Proposal to put 232Th Source in K for > 2MeV

GammaDetectionBobby Lanza

May 1, 2008

Neutron Meeting

The case for 232Th

• Why are ’s with E > 2MeV important?– Muons interacting with the bedrock at Soudan create

photons at this energy scale.– Source of background.

• What can K do? ’s above the 2MeV threshold can impart enough energy to

electrons to make them Cherenkov radiate in K.– Calibration with a test source would inform possible future

tests at Soudan.

•Why 232Th instead of the Depleted Uranium we have?– DU has many sticking points in its decay chain (long lived daughters), before

the high energy gammas.

– DU chemically purified approx. 30 years ago, so not in equilibrium yet.

Sticking Points

> 2MeV ’s

– 232Th Approx. 10-15 yrs old (longer than combined daughter half-lives), so likely in equilibrium.

– Above threshold gammas available from 208Tl --> 208Pb decay.

2.6 MeV ’s

We have a 232Th Source

• 0.1g of 232Th in liquid solution.

• 400 decays per second expected.

• Standard calibration source.

Near Future (Proposed)

• Design simple containment vessel for 232Th & install in K.

• Take data with liquid 232Th source.

• Do Monte Carlo & compare to data.

--Thanks--