# Detecting scintillation flash using semiconductors

#### waht

Although photomultpliers are the most sensitive light detectors, are there any other radiation counters that utilize photo-transistors, or other means, to detect photons emitted form a scintillation crystal when hit by incoming radiation?

Related Nuclear Engineering News on Phys.org

#### mgb_phys

Homework Helper
Avalanche Photo Diodes (APDs) in geiger mode can easily do single photon and are often better QE than PMTs

#### waht

Cool didn't know that.

Just wondering if there are any commercial radiation detectors that already utilize these diodes? According to google, avalanche diodes were developed quite recently.

#### Xnn

There are solid state devices (semiconductor detectors such as Germanium), that are fundamentally different from scintillation detectors and have no need for photomultipliers.

#### Morbius

Dearly Missed
Just wondering if there are any commercial radiation detectors that already utilize these diodes? According to google, avalanche diodes were developed quite recently.
waht,

Solid state radiation detectors have been the NORM for nuclear laboratories for DECADES
because they are far SUPERIOR to gas-filled [Geiger] and scintillation detectors. For example,
the solid-state detectors also give you an accurate reading of the energy of the detected radiation;
as opposed to something like a Geiger detector where the device saturates for any radiation above
the trigger level.

Commercial detectors are available from such companies as AMETEK subsidiary ORTEC.

http://www.ortec-online.com/detectors/photon/detectors.htm [Broken]

Courtesy of Lawrence Berkeley National Laboratory:

http://sensors.lbl.gov/sn_semi.html [Broken]

Lawrence Livermore developed a portable spectrum analyzer detector capable of determining
the identity of the radioactive nuclei for Homeland Security applications called RadScout:

This was commercialized as the ORTEC "Detective" series:

http://www.ortec-online.com/psis.htm [Broken]
http://www.ortec-online.com/detective-ex.htm [Broken]

Dr. Gregory Greenman
Physicist

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#### waht

That's neat. I've been going over some of those germanium designs. Those ortec meters are really advanced, nice.

I'm asking because I'm exploring a possibility to build a simple detector to count muons from the atmosphere. I don't want to use geiger nor photomultiplier tubes. Instead I'd like to replace photomultiplier with some semiconductor photo-diode off the shelf, sensitive enough to pick up flash a from the scintillation crystal.

Some of those germanium detectors need to be cooled with liquid nitrogen, so I'm not sure if this is possible (off the shelf).

#### Morbius

Dearly Missed
Some of those germanium detectors need to be cooled with liquid nitrogen, so I'm not sure if this is possible (off the shelf).
waht,

As I recall; there are a couple types of solid-state germanium detectors; "lithium-drifted" and "intrinsic".

When I took a nuclear measurements lab course at MIT, our instructor told us he only purchased the
"intrinsic" germanium detectors. Both the intrinsic and lithium-drifted detectors need to be cooled with
liquid nitrogen in order to work. However, if the lithium-drifted detectors ever warm-up; they are ruined;
and they are not inexpensive.

I recall my professor remarking that although the intrinsic detectors were more expensive; he didn't have
to worry about a student forgetting to fill the dewar and ending up with a ruined detector. The intrinsic
ones won't work unless they are cooled - but at least if someone fails to fill the dewar, they are not
ruined.

Dr. Gregory Greenman
Physicist

#### Xnn

GeLi detectors have fantastic resolution. Of course I didn't have to pay for the crystals or the liquid nitrogen!

Muons are not directly or easily detected. It more of a research project.
Here's a link to an interesting article on Muon detection:

Is sounds like a fun, but personally I'd suggest gaining some experience with cloud chambers first.

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#### waht

Staff Emeritus
Let's get back to the OP's original question and application.

The energy resolution of a Ge(Li) or HPGE detector won't help him with cosmic rays and scintillator, as everything he's looking at is minimum ionizing anyway. This isn't worth the expense.

