[ RadSafe ] Re: New Method for Making Improved Radiation Detectors

Fri Jun 1 18:32:16 CDT 2007

Dimiter --

You're absolutely correct -- the resolution on these CZT detectors is pretty amazing for room-temperature spectrometers. Not only do they separate the Co-60 1173 and 1332 peaks well, but they also truly separate the Zn-65 1116 peak from the Co-60 1173 peak in our gamma standards -- something that I've never seen a NaI spectometer do. Unfortunately, due to their small size (any where from 7 x 7 x 3.5 mm to perhaps 10 x 10 x 5 cm) and low efficiency (typically ~2-3% relative efficiency) we've found CZT-based instruments to be of limited use -- at least for our purposes. 

We've been using and evaluating a number of handheld spectrometers for quite some time, and both for our routine incident response and homeland security work, NaI-based spectrometers are still the "workhorses". We are, however, investing in a lanthanum-bromide (LaBr3) spectrometer for high(er) resolution room-temperature spectometry. In my opinion, LaBr3 has the advantage of high-resolution, like CZT, but at an efficiency similar to (or in some cases surpassing) NaI spectrometers, and at a cost that isn't "obscene". If the detector costs come down a little, I can see LaBr3 spectrometers being the "sweet spot" for room-temperature spectrometry -- at least until the next new, great thing comes along.

Currently, for in-situ work, we have a field portable (but not conveniently so) liquid-nitrogen cooled high-purity germanium (HpGe) spectrometer, and we should soon be receiving funding to invest in one of the electrically-cooled portable HpGe units currently on the market.

Jim Hardeman, Manager
Environmental Radiation Program
Environmental Protection Division
Georgia Department of Natural Resources
4220 International Parkway, Suite 100
Atlanta, GA 30354
(404) 362-2675
Fax: (404) 362-2653
Personal fax: (678) 692-6939
E-mail: Jim_Hardeman at dnr.state.ga.us 

>>> Dimiter Popoff <didi at tgi-sci.com> 6/1/2007 18:05 >>>
Thanks for posting that - pretty interesting, apparently the CdZnTe
detectors keep on improving. This is the first time I see both
the 1173 and 1332.5 lines on a CdTe spectrum, and the resolution
appears to be decent - far from Ge, but well, no LN2.
I wonder how good (if usable at all?) the efficiency would be,
there are too few counts between the two peaks (which is not how
things are) and I suspect that the spectrum might be looking like
shown in log scale while being actually in linear... 

Whatever the details, looks like great progress for CdZnTe.

(I found the article with the photo/spectrum at
http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=07-57 )

Dimiter

P.S. See my "walking" photo gallery:
http://www.flickr.com/photos/8359035@N02/sets/72157600228621276/  :-)

------------------------------------------------------
Dimiter Popoff               Transgalactic Instruments

http://www.tgi ( http://www.tgi/ )-sci.com
------------------------------------------------------

> Date: Fri, 1 Jun 2007 10:17:04 -0700 (PDT)
> From: ROY HERREN <royherren2005 at yahoo.com>
> To: radsafe at radlab.nl 
> Subject: [ RadSafe ] New Method for Making Improved Radiation Detectors
> 
> For release on May 31, 2007, 1:00:00 PM
>   Contacts: Pete Genzer, genzer at bnl.gov, (631)344-3174 or 
> Mona Rowe, mrowe at bnl.gov, (631) 344-5056
> 
>    New Method for Making Improved Radiation Detectors 
> UPTON, NY * Scientists at the U.S. Department of Energy's
> Brookhaven National Laboratory, with funding from DOE's
> National Nuclear Security Administration, have devised
> ways to improve the performance of radiation detectors,
> such as those used by law enforcement agencies to locate
> and identify radioactive material.   The improved sensors,
> for which the Laboratory has filed a U.S. provisional
> patent application, can be used at room temperature, 
> which makes them more practical and cost-effective than
> existing detectors with similar performance, which must
> be operated at very cold temperatures using expensive
> liquid nitrogen. They can also more accurately detect
> the X-rays and gamma rays emitted by radiological sources
> such as dirty bombs and other illicit materials.   "Improving
> the performance of radiation detectors could improve 
> the efficiency and accuracy of cargo screening at U.S.
> ports," said Brookhaven physicist Aleksey Bolotnikov,
> one of the inventors.   Radiation detectors work by detecting
> electrons and "holes" * vacancies left by liberated electrons
> * when ionizing radiation or high-energy particles strike
> the detector crystal. When the free electrons and holes
> flow toward electrodes (an anode and a cathode) at either
> end of the detector, they generate a signal that can 
> be measured and recorded.   In an ideal detector, all 
> of the electrons and holes created by the ionization 
> process would arrive at the electrodes. But in reality,
> holes travel a very short distance before getting trapped
> by defects in the crystal. Also, because the electrostatic
> field inside the detector causes some of the electrons
> to drift, not all of them arrive at the anode. These 
> losses lead to a subsequent inaccuracy in radiation measurements.
> The Brookhaven-designed sensors improve on this situation
> by combining methods to shield the detector and focus
> the electrons toward the anode. In addition, the electrodes
> at each end of the detector give information about how
> many electrons/holes get trapped. This "correction factor"
> can then be used to reconstruct the number of electrons/holes
> originally created by incident gamma rays or high-energy
> particles.   "Together, these techniques enhance the energy
> resolution and efficiency of these detectors. In practical
> terms it means that the improved devices will be able
> to detect more minute quantities of radiation, detect
> radioactive materials more quickly or from greater distances,
> better identify the source of the radiation, and distinguish
> illicit sources of concern from common naturally occurring
> radioactive materials," Bolotnikov said.   The patent 
> application covers the improved high-energy detectors,
> as well as methods for making and using them. Details
> of the electrode design and processing methods are also
> included.   This technology is now available for licensing.
> For licensing information, please contact: Kimberley 
> Elcess, Principal Licensing Specialist, Brookhaven National
> Laboratory, (631) 344-4151, elcess at bnl.gov.   Note to 
> local editors: Aleksey Bolotnikov lives in South Setauket,
> New York.         To see the National Nuclear Security 
> Administration's press release, click here.    One of 
> ten national laboratories overseen and primarily funded
> by the Office of Science of the U.S. Department of Energy
> (DOE), Brookhaven National Laboratory conducts research
> in the physical, biomedical, and environmental sciences,
> as well as in energy technologies and national security.
> Brookhaven Lab also builds and operates major scientific
> facilities available to university, industry and government
> researchers. Brookhaven is operated and managed for DOE's
> Office of Science by Brookhaven Science Associates, a
> limited-liability company founded by the Research Foundation
> of State University of New York on behalf of Stony Brook
> University, the largest academic user of Laboratory facilities,
> and Battelle, a nonprofit, applied science and technology
> organization.   Visit Brookhaven Lab's electronic newsroom
> for links, news archives, graphics, and more: http://www.bnl.gov/newsroom 
>    
> Roy Herren
>        

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