# Break of Sr-90/Y-90 secular equilibrium during the preparation of liquid scintillation sources

Philippe Cassette, Isabelle Tartès, Florent Jaubert

► To cite this version:

Philippe Cassette, Isabelle Tartès, Florent Jaubert. Break of Sr-90/Y-90 secular equilibrium during the preparation of liquid scintillation sources. LSC 2008 - Advances on Liquid Scintillation Spectrometry, May 2008, Davos, Switzerland. cea-05457782

HAL Id: cea-05457782

https://cea.hal.science/cea-05457782v1

Submitted on 5 Feb 2026

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<figure><img src="image_1.png" /></figure>

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# Break of <sup>90</sup>Sr/<sup>90</sup>Y secular equilibrium during the preparation of liquid scintillation sources

Philippe Cassette, Isabelle Tartès and Florent Jaubert

Laboratoire National Henri Becquerel, CEA-LNE, CE-Saclay, 91191 Gif sur Yvette Cedex, France
# Origin of this study, calibration of a $^{90}$Sr/$^{90}$Y standard solution

* Activity per unit of mass: ~ 520 kBq/g

* Carrier concentration: 10 µg/g $SrCl_2$, 10 µg/g $YCl_3$ in HCL 0.1 M

* Date of preparation: 4/7/1996

<figure><img src="image_2.png" /></figure>

Source preparation: 5-10 mg of solution in 10 ml of scintillator
# Ultima Gold, evolution of counting rate with time (full window)

<figure><img src="image_3.png" /><figcaption>Sr/Y-90 Ultima Gold (1-1024) 5 mg
Reference date 20/06/2007</figcaption></figure>
# Hionic Fluor, evolution of counting rate with time (full window)

<figure><img src="image_4.png" /><figcaption>Sr/Y-90 Hionic Fluor (W1-1024) 5 mg
Reference date 20/06/2007</figcaption></figure>
# Ultima Gold AB, evolution of counting rate with time (full window)

<figure><img src="image_5.png" /><figcaption>Sr/Y-90 Ultima Gold AB (W1-1024) 5 mg
Reference date 20/06/2007</figcaption></figure>
First observations

• Sources with Hionic Fluor: stables

• Source with Ultima Gold AB: instables

• Sources with Ultima Gold:

• increase of counting rate during 10 days

• stables after 10 days

What is the reason for this increase of counting rate?
<figure><img src="image_6.png" /><figcaption>Sr/Y-90 spectrum, Ultima Gold</figcaption></figure>
Sr/Y-90 spectrum, Hionic Fluor

<figure><img src="image_7.png" /></figure>
# Source with Ultima Gold

Evidence of equilibrium distortion

Further experiments:

* Vial previously rinsed with carrier solutions: (Sr, Y, Sr+Y) __________ slight improvement but still disequilibrium

* Polyethylene + PTFE vial __________ no improvement

* Increase of aqueous content (100 mg of carrier solution added) __________ stable sources
Ultima Gold, addition of 100 mg of carrier solution
Evolution of counting rate with time

Sr/Y-90 Ultima Gold (1-1024) 100 mg

Reference date 20/06/2007

<figure><img src="image_8.png" /></figure>
# Origin of the problem

1. Where is ⁹⁰Y?

2. Why?
Where is ⁹⁰Y?

⁹⁰Y is still in the source but is detected with a low efficiency
Hypothesis: ⁹⁰Y is deposited on the wall of the vial

But, does this induce a decrease in detection efficiency?

Answer: Monte Carlo simulation
# Monte Carlo simulation of electron-matter interaction
## Penelope (Salvat et al.)