I assume that the OP wants to avoid PMTs because of cost. I'm afraid that this will be hard to do. A tube is a few hundred dollars, but it's probably $2000 for a setup. You need a tube, and a preamp, and an amplifier-shaper-discriminator, and a HV source for the tube, and a LV source for the preamp, and all this adds up. (The cost for a second tube, of course, is smaller, since several of these components can be shared) Replace the tube by an APD or a silicon PMT, and you still need all the periphery. Different actual components, to be sure - for example the voltage requirements are different - but the total system cost for a one channel system is not grossly different. Understand you are looking at very, very low levels of light here. Perhaps a hundred photons. #### waht The energy resolution of a Ge(Li) or HPGE detector won't help him with cosmic rays and scintillator, as everything he's looking at is minimum ionizing anyway. This isn't worth the expense. I assume that the OP wants to avoid PMTs because of cost. I'm afraid that this will be hard to do. A tube is a few hundred dollars, but it's probably$2000 for a setup. You need a tube, and a preamp, and an amplifier-shaper-discriminator, and a HV source for the tube, and a LV source for the preamp, and all this adds up. (The cost for a second tube, of course, is smaller, since several of these components can be shared) Replace the tube by an APD or a silicon PMT, and you still need all the periphery. Different actual components, to be sure - for example the voltage requirements are different - but the total system cost for a one channel system is not grossly different.

Understand you are looking at very, very low levels of light here. Perhaps a hundred photons.
Beside the cost of PMT, the electronics to interface a PMT is very simple. I'm EE major. But I guess the low level photons we're dealing with is going to be an issue.

Staff Emeritus
Simple, but it still costs money. You need some low-noise amplifiers, for example.

I built a 432 channel system, and it ended up with a per-channel cost of $400. It was$150 per tube, $150 for on-detector electronics, and$40k for off-detector electronics. This was generally considered quite cheap.

#### vanesch

Staff Emeritus
Gold Member
The energy resolution of a Ge(Li) or HPGE detector won't help him with cosmic rays and scintillator, as everything he's looking at is minimum ionizing anyway. This isn't worth the expense.
Indeed, detecting muons with Ge xtals is pretty silly (and expensive). What you need is a relatively large detection volume, and you don't need precise detection, so I would opt for a gas detector. No need to go through scintillation. A big tube with a wire in it under HV, and you don't need much. You will need the gas filling (and hence access to a vacuum pump and such) and a tight container. But then for a simple Geiger tube, you don't even need much electronics (a HV power supply, some resistors, a HV capacitor and then a speaker or a pulse counter).

#### mgb_phys

Homework Helper
I built photon counting geiger mode APD units 10years as a grad student for about $500. They had a fibre pigtailed APD from EG+G Canda that was about$250 at the time, a little single stage peltier cooler to get the APD down to 250k and some circuitry that quenched the diode, and output TTL pulses- it counted photons upto about 3Mhz. The unit was about the size of an altoids tin.

I'm guessing that scintillation detectors are still better than semiconductors if you want large area coverage ?

#### waht

I built photon counting geiger mode APD units 10years as a grad student for about $500. They had a fibre pigtailed APD from EG+G Canda that was about$250 at the time, a little single stage peltier cooler to get the APD down to 250k and some circuitry that quenched the diode, and output TTL pulses- it counted photons upto about 3Mhz. The unit was about the size of an altoids tin.
How did you interface the fiber to a scintillation crystal?

#### mgb_phys

Homework Helper
How did you interface the fiber to a scintillation crystal?
I didn't - these were for astronomy.

I haven't worked with particle physics detectors, but the ones I have seen are large (1m long) complicated curved bits of plastic that end in an output face a couple of cm square.
You could couple that into a fibre fairly easily. The fibres that came with these diodes were 200-250um multimode (don't remember the NA).

I really just meant that APDs are very easy to work with compared to PMTs.

#### waht

I didn't - these were for astronomy.

I haven't worked with particle physics detectors, but the ones I have seen are large (1m long) complicated curved bits of plastic that end in an output face a couple of cm square.
You could couple that into a fibre fairly easily. The fibres that came with these diodes were 200-250um multimode (don't remember the NA).

I really just meant that APDs are very easy to work with compared to PMTs.
I think I saw such a paddle in fermilab, but it was coupled with a PMT whose surface area of contact was many times bigger than that of a fiber. I'm going to do more research on APDs.

#### mgb_phys

Homework Helper
I think I saw such a paddle in fermilab, but it was coupled with a PMT whose surface area of contact was many times bigger than that of a fiber.
That's the advantage of PMTs of course.
I wouldn't have though it was too difficult to couple to an APD, you can get large area ones but sensitivity and time response go down with area.
Obvious ways to couple to a scintillator would be either a microscope objective or I suppose (having never tried it!) get a similar shaped bit of plastic, heat it to softening point and draw it out to neck down to a thin stand. Cleave the end and join to the fibre with index matching glue and polish the other end and stick that to the scintillator with index matching gel.

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