YEGOR VEKHOV,  YEGOR.VEKHOV@NIST.GOV

12/21/18

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Adjustable Copper single crystal holder for Dil Fridge neutron experiments at

NCNR

This sample holder is designed for and can be used with the ICE dil fridge and Oxford dil

fridge inserts available for users at NCNR. The Holder allows single crystal sample alignment

within two degrees of freedom (see Sample aligning paragraph) prior to mounting it into the dil

fridge. The Holder is designed to provide good thermal conductivity between the sample and the

mixing chamber of the dil fridge.

a) b)

Figure 1 – Assembly of the Single crystal holder at the ‐12.5° position: (1) Brass M6 threaded stud for ICE dil fridge

mount or M6 male to 5/16‐18 male adapter for Oxford dil fridge mount; (2) Sample holder base; (3) Sample holder

stud; (4) Sample holder substrate; (5) Sample; (6) M2.5 brass screws, length 8mm; (7) Brass washer for number 3

screw size; (8) M2.5 brass screw, length 5mm; (9) Rotation axis, R38mm, located 5.5mm apart from the Sample

holder stud surface.
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12/21/18

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Sample holder material: Oxygen‐free Copper body, brass screw and washers.

Maximum sample dimensions: cylinder with the length up to 30mm and the diameter up to 6mm.

Other sample shapes possible – contact Sample Environment for assistance.

Sample attachment: Copper foil (not shown in Figs. 1‐2) is recommended to attach a sample to

the Sample substrate using two M2.5 brassscrews. In addition, Hydrogen‐free glue, Cytop M, can

be used to improve thermal conductivity between a sample and the Sample holdersubstrate. Per

well‐timed user request (at least 3‐4 weeks prior to the experiment), a custom‐made Sample

holder substrate can be designed and made to fit a particular sample shape and size – contact

Sample Environment for assistance.

Sample aligning:  

(1) +/‐ 12.5° from the vertical position relative to the sample axis (as shown in Fig.1 and

Fig.2);  

(2) 360° relative to the axis normal to the Sample substrate (Fig.1, #4). In other words,

Sample substrate rotates 360° together with the sample attached.  

Figure 2 – Assembly of the Single crystal holder at the

vertical position (0°, in this case the notch on the

Sample holder stud is aligned with the middle notch

on the Sample holder base. Each next notch on the

Sample holder base, counting from the middle one,

when aligned with the notch on the Sample holder

stud, adds 5° to sample rotation.
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12/21/18

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Sample thermalization. Most NCNR users do care about knowing the real temperature

their samples can be cooled to. When a dil fridge is used on high flux instruments, like the

Multiple Axis Crystal Spectrometer (MACS) at NCNR, one should expect noticeable sample

overheat. To evaluate sample overheat, this Sample holder has been tested to estimate the

temperature at the position where a sample attaches to the Sample holder substrate. Offline (no

neutrons) measurements have been performed with a RuO2 calibrated sensor attached to the

Sample holder substrate replacing a real sample. A wire heater was wrapped around the Sample

holder stud close to the temperature sensor to mimic the heat generated by a neutron flux. The

heater and sensor, in turn, were used to stabilize the temperature while the mixing chamber

sensor readings were recorded. It should be noted, the mixing chamber sensor is the only one

that can be used for sample temperature estimation during a neutron experiment under 1.5K.

For better thermal conductivity, it is very important to use Apiezon N vacuum grease in between

all matching surfaces of the Holder except those occured in the neutron beam.

Figure 3 shows how much warmer the sample position is, compared to the mixing chamber

of the dil fridge at its base temperature. No heat is applied directly to the mixing chamber heater.

The neutron beam on the MACS instrument often overheats the mixing chamber of the ICE dil

fridge insert up to 100 mK. The cooling power of thisfridge is about 20 μW at 100 mK. This means

the temperature at the sample position is 100 + 40 = 140 mK. The sample temperature, in turn,

could be even higher and can be estimated using, for instance, temperature dependent sample

properties measured by neutrons.  

0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.13 0.14 0.15

0.01

0.02

0.03

0.04

0.05



Tsample - Tm.ch.

Tm.ch. (K)

Figure 3 – Measured (offline, no neutrons) overheat, ΔT, as a function of mixing chamber temperature measured

during neutron experiment. This is a steady‐state overheat at the Sample position for the Sample holder attached

to the ICE dil fridge insert. Apiezon N vacuum grease was used (and should be always used) in between mixing

chamber and the Sample holder base and in between the Sample holder base and the Sample holder stud.