I would be surprised if it had significant contamination, but I've been surprised before.
The main nuclides of concern are typically considered to be 131-Iodine and 137-Cesium. With a half-life of only 8 days, the 131-Iodine would not be a concern now, so that leaves us with 137-Cesium.
137-Cs emits beta and gamma radiation. A GM tube is not going to be effective at detecting low levels of gamma radiation. A sodium-iodide scintillation counter connected to a pulse-height-analysis system could efficiently pick up the 667-keV gamma, confirm the energy, and in doing so would confirm the identity as 137-Cs.
At some degree of contamination an end-window GM tube or a pancake GM tube would notice the beta radiation if slowly swept over the surface of the violin. For low levels it is difficult to notice the increased count rate if the meter has an analog meter, or if you are simply listening to "clicks." It is easier to detect low levels of radiation with a GM tube if it is connected to a scaler (digital counter) that can count the events. Hold the detector at a spot on the surface of the item that is possibly contaminated, and count the events for one minute, or 5 minutes, etc. There will be a background count, so you need to count the background for one minute, or 5 minutes, etc. and then see if the count at the surface is significantly higher than the background count.
Remember that the uncertainty in the count is approximately the square root of the count. So if you get a count of 100 events in five minutes, that should be considered 100 +/- 10.
Michael D. Edmiston, PhD.
Professor of Chemistry and Physics
Chair, Division of Natural and Applied Sciences
Bluffton, OH 45817
From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Anthony Lapinski
Sent: Thursday, February 02, 2012 4:12 PM
To: email@example.com; firstname.lastname@example.org
Subject: [Phys-l] radiation
I was wondering if anyone could help with this:
Our science department got this email from a parent at my school:
My daughter is a middle school student. We are considering buying her a violin that was made in Japan in 2011, during the nuclear disaster. For our peace of mind, we would like to have it tested to ensure that it is not contaminated.
Should the parents worry? Could a Geiger counter detect anything?