 is in equilibrium with Y90
In contact with the skin a Sr90 point source gives 1.4 µSv/h for one Bq
and Y90 gives 1.9 µSv/h for one Bq
(datas from https://www.researchgate.net/publication/315653359_Calculation_of_skin_dose_due_to_beta_contamination_using_the_new_quantity_of_the_ICRP_116_The_'Local_Skin_Dose' )
So for 0.1 µCi (3700 Bq) it comes :
3700x(1.4+1.9)=12 mSv/h

 

[mfb]

That would be the local (~1mm²) skin dose if there would be direct contact to an unsealed and unshielded source. The actual dose is much lower, but even that pessimistic estimate is not a dose of concern.

 

[Fervent Freyja]

I agree, the TA has didn't exercise common sense in this situation... Did you read your lab printout? Forceps, tongs, or clamps should have been mentioned.

Most universities are supposed to have the protocols printed out for handling all materials and equipment available for students somewhere within the lab (liabilities). I wouldn't go forward with it to other staff besides your Professor unless you found any lab safety rules were broken first.