<figure><img src="image_9.png" /></figure>

$^{90}$Y spectrum in 100 channels
Energy spectrum transferred to the
LS cocktail

<figure><img src="image_10.png" /></figure>
# UG composition

<figure><img src="image_11.png" /></figure>

Creation Date: 12-01-2003

Revision Date: 03-20-2007

## Material Safety Data Sheet

### 1. Chemical Product and Company Identification

<table><tr><td>Material Name</td><td>ULTIMA GOLD / 2*5 L</td></tr><tr><td>Version #</td><td>02</td></tr><tr><td>Item #</td><td>6013329</td></tr><tr><td>Identification Of The Company/Undertaking</td><td>PerkinElmer Life and Analytical Sciences<br>710 Bridgeport Avenue<br>Shelton, CT 06484<br>Technical Support 800-762-4000</td></tr><tr><td>Emergency Telephone Number</td><td>CHEMTREC 800-424-9300<br>Emergency Phone 800-762-4000</td></tr></table>

### 2. Composition / Information on Ingredients

<table><thead><tr><th>Hazardous component(s)</th><th>CAS #</th><th>Percent</th><th>PEL</th><th>TLV</th></tr></thead><tbody><tr><td>TRIETHYL PHOSPHATE</td><td>78-40-0</td><td>1 - 2.5</td><td></td><td></td></tr><tr><td>Non-hazardous component(s)</td><td>CAS #</td><td>Percent</td><td></td><td></td></tr><tr><td>P-BIS(O-METHYLSTYRYL)BENZENE</td><td>13280-61-0</td><td>1 - 2.5</td><td></td><td></td></tr><tr><td>SODIUM DIOCTYL SULFOSUCCINATE</td><td>577-11-7</td><td>1 - 2.5</td><td></td><td></td></tr><tr><td>ETHYLENE OXIDE-NONYLPHENOL POLYMER</td><td>9016-45-9</td><td>10 - 20</td><td></td><td></td></tr><tr><td>2,5-DIPHENYLOXAZOLE</td><td>92-71-7</td><td>1 - 2.5</td><td></td><td></td></tr><tr><td>DIISOPROPYLNAPHTHALENE</td><td>38640-62-9</td><td>60 - 80</td><td></td><td></td></tr><tr><td>PHOSPHORIC ACID, 2-ETHYLHEXYL ESTER, COMPOUND WITH 2,2'-IMINOBIS[ETHANOL]</td><td>73070-48-1</td><td>10 - 20</td><td></td><td></td></tr></tbody></table>

HDEHP
(compound with 2,2-iminodiethanol)
# Is the problem related to HDEHP?

Test: addition of HDEHP (50 g/l) to Hionic Fluor
# Hionic Fluor + HDEHP
## Evolution of counting rate with time

Sr/Y-90 Hionic Fluor + HDEHP 50 g/l (1-1024)

Reference date 20/06/2007

<figure><img src="image_12.png" /></figure>
Hionic Fluor + HDEHP

<figure><img src="image_13.png" /></figure>
Conclusion

The problem is likely to be related to the presence of HDEHP
which cause Y deposition on the wall of the vial...
... but the mechanism involved is unknown

This artifact can be easily suppressed by increasing the
aqueous phase proportion ... or by using another scintillator.
So, what better scintillator to use?

* Ultima Gold AB with 100 mg of carrier solution
* the instability is still worse

* Hionic Fluor seems to be better...
# Hionic Fluor 2 different bottle from the same batch
## Evolution of counting rate with time (1-1024)

<figure><img src="image_14.png" /></figure>

SQPE

778.7 ± 1.4

783.6 ± 2.1
Sr/Y-90 spectrum, Hionic Fluor, same batch, different bottles

<figure><img src="image_15.png" /></figure>
Hionic Fluor 2 different bottle from the same batch
Evolution of counting rate with time (1-690)

<figure><img src="image_16.png" /></figure>

Negligible SQPE difference but significant difference in counting rate
Conclusion

* Sr/Y-90 LSC measurement can be tricky, even if 90Y it is a high-energy radionuclide. The simple assumption of 100 % detection efficiency does not always stands

* Very small aqueous content in the source is not always suitable

* Chemical separation effects can be expected, so solution stability must always be checked prior to any measurement

* Liquid scintillator variability can be important between two batches but also between two samples of the same batch...

* ...and variability is not always revealed by the value of the quenching index